EAAAirVenture OshkoshShopJoin

Is it Trim or not?

Posted By:
Scott Ehni
Homebuilder or Craftsman
#1 Posted: 2/14/2011 17:40:43

On my turbine 701 I always have allot of nose up trim to neutralize the stick. The weight and balance is in the middle of the envelope and I have plenty of elevator control. In the pictures of the plane in flight the elevator appears to be in the neutral position(level on top on a Zenith 701)and I am thinking of putting a simple indicator in the cockpit to check this in flight. On the 701 the unbalanced elevator is vary heavy in the nose down direction. Is the trim just holding up the unbalanced weight(I could put a bungee on that and get rid of the extra drag from the trim) of the elevator? If it is actually trim I could adjust the stabilizer angle to correct it.

Scott Ehni

Todd Caswell
#2 Posted: 3/1/2011 11:44:09

Is this a problem when 701 is a full power / cruise power / idle in flight?

Does the aircraft fly normally (light on the controls) when the engine thrust is not an issue?

If the engine is a causing this then the mounting angles of engine are at fault.

On the other hand if the engine thrust is removed from the picture, then has the elevator been statically balanced? Any changes to covering/paint can change the weight of the elevator.

This is a "kit" right? I would check my rigging angles of the wing, stabilizer and elevator/trim. I would also consult with the kit mfg to see if this is "normal". If there are lots of these aircraft kits out there, this is probably not an issue on the others or the kit mfg would have made changes to the control system. Adding or changing the components to a designed aircraft control system could be very dangerous, I would not recommend changing the kit design (i.e. adding bungees)

Dave Prizio
Young Eagles Pilot or VolunteerHomebuilder or Craftsman
#3 Posted: 3/1/2011 15:41:16

It is worth checking the thrust line of the engine to be sure it is right, but I think the problem may be that your horizontal stabilizer is mounted with the incorrect angle of incidence. Check this out and adjust it as necessary.

Although I am not familiar with the details of building a 701, I am pretty sure that the procedure for setting the incidence angle would be in the building instructions. If not call the factory and ask them. A quick check with a Smart Level should tell you if your problem is there.

Good luck sorting things out.