CAN JET GLIDE AFTER FULL ENGINE LOSS? please help.
Steve Rogers
jet which lost ALL engine power and was able to glide to safety. I tuned
in when the jet had approximately 30+ miles to glide prior to landing
(at an abandoned airstrip).
I, as a layperson, presume that airspeed at the time of loss, altitude, and
perhaps the term "glide path" are significant factors; however, I am unable
to fully understand why a large jet (ie 727 or 737) is able to glide this
distance. If a plane losses full engine power and the pilot does not
lose control of the plane, how far should the plane be able to glide in
general.
Your response is GREATLY appreciated!
Steve Rogers
George Reaves
Ajy aircraft can glide for some distance even with complete power loss.
The pilot must keep from stalling the aircraft. There is a speed at which
the aircraft will glide the farthest, in the even of a powere loss a pilot
should immediatly establish this speed and retrimm the aircraft to hold this
speed. Now there is also aspect ratio, or the ratio between the chord and the
span, or span and area. They work out to be the same. if an aircraft as an
aspect ratio of say 10 to 1 then it will fly forward 10 feet for every 1 foot
it drops. So, if a 757 as an aspect ratio of 5 to 1 and its is 6 miles high,
or about 35,000 feet, it could theoretically glide 30 miles if flown
properly. The even that the TV show was based on did occure. The captain of
the aircraft was a glider instructor, and extremely experienced in flying
unpowered aircraft. This is probably the only thing that alloweded him to
safely maintain control of the aircraft.
I did not see the film, however, from taling with several friends that
did I would say that less than 1/2 of the film was actually correct. If you
have any further questions feel free to ask.
Hope all of that helped.
George
reav...@delphi.com
Michael
<reav...@delphi.com> wrote:
> [snip] Now there is also aspect ratio, or the ratio between the chord and the
> span, or span and area. They work out to be the same. if an aircraft as an
> aspect ratio of say 10 to 1 then it will fly forward 10 feet for every 1 foot
> it drops.
What? Huh? Aspect ratio = glide ratio? Really? Are you sure about that?
Paul Raveling
|>
|> I, as a layperson, presume that airspeed at the time of loss, altitude, and
|> perhaps the term "glide path" are significant factors; however, I am unable
|> to fully understand why a large jet (ie 727 or 737) is able to glide this
|> distance. If a plane losses full engine power and the pilot does not
|> lose control of the plane, how far should the plane be able to glide in
|> general.
In still air, gliding distance would be...
d = glide_ratio * initial_altitude
= lift/drag_ratio * initial_altitude
A worthy and simple exercise is to show that glide ratio = L/D;
this follows from the definition of lift as force perpendicular
to the aircraft's direction of flight and drag as force
in the direction of flight.
For jet airliners the numbers I've heard for L/D have typically
been a bit over 20:1, about like low performance gliders.
(The state of the art is about 45:1 in sailplanes with
15-meter wingspans, 60:1 or slightly less in those with spans
in the range of 20 to 25 meters.) Airliners have fairly good
L/D, and therefore good glide ratio, because they're
designed well for low drag.
So at 20:1 in still air an aircraft starting from ~21,000
feet above ground level (4 miles) could glide about 80 miles.
When an airliner does this it'll have a fairly high descent
rate because its airspeed is high, at least in comparison
with normal (non-Space Shuttle) gliders. Without taking time
to compute, I'd guess at least 1,000 fpm for sink rate at
best glide speed.
Best glide speed itself is proportional to the square root
of wing loading (weight per square foot of wing area). This
can vary A LOT for airliners, since they can operate at a
wide range of weights as a function of payload and fuel aboard.
---------------------
Paul Raveling
rave...@netcom.com
or
prav...@us.oracle.com
christian j dolese
angle of descent that will be varible ;the maximum distance is achieved
by maintaining best glide speed throughout the descent and also dependent
on the headwind/tailwind component
>
christian j dolese
aspect ratio = glide ratio , i don't think so - what book have you been
reading?
George Reaves
I goofed, and have had the thrill of being told so multiple times.
