Is this aerodynamic behavior possible?
Thread Starter
Joined: Jul 2003
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From: Canada
Is this aerodynamic behavior possible?
Hi
I am wondering if the following aerodynamic behavior is possible with a Jet airliner aircraft:
The Jet airliner aircraft is flying at 2000 ft or so
Weather calm, wind calm
Aircraft is in level flight
Clean confguration
We put the engines on IDLE
Based on this scenario, is it possible for the IAS to keep increasing despite the engines being on IDLE? I mean by increasing not a few knots but to keep gaining more indicated airspeed. Is it possible with some airliners?
This a debate I am having with someone and I would like to hear professionals give their opinions about it please.
Thanks!
I am wondering if the following aerodynamic behavior is possible with a Jet airliner aircraft:
The Jet airliner aircraft is flying at 2000 ft or so
Weather calm, wind calm
Aircraft is in level flight
Clean confguration
We put the engines on IDLE
Based on this scenario, is it possible for the IAS to keep increasing despite the engines being on IDLE? I mean by increasing not a few knots but to keep gaining more indicated airspeed. Is it possible with some airliners?
This a debate I am having with someone and I would like to hear professionals give their opinions about it please.
Thanks!
Joined: Jun 2000
Posts: 1,003
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From: Geriatrica, UK
No of course not! But it's a lovley fantasy. Imagine where it might end? Supersonic with the engines at cut-off where the only way to slow down is to start them all up and open up to max contingency....
But seriously, even the heaviest of aircraft can be affected by Wave Lift in the lee of a mountain range in strong winds. I can see the possibility of a short-term wave effect in extreme conditions that would cause an apparent (real, even) increase in energy of a jet airliner. But it can work the other way too.
There was an airfiled called Crosby-on-Eden near Carlisle on the English/Scottish border where there was an RAF Maintenance Unit where they prepared Brigands (I think) for delivery to operational units during WWII.
The Brigand was a pig on two engines let alone one. They lost a lot of them just after take-off either because of real engine failure or practices coupled with a strong Easterly wind and the kind of atmospheric conditions that favoured standing wave. I refer, of course, to a strong down draught that would rob the aircraft of what little energy it had just after take-off. This can arise form an unstable atmospheric layer of 2000-4000ft sandwiched between two more stable layers. (Think of a spring analogy).
And, yes, this can be found at very low levels.
I have flown a Jet Provost in strong North Westerly winds in the lee of the Penines and gained height at constant low power settings and best gliding speed. It helps to have the lenticular cloud to visualise the up and down side of the wave and then you just fly along the up side. I've done in sailplanes too; its a lot easier.
Hope you win your bet?
But seriously, even the heaviest of aircraft can be affected by Wave Lift in the lee of a mountain range in strong winds. I can see the possibility of a short-term wave effect in extreme conditions that would cause an apparent (real, even) increase in energy of a jet airliner. But it can work the other way too.
There was an airfiled called Crosby-on-Eden near Carlisle on the English/Scottish border where there was an RAF Maintenance Unit where they prepared Brigands (I think) for delivery to operational units during WWII.
The Brigand was a pig on two engines let alone one. They lost a lot of them just after take-off either because of real engine failure or practices coupled with a strong Easterly wind and the kind of atmospheric conditions that favoured standing wave. I refer, of course, to a strong down draught that would rob the aircraft of what little energy it had just after take-off. This can arise form an unstable atmospheric layer of 2000-4000ft sandwiched between two more stable layers. (Think of a spring analogy).
And, yes, this can be found at very low levels.
I have flown a Jet Provost in strong North Westerly winds in the lee of the Penines and gained height at constant low power settings and best gliding speed. It helps to have the lenticular cloud to visualise the up and down side of the wave and then you just fly along the up side. I've done in sailplanes too; its a lot easier.
Hope you win your bet?
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Joined: Feb 2000
Aviation Qualifications: CPL
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From: UK
I'd suggest yes it's possible, but not at constant height and generally the odds are against it.
If the aircraft has a significant pitch change with power such that the aircraft tends to pitch nose-down when the throttles are closed. Thus the throttle closure would cause a dive (hopefully a gentle one) during which airspeed would increase. This you'd associate with a low thrustline, which is the case on most modern airliners, combined with a horizontal or tail-down angling of the thrustline, which I'm not qualified to comment on.
Highly unlikely, but you could couple this with Fobotsco's scenario and envisage constant height and increasing airspeed (courtesy of sustained rising air).
G
If the aircraft has a significant pitch change with power such that the aircraft tends to pitch nose-down when the throttles are closed. Thus the throttle closure would cause a dive (hopefully a gentle one) during which airspeed would increase. This you'd associate with a low thrustline, which is the case on most modern airliners, combined with a horizontal or tail-down angling of the thrustline, which I'm not qualified to comment on.
Highly unlikely, but you could couple this with Fobotsco's scenario and envisage constant height and increasing airspeed (courtesy of sustained rising air).
G
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Joined: Feb 2000
Aviation Qualifications: CPL
Posts: 14,480
Likes: 178
From: UK
Postscript.
Having noticed that you've posted this also to Questions and Tech Log, this thread is moved to Tech Log where the moderator there is invited to do as he sees fit with it. Please don't do this again, it's naughty.
Genghis
Flight Test Forum Moderator.
Having noticed that you've posted this also to Questions and Tech Log, this thread is moved to Tech Log where the moderator there is invited to do as he sees fit with it. Please don't do this again, it's naughty.
Genghis
Flight Test Forum Moderator.
