A&P mechanic here, those rivets failed in the force direction of tension. Pretty much all rivets are designed to hold in the force direction of sheer, not tension. They clearly had a tension load and that caused the failure. If you can figure out what was causing the tension load and remove it, you'll be fine. Good luck sir and thanks for the update. Please keep us posted.
@Acirema Reidlos, Hello!!; I'm also an A&P tech , with structural experience .... You do have a point of how solid rivets are designed to be loaded in fastening sheets together... I do not know what the thickness or the material type is, of what the rudder control horn is, but as a general rule , the diameter of the rivets should generally be 2.5-3 x the thickness of the thickest sheet... That lower driving rib looked just a bit humble... Yes that probably was the original design that Sonex made, but it still looks pretty thin... And almost an entire row of rivets practically pulled right through that rib, also, both rows of rivets are very close, if not encroaching into the bend radaii of that base driven rib.. If the rib has to be of O.E.M. thickness and material type, couldn't a doubler of the same material type, be installed inside of the negative depression of that rib, and put an AN 470 type of a manufactured head on the inboard end (facing down) on that rib?? This way, the solid rivets won't pull through as easily, as the ones that were originally there did... And about that tail wheel steering tie-rod; why is it even needed? Several planes that are tail-draggers have dampened/spring-centered free moving casters for the tail-wheels... At low speeds, the steering can be controlled by differential braking of the main gear brakes... When the plane begins to build speed, the rudder will use aero-dynamic forces to control the YAW, before & after the empenage starts flying... Of coarse , any changes from the basic OEM design should be approved by Sonex Aircraft.. And because of what was shown here, changes (by Sonex) just might be suggested for these planes, in this area, and maybe other areas of their various designs....... It is not unusual for planes and equipment of many types, to develop unforseen problems with their O.E.M. designs.... As long as the manufacturer studies the issues to clear problems that could develop... And Sonex got to this customer IMMEDIATELY , to work out a solution to these issues... They probably notified all owners of these planes, of the suspected issues, and have advised them how to check for these issues... That is a reasonable action taking place to attempt to increase the safety factor of these planes....
@@michaelmartinez1345 Yes, that caught my eye also. Thick control horn (seems to be about appropriate), but the rib is really thin. I bet they made all the ribs from the same thickness sheet to keep things simple. I'd say that if the rib were the "right" thickness, it would be very difficult to bend without cracking. The better path would be to put a doubler on the inside of the rib that is the same thickness as the control horn material.
@@KlingbergWingMkII when re-making things like ribs out of sheet metal, the bend radius and material type and thickness is an important consideration . If the metal is thicker, it might need a larger bend radius.... Also the bend tangent lines of a larger radius will be located in different places, on the pre-forming layout....Also, the rudder panel is tapered, which means every rib is different... This is why a doubler , located inside on a new pre-formed part makes a lot of sense... My guess is most of the problem of this situation was caused by the push-pull rod to the tail wheel of this tail-dragger aircraft.. Why not eliminate the push-pull rod, and put a dampener /centering springs on a caster tail wheel assy, like so many other tail-draggers use.... At slow speeds steer with differential braking between the two main landing gear brakes, and as the plane has more power applied, propeller slipstream and forward motion will give the empenage & control surfaces more flight control authority...
Single pushrod tailwheel linkage bad design...at a minimum should be the time proven dual cable in pull--pull With spring connectors.....The control horn should be embedded Slot mounted with Substantial rudder rib frame structure on Both sides of control horn, Not just end butted.....Looks like chinesium toy construction there.....Is this the "standard" design for rest of airframe ??
Hi, I am an AME (Canadian version of A&P + IA), also an engineer, pilot with over 1k hour of tailwheel experience, and once did some test flights on a Sonerai II (the immediate predecessor of the Sonex line of aircraft). Several of the other comments have suggested changing to a sprung steering system like would be found in most certified tailwheel aircraft. While a very good suggestion in general, that is not an option on the Sonex without first changing the braking system. The Sonex does not have differential braking so requires the direct steering control of the tailwheel offered by the solid pushrod, otherwise you would have no positive directional control when taxing at slow speeds. Modifying the braking system to a differential brake system was my very first suggestion to the owner that had me test fly his Sonerai, it just gives you so much more directional control authority. As for the non standard push rod on your aircraft, that was no doubt necessary to make up for the rudder being shortened on the bottom end, there is probably another story behind why that happened. I would just go ahead and order all the parts for a new rudder now and save the time of deciding later what you probably already know you are going to have to do. Your analysis of the top mounting of the pushrod being the source of the tensional failure of the rivet joint looks to be spot on. Someone else brought up substituting Cherrymax rivets in place of the supplied pop rivets, it is not a horrible idea for an application that has a demonstrated history of failure, but I would point out the rivets did not fail, the aluminum rib failed resulting in the rivets pulling through. If you are concerned with reinforcing the joint I would first suggest a doubler on the inside of the rib, one sheet size thickness up from whatever the rib is made up of (ie. if the rib is 0.025" use 0.032" for the doubler). Then the Cherrymax or even solid rivets might make sense but again it was not the rivets that failed. The downside is Cherrymax are more expensive and require a special pulling tool but they are approved to replace solid rivets in certified aircraft. If I owned or was building a Sonex, I would definitely be upgrading to a differential braking system but that is just my personal bias. That would have the side benefit of allowing you to replace the pushrod with something else that would prevent the transfer of tailwheel loads to the rudder.
Excellent comments. I think I’m just going to replace the entire rudder as you said. I’m going to take this approach…since this is really an isolated failure, I’m going to build everything back according to the actual specs, and then make this a part of my routine preflight and inspect the area regularly. All of your suggestions are appreciated.
Very interesting, have a friend who built one of these and had major issues with the AeroVee engine in his, and a total failure of another in a Onex he was test flying for a friend. Ignition problems in his and oil feed in the other. A Sonex that was built here by another mate was the subject of some discussion in that differential braking was not possible with the single brake lever so relying on the tailwheel link for steering, having had one of those break on two occasions on our RV6 I was wary of that idea so we fitted two brake levers on the same shaft so that one could apply pressure to each brake individually worked really well and of course if the link did break or separate you were not faced with a ground loop. In the case of our RV I removed the link and fitted the Vans deluxe tail wheel springs which have worked very well since.
@Jonathon Ludgator, I did not realize the Sonex has no capability for differential braking... I'm now wondering if a turning brake hand powered actuator (used on OhV buggies) , could be used for diff. braking on the MLG brakes....Not having the option for differential braking, does create concern for this design... I'm not in favor of the radically-offset tail wheel push-pull rod, that Sonex designed either....
I apologize for the comment 7 zero tango. I'm sure your a competent builder. Probably best thing would be to build a new rudder get the right parts. Good luck to you and Good flying.
As an aircraft engineer (A&P) I would be mortified that that was missed during several inspections! That is precisely the stuff that a good inspection should be looking for. Your last inspection did not even look at that let alone lift the tail to inspect the tail wheel and attachment. Multiple washers and a over length bolt is a immediate flag 🚩and can be seen from 6 feet away. You should be looking for a refund as they did not inspect your airplane. In fact what else did they miss?! I would be going over that airplane with a fine tooth comb.
As an amateur pilot and non-mechanic I’m learning the questions I didn’t even know to ask in a hurry. You try to do your best and hire more knowledgeable people to help but nothing changes where we are right now.
It's always the smallest details that make the difference. Great analysis, and even greater discovery before you flew. As I was always taught, it's better to be on the ground wishing you were flying, than to be flying wishing you were on the ground.
Watched the first video again and noticed that the 'raised' height of the rudder--as pointed out by Sonex-- might be causing other problems. The horn looks to be interfering witht the fuselage -and- it appears that the rudder side hinge might actually be pulling away from the rudder itself (hard to tell in the video). I think the rudder must have been incorrectly built with the hinge mis-aligned, which led to the non standard control rod, which led to the current issues. Rebuild the whole rudder!! So glad you're safe!!!!
Hi there, I just stumbled on your sonex rudder video(s). As someone who aspires to build an airplane in the future, maybe even a sonex, content like yours is beyond helpful. Thanks buddy, happy landings. Ed.
Excellent update, thank you! Just a thought: if you held the tailwheel centered and applied left rudder pressure, it would have a similar affect as pushing the tailwheel to the right. In other words, left rudder cable tension combined with tailwheel resistance towards the right applies downward pressure on the drive horn, and would be at its maximum when the position of the tailwheel is to the right.
