Airfoil Shape Question - RC Groups
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Jul 09, 2018, 11:30 PM
Registered User
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Airfoil Shape Question


Hello!

My question is if this looks like any of the existing airfoils in terms of camber and general shape? On what type of RC planes have you seen them? Pictures attached. Thanks!
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Jul 10, 2018, 02:00 AM
Wake up, feel pulse, be happy!
Piece's Avatar
It looks like a chubby foam taco but there's no reason it shouldn't fly. Probably won't win any prizes for efficiency, though.

The lack of a visible spar structure is the only thing that stands out as a potential issue. You'll have to judge for yourself whether or not it's strong enough for its intended application.
Latest blog entry: My feet smell funny
Jul 10, 2018, 08:07 AM
Build, crash...repeat
AleRRon's Avatar
It’ll probably work because RC planes are pretty forgiving, but it’s not quite a typical airfoil. Looks like it’s missing the trailing edge. For a more normal shape airfoil look up Clark-y or for an RC specific wing look up Kline Fogleman in this forum.
Jul 10, 2018, 08:50 AM
Registered User
The trailing edge is there, it's just that theres black tape for the moment.
Jul 10, 2018, 09:04 AM
Retired CAD guy
birdofplay's Avatar
Airfoil schmairfoil !

I used to worship the Airfoil gods pouring over all the sims and curves and data points.
Wondering at all the odd shapes and attempting to accurately recreate them for my models.

Then about 20 +- yrs ago along came XPS FOAM ,
along with electric motors an a series of, all around, power to weight ratio improvements.

Instantly I was able to fly aerobatics and do 4 dozen + touch and go's and
hang effortlessly in the air without a fancy airfoil. In fact NO airfoil at all.
It was a flat sheet or 1/4 foam and didn't even have a rounded LE or tapered LE.
Dead simple yet effective enough for model plane use.

The Airfoil Gods died that day !

Sure if you really have to have that last 10% of "performance" for some special
purpose or contest then a true airfoil is what you need.

But to get in the air quickly and with minimal effort , basically, to heck with the airfoil.

Look and any Full sized airplane.
Transports, Fighters, Soaring gliders ...
They all fly at "some" angle of attack, JUST LIKE A KITE !
That's IMPACT LIFT , not all that Bernoulli stuff !

IF you've built your model so pretty and detailed and heavy
THEN you likely will need that last 10% of Lift improvement created for an airfoil.

But if your just getting into modeling and want to get in the air quickly
and with less effort then don' t fall prey to the AirFoil Gods and don't bother
worshiping at their alter for countless hours and hours.
Jul 10, 2018, 11:27 AM
Scratch builder
See the wing videos in this thread. Your on the right track. Look at his shape compared to yours.

https://www.rcgroups.com/forums/show...ild-University

Welcome to RC groups! Much info in this thread. Wing thickness should be 20% of the chord (leading edge to trailing edge) or less.

Not a firm rule! Gliders are thin, maybe less than 10%.
Last edited by KenSt; Jul 10, 2018 at 11:38 AM.
Jul 10, 2018, 12:42 PM
Wake up, feel pulse, be happy!
Piece's Avatar
Quote:
Originally Posted by birdofplay
Airfoil schmairfoil !

I used to worship the Airfoil gods pouring over all the sims and curves and data points.
Wondering at all the odd shapes and attempting to accurately recreate them for my models.

Then about 20 +- yrs ago along came XPS FOAM ,
along with electric motors an a series of, all around, power to weight ratio improvements.

Instantly I was able to fly aerobatics and do 4 dozen + touch and go's and
hang effortlessly in the air without a fancy airfoil. In fact NO airfoil at all.
It was a flat sheet or 1/4 foam and didn't even have a rounded LE or tapered LE.
Dead simple yet effective enough for model plane use.

The Airfoil Gods died that day !

Sure if you really have to have that last 10% of "performance" for some special
purpose or contest then a true airfoil is what you need.

But to get in the air quickly and with minimal effort , basically, to heck with the airfoil.

Look and any Full sized airplane.
Transports, Fighters, Soaring gliders ...
They all fly at "some" angle of attack, JUST LIKE A KITE !
That's IMPACT LIFT , not all that Bernoulli stuff !

IF you've built your model so pretty and detailed and heavy
THEN you likely will need that last 10% of Lift improvement created for an airfoil.

But if your just getting into modeling and want to get in the air quickly
and with less effort then don' t fall prey to the AirFoil Gods and don't bother
worshiping at their alter for countless hours and hours.
If you're using a solid object to push against the air, then it's an airfoil by definition, no matter how blocky its shape may be. Flat plate wings work great in places where ease of construction outweighs aerodynamic efficiency, but you're still using an airfoil, and all of the exact same physical laws still apply.

