Electric Elevator Trim Range

[MikeJ 7A]

The manual states the max elevator ranges as 25 up / 35 down, which is a total sweep of 60 degrees.

My trim tab has at least that range of motion with no problem.

But the electric trim motor can only drive about 45 degrees of sweep from stop to stop.

I expect that's "enough", but I wonder if I should bias towards trim "down tab" to give greater "slow flight, or nose up" trim authority?

Any insights from those of you that are flying?

Mike

(getting ready to start on my SB wings!)

 

[Mel]

Your assumption is correct.

The tab should be biased toward more "nose up" trim. i.e. "down tab".
Typically you will only need "nose down" trim to correct for aft C/G conditions. You will use "nose up" trim on almost every landing to compensate for flap settings and slow flight.

 

[uk_figs]

7 pitch trim is sensitive

I have found that the 7 pitch trim is very sensitive and I doubt that I have got anywhere near the full operating range in the 130 hours I have on the plane so far which includes various CG conditions including full loads and full baggage etc.
The stick forces are light so even with out of trim conditions on final it is still easy to fly.

 

[MikeJ 7A]

At least for now, I've set it the max trim tab down ("nose up trim") to 30 degrees which puts the trim tab up ("nose down trim") limit at 15 degrees.

You have to put a pretty good bend on the lower skin of the trim tab (forward of the spar) in order for it to reach 35 degrees down (which I did).

Knowing what I know now, I'd probably wouldn't have needed to put nearly as much bend in to reach 30 degrees trim tab down.

 

[Walt]

I don't think I've moved mine more than about 1/2" up/dwn at the tab TE, maybe 10 degrees? Definately nowhere near 30 degrees!

 

[DGlaeser]

trim tab range

I suggest keeping it equal in each direction for 2 reasons.
First, you won't need anywhere near the full range in either direction, so a bias is immaterial.
Second, in case of a runnaway trim malfunction, if will always be in the worst direction (Murphy's Law) so you don't want excessive trim in either direction. If anything, you want less trim tab movement, not more.
I did a runnaway trim test during Phase 1, and control pressures get really heavy really fast until you slow down below 100 kts. Then they are just darn heavy.