[Just thinking (OP)]

How can a plane fly upside down? There are many wing designs and levels of aircraft performance but my post is aimed at the very basic level. Let's start with a basic Cessna aircraft it has the typical standard airfoil square wing the rounded tapering top surface of the wing is designed to reduce the air pressure and suck the wing up while the bottom surface of the wing compressors the air and pushes the wing up. So the big question is if the wing is designed to lift the aircraft how is it possible for the plane to invert its attitude and maintain level flight. So can you answer this tricky question or do I need to explain it to you?

[Bored chemist]

You have spotted one of the great myths of science.

https://www.scientificamerican.com/article/no-one-can-explain-why-planes-stay-in-the-air/



Planes actually fly by pushing air down.

[Just thinking (OP)]

Planes actually fly by pushing air down.

I will have to think long and hard about that. Thanks for the link I found that very interesting.

[Bored chemist]

https://en.wikipedia.org/wiki/Lift_(force)#/media/File:AirfoilDeflectionLift_W3C.svg

[Just thinking (OP)]

https://en.wikipedia.org/wiki/Lift_(force)#/media/File:AirfoilDeflectionLift_W3C.svg

That is very true for initial tack off and for rapid clime but how can this work when inverted. And it can.

[vhfpmr]

https://en.wikipedia.org/wiki/Lift_(force)#/media/File:AirfoilDeflectionLift_W3C.svg

That is very true for initial tack off and for rapid clime but how can this work when inverted. And it can.

Hold your hand flat, like a wing, and stick it out of the window of a moving car (without letting people think you're signalling a turn). You can feel the air pushing your hand up or down as you adjust the angle of attack.

Look at the strange attitude of the fuselage here because the pilot has had to keep the wing angle of attack the same in space, but reversed relative to the plane, the green line shows the horizontal, but the black line is where the horizontal normally lies when the plane is flying the right way up. If the pilot had kept the fuselage nearer horizontal, as it is when not inverted, the wings would have been pushing the plane toward the ground.

Inverted.png (104.38 kB . 369x218 - viewed 8031 times)

[Just thinking (OP)]

    Quote from: Bored chemist on Yesterday at 21:20:27

        https://en.wikipedia.org/wiki/Lift_(force)#/media/File:AirfoilDeflectionLift_W3C.svg

    That is very true for initial tack off and for rapid clime but how can this work when inverted. And it can.

Hold your hand flat, like a wing, and stick it out of the window of a moving car (without letting people think you're signalling a turn). You can feel the air pushing your hand up or down as you adjust the angle of attack.

Look at the strange attitude of the fuselage here because the pilot has had to keep the wing angle of attack the same in space, but reversed relative to the plane, the green line shows the horizontal, but the black line is where the horizontal normally lies when the plane is flying the right way up. If the pilot had kept the fuselage nearer horizontal, as it is when not inverted, the wings would have been pushing the plane toward the ground.

* Inverted.png (104.38 kB . 369x218 - viewed 7 times)

Well done you have hit the nail on the head with only one little detail missing. With the plane inverted we will need to increase the power as there will be moor drag as the attack angle is increased and as a result of increased attack angle, the inverted wing is generating the low pressure to generate lift. So just as you described the hand out of the car window even a flat surface can produce lift. A flat surface is moor dependant on the positive pressure from the underside.

[Petrochemicals]

A plane is a mixture of thrust drag lift and gravity, all pivoting around the centre of gravity. They can fly upside down by the angle of attack and thrust. Part of a planes power is akin to a rocket, the thrust component. Part of it is the the angle of attack, a plane's wings ane not perpendicular to the fuselage, they do indeed plane the air. By altering the planes angle of attack that is largely influenced by the gravitational component around the centre of gravity the plane achieves upside down flight. This is demonstrated by the stunt plane.

Inverted.png (104.38 kB . 369x218 - viewed 8031 times)

The wings on a stunt plane are designed to fly in Australia and the set to the fuselage are equal, the profile of the wing chord is the same, the angle on the fuselage is 90 degrees. This allows the economic and easy stunt antics. They are not the economy that Easy jet look for though.

The thrust moves the plane forward, gravity makes the plane sink, as the thrust draws the plane from the nose the equal wing profile (chord) sinks downward, thusthe wing is not parrallell to the airflow, the wing is side on if you understand the exaggeration. The airflow then creates the lift. This is turbulence on the wing though and is inefficient and can lead to a stall and the falling from the sky (which I am assured planes do not do).

Basically on a normal wing it is a managed fall by the use of thrust.  Very very inefficient.

[alancalverd]

There's a considerable difference between inverted flight, controlled inverted flight, sustained inverted flight, and inversion at the top of a positive-g loop.

