#### Re: Thrust Line & Bellyboard

JohntenHave <Jtenhave@...>

Joseph,

Do not guess.

let me give you an outline of how to calculate what you need.

Firstly work backwards from what it does (or more accurately) what
you want it to do. In this case deploy and slow the aircraft down.

So work out the area, and how fast it could inadvertently be deployed
(do not be tempted to think this will never happen to me!). That will
give you the load to be reacted. Guess high speed. Assume opens at 90
deg to airflow. The Safety factor is then applied to the load. Say
2.5. Next figure out how the loads will flow, i.e. from the uniform
distributed load on the plate to the attachment points and the
actuator attachment.

Next trick is to analyse the loads at the concentration points for
the load cases, eg shear around the head if you are trying to pull
the bolt through the material, compressive stress if you are trying
to load the fastener in shear, edge distance analysis for failure due
to pull out, etc, get the picture?

Put sufficient material in place to react the safety factored load.

Then consider the whole plate as a beam attached with a pin joint at
one end and a simple support at the actuator and consider the
bending lengthways and across the beam. Make sure the load does not
exceed the allowables for hand layup.

Next port of call is to put your feet on the desk and think about
failure modes, what could happen if it broke? If it broke, where
would be the best place for it to break? If you were in a crash and
it was deployed would it spear you or would you prefer it to break
before it got to you?

Then think about where the loads go in the fuselage, With this sort
of thing, it is often better to make sure that the parent structure
does not fail under limit load whilst the airbrake remains intact.
i.e match the strengths or deliberately design the part to fail first.

Then lay out the materials to meet the requirements. As a flat sheet
you might well find that for most of the loads that the part sees, it
is too strong but it is simpler to make, and light enough to tolerate.

Last check, reverse engineer what was done before as a cross check (
and be prepared for a few revelations...)

Hope this helps

John

-- In Q-LIST@..., "Sam Hoskins" <shoskins@m...> wrote:
I would do the layup on the unblemished belly. After that's done,
then dig
out the foam per plans. I have now idea about the orientation.
Maybe one
of our composite engineers could chime in.

Sam

http://samhoskins.blogspot.com/

_____

From: Joseph Snow [mailto:1flashq@a...]
Sent: Wednesday, March 02, 2005 7:20 PM
To: Q-LIST@...
Subject: Re: [Q-LIST] Thrust Line & Bellyboard

Ok, that makes sense. I could cut out the 10" x 11" skin, remove
1/8" foam,
then vacuum bag the layup. Any idea on orientation of the carbon
fiber
cloth, i.e., front to back, side to side, 45 deg. ? I have never
used
carbon fiber cloth. Should it be Uni or Bid?

Joseph

Quickie Builders Association WEB site
http://www.quickiebuilders.org

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