MovieChat Forums > Top Gun (1986) Discussion > Passenger Jet flying inverted

Passenger Jet flying inverted

posted 9 years ago by bubblenator
11 replies | jump to latest

OK this is a question from the movie Flight with Denzel Washington and I'm posting it on here because there are a lot more "aircraft knowledgeable" or former military on here than on the film board. So:

So basically Denzel Washington is the Captain in which he is flying a McDonnell Douglas MD-80 or similar and before crashing it flies the large passenger plane INVERTED. There was an "Act of God" and they were nose diving very quickly, he says retract the flaps, retract the gears and trim us nose down then rolls the plane 180 degrees thus then flying inverted. It does say they are losing oil pressure and the engines are burning up however something is troubling me...

Now this may be aerodynamically possible however I would have thought that these types of passenger planes don't have "inverted fuel tanks" and rely on gravity to get the fuel and oil to the engines and hydraulics compared to Fighter Jet fuel tanks?

So maybe after a couple of minutes of no fuel getting to the engines they would have stalled and he wouldn't have had the power to roll it back over and glide into an open field?

Thanks.

If you are not willing to give up everything, you have already lost

[–] CGSailor 9 years ago

The MD-88 uses fuel pumps to feed their engines, however the fuel pickup tubes are in the bottom of the tanks. Any prolonged inverted flight would starve and shutdown the engines as soon as the fuel lines themselves are emptied. Several Airliner type planes have been barrel rolled inverted, but not remained IN inverted flight.

During a barrel roll, there is not enough time to fully starve the fuel lines, and there is a bit of centrifugal force allowing the fuel to continuously feed.

Planes specifically designed to fly inverted( Like military jets and aerobatic planes) have several ways around this problem.

One is a flexible fuel pickup tube with an attached weight. as the plane inverts, the weight causes the flexible tube (Called a Flop Tube) to move with gravity so now it is feeding from the top of the tank (which is now "down")

Another is to have a special fuel sump tank that fuel is drained into from the main tanks which is then connected to the suction side of the fuel pump system. When the plane inverts, this tank is situated above the engine. A Check valve prevents fuel from gravity draining back into the main tanks.

Flop tubes are more common on Prop Aircraft.
Military Jets use the Sump method with several internal Feed tanks for the engines which are kept pressurized. Even so.. most military Jet do not fly inverted for any lengthy period of time. Most Airshow maneuvers where they are flying inverted only last a few seconds at most. (it just seems longer). The F-15 Eagle for example is limited to about 30 seconds of inverted (or negative G flight).

During non-Airshow maneuvers... i.e. Aerial Combat... Most inverted attitudes are still under positive G forces.

What you see in the movie Flight is pure Hollywood Bovine Excrement.

I joined the Navy to see the world, only to discover the world is 2/3 water!

[–] bubblenator 9 years ago

Thank you CG Sailor for your detailed answer!

Military Jets use the Sump method with several internal Feed tanks for the engines which are kept pressurized.

When I was trying to search about it I did come across the this thing you call a Flop Tube which has "flexible fuel pickup tube with an attached weight". I haven't heard the "Sump method" which seems the same as the Motor Oil sitting in a tank at the bottom of your car.

Even so.. most military Jet do not fly inverted for any lengthy period of time. Most Airshow maneuvers where they are flying inverted only last a few seconds at most. (it just seems longer). The F-15 Eagle for example is limited to about 30 seconds of inverted (or negative G flight).

I'm really surprised that an air-to-air superiority military aircraft like the F-15 can only fly Inverted for 30 seconds. I guess the only reason if you're going to be flying MORE than 30 seconds Inverted would be Evasive Maneuvers in a dogfight and/or evading missile(s) fired at them. Correct me if I'm incorrect.

However since 1991 Gulf War US Fighter Jets have flown with impunity patrolling No-fly Zones such as Operation Northern and Southern Watch, Operation Deny Flight and more recently Operation Odyssey Dawn. These were all obviously done after hundreds of SEAD bombings from Cruise missiles and Stealth Bombers giving Fighter and Attack jets/helos to fly and patrol without the fear of being shot down.

