Calculate Drag for a Flat Plate Foamy

[HugePanic]

Hi,

i try to calculate the Drag for a Flat plate Foamy.

I find lots of good forumals, but i am not sure wich to select for calculation.

Given is a Wing (may bee two), horizontal + vertical stabalizer and a fuselage.

What i dont have is the plates (depron) roughness.

how to calculate the wings drag? i have no cd for the complete wing. how can i estimate a good value?? what about the wings profile? (sharp LE, square LE, thickness....)
The most influence is shape, roughness and induced drag, right?


For the stabalizers its the same i think, just without the efffect from lift. (without induced drag)

fuselage could be caluclated with the cd of a square-box (cd=1). but a typ fuselage is longer. how to compensate this??

Re is about 200000 to 2000000

Any ideas, links, experiences???

[lincoln]

Soartech 8 has wind tunnel data for a flat plate. If you can't find it easily, give me a couple of Cl's of interest and I'll give you an approximate Cd. Cd at 0 lift tended to be at 0.014 for Re of 100k to 300k. Cd at Cl of 0.025 was around .019, but in between those two the answers varied. At Cl of 0.3 we have Cd of around .023, for Cl of 0.4 we have Cd around .034, and above that, forget it. I think, for the higher Cl's, the roughness won't matter much.

[richard hanson]

Hi,

i try to calculate the Drag for a Flat plate Foamy.

I find lots of good forumals, but i am not sure wich to select for calculation.

Given is a Wing (may bee two), horizontal + vertical stabalizer and a fuselage.

What i dont have is the plates (depron) roughness.

how to calculate the wings drag? i have no cd for the complete wing. how can i estimate a good value?? what about the wings profile? (sharp LE, square LE, thickness....)
The most influence is shape, roughness and induced drag, right?


For the stabalizers its the same i think, just without the efffect from lift. (without induced drag)

fuselage could be caluclated with the cd of a square-box (cd=1). but a typ fuselage is longer. how to compensate this??

Re is about 200000 to 2000000

Any ideas, links, experiences???
After you are done - -what will you change?
You simply can not improve on the flat plate for a small aerobatic model.
On models at 4-6 oz sq ft - the flat plate offers the best in setup for a very aerobatic setup
stalls ? forget it - the models simply don't respond to the textbook stuff .
Those who don'tfly em will poo poo this but the proof is in the pudding. The photo of Martin Muller --he has a very complete understanding of these --look for videls of him
My large model is good for outdoor ,mild breeze- fast -slow excellent control

[HugePanic]

i just try to get my head into it! :)

currently i am searching inforamtion for foam-aerodynamics and around propellers and electric(brushless) motors.

i just want to understand more of how this all works together....

thx for the replies...

mfg
Matthias

[creyes123]

NACA did a lot of research into so called "flat plate aerodynamics." I looked into this for my calculator, but was surprised to learn that the penalty for using a flat plate (i.e., flat airfoil on the wing) was not large as long as the wing loading is kept low. Max Cl is less (about 0.9, from what I recall). The drag is higher, but that is not a bad thing on this type of model.

Searching the Internet should yield some NACA reports. Otherwise the books listed on my website have information.

Carlos Reyes
RCadvisor.com (http://www.rcadvisor.com)

[Brandano]

indeed, an ideal flat plate with a thickness of 0 and a wing loading of 0 has only surface drag, and that would be pretty close to 0... :). A low wing loading means a low AOA, meaning low drag, especially on thin profiles. However, sharp maneuvering would make the wing stall quicker than one with a nice cambered shape. Mind you, this can be a bonus too, depending on what you intend to do with the plane.

[richard hanson]

indeed, an ideal flat plate with a thickness of 0 and a wing loading of 0 has only surface drag, and that would be pretty close to 0... :). A low wing loading means a low AOA, meaning low drag, especially on thin profiles. However, sharp maneuvering would make the wing stall quicker than one with a nice cambered shape. Mind you, this can be a bonus too, depending on what you intend to do with the plane. You would be surprised at how many old armchair aerodynamic "Xspurts" can't get around the fact that a dead flat , sharp edged surface wing -at extremely low loadings ,is an ideal setup

[creyes123]

At very low aspect ratios (less than 3, from what I recall), the airfoil also makes very little difference. I have a great Keith Shaw story to tell regarding this, but I'll save it for another time.

Also, at very high angles of attack (25 degrees?), the airfoil also makes little difference. Any wing will act like a flat plate at such angles.

Carlos
RCadvisor.com (http://www.rcadvisor.com)

[BMatthews]

You would be surprised at how many old armchair aerodynamic "Xspurts" can't get around the fact that a dead flat , sharp edged surface wing -at extremely low loadings ,is an ideal setup

It's an ideal setup for these models because of the way they fly. That's the thing. It takes the "bad points" of the flat plates and uses them to advantage in this manner of flying. The abrupt and high drag stall is an advantage when you want your model to transition from forward flight to an instant hover without zooming upwards.

However even lightly loaded a flat plate is not a good choice for something like an electric pylon racer. In that case the properties that work so well on the 3D flat foamies will hurt the pylon racer. But I think you've also admited that in other posts here and there. And how can you measure the drag from the wing and side strakes when it's in a 45 to 70 degree harrier maneuver? Nope, I'm afraid I'm with Dick on this one. Just accept them for what they are and enjoy.


Back to Hugepanic-
Truly I think you're wasting your time in trying to analyze the drag from the flat plate airfoils and fuselage. The models that are built using the flat plate style are not the sort to spend enough time flying in one direction for long enough to make such a number in any way meaningful or at all useful. And the only other factor is that you want to have about 1.5 to 2 times the model's weight in thrust from the motor. And again when you have that sort of oomph it makes worrying about the drag a moot point.

[east6008]

I was very grateful for the flat plate wing and poor gilde of my micro RTF
yesterday when it got into a thermal.
I find these very much like the old hand launch gliders of the 50's, very
sensitive to light lift and tons of fun--with 2 big differences (1) less running
(2) I get the airplane back