Have you flown upside down? Answer this!

[katdude]

So, perhaps many of you folks here have flown upside down in an airplane like the T-6. We all know that the shape of a wing is what causes lift due to air on top of the wing moving faster than below the wing, which creates a pressure differential. Low pressure over the wing, high presure below the wing, inturn produces lift which balances weight. Thrust forward balances Drag backward.

Now, when you fly inverted and level at the same altitude- the lift should be pointing toward the earth because the same shape of the wing is upside down. This adds to the weight. So what force is balancing upward the (weight + downward lift) that's pointing down?

[black hills tj]

8 minutes ago, katdude said:

So, perhaps many of you folks here have flown upside down in an airplane like the T-6. We all know that the shape of a wing is what causes lift due to air on top of the wing moving faster than below the wing, which creates a pressure differential. Low pressure over the wing, high presure below the wing, inturn produces lift which balances weight. Thrust forward balances Drag backward.

Now, when you fly inverted and level at the same altitude- the lift should be pointing toward the earth because the same shape of the wing is upside down. This adds to the weight. So what force is balancing upward the (weight + downward lift) that's pointing down?

Not all airframes have an asymmetric wing 😉

However, in order to maintain inverted, level flight an aircraft with the common airfoil design would need to use a flight control surface such as horizontal stabs to compensate for lift direction.

[katdude]

So the recent Seattle stolen plane crash involving Bombardier Dash 8 Q400 had inverted flight for some time. It has a symmetrical wing? Or he used the horizontal stabs to compensate? Perhaps a Cessna 172 can fly inverted too.. not gonna try it myself though lol

[black hills tj]

22 minutes ago, katdude said:

So the recent Seattle stolen plane crash involving Bombardier Dash 8 Q400 had inverted flight for some time. It has a symmetrical wing? Or he used the horizontal stabs to compensate? Perhaps a Cessna 172 can fly inverted too.. not gonna try it myself though lol

Many airframes are limited in inverted flight only by the oil and fuel systems properly feeding the engine.

[BashiChuni]

op is a known troll. stop feeding him and kick him back to sit under his bridge

[pawnman]

8 hours ago, katdude said:

So, perhaps many of you folks here have flown upside down in an airplane like the T-6. We all know that the shape of a wing is what causes lift due to air on top of the wing moving faster than below the wing, which creates a pressure differential. Low pressure over the wing, high presure below the wing, inturn produces lift which balances weight. Thrust forward balances Drag backward.

Now, when you fly inverted and level at the same altitude- the lift should be pointing toward the earth because the same shape of the wing is upside down. This adds to the weight. So what force is balancing upward the (weight + downward lift) that's pointing down?

Between this and your energy question, I think you need to spend some time on Wikipedia before you bring us your next great revelation.

[katdude]

1 hour ago, pawnman said:

Between this and your energy question, I think you need to spend some time on Wikipedia before you bring us your next great revelation.

This Q and A forum is for all questions, including ones that some people find stupid because they know the answer. There is no answer to this question on Wikipedia. I found some learning value in the answer @black hills tj gave, and I appreciate it. Other people lurking silently around may find it useful too.

These great revelations or “Aha..” moments are how all students learn and I haven’t even been to UPT yet. I believe that’s how IPs enjoy teaching their students, and guessing from how you reacted I can tell you have never been an IP.

[pawnman]

3 hours ago, katdude said:

This Q and A forum is for all questions, including ones that some people find stupid because they know the answer. There is no answer to this question on Wikipedia. I found some learning value in the answer @black hills tj gave, and I appreciate it. Other people lurking silently around may find it useful too.

These great revelations or “Aha..” moments are how all students learn and I haven’t even been to UPT yet. I believe that’s how IPs enjoy teaching their students, and guessing from how you reacted I can tell you have never been an IP.

Nope, but I've been an instructor weapon systems officer for almost ten years. My answer to the students would be the same as my answer to you... Read some on your own, and if you still don't understand, then come ask. If you ask me something dumb, like "why can't we drop bombs upside down?", I'm going to tell them to go do some of their own research first.

If this is the level of academic rigor that now gets people into UPT, I weep for the future of the Air Force.

[jazzdude]

Eh, I'll throw you a bone.

 

The shape of the airfoil, camber, is only one factor in lift. Trying to explain lift only with Bernoulli's equation is overly simplistic.

 

A high lift wing is going to have that text book curved top, flat bottom, since it is designed to be efficient while flying upright. As others have mentioned, aerobatic wings tend to be symmetrical. So how do they generate lift with a symmetric wing? Angle of attack.

 

A high lift wing could fly inverted, but it won't be very efficient, requiring a greater angle of attack than if it were upright. Maybe this inverted angle of attack required exceeds the critical AOA, resulting in stall and a plane that cannot maintain level inverted, or maybe not. The T6A at ~220 knots level has a pitch roughly at 0° to maintain level. Inverted level is roughly 15° nose up, which is held there with forward stick pressure. Also, more AOA means more induced drag, requiring more thrust to maintain level flight. Don't think of the horizontal stab as providing lift for inverted flight though, think of it as a mechanism to set your AOA regardless of whether you are upright or inverted.

 

For a symmetric wing, the level AOA upright vs inverted would be very similar. Lift is almost solely based on AOA in these wings.

 

There's your 2 cent overview of inverted flight. Aerodynamics for Naval Aviators is a good read if you want to nerd out on aerodynamics, or you can just push the "I believe" button.

 

Now for some homework...

 

1) how do some airplanes fly knife edge (90° bank) and still maintain level flight?

 

2) is flying level inverted the same as passing through inverted in a loop or barrel roll? Or is there another force to consider?

 

 

 

[katdude]

@jazzdude Thank you so much! Considering AoA makes perfect sense to me and I push the “I believe” button!

Answers to 

1.  For flying knife edge the whole plane fuselage has to act as the airfoil and the nose be up slightly so there is a positive AoA that is maintained by the rudders.

2. Level inverted is not the same as inverted in a loop or barrel roll. Centrifugal forces have to be considered in this case.

Correct me if I am wrong, but now I see how it works 🙂

[jazzdude]

#1 is right on, for #2 I'd say it's inertia. It's why if you get enough smash that you can pitch up and do a bunch of aileron rolls in a row while flying more or less an arcing path. Centrifugal force is applicable to the oil/fuel systems, so as long as there's positive g, they should work fine.

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