There is a fundamental design problem with the rigid push/pull tail wheel steering rod. It will always impart a bending moment on the rudder control horn as the spring tail wheel moves vertically.
I think it’s worth putting a go pro mounted back there to watch what’s going on… a lot of good ideas in this thread… but being able to see what’s going on back there might shed some light Also there is the possibility of wheel shimmy .. that can from time to time cause strong loads
@Scratch Builder, that is a great idea... A go-pro video of the area of concern... The plane would not even have to take-off... Just fly the empenage, then set it back down to see what happens... Do that several times, and the answer of what is happening, just might come out...
You make an excellent point about preflight and walk around it's not something to ever be taken as routine as routine one should always approach the craft as though something is wrong and it's just a question of finding it
There's a bunch of things going on there; I'll begin by pointing out that tailwheels usually operate with a caster angle which puts even more of a vertical moment on an offset control rod arrangement. That the lower rudder rib seems to be formed to a tight radius at the flanges suggests that it is made from a softer aluminum alloy (could be post-heat treated but I wouldn't bet on that). Being made of flat stock the rudder horn will have low resistance to twisting which would load up the rivets to the rib one at a time. The "zipper effect". Personally, I'd go for a redesign---one where rivets are only loaded in shear. Perhaps a CNC-milled billet bell crank replacing the lower rudder rib? Or a Band-Aid strap (U-shape) wrapping under the bell crank and riveted to the forward rudder skin might be a quick and dirty fix.
Ah, so the story is starting to develop. Construction was clearly not to plans. I'd now be reviewing the entire construction of the plane because who knows what else is incorrect.
Before you go cutting up sheetmetal to make a new rudder, maybe check to see if the fin itself is to correct dimension as it may be the cause of the rudder sitting high.
RUclips is great for this kind of problem solving. Now... I believe C. G. & Earl Greystone advice is your best answer here. I would communicate with them and take advantage of their experience. Your life is on the line here and I would go over the entire aircraft with an experienced builder. The "homebuilt" aviation community is pretty good about this kind of thing.
Stop,Stop... Earl Greystone is 100% correct. Having a solid linkage to that tail wheel is the wrong design. I don't care how long Sonix's have been flying, I would bet that if you go and look at all of those previous aircraft with a solid linkage you will find fastener fatigue or sheetmetal fatigue cracks. I can't fathom a way they're getting around it. The steering of that tail wheel, if it's tied to the rudder directly needs to have a sprung system or you're always going to be inducing a load on the most critical attach point for your control system Bell crank. Generally your control system Bell crank should be mounted separately and independent of the steering system
"I don't care how long Sonix's [sic] have been flying..." is the same thing as saying "I don't care about all of the real-world experience out there, I'm going to go with my gut feeling instead of the actual evidence". If you haven't ever built it or maintained it, and if you haven't ever looked at the plans to understand how it is engineered, then your opinion is not as valid as the tens of thousands of hours of operation that actual Sonex airplanes have experienced.
@@noelwade Thanks for that perspective. The next time I'm on a post Columbia Return to Flight Team, or C-17 post MLG pods all over the runway despite my delay of flight actions post discussions with the design team overturning my delay .. or...or... (the list is interesting) I will take your perspective into consideration. Not trying g to be a smarty pants, but if I had a dollar for every time somebody tried to convince me "that never having a prior failure was good engineering," I'd be rich. This gentleman's incident is equivalent to the actual pre Space Shuttle Columbia piece of foam that was the cause of all the lost lives and an example of the O-ring that never ever was going to fail on Challenger and...
@C. G. - Have you engineered, built, or maintained any components of the Space Shuttle program, C-17 systems, or indeed any aircraft? Not trying to be a smarty pants, but I've read all of the accident investigation board reports and analyses for the incidents you mention - and I have to say that none of them were very applicable when it came to building my Sonex airplane. But I *have* built a Sonex, which involved spending hours with my hands on the actual parts, learning how they go together, and understanding how they interact. I've also spent hundreds of hours conversing with other people who've actually built Sonex aircraft and flown them. I've also owned 3 other "experimental" aircraft and been hands-on in modifying and improving them. So unless you have commensurate experience, I will continue to trust in the evidence of tens of thousands of hours & landings on real flying Sonexes over your opinion. (Also, Columbia and Shuttle are both red-herring arguments; since the engineers of those vehicles *did* raise concerns and failure modes but they were dismissed by management. That is a wholly different situation from an outsider with no experience raising concerns when the engineers of the vehicles have already analyzed and explained the issue)
To be clear: I don't have a problem with you, C.G. I have a problem with the kind of blunt/blanket statement "a solid linkage to that tail wheel is the wrong design." That is a statement backed up by no facts in evidence. Yes, its an unusual design; but you have not presented any evidence to prove that your point is valid. If you had done a careful engineering analysis of the entire system and could show you work, then it'd be worth listening to and looking over your analysis. If you had a long pedigree of designing tailwheel aircraft and could point to that experience, then your assertion would be worth serious consideration. But a blanket statement backed up by only opinion is not helpful to anyone. Its not helpful to the owner who posted this video, and its potentially misleading for others who come along later and decide to further modify this system (when modifications where what caused the problem in the first place).
I would want the axle of the tail wheel almost under its pivot point rather than behind it. Yes, it would hang down lower, create more drag, and not look as cool, but having the axle so far behind it’s pivot point turns it into lever that can put lots of force on the rudder control linkage.
Seems to be a consensus that the bottom rib needs to be a lot thicker too, and the thick plate beneath it keeps it from bending under stress, so that leaves the rivets as the (hidden) point of failure. If the thick plate doubled as the rib, in other words riveted directly to the sides of the rudder, seems like a better solution maybe? It will be interesting to see if other sonex owners, now aware of your problem, discover similar issues on their own planes. Keep us posted, and glad your still around to do it!
Yeah or maybe it would have pulled the rudder right off the hinges at that point. See the problem is the stress has to go somewhere and with this setup the adverse stresses are the cause. The failure was the symptom. I’ve bought everything the rebuild the rudder so I’ll have you guys a new video shortly.
excellent follow-up. makes sense. these are the types of things people change without thinking it through. Failure analysis can be a fun part of engineering. You learn so much more about why things do/don't work through failure. But we try to keep the failures to be the nonharmful types, or do the harmful ones in the lab under controlled testing.
@@LeanofPeakAviation agreed. this kind of failure is not one you want to have in flight. But it's good you trusted your gut. I learned in combat to trust my gut instinct. My conclusion is that our "gut" is really our subconscious picking up on details our conscious mind doesn't, and when it sees something you don't, it alerts you. Kind of a left brain right brain thing. One side of our brain controls speech, the other does more analyzing or something like that. And if one side figures something out, it struggles to communicate it to the other half of the brain. That's my theory at least. It served me well and kept me alive, and helped me to detect/defeat ambushes I otherwise shouldn't have been able to. Whenever I get the gut feeling about a flight, I refuse to go fly until I figure out what the issue is.
@@LeanofPeakAviation just finished almost 4000 mi in July to Ohio and then Montana and back to Oregon.. my tail wheel screws came loose my prop started flaking and my cowling was wearing into my valve covers so I've ordered a new valve covers and the prop is getting repaired... My confidence in the airframe and the engine have shot way up... Now I'll do a thorough inspection of the rudder area
@@1bengrubb Hey Ben, Ex RV4 builder/pilot here. Seems kinda sketchy for your cowl to contact your valve covers. Baffle seal maybe, but not fiberglass to metal. I would worry about the vibration of the engine being transmitted into the airframe instruments, etc. Anyway, been following some of your adventures on RUclips. Kinda reminds me of me. After 4 years building my early kit RV4 plus another 6 years flying the hell out of it, I sold it about 2002-3 to get back to the real thing, HG. Good luck, listen to your aircraft. it has been talking to you.....Joe Evens
@@charlesevens5377 hey thanks Joe. You seen the picture of a 1x how the valve cover stick out the cowling? The instructions say it's not necessary for the top of the cowling to attach the fuselage so I think the wind pressure is pushing the cowling against the valve covers... My brother bought me a $50 hang glider from a storage sale bought me a secondhand climbing harness and some rope and I was flying!
