need some advice regarding wingloading ?

[epkoncept]

Hi;
I'm a total newbie when it comes to DSing.
I have some foamie wings that I like to slope with, however, they do have a S400 in the rear for getting out of trouble. What I would like to find out is: is there any rules of thumb for the wing loading with respect to the prevailing wind speed ?
I have three wings, one is a WW E Slayer AUW of 30 oz, I have a homebrew copy of the E Slayer with a Clark Y foil, AUW of 20 oz, and another but at about 23 oz, ie heavier servos and more glue.
The 20 oz floats much better than the 30 oz, which also has a pseudo symmetric foil. I realize that the results are obvious but I would like to know what sort of AUW I should be aiming for in a wing for various wind conditions ? Just for reference, root is about 11" tip is 5", span 48".

EP

[Ollie]

For launching and landing you need enough wing loading to be able to penetrate into the wind at normal glide trim (without having to use much down elevator). DSing a wing with motor and propulsion batteries aboard will impose excessive bending loads on the wing at moderate DS speeds. Once DS has begun, the speed is not determined by the wing loading which drops out of th DS speed equation. In most cases failure occurs because of flutter, pilot error or bending loads before the model stops gaining speed with each lap.

[epkoncept]

ollie:
Since I am a newbie, can you extrapolate upon your previous reply ? 1) when you say moderate DS speeds, roughly what range of speed are you refering to ? I did have a foamie wing
snap a wing when pulling out of a dive, I should not have removed the carbon spar !. 2) " Once DS has begun, the speed is not determined by wing loading,....." I don't think I fully understood this comment . Is it because the air surround the plane is moving with the plane, so the ground speed might be very high, but the relative windspeed is low ? 3) "....failure occurs because of flutter,.... " Is this flutter like aileron flutter when
turbulence at the gap causes loss of control and flutter or is the fluttering of the wing due to extreme wind pressure ? I've noticed that on a windy day, the wings are flexing visibly even with a
hefty arrow shaft inside the wing ! Is that the flutter or is it just the control surfaces ?

EP

[Ollie]

EPP is inherently flexible and not very strong. A moderate speed is a speed at which a foamy begins to bend unacceptably. Epp can be stiffened with filament tape and spars but it will never be able to achieve the high speeds that stiffer and stronger materials allow.

Every pass through the boundary layer in the downwind direction adds speed and kinetic energy to the DSing model. Once in this groove, the plane is no longer dependent on dissipating the potential energy of altitude to keep flying. The sinking speed, which determines the rate at which potential energy is consumed, is no longer relevant and, so, neither is wing loading which is one of the things that determines sinking speed.

Flutter is a complex and varied thing. Any control surface can flutter if it is not rigidly hinged, its position rigidly controlled by the servo and linkage and it is not aerodynamically and statically balanced. Any flying surface such as a wing or tail can flutter if it is not stiff enough. A flying surface can flutter in twist or in longitudinal bending. Anything can flutter if the air speed is high enough. The trick is to make the structure stiff enough that it prevents flutter at the speed you want to fly.

Stiff structures tend to be brittle structures so they are not as survivable on impact as flexible things made of EPP foam. So the choice is between the survivability on impact of EPP versus the survivability against flutter of stiffer materials. You can't make a silk purse out of a sow's ear.

[epkoncept]

Ollie:
thanks for the additional details.
You are 100% correct about the material comprimises. I remember hearing the slope planes structures "sing" as they flew
by. I think it was a very "carbonized" plane, The skin and the structure emitted a very high pitched sound as it flew by. My EPP and EPS wings are totally silent in comparison, and probaly fly at about 1/3 the speed. I guess I don't get control surface flutter since I fly so slow, and my ailerons are made of 1 layer of fan fold foam, so they are soft and flexible they I think they are very well damped.I don't think I might get a ground speed of about 40 mph in a dive with the wind ! I have -ve ground speed sometimes when flying into the wind !!
EP