Stickers on molded wings - does it matter?

[Neil Walker]

I have a nice 60" molded glider (Bird, HN 354 (http://www.soaringusa.com/products/product.htm?product_id=16345&category_id=257)) but it is mostly white with just a bit of red on the leading edge and tips. I'd like to put some sort of design over the top of the wing to aid in visibility - so obviously it would have to cover a significant area, for argument's sake let's say 1/4 to 1/3 of the surface. I'd like to do it in sign vinyl. I couldn't care less about the weight, but will the thickness of the vinyl and irregular pattern affect the airfoil in any way? Am I better off spending the time on a good paint job?

[vintage1]

Unless you are squeezing the thing to its limit for competition, it won't affect it enough to be an issue.

[Neil Walker]

Thanks for the response. Someone else told me I should just try it and if I actually notice a difference then I should try out for the F3J team :D

[Ricardo RW]

I remeber seen somewhere that the height of a decal must be smaller than boundary layer, and this is important on the first quarter of the chord where the flow is laminar. Aft the 25% of the chord the air is turbulent and maybe the decal will help adding turbulance.

If I remember well I would swear that I read it from a M. Drela note, but I could be wrong.

Take care.

[Batmanwpg]

Try http://www.mh-aerotools.de/airfoils/ to find the height of the boundry layer

[jbeanelliott]

Question: Do model planes achieve laminar flow over the wings at the Reynolds number and speeds they fly at?

If the wings do not achieve laminar flow then does the height of the boundary layer have any meaning?

Enquiring minds want to know. Thanks. -John Elliott

[Neil Walker]

If I remember well I would swear that I read it from a M. Drela note, but I could be wrong.


I remember this too from Dr. Drela but I couldn't find the original post...

[MarkusN]

Question: Do model planes achieve laminar flow over the wings at the Reynolds number and speeds they fly at?

Actually model aerodynamics often has the inverse problem: making sure the boundary layer transits to turbulent early enough to avoid laminar separation.

[ThermalThief]

If you look for sign vinyl make sure you ask for high performance or cast. These should be about 2mil in thickness and have a glossy surface.
If you get calendared or indoor grade vinyl it will be 4-6mil and may or may not be glossy depending on brand and quality. The calendared vinyl is streched to thickness during manufacture and is less stable as sun and heat can cause it to pull up edges. However, it will stick to foamies better :)

Ken

[ghoti]

If any blisters remain under the trim you can remove them by pricking them with a pin and flattening the blister with a warm covering iron. Don't overdo it and melt the foam! Try on scrap first. This will keep things smooth Bill

[Gary Warner]

If the wings do not achieve laminar flow then does the height of the boundary layer have any meaning?

Enquiring minds want to know. Thanks. -John Elliott

Yep. The larger it is the thicker the airfoil will act. Your 'effective' airfoil shape traces the outside of the boundary layer (within about 80% of its thickness).

[MarkusN]

Yep. The larger it is the thicker the airfoil will act. Your 'effective' airfoil shape traces the outside of the boundary layer (within about 80% of its thickness).

Also, because the BL is resilient, small differences in airfoil shape won't get their full effect. Say you have an airfoil with quite a bit of aft camber (which makes for lots of lift) That little twist at the trailing edge will be obscured to the flow within the "mush" of the BL and you won't achieve full lift. This is one reason why max lift usually is lower at low Re.

[macboffin]

Simple test.Trim out glider to fly straight and level. Weigh stickers for ONE wing, add to one wing, add balancing weight to other wing.Fly it, see if it pulls to one side or is inclined to drop stickered wing first at stall.
Remove balance weight, add stickers to other wing, fly again.
I doubt there will be much difference, except that turbulation effect might improve performance slightly.