Just an informed guess. I do fly a tiny homebuilt taildragger myself and the tailwheel on my plane is connected to the rudder by springs. Those springs were initially quite stiff which made the handling rather direct to the point where it was hard to manage. I have since loosened the connection and it handles much more docile. Also, the forces introduced into the rudder and controls by the tailwheel are less severe now. With this experience, having the tailwheel connected by a completely stiff pushrod seems like a bad choice to me. Then there's this particular design with an additional ball joints in the rod - what is that supposed to do? All it seemingly does is introduce more wear and tear by going "click-clack" all the time. Now, apparently the plane doesn't have a differential brake system - for a taildragger that is just stupid. You need that. period.
Yeah have you seen the RV steering rods? There’s a spring in them. RV has been using them for years. They have a great control feel but also relieve that adverse force.
The geometry on the tail wheel fork is at an angle that will induce oscillation , all the mass is aft of the pivot point. 100% trail ,it will shimmy and turn your control rod into a jack hammer. Look at scott tail wheel as a example, the fork pivot and axle are about 45 degrees.
I actually sent you that email BEFORE seeing this video.Could converting to cables and springs for the tailwheel control be a fix for this problem also?
What I don't understand is why the design has the tailwheel trailing behind the pivot point instead of directly beneath it. If someone were to pull the tail of the plane one way or another, say maneuvering it around the hanger by hand, it would put undo stress on all the linkages. If it were directly under the pivot point, it wouldn't.
In other words. Why did this fail? That's a conversation starter for engineers. "I am going to make sure this can't fail!" That is a better conversation for the world (-"
I think even the correct design is flawed. In my view a line between the pushrod end joints should be parallel to the axis of the rod the tailwheel is on. Then you have motion that uses parallelogram geometry. The current geometry can produce some big loads when the tailwheel is deflected upwards, and there will be some 'bump steer'. Moreover, I think I would prefer to separate the tailwheel connection from the rudder control cables a little further forward in that control system. I think further failure would be slow, because all the rivets on the right side of the bottom rudder rib were holding on.
I wonder if sequentially larger rivets on the load end would also help retain that piece to prevent any deflection? Certainly correcting the angle to take the slack out of that will be very helpful. Is there any discussion with a hardened stainless steel washer for potentially the 1st 3 or 4 holes on the lowend to prevent that soft aluminum piece from deforming?
I have used that technique a number of times on various parts of racing cars over the years. Obviously, the forces which caused the failure will have to be identified and eliminated, but adding washers as you describe is a good bit of insurance going forward.
@@oddshot60 I'll be interested to see what your solution is some of the engineers below agreed with you by eliminating the angle and the tension in the linkage. it's so frustrating how every solution adds weight. good luck and stay safe I'll be watching
Someone installed a non original link assembly with a bad geometry that set up the rudder to fail in the future. They probably did not know that they didn't know what they were doing.
Agree totally. It’s a nifty looking control that’s more adjustable and has cool little ball joints on the ends…I doubt he ever imagined this would happen.
Yes what you identify at 2.40 is the cause. A sideways force to the right on the tailwheel is a moment that will cause the control horn to be pulled down, putting those rivets under tension. As this will happen routinely on landings and ground operations, it should have been a design condition that was considered. Messing with 10mm of rudder height, the angle of the tailwheel arm - these are very secondary/irrelevant. Rebuilding the current design will not stop it reoccurring. The bending moment should be transferred to the side-skin of the rudder, so that rivets can work in shear (as they are designed to)
Just come across these videos, so a bit late comment. I agree with all you say, but could the problem be solved by adding limiters to the steer angle travel in the tailwheel assembly, so it can't use the rudder horn as a "lock stop"? Could be set just beyond the normal tail travel, so they don't interfere with flight controls, but still can't exert excessive forces in a heavy sideways landing or rough taxi.
Was the rudder length changed? I'm curious as to what You will find, when the correct parts come in... That push-pull rod with the bends on both ends, is a very unusual design... Especially when directly connected to a flight control that is always used....
It could happen two ways…first the rudder could have been made or cut too short, second the placement of the hinge could have been off. I’ll be looking closely at it.
@@LeanofPeakAviation I bet that you will find out that it was off by one lug of the hinge material - the hinge was mis-installed (lugs aligned instead of staggered) and then someone trimmed the "long" end of the rudder.
Why no just use chains and springs like most certified planes and RV's do? Chains/springs should place only minimum tension load on the rudder control horns, if any.
Question from a non aircraft builder, but someone familiar with rivets. Those rivets looked like they are going through a relatively thick piece of material (the bellcrank) into a relatively thin piece of material (the lower rudder cap), and I don't see any backup washers on those lower rivets. Not sure what the order of assembly is on this part, which might explain the use of what appear to be blind pop rivets - but using backup washers on that high stress connection seems like a no-brainer to me. Can any experts explain why that wasn't the process here?
Backup washers are not something that you are going to see in aircraft construction. First rivet joints are designed so that the rivets are normally loaded in sheer. Second the number of rivets used in the joint is carefully calculated so that the joint has the same strength as a continuous piece of material. If for what ever reason you needed to protect for pull through you would go with an aluminum doubler plate rather than backup washers. Galvanic corrosion from dissimilar metals is always an issue to be avoided with aircraft structures.
Can you buck the rivets to the horn and then use the cherrys to attach the rib to the rudder ? You will get better strength from the bucked ones and the cherrys would be in shear as they should be. This won’t solve the issue of the failure as it will simply move the fail point to the cherrys in shear. However, it will or should add strength when you ultimately find the smoking gun on the problem. I would lean toward a rudder rebuild also. It’s difficult to determine additional stress from the failed part. If you’re doing Acro I would be very cautions. Don’t overlook bulkheads and tailwheel attach points in your inspection.
I could. I could also use cherrymax rivets which are used as solid rivet replacements in many cases. I went ahead and ordered everything to rebuild the rudder. I’m just going to do it.
My eyes aren't what they used to be, so I can't tell very well what the blueprint called for in regard to the original design. However, you correctly noted that the angle between clevis point to clevis point isn't very different. Unless those ball joints are running out of motion and binding, going to a straight pushrod isn't going to make any difference on the forces. And just moving it from the top to the bottom isn't going to make a difference regarding it getting pulled down when you manually push the wheel to the right either. You will still be loading the control rod in tension and it will still pull down on the control horn. In fact now pushing the wheel to the right will both be putting tension in the pushrod (pulling down on the control horn) and the moment from the pushrod being mounted below the control arm is going to be bending the front of the control horn down at the same time. Making the rudder 10mm longer will be directionally correct, but won't make a huge difference in the angle of the control rod and therefore won't make a huge amount of difference in the vertical vs. horizontal force components either. I know there is always the danger of finding the next weakest failure point when deviating from plans, but if this was my plane I would be adding a doubler to the lower rib of the rudder and taking a good hard look at every part of the rudder between the control horn and lower rudder hinge.
I've heard it said there are old pilots and there are bold pilots. But there are no old bold Pilots. This is what they are talking about. A lesser pilot would have gone flying that day. You sir will be an old pilot.
In my plane a Rudder connection is a primary and the tail wheel control is secondary and handelt by springs. Metal or Rubber. People all over the world chould check this priority order to their plane.
i was shocked as soon as i see the angle difference. wtf they were thinking whoever put together the plane. hopefully whoever did this didnt do the same lazy work with the rest of it.
Certified airplanes use solid rivets or cherry structural blind rivets that lock with a steel serrated stem. Labor intensive & costly. Cheap pop rivets or avex rivets do no stand the test of time. Also homebuilt aircraft do not have heat treated structural sheet metal like a certified plane. That's why a certified plane can have 10,000 hours on the airframe with no loose smoking rivets like a homebuilt. My advice to you new pilots or first time plane buyers stay away from experimental planes.
The fact that this issue took a while to get this severe and you or the inspecting mechanic didn't catch it is scary. If you used a mechanic to do the Conditional, first thing is fire them and never use them again. Secondly you should really take a step back and figure out how you can train/teach yourself to do a better job of preflight/inspections. Not sure how often you fly but waiting until the Conditional yearly to deep dive into systems is asking for trouble. I change my oil every 25 hrs and do a pretty good inspection of the whole plane while I'm at it. At the lastConditional, that tail end should have been raised and tailwheel inspected. At that point there is absolutely no way any competent person wouldn't have seen the issue
I think this failure wasn't totally as Sonex claim, "the dodgy steering pushrod". Looks to me to have been a shock loading on the tailwheel whilst at full right deflection. This is a shortcoming of a solid direct steering tailwheel, shock loads are directly transferred to whatever is on the other end of the steering link in this case the rudder horn. This could have been initiated by something like having full right rudder deflection during a groundloop, fighting a strong crosswind with the tail down or tailwheel in a hole or a clump of grass or something. What surprised me is this rudder control horn is nothing like the rudder found on the sonex and waiex. If built correctly the Sonex has the drive horn on top of the rudder end rib. With the shop head of the rivets against the thicker 1/4" material as is standard metalworking practice. This way the rivets on the drive horn on the sonex are not in tension. The other variation is the quantity of rivets from the rib flange to the rudder skin, sonex has 15 rivets the onex has only 5. The Same load on the Sonex would be seen as sheer by these 15 rivets. The onex has the shophead on the thinner material and the rivets that pulled through loaded in tension. Poor design on the onex. If I were fixing this I would be sandwiching the replacement rib with a light plate above the rib and add more rivets to the rib flange to rudder skin, to deal with the sheer load. As a bear minimum I would flip the orientation of the complete set rivets where they pulled through, this would still leave the rivets in tension but far more unlikely to pull completely through.
