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

"G.R. Patterson III" wrote in message ...
David Megginson wrote:

Perhaps it's because the O-320 (and O-360?) is able to
have all four cylinders equidistant from the carb.

Doubt it. The carb on *my* O-320 is located behind the engine. No way all four
cylinders are equidistant from the carb. I doubt that Lycoming has set up a
tuned induction system either, but it's possible.


It seems to vary from one installation to the next. My carburated
O-360 will not run LOP. Well, it runs, but not very smoothly. My
flight manual lists a procedure for LOP (called economy cruise), but
my engine goes rough approximately 10 degrees LOP.

John Galban=====N4BQ (PA28-180)

"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

"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

"Paul Sengupta" writes:

Don't think I can use Gamis here in the UK.

In Canada, I think, U.S. approvals (STC, TSO, etc.) are acceptable for
U.S.-certificated planes. Is that not the case in the U.K.?

Uneven fuel distribution is the only reason I can think of that you
would get the shudder during leaning. In an ideal engine with perfect
fuel distribution, as you lean, the engine would simply produce more
power, then less power, then quietly shut off. The shuddering is from
different cylinders being at different parts of that progression
instead of all in sync.


All the best,


David

"G.R. Patterson III" writes:

Doubt it. The carb on *my* O-320 is located behind the engine. No way all four
cylinders are equidistant from the carb. I doubt that Lycoming has set up a
tuned induction system either, but it's possible.

Is that a Continental O-320 (if such a thing exists)? The Lycoming
O-320 operator's manual suggests that all Lycoming O-320's have the
carb underneath:

Avco Lycoming O-320 series engines are equipped with a float type
carburetor. Particularly good distribution of the fuel-air mixture
to each cylinder is obtained through the center zone induction
system, which is integral with the oil sump and is submerged in oil,
insuring a more uniform vaporization of fuel and aiding in cooling
the oil in the sump. From the riser the fuel-air mixture is
distributed to each cylinder by their individual intake pipes.

Putting the carb back by the accessory drive would probably mess up
the distribution quite a bit. How well does your engine run lean of
peak?


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