Thick airfoils on fun fly models ?

[dvint]

Do these have a poor power off glide ?
Thanks

[Ollie]

In a very low aspect ratio wing, gliding at slow speed, induced drag dominates and tends to mask other considerations. The profile drag of a thin airfoil is usually less than the profile drag of a thick airfoil. The effect of the difference in profile drag has to be considered in the context of the over all drag budget which also includes parasitic drag and induced drag. Whether the difference on profile drag between thick and thin matters much depends on the rest of the design. In a low aspect ratio design with an aerodynamically dirty fuselage, uncowled engine, large tail area, exposed landing gear, etc., the difference in profile drag will be very hard to see. In a high aspect ratio hotliner with a slim and streamline fuselage, no landing gear and small tail area, the difference in glide angle between thick and thin airfoils will be immediately evident.

[Bill Glover]

What Ollie said! The kind of plane that has this sort of airfoil is never going to glide very efficiently anyway due to the low a/r and normally fairly draggy fus & u/c.

I fly one with a 20% thick wing (NACA 0020), it was originally IC with a piped .36 but I converted it to AXI 2820/12 and 14 cells earlier this year. The low wingloading allows it to fly relatively slowly and the glide really isn't bad ... for that sort of model. With the prop stopped (ESC brake on) it actually is quite 'floaty' on landing, much easier with a touch of power applied and the drag from a slowly turning prop.

[Sparky Paul]

Originally posted by dvint
Do these have a poor power off glide ?
Thanks
.
Yes.
No penetration. Good control, but the glide isn't "stretchable" all that much.

[Bill Glover]

Here's mine, even with a wire-braced tail etc. the glide really isn't bad. Not going to catch any thermals though ;)

[Sparky Paul]

Flying this one today....

[airboss]

ollie concentrated on the drag dynamic

lift to drag ratio goes up as thickness increases
lift increases too
increase thickness=drag increases more than lift so airplane will have a slower top speed (and glide characteristics)and a slightly slower stall speed

decrease thickness=narrower speed range with a higher top speed and stall

racers=thin wing, narrow range
sport & scale=soft, gentle handling qualities of 16 to 18% airfoil
gliders want optimum=12 to 12.5% long, long wing

the VIRUS and VIRUS POLY series as well as other thick wing slow flyers are very good at power off flight
usually have 16% thickness to chord and wingtip lift devices to reduce tip stall at slow speeds

allen

[Ollie]

For symmetrical airfoils, generally speaking, profile drag goes up faster than lift as the thickness increases. The maximum lift to profile drag ratio of symmetrical airfoils is not improved by increasing the thickness beyond 8 to 10% thickness. In any case, differences in the lift to drag ratio of airfoils are completely swamped out by the dominating induced drag of low aspect ratio wings when the airfoils are operating near their best lift to drag ratios.

Drag is not a problem under sufficient power, only when range under power-off glide is a consideration.

[Bill Glover]

Originally posted by airboss
decrease thickness=narrower speed range with a higher top speed and stall

racers=thin wing, narrow range


With racers I think wing loading is more relevant. The IC pylon models I used to compete with had extremely thin sections, but with quite low wing loading they also had an extremely slow (and gentle) stall. Many people landed them fast simply because they couldn't get the technique of losing speed with a very sleek model.

[Aio_1]

Thick wings can produce lots of lift. However with very low wing loadings and aspect ratios fun flys won't penetrate much.

[Haldor]

A thicker wing will also stall at a greater AoA - up to a point ;)

[Ollie]

The wing stalls at the airfoil stall angle of attach plus an induced angle of attack. For low aspect ratio wings the induced angle of attack is so large that it swamps out small diferences due to airfoil thickness. At low aspect ratios the wing aspect ratio tends to dominate most airfoil considerations. Furthermore, with low aspect ratios, a substantial portion of the wing is operating in the tip vortex where there is substantial spanwise flow. This spanwise flow decreases the lift available from the airfoil near the wing tip compared to the rest of the wing.