Fixing the HobbyKing pulsejet (part 2)
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- Опубликовано: 9 фев 2025
- Modifying the HK pulsejet for RC planes so that it would actually run was pretty simple but the absolutely awful quality welding that I mentioned in my review soon came into play and the engine split right along the weld-line where someone had been way-too busy with a grinder.
If you find your HK pulsejet won't do much more than pop and bang then you can try drilling out the fuel metering jet to 1mm from its standard 0.9mm diameter.
In colder weather, the HK pulsejet (like all pulsejets) benefits from a little pre-heating of the combustion chamber to improve fuel vaporization during the starting process.
The next step will be to repair this engine by welding up the crack but this may require a new strip of stainless to be formed and welded into place because the metal around the crack has been ground so think that any attempt to weld it would probably fail.
Stay tuned... some welding and fettling coming up soon as I repair the engine (again) and fit it to the Mini Talon.
Thanks for part 2 Bruce, been a fan of yours for a long time. First ran across you years and years ago while searching for pulsejet information. Wanted to buy one of your powerheads back in the day.
Hey Bruce! I was so shocked to see this follow up in my news feed but once again you have inspired me to pull an almost forgotten piece of hobby awesomeness and have another go at getting it going! :D
Keep up the good work mate :D
Thank you Bruce, drilled mine out, heated with hot air paint gun, it runs !!!!!! Blimey it's loud ! Thanks again, Chris UK
thank you! your video came at the perfect time, i was thinkiing along the same lines of drilling out the jet hole and my spare jet came yesterday, now i know i was thinking right!
Great video Bruce. Hope you don't go crazy trying to repair the tailpipe. Looking forward the the Mini Talon first flight.
I have entered the engineering side of youtube.
Great Bruce, really looking forward to seeing you weld with the tig , would love to see some how too videos on mig and tig , very helpful mate
Glad you finally got it running but advising on using a gas torch with that fuel soaked piece of wood seems like a potential Darwin award.
Great video! It wouldn't surprise me if the pre-heating with the heatgun started the micro fracture - what terrible quality.
It'd be great if HobbyKing offered you a replacement, or removed the product for sale as being defective.
I find it interesting how more and more people seems to notice the weather is out of the ordinary. Warmest december in Sweden ever! Maybe all the heat from NZ went to the northern hemisphere?
+RcLifeOn Yeah... it's 11 degrees at 9:20am here -- and this is supposed to be SUMMER! I had to put the electric blanket on last night and the wind has been relentless.
+xjet
I turned my freakin A/C on yesterday!
(Ohio)
Warm winter here in England too haha
Hello from Michigan, I was out flying today in 60+ F Weather in mid-Dec. No complaints.
+RcLifeOn We have an El Ninjo year - happens all 4 to 5 years.
I wonder if the paper thin ground joint is a common feature of all of these motors, or if this is just the unlucky bad one that Bruce has got. Has anyone else bought one and had success with it? Knowing HK quality control, it wouldn't surprise me if the 0.9mm fuel hole was fine for another motor, and it was just the large manufacturing tolerances messing this one up.
I'm very keen to see the next part of this video Bruce. Now if you can just make all the other part 2's that have been promised over the years, we'll be in luck! :P
+Chris Tate I've heard of others who have had similar failures -- and others who have not so it's all down to lack of consistency and poor QC.
It was 15 C here in Cornwall, Ontario on Friday. I am loving it. :)
The crack is not in the weld itself, but in the heat affected zone. So the thickness might not be the problem, but the chosen steel grade and welding skill. But definitely crap ;)
Cant wait to see the welding repair and it flying.
Those drill bits have gone up in price now. I still have 5 new packs left :D Shame about the blow out on the motor!!
