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salutti tutti,
Mike and others...
Early this year I closed a set of LIV wings which
are now installed on the fuselage. The wing is perfectly straight, ie
at x% chord at BL 25.5 the wing surface is a perfectly straight line
to the corresponding x% chord at the tip, which is the design
intention. Imagine a 4 metre straight edge placed on the wing surface, at
any % of chord at BL25.5, top or bottom surface of the wing, the wing
surface is perfectly straight to the same % chord at the tip. Of course the
leading edges and trailing edges are, from root to tip also perfectly straight
lines.
When mounted to the fuselage the wing
incidence is 1.6 degress nose up + - 0.05 degrees at BL25.5, it is
0.3 degrees nose low + - 0.1 degrees or better at BL 171. My
wing has 1.9 degrees of washout between BL25.5 and BL 171 with less than
0.1 degrees of difference anywhere along the span. Considering that in the
design the washout is 2.0 degrees between the root at BL 0 and BL 171, 1.9
degrees of washout between BL25.5 and BL 171 is about right.
This wing jig was built with bits of ply and crude
simple hand tools. (Was it Bob P's comment "bit's of 1/2" ply cut with a jig
saw"?....to this I say metaphorically; your block of flawed marble, might
be, to Giambologna "The Rape of the Sabine Women" 1583) The wing
kit was one of those old fashioned "slow" build wings which had been
partly built but poorly so we made the decision to strip and rebuild. I
developed the BL 25.5 and BL171 profiles from data and found some
variation from the blueprints. I carefully calculated flap track angles and
position and set the flap tracks accordingly. We'd purchased new flap
tracks and flap roller plates from Lancair and upon receipt of the flap tracks I
noticed the flap tracks to be slightly different from our originals so I
installed the rollers onto the roller plates then to the flap tracks and lo
and behold the plates were unable to travel the full travel of the flap
track slots locking up a little past about 30 degrees of travel. (Shame on you
Lancair that no-one notices such simple things) After machining the track slots
just a little I had the full 40 degrees of travel so went ahead and used
them. After building the flaps and connecting the port and stbd flap bellcranks
with an interconnecting pushrod I measured 7.5 pounds on the pushrod to
pull both flaps up to the fully extended position. Incidentally in the
retracted position each of the flap track rollers is snug to it's forward
position in it's respective slot plus or minus a poofteenth of nothing, as
is the case in the fully extended position.
In my opinion if Lancair's Building "Assist"
Program is not giving you results like this then it's a waste of time and money.
To be building wings with 1.7 degrees of incidence (in)difference is truely
and extraordinarily bad considering that the Company is supposed to be the
expert on Lancair building. No matter where it's been done Phillipines,
Redmond, Timbuktu, a wing built out of spec pulled into an accurate jig and
then closed up, when closed and released from the jig will spring back to
some extent, I know this from experience from "fast build" wings. Perfectly
straight and accurate jigs will produce perfectly straight wings
PERIOD. If I in my efforts produced such poor and dangerous
wings I'd be truely ashamed and give up building these aeroplanes I love so
much.
I also believe that using eccentric bushes to
change wing incidence is not just poor practice but quite potentially dangerous.
Perhaps Lancair Company might give the details of who in the Company has
analysed this procedure, their qualifications and the analysis results including
but not limited to the load carrying capability of the twisted spar at it's
maximum load, the stall response of the asymmetric wing and stall progression
from root to tip as is the design intent, the stall response under gust loads
upto the structural limit of the aeroplane (the top of the green arc of the ASI)
and beyond, the stall response with flaps partially and fully extended, the
consequent differences in flap rigging and aileron rigging
etc.
I await Lancair's response....
ciao,
Roberto d'Italia.
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