Aspect ratio is not the same as glide ratio. Bummer !!! I think that this
thread as generated enough responses, most of them accurate. Here is my
final word.
E=L/D=Cl/CD
Assume parabolic
E=Cl/(CD0+K*CL*CL)
now taking the derivative and setting equal to 0 will
produce E max, if you do the second order check for a
maximum condition. SO
Cl, ath Emaximum = sqrt(CD0/K)
or Emax = 1/(2*(KCD))^1/2
Typical values for Emax are:
Sailplane 35 - 45
M 0.8 Tran18 `
Fighters (Subsonic) 10
FIghters (Supersonic) 7
Maximum range is a factor of Emax. The instant aneous max
range will occure at Emax for gliding flight. This can be
proven by taking various derivatives of the force equations.
The above explanation is for the technical guys reading this
the source is Aircraft Performance by Hale. My appoligies
for confusing the issue.
George
reav...@delphi.com
John S. Fowler
I had the opportunity to fly with a couple of pilots in a USAir 737 a couple
of years ago on a proficiency training flight. During stall practice, they
pulled the power back to flight idle and maintained level flight. I estimate
the jet lost about 1 knot of airspeed every 2 seconds. Of course, there is a
small amount of thrust at flight idle, but not that much.
SR - ILM
-------------------------------------
SR - ILM
Moshe Braner
>
> Any aircraft can glide for some distance even with complete power loss.
>The pilot must keep from stalling the aircraft.
That "stalling" means slowing down too much. That needs to be done whether
the engines are working or not. Not enough air flow against the wings means
not enough lift to support the plane. On the other hand, even a
helicopter can glide to a safe landing in the case of power loss,
as long as the rotor is allowed to keep rotating fast enough
(driven by the relative airflow).
> There is a speed at which
>the aircraft will glide the farthest, in the even of a powere loss a pilot
>should immediatly establish this speed and retrimm the aircraft to hold this
>speed.
It's no big crisis if the speed is wrong, just that the glide will be
somewhat steeper.
> Now there is also aspect ratio, or the ratio between the chord and the
>span, or span and area. They work out to be the same.
They're not the same. If the (mean) chord is C, the span S, and the wing
area A, then A = S * C. The aspect ratio is S / C, which can also be
expressed as S^2 / A, if you substitute A/S for C.
>If an aircraft as an
>aspect ratio of say 10 to 1 then it will fly forward 10 feet for every 1 foot
>it drops.
It is true that higher aspect ratio allows a shallower glide, but the
numerical relationship is not that simple. For a clean aircraft, the
glide ratio is higher than the aspect ratio. E.g., a good glider has
a typical aspect ratio of about 20, and a glide ratio of about 40.
For a typical light plane the aspect ratio is more like 8, and the
glide ratio about 9.
>The captain of
>the aircraft was a glider instructor, and extremely experienced in flying
>unpowered aircraft. This is probably the only thing that alloweded him to
>safely maintain control of the aircraft.
Any pilot can (and should!) be able to control the plane with no power:
many landing approaches in light planes are done with almost no power
(engine almost idling). But landing a big jet with no power is very
unusual, and the pilot of the "Gimly Glider" certainly made use of
his glider experience. The hard part was not controlling the long glide,
but STEEPENING the glide by just the right amount at the end to touch
down long before the far end of the runway.
- Moshe
Haynes Lee
Over a decade ago a 767 ran out of fuel in mid-air. I forgot
where it ran out of fuel but it glided a _long_ way to Gimli,
Manitoba, Canada where it landed on a drag race strip.
No one was hurt but of course, an inquiry blamed everything
on the pilot anyway.
Lee McGee
|> So, if a 757 as an aspect ratio of 5 to 1 and its is 6 miles high,
|> or about 35,000 feet, it could theoretically glide 30 miles if flown
|> properly.
That would be a "brick". Maybe a biplane with a lot of wires hanging out
in the wind, and a small wing, etc. A modern airplane has a much better
glide ratio than that!
