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Is It Possible?

Thu Sep 21, 2000 2:42 am

Excuse me for my bad English but I'd like to know if modern airliners can theorically fly capsized.
Thank you 4 your replies
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RE: Is It Possible?

Thu Sep 21, 2000 6:40 am

If you mean 'upside down' in the air, yes it is very possible from an aerodynamic point of view.

Mechanically, however, the engines would have to be modified to allow this to happen for more than a few seconds.

The engine lubricating oil system would need to be modified to scavenge the oil from more than the bottom of the bearing cavity.

A wing doesn't care which way is 'up'; as long as the airflow is uninterrupted, the wing will produce lift and hold the aircraft in the sky.

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RE: Is It Possible?

Thu Sep 21, 2000 7:14 am

The only wing which doesn't care which way is up is a symetrical airfoil. Something an airliner doesn't have.

It is not possible for an airliner to be intentionally flown inverted and maintain altitude.
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RE: Is It Possible?

Thu Sep 21, 2000 12:44 pm

I believe an inverted typical airfoil can maintain this upside down condition with great power--for a while. Many aerobatical aircraft can maintain this condition for longer periods of time.

An airfoil that is identical on top as the bottom requires elevator action to point the aircraft in a direction for lifting it above its present altitude.

An airfoil that provides for greater relative wind on top than on bottom will rise with enough speed (from power). This type cannot fly inverted without great input from the tail and engines, and is doubtful if most of this type can maintain inverted flight.

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RE: Is It Possible?

Thu Sep 21, 2000 4:29 pm

There is a very nice picture from the Boeing model 80 (707 prototype) that shows the Seatle area from a window and if you look close you'll notice the engine is hanging from the wing "up". Tex Johnson (Boeing Test Pilot) executed a barrel roll while demonstrating the aircraft over Lake Washington.
A United crew was fired for doing the same maneuver in a 727.
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RE: Airgypsy

Fri Sep 22, 2000 2:10 am

Yes, this was a fun event. The late Tex Johnston also got to fly inside that plane recently on its final journey. It was powered by turbofans instead of its original turbojets. But the Discovery Channel missed this and spoke of its turbojets. This plane had been modified so many times by its final flight it is amazing that it even looked similar.

I admire Tex of the past, and kinda wish he didn't recently die.


Ps-that 367-80 did not maintain lever flight inverted. But I think you know that.
Topic Author
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RE: Is It Possible?

Fri Sep 22, 2000 2:18 am

Thank you very much for you're replies.
As usual you're really kind and informed.
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RE: Is It Possible?

Tue Oct 03, 2000 10:27 am

I have re-evaluated my response. I don't think a standard airfoil can maintain level inverted flight.

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RE: Is It Possible?

Wed Oct 04, 2000 2:27 pm

HEHE  , I love hearing some of the old Tex Johnson stories.

As this story goes, the then head of Boeing (can't remember his name) was entertaining the Pan Am heavies on a barge on the lake. After almost choking at the sight of his prototype doing a barrel-roll he asked a near-by person if he could have one of their heart tablets (he actually had no diagnosed heart problems).

At the debrief, he called Tex in and asked what the hell he thought he was doing. Tex replied something like "its OK, I have found that if you pull the stick back as you enter the roll the aircraft maintains 1 possitive G, and thinks it is still flying the right way up".

After a moments silence and thinking about the reply, the Boeing head realised that Tex had been doing this regularly in the skies around Boeing field to perfect the manouvre and sacked him on the spot. No fear for Tex, as I believe Boeing sacked him a number of times during his carrier for being too much of a "cowboy", but never actually went through with the dismissal. Who else would be mad enough to fly an untested aircraft?

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RE: Is It Possible?

Mon Oct 09, 2000 10:45 am

An airfoil does not have to be symmetric to fly inverted.
The symmetric airfoils seen on aerobatic types are of course, more efficient inverted, but some asymmetric airfoils can do it. The other consideration is whether or not the powerplant can keep running upside down. Aircraft other than aerobatic types are intended to remain upright (other than turning), so their engines are built to remain upright too. The engines on 20 series Learjets will run upside down, and there are probably other exceptions.
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A 727 Flew Upside Down?

Mon Dec 18, 2000 8:14 am

Can someone tell the story of the United crew that flew a 727 upside down?? Were there pax onboard? Was it just briefly like a roll or actually flown upside down?
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