A

Allan Stern

Well Known Member
To pitch the nose down with the trim tab, which way should the tab go, up or down. Have changed wires and did not look at tab direction before I pulled them.
Thanks
Allan Stern
 
Interesting you should bring this up. Believe it or not approximately 1/2 of the aircraft I inspect for airworthiness have the pitch trim backwards. As a matter of fact, the last one I did had this problem.

Reason it out. If the tab goes up, it will push the elevator down, thereby pushing the nose down. Conversely, if the tab goes down, it will push the elevator up, thereby pushing the nose up.
 
trim tab

Thanks Mel, That was the original problem when the plane was inspected by my DAR and I switched wires at the trim motor. But have replaced my stick grip with an infinity one and had to change wires. Just wanted conformation on the idea.
 
What about aileron trim tab on the left wing of my -6A?

I wired my aileron trim tab so when I push the HAT switch to the left, the trailing edge of the tab goes down, it is supposed to add ''lift'' so to speak, raising the trailing edge of the aileron and thereby lowering that wing?? So for ailerons, trim tab trailing edge pointing down equals down wing, and on elevator, lowering the trim tab trailing edge equals nose up? :confused: . Which half am I in???
 
WenEng said:
I wired my aileron trim tab so when I push the HAT switch to the left, the trailing edge of the tab goes down, it is supposed to add ''lift'' so to speak, raising the trailing edge of the aileron and thereby lowering that wing?? So for ailerons, trim tab trailing edge pointing down equals down wing, and on elevator, lowering the trim tab trailing edge equals nose up? :confused: . Which half am I in???
Click to expand...

Same physics at work in both cases. Elevator trim tab down equals elevator up equals tail down equals nose up.:rolleyes:
 
Electric Trim System Question

Mel said:
Interesting you should bring this up. Believe it or not approximately 1/2 of the aircraft I inspect for airworthiness have the pitch trim backwards. As a matter of fact, the last one I did had this problem.

Reason it out. If the tab goes up, it will push the elevator down, thereby pushing the nose down. Conversely, if the tab goes down, it will push the elevator up, thereby pushing the nose up.
Click to expand...

So, Mel, on a semi-related point to this thread, I don't have any problem understanding which way the trim tab and elevator need to move and how it needs to be wired, but I do have a question about the method that this trim system uses to trim the airplane.

I have oodles of time in Cessnas with manual trim and also with combined manual/electric trim systems. I am used to seeing the trim tab move in the opposite direction of the elevator when you raise and lower the elevator (unless the trim tab is in its neutral position of course).

But in the case of the electric trim system on the RV, it seems to me that the trim tab for the RV stays in its pilot-selected position relative to the elevator regardless of which way the elevator is moved, since its position is solely determined by the rod arm attached to the electric trim servo., which is all housed in the left elevator.

I just wanted to verify if my understanding of this system is correct or not, since it seems to work a bit differently than other trim systems I am familiar with. I tried to seek more info about the trim system in the plan book, in the test flight section, but I did not find the answers I was looking for.
 
As Mike says, this is an anti-servo tab. You normally don't see it on an airplane with horizontal stabilizer and elevator. Normally anti-servo tabs are seen on stabilators like Piper Cherokees and RV-12s.
 
Anti-servo Tabs

I also seem to recall them on LearJets.

Of course those devices and a bunch more to keep that thing "Safe" :confused:
 
My Air Tractor has assist....

...on all three control surfaces to help lighten the stick/rudder/aileron forces.

The dual elevator trim tabs double as servo tabs as well....quite interesting setup. Then again, the 50' wingspan has ailerons half the size of RV wings!:eek:

Best,
 
Names

An aerodynamic balance tab and servo tab are the same thing. They assist the pilot in moving the control surface. [move in the opposite direction to the surface]. The Zlin 242L that I flew had one on the elevator.

Anti-servo tabs work in the same direction as the control surface to increase the force required. The Seminoles I've flown had one on the stabilator.
 
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