Aerodynamics Discuss the physics of flight revolving around the aerodynamics and design of aircraft.

touch n go airfoil recommendation

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Old 11-23-2018, 08:44 AM
  #1  
whiskey29
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Default touch n go airfoil recommendation

Hi,

I was delegated a task to build a plane for touch n go competition,
I know I need to build it light so I can do tighter turns for landing,
Initially I was going to build the model with wide body to give it drag to diminish the speed quickly.
May be someone can suggest an airfoil to look at, I tried to learn and read about the coefficient, however I have no number for the base of comparison.
I was thinking something thick so it supports better structure for the harsh landing too, also giving high drag.
Thanks in advance
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Old 11-23-2018, 09:22 AM
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Don't get caught up too much on airfoil data when it comes to powered models. Either a Clark Y or semi symmetrical airfoil of 16% to 18% and a high point 30% back from the leading edge will do just fine. Airplane setup and trim IMO will be much more important.
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Old 11-23-2018, 01:07 PM
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Airfoil type isn't going to do much for you unless it comes down to you and someone else being very closely matched. What is more important is your abilities with that specific airplane. Beyond that, I think most any good sport plane can do the job. Depending on what rules are used for the touch and go, you may want to add flaps, bigger rudder, etc. I'd also stick with something intended for a .30/.35 and then stick a .40 on it for some extra punch when needed.

I use to use a Proctor Mini Antic for all my fun fly events. It wasn't as fast as most but then it didn't require as much air space either. For T&T I'd take off and climb a bit. Do a hammerhead turn (very authoritative rudder) and touch down in the opposite direction. Another hammer head and repeat. If the pattern had to be sort of followed, it could turn tighter than anyone else and with it's predictable sink, touch again when and where I wanted.

Thing is though, and this is the whole point, I was one with that model when ever I flew it. I have many, many hours on that plane. It has wore out 3 OS .35's in its 38 years of flying. I knew what it was going to do before it did and could almost fly it with my eyes closed.

So the bottom line is, like everything else in this hobby, you need to practice, practice and more practice!
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Old 11-23-2018, 01:08 PM
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Lots of T&G's in a short time was one of the old fun fly model events. Really thick full symmetrical airfoils and really wide ailerons. Sometimes set up as flaperons or perhaps spoilerons. Very light with lots of power.

Do an image search for "funfly model airplane" and you'll see lots of examples. And a search after that for "funfly model airplane plans" will turn up a few examples to study.

Some manner of shock absorbing gear wouldn't hurt either.
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Old 11-23-2018, 01:14 PM
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at least, with the Clark Y airspeed and lift are somewhat more lineal than other profiles. touch and goes,.... I would think,..... might be easier to organize by an airfoil that increases and decreases lift by throttle position.
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Old 11-23-2018, 05:53 PM
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Thank you for the replies.

I could not agree more practice, practice and practice is a good key to success,
however, good equipment must follow, right ?

I forgot to mention that the local rules states the airplane must have the three wheels on the runway for 30 feet of distance in front of the pilot.
Its more like touch and roll and go, if it were touch only, we can worry less about the landing speed as long as it touch before go again.

I will try the hammer head method, now I am also thinking shorter wing and bigger rudder

So the airfoil I looked at was clark Y and Naca 2415, which is thicker.
I have to dissagree that airfoil is not important in this matter,
I could choose 66012 that we use for pylon race, I am sure result would be different.

I agree setting the airplane right is the key, its always the key to get airplane flying right,
our first version used a plan that was given by deceased Argentinian aeromodeller,
didnt have a change to ask his airfoil, but I modified it for our rules to keep it on the ground better.

