So i'm building my first extra... and I have come up with a mild query..

Where is the "zero trim" poing on wings and tail etc.

All other planes I've build, the aileron has been a cut out or the elevator just a flat pannel... in this there are no guide-lines and the tail is profiled too..

as a "guess" I strapped two straight bars onto the control surface and as the 2 bars stuck out farther than the leading edge of the wing.. tried to make the distance from these bars to leading edge, equal.

Or is there another way of doing this? :|

You may find some examples here:

http://www.robart.com/how_to/incidence_meter.aspx

Regards!

and if you dont have one??

you should try to borrow one, or buy one. There is no easy way to set the incidence between engine, wing and stab without one. And, it will make a noticeable difference if they are off. [:@]
zx32tt

I totaly agree... but surely there must be a simple way to put some ailerons into a "pretty close" area for a maiden flight of an ARTF?

not talking about f3a setup here.. i'm talking.. i want know that when i open the throttle on the runway.. i'm not about to end up with a case that the radio does not have enough trim left to correct...

ceecrb1,

What you are doing may introduce errors, due to the airfoil.

What you need is to measure the throw deflections:

http://www3.towerhobbies.com/cgi-bin...?&I=LXET68&P=7

http://www3.towerhobbies.com/cgi-bin...?&I=LXK260&P=7

http://www.aero-works.net/store/sear...CategoryID=124

The simplest way to do it is taking relative measurements from a flat surface to the LE, TE and aileron or elevator TE.
As a bonus, that will identify also any warp of the wing or horizontal tail.
That is how full scale airplanes are aligned.

I have acu throw.... but as you set the zero of that to where the aileron is... it doesnt help my problem...

so basically i "draw a line" from LE through the wing to TE and the extension of that is the "zero" of aileron??

Yes.

The only problem is that you cannot see the line after you drew it, you have to be able to measure it.

A ruler, patience and a flat surface is all you need.

Got that!

Especially as I cant fly till the rudder servo + lipo & BEC arrive in the post.......

Your method with the bars would allow you to set both to the same but it won't ensure that they are set to the zero line. How about you repeat the process but with bars on both the top and bottom. Then set it so that both the top and bottom distances are matching. That'll mean that your ailerons are set to zero or near enough. Also to avoid errors due to angles make both bars the same length and long enough that the ends are very close to being vertically in line with the leading edge. A little out either way won't matter because if they are both the same distance you'll still be able to center the aileron to the wing with a good degree of accuracy.

Oddly enough the Robart guage won't help you actually center the ailerons. It'll let you set them to the same angle but that angle may not be actually centered. unless you can put one on the wing where it centers on the hinge line and the other on the actual aileron. But few models have a gap that would allow that.

You can do the same on the elevator and rudder but I've always found that just eyeballing them for neutral was close enough.

Now if all this was for the actual alignment and glueing the wing and stabilizer into place then I'd want to do things to a much greater degree of finess so I knew that the model was all set up nicely to 0-0-0 to within less than 1/2 degree. Ideally to within less than 1/4 degree. But for just setting the surfaces for the first flight your method but with two sticks will work just fine.

Looks like I wasnt giving enough details.. what you just described with 2 bars, equal in length and one on top and one below... reaching to the LE of the wing... is basically what i did....

setting the aileron roll trim is very easy in flight.. but its entirely possible that I set it up and the plane spends its all time with a slight "flap" or "spoiler" effect...

Oh, when you said one on each side I visualized one on each wing PANEL .....

Yeah, with the two bars and measuring that way you can set the aileron so that you don't end up with a slight flap effect either way. Nicely figured out.

Yes sir, I agree the two bars will get it done. Nice idea.

Ceecrb1,

In the attached diagrams, note that the thicker portion of the airfoil makes the measurement off.

That is no problem for symmetrical airfoils, like the Edge’s, but it will be if trying centering throw deflections for cambered airfoils with the two sticks method.

For non-symmetrical airfoils, the central throw deflection is a continuation of the cambered central line of the airfoil.

Robart meters ?
phooey worthless as teats on a boar.


assemble the plane
set it level stand directly behind it - loook at light n shadows above and below the wing panels
If you position the light and yourself correctly -you can see extremely fine differences
far better than those clumsy incidence things.
better than yo can measure with a ruler


OR ask an old woodworking craftsman to come and take a peek
he will show you haw to see alignments down to a few thou-

I use this technique becaus you also see any hinging errors .

You always make my day Dick. Good ole fashin gitRdone.

being a moron i know.. but not totaly understanding what u mean...

You setup model on a table - so that you can stand behind it and see at eye level, the trailing edges of both wings.
centered.

The sunlight or lights should be centered on fuselage -if possible
looking from one panel to the next -back and forth -you will see even very slight differences in shadows and highlights
any differences should easily show themselves
especially the hinge line
This takes a few attempts at getting lighting you like
a lot of light is NOT required -just try to center the light source
any diffrences in thicknesses - hinge lines - warps all become obvious.
Those silly levels will show differences -or NOT show differences if leading edges are not identically shaped
hinge location will also trick you
Learn this procedure and give the Robarts to the children to play with

A small halogen table lamp works wonderfully as a "mobile sun" for this sort of thing. While I have not used it for alignment purposes such as Dick is suggesting I use it a LOT when shaping blocks or chuck glider wings. A lamp and the edge of the sanding block to cast an angled shadow will act like a profile guage. And very accurately too. So with the right angles and maybe some shadows you can do a lot of things.

When I was building models for customers on a full time basis , I tried the bubble level aand the plumb bob level setups
Checking the results with eyeball said these methds were not worth a poo poo.
So- I made a squared setup using four levels - these created a perectly square base referrence
I then measured up to the model from the squared beams
-resolution of 1/32" (.032) was easy.
But the setup was time consuming
basic problem being the "matched "parts of left and right wing panels or left and right horizontal panels ( the small wing on the back, according to some) were often mirror images and not matched left and right pieces
This condition is commonly caused by sanding techniques etc.,
Once the model is assembled -the result is like having one panel upside down.
The measuring devices see only TE and LE-
the observation technique described by Matthews and me -reveals thicknesses above and below the center line.

The eye can see extremely tiny variations - micrometer sized stuff - even old eyes with degenerative problems.
Place two long scales (one meter etc., ) on a table - supported on edges and spaced apart say a meter and such that you can sight along the tops to see if they are perfectly parallel.
-using a tiny bubble level taped on top one scale - adjust scales till visual referrence shows perfect parallel settings
Does th bubble show the critical changes of say a few thou ?
most bubbles do not
I have good quality bubble setups and tools from Starrett - brown n Sharp etc..
still- I find the visual referrence to be the most accurate.

agreed............

visual takes a bit of concentration but it's accurate

takes almost no time to setup and no skill at using whatever tools you think you need

I still don't get it...........[sm=confused.gif]

It'a all about using shadows or the shading as the surface reaches the "horizon" to the light source. When the light is almost but not quite parallel to the surface you can see things in pretty amazing detail by the shadings of the light.

If you want an eye enhancer, try a transit.

MattK

sic transit gloria mundi?