How do most measure the deflection of the flaps and elevator? I imagine using a protractor of some sort. Do you pull the leadouts as far as they will go and use that measurement? I see a problem doing that.

I have a set of protractors that slip into the flap/elevator gaps to the fuselage.  I do pull the leadouts as far as they go because I use stops that only lets me have 60 degrees of ballcrank movement both ways.  I have settled on 1 1/2" of leadout movement from center to full up/down(I actually use about an inch) and that matches how I fly.  I try and keep all of my planes the same.  So, with the bellcrank centered (on the leadout position) and flaps and elevator at zero I move each line and mess with all of the control settings until I get equal movement giving me equal deflection.  For a new plane, I do this with the controls out of the plane and mounted on a frame that puts them exactly where they will be in the plane.  I use a fake balsa bellcrank so that I can move the pivots and pushrod holes before I drill the real one. (the pix has the actual).  Everybody has their own way of getting there, all that matters is that you get there!

Ken

If you want an actual number and don't have a protractor, you can use a smart phone if you have one. On the iphone it is under Utilities/Measure and toggle to the bubble level. It works fine and is probably accurate to about 1 degree. Just set the plane up level on your bench using the edge of the phone. Then deflect your controls and measure each surface. If the surfaces have taper (chordwise) then take that into account. Yes, I deflect the surfaces all the way using the leadouts. The way you set up your handle, you may not actually achieve that angle--but that angle is available. Once the plane is built (bellcrank inaccessible) the control ratio to the bellcrank is only adjusted at the handle. Of course, you can change flap deflection by speeding up or slowing down the flap individually if you move positions of the input pushrod to the flaps at the flap horn. Etc., etc., etc.

On some planes and with some paint trim schemes the angles by eyeball can be misleading. And what one person "sees" as 30 degrees can be quite different from someone else's estimate. The protractor/angle-ometer takes away that guesstimation error.

Easy to do; a bit harder to figure out what might need to be done to the plane once you have results. Of course, a huge bias of Up vs. Down and some issues at the handle might be the reason I would start looking at surface deflection. I set it up even when I build, but I end of rebuilding lots of OPPs (Other People's Planes) so......

You hang it from a nail in the rafter , and pull down.
If your lucky the wingtip lands on your bare toe , when the nail pulls out .

A piece of paper or cardboard , cut , and taped ( drag a finger across to de stickyfy mega sticky tape - so it dosnt ruin the paint )
thrown thru the end , maybe with a notch for the wire & neutral line pre drawn , pencil full deflection marks on it ,
the get a protractor , pull out the stencil & measure on the bench .AND youve got a record .

Just folding a corner ( 90 deg. 0 of paper gets you 45 deg , for a rough ' exact ' check .

Depends if the last bit ( off travel ) is gooey . As in , if youhang it on one leadout - is it ' at the stop ' or does the pulling on it ( Ahem ! )
get more ' shift ' off the flaps , etc .
CAREFULL .
Er .

Theres anther thought , having overmuch movement - free - and setting handle radtio for useable movement , if you loose it & gotta run ,
whacking the handle flat , can get a ' stall turn ' ' avoidance ' out off it . Whaking back the handle hard, when its freeflighting downhill at
four foot , can pull a lot off the inertia / speed out of it . Extreme measures for extreme conditions , or loose units .

You want to measure at a variety of up or down leadout movements and make sure the rate of movement is the same both ways, the rate of flap to elevator movement is the same both ways, and the flap to elevator ratio is what you expected

That’s one way to go about it.