LearnedInUk

My Feedback: (29)

Here is my problem, maybe I can't figure it out because I have looked at it too long. Or maybe it's the booze...

I have a 33% Extra that I want to make sure the control surfaces are zero degrees relative to the leading edge. Meaning that the trailing edge is exactly even with the leading edge. Which I assume is needed to ensure straight flight!? Normally I just eyeball it and consider it good. But as my skills improved I want to make sure my plane is setup just right.

I have tried to measure the leading edge from the ground and the trailing edge but with incidence that one goes out the window. I have used an angle meter but again with incidence it is impossible.

Help!! How do you all accomplish this??

surf

If the airfoil is symetrical, measure the top and bottom from leading edge to trailing edge until they are equal.

Rcpilot

My Feedback: (78)

Put a metal ruler or straight edge on the wing tip.

Line it up on the centerline of the leading edge. Now line the other side up with the trailing edge of the aileron or elevator.

Pretty easy to see if they are neutral or not.

The pictures are exaggerated to make the point. You can line the straight edge up with the leading edge of the wing or stabilizer. Then run it back to the trailing edge of the control surface. Should be clear as day if it's not lined up.

Actually, the third pic isn't how it will look if it's messed up.

The fourth pic is how it will look if they aren't lined up.

Jake Ruddy

My Feedback: (40)

You want to make sure it is 0 compared to the fuse so your fuse has to be level first. Take a level and place it on the fuse without the canopy installed and get it leveled first. Then you could take a ruler and place it on the stab/elevator tip and draw a line from the center of the leading edge to the trailing edge. You can verify this now by measuring the hieght of the rule at each end before drawing the line (if you want perfect). Now you can check incidence if you like.

In my mind, chances are that the model will need trim to fly so getting it perfect at this point is a waste.

I would be much more concerned with whether or not your elevators are moving at the exact same time throughout the entire range of travel. The easiest way to see this is to take 2 straight skeewers or brass tubing and tape one to each stab so they meet behind the rudder. The further out the better. Then you can move your elevators to see if the tubes match at center, top, bottom, and travel the same. Remember, the tubing needs to be secured in the same spot on both stabs and use some sticky tape so it's secure without play.

It takes a lot of time to really get everything as close to perfect as possible, however in the end it's more than worth it

Once you have that perfect then you can go back to your incidence and 0 things out.

LearnedInUk

My Feedback: (29)

Thanks for the advice so far.


While I agree with the second statement I disagree with the first and that's the reason for my confusion. My reasoning is that with dual elevator servos let's say the left control surface is 2 degrees deflected up and the right is neutral. In flight it will want to want to roll slightly left and then I will think I need aileron trim which will only exaggerate the problem. So unless I am sure I am neutral to start trimming won't fix the problem and may make it worse unless I were to tweak each elevator servo individually.

RCpilot I did the ruler trick at first but still am unsure that is accurate enough. I may be too anal about it which would not shock me.

JoeAirPort

My Feedback: (41)

You can easily "eye" this looking at your elevator halves from the rear of the plane while working them with your transmitter. I do this on all my bigger planes and I get them perfect just with sighting them. Basically you level your eyes with just above the trailing edge of the elevator surfaces. Make sure the entire elevator surface plus stab looks like a thin slit on edge. Move your head up and down trying to get this to happen. Now you will be able to see the smallest of differences in the surfaces. Now I'm assuming the incidences are all checked and good because the should be done before this. In fact you could use the incidence meter to match the elevator halves at neutral but you'd still need to use my method of "sighting" the elevator surfaces at full deflections. So view your elevator halves at neutral, full up, and full down and sight them. Make adjustments to match them up.

Another really good method is to take to long thin pieces of anything...CF, wood dowel, 1/4"x1/4" square stock, push rod, etc....tape them to your elevator surfaces and make sure the tips almost touch at neutral. But they must be matched at neutral first !!! Either sight them or use an incidence meter. Now make sure these sticks or whatever track exactly at all degrees of deflection.

I think what Jake was saying, and I agree 100%, is that you will "flight trim" your plane anyway so the the trims have to be determined in the air, not on the ground. But what you want to do on the ground are two things: 1) Make sure both stab/elevator incidences are 0. 2) Make sure the elevators track each other dead nuts. I can do this close enough by eye just using my transmitter. I do have to get on the ground to view the "full down" elevators.

Jake Ruddy

My Feedback: (40)

What I meant was if you spend the time to get your elevator perfectly 0 in relation to your stab it's going to change as soon as you take off. Your CG and thrust will effect this right away. Meaning your model may require up or down trim to fly level.

The way your counterbalances are it makes it tough to tape them in order to keep the elevators at 0 in relation to your stabs. You need to accomplish that so you can then verify your stabs are 0 compared to your wings.

If you setup your elevators so they move at the same time then you can use servo power to hold your elvators at 0 compared to the stab. Then continue with your incidence to your wings.

Hope this helps!

BaldEagel

Another thought with you airframe, draw a line down you elevator tips from TE too LE in the centre as its semetrical it should be easy to eye ball when you get it right, then measure the depth of the tailplane recess for the counterballance of your elevator, halve it and draw a line on the recess at this position, line the two marks up and you are as near as damm it there, then when you trim in the air if all changes and you start again from basics with the incidence of your wing and stab, Oh yes and thrust line, Oh what fun.

Mike

pe reivers

To "zero" any surface, one must put it in a plane parallel to the work bench (a flat one of course!)
Then it is possible to measure to the bench plane all around and chaeck for twist and setup.
Any incidence is of no importance, since it must be corrected in setting up the plane relative to the bench surface.
I take it and suppose we are not talking of trimming the plane, but that the sole objective is to check out your building skills.
Flight trimming a plane and ending up with all control surfaces in perfect lineup with the main surfaces of wing and stab is quite a different story.

LearnedInUk

My Feedback: (29)

Thanks to all for the suggestions. Based on what I have read it appears I may be too anal (like there is such a thing [sm=72_72.gif]) about the relationship between leading and trailing edges. I have been "eyeballing" it for years and it has served me well, I was just looking for the extra step to make sure it is perfect.

So I will do three things.
Eyeball it
Level the plane and measure distance from leading and trailing edge to flat work table. This assumes there in minimal incidence.
Check throws to ensure equal on both halves.

Thanks for all the help

Flyfalcons

Just to make sure, you're talking about zeroing the elevators to the stabs, which already have their incidence set? If so, I just eyeball that from behind, and do the same to match the elevator halves with each other. Doing this I've only needed to use a couple clicks of trim at most when test flying the plane. Your CG could affect that anyway and require some up elevator or down elevator trim anyway; all you can do is get it close and throw it in the air.