Left elevator trim actuator tightness

I've just made the cover plate with the electric trim servo attached. To the servo I attached the properly fabricated trim actuator arm using the correct hardware.

How still should the movement be at the servo end of the arm? Mine has friction but will rotate without a lot of torque - but it isn't free either.

I suppose no slop is better than looseness, but I wonder how tight is too tight?

Can anyone describe the right amount of friction here? Is a lubricant in the joint needed and if so what kind?

Also, is there a picture of what the retaining pin should look like when the two leafs are spread?

There will be very little rotational movement on this joint.
My preference would be no play over no friction.

No play is what you want. Mine is exactly like you describe yours and my opinion was it was perfect.

However, I have another issue with the trim setup. When I ran the motor to both stops I was surprised about the position of the trim tab. Full nose up was extreme and full nose down had the trailing edge of the trim tab barely out of line with the trailing edge of the fixed left elevator trailing edge. That left an implied neutral position of the tab 20° down from the top surface of the elevator.

I sent pictures to Van's and they said the full nose down position looked wrong but couldn't say whether it was or not. It is an unresolved issue for me for now. I moved on waiting to see if anyone else runs into this. Not urgent now as there is so much of the airplane yet to ship.

Thanks! Always good advice here...

n982sx said:

However, I have another issue with the trim setup. When I ran the motor to both stops I was surprised about the position of the trim tab. Full nose up was extreme and full nose down had the trailing edge of the trim tab barely out of line with the trailing edge of the fixed left elevator trailing edge. That left an implied neutral position of the tab 20? down from the top surface of the elevator.

I sent pictures to Van's and they said the full nose down position looked wrong but couldn't say whether it was or not. It is an unresolved issue for me for now. I moved on waiting to see if anyone else runs into this. Not urgent now as there is so much of the airplane yet to ship.

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Full nose down trim should produce a deflection of about 1 inch (up) at the trailing edge.
Full nose up should produce a deflection of about 3 inches (down).

A lot more nose up trim is required, than nose down (to account for the high pitching moment of the big flaps, higher angle of attack required at slow speed, etc.). Middle of the servo range is not the middle of the tab travel range.

Oh - any examples of how the retaining pin should have it's leaves spread?

rvbuilder2002 said:

Full nose down trim should produce a deflection of about 1 inch (up) at the trailing edge.
Full nose up should produce a deflection of about 3 inches (down).

A lot more nose up trim is required, than nose down (to account for the high pitching moment of the big flaps, higher angle of attack required at slow speed, etc.). Middle of the servo range is not the middle of the tab travel range.

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Thanks for that.

That is not what I get unfortunately. More like 4 inches down (nose up) and <1/4 inch up (nose down).

Not sure why. I have gone over the plans and the only holes not prepunched by Vans that could cause a misalignment seem to be the hinges. However my trim tab trailing edge is in perfect alignment with the left elevator trailing edge so that implies my hinges are drilled correctly.

Van's had me check that I had the correct trim tab motor and the length of the control arm. Both check out.

I know the arm has two bends in it. Is it possible the arm is installed upside down?

I have not yet tried the servo on my trim tab for travel but I would like to comment on the arm itself. I really like this idea vs. the former stainless steel rod and plastic turnbuckles. Although I have never had a problem with the plastic turnbuckles I really wondered about how long that plastic will last with time. In fact I am seriously considering changing the standard setup on my rocket with an arm like the one used on the RV14. I can used the current hole to hole measurement to get the right length for my plane. Although I do not know the reason for this change by Van's I applaud them for thinking past what has been considered normal. I am finding lots of things like this on the RV14 vs the other models that i have worked on, good job Vans!

n982sx said:

Thanks for that.

That is not what I get unfortunately. More like 4 inches down (nose up) and <1/4 inch up (nose down).

Not sure why. I have gone over the plans and the only holes not prepunched by Vans that could cause a misalignment seem to be the hinges. However my trim tab trailing edge is in perfect alignment with the left elevator trailing edge so that implies my hinges are drilled correctly.

Van's had me check that I had the correct trim tab motor and the length of the control arm. Both check out.

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It is being looked into.
I will post back in this thread when I know more.

rvbuilder2002 said:

It is being looked into.

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Great, can't wait to hear the result.

HeliCooper said:

I know the arm has two bends in it. Is it possible the arm is installed upside down?

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No, the bend only affects clearance. The length hole to hole doesn't change. In this case, if it was turned over it would not clear the lower elevator skin. It appears to be installed correctly according to the illustration in the instructions.

Tom Martin said:

I really like this idea vs. the former stainless steel rod and plastic turnbuckles.

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I agree it is a nice simple but solid design.

Just got an update on this from Van's. The originally shipped push rod was too short and is being replaced. Kits shipped before July need the new trim tab push rod.

I sent pictures of the original trim tab to Van's in May showing this problem. Up thread rvbuilder2002 wrote back that my problem was being looked into. Glad to see it's resolved.

Just need to get the new trim tab.