Very good comments… I did look at the Sonex design and was very curious to why they chose to put the horn on the bottom of the end rib in the Onex… Especially after receiving the new end rib in the mail yesterday… It’s not a very confidence inspiring little piece of sheet metal. That being said, for every desired range of motion on the tailwheel there is a point in space where an Appropriately sized drive rod will allow that range of motion without The significant forces we saw in this set up…so I’m very curious to see what happens when we trial everything according to specs.
Who inspected that aircraft once it was built in order to get the Airworthiness Certificate. This is why I will never do conditioning inspections or be a build coach!
I've flown all my life and something I really want to do in my retirement was to restore a vintage plane or build a home belt after 5 years of studying this home built situation I've come to the conclusion that there are more flaky people out there trying to build a airplane then I want to even consider dealing with I bought just for a couple of Parts a whole package deal from a fella that abandoned his project this was the biggest bunch of garbage I ever saw in my life he absolutely destroyed thousands of dollars worth of aircraft quality material these people are giving this Hobby and sport such a bad name that I'm out I do not want to be involved with the home built fraternity at all!
@@steve2736 I suspect he was having a hard time fitting the original part based on the online forums. This seems to be a common area of modification. But yes the change in geometry definitely had an adverse outcome.
Bad design from Sonex! All the shock loads go Directly into rudder control horn! Re design With a 1/2 “ solid block Of 6061 aluminum for The rudder bottom end Cap and use machine Screws with an aluminum skin doubler on outside of rudder at Least up to the next Rudder rib. Connect Tail wheel with springs In a pull pull configuration.
No, sorry but you do not understand the aircraft design/plans. Please do not try to redesign an aircraft that you have never seen the full plans of and don't understand how it was engineered. Offering advice like this can result in a far more dangerous "solution"! The shock loads from the tailwheel go into the flexible titanium rod that attaches the tailwheel to a beefy set of structures inside the aft fuselage. When built *per the plans* (this tailwheel was _not_ built to the original specs), the small tailwheel control-horn only transmits modest loads through the pushrod to the rudder horn. The rudder horn itself is an incredibly beefy part and can take these loads (as proven by tens of thousands of flying hours on existing airframes without this being a problem), *if* the control linkage is properly set up. In this case, the original builder of the airframe did not follow the plans and the control linkage is not only at a steeper angle but it physically overlaps part of the control horn when the tailwheel is deflected to one side. This overlap is the crux of the problem - because vertical motion of the tailwheel when there is overlap will physically push down on the control-horn. In the stock configuration, the control linkage is mounted differently and is designed so that vertical motion is compensated for by the rod-end bearing and the control linkage itself never contacts the rudder horn to apply an upward or downward torquing force on it.
@@SoloRenegade Thanks, that link showed alternative steering casters and a very nicely formed control rod with heim joints as opposed to the welded control rod assembly
@@ed_cetera would be interesting to take a look at. i don't have any issue with the design if built properly, but I'd be curious to compare different designs.
At about 45 sec in a big mistake is made: NEVER scale the drawing, do not use drafted perspectives as reference for components! You have the wrong part or the drawing differs from the build. Are the rivets to spec per the drawing - csk, button head, etc? Lots of questions here that demand a thorough inspection by a sheet metal tech, IE, etc. Best on the correction!
IS THIS THE PLANE THAT IS FOR SALE . I WOULD BE INTERESTED IN IT BUT I LOST THE SITE THAT YOU WERE ON. I DIDN'T GET THE PRICE OF THE PLANE I WOULD LIKE TO HAVE HAVE SOME INFO ON IT. HOW WOULD I GET IN TOUCH WITH YOU. IF YOU STILL HAVE IT.I LIVE IN N.C. IM INTERESTED
Maybe attach the rod to the bottom of the horn ? and use 3-4 10/32 machine screws and rivets to attach the rib to the horn ? Make the parts so they cant fail !!! Gary k
you want certain parts to be able to fail. By controlling what WILL fail, you ensure that in the event something were to fail, it's not something life threatening. If you over do the wrong parts, you can then induce a life threatening failure somewhere else in the design. This likely never would have happened had the control rod been built and attached properly. So that is what needs to be fixed. Don't go creating additional problems changing things that don't need to be fixed.
wow...I see a lot of posts that experimental is way better than certified but this kinda gives me pause, ie the build quality. I guess however through the miracle of modern media you can get the word out to other owners fairly quickly.
I once had a throttle cable snap on me during my takeoff in a Cessna 172. Experimental planes aren’t inherently more dangerous but as we’ve seen you really have to watch the build quality, especially modifications to the structure. Build your own and you’ll be fine!
Nope. Rivets failed. Dont kid yourself. Frankly I don't like that design one bit! And I am a PP, motorcycle risk taker type A. Nope nope. You are on the right track. Redesign.
The rivets failed because a non-stock part was used that physically overlaps the control horn and presses down on it when the tailwheel is over to one side. No re-design is necessary; they just need to rebuild the part per the stock plans so that the physical parts don't overlap.
Its not a design flaw with the aircraft - the aircraft was not built with the control linkage specified in the plans. The original builder of the airplane substituted their own part. This change caused a physical interference between the parts when the tailwheel is over to one side.
Man.....Really sketchy designed lightweight rudder--tailwheel control linkage + doing aero......You seem determined pushing the fast track towards punching your "ticket" to the afterlife !! Totally independent & separated rudder to tailwheel linkages except maybe RC model aircraft
A&P mechanic here, those rivets failed in the force direction of tension. Pretty much all rivets are designed to hold in the force direction of sheer, not tension. They clearly had a tension load and that caused the failure. If you can figure out what was causing the tension load and remove it, you'll be fine. Good luck sir and thanks for the update. Please keep us posted.
@Acirema Reidlos, Hello!!; I'm also an A&P tech , with structural experience .... You do have a point of how solid rivets are designed to be loaded in fastening sheets together... I do not know what the thickness or the material type is, of what the rudder control horn is, but as a general rule , the diameter of the rivets should generally be 2.5-3 x the thickness of the thickest sheet... That lower driving rib looked just a bit humble... Yes that probably was the original design that Sonex made, but it still looks pretty thin... And almost an entire row of rivets practically pulled right through that rib, also, both rows of rivets are very close, if not encroaching into the bend radaii of that base driven rib.. If the rib has to be of O.E.M. thickness and material type, couldn't a doubler of the same material type, be installed inside of the negative depression of that rib, and put an AN 470 type of a manufactured head on the inboard end (facing down) on that rib?? This way, the solid rivets won't pull through as easily, as the ones that were originally there did... And about that tail wheel steering tie-rod; why is it even needed? Several planes that are tail-draggers have dampened/spring-centered free moving casters for the tail-wheels... At low speeds, the steering can be controlled by differential braking of the main gear brakes... When the plane begins to build speed, the rudder will use aero-dynamic forces to control the YAW, before & after the empenage starts flying... Of coarse , any changes from the basic OEM design should be approved by Sonex Aircraft.. And because of what was shown here, changes (by Sonex) just might be suggested for these planes, in this area, and maybe other areas of their various designs....... It is not unusual for planes and equipment of many types, to develop unforseen problems with their O.E.M. designs.... As long as the manufacturer studies the issues to clear problems that could develop... And Sonex got to this customer IMMEDIATELY , to work out a solution to these issues... They probably notified all owners of these planes, of the suspected issues, and have advised them how to check for these issues... That is a reasonable action taking place to attempt to increase the safety factor of these planes....