Sets of metering can be had/made, and play a big part run stability, starting ease and reed life. IIRC a set of about 10 or so went by number drill sizes, and selection was a function of OAT, RH, barometric pressure, fuel blend, tank position within the specific model engine combination, star/planet alignment along with 8 or 14 other parameters. Metering jet selection was a 'black art' but once determined, things went smoothly... until something changed a little.... BTW, I looked a little last night and saw a someone using a leaf blower for starting! That would allow complete removal of the start nozzle; looked pretty clever! (Bicycle pumps were the starting norm back in the day...)
+rwbishop Have you seen Colin Furze's pulsejet-powered go-kart? That had a leaf blower for starting. I recommend you check RUclips and subscribe if not, because pulsejet. And he is absolutely brilliant and totally mad.
+pillsnotbills I can do better than that.
ruclips.net/video/clOmc3WI5fk/видео.html
***** Ah Bruce, you got me. I had not seen that, your oldest video dating from the dawn of RUclips. Brilliant. I've only been watching your videos for 3 years and missed most of the older ones. I shall have to correct that oversight, somehow.
The Clickspring channel has a tutorial on modifying drilbits for brasswork. It probably isn't practical for a drillbit that small, but it may still be worth looking at.
I never get your book you published years ago to learn about pulse jets since you are the expert. I think it cost me $5 but it was years ago so I just gave up on trying to get a copy.
I would use some scrap copper inside behind the weld so you dont blow holes everywhere. Great video
I know why its cold over there: We have all your heat over here! Its like 80deg Fahrenheit here in florida, in December! Its the warmest december I can remember...
+Low Elevation RC It was 15 Deg C here in Quebec yesterday. It only 4 Deg C today.
You think 80 is hot ? Lol. Imagine living in 106.
Thanx Bruce you are a star !!
you shouldn't have to do a damn thing to these motors. They should run right out of the box without correcting faults the manufacturer should have done before they even went on the market.
thanks for showing and explaining why NOT to buy the hobbyking crapjet!! +1
Cool how you can see it increase in length as the thing heats up and expands :P
2024 Bump ... Thanks to YOU and YOU Tube ... a person like ME gets GOLD on the YT University!!
The most useful pulsejet was used on the V1.
Don't forget to do the DB meter test after the Pulsejet is repaired.
the part 2 trolling at the beginning haha. nice video. A like from me. ;)
I think the Dynajet came with a neoprene tubing but maybe by enlarging the fuel line diameter you could get away with a .9 mm hole or make it less fussy.
Congrats on sorting it out, Bruce but yikes! Can't believe how crappy that seam was welded and dressed =(
What a pity HK can't find a cheap way to hydroform these things.
I might have to make a valved pulsejet at some point.
when you weld stainless, the back side has to have a shield gas or a back-side flux applied, so this also did not help the ground-weld situation out. It is VERY common for Chinese built Automotive Exhaust system manufacturers to not protect the back side of the weld...It "cauliflowers" if not.
+unionse7en Yeah, most of the time, instead of back-purging, I use a fairly thick adhesive aluminium tape. That excludes the air from the back of the weld (so stops those nasty oxidations) and it also helps sink away the excess heat so you're less likely to blow a hole.
Sweet!
I would love to see you do a challenge something like an endurance flight on a wing or the like
Think it would be possible to make a pulse jet from some threaded pipe, or car exhaust tubing? I was planning on either using threaded steel plumbing pipe or clamped together exhaust tubing. I'm leaning towards exhaust tubing because I can use some larger diameter tube to make the combustion chamber, then play with the lengths of the exhaust tube to see if it produces more or less thrust. I don't have any experience welding, but I wanted to build a basic pulse jet for fun, I don't plan on it powering anything, or doing much other than pissing off everyone for about 10 miles since I live in a small hollow. The sound will travel like nothing else, should be VERY amusing.
omg this guys sure does take the long way around to get the simplest point across its totally agonizing.
Hi Bruce, I'm looking at a small pulsejet, have you ever made an auto-start version? Where you don't need to either blow a leaf blower through it or air compressor?
