end of the fuselage were double the height then we could hang engines
actually 8X heavier and have the same stresses (cubic function for a box
shape). Moving the engine closer is a linear relationship as far as stresses
are concerned but even that helps when we are talking about 300 lbs hanging
out there.
Another thing that may be of interest is that there is a square relationship
in the momentum generated by vertical impact. If on a bad landing the impact
speed only doubles, the resulting inertial loads at the firewall will
quadruple!!! So bumpy landings and bumpy runways will have a big impact on
the life of the firewall and everything the engine hangs onto as well as
the landing gear...and the tail....and the wings....and my back!!!...and my
teeth (just kidding)....
I am practicing my landings.......and investigating engine weights......and
firewall beef ups.......
Paul Kucera
Rebel builder 453R
----- Original Message -----
From: Brian Cross <rebelair@idirect.com>
To: Murphy Rebel Builders List <murphy-rebel@dcsol.com>
Sent: Sunday, December 05, 1999 2:19 PM
Subject: RE: Rebel "652" Wing tanks
notHi There Folks
The thought that Bob expressed about moving the firewall back is a very
valid one when dealing with the heavy 0320 engines. A 3" movement does
goessound like very much, but, if one were to do the stress analysis on it, it
means a great deal. I would have to double check my text books, but I'm
sure that the induced bending stresses in an overhung load such as this
reductionup the square of the distance away from the structure, i.e. double the
distance and you have 4 times the bending stress. In other words, a 3"
movement on a moment arm of about 27" will equate to a significant
farin stress of the nose area. Will it be enough to prevent problems? So
orso good in my case, but time will tell or should I say one of my bad
landings will tell!
That was a strong enough argument for me to move the firewall back. With
careful placement of the stick i.e. mounted centrally over the 2" cross
tubes as per the original design but with bent sticks to prevent it from
touching the dash, there is no difficulty at all with stick interference
theforward visibility especially with the speed cowl which really improves
*----------------------------------------------------*view over the nose. With this setup I am very happy with results. After
flying Cessnas, I feel I can see the whole world out front and the only
difficulty I have with the aircraft is to make it stop climbing!
(Seriously, until you get used to all the view over the nose).
Best Regards
Brian #328R
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