Passenger jets make very, very good gliders actually. If you look at the
overall aircraft planform, you see a very nice aerodynamic, low-drag
shape.
You just have to move them faster. A 767 can probably glide at a 16 to
one
ratio at a best glide speed of a *fast* 220 knots (estimated best L/D
speed). Don't get slower than that -- that would not be the best
glide speed, and the aircraft will sink rapidly, even if not stalled. :^(
Best glide speed is best glide speed and the pilot has to adhere to it for
best glide performance. Maybe an air carrier pilot listening in to this
thread
can provide some actual numbers?
So from 35,000 feet, this hypothetical 767 might glide 106 miles at 16/1.
That glide will take 25 minutes at that airspeed. That makes for
11,236 square miles of potential emergency landing places.
They had better be pretty large landing places, as big jets move pretty
fast.
The Gimli incident was real; it is well described in the excellent book
"Emergency! Crises in the Cockpit", probably available from your
local aiport shop, or Sporty's catalog, etc.
--
Lee McGee lmc...@corp.sgi.com | IAC #21900
(415)390-2403 FAX (415)961-9584 _____________/_|_\_______________
BELLANCA _\_|___|_/_
"Somebody said they saw me, 7ECA \[#o#]/
Swinging the world by the tail; CITABRIA e/ ~+~ \e
Bouncing over a white cloud,
Killing the blues." - Roly Salley
Crone
> speed. Now there is also aspect ratio, or the ratio between the chord and the
> span, or span and area. They work out to be the same. if an aircraft as an
> aspect ratio of say 10 to 1 then it will fly forward 10 feet for every 1 foot
> it drops. So, if a 757 as an aspect ratio of 5 to 1 and its is 6 miles high,
> or about 35,000 feet, it could theoretically glide 30 miles if flown
> properly. The even that the TV show was based on did occure. The captain of
Please ignore this section. This junior aero engineer obviously has no
clue what he's talking about.
Stephen Morris
>one
>ratio at a best glide speed of a *fast* 220 knots (estimated best L/D
>speed). Don't get slower than that -- that would not be the best
>glide speed, and the aircraft will sink rapidly, even if not stalled. :^(
>Best glide speed is best glide speed and the pilot has to adhere to it for
>best glide performance. Maybe an air carrier pilot listening in to this
>thread
>can provide some actual numbers?
>
>So from 35,000 feet, this hypothetical 767 might glide 106 miles at 16/1.
This thread has generated quite a response, though some of it has
been wildly inaccurate. The short quote above is, however , pretty
close to the right answer. The actual glide performance will vary
according to weight, speed, wind and ISA deviation. We descend from
cruise with both at idle at 290 kts and reckon on travelling
roughly 3 1/2 N miles per 1000 ft. So from 35000ft I would expect
to travel around about 120 N miles. I am deliberately being a
little vague as the actual performace does vary quite considerably
and of course the computer does most of the hard work so the actual
figures are slightly irrelevant, but these generally seem to be
correct.
I seriously doubt that the gliding experience of the pilot in
question would have had any bearing on the successful outcome of
the incident. The massive speed and trim changes and configuration
channges in the last couple of thousand feet are quite unlike
anything that you meet in a glider. I've done a little gliding and
I've tried an engine out approach in a 767 simulator and it didn't
help me much. I guess he was one of those talented guys we meet
from time to time, who also had a lot of luck with him on the day.
Steve Morris Cheshire UK
Sean Cooke
> A 767 can probably glide at a 16 to
>>one
>>ratio at a best glide speed of a *fast* 220 knots (estimated best L/D
>>speed). Don't get slower than that -- that would not be the best
> roughly 3 1/2 N miles per 1000 ft. So from 35000ft I would expect
> to travel around about 120 N miles. I am deliberately being a
> anything that you meet in a glider. I've done a little gliding and
> I've tried an engine out approach in a 767 simulator and it didn't
> help me much. I guess he was one of those talented guys we meet
> from time to time, who also had a lot of luck with him on the day.
>
Ok so slipping a 767 is something you do all the time??? Give him a break.
later
Sean Cooke