danijelc

Hi,
I have drawing for PIPER PAWNEE,80" wingspan,but there is no drawing for wing.Only type of airfoil is writen(NACA 2412).This is
semi-simetric airfoil and this is all what I know about it.If somebody know something about this airfoil,please inform me.I am intersted about speed(stall speed also),stability,acrobatic possibility and if possible tell me diference between NACA 2412 and CLARK Y
If somebody have idea for some other airfoil for this model,please tell me.

Thanks!
Danijel

Tall Paul

There's not a lot to choose between a Clark-Y and the NACA 2412.
Either will work just fine on your plane.

R8893

My Feedback: (20)

Danijel,
I have a book on airfoil sections for full sized aircraft. The NACA 2412 data is given at a Reynolds number of 3,120,000 and may not be accurate for model sizes. I am a chemical engineer so I can't stand behind any aeronautical calculations. I have some other data and modeling experience that tells me that airfoil results at modeling dimensions follow similar patterns. The data I have shows the stall at 20 to 22 degrees angle of attack for Reynolds number of 3 to 8 million with a lift coefficient of 1.4 to 1.6. Your stall speed will depend on model weight and wing area. I have used NACA 23018 on an original design (looks similar to an amateur designer although much thicker) and it flew very well including aerobatics. I too (like Tall Paul) suspect the 2412 would work well on your model. If you need stations to plot the airfoil you can send a PM and I will copy for you.

I just looked deeper into my collection of data and found a hand drawn graph comparing Clark Y and 2412 at Reynolds number of 80,000--model size data. Can't remember where I got it. Clark Y stalls at 10 degrees AOA with lift coefficient of 1.0. 2412 stalls at 12 degrees AOA with lift coef of 1.2. I would say the 2412 is a better choice for your model.
Chuck

danijelc

Thanks!

BMatthews

2412 was a commonly used airfoil in many of the more succesful early RC birds of the 50's and 60's so you won't go too far wrong if you use it for your model. It has 1.92% camber compared to the Clark Y's 3.43%. Both are 12% or very close to it (11.7 for ClarkY). So the 2412 will be more capable if you start doing much inverted flying or general stunting. The ClarkY should have the advantage in lower landing speeds and ease of building. The 2412 having a curved lower shape will reguire some jigging of some form. But for a major building effort that comes with an 80 inch model this isn't much to deal with either way.

I got all this from Profili2 BTW. It's got both airfoils in the database. With it you can design your wing section and print templates complete with spars, sheeting and leading and trailing edges.

If you think you tend to build heavy then I'd suggest you choose the Selig 8035. It's a slightly thicker section designed for use on scale warbirds that often have higher than normal wing loadings. It's suppposed to have a very kindly stall charactaristic when built using a fully sheeted wing to retain an accurate shape.

Hans Meij

You did mean to say the Selig 8036
The 8035 is a symmetrical aerobatic airfoil.

danijelc

Ok,thanks to all of people who gave me information about airfoils,but i have one more question.
Dihedral?Is it same value for low wing and high wing planes.On my high wing model(72" wingspan) is about 4 cm on each wing.
On new model i will use NACA 2412 profile.
Thanks!
Danijel

BMatthews

My bad, you're quite correct, it was the 8036 I meant.

BMatthews

On low wing models some dihedral is often used to avoid adverse rolling tendency when using a lot of rudder. The old Topflight Contender was a good case in point. Low wing with no dihedral at all. When trying to wingover or knife edge folks report that the model wants to roll away from the yaw slightly. Even a couple of degrees of dihedral in that case would have stopped that tendency.

So a 2 or 3 degrees would be a good thing. If you want the model to be self righting to some degree you'll need more for a low wing, as much as 4 or 5. If you intend on three channel control (no ailerons) or want even more self righting ability then more is needed. For this last case there should be enough that the wingtips are at least as high as the thrust line as a general rule of thumb.

danijelc

Sorry,i forget to ask what about AOA of wing when modell is aligned with centerline.
Danijel

rmh

That old Contender was an extremely low aspect ratio setup - and was pretty stable .
The rudder placement was above thrust line . Adverse yaw wasn't all that bad.
On our low aspect ratio stuf (3-1 aprox), dihedral for stability is not needed . pretty much true for any really low aspect ratio setup
On my 3D stuff- Wing is closer to thrust line and rudder area is about 2/3 above it
back when I had the Contender (1970), I also tried doing a 40 Quickey type -with a flat wing.
pretty lousy on stability when trying any rudder corrections . lots of adverse yaw.

BMatthews

I am guessing that you actually mean when the AIRFOIL is aligned with the centerline?

You need to remember that the AoA changes with flight speed. The slower the model is flying the higher the AoA needs to be in order for the wing to make the lift it needs. At slow speeds near the stall the wing may be flying with a 5 to 7 degree angle of attack. At high speeds it may be as little as 0.5 to 1 degree AoA even for a symetrical airfoil. With a cambered airfoil like the 2412 high speeds may even see your AoA at 0 or a 1/2 degree negative. It all depends on the amount of lift your wing needs to generate to maintain steady flight.

During all these changes in flight speed and AoA your fuselage just follows along for the ride. In truth our models do not really need any incidence angles in the fuselage to wing. That angle comes from full sized aircraft where drag and speed are primary concerns and the wing is always set at the right incidence angle compared to the mininmum drag attitude of the fuselage to ensure the least fuselage drag at cruise speed range. But our models seldom fly at a steady state for more than a few seconds. Usually we are turning or looping or tossing it around so economy of drag is not an important factor..... unless you're a racer or fly sailplanes.

So for general sport flying models that spend a lot of time upside down make it all 0, 0, 0 (engine, wing, tail) angles with your 2412 and a close to neutral CG location . For trainers that spend all their time right side up building in some trim to compensate for the forward CG is worthwhile so something like -2, +2, -1 and a cambered wing section and it'll trim out with little if any elevator trim being needed. Such angles also ensures that the model flys with the fuselage at an angle that looks right to our eyes. Aerobatic models would look funny if the fuselage was level when upright and pointed nose high when upside down. Adding positive incidence to the wing compared to the fuselage would cause just this situation in an aerobatic model because the wing needs to fly with positive angle when upright but negative angle when inverted so the fuselage have to aim with the wing.

Tall Paul

With the chord line of the airfoil horizontal, a cambered section will have lift at this "zero incidence".
Typically the zero life line will be at a negative alpha, (angle of attack, not angle of incidence).
The NACA 2*** family shows a consistency for the camber, zero lift changing more negatively as the Re increases.
Re is a factor based on chord and airspeed. The more of either, the better the profile performs.
http://www.nasg.com/afdb/index-e.phtml

danijelc

OK,i will choose:NACA 2412
Dihedral:2 deg
Wing incidence to fuselage: 0 deg

Thanks!

fokker38cc

Hi
I like good luck for you and it will be a beatiful plane.
My father are croatians. (moji oci su hrvati kako i vi)
Happy landings
Jose

mulligan

For future reference, you can find airfoil coordinate data here:

http://www.ae.uiuc.edu/m-selig/ads/coord_database.html