Fly It to the Ground

"EridanMan" wrote in message
oups.com...
No, of course not. I'm just pointing out that 9Gs vertical isn't all
that
bad either, as crashes go.

But its a question of whats more likely to give way enough to allow you
a 9G deceleration, the hard ground, or a bunch of softer stuff along
the ground

Why is that a question? I don't disagree that one should land in as
controlled a manner as possible, with as little forward AND as little
vertical speed as possible, with vertical speed having the priority. I'm
just pointing out that 9Gs is pretty survivable no matter which direction
you're going.

And for the record, as long as the deceleration is given at 9Gs, it doesn't
matter whether you hit something hard or something soft. The impact is the
same.

Pete

"Jose" wrote in message
...
Off the top of my head, don't the current Part 23 regulations require
seats that can sustain over 20Gs?

Dunno. But I do remember a safety seminar I attended some time back where
I learned that aircraft seat belts only need to withstand about two gs,
and automotive seatbelts are required to withstand something like seven.

That number is so obviously wrong, I just had to look it up.

From 23.562(b)(2), the seatbelts (and other restraint components) need to
restrain the occupant when subjected to a peak deceleration of 26g for the
front seats, 21g for other seats (impact vector offset 10 degrees from the
longitudinal axis of the airplane).

I was unable to find a direct reference for the vertical deceleration for
the seats. 23.562(b)(1) requires the seat (and other restraint components)
to withstand a deceleration of 19g for the front seats, but this is with the
airplane pitched up 60 degrees from the impact vector (or in other words,
with the impact vector at a 30 degree angle from the vertical axis of the
airplane). Unless my bad math day continues, this means the actual vertical
strength of the seat needs to be something less than 19g. So I don't know
where I recalled the "over 20g" from, but if it's in Part 23, I can't find
it.

Some other interesting trivia I discovered:

Load limits for the seats, restraints, etc. are predicated on a maximum
passenger weight of 215 lbs. Certain dynamic tests are done with the FAA
standard 170 lb test dummy. Makes me wonder just how well a 300+ lb
passenger would do in my airplane if there ever was an accident with such a
person along (and I've carried at least two different people that I can
recall off the top of my head who are over 300 lbs).

Anyway, suffice to say, obviously airplane seat belts need to hold up to
quite a bit more than 2gs. But if you're a big person, or you carry big
people, your airplane may not be designed for you or your passengers.

Pete

Peter Duniho writes:

I'm just pointing out that 9Gs is pretty survivable no matter
which direction you're going.

Just being bumped from behind at a traffic light can easily produce 9
Gs. This level of acceleration is too low to produce direction
injury, but if it is sustained (as in aerobatic flight) it can produce
cardiovascular problems, most of which are temporary.

And for the record, as long as the deceleration is given at 9Gs, it doesn't
matter whether you hit something hard or something soft. The impact is the
same.

For high accelerations, the product of acceleration and time at that
acceleration is important (or the integral of acceleration over time).
At 9 Gs, though, no direct physical injury is likely to occur no
matter how long it lasts.

I've seen an amusement park ride that "ejects" people upwards at 6 Gs
for about 500 ms. It doesn't produce any harmful effects.

--
Transpose mxsmanic and gmail to reach me by e-mail.

Mxsmanic wrote: brevity snip

At 9 Gs, though, no direct physical injury is likely to occur no
matter how long it lasts.

Eventually brain death at +9 or yer eyeballs popping at -9...
-----

- gpsman

wrote in message
oups.com...

EridanMan wrote:
I read a statistic somewhere that if you touch-down at 50 mph, assuming
a constant 9G deceleration (Easily Survivable), you only need 10 feet
to come to a full stop.

Increase to 70mph, and you need 40 something feet.

Fly her all the way into the ground, make a shallow, full stall
landing, and you'll probably survive... The real danger comes when
people place too much value on not harming the aircraft.

I'd been told some time ago that once something really bad starts to
happen, it's no longer your aircraft--it belongs to the insurance
company. Your job is to keep yourself and your passengers healthy.


If the engine has just done something nasty like throw a rod, the best thing
financially is to have an off field landing and total the plane. If you
land on a runway without damage, the insurance company pays nothing.

Danny Dot

"Kyle Boatright" wrote in message
You've mischaracterized what I wrote. I clearly stated that you're better
off in a field if the road has vehicular traffic or if you don't know the
road to be free of wires. Those things lead to aircraft hitting the ground
out of control after the pilot stalls or collides with an obstacle. A
field
is a better choice because it reduces the odds of an out of control
impact.
Presumably, I should add "most of the time", because you appear to be
holding me to a standard of 100% certainty.