I want to try maybe a small can of compressed air and on-board igniter, and some simple electronic timer to perform the ignition sequence, maybe Arduino?
Cheers
Dan
If engine is cold you can use ether starting fluid in spray can to start. It will start with one pump.
The HobbyKing Pulse Jet is a remake of a DynaJet Pulse Jet.. looks exactly like the original !
To aid vaporisation in many applications people add acetone.
to be fair, these come with jets that are precisely set up for high octane type fuels and its a given that if you use less combustible fuels, you need to adjust the actual jet as was shown here. being 0.9mm originally, i would have a guess that this 0.9mm was designed for lpg or butane rather than liquid fuel. nothing wrong with re-tuning the fuel jets. its a thing most people should learn if theyre going to use and play with pulse jets.
No, the Dynajet (of which this is a clone) was originally designed to run on Colemans fuel, a very low octane form of gasoline. To run a pulsejet on gas (LPG, propane or butane) would require a much, much bigger hole.
@@xjet maybe so, but the chinese one i got of ebay was setup for butane cylinders, the jet was so small, i used a thin guitar string to clean the jet out. But, just realised butane was pressurised which may be the difference here.
Northern Hemisphere cold? It was 61F in Washington DC today and it's supposed to be 70F this weekend (again)! El Nino baby!
Thumbs up for a Part Deuce!
This weekend it has been in the mid 70's in Atlanta Bruce. I was wondering how you'd keep it from melting the foam.
Hey Bruce. Good to see that there is at least a possibility of getting this thing to run. You have shown us the difference between the new and old fuel jets, but you didn't tell us WHICH jet you used when you got it to run. Will this engine run on either jet once you drill out that hole?
Show us how good you are at welding. I thing that would be great. good luck.
i was thinking about one of these but now i wonder if I could get Bob Maddox to build me a little one.
Maybe its worth buying mini reamers, in silversmith supplies or so: that way you can accurately and gradually make the hole bigger AND measure it with a digital caliper?
I know nothing about this stuff. I was surprised to find this engine only cost £60 here which to me doesn't bode well for longevity. On a new one would the metal be think enough to stand being reinforced with welding before being used? And as for pre-heating in the field wouldn't a couple of flasks of hot water do the trick if the fuselage could stand it?
Yes, back to pulsejets...
13 deg c in the south of the uk the weather has gone mad just like hk selling crap like that pulsejet lol
I'm looking to get into pulsejet models because I now live in an area where I can run it at my house. Obviously this kit is pure crap, I had slightly higher hopes as I can handle drilling but I don't have the setup to do welding/lathing. What would be y our recommendations for getting into pulsejets that isn't crazy expensive but isn't garbage either? Also are there any decent aircraft body kits out there for pulsejet? or just straight build your own?
Have you finished the final part of the scratch built coreflute plane project yet bruce? ;-)
I drill my jet and is working great on 100 octanes leaded gas but witch fuel you think can get more thrust ?? I order 2 jet more from hk to make some test
hi, I have a hk pulse jet also, I wonder if it is possible to internally
fix this engine in a jet made of vibrating, of course with the
necessary modifications? since already grateful
Bruce, great review as always. Would it be possible to somehow add throttle control on a pulse jet? Also will you be reviewing the TBS Crossfire anytime soon? Your prior LRS reviews were very helpful and I am now in the market for such a system - your opinion matters!
How does the fuel get into it when the level of fuel is lower than the pipe?
I have a larger version of this pulse jet that was my father's . It was made in the 1940's. I've always wanted to run it, but didn't know what was needed. What is the high voltage source for the spark plug..
LM555, car ignition coil. 12v operation.
Umm oh yeah you need a 3055 transistor.
Or you can actually do it with an electro-mechanicle breaker system. But that requires fabrication skills.
Thanks, I've done a few projects with a 555 timer chip. I grok the jest. Should be fairly simple.
It would be interesting to know the thrust if you could figure some way to measure it. Also, how much does it weigh? And what kind of fuel are you using and how much does it use per minute?
