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Re: REFLECTOR: Heating and bending

  I'd agree with Al. There's not much thickness to the bulkhead sandwich so
not a lot of pressure is required to flatten it. Conversely it can't apply a
lot of pressure on the surrounding area.
  My firewall was warped and I flattened it before glassing the plywood.
That helped some but didn't completely solve the problem. I glassed it in
place so the section from the spar top down was flat and plumb. The part
above the spar was canted forward. When putting the fuselage top on I cut a
plate of 1/4" steel to fit the space, straightened and flattened the
bulkhead before glassing.
  I've done quite a bit of heating with a heat gun and never had any
difficulty reheating an area when needed. I'm only using heat for a short
time, not as long as would be required for postcuring so I don't think the
Tg is affected much if at all.
  I'd pull it into place and finish glassing. I'd be most concerned to make
sure the engine mount areas are as even and plumb as possible.   -Bill

prototype 'Super' Chipmunk N18EF
Velocity Classic RG N6098S in the works

-----Original Message-----
From: Al Gietzen <alventures@email.msn.com>
To: reflector@awpi.com <reflector@awpi.com>; David Doshay
Date: Friday, February 12, 1999 1:02 AM
Subject: Re: REFLECTOR: Heating and bending

>>I was thinking that I would like to heat about 3/4 of  the
>>firewall and pull it back, and then let it cool true. My question
>>is whether or not I need to pull it beyond true to avoid
>>having it spring back.
>>Of course I could just pull it back to true and glass it into
>>place, (no heat at all) but then this part will be under stress
>>and ... well it is hard to know exactly how the airframe will
>>move in reaction to that stress. Maybe not at all, maybe it will
>My experience with the door (remember my solar heating solution?) is that
>the idea is to hold at temperature in proper configuration until the
>stresses are gone.  Then when it cools it stays there.
>However, it seems to me that the way to go is hold it straight and glass it
>in.  You're talking very very low stresses compared to all the structure
>around that bulkhead.
>Al Gietzen