Re: REFLECTOR: Leveling

[gpoole@zeta.org.au (Mr Greg Poole)]

Benjamin David Cowan said
>    Well, it is now clear that my bottom fuselage is somewhat twisted.. in
>order to get bulkhead locations level side to side.. I end up with a cowl
>that is 3/4 inch high on one side...  Any suggestions? Is this a freak
>occurance? Also, I went ahead while I had the thing loose again and turned
>it over and cut out the nose gear door hole according to the factory
>markings... Cut it perfectly straight... And at a glance it doesn't look
>like its perfectly centered to the centerline.. Perhaps not crucial.. Do
>the factory markings tend to be off? It's possible the twist has affected
>my center line I suppose also.. The way I figure it, even if the fuselage
>were twisted, bringing it into level at two or three bulkhead locations
>should bring it to a straight alignment, provided that it is semetrical..
>When canard bulkhead and firewall are level the back end is way off..
>Conclusion,,, fuselage is Asemetrical.. What should I do?? It's not going
>to untwist in the air is it?? I assume I'm going to have to just level the
>bulkheads and worry about the back later... right?
>
>Any comments or suggestions are much appreciated..
>
>B. David Cowan
>
>SW RGE



Dear B. D. Cowan,

Quite right - you well answered your own question!

...But you got me curious, so I immediately went out with my trusty digital
level (..didn't want to spill any water folks!) and checked my Velocity
which happens to be the same model as yours. Maybe I am lucky, but I didn't
find quite the same level of twist  you observed. Someone who dropped a
comment on what a minor variation  of level (say 0.5°) translates to over a
one metre distance was right - it certainly magnifies over the width of a
Velocity!

My fuse did not vary in level by any more than 0.2° across it's width from
canard bulkhead to firewall positions. Like yours, more twist was evident
from firewall back to the rear of the engine cowling - but nothing to worry
about. While measuring I checked the symmetry of each side of the fuselage
and it is certaily not mirror image - but well and truly passable in the
scheme of things.

I sincerely hope no one ever tries to force their fuselage to level before
installing bulheads, but concentrates on ensuring level was obtained in the
real important places such as canard and carry through spars. If my
understanding is correct, fibreglass is one of those substances that
maintains a shape memory and will "boing!" (as somebody else aptly put it)
back into position if given half a chance unless plastically deformed
through heat, sheared through force, or  braced effectively. Trying to
permanently correct twist down the long axis of a fuselage would be
extremely difficult I would think. Why anybody would bother - given the
relativities between the effect of wing surfaces against any minor forces a
slight twist in the fuselage might impart - is beyond my comprehension.

Cosmetically I also doubt whether any of these variations are going to be
at all obvious once your Velocity is constructed. Would be interested in
comparing notes with you as we both progress through construction if you
are interested.

Regards,

Greg.

Greg Poole (Building a Std RG Elite Velocity - "down under")