Very interesting learning about these pulsejet engines, I think I understand the basic working principles ,but I have some dumb ass questions. Do they require compressed air to operate? and do they need constant ignition ?
+mick thebass you need compressed air for starting but not for running and you don't need a constant ignition
Ah thanks F1, I'll try find a tutorial vid. I guess the air is drawn in by the escaping gasses then trapped in the chamber by a reed valve ? and the fuel is ignited by the latent heat contained in the walls of the chamber.
not a problem. there's plenty of tuts out there :)
Hey I am trying to build a Lockwood style pulse jet using gi metal plumbing fitting trying to start using acetylene gas it's just gives a loud bang or just burns flame even with LPG it just burns fuel as a burner but doesn't do anything
Hi Bruce can you please illustrate how the metering jet works. On starting the engine with your outside air supply I presume it creates a venturi over these two holes on the side of the fuel tube and when started the air pulsing in from the front of the motor takes over and assisted the fuel to enter the chamber for combustion creating a possible atmosphere changing to a negative atmosphere assisting recharging of the fuel.
Would a series of smaller holes around the this tube create better atomisation of the fuel, making starting easier, also the venturi affect would be greater when the engine starts.
The fitting of a conical ring mounted just before these holes so when the pulses running parallel to the tube enter the funnel shape and increase in velocity and as it emerges over the holes (spray bar holes) in creases the ventri and finer atomisation.
Or maybe I'm completely wrong on how this engine works?
Chris
I wonder if maybe the motor would run on the .9 mm fuel inlet if the motor didn't have a big hole in it.
Great job! What's your relation to MrTeslonian? He did a great job, too. Many thanks!!
Use map gas in the field to warm up housing.
ever consider that when you made a larger flue hole that you over pressurized the chamber and exceeded the eng. specs ?
+dennis tresselt No... the combustion doesn't work that way. The limiting factor is the amount of air that can be drawn in during the intake cycle. If you increase the amount of fuel too much you simply end up with a rich mixture that doesn't burn properly and you actually get *less* power with lower combustion pressures. I'll cut away some of the material near the crack and measure the thickness but I'm thinking it's as low as 0.1mm in places -- virtually foil rather than sheet metal.
+xjet sure... but a lean fire will burn hotter that a 16.1/1 or whatever the correct ratio is.
also, i think it was running lean from the factory..... thus why it would not run till you made a larger jet.
however.... the colder it gets, the more dense the air....
my 2 stroke runs lean the colder it gets, and richer the hotter it gets due to that air density change.
i think you might have run it lean....hotter fire... and it melted.
still... it should not melt like that even if it was lean....thats a BAD weld
+kain hall That's right... I've run pulsejets I've built myself for very long periods without any weld or metal failures because I don't grind back the welds just to make them look pretty :-)
I don't know anything about these Jet motors but I can tell you that anything that gets red hot almost orange the welding usually fail on tubing do all these jet motors of this type are welded there and that location
hey I have serious question is it okay to use liquid fuel like petrol and fire won't go back in the tube?
Is there any good engines that people sell because I would rather not weld? Or is there anyway to make an engine without welding
Hobby King will give you a new one - NO CHARGE.
I bet you could repurpose a BSA or Triumph vintage sausage muffler for pulse jet construction. Just finished a nightmare 20g tig tank job. Uhggg
I’m trying to find out where to buy one. Any ideas?
Have U ever considered a Miniature Warming Tent & or Tunnel [ Hot-House style] ? Just a Thought. YYZ60++-Planker.
Good video
It annoys me that this sort of garbage is still sold. it prob cost $2 to make. your puksejet builds look much stronger Bruce. I would not waste my money on the hobbycrap pulsejet. send it back mate and demand a good one.....
Thanks
Where can I buy a pulse jet engine that works out of the box?
Could u preheat the fuel on its way instead?
Think ill make a simple butane injector system along with aluminum ball bat and see if it works??