I just remember the fulfly air craft that was popular before 3D flight, they usually have very thick wing and wide chord..
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Old 11-24-2018, 07:10 AM
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I can't agree that the airfoil makes no difference,. pick a thin airfoil that requires high speed and stall quickly/violently vs. a a nice fat airfoil that can float along at walking speed and see which one results in more broken planes when doing touch and goes..
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Old 11-24-2018, 08:04 AM
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I guess you guys missed where I stated an airfoil with 16% to 18% thickness. That would only be to bleed off speed quickly. My latest design has an airfoil section only 12% and 14% thick and will slow down very nicely. A thin airfoil does not automatically mean unstable or will tip stall easily. On our models the airfoil curvature has little effect, the thickness has effect on drag and where the high point is placed has some affect on stability. To avoid tip stalls the tip airfoil can have the high point moved forward a little, on a tapered wing you can increase the thickness percentage. Example, my Divergent design uses 12% airfoil thickness at the root and 14% airfoil thickness at the tip. Wing loading is also a big consideration. You simply can't select an airfoil and expect your desired results, you have to design a complete package.
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Old 11-24-2018, 01:50 PM
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your latest design has two wigs , right ?........how much more drag does that introduce ?. given that,....I would say you could reduce the airfoil thickness and maintain some decent deceleration. drag is exponential,.....two wings with a slightly thinner profile will produce more than "twice" the proportional drag than one wing with a slightly thicker profile.
let's stick to comparing apples to apples. and in a n above post you stated that a Clark Y would be a decent choice. I think the concept of designing the entire package to best use is pretty obvious requirement,...that said, discussion of aifoil section has to start somewhere no matter what complete system is being designed.....pick an airfoil and design a system around it, or pick a system and design the airfoil around it,...either way specific airfoil profile has to come into the process somewhere. so I don't see the point in your most recent post.
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Old 11-24-2018, 02:55 PM
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Perhaps you are more interested in being argumentative then seeing the point. My last post is an explaination that thin airfoils can be quite stable a slow speeds. I did not claim that the bled off energy quickly.

Airfoils: depends on how specific you would like to get however IMO there it 90% of the time is a wasted effort unless designing a sailplane or a pylon racer. That is when staying within the same family of airfoils. Clark Y, Semi Symmetrical and Symmertical are generally the three choices. Choose which one to go with based on aircraft requirements, choose the thickness and then set the high point at 30%, draw a smooth transition from leading edge to trailing edge. Works every time.

Last edited by speedracerntrixie; 11-24-2018 at 02:57 PM.
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Old 11-24-2018, 03:08 PM
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Oh lord here we go again the professors are at it again, hijack the ops thread and argue about who knows best, should be called father knows best.

This what your looking for?????? Airfoils are fat and symetricle.

look up The Yellow Jacket Speed 400 Fun Fly Plane plans should be available for download.


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Old 11-29-2018, 07:32 PM
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Let's try to not let this become an opportunity to become dingleberries guys. It's too close to Christmas, and Santa is watching.
To the OP- have a look at some of the purpose built fun fly planes. Appowner gave you the right advice early on- check out some of the successful designs that have been around for a while.
I agree that a thick symmetrical airfoil is the way to go. I'm not nearly as well versed in aerodynamics as Speedracerntrixie is, so I can't cite a textbook or decades of experience in designing aircraft to back that up. What I can do is point out that pretty much every competitive design has had that kind of wing, so it stands to reason that that's what works.
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Old 11-29-2018, 08:45 PM
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Yes, a thick symmetrical airfoil sounds about right. I would opt for a Ugly Stik type airplane with trike gear and split flaps/ailerons that can be thrown into crow mode.
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Old 11-30-2018, 05:33 AM
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Taurus, NACA 2419, airspeed controller for throttle to maintain an airspeed of 40 km/h switched on at 0m50sec .
Start with touch and go, after that touch, rolling and go. The goal for me was to make the longest possible touch, roll and go at our field.
Have attention for the under carriage!

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Old 12-01-2018, 05:17 AM
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The OP may have already thought about all this, but there is definitely more to designing a good fun fly plane (or any purpose built plane) than choosing the right airfoil. You need a tougher than usual landing gear setup, preferably with some shock absorption, big control surfaces for maneuverability, and the lightest possible weight. The venerable old Ugly Stick with a stronger undercarriage and flaps added has been a constant contender because it's pretty close to ideal, but as these kinds of events have continued year after year improved designs have surpassed it.
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Old 12-01-2018, 08:09 AM
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Actually all you really need is a pilot who knows what they are doing with that airplane.

