I've seen mention on here that there might be call for thinning out wings of electric models over their glow counterparts.

Can anyone give me details on why that would be...?

No doubt someone will, but I doubt if he can.

...where I should start looking for an appropriate airfoil?

The obvious place is on the airplane of the World Champion. He wrote an article in Stunt News on the science behind it.  I use an Impact airfoil, the same one as for the IC version.  It works fine, too.

It would not be practical to inset a flap into NACA0018.  Plot the foil, then measure 2 or 2 1/4" in from trailing edge..... BEHOLD the flap must be about 3/4" thick.  Totally impractical!

This is my favorite section.  Plot and then adjust the rear a little bit to be 3/8" Now, make 3/8" flaps in your usual construction.  I know, what you  end up with isn't exactly according to Hoyle, but the front part of the foil is the most important, anyway.

Floyd

I thought it was a good question.

You'd include them.  Trouble is, there are enough folks using the other convention that you gotta ask each time. 

This comes from the misconception that flaps are independent surfaces superposed on wings.  It's kinda a subtle point.  Lots of physical things are linear and effects can be superposed. Aerodynamic stuff generally isn't, and assuming that it is can mess you up.  Other examples of popular stunt superposition fallacies are trim tabs countering wing warps and the effect of side wind relative to airspeed. 

It would not be practical to inset a flap into NACA0018.  Plot the foil, then measure 2 or 2 1/4" in from trailing edge..... BEHOLD the flap must be about 3/4" thick.  Totally impractical!

Floyd

Hi Floyd

As someone mentioned, my nephew & I took the full airfoil/falp approach way back when. below I posted the view as shown on my Eclipse airticle from way back.  I would stop short of calling it totally impractical - they actually worked quite well.  In another thread on flaps, Brett posted some really good insights about the implications of the thick hingeline - and how the added hinge seals all worked together.

Now here's a question you don't see often: what's the best reason for flaps - added lift or added drag?  I think the answer is mostly the first but do not discount the second effect.  When deflected I suspect that the thick flaps separate flow at the hingeline and get draggy while providing a boost in lift - kind of like a split flap would.  I like low drag designs, but there is a place for drag too, especially when you can turn if on/off.

The Eclipse used a NACA 0018 root with a modified NACA 0021 tip - modified by moving the highpoint forward from 30% to 25%.  Worked fine.  When I built my first purely electric design I thinned the foil to about 16% constant, and modified the aft part of the airfoil to taper into a 5/16" flap.  This design uses much less power than other similar sized airplanes, and performs very well in the wind - because it penetrates so well.

However as recent contest results have shown, IC derived thick airfoils work just fine with electrons too.


I plan on sticking to "thinnish" airfoils, however anything below about 15% runs the risk of losing structural stiffness - I am not a fan of flexible flyers!

Greg,
The subject of full airfoil with flap has come up before, the short answer is that it looks better then it works. Most of the people that tried it feel it wasn't as good as a plain old Noble style airfoil with trailing edge flap. Do a search on Al Rabe and you will find the test he did on airfoils. He at first thought this was going to be the best airfoil ever. After he tested it on his makeshift car mounted test rig he said it was a very big disappointment and the standard layout produced more lift for a given deflection with less drag.

The basic idea behind using thinner airfoils on electric was because the "motor" reacts very fast to increase loads to continue to pull the ship through maneuvers and maintain speed. This keeps the lift up and thus you can get away with a little less thickness. Also for going down hill the motor holds (brakes) quicker and again regulates speed so you don't need the added drag of the thick foil to hold the speed down.

Best,     DennisT

It would not be practical to inset a flap into NACA0018.  Plot the foil, then measure 2 or 2 1/4" in from trailing edge..... BEHOLD the flap must be about 3/4" thick.  Totally impractical!
Floyd

Just returning from the Lugo/Italy contest where young Marco Valliera won in a very convincing manner flying his electrified shark both in high wind and dead calm hot weather. Here is the Shark wing root...

Peter Germann

Peter,
I have heard that the Shark wing flaps are hinged in a way that allows the flap leading edge to slightly protrude above the trailing edge of the wing as it deflects. This is suppose to add effectiveness. Any chance you could show a shot looking down on the wing to show the hinge position and maybe a side shot with the flap fully deflected?
Best,          DennisT

Hi, Dennis
I took the picture from one of Lauri Malila's Sharks wich I have since returned to him. As we will meet at the upcoming swiss nats next weekend,  I will ask him to publish pictures as per your request.
However, from what I remember the hinge turning point is at the very center of the flap's leading edge radius which means that it does not protrude when deflecting. The particular airplane I've examined deflects the flaps by approx. 30° when the elevator is up or down approx. 45°

Black bugs.

They aren't real, Dennis, and they'll go away along with the purple kangaroos. 

I've seen mention on here that there might be call for thinning out wings of electric models over their glow counterparts.

Right, several guys here got idea to save power and energy with thinner airfoil. Yes, it is true, thinner airfoil has lower drag, but that thinking has one small hole in logic: thinner airfoil also make less lift (maximal lift coefficiet), it means wing must be larger for the same weight and since the drag formula has also wing area as a parameter, the drag of larger wing will be aproximately same 

but there is also another reason for thicker airfoil, thicker airfoil has more drag in level flight then thinner one, but thinner will go to larger grags in maneuvers (partial stalling) so thicker one can keep better speed stability in corners and that is what counts in figures.

the same is with airfoiled flaps, such an airfoil has low drag in level flight, but it slows in corners, it is well visible, I can tell from 100 meters if the model has NACA type  airfoiled airfoil or my with thinn hingeline.

if you ask which is better in real world, it is hard to say, because some people need corner done like with knife in butter, and some simply need that stopping in corners

Nice presentation, but the theory raises one's eyebrows here and there.