Most Cessnas will not sustain inverted flight because the engines don't work upside down for very long. Even the 152 Aerobat is not certified for sustained inversion though you can push though a fair bit of negative g.

The standard Cessna wing has a very steep and asymmetric laminar-flow aerofoil and Fowler flaps, which give you optimum lift and drag control for getting in and out of small fields but aren't at all efficient when inverted.

Aircraft designed and rated for aerobatics, such as the Extra 300, have almost symmetric aerofoils and simple flaps (if any) so they work just as well at any orientation to the ground, plus a lot more power to weight ratio, and fuel and oil systems that work upside down. Likewise most fighters.

One of the problems of Spitfires and Hurricanes was the failure of the float carburettor in a steep dive or sustained inversion. Their opposition. ME109s and the like, had direct fuel injection. I never understood why the Merlin engine, and indeed most petrol-engined cars, did not adopt this vastly superior system, which only appeared in most small planes in the 1990s

[Bored chemist]

I never understood why the Merlin engine, and indeed most petrol-engined cars, did not adopt this vastly superior system, which only appeared in most small planes in the 1990s

It is unusual for cars to be driven upside down.

I'm trying to work out how you connect the fuel pipe to the tank in a way that still works if it's upside down.
I know one of the early approaches was a flexible pipe in the tank, with a weight on the end of it, but I'd like to think there's something more sophisticated.

[alancalverd]

Various tricks. Collapsible bladder tanks are a good one, or a small buffer tank that is filled whenever fuel is available, and feeds from the centre. Or two pumps.The Extra uses an auxiliary "acro tank" with a flop tube.

That said, an aerobatic glider (e.g. Blanik L13) flies pretty well upside down without an engine.

[Just thinking (OP)]

How can a plane fly upside down? There are many wing designs and levels of aircraft performance but my post is aimed at the very basic level. Let's start with a basic Cessna aircraft it has the typical standard airfoil square wing the rounded tapering top surface of the wing is designed to reduce the air pressure and suck the wing up while the bottom surface of the wing compressors the air and pushes the wing up. So the big question is if the wing is designed to lift the aircraft how is it possible for the plane to invert its attitude and maintain level flight. So can you answer this tricky question or do I need to explain it to you?

The Cessna 172 for example weighs in at close to one tone fully loaded one and a half ton so if the wing can lift this weight when inverted one would think that now we have one and a half ton of plane and over one and a half ton of inverted wing lift giving a total of over three ton of force pulling down so the question is how can these basic aircraft maintain inverted flight even for a very short time. The wing will have to generate over one and a half ton of lift when inverted this completely contradicts the basic principle and wing design for flight. But yet it can.

[Just thinking (OP)]

I'm trying to work out how you connect the fuel pipe to the tank in a way that still works if it's upside down.
I know one of the early approaches was a flexible pipe in the tank, with a weight on the end of it, but I'd like to think there's something more sophisticated.

Maybe a type of slide valve with feed pipes top and bottom of the tank.

[Bored chemist]

so the question is how can these basic aircraft maintain inverted flight even for a very short time.

By altering the angle of attack.
See above.

[Just thinking (OP)]

By altering the angle of attack.
See above.

That is the main part angle of attack for the Cessna 172 we would need maximum forward velocity and full throttle then invert and hold with as much angle of attack as posable the increased angle will allow for greater positive pressure on the lower surface of the wing and generate a pore but just adequate negative pressure over the upper surface.

[alancalverd]

See reply #8 above.

The C172 is not certified for sustained inverted flight for several reasons. Holding full throttle won't help because even with the latest IO-360 fuel injection motor the gravity-fed fuel and oil systems won't allow the engine to develop any power at all after a few seconds. You might even set fire to the engine compartment if you push all the buttons at once and roll an old O-320 carburettor model.

Of course things may have changed since I last flew a 172, five days ago, but the NACA2412 aerofoil has been pretty constant since 1955.

An aerobatically-certified aircraft will generate almost equal lift with the wing inverted because the aerofoil is almost symmetrical. 

[Bored chemist]

I think the angle of attack makes the difference between
" flies upside down badly until the engine realises it has no fuel supply" and
"power-dives"

[Just thinking (OP)]

An aerobatically-certified aircraft will generate pretty much equal lift with the wing inverted because the aerofoil is almost symmetrical. 

That is true the purpose design of the aerobatic plane it also has a lot moor engine power wing strength and typically relies on greater positive pressure and less negative pressure across the wing. But the fact remains that the 172 can fly inverted for those silly enuff to try.

[alancalverd]

Drivel.
See reply #10.
But I haven't inverted a glider for about 50 years, so maybe the laws of aerodynamics have changed.

[Just thinking (OP)]

But I haven't inverted a glider for about 50 years, so maybe the laws of aerodynamics have changed.

The glider is reliant on thermal lift for the most part so this still remains true when inverted.