@@michaelmartinez1345 Yes, that caught my eye also. Thick control horn (seems to be about appropriate), but the rib is really thin. I bet they made all the ribs from the same thickness sheet to keep things simple. I'd say that if the rib were the "right" thickness, it would be very difficult to bend without cracking. The better path would be to put a doubler on the inside of the rib that is the same thickness as the control horn material.
sonex themselves replied they found a modification to the control rod that applied pressure that caused the problem
@@KlingbergWingMkII when re-making things like ribs out of sheet metal, the bend radius and material type and thickness is an important consideration . If the metal is thicker, it might need a larger bend radius.... Also the bend tangent lines of a larger radius will be located in different places, on the pre-forming layout....Also, the rudder panel is tapered, which means every rib is different... This is why a doubler , located inside on a new pre-formed part makes a lot of sense... My guess is most of the problem of this situation was caused by the push-pull rod to the tail wheel of this tail-dragger aircraft.. Why not eliminate the push-pull rod, and put a dampener /centering springs on a caster tail wheel assy, like so many other tail-draggers use.... At slow speeds steer with differential braking between the two main landing gear brakes, and as the plane has more power applied, propeller slipstream and forward motion will give the empenage & control surfaces more flight control authority...
Single pushrod tailwheel linkage bad design...at a minimum should be the time proven dual cable in pull--pull With spring connectors.....The control horn should be embedded Slot mounted with Substantial rudder rib frame structure on Both sides of control horn, Not just end butted.....Looks like chinesium toy construction there.....Is this the "standard" design for rest of airframe ??
Hi, I am an AME (Canadian version of A&P + IA), also an engineer, pilot with over 1k hour of tailwheel experience, and once did some test flights on a Sonerai II (the immediate predecessor of the Sonex line of aircraft). Several of the other comments have suggested changing to a sprung steering system like would be found in most certified tailwheel aircraft. While a very good suggestion in general, that is not an option on the Sonex without first changing the braking system. The Sonex does not have differential braking so requires the direct steering control of the tailwheel offered by the solid pushrod, otherwise you would have no positive directional control when taxing at slow speeds. Modifying the braking system to a differential brake system was my very first suggestion to the owner that had me test fly his Sonerai, it just gives you so much more directional control authority. As for the non standard push rod on your aircraft, that was no doubt necessary to make up for the rudder being shortened on the bottom end, there is probably another story behind why that happened. I would just go ahead and order all the parts for a new rudder now and save the time of deciding later what you probably already know you are going to have to do. Your analysis of the top mounting of the pushrod being the source of the tensional failure of the rivet joint looks to be spot on. Someone else brought up substituting Cherrymax rivets in place of the supplied pop rivets, it is not a horrible idea for an application that has a demonstrated history of failure, but I would point out the rivets did not fail, the aluminum rib failed resulting in the rivets pulling through. If you are concerned with reinforcing the joint I would first suggest a doubler on the inside of the rib, one sheet size thickness up from whatever the rib is made up of (ie. if the rib is 0.025" use 0.032" for the doubler). Then the Cherrymax or even solid rivets might make sense but again it was not the rivets that failed. The downside is Cherrymax are more expensive and require a special pulling tool but they are approved to replace solid rivets in certified aircraft. If I owned or was building a Sonex, I would definitely be upgrading to a differential braking system but that is just my personal bias. That would have the side benefit of allowing you to replace the pushrod with something else that would prevent the transfer of tailwheel loads to the rudder.
Excellent comments. I think I’m just going to replace the entire rudder as you said. I’m going to take this approach…since this is really an isolated failure, I’m going to build everything back according to the actual specs, and then make this a part of my routine preflight and inspect the area regularly. All of your suggestions are appreciated.
Very interesting, have a friend who built one of these and had major issues with the AeroVee engine in his, and a total failure of another in a Onex he was test flying for a friend. Ignition problems in his and oil feed in the other. A Sonex that was built here by another mate was the subject of some discussion in that differential braking was not possible with the single brake lever so relying on the tailwheel link for steering, having had one of those break on two occasions on our RV6 I was wary of that idea so we fitted two brake levers on the same shaft so that one could apply pressure to each brake individually worked really well and of course if the link did break or separate you were not faced with a ground loop. In the case of our RV I removed the link and fitted the Vans deluxe tail wheel springs which have worked very well since.
@Jonathon Ludgator, I did not realize the Sonex has no capability for differential braking... I'm now wondering if a turning brake hand powered actuator (used on OhV buggies) , could be used for diff. braking on the MLG brakes....Not having the option for differential braking, does create concern for this design... I'm not in favor of the radically-offset tail wheel push-pull rod, that Sonex designed either....
I apologize for the comment 7 zero tango. I'm sure your a competent builder. Probably best thing would be to build a new rudder get the right parts. Good luck to you and Good flying.
No worries! I’ve ordered parts to rebuild the whole rudder and control system. Hopefully it works out!
As an aircraft engineer (A&P) I would be mortified that that was missed during several inspections! That is precisely the stuff that a good inspection should be looking for. Your last inspection did not even look at that let alone lift the tail to inspect the tail wheel and attachment. Multiple washers and a over length bolt is a immediate flag 🚩and can be seen from 6 feet away. You should be looking for a refund as they did not inspect your airplane. In fact what else did they miss?! I would be going over that airplane with a fine tooth comb.
As an amateur pilot and non-mechanic I’m learning the questions I didn’t even know to ask in a hurry. You try to do your best and hire more knowledgeable people to help but nothing changes where we are right now.
It's always the smallest details that make the difference. Great analysis, and even greater discovery before you flew. As I was always taught, it's better to be on the ground wishing you were flying, than to be flying wishing you were on the ground.
Watched the first video again and noticed that the 'raised' height of the rudder--as pointed out by Sonex-- might be causing other problems. The horn looks to be interfering witht the fuselage -and- it appears that the rudder side hinge might actually be pulling away from the rudder itself (hard to tell in the video). I think the rudder must have been incorrectly built with the hinge mis-aligned, which led to the non standard control rod, which led to the current issues. Rebuild the whole rudder!! So glad you're safe!!!!
Yes, you should ask yourself why the builder modified this rod. It was not done so just for no reason. Rebuild the entire rudder.
Enough have said it now…I’m convinced. Waiting on parts for a new rudder.
I am glad you did a follow up.
Still a couple things to look at but I’ll keep posting on it as we go.
Hi there, I just stumbled on your sonex rudder video(s). As someone who aspires to build an airplane in the future, maybe even a sonex, content like yours is beyond helpful. Thanks buddy, happy landings.
Ed.
Thank you for the update. Will continue to follow.
Excellent update, thank you!
Just a thought: if you held the tailwheel centered and applied left rudder pressure, it would have a similar affect as pushing the tailwheel to the right.
In other words, left rudder cable tension combined with tailwheel resistance towards the right applies downward pressure on the drive horn, and would be at its maximum when the position of the tailwheel is to the right.
Thanks for the details on this failure on your aircraft. Keep us posted please, very much appreciated! Fly Safer ...
There is a fundamental design problem with the rigid push/pull tail wheel steering rod. It will always impart a bending moment on the rudder control horn as the spring tail wheel moves vertically.
if you design for the known forces, it's not an issue at all.
I think it’s worth putting a go pro mounted back there to watch what’s going on… a lot of good ideas in this thread… but being able to see what’s going on back there might shed some light
Also there is the possibility of wheel shimmy .. that can from time to time cause strong loads
@Scratch Builder, that is a great idea... A go-pro video of the area of concern... The plane would not even have to take-off... Just fly the empenage, then set it back down to see what happens... Do that several times, and the answer of what is happening, just might come out...
Thanks for the update. Fly safe!
You make an excellent point about preflight and walk around it's not something to ever be taken as routine as routine one should always approach the craft as though something is wrong and it's just a question of finding it
There's a bunch of things going on there; I'll begin by pointing out that tailwheels usually operate with a caster angle which puts even more of a vertical moment on an offset control rod arrangement. That the lower rudder rib seems to be formed to a tight radius at the flanges suggests that it is made from a softer aluminum alloy (could be post-heat treated but I wouldn't bet on that). Being made of flat stock the rudder horn will have low resistance to twisting which would load up the rivets to the rib one at a time. The "zipper effect". Personally, I'd go for a redesign---one where rivets are only loaded in shear. Perhaps a CNC-milled billet bell crank replacing the lower rudder rib? Or a Band-Aid strap (U-shape) wrapping under the bell crank and riveted to the forward rudder skin might be a quick and dirty fix.
Great to see your on the road to repair and back flying safely. All the best!
Ah, so the story is starting to develop. Construction was clearly not to plans. I'd now be reviewing the entire construction of the plane because who knows what else is incorrect.