One of the biggest drawbacks is actually structural, not aerodynamic. It becomes very difficult to hide a lightweight and rigid spar structure inside a wafer-thin panel, so these wings are limited in the bending and twisting loads they can handle (particularly in torsion).

If you increase thickness to improve strength, the next logical step is to begin tapering the edges of the rectangle for less drag. The familiar teardrop "airfoil" shape is found in pro bike helmets and tropical fish for a reason, and that reason is not Daniel Bernoulli.

"Airfoil politics" come into play when you start trying to optimize your slippery teardrop for specific flight envelopes. For that discussion, scroll down to Batata's delta wing thread and read everything posted by Don Stackhouse.
Latest blog entry: My feet smell funny
Jul 10, 2018, 02:25 PM
Registered User
For reasonable efficiency I use the flat bottom and the 1/3 rule .

Maximum wing thickness at 1/3 chord. This where to put the spar.
The actual leading edge at 1/3 of the maximum wing thickness.
The underside curves up towards the leading edge at 1/3 of the LE to spar distance.
Like this.
Name: 1to3Airfoil.jpg
Views: 19
Size: 28.8 KB
Description:
Nothing special but its rather better than a flat plate!
Jul 11, 2018, 11:13 AM
Scratch builder
From above: "For reasonable efficiency I use the flat bottom and the 1/3 rule ."

What is total thickness related to?
Jul 11, 2018, 12:01 PM
flyin' fool
goldguy's Avatar
I'm a big fan of flat, been using it since I was a kid over 7 decades ago. Here's my findings on flat ....................

If you go with the flat plate 'airfoil', leave the leading edge flat and at 90 degrees. When positive, the top edge of the LE will act as a 'turbulator' to improve lift.
Last edited by goldguy; Jul 11, 2018 at 12:14 PM.
Jul 11, 2018, 12:04 PM
flyin' fool
goldguy's Avatar
If your prefer a bent foil, go with the old tried and true 4/40, that's 4% thickness at 40% back from the LE. It's been around for 5 decades or so. You can just bend the flat foam or crack it into an angle as done with the simple Jedelsky. The curved shape provides the strength.
Last edited by goldguy; Jul 11, 2018 at 12:16 PM.
Jul 11, 2018, 12:37 PM
Registered User
KenSt
The thickness is whatever you want.
For instance a basic Clark Y section is 11.7%. Some specially designed full size low speed sections can as much as 20% thick.
The way air acts does not scale proportionally so as a general rule the smaller the plane the thinner the wing needs to be as at small sizes air tends to behave more like "treacle" than a gas which is why a flat plate works so relatively well but in truth its actual lift to drag performance is poor.

It is physically impossible for a 12" span glider to achieve the same lift to drag performance as a full size 25 m sailplane.
Jul 11, 2018, 10:10 PM
flyin' fool
goldguy's Avatar
Or...………. go with the family of KF airfoils, very popular here in this form. They're strong, simple, light and they work. This airfoil has opened up a whole new class of foam model airplanes.

Regardless of which you choose, the most important aspect for success is to build light.
Jul 12, 2018, 10:11 AM
pull up -- PULL UP!!!
Quote:
Originally Posted by goldguy
I'm a big fan of flat, been using it since I was a kid over 7 decades ago. Here's my findings on flat ....................

If you go with the flat plate 'airfoil', leave the leading edge flat and at 90 degrees. When positive, the top edge of the LE will act as a 'turbulator' to improve lift.
It never occurred to me that flat and square was a legitimate contender. I've always rounded the LE. I did build an EPP trainer kit once that had flat and square LE wings and while it flew okay it wouldn't glide very far and I assumed that was a result of drag, so rounded the wings. I think it glides better, but didn't put any effort into measuring things so maybe I'm just seeing what I want to see.

Do you stay flat & square even for KFm's? That seems, well...brickish.
Jul 12, 2018, 11:06 AM
Build, crash...repeat
AleRRon's Avatar
So many things work, but how well they work depends on the application- if youíre picky. I have flown a plane with a flat wing with stiffener spar and surprised at how well it flew, until I pulled some high G turns and saw how much they bent. So I added another flat plate on the forward half and made it into a kfm2 which I thought just flew better. But if you fly more gently the flat wing is no problem.
Iíve made simple Clark Y airfoils and love them for the lift. Kfm2 and kfm3 wings are easy to build and fly great. There are plans in this forum for delta wings using a sort of kfm2 and I built and flew them and they are great flyers too.
If you want a very aerobatic plane that flys as well inverted as upright, you need a symmetrical airfoil.
Foam board is cheap, so you can build and try them all.


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