help. my wing's weird
 

I have just installed a new wing onto my Spad. When i fly fast the AC wants to dive and when I slow it up it wants to climb (hands off, as I slow down the plane will loop itself slowly). My C. of G. is slightly forward. I am pretty sure the thrust line and the horizontal stab. are along the same axis (or at least parallel). The wing looks good (no twists, warps or wash-out) and is semi symmetrical with a little more camber on the top than the bottom. As for my angle of incidence, well I think that is where the problem may lie. I do know that there is at least 2 deg. positive angle of incidence, but I have no means of accurately measuring it.

Can anyone help?

RE: help. my wing's weird
 

Id check in the spad pages. They probably have the most experience with these sort of wings.
Ill be building one next week.

RE: help. my wing's weird
 

Sounds like it may need some engine downthrust.

RE: help. my wing's weird
 

You have way to MUCH downthrust.

RE: help. my wing's weird
 

My boo boo, your right Rodney. Not thinking to swift at the time.

RE: help. my wing's weird
 

Yep - too much downthrust or some really bad incidence problems. Looking at the pics, the incidence doesn't seem abnormal, but I can see the downthrust. Doesn't look like more than about 3 degrees though. It shouldn't be causing that sever of a trim change if I'm right about the angle.

RE: help. my wing's weird
 

Hi CORO, Are all the flying surfaces good and stiff? If you have loose, buckling surfaces it's going to be a handfull and get worse with speed. Most planes are in their comfort zone if the CG is 25% back [of the wings chord[including ailerons]] from the leading edge. I know you said that you thought it was nose heavy, do the math and place marks were the CG should be, then compare. Almost anything can be trimmed to behave halfway decent if the controls are tight, the surfaces are stiff, and the CG is in the ballpark. The incidences are easy enough to check with a ruler working off of a nice flat work table. The engine thrust can be checked by positioning the prop vertical,[the fuselage and wing should already be level] then grab a triangle, or square and back away from the plane some. Looking at the square and the prop in the background, you should be able to eyeball it. Absolute perfection isn't necessary, but if you have stuff a little out of whack everywhere, then all this will stack up against you.

RE: help. my wing's weird
 

If it's not the wing or tail flexing at higher speeds (quite possible and probably the most likely answer) or being caused by too much downthrust (again possible but should be easily measured) then it may be what looks like too small a stabilizer.

If the wing section is symetrical then you can get away with a small stabilizer area but if the wing section is flat bottomed with an arced top then it may be that the wing pitching forces are overpowering the stabilizer's attempts to hold it in control. The tail area should be at least 15% of the wing area. And even that is marginal. If it's less than 15% then you may have your problem right there.

RE: help. my wing's weird
 

Never mind folks......These two came together today and solved my wing problems:(

RE: help. my wing's weird
 

And the Relic only sustained a wing split, glided in...I just wanted to know what glue Relic was using...;)

RE: help. my wing's weird
 

HI BRUCE! That was a very sharp observation about stab area VS airfoil type! It makes perfect sense. I think the SCALE COMBAT rules allow either a 5% or 10% enlargement, which still looks small when compared to most sport designs. CORO!, don't you guys know that the GERMANS shouldn't be fighting against each other? That was an ingenious way to solve an aerodynamic flaw!

RE: help. my wing's weird
 

Before the FW-190 had it's mid-air I increased the angle of incidence by placing a 1/4" strip of wood at the T.E. The airplane still nosed over a bit at full power/high speeds, but only a little. Also the tendency to climb at lower speeds was also significantly reduced. I think the problem lay in the bit of down thrust I accidentally built into the airplane. The tail surfaces may also be the problem, but other planes we built exactly to scale never had the same problems. I think it's all just a big balancing act with theses scratch built machines. Thanks for the info, and I'll pay a little more attention to the angles on my FW-190 'the second'.