Yup.
Thanks for sharing the info.
Before you go cutting up sheetmetal to make a new rudder, maybe check to see if the fin itself is to correct dimension as it may be the cause of the rudder sitting high.
RUclips is great for this kind of problem solving. Now... I believe C. G. & Earl Greystone advice is your best answer here. I would communicate with them and take advantage of their experience.
Your life is on the line here and I would go over the entire aircraft with an experienced builder. The "homebuilt" aviation community is pretty good about this kind of thing.
Stop,Stop... Earl Greystone is 100% correct. Having a solid linkage to that tail wheel is the wrong design. I don't care how long Sonix's have been flying, I would bet that if you go and look at all of those previous aircraft with a solid linkage you will find fastener fatigue or sheetmetal fatigue cracks. I can't fathom a way they're getting around it. The steering of that tail wheel, if it's tied to the rudder directly needs to have a sprung system or you're always going to be inducing a load on the most critical attach point for your control system Bell crank. Generally your control system Bell crank should be mounted separately and independent of the steering system
If it can't be sprung as per other comments, perhaps ball joints at each end, it should not be rigid.
"I don't care how long Sonix's [sic] have been flying..." is the same thing as saying "I don't care about all of the real-world experience out there, I'm going to go with my gut feeling instead of the actual evidence".
If you haven't ever built it or maintained it, and if you haven't ever looked at the plans to understand how it is engineered, then your opinion is not as valid as the tens of thousands of hours of operation that actual Sonex airplanes have experienced.
@@noelwade Thanks for that perspective. The next time I'm on a post Columbia Return to Flight Team, or C-17 post MLG pods all over the runway despite my delay of flight actions post discussions with the design team overturning my delay .. or...or... (the list is interesting) I will take your perspective into consideration. Not trying g to be a smarty pants, but if I had a dollar for every time somebody tried to convince me "that never having a prior failure was good engineering," I'd be rich.
This gentleman's incident is equivalent to the actual pre Space Shuttle Columbia piece of foam that was the cause of all the lost lives and an example of the O-ring that never ever was going to fail on Challenger and...
@C. G. - Have you engineered, built, or maintained any components of the Space Shuttle program, C-17 systems, or indeed any aircraft? Not trying to be a smarty pants, but I've read all of the accident investigation board reports and analyses for the incidents you mention - and I have to say that none of them were very applicable when it came to building my Sonex airplane.
But I *have* built a Sonex, which involved spending hours with my hands on the actual parts, learning how they go together, and understanding how they interact. I've also spent hundreds of hours conversing with other people who've actually built Sonex aircraft and flown them. I've also owned 3 other "experimental" aircraft and been hands-on in modifying and improving them. So unless you have commensurate experience, I will continue to trust in the evidence of tens of thousands of hours & landings on real flying Sonexes over your opinion.
(Also, Columbia and Shuttle are both red-herring arguments; since the engineers of those vehicles *did* raise concerns and failure modes but they were dismissed by management. That is a wholly different situation from an outsider with no experience raising concerns when the engineers of the vehicles have already analyzed and explained the issue)
To be clear: I don't have a problem with you, C.G. I have a problem with the kind of blunt/blanket statement "a solid linkage to that tail wheel is the wrong design."
That is a statement backed up by no facts in evidence. Yes, its an unusual design; but you have not presented any evidence to prove that your point is valid. If you had done a careful engineering analysis of the entire system and could show you work, then it'd be worth listening to and looking over your analysis. If you had a long pedigree of designing tailwheel aircraft and could point to that experience, then your assertion would be worth serious consideration. But a blanket statement backed up by only opinion is not helpful to anyone. Its not helpful to the owner who posted this video, and its potentially misleading for others who come along later and decide to further modify this system (when modifications where what caused the problem in the first place).
OK, I need to know how this go's so I subscribed lol.
Me too!
Thanks for the update!
Safe flying!
I would want the axle of the tail wheel almost under its pivot point rather than behind it. Yes, it would hang down lower, create more drag, and not look as cool, but having the axle so far behind it’s pivot point turns it into lever that can put lots of force on the rudder control linkage.
Exactly right.
It basically has 90 degrees of caster rather than 5 or 10..
Seems to be a consensus that the bottom rib needs to be a lot thicker too, and the thick plate beneath it keeps it from bending under stress, so that leaves the rivets as the (hidden) point of failure. If the thick plate doubled as the rib, in other words riveted directly to the sides of the rudder, seems like a better solution maybe? It will be interesting to see if other sonex owners, now aware of your problem, discover similar issues on their own planes. Keep us posted, and glad your still around to do it!
Yeah or maybe it would have pulled the rudder right off the hinges at that point. See the problem is the stress has to go somewhere and with this setup the adverse stresses are the cause. The failure was the symptom. I’ve bought everything the rebuild the rudder so I’ll have you guys a new video shortly.
@@LeanofPeakAviation Please checkout my comment below about eliminating the tailwheel stress.
Great followup…well done!
excellent follow-up. makes sense. these are the types of things people change without thinking it through. Failure analysis can be a fun part of engineering. You learn so much more about why things do/don't work through failure. But we try to keep the failures to be the nonharmful types, or do the harmful ones in the lab under controlled testing.
I would have much preferred to learn this in a lab! I just need to build the next plane…
@@LeanofPeakAviation agreed. this kind of failure is not one you want to have in flight.
But it's good you trusted your gut. I learned in combat to trust my gut instinct. My conclusion is that our "gut" is really our subconscious picking up on details our conscious mind doesn't, and when it sees something you don't, it alerts you. Kind of a left brain right brain thing. One side of our brain controls speech, the other does more analyzing or something like that. And if one side figures something out, it struggles to communicate it to the other half of the brain. That's my theory at least. It served me well and kept me alive, and helped me to detect/defeat ambushes I otherwise shouldn't have been able to. Whenever I get the gut feeling about a flight, I refuse to go fly until I figure out what the issue is.
Checking my ONEX!!! thanks a bunch!!
Yeah dude can you believe it? Be safe.
@@LeanofPeakAviation just finished almost 4000 mi in July to Ohio and then Montana and back to Oregon.. my tail wheel screws came loose my prop started flaking and my cowling was wearing into my valve covers so I've ordered a new valve covers and the prop is getting repaired... My confidence in the airframe and the engine have shot way up... Now I'll do a thorough inspection of the rudder area
@@1bengrubb Hey Ben, Ex RV4 builder/pilot here. Seems kinda sketchy for your cowl to contact your valve covers. Baffle seal maybe, but not fiberglass to metal. I would worry about the vibration of the engine being transmitted into the airframe instruments, etc. Anyway, been following some of your adventures on RUclips. Kinda reminds me of me. After 4 years building my early kit RV4 plus another 6 years flying the hell out of it, I sold it about 2002-3 to get back to the real thing, HG. Good luck, listen to your aircraft. it has been talking to you.....Joe Evens
@@charlesevens5377 hey thanks Joe. You seen the picture of a 1x how the valve cover stick out the cowling? The instructions say it's not necessary for the top of the cowling to attach the fuselage so I think the wind pressure is pushing the cowling against the valve covers... My brother bought me a $50 hang glider from a storage sale bought me a secondhand climbing harness and some rope and I was flying!
Thanks again for sharing I can't wait to see more
Thanks for the update, hope you get back in the air soon!
You may have saved several lives , glad ypu got it sorted.
Just an informed guess. I do fly a tiny homebuilt taildragger myself and the tailwheel on my plane is connected to the rudder by springs.
Those springs were initially quite stiff which made the handling rather direct to the point where it was hard to manage. I have since loosened the connection and it handles much more docile. Also, the forces introduced into the rudder and controls by the tailwheel are less severe now.
With this experience, having the tailwheel connected by a completely stiff pushrod seems like a bad choice to me.
Then there's this particular design with an additional ball joints in the rod - what is that supposed to do? All it seemingly does is introduce more wear and tear by going "click-clack" all the time.
Now, apparently the plane doesn't have a differential brake system - for a taildragger that is just stupid. You need that. period.
Change that linkage system to the tried and true spring system with springs on both sides.
Thank you for sharing your experience.
hello thanks so much for sharing this with us saludos
Hope it helps someone!
Very nice discussion.
Thanks.
A simple compression spring on each side of a pivot pin mounted on the rudder horn,will breakup the dog fight between the rudder and the tail wheel.
Yeah have you seen the RV steering rods? There’s a spring in them. RV has been using them for years. They have a great control feel but also relieve that adverse force.