So ultimately there would be no reason for any of these Fighters Jets to fly Inverted in these Operations!

So does this apply to all the other teen-series? F-14s, F-16s, F/A-18s just out of interest and what about the new fifth generation F-22s and F-35s, are they too limited to 30 seconds or less of Inverted flying? If you're not sure I might have to check with other former military pilots/aircraft mechanics on F-16.net.

Thanks.

If you are not willing to give up everything, you have already lost

[–] CGSailor 9 years ago

I'm really surprised that an air-to-air superiority military aircraft like the F-15 can only fly Inverted for 30 seconds. I guess the only reason if you're going to be flying MORE than 30 seconds Inverted would be Evasive Maneuvers in a dogfight and/or evading missile(s) fired at them. Correct me if I'm incorrect.

You're incorrect.
When a fighter is dogfighting or performing an evasive maneuver, it is almost always under POSITIVE G LOADS. Not negative G loads.

When you are flying along straight and level, fat dumb and happy like a private pkane or Comair... you are experiencing just 1g. The force of gravity.

When a fighter plane starts banking and turning hard it is exerting greater forces on the aircraft, and the pilot inside, and these are measured as multiples of g. many modern fighters pull up to 9g's of force.

These forces are either positive or negative.

Usually the loads are positive, but if the pilot was to shove the stick forward and to rapidly drop the nose into a dive, the loads are negative. things loose in the cockpit will float at 0g and fly up to the canopy if greater than negative g. -1g or -2g for example.

When a plane is flying straight and level, but inverted upside down, it is experiencing -1g.

When you talk as you did in the quote above, about flying inverted for more than 30 seconds while dogfighting... the plane is not flying with negative g's. No pilot is going to hang out upside down flying and maneuvering by pushing his nose into negative g's... he is going to ROLL his aircraft and pull positive g's.

Even if a plane is inverted, positive g's means that things in the plane feel as though it is rightside up and not inverted.

Let me walk you through a simple maneuver.
The "Split S"

When you are flying straight and level and pull back on the stick, the nose climbs and you feel crushed heavier into your seat as positive g's climb higher than 1.

If you push forward on the stick, the nose drops and you feel lighter, then float, then your body wants to lift OUT of the seat and you are restrained by your harness. this happens as you go from +1g to 0g to -1g and greater.

Now for the split s.
You are flying straight and level. Suddenly there is a threat ahead and you want to reverse course and go back the other way and at the same time you want to drop altitude and get low and fast to get away and hide.

You do NOT bank the aircraft and execute a banking 180° turn and drop the nose into a descent.
No... You rapidly roll the plane inverted, then pull the stick back into your lap hard. The nose pulls up hard... but since you're upside down, "up" is towards the ground. you are still pulling hard positive g's. You are still being shoved hard down into your seat, not hanging from your harness. You fuel and oil is still being affected as though you are rightside up. Even though the plane is upside down. You then perform a half loop. starting upside down at the top, pulling your nose down and through the half loop, ending at the bottom, straight and level... rightside up and at a much lower altitude... with much greater speed picked up in the dive and heading 180° opposite of your heading before the maneuver.

A plane cannot take as many negative g's as it can positive g's. While it may be rated to take 9g's, a plane can only take 3-4 negative g's. Negative g's are also much harder on a pilot and while there are tools and methods to combat positive G-Loc... where the blood rushes from your brain to your lower extremities under high positive g. Very little can be done for it's opposite number... the RED-OUT Where too much blood rushes to your head.
Squeezing yout thigh muscles... Performing the diaphram "hic" breathing... and the g suit, can all work to squeeze blood from you legs and lower abdomen back to your head and upper body. Little can be done against blood rushing too your head.

Again... no fighter jet is going to spend any significant amout of time inverted in a negative g regimine. 30 seconds is forever for a fighter to be flying in negative g.

I joined the Navy to see the world, only to discover the world is 2/3 water!

