Greg Esres wrote in message . ..
The engine mount on most light aircraft is designed to withstand 9
G's minimum.

Where do you get this figure?


Canadian Aviation Regulations 523.561 gives some numbers for
protection of occupants in an emergency landing (a crash). Seats and
belts, for example, have to withstand 9 Gs forward, 6 Gs downward, 3.0
upward for Normal and 4.5 for Aerobatic. Items of mass within the
cabin must be able to withstand 18 Gs forward.
The structure itself must be able to withstand, in the event of
"complete turnover" during a crash, 9.0 Gs forward, and some lesser
numbers in other directions. This structure would include engine
mounts.
Somewhere else in the many sections are more numbers specifying
componemt strengths. The FARs would have an equivalent section. The
minimum legal flight load strengths for any Normal Category airplane
is 3.8 Gs. Note that flight loads and "emergency landing" loads are
not the same, but the airplane must meet those requirements.
A 3.8 G engine mount would be most dangerous. In training students
in our Citabria, we have seen well over 3 Gs on the G meter in botched
landings. The wings and tail don't much care about that impact, since
they don't experience any air-load increases, but the gear, fuselage
and engine mount do. Imagine, for a minute, the effect of an engine
departing the airframe in such a spot: airspeed at or near stall
speed, an airplane that's suddenly 350 pounds lighter, and a CG back
around the trailing edge of the wing. People killed, maybe, for the
lack of one pound (or less) of 4130 tubing?


Dan