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Old 08-31-2005, 01:52 PM
Jonathan Cude's Avatar
Jonathan Cude Jonathan Cude is offline
 
Join Date: Jan 2005
Location: KS
Posts: 57
Default one wing at a time

Setting the wings was a chore in my two car garage. I didn't follow much of the prescribed method (plumb bobs to the floor, etc.)

Here's what I did. It may sound crazy but my wings are "super straight".

1. put on one wing.

2. stretch a string from the tip, between the leading edge and main wing skin, to the opposite side of the fuselage. The skin should naturally hold the string in place rather nicely. There is a rivet line on the wing spar that lines up with a rivet line on the bottom of the fuselage when the wings sweep is 0 degrees. Use the string line to make sure the rivet lines are straight.

3. here's the catch. you must clamp an ~8" long piec of angle or something to the wing tip to make the string line not rub on the bottom of the fuselage (remember the dihedral of the wing!).

What about parallax you say? Use the shiny aluminum wing skin as a mirror, and when the reflection of the string and the string itself are aligned, you are looking at it from the correct direction (think of an analog multi-meter).

If you see how this method works, its cave man simple (even though the directions may not seem like it!) It requires no math, no tape measure, only a string and your 20/20 vision.

My wings have no sweep at all ~.001 degrees or so I think. But even a sweep of say an inch at the tips might not affect flying quality to any noticeable amount.

However, setting the incidence is very critical. Pay more attention here than anywhere. Build a spacer like vans suggests, but build only one and use only it.

For incidence, the actual angle is not very critical... having both wings at the same angle is.

I calculated the effect of differential (left wing to right wing) incidence angle on roll for the RV-7(A). I don't remember it, but could find the data if anyone is interested.

A few degrees of differential incidence could cause the aircraft to be uncontrollable. That is, the ailerons wouldn't be effective enough to overcome the roll moment the wings are creating. Lets also not forget the yaw moment created with differential Drag that is also created!

What a mess, no one seems to ever discuss this topic that much, hundreds are flying, so it must not be that big of a deal?

Jonathan
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