Can anyone answer my question about using the trim tab on a PA28 following an elevator jam? Would it be necessary to maintain a higher approach speed to ensure trim tab authority?
In a PA28, the trim tab will work in the oposite sense, as Confab says. The reason is because, when you wind the trim wheel forward (nose down) this results in the trim tab moving up. If the stabilator is jammed, the upwards movement of the trim tab would work just like the upward movement of a traditional elevator - causing a nose-up attitude change.
To answer your question about the higher approach speed, I
think the correct answer is "it depends". I would guess that the small size of the trim tab would mean that you only have a small range of attitudes, and therefore speeds, available to you. But exactly which speeds would fall into that range would depend on the position of the stabilator at the point when it becomes jammed. If it became jammed in a rear-up position, this would result in a nose-high attitude and a low speed, in which case a little forward trim might well bring you down to somewhere close to normal approach speeds.
On the other hand, if the jam occurs in a rear-down position, this would result in a nose-low attitude, and moving the trim wheel fully forward might well result in a speed which is still considerably above the normal approach speed. In which case I think you are pretty much stuck with that speed, and will need a nice long runway for braking after landing.
Now here's another question, though: use of flaps. Assuming that any real kind of flare would be impossible, I would probably favour using a little flap as possible, since this will give me a higher nose attitude than an approach with flaps. So, if I could achieve a sensible speed, I think I would make the approach flapless.
But what about if the speed remains very high, even with full forward trim? Now, I'm thinking that a little flap might well help slow me down and achieve a more normal approach speed.
I would guess that what you are aiming for here is to land on the main wheels first, at whatever speed that happens to be - or at least a 3-point landing. Because if you land on the nose wheel first, regardless of your speed, you're going to be bouncing rather badly, with no way of controlling the bounce. And if you assume you won't be able to flare, then a landing on main wheels first must require an approach with a nose high attitude if at all possible.
Does anyone else have any thoughts on use of flap in this scenario though???
FFF
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