In response to suggestion on my previous builds that I should use a KF airfoil on my wings, I decided to do some testing to examine their characteristics.
I just came across your video. I have been using KF airfoil on all my plane's wings for past ten years. I agree with you, this is a good airfoil. It's simple to build, and add strenght to the wing. Job well done explaning and experimenting with this great airfoile. Two thumbs up!!
Great work, it's good to see how inovative you have been in building the tunnel and making your own testing instruments. Two things though that may give you more accurate results: 1... you should really test the lift and drag at about 2 degree increments from 0 to 20 degrees. And 2.... the air foils need to be bigger not to be working at very low Reynolds numbers - which will give you inconsistent results.
This was very helpful, I think my next build will be a kf airfoil because low stall and higher lift at higher aoa to me are both huge advantages over reduced drag and low aoa lift, with rc planes were not trying to travel (usually) were trying to have fun, so these are pretty neat characteristics for rc.
kudos! that's backyard science done right! =) i have to say, i'm a little proud, that your results match up with my clonclusions and assuptions. apparently KFs are great for theyr simple construction, and the stall characteristics andover all nice "feel" and handling, that everybody praises. while traditional airfoil profiles still have the edge in performance. one thing, though: i'm convinced, that the exact profile of the leading and trailing edges has a big impact. i did an experiment with 3 identical 25*7cm strips of 4mm depron as airfoils, on the same, equally simplistic body, with a 5 cent coin as ballast. #1 left as is, #2 with the edges simply sanded round, and #3 with a typical airfoil front profile, and tapered down into a narrow edge towards the back. quite like a sail plane's thin wing profile. unsurprisingly #3, besides being a tad lighter, was noticably faster, had more lift, and a very good glide slope. i had to move the coin foward. rounding the edges really only made it look nicer. peace~
The usual way to put this data is to have a lift of drag function for a fixed airspeed at varying angle. Search for "airfoil OR aerofoil OR profile polar" and wiki for "Drag Polar". Good job!
One thing to keep in mind is that an airfoil that is no good at one Raynolds number might be good at another. In this case there is an advantage at low RN and high AoA.
I think there are a lot of problems, that need to be adressed, before you spend too much money and time into something, that will always have trouble, yielding comparable results. - the profiles are very small in width and length - short length will result in quite low reynolds numbers, which probably will not gain comparable results for model airplanes - small width will add a lot of drag, that doesn't come from the profile itself, but induced drag. (it sais more about the wing shape, than the profile) - the profiles are pretty bumpy and seem less thick on the inside, sompared to the outside. especially on laminar flow airfoils, bumps will increase drag significantly - that wind tunnel causes turbulent flow by (inlet-, outlet-, corner-) design.. and rotating airflow by the turbine (and design), so your flow-/profile- angles will greatly vary in time In most cases a proper airfoil (with turbulators, if needed) will be better than a KF airfoil, without having structural, and aerodynamic shortcomings. But you found a really interesting and fascinating aspect of aerodynamics there. If you are interesting in reading into it further, you may want to find articles about flow separation / separation bubbles and boundary layers. Unfortunately I can't recommend any english literature, since it's not my native language and I dont' have anything english on that topic. But google should provide some first stepping stones on those topics. further information can be found on michael seligs uiuc homepage for example. he's much into (model airplanes) low reynolds profile design.
Certainly a possibility. However due to the fact that it was a side by side comparison, I believe both models would have been exposed to the same conditions which should negate any effects that this would cause.
Yes, given the aspects of price, -ease- and more importantly *speed* of fabrication of a fanfold foam wing, or other cut-n-clue assembly style. No, these are not for competition level pattern or speed wings. They are for slow fliers, and combats and other 'disposables.'
Your wind tunnel should have some sort of filter. This filter will make the direction and strength of wind is more uniform. You can make it from a straw pieces are arranged like a honeycomb. Just googling.
+Boekan Arsheetec He was using the fan as an exhaust rather than a blower, so the filter shouldnt be necessary since there is no turbulence at the intake.
Nice, hands-on approach. Seeing that your data matched up with previous tests, I would say that your possible inaccuracies in measurements is not as significant as one might thing. Avoiding stalls is a favorable characteristic to have. Now, what TYPE of KF will you use? :)
Subtle but well-meant hint: Don't wave your empty hand but seize an example of your topic and begin to show details. Need not be much but will be better than nothing (in your hand), Good content though!
Наука
I just came across your video. I have been using KF airfoil on all my plane's wings for past ten years. I agree with you, this is a good airfoil. It's simple to build, and add strenght to the wing. Job well done explaning and experimenting with this great airfoile. Two thumbs up!!
Great work, it's good to see how inovative you have been in building the tunnel and making your own testing instruments. Two things though that may give you more accurate results: 1... you should really test the lift and drag at about 2 degree increments from 0 to 20 degrees. And 2.... the air foils need to be bigger not to be working at very low Reynolds numbers - which will give you inconsistent results.
Thank you for the advice and feedback. I really want to revisit this project with a more advanced setup, I will take these points into consideration.
This was very helpful, I think my next build will be a kf airfoil because low stall and higher lift at higher aoa to me are both huge advantages over reduced drag and low aoa lift, with rc planes were not trying to travel (usually) were trying to have fun, so these are pretty neat characteristics for rc.
