Testing your glide. Are people doing this?

"Jay Honeck" wrote in
newsLunb.50518$HS4.232034@attbi_s01:

OK, this is going to sound really silly, but I'm not a pilot,
If planes glide so well, then how come they crash?
It would seem reasonable, that if they glide, and they have an engine
failure etc. that they'd glide them in, not leave smoking craters
like the news tends to show.
Am I missing something here?

A few disparate points to help you understand the situation better:

- Little planes tend to glide a lot better than big planes.

Sorry Jay! - you need to clarify this. Most little planes do NOT glide
better than big planes. Modern airliners have much better glide ratios
than our factory riveted aluminum craft.

However, those big planes gliding better also *land* at MUCH higher
speeds, and need more runway. Try that on a golf course!

There are a number of cases where jet airliners lost all power and glided
to a perfectly save landing:
- Gimli glider (Air Canada 767)
- A 737 in the south landed on a grass levee when both engines flamed out
after ingesting hail
- A 767 being hijacked glided fine to a water ditching, until the
hijackers attacked the pilots and one of the engines made contact with
the water

- Where you lose your engine is important. A little plane losing its
engine over Iowa might make the local newspaper, but everyone will
walk away. The same engine failure over downtown Chicago is going to
make national news.

- Smoking holes are created when planes glide into something -- hard.
No matter how well you can glide, sooner or later Mother Earth
reaches up to smite you. If there is a big building or mountain in
the way when you run out of glide, well...

- Smoking holes happen when a pilot allows the plane to slow to a
speed at which the wing no longer creates lift. This is the "stall"
speed. A wing/plane that is stalled takes on the flight
characteristics of a load of sand, and comes down in a hurry, creating
a smoking crater.

Hope this helps.

"Prime" wrote in message
...

Sorry Jay! - you need to clarify this. Most little planes do NOT glide
better than big planes. Modern airliners have much better glide ratios
than our factory riveted aluminum craft.

Airliners glide better than composite light airplanes too.

Mike
MU-2

"Michael Nouak" wrote
I'm not saying you're wrong, however I am curious: You "could do
125nm easily" how? With the engines shut down? 'Cause that's
what a glide is to me. At idle you're still producing thrust,
even more so a flight idle.

Based on the chart numbers for an idle thrust descent,(about 1200#
total for all 4 engines) there wasn't much thrust being developed.
In the old days, our standard descent speed was probably 50-60 kts
above the speed for best L/D and we still flight planned for a
descent distance of 120 nm from FL370 at idle thrust.

Bob Moore

On Tue, 28 Oct 2003 at 16:27:33 in message
VNwnb.51170$HS4.234123@attbi_s01, Jay Honeck
wrote:

But is that true of all airliners? I guess I would have thought that a
600,000 pound un-powered jetliner wouldn't glide very well.

The weight makes a difference to the rate of sink but I see no obvious
reason why it should make a big difference to the glide angle. After
all, airliners need good lift drag ratios to make them economical.

The BOAC 747 that lost all engines due to volcanic ash expected to be
able to glide 141 nm from 37,000 ft taking 23 minutes. That's a glide
ratio of over 20 to 1 and around 1600 ft a minute and 240 knots.

They did worse than that because they did not know the best speed and
they needed to maintain the engine start speed. Not only that but they
had no reliable speed measurement either. One pilot had 320knots and the
other had 270 knots on their ASIs - 50 knot difference!. Then they had
to sacrifice height because of loss of pressurization. Of course when
they passed out of the ash they were able to restart.

Ref: Air Disaster Volume 2 by Macarthur Job
--
Francis E-Mail reply to

In article , "Montblack"
writes:

From what I gather, one of the main reasons for some of these smoking hole
crashes is a malfunctioning switch, in the pilot's head, that says "Must
save this
airplane."

That switch needs to be set to, "Where should I put this (insurance
company's) plane down to safely dissipate the most energy, before those
forces get to us people?"

Runways, fields, roads, golf courses, high school soccer field, etc.


At a lecture on "How to crash your plane" that very point was made. He
suggested one of the best choices was a field of fully grown corn. Puts a lot
of "stopping" on the wings even before the wheels touch. Makes you less likely
to pitch over. He even suggested small trees ( and try to go between them and
let the fwings hit.

Chuck

"Michael Nouak" writes:

NOT TRUE!! A B-747 has about the same glide ratio as the B-707s
that I flew for 17 years, 20:1 or better. From 35-37,000'(6nm),
we could do 125nm easily.

I'm not saying you're wrong, however I am curious: You "could do 125nm
easily" how? With the engines shut down? 'Cause that's what a glide is to
me. At idle you're still producing thrust, even more so a flight idle.

So, how did you achieve this ratio? In a true glide (presumable tried out in
a sim), or at flight idle? And if the latter, what would be the difference
in glide ratio compared to a true glide?

A real life example:

http://www.wadenelson.com/gimli.html

They managed about an 11:1 glideslope, but the flight crew had no
documentation on optimal glide speed for a 767 (they just guessed 220
kias), and they left the engines windmilling.


All the best,


David

"David Megginson" wrote in message ...

They managed about an 11:1 glideslope, but the flight crew had no
documentation on optimal glide speed for a 767 (they just guessed 220
kias), and they left the engines windmilling.

Can you feather or otherwise stop a turbofan? The compressor seems
to spin around by itself even in a slight breeze on the ground.

David Megginson wrote

They managed about an 11:1 glideslope, but the flight crew had
no documentation on optimal glide speed for a 767 (they just
guessed 220 kias), and they left the engines windmilling.

There is no way that the engines can be prevented from windmilling.
In fact, depending upon altitude, 220 kts should provide enough
engine rpm to do an "air start" if required.

Bob Moore

"David Megginson" wrote in message
...
"Michael Nouak" writes:

NOT TRUE!! A B-747 has about the same glide ratio as the B-707s
that I flew for 17 years, 20:1 or better. From 35-37,000'(6nm),
we could do 125nm easily.

I'm not saying you're wrong, however I am curious: You "could do 125nm
easily" how? With the engines shut down? 'Cause that's what a glide is
to
me. At idle you're still producing thrust, even more so a flight idle.

So, how did you achieve this ratio? In a true glide (presumable tried
out in
a sim), or at flight idle? And if the latter, what would be the
difference
in glide ratio compared to a true glide?

A real life example:

http://www.wadenelson.com/gimli.html

They managed about an 11:1 glideslope, but the flight crew had no
documentation on optimal glide speed for a 767 (they just guessed 220
kias), and they left the engines windmilling.

Great story and outcome, I sure hope that they didn't violate any aviation
regulations though, wouldn't want them to be accussed of being "law
breakers"! LOL

That helicopter story was great also, it took real courage to do that.

Dashii


All the best,


David

David CL Francis writes:


The weight makes a difference to the rate of sink but I see no obvious
reason why it should make a big difference to the glide angle. After
all, airliners need good lift drag ratios to make them economical.

Bingo. Less drag == more glide == lower fuel consumption == fewer $$ losses..

Add to the list of "gliders" the one that deadsticked into the Canary Islands
recently after a big fuel leak..


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