[–] IronHorseColonel 9 years ago

Technical facts aside, like Sailor mentioned, the key element is the 'act of god' piece. Whether or not god has anything to do with it is neither here nor there. Unbelievable things happen. Look at the plane crash in Taipei. While its not inverted, you come away after watching it like there is no way that just happened. The Taipei Crash for me is even more unbelievable then 'Flight'. Actually I find it more remarkable than the Hudson Crash. What it all means is that some things that end up happening exceed reality, at least the reality of the spec sheets. The manufacturer says I can't do this with a system, but that doesn't stop it from happening. Does that mean what happened in the movie can happen? No it doesn't. But there is no known test program for commercial aircraft that could prove it couldn't happen.

[–] bubblenator 9 years ago

The Taipei Crash for me is even more unbelievable then 'Flight'. Actually I find it more remarkable than the Hudson Crash.

Well the Hudson crash shows that if you are a good enough pilot and in a certain type of passenger jet (I'd like to see an Airbus A380 try a water landing) water landings are possible without crashing and keeping it wings level so one doesn't dig into the water and break up the fuselage.

We'll all see how Hollywood makes of it when Clint Eastwood movie Sully comes out next year. I'm no expert but I read that Sully did an unpowered ditching at about 150 mph:240 km/h and I'm guessing that he flared the nose a tad just before impact.

Back to Inverted flying does 30 seconds of continuous barrel rolls effect fuel uptake in jets? I could POSSIBLY see that happening.

If you are not willing to give up everything, you have already lost

[–] CGSailor 9 years ago

Back to Inverted flying does 30 seconds of continuous barrel rolls effect fuel uptake in jets? I could POSSIBLY see that happening.

SMH... It is like I am talking to brick wall.

When I was talking of a limitation of inverted flight... we are talking about flying along straight and level while upside down. Or to be more accurate... Flight in ANY attitude while under NEGATIVE G's

When you evinced incredulity at a Fighter jet designed to dogfight not being able to hand more than 30 seconds inverted... I TRIED to explain to you the difference between positive and negative G's, and while a Dogfighting fighter may be in some inverted attitude repeatedly... it does so under positive G's and thus behaves as though rightside up and NOT upside down.

You still do not seem to grasp it.

Here is a Video of legendary Airman, Bob Hoover, barrel rolling a plane through being inverted while maintaining a perfect 1 positive G the entire time. By holding a perfect 1G positive roll, even though he was inverted, everything still flowed just as though he was flying right side up straight and level.
This would include fuel in the tanks as well as the Iced tea in the pitcher and Glass.

https://youtu.be/pMWxuKcD6vE

I joined the Navy to see the world, only to discover the world is 2/3 water!

[–] bubblenator 9 years ago

You still do not seem to grasp it.

Thanks for the video it helped explain the difference between Positive and Negative G Forces which I promise I tried to search the difference between the two Forces before trying to grasp it. So if I'm correct if you are flying INVERTED then push down on the yoke to perform a loop-the-loop first of all you will be pulling Positive Gs to begin with...

Then to make it even more confusing for a layman on G Forces is NASA's use of the C-131 Samaritan then the KC-135 Stratotankers which as you know are for training Astronauts. Then they are required to fly the the plane in parabolas (58,000 times in its lifespan) to create a short time burst of zero Gravity or at least "Reduced gravity".

So as parabolas are the are going to have aircraft always flat and never INVERTED as it's simply going up down nose first and then nose up on the rise so it SEEMS that the Pilots of these would experience both Positive and Negatives G Forces in these training missions?

If you are not willing to give up everything, you have already lost

[–] CGSailor 9 years ago

So if I'm correct if you are flying INVERTED then push down on the yoke to perform a loop-the-loop first of all you will be pulling Positive Gs to begin with...

A G force felt from a source other than gravity is because of a change in your vector, either in it's direction, or in it's speed because of an acceleration/deceleration.