+Travis Pratt Thanks! Good luck on the build. I've come to really like the flight characteristics of KF airfoils.
Thanks for the comment! It is certainly on the to do list. At the moment I am trying to come up with a method of airflow visualization.
kudos! that's backyard science done right! =)
i have to say, i'm a little proud, that your results match up with my clonclusions and assuptions. apparently KFs are great for theyr simple construction, and the stall characteristics andover all nice "feel" and handling, that everybody praises. while traditional airfoil profiles still have the edge in performance.
one thing, though: i'm convinced, that the exact profile of the leading and trailing edges has a big impact. i did an experiment with 3 identical 25*7cm strips of 4mm depron as airfoils, on the same, equally simplistic body, with a 5 cent coin as ballast. #1 left as is, #2 with the edges simply sanded round, and #3 with a typical airfoil front profile, and tapered down into a narrow edge towards the back. quite like a sail plane's thin wing profile.
unsurprisingly #3, besides being a tad lighter, was noticably faster, had more lift, and a very good glide slope. i had to move the coin foward. rounding the edges really only made it look nicer.
peace~
Everyone needs a wind tunnel! ;)
fantastic video mate. I'd love to see some of the other kf airfoils, aparently KFm3 has pretty good lift properties.
Primative but certainly interesting. More testing than I have done in a controlled setting. Good job, you gained a subscriber!
Awesome!
Excellent video Tim! You should try testing different KF airfoils. I achieved best results with the KFm4 on my pusher jets. Keep up the good work.
The usual way to put this data is to have a lift of drag function for a fixed airspeed at varying angle. Search for "airfoil OR aerofoil OR profile polar" and wiki for "Drag Polar".
Good job!
One thing to keep in mind is that an airfoil that is no good at one Raynolds number might be good at another.
In this case there is an advantage at low RN and high AoA.
I think there are a lot of problems, that need to be adressed, before you spend too much money and time into something, that will always have trouble, yielding comparable results.
- the profiles are very small in width and length
- short length will result in quite low reynolds numbers, which probably will not gain comparable results for model airplanes
- small width will add a lot of drag, that doesn't come from the profile itself, but induced drag. (it sais more about the wing shape, than the profile)
- the profiles are pretty bumpy and seem less thick on the inside, sompared to the outside. especially on laminar flow airfoils, bumps will increase drag significantly
- that wind tunnel causes turbulent flow by (inlet-, outlet-, corner-) design.. and rotating airflow by the turbine (and design), so your flow-/profile- angles will greatly vary in time
In most cases a proper airfoil (with turbulators, if needed) will be better than a KF airfoil, without having structural, and aerodynamic shortcomings.
But you found a really interesting and fascinating aspect of aerodynamics there.
If you are interesting in reading into it further, you may want to find articles about flow separation / separation bubbles and boundary layers.
Unfortunately I can't recommend any english literature, since it's not my native language and I dont' have anything english on that topic.
But google should provide some first stepping stones on those topics.
further information can be found on michael seligs uiuc homepage for example.
he's much into (model airplanes) low reynolds profile design.
Certainly a possibility. However due to the fact that it was a side by side comparison, I believe both models would have been exposed to the same conditions which should negate any effects that this would cause.
You've gotten way taller. Good job growing. Do a kv to prop thrust comparison. Or brushless motor rewind.
Yes, given the aspects of price, -ease- and more importantly *speed* of fabrication of a fanfold foam wing, or other cut-n-clue assembly style. No, these are not for competition level pattern or speed wings. They are for slow fliers, and combats and other 'disposables.'
Great video. You should do more aerodynamic test video like this. Awsome wind tunnel by the way. I like the lift and drag meter to. I subscribed.
please do the same tests again, but comparing the different KF steps. especially #1,2 and 3. thanx.
+RCPro Driver Seconded. I'd like to see this.
Cool, thanks!
Nicely done!
nice video!
You could try attaching strings to the surface of the airfoil. I've seen this method used before. Just an Idea.
Your wind tunnel should have some sort of filter. This filter will make the direction and strength of wind is more uniform. You can make it from a straw pieces are arranged like a honeycomb. Just googling.
+Boekan Arsheetec He was using the fan as an exhaust rather than a blower, so the filter shouldnt be necessary since there is no turbulence at the intake.
Thanks Tim, how about a test at about 5 degrees which may simulate a cruise condition? I would love to see the difference at that AoA.
Clear and thorough explanation. Very well done.. Are you an AE student?
Nice, hands-on approach.
Seeing that your data matched up with previous tests, I would say that your possible inaccuracies in measurements is not as significant as one might thing.
Avoiding stalls is a favorable characteristic to have.
Now, what TYPE of KF will you use? :)
interesting results :)
nice charts!
what are we building next im ready to build another plane
what was that instrument @ 2:18 ?
wana knw more about that one.
could u give me more details
After a quick search on the net I could not find the Cl-AoA graph of KFm airfoils, have you seen any?
Stipa-Caproni
There's an awful music track running in the background? is that on purpose or is my itunes playing up???
Subtle but well-meant hint: Don't wave your empty hand but seize an example of your topic and begin to show details. Need not be much but will be better than nothing (in your hand), Good content though!