[hecilopter]

In my first 100 hrs of flying, I've been making note of various things to query others about (speeds, props, etc.). The thing I'm wondering about this time is how much elevator trim do you need to use to maintain level cruise flight and which direction? I have noticed on mine it is about a 1/4 inch of DOWN trim for level flight, ie. if I land and look at the trim tab on the elevator, it is UP about 1/4 of inch. RV-7A, XP-360 carbureted, Harzell blended airfoil prop, full tanks. It doesn't seem to matter if I am solo or have a passenger. Does this seem to be the norm for a 7A? It would seem you would want it centered ideally at cruise.

Thanks for the input!

Rusty

 

[Kahuna]

Where are the elevator tips at cruise?

 

[akarmy]

This is one I have been wondering about also...

My tips (counterbalance) are about 1/4 - 3/8" up, so it's taking down elevator for level cruise. So the question is... in an ideal world, should the HS be lowered a bit? Of course that would mean a new intersection fairing, etc. not much fun..

 

[hecilopter]

Elevator tip location

From all pics I have seen, the elevator tips are in line when at cruise.... In fact, you can see the slight trim up condition in this photo.

 

[Kahuna]

I cant see the other one. But if your aligned in cruise on both.... Keep flying and dont worry about the tab. How is the balance on the ground?

 

[hecilopter]

Balance on ground

I still have the elevator balance on the ground biased to UP elevator since I have not painted yet. It is not much but it goes to full up elevator left on its own. After paint I can balance exactly. Do you think this could be the culprit? The elevator tips are exactly the same in flight, it is perfectly straight.

Thanks!

 

[aadamson]

Curious

From all pics I have seen, the elevator tips are in line when at cruise.... In fact, you can see the slight trim up condition in this photo.

I always get my wires crossed thinking about trim tabs, etc, but this picture looks like, if in cruise flight, that the elevator is slight in an "up" additude (I'd say about 1/4 - 1/2") in relationship to the horz stab. you can see that the counterbalance tips is slightly down at the front. Then the trim tab is also "up" or putting down pressure on the back of the elevator trying to counteract the "up" that is already in the elevator.... We aren't talking about very much, but can see those angles pretty well in that picture.

 

[jcoloccia]

I still have the elevator balance on the ground biased to UP elevator since I have not painted yet. It is not much but it goes to full up elevator left on its own. After paint I can balance exactly. Do you think this could be the culprit? The elevator tips are exactly the same in flight, it is perfectly straight.

Thanks!

I'm guessing that's exactly what it is. Having the elevator unbalanced is equivalent to putting a little back pressure on the stick. When it's balanced, you'll need less down trim (trim tab UP) to put the elevator where it needs to be.

Once you get the wheel pants and fairing on, you'll gain a little more speed in cruise and the elevator position to maintain level flight may put the elevator flat, or maybe even down. Who knows...that's going to be a function of your ultimate cruise speed, balance, etc etc etc.

Geez...you know, seeing all you folks flying around always motivates me to get my butt into the workshop!

edit: got my pulls and pushes backwards....doh

 

[Bob Axsom]

Things must be going pretty well

I am constantly dialing the pitch trim with power changes, fuel burn, etc. as I fly to take the pressure off of the stick. You may be approaching the "sorting the fly stuff from the pepper" point in your evaluation of the airplane.

Bob Axsom

 

[keen9a]

Wheel Pant & Fairing Effect

When you add the wheel pants and gear fairings, the trim will most likely change to more nose-down. This is because you've just reduced a lot of drag from below the center of gravity. The nose-down moment caused by the drag now needs to be provided by the elevator.

Of course, there will also be an effect from the speed change that's not as easy to predict.

 

[hecilopter]

Thanks everyone for the replies!

I actually do have the wheel pants and fairings on now and I still have the need for the slight down trim. I can't wait to get painted and get the elevator perfectly balanced. Maybe this will all go away! I'm probably being too picky but just want to eliminate any unecessary drag I possibly can!

Thanks!

Pic with wheel pants on...

 

[Bob Axsom]

Its all about stability

The three biggest variables affecting your trim, assuming everything is "straight" are flight weight (a new deal every flight and changing during the flight), the Center of Gravity (also a new deal every flight and changing during the flight), and the for&aft difference in angle between the wing and the horizontal stabilizer. If you are cranking the nose down already, that situation will get worse after paint - the long arm of the tail multiplies weight added there. If you raise the leading edge of the stab with shims to go more toward zero-zero with respect to the wing angle the efficiency goes up but you sacrifice stability. Any added weight requires more lift to maintain level flight - higher angle of attack more induced drag, etc. etc. so don't add weight in the nose unless the CG is bad already.

Bob Axsom

 

[akarmy]

This is one I have been wondering about also...

My tips (counterbalance) are about 1/4 - 3/8" up, so it's taking down elevator for level cruise. So the question is... in an ideal world, should the HS be lowered a bit? Of course that would mean a new intersection fairing, etc. not much fun..

Here's a visual of my cruise configuration... This was at 11.5K, 180TAS level flight.

Thoughts?

 

[N79PT]

Look at Van's Test Flight Pages

I'm still in the test phase on my RV6A (38.0 out of 40hrs). About two weeks ago I was reviewing the various stability tests in the construction manual in the Test Flight section. If memory serves, 1/4 inch up on the elevator counterweight as the picture depicts should be good. Review the chapter for more info.
Greg