+xjet You're going to have to try pretty darn hard to do welding worse than what's already on the engine. It's a bit of a worry though about the strength of the rest of the welding.
Hobby King has unfortunately discontinued these. That sucks!
I can see a stainless / platinum reed valve and body would likely work better I'm unsure about the alloy itself but a small percentage should work anyway if working well the heat produced would become difficult to manage it will likely fire with a 2mm or larger intake opening as well.
Well I see the basics cast iron the heaviest least of expense but $10.00 rockets flying round everywhere you look could become annoying..
Thx for sharing!
does anyone know if there’s somewhere I can get these? It looks like they aren’t selling them anymore.
Dam that thing can blow up on you with welds like that
clearly the design team isnt talking to the manufacturing team. Probably a language barrier....if you know what I mean ;)
I get that these engines are crap, well the tailpipes are anyway. Does anyone make or have a source for replacement tail pipes?
So you over fuelled it and it broke.
Understand why it had restricted fuel?
+Bruce Baxter You clearly don't understand how a pulsejet works :-(
Clearly.
Umm,
No, it's not clear,
do tell me how you worked that out?
+Bruce Baxter A pulsejet produces its maximum power when the air-fuel ratio is stoichiometric. If you richen or lean the mixture from that point, it produces *LESS* power, not more. So, overfueling will cause the engine to run cooler and produce less power -- just as when you run a car engine too rich.
Ah, I see you are unable to read a question and answer it.
Try again, all you did was reinforce my point.
+Bruce Baxter Okay, I must defer to someone who is obviously an expert in pulsejets, what would I know? :-)
Anyone running a shortened version, I need to cut about 4" off mine for a better fit, but not sure if it will really affect how it runs?
You have all the same inflections as EEVBlog >
what draws the fuel into the combustion chamber
on startup, compressed air past the injector pulls atomized fuel, then as it fires, the air intake pulls it along on with each flame pulse
C'mon Bruce, it's a good excuse to fix that old TIG.
it wasnt being cooled by flying thorugh the air. Could that have been the problem? They are not meant to run stationary.
A well designed and constructed pulsejet will run for hours without cooling. Some of my ones have run for over 20 hours in a static condition and not suffered any structural failure.
What in the world is that thing and what's it used for? ???
GOOD OLD HOBBY KING SHITE
don't you have another youtube chanel? I'm pretty sure I'm subscribed to it, and have been for a while..
Yep, RCModelReviews
***** ok. thats probably it, thank you!
Dear Sir,
I am very interested in your channel. can you please show me how to use a fuel pump in the pulse jet, and how to time the fuel valve.
Regards'
May I ask why you'd want to use a fuel pump in a pulse jet engine?
Aaron Matt
Hi, because I want to use it on an rc airplane, so the tanks will be low in the fuselage, and to insure continues running
Only way I could figure doing is by having a pump push the fuel into a bowl above the engine and have a tube running from the bowl to the engine. You'd also have to run a return line from the bowl to the tank so it doesn't pressurize and force fuel into the engine. I should have prefaced by mentioning that I've never owned, operated or really messed with a pulse jet, but from what I understand about their operation that would be the way I would solve that problem.
l think it is originally designed for "white" gasoline--use for camping torch/ stove
Hello, i want to make this one but... how the fuel enters to machine? " xjet
the pressure differential of the compressed air flowing past the injector draws fuel
There is no excuse for anything to be sent out to the public like that. Someone like me has no experience at welding on metal like that and shouldnt have to anyways. I bet there are other companys out there willing to manufacture that motor. The only parts you would need is the end parts.
At Hemmmmmmmmmm, There are many of us with the skills to mig tig.
If you don't know how,,,,, Learn Damnit!
Warren Osborne So you are saying if I am not a brain surgon,then I should learn.hummm
plenty of good ol boys can't manage it.
Still, you shouldn't have to weld a motor you just bought.
whats your idea of cold?