I have a stock Proctor Mini-Antic that I'll fun fly against anyone. And it's 38 years young!
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Old 12-01-2018, 09:04 AM
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Interesting thread - I am contemplating a similar project. I wanted a balsa .40 glow to knock around for 3D practice. Have several engines, and lots of balsa. Not much "new" out there for that, especially if you eliminate profiles.
That other RC forum has a long thread dedicated to the Hangar 9 Twist under 3D glow. In looking at it, I was struck by a very high similarity to an old Model Aviation plane I built two of back in the early 90's - "Jumpin' Geo" I think I will be mating the Geo wing to a Twist fuse. Google the name, and you can read the Model Aviation construction article - lots of info about the design reasoning for fun fly events and why the choices for that design. Designed just when "fancy" radios were starting to come out, so used a sliding servo tray to couple spoileron/flaperons to the elevator to get super, super tight loop-to-land performance. It was a superb flyer. Very docile on low rates, and wild on high. I flew one for several years, and the other I gave away and is still flying. Borrowing the base elements should also get you a great plane. No, you do not have to build the "geodetic" wing, but it is really, really cool!

The Geo uses a very fat fully symmetrical foil, big control surfaces, and is very short coupled. It was typical for its day - using a big nose gear, and long wingtip skid wires as the only landing gear. Everything pared down to save weight. Like the OP, I want a more traditional gear setup, hence borrowing the Twist fuselage (there are plans available on that other forum for the "Tweplica" that is a scratch built Twist). Plus I prefer putting most of the radio gear inside the plane, and wanted a longer tail moment - although that will reduce maneuverability for loop-to-touch, and likely will increase weight a bit. The Twist wing is almost exactly the same, except that the Geo airfoil is just a slight bit fatter (~1/16th inch).

Despite how complex the wing looks, it is a really simple plane to build - it can all be done with a hobby knife and a razor saw if that is all one has - and it builds pretty fast. If I remember right, I cut and framed up the two of them in one weekend back in the day.

And, it is so basic, powering it with electric would be a no brainer.
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Old 12-01-2018, 09:23 AM
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darn

Last edited by Propworn; 12-01-2018 at 09:28 AM. Reason: dual post
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Old 12-01-2018, 09:26 AM
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Originally Posted by jester_s1 View Post
The OP may have already thought about all this, but there is definitely more to designing a good fun fly plane (or any purpose built plane) than choosing the right airfoil. You need a tougher than usual landing gear setup, preferably with some shock absorption, big control surfaces for maneuverability, and the lightest possible weight. The venerable old Ugly Stick with a stronger undercarriage and flaps added has been a constant contender because it's pretty close to ideal, but as these kinds of events have continued year after year improved designs have surpassed it.
Most of the fun fly competition planes flown in the early days were with a single wheel dual spring gear tall enough the prop did not strike the ground with a hard landing and stop the engine. Now the preference is electric and two wheels. No engine stoppage due to contact with the ground.

Fellow in our club who still flys funfly now does the same indoor with the indoor flyers with no airfoil at all just flat foam.
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Old 12-06-2018, 10:12 AM
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The need for a landing roll of some 30 feet in contact with the ground will certainly be a game changer. And it does point towards the idea of using trike gear.

You'll want to set up the model with a bit of a nose down stance when on all three wheels. Assuming a symmetrical airfoil that will prevent it getting light and lifting off the ground. Using a negative angle like this is an old pattern model trick that was done just for this reason. You don't need or want much, just a couple or three degrees negative angle for the wing. You may not even need that much if you choose to use upward deflected flaperons as noted below.

If you run full span flaperons you might also mix in some small amount of negative flap so as to require that you get the nose higher for the landing approach and to add additional drag to the model through essentially running with negative airfoil camber. Set up the mix so that idle and very low throttle has some up flap And by mid throttle and higher from there that it's back down to flat. Many Tx's work that way with the mixes where you set the amount of the mix either side of center. If your Tx works that way then it'll be easy to do. How much? You'll have to play with that but I'm thinking maybe a max of 15 to 20 of up flap. But if it starts to affect how the aileron function responds you may need to go with less.
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Old 12-06-2018, 01:56 PM
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Yep - with my Geo, I had the old Ace MicroPro set to drop flaperons at high throttle, to get it off the ground and up as soon as possible, and as I went inverted in the loop, low throttle gave spoilerons, both to kill the lift and give lots of drag on the way down to make the touch.
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