Xrod

My Feedback: (2)

I am building a 1/6 Pica Waco and plan to buy an incidence meter to check my setup. The manual does not mention what these numbers should be so I measured directly off the plans and this is what I came up with. Top wing -2 degrees, bottom wing -1 degree, horizontal stab +1 degree. Can this be right? I thought that the top wing should have a greater positive incidence to stall first. Can anyone shed light on this? Can any builders of the Pica Waco tell me what numbers have worked well on thier models? Thanks in advance for any help. Planning to post this under "scale" as well.

OVER WORKED

Xrod, Because nobody answered this for you I thought I would. As you may or may not know I just finished the design of a 1/5 scale Waco for Kangke, and the wing incidences you list are correct. It's important to have both wings carry about the same loading and with the large stagger of the Waco a couple of problems arise. The upper wing is larger than the lower and the lower wing is in the down wash of the upper, this helps keep the flow over the lower wing. To get them both to stall at approx the same time neg incidence is used in the upper wing. This problem is compounded by the fact you have an under-cambered airfoil {yes a clark Y is under-cambered }. If you use positive incidence in the upper wing it will carry so much of the load that the lower may not do anything, it also has the same effect as moving the C.G. back because you moved the center of lift forward. You will also find that too much positive incidence in the top wing will cause SEVERE pitch coupling to the belly when in knife edge.

Xrod

My Feedback: (2)

Ray,
Thanks for taking the time to respond to my question and for shedding light on the negative incidence. Yes, I noticed the undercamber, and wondered if that was throwing off the line that I drew through LE and TE. I can't wait to see the kit you designed in 1/5 scale...good luck with it. What are your engine reccomendations for the airplane? Is it the YMF?

Steve

OVER WORKED

Check this thread.
http://www.rcuniverse.com/forum/m_13...tm.htm#1318772

Jennyboy

I just took possession of a Kangke Waco that hasn't flown for some years and saw your post 2002 that you may have designed this model. If so could you tell me the incidence degrees of the wings and what type of airfoils? It looks to be a 1/5 scale with a 32cc or so gas engine.