The geometry on the tail wheel fork is at an angle that will induce oscillation , all the mass is aft of the pivot point. 100% trail ,it will shimmy and turn your control rod into a jack hammer. Look at scott tail wheel as a example, the fork pivot and axle are about 45 degrees.
@@mileskifield That’s also something I haven’t explored. Thank you.
“I’m an A&P…” Remember, that aircraft had already been inspected, at least twice, by A&Ps.
I actually sent you that email BEFORE seeing this video.Could converting to cables and springs for the tailwheel control be a fix for this problem also?
A more traditional linkage would certainly avoid this problem.
Great video. I would be inclined to inspect the entire airframe with an eagle eye before I took it up. Fly safe
What I don't understand is why the design has the tailwheel trailing behind the pivot point instead of directly beneath it. If someone were to pull the tail of the plane one way or another, say maneuvering it around the hanger by hand, it would put undo stress on all the linkages. If it were directly under the pivot point, it wouldn't.
In other words. Why did this fail? That's a conversation starter for engineers. "I am going to make sure this can't fail!" That is a better conversation for the world (-"
I think even the correct design is flawed. In my view a line between the pushrod end joints should be parallel to the axis of the rod the tailwheel is on. Then you have motion that uses parallelogram geometry. The current geometry can produce some big loads when the tailwheel is deflected upwards, and there will be some 'bump steer'. Moreover, I think I would prefer to separate the tailwheel connection from the rudder control cables a little further forward in that control system. I think further failure would be slow, because all the rivets on the right side of the bottom rudder rib were holding on.
I wonder if sequentially larger rivets on the load end would also help retain that piece to prevent any deflection? Certainly correcting the angle to take the slack out of that will be very helpful. Is there any discussion with a hardened stainless steel washer for potentially the 1st 3 or 4 holes on the lowend to prevent that soft aluminum piece from deforming?
I have used that technique a number of times on various parts of racing cars over the years. Obviously, the forces which caused the failure will have to be identified and eliminated, but adding washers as you describe is a good bit of insurance going forward.
@@oddshot60 I'll be interested to see what your solution is some of the engineers below agreed with you by eliminating the angle and the tension in the linkage. it's so frustrating how every solution adds weight. good luck and stay safe I'll be watching
That whole control rod on the side is going to produce uneven loads on the rudder no matter where it’s attached. Look for piper type control, proven.
I believe you should have replace those tail wheel rods for springs
Someone installed a non original link assembly with a bad geometry that set up the rudder to fail in the future. They probably did not know that they didn't know what they were doing.
Agree totally. It’s a nifty looking control that’s more adjustable and has cool little ball joints on the ends…I doubt he ever imagined this would happen.
Use cherry max rivets not the pop rivets. Cherrymax has a steel core and locking collars that will not collapse. They are structural rivets.
really surprised none of that was caught in inspection.
This problem could effect ALL taildragger Sonex airplanes. ONEX, SONEX and even the WYEX and Glider
Yes what you identify at 2.40 is the cause. A sideways force to the right on the tailwheel is a moment that will cause the control horn to be pulled down, putting those rivets under tension. As this will happen routinely on landings and ground operations, it should have been a design condition that was considered. Messing with 10mm of rudder height, the angle of the tailwheel arm - these are very secondary/irrelevant. Rebuilding the current design will not stop it reoccurring. The bending moment should be transferred to the side-skin of the rudder, so that rivets can work in shear (as they are designed to)
Just come across these videos, so a bit late comment. I agree with all you say, but could the problem be solved by adding limiters to the steer angle travel in the tailwheel assembly, so it can't use the rudder horn as a "lock stop"? Could be set just beyond the normal tail travel, so they don't interfere with flight controls, but still can't exert excessive forces in a heavy sideways landing or rough taxi.
Was the rudder length changed? I'm curious as to what You will find, when the correct parts come in... That push-pull rod with the bends on both ends, is a very unusual design... Especially when directly connected to a flight control that is always used....
It could happen two ways…first the rudder could have been made or cut too short, second the placement of the hinge could have been off. I’ll be looking closely at it.
@@LeanofPeakAviation I bet that you will find out that it was off by one lug of the hinge material - the hinge was mis-installed (lugs aligned instead of staggered) and then someone trimmed the "long" end of the rudder.
Why no just use chains and springs like most certified planes and RV's do? Chains/springs should place only minimum tension load on the rudder control horns, if any.
Question from a non aircraft builder, but someone familiar with rivets. Those rivets looked like they are going through a relatively thick piece of material (the bellcrank) into a relatively thin piece of material (the lower rudder cap), and I don't see any backup washers on those lower rivets. Not sure what the order of assembly is on this part, which might explain the use of what appear to be blind pop rivets - but using backup washers on that high stress connection seems like a no-brainer to me.
Can any experts explain why that wasn't the process here?
Backup washers are not something that you are going to see in aircraft construction. First rivet joints are designed so that the rivets are normally loaded in sheer. Second the number of rivets used in the joint is carefully calculated so that the joint has the same strength as a continuous piece of material. If for what ever reason you needed to protect for pull through you would go with an aluminum doubler plate rather than backup washers. Galvanic corrosion from dissimilar metals is always an issue to be avoided with aircraft structures.
Build the “Peace of Mind” AKA Rudder.
Can you buck the rivets to the horn and then use the cherrys to attach the rib to the rudder ? You will get better strength from the bucked ones and the cherrys would be in shear as they should be. This won’t solve the issue of the failure as it will simply move the fail point to the cherrys in shear. However, it will or should add strength when you ultimately find the smoking gun on the problem. I would lean toward a rudder rebuild also. It’s difficult to determine additional stress from the failed part. If you’re doing Acro I would be very cautions. Don’t overlook bulkheads and tailwheel attach points in your inspection.
I could. I could also use cherrymax rivets which are used as solid rivet replacements in many cases. I went ahead and ordered everything to rebuild the rudder. I’m just going to do it.
My eyes aren't what they used to be, so I can't tell very well what the blueprint called for in regard to the original design. However, you correctly noted that the angle between clevis point to clevis point isn't very different. Unless those ball joints are running out of motion and binding, going to a straight pushrod isn't going to make any difference on the forces. And just moving it from the top to the bottom isn't going to make a difference regarding it getting pulled down when you manually push the wheel to the right either. You will still be loading the control rod in tension and it will still pull down on the control horn. In fact now pushing the wheel to the right will both be putting tension in the pushrod (pulling down on the control horn) and the moment from the pushrod being mounted below the control arm is going to be bending the front of the control horn down at the same time.
Making the rudder 10mm longer will be directionally correct, but won't make a huge difference in the angle of the control rod and therefore won't make a huge amount of difference in the vertical vs. horizontal force components either.
I know there is always the danger of finding the next weakest failure point when deviating from plans, but if this was my plane I would be adding a doubler to the lower rib of the rudder and taking a good hard look at every part of the rudder between the control horn and lower rudder hinge.
I’ve actually ordered parts to completely rebuild the rudder at this point.
Oh the joys of buying a used homebuilt
I've heard it said there are old pilots and there are bold pilots. But there are no old bold Pilots. This is what they are talking about. A lesser pilot would have gone flying that day. You sir will be an old pilot.
I sure hope so! Thanks for the comment
In my plane a Rudder connection is a primary and the tail wheel control is secondary and handelt by springs. Metal or Rubber. People all over the world chould check this priority order to their plane.
i was shocked as soon as i see the angle difference. wtf they were thinking whoever put together the plane. hopefully whoever did this didnt do the same lazy work with the rest of it.
Certified airplanes use solid rivets or cherry structural blind rivets that lock with a steel serrated stem. Labor intensive & costly. Cheap pop rivets or avex rivets do no stand the test of time. Also homebuilt aircraft do not have heat treated structural sheet metal like a certified plane. That's why a certified plane can have 10,000 hours on the airframe with no loose smoking rivets like a homebuilt. My advice to you new pilots or first time plane buyers stay away from experimental planes.
The fact that this issue took a while to get this severe and you or the inspecting mechanic didn't catch it is scary. If you used a mechanic to do the Conditional, first thing is fire them and never use them again. Secondly you should really take a step back and figure out how you can train/teach yourself to do a better job of preflight/inspections. Not sure how often you fly but waiting until the Conditional yearly to deep dive into systems is asking for trouble. I change my oil every 25 hrs and do a pretty good inspection of the whole plane while I'm at it. At the lastConditional, that tail end should have been raised and tailwheel inspected. At that point there is absolutely no way any competent person wouldn't have seen the issue
Throttle back Maverick. $10 says given enough time someone can find something wrong with your aircraft you were unaware of.
