The Murphy Builders Site

I wonder if anyone can help me determine appropriate material sizing for
construction of an engine mount for an engine that weighs between 450
and 500 pounds and will produce up to 450 HP and 450 ft-lbs of torque.
Assuming I am using round steel tubing I need to know the size of tube
and wall thickness. I also need to know what thickness of plate should
be used for gussets, brackets, or other reinforcements.

As a starting point perhaps someone knows what the engine mount material
sizes are for a standard 300HP Lycoming O-540, or for the 400HP M14?

Thanks.

Mike Kimball
044SR



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Not that I know what I am doing...but I made mine using both 1" x .049 and
7/8" x .049 4130 for my legs and .050 for gussets and finger patches for the
M14. Mount bolts were 7/16 through a stud, not down a tube on a washer like
the MAM one. I think the Murphy M14 mount is 7/8" and not sure on wall
thickness. I believe they have 3/8" bolts.

The Pitts Model 12 doing unlimited acro with the 400+ HP use 1" by .049 and
.050 gussets and finger patches. They mount through studs with 1/2 bolts.

Scott
Moose 174

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Mike
Kimball
Sent: Saturday, July 17, 2004 3:07 PM
To: rebel-builders@dcsol.com
Subject: Engine mount material size

I wonder if anyone can help me determine appropriate material sizing for
construction of an engine mount for an engine that weighs between 450
and 500 pounds and will produce up to 450 HP and 450 ft-lbs of torque.
Assuming I am using round steel tubing I need to know the size of tube
and wall thickness. I also need to know what thickness of plate should
be used for gussets, brackets, or other reinforcements.

As a starting point perhaps someone knows what the engine mount material
sizes are for a standard 300HP Lycoming O-540, or for the 400HP M14?

Thanks.

Mike Kimball
044SR



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In "Auto Engines for Experimental Aircraft", Richard Finch suggests 1"
od x 0.063 for 350 hp. V8 engines weighing 600 lb or less.

7/8 x 0.049 for 200 hp. V6 weighing 425 lb or less
3/4 x 0.049 for anything smaller.

FWIW I'd be a little cautious about using a rule of thumb though unless
you can use a fairly low stress design. I've seen beautifully
triangulated mounts that don't require heavy gauge tubing and also
poorly triangulated and even cantilevered designs that seem very
questionable. In general I think you want to lean towards heavier stock
on any long tubes that are in compression. Rectangular tubing might be
better for anything that is cantilevered. From what I have observed,
thicker stock seems much more forgiving of less than perfect welds and
may avoid at least some gussets. I tend to think of gussets as something
that is added to fix/repair a weak spot or a band aid for a design that
can't be nicely triangulated. Tubes work best in straight compression or
tension and less well if gussets are transferring bending forces.

Ken

Mike Kimball wrote:

I wonder if anyone can help me determine appropriate material sizing for
construction of an engine mount for an engine that weighs between 450
and 500 pounds and will produce up to 450 HP and 450 ft-lbs of torque.
Assuming I am using round steel tubing I need to know the size of tube
and wall thickness. I also need to know what thickness of plate should
be used for gussets, brackets, or other reinforcements.

As a starting point perhaps someone knows what the engine mount material
sizes are for a standard 300HP Lycoming O-540, or for the 400HP M14?

Thanks.

Mike Kimball
044SR

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