You've taken offense at my reply. Please don't let that detract from the
quality of the discussion.

Wires over the roadway are bad, and I agree that wires could cause a loss of
control, which is bad. However, just ask any cropduster, fields may have
wires running overhead also.

The danger of traffic on the roadway would lead to loss of control AFTER
ground contact (supposing the pilot hasn't frozen with panic). this loss of
control is no different than breaking a gear off and cartwheeling across the
field- been there, done that. Ripped the seats out of the rails.

The idea is to work with probabilties, and you're probably better off in a
field than on a public road if survival is your primary consideration.

To recharacterize what I wrote for you- assigning probabilities must include
more information than a transient pilot will likely have until the emergency
is actually happening.. My response to your post is that the field will not
neccessarily have a better survivability factor than the road. My intention
was to broaden the factors to be considered when envisioning this scenario.

D. (better at crashing than anyone I know)

"Danny Dot" wrote in message
...

wrote in message
oups.com...

EridanMan wrote:
I read a statistic somewhere that if you touch-down at 50 mph, assuming
a constant 9G deceleration (Easily Survivable), you only need 10 feet
to come to a full stop.

Increase to 70mph, and you need 40 something feet.

Fly her all the way into the ground, make a shallow, full stall
landing, and you'll probably survive... The real danger comes when
people place too much value on not harming the aircraft.

I'd been told some time ago that once something really bad starts to
happen, it's no longer your aircraft--it belongs to the insurance
company. Your job is to keep yourself and your passengers healthy.


If the engine has just done something nasty like throw a rod, the best
thing financially is to have an off field landing and total the plane. If
you land on a runway without damage, the insurance company pays nothing.

Danny Dot

I'd prefer to pay to fix an engine than to have someone get hurt or killed
in an effort to total the airplane.

KB

"Capt.Doug" wrote in message
...
"Kyle Boatright" wrote in message
You've mischaracterized what I wrote. I clearly stated that you're better
off in a field if the road has vehicular traffic or if you don't know the
road to be free of wires. Those things lead to aircraft hitting the
ground
out of control after the pilot stalls or collides with an obstacle. A
field
is a better choice because it reduces the odds of an out of control
impact.
Presumably, I should add "most of the time", because you appear to be
holding me to a standard of 100% certainty.

You've taken offense at my reply. Please don't let that detract from the
quality of the discussion.

Wires over the roadway are bad, and I agree that wires could cause a loss
of
control, which is bad. However, just ask any cropduster, fields may have
wires running overhead also.

The danger of traffic on the roadway would lead to loss of control AFTER
ground contact (supposing the pilot hasn't frozen with panic). this loss
of
control is no different than breaking a gear off and cartwheeling across
the
field- been there, done that. Ripped the seats out of the rails.

The way I see it, vehicular traffic (and particularly the variability of
traffic - what looked like a big space suddenly closes or traffic gets to
your chosen landing site at just the wrong moment) is a variable that has a
good chance of forcing the pilot to maneuver at the last minute. That's a
bad thing, and often leads to someone stalling and crashing from 50' (my
arbitrary loss of control altitude), which is usually fatal. As opposed to
a controlled touch down in a field, which is usually survivable.



The idea is to work with probabilties, and you're probably better off in
a
field than on a public road if survival is your primary consideration.

To recharacterize what I wrote for you- assigning probabilities must
include
more information than a transient pilot will likely have until the
emergency
is actually happening.. My response to your post is that the field will
not
neccessarily have a better survivability factor than the road. My
intention
was to broaden the factors to be considered when envisioning this
scenario.

D. (better at crashing than anyone I know)

"Kyle Boatright" wrote in message
. ..

snip

If the engine has just done something nasty like throw a rod, the best
thing financially is to have an off field landing and total the plane.
If you land on a runway without damage, the insurance company pays
nothing.

Danny Dot

I'd prefer to pay to fix an engine than to have someone get hurt or killed
in an effort to total the airplane.


I had to make this decision a few year ago. I chose the runway and paid for
an expense overhaul.

If the engine has just done something nasty like throw a rod, the best
thing financially is to have an off field landing and total the plane.
If you land on a runway without damage, the insurance company pays
nothing.

Having just had an engine failure that forced an emergency off-field
landing, I can't believe that when suddenly faced with no power, anyone
would make a conscious effort to land off field **if** a RUNWAY is
accessible, just to come out better financially! We had no accessible
runway, but if we did, we sure as hell would have used it ... we were
thinking about saving our butts, period. In those few precious seconds,
insurance never entered our minds.