"Gary Drescher" wrote in message news:wKGLb.9047$8H.23200@attbi_s03...
"Dan Thomas" wrote in message
om...
"Gary Drescher" wrote in message
news:bnzLb.6520$8H.20195@attbi_s03...
"Dave S" wrote in message
. net...
Now... a question about realities.. The POH nazi's will say that the
Word as written is good, praise be to the POH... if I base flight
decisions and speeds on MY calculated numbers rather than the max
weight
sea level standard day numbers published in the almighty POH.. am I
going to be asking for trouble here?

It depends on what you mean by 'trouble'. The laws of physics prevail
over
the POH in determining whether your engine mount will break...

Why do folks worry about engine mounts breaking? They are far
stronger, in most cases, than the rest of the structure. For
production airplanes, the legal standards for certification include a
9G strength for fuselage/cabin structure for crashworthiness, and I
have seen other specs calling for the same 9Gs specifically on engine
mounts.

Are those regulatory specs?

Yes, they are. being a Canadian, I can quote the CARs but the
FARs are a different matter. I'l see what they have to say. In any
case, when have you ever heard of an engine departing an airplane in
turbulence or during violent maneuvering? Our Citabria has a G-meter
in it, and we have seen some pretty big numbers when students get
clumsy on landing.
Landing forces don't affect wings much, since they're still
generating lift and the landing forces on the structure tend to be
negative, and if the engine mount was a 5G structure like the rest of
the airplane it would have fallen off long ago. A missing 300 pounds
or so during a hard landing would be disastrous: CG way back near the
trailing edge, an airplane suddenly much lighter, and airspeed still
sufficient to flip the whole works over into a crash and burn
scenario, all for the lack of another pound or so of tubing.
The only times I have heard of engine mounts failing on light
airplanes is when a prop throws part of a blade, or maybe the whole
blade on a constant-speed prop. The imbalance is more than enough to
rip the engine off the airplane. Blades will fail when propeller nicks
are left untreated and cracks develop. The prop is the most highly
stressed bit of metal on the whole airplane, and THAT'S what pilots
should be concerned about, not engine mounts.

Dan