Originally Posted by Weasel
Consider by adjusting the horizontal stabilizer angle of incident in that direction, you are reducing the amount of available tail down force at low speeds in the flare with forward most CG loading. Each plane is unique and should be tested to determine change effects.
I could not agree more. Full envelope flight testing is frequired when doing such a rigging change. My results:
- RV-8A solo and no baggage (most forward CG condition). Before the shim, elevator trim tab on landing was mid range nose up postion. After the 0.040” shim, the elevator trim tab was right at full nose up travel (but stick Force was still neutral). Any loading other than most forward CG the trim tab was less than full nose up on landing.
- RV-10 solo and no baggage (most forward CG condition). Before the shim the elevators were slight trailing edge low in cruise. After shim the elevators were in the trail during cruise. The RV-10 nose up trim authority is huge and I really did not see much of a change in elevator trim setting before and after shim. The relative moment arm on the RV-10 is much less than the 8A so even though the shim was a little bigger, it had less effect. I do not recommend going bigger than 0.063” or so with an RV-10. I’ll also note that serveral data runs showed a zero to 2 knot gain in speed with the shim. Do not expect miracles unless your rigging is further out than mine to begin with.
So bottom line, changing the HS angle of attack would be down the list of things I check when working rigging. Most common rigging problems I’ve seen on RVs are:
- Flaps do not go up as far as they should
- Asymmetric flap and/or ailerons
- Flap and/or aileron twist
- Alieron hinge point to high or low on inboard and/or autboard mount
- Once flaps and aileron rigging is corrected the builder finds his wingtips are out of wack (another reason to defer mounting wingtips until after the other rigging is done).
- Wheel pants not mounted in trial (first thing I look at if the owner reports his ball is out one way or another). First test is see how much the ball is out flying with no wheel pants.
As I mentioned before, rigging is not trivial and is very much an iterative process.