Wing Design and Covering

[Murocflyer]

I'm still working on my slow flyer wing. I just started covering it at the wing tips. Wing is 60" long and 12" wide. After applying the covering to the tips, I noticed that the covering is dipping in between the ribs. Note picture below. For aerodynamic reasons and purpose of this design, should I fill in the rest of the spar to match the height of the ribs to increase the airfoil thickness? Will this create more lift, or is the amount that the covering dips in between the ribs totally insignificant?

Thanks for the help!

Frank

[Sparky Paul]

The anorexic covering is a routine situation when there's no upper spars to prevent it.
For a park flyer, it's probably not worth anything about it.
When you get interested in real performance, then maintaining the profile all along the span can be important, but for low speed sport fliers, there's not much benefit from supporting the covering with multiple spars.
A sheeted leading edge would be optimum, but overkill in terms of weight relative to any performance benefit.

[Murocflyer]

Sparky Paul,

Once again, thank you for the quick response, I noticed I didn't include the picture. Here it is anyway. I'll press on with the covering then.

BTW, I did get a couple books to help me in my RC design and building, so hopefully I won't have to ask so many dumb questions in the future.

Thanks again for the help.

Frank

[Tom Harper]

Muroc.

Older texts make the argument that droop between ribs has an advantage in small models. The scalloping produces spanwise gradients that delay or prevent separation. So for slow speed flight it may be a benefit.

[Sparky Paul]

This is the standard Gentle Lady wing... not to worry about covering sag... :)

[davidfee]

Martin Hepperle (MH airfoils) has done some work on this recently. You can see his results on his website: http://www.mh-aerotools.de/airfoils/index.htm . Click the "aerodynamics" button, then click on "Aerodynamics of Spar & Rib Structures." His conclusion was that covering sag did seem to be beneficial below Re=100,000.

[Murocflyer]

Fellas,

Thanks for the replies. Glad to know I'm all right. Below is the finished product. As soon as I finish up my build on my Soarwatt, and a couple of other projects, I'm going to design a fuselage for this wing with what I hope will have a twin tail on it. Just got to figure out the best way to turn two rudders with one sevo.

Thanks again for the info. I'll check out that site shortly.

Frank

[Pat Daily]

more ribs or half ribs help

[Murocflyer]

Update.

After reading Martin Simons' Model Aircraft Aerodynamics, I noticed on page 110 section 8.7 covers this topic well. The author agrees with your statements above. You guys were right on the money!

Thanks again,

Frank