Va and turbulent air penetration speed.

"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?

In any case, it's just an example. The crucial point is that Va is a speed
that limits the _acceleration_ that the control surfaces can impose before
the plane stalls, whereas Vno is a speed that limits the _force_ that the
wings can develop before the plane stalls. Therefore, staying below Vno is
what keeps the wings attached and intact, whereas staying below Va is what
keeps _other_ parts of the plane attached and intact (because the plane's
acceleration determines the force exterted upon other structures). This
distinction is key to understanding why Va is proportionate to the square
root of weight, whereas Vno is independent of weight. (Whether or not the
engine mounts are the weak link in the rest of the plane presumably varies
from one aircraft to another.)

--Gary


Dan

"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

"Dan Thomas" wrote in message
om...

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.


Nah. Properly designed engine mounts would never let that happen.

"Tony Cox" wrote in message link.net...
"Dan Thomas" wrote in message
om...

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.


Nah. Properly designed engine mounts would never let that happen.

Cessna 185 operated by JAARS Inc, South America, about ten years ago.
Threw a blade and the engine tore off the mount before the pilot could
shut it down. It turned sideways in the cowl, and the cowl was the
only thing keeping it from departing entirely. The O-520 mount is a
bed mount; if it had been the usual rear mounting the engine would
have fallen off.

Dan

*****The O-520 mount is a
bed mount; if it had been the usual rear mounting the engine would
have fallen off.****

No, it isn't a bed mount in a Cessna 185. The mount attaches to fourpoints
on the firewall.

A cessna 206, however, has a bed mount.

Karl
"curator" N185KG

"karl" wrote in message ...
*****The O-520 mount is a
bed mount; if it had been the usual rear mounting the engine would
have fallen off.****

No, it isn't a bed mount in a Cessna 185. The mount attaches to fourpoints
on the firewall.

A cessna 206, however, has a bed mount.

Karl
"curator" N185KG

The mount attaches to the firewall, but extends underneath the
engine and attaches to four mounts on the *bottom* of the case. These
are the mounts that failed, not the tubing. The engine in question was
resting on that structure when the noise was finished.

"Dan Thomas" wrote in message
om...
"Tony Cox" wrote in message
link.net...
"Dan Thomas" wrote in message
om...

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.


Nah. Properly designed engine mounts would never let that happen.

Cessna 185 operated by JAARS Inc, South America, about ten years ago.
Threw a blade and the engine tore off the mount before the pilot could
shut it down. It turned sideways in the cowl, and the cowl was the
only thing keeping it from departing entirely. The O-520 mount is a
bed mount; if it had been the usual rear mounting the engine would
have fallen off.


What's a bed mount, Dan? I've always thought (hoped) that my
182 cowling would contain the engine. And there is always the
fuel line, throttle cable, and battery cable as a last line of defense

"Tony Cox" wrote in message ink.net...
"Dan Thomas" wrote in message
om...
"Tony Cox" wrote in message
link.net...
"Dan Thomas" wrote in message
om...

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.


Nah. Properly designed engine mounts would never let that happen.

Cessna 185 operated by JAARS Inc, South America, about ten years ago.
Threw a blade and the engine tore off the mount before the pilot could
shut it down. It turned sideways in the cowl, and the cowl was the
only thing keeping it from departing entirely. The O-520 mount is a
bed mount; if it had been the usual rear mounting the engine would
have fallen off.


What's a bed mount, Dan? I've always thought (hoped) that my
182 cowling would contain the engine. And there is always the
fuel line, throttle cable, and battery cable as a last line of defense


I couldn't trust a few wires and cables to keep the weight of the
engine attached to the firewall.
I spoke with a former 747 pilot who was into Formula 1 racing. He
had a single-seat (Cassutt?) racer that used an O-200 turning a tiny
prop at 4400 RPM to get the flat-out speed he wanted. I asked him
about the prop failure/engine departure scenario, and he told me that
he (and his buddies, in their airplanes) had a stout cable wrapped
around the engine and bolted to the firewall to cover this
eventuality. Apparently it had happened more than once before to other
unfortunate racers.

Dan