Trim Question?

[dlwoolsey]

This will probably be another stupid question from me but here it is. I have a sportsman 2+2 by Wag Aero that I did not build. I noticed that with 1/2 fuel, solo and in level flight the airplane requires alot of nose down trim. Is this normal or could it indicate an aft CG? The weight and balance that came with the airplane shows that it is within CG but it seems that the trim should be neutral when solo and light. Any ideas?

Duane Woolsey N65WA

 

[fobjob]

Under those same conditions, my factory cub is at it's most nose-heavy. When I got it, however, the wing had been mounted at a zero angle of incidence. (long story)This required a LOT of nose-down trim to fly level, due to the lack of pitching moment from the wing. What angle to the stab does the elevator assume when you are flying level?

 

[dlwoolsey]

The 2+2 has a fixed stabilizer and a trim tab. The angle is between 15 and 25 degrees or deflected about 3-4" at the rear.

 

[fobjob]

Well, I'm assuming that is in the DOWN direction??

 

[dlwoolsey]

yes in the down direction.

 

[fobjob]

That means that it should stall-spin readily when lightly loaded. My 18 would go 7 turns before recovery. Mounting Micro VG's on the wings reduced that to 1/3 of a turn. Might want to think about that...
One of several things can be wrong. My 2+2 plans seem to indicate that the wings are mounted at a zero angle of incidence, like the PA-12... easiest thing to check would be for stray gun safes or bowling balls in the tail cone...too much tail weight. Measuring the weight on the tailwheel might be illuminating... check to see if the leading edge of the horizontal stab is mounted at the correct height.
Then I would attempt to measure wing angle of incidence and twist. Plans say level upper door frame, I would triple check to make sure that was put in straight. Inboard rib of wing should be level, cub is +1.843 degrees. Wing can be raised with adaptors on forward spars, or so I've heard. A longer engine mount and cowling might be easier. You probably would want to assess the hazard of it being prone to stall-spin....that would go far to tell you if there was a really big problem or not...

Another possibility would be that the ailerons were rigged at an up(negative) neutral position...

 

[dlwoolsey]

I have checked some of the things that you mentioned. I will consult my plans and then put a level to the airplane and make sure that it was built right. I will also do another weight and balance to make sure that it is where it is supposed to be. I can move the battery to the firewall from behind the rear seat storage and see how that affects things if the weight and balance shows that it is needed. Thanks for the input. I will look for more enlightenment from this group after I have checked everything out a little bit more.

 

[C-FIJK]

here is what i did yo set the stabilizer go out and fly it look back when you are in straight and level trim flight , check to see where the elevator is if it is down or up above the stabilizer ! look to see how much 1/2 inch 1 inch ???? then re-adujst the fixed stabilizer with a spacer and this will fix your problem should be level in level flight

No need to move the battery

Also if you can take a pic of it in flight and post it I can help you from there
Gerry

 

[fobjob]

Gerry, under forward-most loading, (maximum nose heavy and forward end of the envelope) elevator should be deflected up about 20 degrees. This results in maximum down force on the stab, maximum stability in the pitch axis, and maximum trim drag. As you add weight(behind the CG), the angle will decrease until it it is in trail at maximum aft CG. At this point, ability to recover from a stall/spin will be minimized.
When you start out with down elevator under forward CG, things are unstable already, and will get ugly fast as you add payload.

 

[C-FIJK]

fobjob i do not want to see the elevator down I just want to see the stabilizer near nutral with the elevator, if we can get dlwoolsey to take a pic of it in flight we should be able to solve ot from there . I built a super sportsman with a io-360 200 hp and a constant speed prop this plane flies hands off

dlwoolsey how is the trim and back pressure when you are landing? I believe we have spoken before on the phone you bought the 2+2 from wag aero ???
Gerry

 

[dlwoolsey]

Gerry we have talked and I have N65WA from Wag Aero. The 2+2 is a great plane I just need to get to know it a little better. I will get a picture and get it posted this weekend. I can trim it all the way down to landing speeds and have little or no stick pressure. I am going to weight the airplane empty this weekend and do another weight and balance to make sure that it fits within the window called for in the plans. from there I will adjust the stabilizer, move the battery or whatever is needed to get it where it needs to be. I for sure don't wnat it to have bad stall spin tendencies but so far that has not been the case. It does seem that what fobjob is saying about having an aft CG is a possibility as I have not done a weight and balance since I got the airplane. The plane had been on floats and had alot of very strange settings when it cam to dihedral, washout/in and needed alot of tweeking to get it to fly straight and stall clean. I will get the picture and the weight and balance and then repost. Thank you both for all of your help.