Pitch trim question. In level flight at cruise, my elevator trim is about 90% in to the nose down position. Almost out of trim control. Is this normal. My W&B came out great and is near the front of the envelope empty, and calculates about normal for me, pax, full fuel, and about 35# of bags. Then its about 3" forward of the aft limit. Why all the nose down trim when light? Is everyones that way.
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Pitch trim question
- Thread starter 49clipper
- Start date
Not Normal for My RV-6A
I have no way of knowing what my actual trim setting in cruise is - I just dial in the setting that takes the pressure off the stick in level flight. For landing I always dial in nose up trim and when I takeoff I take out nose up trim from the previous landing to give me a steady rate of climb at around 100 kts. It all seems very normal without any running out of trim sensation. I do have a heavy constant speed prop, an O-360-A1A and a nose landing gear but the CG correct.
Your symptoms seem to indicate that you have a trim indicator that may be inaccurate or a rigging problem with the wing or stabilizer incidence angle.
Bob Axsom
I have no way of knowing what my actual trim setting in cruise is - I just dial in the setting that takes the pressure off the stick in level flight. For landing I always dial in nose up trim and when I takeoff I take out nose up trim from the previous landing to give me a steady rate of climb at around 100 kts. It all seems very normal without any running out of trim sensation. I do have a heavy constant speed prop, an O-360-A1A and a nose landing gear but the CG correct.
Your symptoms seem to indicate that you have a trim indicator that may be inaccurate or a rigging problem with the wing or stabilizer incidence angle.
Bob Axsom
L.Adamson
Well Known Member
I looked through my in flight pics for a panel pic showing the trim position, but the pics just didn't go that low on the panel. However, I know that I'm never that close to extremes of pitch trim, whether alone or with a passenger. I only have to momentarily blip the trim button one way or another.
L.Adamson ---RV6A/ Hartzell CS prop/ 0360
L.Adamson ---RV6A/ Hartzell CS prop/ 0360
49clipper
I put the manual trim knob in the normal position in flying level trimmed out, and then looked at the trim tab on the ground. It sticks up like a spoiler. I then leveled everything and checked the H. Stab incidence and its right on (0degrees). I then checked the wings again and found the left to have negative incidence in relation to the right one. Vans does not think that would cause my nose down trim situation. They say to go fly it and check how far out the elevator is in level flight. They say 3/8"-3/4" up at the conunterbalance is normal. If memory serves, that is about where mine is. I need to check it again to be sure. I think I will increase the shim under the HS to change the incidence and see if that helps. Vans concurred with that as an experiment. Don't get me wrong, it flys fine, its just that I don't think a trim tab should be so out of alignment (like 75 degrees) to be trimmed.
I put the manual trim knob in the normal position in flying level trimmed out, and then looked at the trim tab on the ground. It sticks up like a spoiler. I then leveled everything and checked the H. Stab incidence and its right on (0degrees). I then checked the wings again and found the left to have negative incidence in relation to the right one. Vans does not think that would cause my nose down trim situation. They say to go fly it and check how far out the elevator is in level flight. They say 3/8"-3/4" up at the conunterbalance is normal. If memory serves, that is about where mine is. I need to check it again to be sure. I think I will increase the shim under the HS to change the incidence and see if that helps. Vans concurred with that as an experiment. Don't get me wrong, it flys fine, its just that I don't think a trim tab should be so out of alignment (like 75 degrees) to be trimmed.
That is what I would do as well
That is what I would do as well. There is no way I would just blindly fly along forever knowing that this trim condition was necessary to maintain level flight. One thought occurs to me - there are shims in the designed installation of the horizontal stabilizer - are yours installed?
My wings when installed prior to rigging were out just like yours. When I leveled the airplane by the canopy deck reference plane and checked them individually, the right wing was correct but the left wing required twisting by lowering the trailing edge before clamping and drilling the rear spar attachment hole on 6-27-98.
Bob Axsom
That is what I would do as well. There is no way I would just blindly fly along forever knowing that this trim condition was necessary to maintain level flight. One thought occurs to me - there are shims in the designed installation of the horizontal stabilizer - are yours installed?
My wings when installed prior to rigging were out just like yours. When I leveled the airplane by the canopy deck reference plane and checked them individually, the right wing was correct but the left wing required twisting by lowering the trailing edge before clamping and drilling the rear spar attachment hole on 6-27-98.
Bob Axsom
jonbakerok
Well Known Member
That ain't right
I don't know what to tell you to fix it, but it sure doesn't sound right to me.
I could load my 6A to 1950 pounds before it approached the aft limit. I had electric trim with a trim indicator and it never needed more than two marks when loaded for a normal flight. During phase one, I tested runaway trim conditions and I could hardly hold the stick when the trim was at the limit.
Of course, that was my plane, which had a C/S prop. You didn't mention your configuration, but you might check your W&B against the other's on Dan Checkoway's site (mine's there). If you've got a wood prop, it'll be more tailheavy, but I still can't imagine that it would make that much difference. I flew mine to Osh once at 1950 lbs, right at the aft limit. It still didn't need that much trim.
Which makes think of something -- a normal RV6 in calm winds will hold altitude when trimmed properly for a long time. Mine would normally go an hour or so, but on that trip to Osh, it wouldn't hold altitude at all. If your plane wants to hunt all the time but your calculations say you're in the middle of the envelope, you might need to re-weigh the plane. Maybe it's a lot more tailheavy than you thought.
I don't know what to tell you to fix it, but it sure doesn't sound right to me.
I could load my 6A to 1950 pounds before it approached the aft limit. I had electric trim with a trim indicator and it never needed more than two marks when loaded for a normal flight. During phase one, I tested runaway trim conditions and I could hardly hold the stick when the trim was at the limit.
Of course, that was my plane, which had a C/S prop. You didn't mention your configuration, but you might check your W&B against the other's on Dan Checkoway's site (mine's there). If you've got a wood prop, it'll be more tailheavy, but I still can't imagine that it would make that much difference. I flew mine to Osh once at 1950 lbs, right at the aft limit. It still didn't need that much trim.
Which makes think of something -- a normal RV6 in calm winds will hold altitude when trimmed properly for a long time. Mine would normally go an hour or so, but on that trip to Osh, it wouldn't hold altitude at all. If your plane wants to hunt all the time but your calculations say you're in the middle of the envelope, you might need to re-weigh the plane. Maybe it's a lot more tailheavy than you thought.
49clipper
Jon,
It does not hunt at all. Wherever I trim it, it stays, although the trim is touchy. It does not take a 1/16 turn of the manual trim to make a big difference. But, from everyone I talked to, that seems to be normal. That trim tab has lots of authority.
Mine has an 0-320-D1A and the Sensenich metal prop, so it would tend to be more tail heavy than with a CS.
I will add another 1/8" shim at the front of the HS this weekend and see what that does. Just think of the drag made by that trim tab in that position. I gotta get to the bottom of this. Guess I will weigh it again too, just to confirm the numbers.
Jon,
It does not hunt at all. Wherever I trim it, it stays, although the trim is touchy. It does not take a 1/16 turn of the manual trim to make a big difference. But, from everyone I talked to, that seems to be normal. That trim tab has lots of authority.
Mine has an 0-320-D1A and the Sensenich metal prop, so it would tend to be more tail heavy than with a CS.
I will add another 1/8" shim at the front of the HS this weekend and see what that does. Just think of the drag made by that trim tab in that position. I gotta get to the bottom of this. Guess I will weigh it again too, just to confirm the numbers.
