Friday, 20 May 2011

Wingtip bows version 1,2,3,4.....

I built the first wingtip bow a few months back, and based the shape on a template I made from the EAA replica.
It turns out a tracing made on a fabric wing, on an aircraft mounted in a museum display, at a 15 degree angle, with the paper taped in place with low tack tape, standing on a ladder, is not the most accurate means of getting an exact shape.
who knew.

I was not happy with the first pair of bows, the laminating and glue up was fine, but the shape just did not look right, so I stared at it for a month or so, hoping it would magically transform into the correct shape,
It did'nt.
but I knew I would end up making another set, so eventually I started version 2.
Only to find out I had reset the jig blocks with an incorrect raduis of about an inch.
another 16 strips of spruce, lots of T88 glue, a few days, and I had a good start on a harp frame.

This was not going well.

Version 3, and by now about 30 board feet of perfect spar grade spruce later, and this one looked really bad, no need to wait a month, I knew this one was way off the desired and rather distinctive Laird shape.
I was getting desperate, they were getting worse.
From left to right Versions 1,2, 3 and the final correct bow. 
OK, it was time to resort to technology, a request made to David, (the computer guy) and in no time a full size template arrived, beautifully printed, and it was the exact shape. David is an incredibly talented fellow, and he tends to work in minute dimensions, and while I try very hard to build the parts to his exacting dimensions, eg; 30.987, I may inadvertently make the part 31.0, seeing as it is wood!
(and David has actually dropped his standards, he used to work to the 5th decimal place).

For a fourth time, I set the 25 or so jig blocks up, planed another 14 strips of spruce, soaked them in hot water and ammonia, and carefully laminated two bows up. (I was getting pretty good at this) I knew right away that the shape was correct, but it is amazing when they are placed beside versions 1,2, and 3 just how far off I was each time.
I apologize to all that beautiful old growth spruce which was needlessly sacrificed in my quest to make the perfect wing tip bow, but as anyone who had played hockey knows, you may play every game in the regular season, but not everyone gets ice time in the playoffs!.
So, once again, it is amazing how much an 80 year old airplane project can benefit from modern computer technology.
now all I had to do was mount and shape them.

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