On 07/04/2013 04:11 AM, Tony Renshaw wrote:
> <tonyrenshaw268@gmail.com>
>
> Gidday, I have set up my port wing, pulling it in tight agains the
> rear face of the cockpit module and setting the incidence. I've used
> a digital level and upon bonding on the LE lift pin socket I found
> the incidence had changed nominally.
Forget this digital level. Been there, done that. It changes everytime,
depending on where you measure and other obscure variables. It drives
you nuts and leads nowhere. And is not precise enough anyway.
Prepare two blocks of some suitable material (wood, blue foam), about 4
cm or so high, and make sure they are of exactly the same size.
Put them on the trailing edge of the wing, at the same distance from the
fuselage.
Now walk away from the airplane. At least 5 meters, more is better.
Bring the top of the leading edge exactly in line with the block on the
trailing edge (just like aiming a gun, you could as well put a needle on
the block and a hairline cross sticking out of the leading edge). On
both sides (port and starboard) you should have the leading edge and
blocks in line at exactly the same eye height. You will notice that
moving your eye just a cm up or down will make a whole difference.
If you do the math, you will find out that this method is many times
more precise than any digital level and you will be able to sight
fractions of a degree. What's more, you can repeat this with the blocks
at varying distances from the fuselage (but keep port and starboard
always at the same distance to cancel the wash out!) and get some
"avarage" out of it to cancel out minor imperfections of the shape of
the wing.
You can get it even more precise if you use some reflecting material, or
put a bright LED on top of the blocks, or use some sort of back light.
It is just like seeing the exact moment of sun rise or sun set. At 20
meters away it is awfully precise to see if both wings are equal: both
leds (or lamps) should rise at exactly the same moment over the leading
edge while you move your head slowly up! Less than just a millimeter of
difference in trailing edge will be clearly visible.
I ended up doing the wings this way, the outcome was stable, repeatable
and very precise, and during curing of the araldite I kept the blocks on
and "sighted" the wings regularly to be sure that nothing moved.
The airplane can be flown right into a stall and just bobs up and down
like a straight Cessna, not even the smallest tendency to wing drop.
> Suffice to say I now somehow have 2.8 degrees
> which is to me unacceptable,
The target was 2.7 if I recall correctly? Then don't worry. I set mine
deliberately at 0.1 steeper because I have a high top and would prefer
just a tad more nose down to cancel out the steeper angle of the roof
and to get more view over the higher firewall. Flies beautifully!
Frans
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