@@Mike-tt8wi never said my plane is perfect but guarantee you wont find something as blatant as a rudder half falling off. Good try though goose!
I think this failure wasn't totally as Sonex claim, "the dodgy steering pushrod". Looks to me to have been a shock loading on the tailwheel whilst at full right deflection. This is a shortcoming of a solid direct steering tailwheel, shock loads are directly transferred to whatever is on the other end of the steering link in this case the rudder horn. This could have been initiated by something like having full right rudder deflection during a groundloop, fighting a strong crosswind with the tail down or tailwheel in a hole or a clump of grass or something.
What surprised me is this rudder control horn is nothing like the rudder found on the sonex and waiex. If built correctly the Sonex has the drive horn on top of the rudder end rib. With the shop head of the rivets against the thicker 1/4" material as is standard metalworking practice. This way the rivets on the drive horn on the sonex are not in tension. The other variation is the quantity of rivets from the rib flange to the rudder skin, sonex has 15 rivets the onex has only 5. The Same load on the Sonex would be seen as sheer by these 15 rivets. The onex has the shophead on the thinner material and the rivets that pulled through loaded in tension. Poor design on the onex.
If I were fixing this I would be sandwiching the replacement rib with a light plate above the rib and add more rivets to the rib flange to rudder skin, to deal with the sheer load. As a bear minimum I would flip the orientation of the complete set rivets where they pulled through, this would still leave the rivets in tension but far more unlikely to pull completely through.
Very good comments… I did look at the Sonex design and was very curious to why they chose to put the horn on the bottom of the end rib in the Onex… Especially after receiving the new end rib in the mail yesterday… It’s not a very confidence inspiring little piece of sheet metal. That being said, for every desired range of motion on the tailwheel there is a point in space where an Appropriately sized drive rod will allow that range of motion without The significant forces we saw in this set up…so I’m very curious to see what happens when we trial everything according to specs.
Who inspected that aircraft once it was built in order to get the Airworthiness Certificate. This is why I will never do conditioning inspections or be a build coach!
I've flown all my life and something I really want to do in my retirement was to restore a vintage plane or build a home belt after 5 years of studying this home built situation I've come to the conclusion that there are more flaky people out there trying to build a airplane then I want to even consider dealing with I bought just for a couple of Parts a whole package deal from a fella that abandoned his project this was the biggest bunch of garbage I ever saw in my life he absolutely destroyed thousands of dollars worth of aircraft quality material these people are giving this Hobby and sport such a bad name that I'm out I do not want to be involved with the home built fraternity at all!
Yeah build it yourself. I’m not buying any more second hand. I’ll build the next one.
@@steve2736 I suspect he was having a hard time fitting the original part based on the online forums. This seems to be a common area of modification. But yes the change in geometry definitely had an adverse outcome.
Bad design from Sonex!
All the shock loads go
Directly into rudder control horn! Re design
With a 1/2 “ solid block
Of 6061 aluminum for
The rudder bottom end
Cap and use machine
Screws with an aluminum skin doubler on outside of rudder at
Least up to the next
Rudder rib. Connect
Tail wheel with springs
In a pull pull configuration.
No, sorry but you do not understand the aircraft design/plans. Please do not try to redesign an aircraft that you have never seen the full plans of and don't understand how it was engineered. Offering advice like this can result in a far more dangerous "solution"!
The shock loads from the tailwheel go into the flexible titanium rod that attaches the tailwheel to a beefy set of structures inside the aft fuselage. When built *per the plans* (this tailwheel was _not_ built to the original specs), the small tailwheel control-horn only transmits modest loads through the pushrod to the rudder horn. The rudder horn itself is an incredibly beefy part and can take these loads (as proven by tens of thousands of flying hours on existing airframes without this being a problem), *if* the control linkage is properly set up. In this case, the original builder of the airframe did not follow the plans and the control linkage is not only at a steeper angle but it physically overlaps part of the control horn when the tailwheel is deflected to one side. This overlap is the crux of the problem - because vertical motion of the tailwheel when there is overlap will physically push down on the control-horn. In the stock configuration, the control linkage is mounted differently and is designed so that vertical motion is compensated for by the rod-end bearing and the control linkage itself never contacts the rudder horn to apply an upward or downward torquing force on it.
I posted a link to a control rod for this aircraft from another company, are links not allowed in your comments ?
youtube is hit/miss with links
@@SoloRenegade Thanks, that link showed alternative steering casters and a very nicely formed control rod with heim joints as opposed to the welded control rod assembly
Yeah I dunno. I didn’t set any specific controls on the channel.
@@ed_cetera would be interesting to take a look at. i don't have any issue with the design if built properly, but I'd be curious to compare different designs.
@@SoloRenegade
look up Peter Anson Engineering and 6″ PNEUMATIC TAILWHEELS AND ACCESSORIES
At about 45 sec in a big mistake is made: NEVER scale the drawing, do not use drafted perspectives as reference for components! You have the wrong part or the drawing differs from the build. Are the rivets to spec per the drawing - csk, button head, etc? Lots of questions here that demand a thorough inspection by a sheet metal tech, IE, etc.
Best on the correction!
All the correct parts have been ordered from Sonex. We are quite certain this part is not the original.
"Conversation starter" Yeah. (-:
IS THIS THE PLANE THAT IS FOR SALE . I WOULD BE INTERESTED IN IT BUT I LOST THE SITE THAT YOU WERE ON. I DIDN'T GET THE PRICE OF THE PLANE I WOULD LIKE TO HAVE HAVE SOME INFO ON IT. HOW WOULD I GET IN TOUCH WITH YOU. IF YOU STILL HAVE IT.I LIVE IN N.C. IM INTERESTED
Lol yeah this plane WAS for sale briefly before this incident. Once I get it fixed up and re-inspected I will be selling it.
You can send me an email at 7zeroTango@gmail.com if you’d like to discuss further.
Maybe attach the rod to the bottom of the horn ? and use 3-4 10/32 machine screws and rivets to attach the rib to the horn ? Make the parts so they cant fail !!! Gary k
you want certain parts to be able to fail. By controlling what WILL fail, you ensure that in the event something were to fail, it's not something life threatening. If you over do the wrong parts, you can then induce a life threatening failure somewhere else in the design.
This likely never would have happened had the control rod been built and attached properly. So that is what needs to be fixed. Don't go creating additional problems changing things that don't need to be fixed.
Like the plans.
Interesting, I don’t know for sure but I suspect that the answer will be made clear once you get the correct Sonex parts in hand to compare.
wow...I see a lot of posts that experimental is way better than certified but this kinda gives me pause, ie the build quality. I guess however through the miracle of modern media you can get the word out to other owners fairly quickly.
I once had a throttle cable snap on me during my takeoff in a Cessna 172. Experimental planes aren’t inherently more dangerous but as we’ve seen you really have to watch the build quality, especially modifications to the structure. Build your own and you’ll be fine!
Not flier but, never will be if this is the sort of shabby engineering and construction go into an aircraft !
but by the grace of God
Nope. Rivets failed. Dont kid yourself. Frankly I don't like that design one bit! And I am a PP, motorcycle risk taker type A. Nope nope. You are on the right track. Redesign.
The rivets failed because a non-stock part was used that physically overlaps the control horn and presses down on it when the tailwheel is over to one side. No re-design is necessary; they just need to rebuild the part per the stock plans so that the physical parts don't overlap.
So this is a design flaw? Presumably the Waiex wouldn't have this issue.
I have 1300+ landings on my Waiex with no apparent stressed rivets. I do have rod ends utilized to take up the vertical loads however.
Its not a design flaw with the aircraft - the aircraft was not built with the control linkage specified in the plans. The original builder of the airplane substituted their own part. This change caused a physical interference between the parts when the tailwheel is over to one side.
Obviously aviation is not a place to "Mickey Mouse" things are engineered for a reason, is your life worth cheaping out
That design is just all wrong...all wrong. Thats an accident waiting to happen and it almost did eh?
And yet there are quite a few of these things flying around and this seems to be an isolated failure…so I dunno. Clearly this exact setup is wrong.
Man.....Really sketchy designed lightweight rudder--tailwheel control linkage + doing aero......You seem determined pushing the fast track towards punching your "ticket" to the afterlife !! Totally independent & separated rudder to tailwheel linkages except maybe RC model aircraft