Bill Freeman wrote:

Paul and Mike,

It seems from the RV4 mount drawing that it may be workable to make
a truncated version of Paul's mount which bolts onto the std non-Dynafocal
mt pts on the factory RV4 mt.  Seems like the side arms could be L shaped
and triangulated, connected to the existing mt pts.  Seems like still room
underneath for the rad.

Paul, I forget the details of the side sections of your mount, have you got a
good isometric view to refresh my memory?

Also, Mike's idea of trying ideas with PVC pipe is a good one.  Remember
to make everything triangulated and you won't go far wrong.  As far as adding
too many tubes, note that 1/2" diam 0.035" wall 4130 tube only weighs 0.1738
lb/ft yet  is good for over 3000 lbs in tension, less in compression due to
buckling, but buckling is less a factor if the runs are kept short.
It takes ~ 6 ft of 1/2"x0.035" 4130 to reach a pound,
where a 1/2" plate 4.5"x 4.5" also weighs about a pound.

Here are some allowable tension loads for a few sizes of 4130
steel tube, with the limit defined by onset of permanent deformation,
not actual fracture.  Fracture is at least 50% higher, except in
buckling which is highly nonlinear.  If you have a 350 lb motor,
design for 3500 lbs in the downward direction, i.e. a 10G "uh-oh"
 landing, and you'll hve PLENTY of margin.

        TUBE            lb/ft       max tensile load, lb
    1/2" x 0.035"    0.1738             3066
    1/2" x 0.049"    0.2360             4162
    5/8" x 0.035"    0.2205             3892
    5/8" x 0.049"    0.3014             5320
    3/4" x 0.035"    0.2673             4717
    3/4" x 0.049"    0.3668             6475

Bill

Bill I have a buckling chart on the ACRE NL web site from
the bible of aircraft design; "Analysis & Design of
Flight Vehicle Structures" by E.F. Bruhn.
None of the loads on motor mount tubes get anywhere near 
these numbers. Buckling and bending mode vibration are the main
criteria for tube size. 

This is an early RV4 motor mount drawing. Since this was drawn I
recommend
using a shallow 4130 steel hat section instead of the two inch
diameter tube and moving it toward the firewall about three inches 
under the front rotor housing. Also the diagonal brace tube is not
shown.
With the hat section the rubber mounts are also raised a couple of
inches. I guess I need to redo this drawing showing the Van's landing
gear socket tubes. If Mike can wait a couple of days I will do
that. The next projects are pay monthly bills and do the remote
anemometers
as I recieved the hall effect sensors from Digi Key today.

Paul Lamar
 
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