When you are flying straight and level, you experience 1 positive G because gravity is still pulling you down at 1G Same as you sitting in a car. Whether that car is stopped, or going down the highway at 70 mph, you are still feeling 1G of gravity pulling you down.

If your plane was flying along straight and level but upside down, you would be feeling the same force of gravity, but it would be Negative 1G because it you are upside down and the force is trying to pull you "up" relative to the inverted plane.

Forces acting on the plane other than from gravity is still measured in G's

Such as the force when the plane turns sharply, YOu have discussed before planes and pilots handling up to 9G's of force in turns. These G's are either positive or negative depending on which way they are affecting the plane.

If the force is pressing the pilot down into his seat, they are positive G's acting in the same direction gravity does in an upright plane.

If the Force is causing the pilot to lift out of his seat and being held against his harness... then they are negative G's and acting as though the plane is upside down.

Whether there plane is or is not upside down is immaterial.

When a right side up plane suddenly has the stick shoved forward and the nose suddenly drops into a dive... those are negative G's even though the plane is not inverted.

When a plane is inverted, but the stick pulled back raising the nose suddenly (though also towards the ground into a dive because it being upside down...t hat is POSITIVE G's because the pilot is pressed into his seat and feels as though he is rightside up.

These G forces acting upon a plane regardless of actual plane orientation is why Vertigo in low visibility and night time conditions is so deadly and a pilot MUST rely upon instrumentation. Just like when that video shows Tea being poured smoothly from a pitcher into a glass even though the plane was barrel rolling... A plane could end up in a smooth, 1G turning descent... a spiral.... and the pilot still feel as though he is not turning or descending, but flying straight and level when he is not.

So back to dogfighting and being inverted and limited to 30 seconds of inverted flight...

When I say limited to 30 seconds of inverted flight, think 30 seconds of negative G's... not actual orientation upside down.

When I fighter plane needs to dive suddenly... he does not push the nose down hard (and get a sudden onset of Negative G's)...

He rolls the plane upside down then pulls back pulling the nose UP sharply (up being upside down though means the nose points towards the ground) and takes a sudden unset of POSITIVE G's
a

when a Fighter has to do a break turn suddenly... He does not use the rudder alone and try to skid the plane flatly through a turn...

No... He banks the plane into the direction of the turn then PULLS the nose up through the turn, taking positive G's.
He does not bank the plane opposite the turn then push the nose down through the turn with negative G's

A Fighter plane in a dogfight and maneuvering is almost always under some form of POSITIVE G's no matter how they are yanking and banking. When the fighter maneuvers, he rolls the plane so that relative UP for the plane is the direction he wants to go then pulls the nose through under positive G's.

They do experience negative and zero G's from time to time as well... but 30 seconds is a long LOOOOOOONNNNNGGGG time in a dogfight. a 30 second limitation is far greater than anything the plane will ever actually be experiencing. Unless deliberate.

Sometimes you will hear a pilot in combat talking about unloading and extending, usually in trying to get away from or get clear of a fight. either to escape, or to get clear and reengage from further out.
Unloading the plane means pushing the nose down just enough to bring the plane to near zero G... Following a similar parabolic path as the Astronauts vomit comet. In this condition there is no wingloading on the plane.. the plane's wings are not supporting the plane's weight against gravity and the plane is following a ballistic arc.
This means that ALL of the engine's output is being used to go faster at the greatest acceleration the plane can muster. Everytime the plane maneuvers, and the plane is "loaded" with G's... speed is bled off and lost to the maneuver. By unloading... no speed is lost in fighting a turn.

I joined the Navy to see the world, only to discover the world is 2/3 water!

[–] 9 years ago

[deleted]

[–] bubblenator 9 years ago

Thanks for the info, I do now know the difference but hey who wouldn't pay to see an Airbus A380 flying inverted!

If you are not willing to give up everything, you have already lost

[–] nutmustardxx 8 years ago

Alaska airlines had a flight that crashed years ago..a md80...it flew upside down for a while pilots were making live reports as they watched it...the Jackscrew in the tail section haD worn off so they has no control over the planes pitch