Flying Inverted in 737

[paulyg123 135]

I did not see this discussed before.  But I just saw the movie Flight and I know the 1st thing we all did was to try to flip a jet over and fly inverted. I know that was a MD80, but is the PMDG 737 flight model accurate in an inverted state?  I am not sure what goes into a flight model, but do the equations fall apart in inverted flight?

 

My test flight on the 737NGX and the LD767 showed very contorlled flight in the inverted position.  The 737 seemed to require more forward yoke to keep the plane level (than the 767) and I was even able to gain altitude in the inverted position.  I amnot sure this would be possible possible in a real commercial plane.

 

 

[tf51d 284]

I don't think you are going to get  many pilot volunteers to pull a stunt like that today, but Tex Johnson did prove that limited aerobatics is technologically possible when he barrel rolled a 707 on one of it's test flights.

[vc10man 732]

And he(Tex) was lucky that as Boeing were looking to make a big sale on it with the watching would-be launch customers, he got away with that one.

[kevinh 409]

Tex Johnson's barrel roll was positive g the whole time.  True inverted flight is a different matter as that involves negative g.  The crew of Alaska flight 261 tried flying inverted in an attempt to pull out of a dive with the stabiliser jammed full nose down.  A desperate move that might well have overstressed the wings.  But it didn't work for them as the the aircraft never pulled out of the dive.

 

I did not see this discussed before.  But I just saw the movie Flight and I know the 1st thing we all did was to try to flip a jet over and fly inverted. I know that was a MD80, but is the PMDG 737 flight model accurate in an inverted state?  I am not sure what goes into a flight model, but do the equations fall apart in inverted flight?

 

My test flight on the 737NGX and the LD767 showed very contorlled flight in the inverted position.  The 737 seemed to require more forward yoke to keep the plane level (than the 767) and I was even able to gain altitude in the inverted position.  I amnot sure this would be possible possible in a real commercial plane.

 

FSX allows negative angle of attack and so negative lift.  Therefore inverted flight in FSX is possible. There's no reason why the equations of motions would fall apart if the sim is inverted, and as you managed it clearly this doesn't happen. Whether the PMDG model is "accurate" inverted who can say. The CL v alpha curve is fairly linear and if PMDG simply extrapolated it in a straight line for negative alpha then it wouldn't be far wrong in terms of body angle for level flight.

[Dumont 9]

Well, this has already been done with a 737-300, with nearly empty tanks and 98 passengers.
The maneuver was executed on Goiania (SBGO), was the last resource, to subdue a hijacker.
At the time it was executed a tunneau followed tailspin.
At the time the aircraft was the prefix PP-SNT (VASP), the last time I researched, the same aircraft used the prefix N698SW.
Try to perform the maneuver with little fuel(1000 KG max), use the 737-600 or 700 with the 737-700 is easier.

João Alfredo

[flyerguy7773 6]

I don't see why it is not possible... I mean yes the wings could get way overstressed, and the negative g's installe aren't fun at all but it isn't unheard of or impossible. They do it in fighter jets and acrobatics aircraft, why not in a 737?? At the core all aircraft are the same and rely on the same principals whether they are 15' long or 250' feet long.

 

 

Remy Mermelstein

777-300 FS Pilot

[Rations 102]

They do it in fighter jets and acrobatics aircraft, why not in a 737??

Probably due to the increased forces commercial aircraft wings experience (from having larger areas) and the increased weight their joints must sustain.

 

Whenever I hear inverted flight, I think of FedEx Flight 705.

[paulyg123 135]

Wel form my knowledge of aerodynamics, the wings only provide lift due tofaster flow over the top of the wing, thus if inverted there can be do lift at all.  Even with the elevator in the full down position (pointing the nose up in inverted flight) the plane should not be able to hold level flight - I was able to do so - that is why I am questoning the flight model.

 

The 707 barrel roll was only inverted for a second in the prcess of rolling, not like the movie for say 1  minute

[flyerguy7773 6]

Yes but whether the longside of the wing in on bottom or top the air is still glowing the same way ( I think I might be wrong though). Therefore the aircraft can still keep lift. How do you think acrobatic aircraft do it?

 

 

Remy Mermelstein

777-300 FS Pilot

[Airbusman330 300]

Concorde also went inverted during a testflight but fighter jets and aerobatic planes are designed for this kind of flying while commercial airliners are not. 

[VIPERGTSR01 22]

Wel form my knowledge of aerodynamics, the wings only provide lift due tofaster flow over the top of the wing, thus if inverted there can be do lift at all.  Even with the elevator in the full down position (pointing the nose up in inverted flight) the plane should not be able to hold level flight - I was able to do so - that is why I am questoning the flight model.

 

Yes but lift is also dependant on angle of attack of the wing, not just the shape of the wing. You can counter act the lift due to shape of wing by increasing angle of attack (to a point, and dependant on wing profile).

 

As for fighter jets and aerobatic planes, they often have a very neutral wing shape (or close to it) and rely on AOA to control lift, so flying inverted is super easy for them.

[KriVa 307]

Aerodynamically, there won't be a problem. You'd have to fly a nose-up attitude, but it would work. The only problem I see is with the fuel. Are the fuel pumps capable of getting fuel from the fuel tanks to the engines? I'm not sure where in the fuel tanks fuel is drawn from, but if it's only from the bottom of the tank, you'll be having a bad day.

[Fabo 213]

 

Wel form my knowledge of aerodynamics, the wings only provide lift due tofaster flow over the top of the wing, thus if inverted there can be do lift at all.  Even with the elevator in the full down position (pointing the nose up in inverted flight) the plane should not be able to hold level flight - I was able to do so - that is why I am questoning the flight model.

 

As said, lift is also dependent on aangle of attack, with negative angle of attack, air would push on the wings, effectively pushing the aircraft down relative to its normal position, i.e. up in inverted flight.

 

 

The 707 barrel roll was only inverted for a second in the prcess of rolling, not like the movie for say 1  minute

 

707 barrel roll did not go "inverted" at all, barrel rolls are low positive g maneuvers, if you were blindfolded in an aircraft you would not even know it did a barrel roll. I have done them, this is how it is.

 

 

Aerodynamically, there won't be a problem. You'd have to fly a nose-up attitude, but it would work. The only problem I see is with the fuel. Are the fuel pumps capable of getting fuel from the fuel tanks to the engines? I'm not sure where in the fuel tanks fuel is drawn from, but if it's only from the bottom of the tank, you'll be having a bad day.

 

Yep, this is the big thing. Not even all aerobats are made to work in sustained inverted flights, they either have to have a constant positive pressure pump (which is a bit problematic considering fuel feed from tank) or an "aerobatic tank" that has gravity feed in opposite direction. Some don't have these and rely on fuel in feeding lines for a couple of seconds on negative G.

[KriVa 307]

 

707 barrel roll did not go "inverted" at all, barrel rolls are low positive g maneuvers, if you were blindfolded in an aircraft you would not even know it did a barrel roll. I have done them, this is how it is.

 

Technically, it did. To go inverted just means that something goes upside down. The 707 did go inverted, but in a positive 1G maneuver. The aircraft itself didn't "feel" any difference in terms of G-forces.

[Fabo 213]

that is why I put it in quotation marks.