Inverted flight : Principle
 

Hello to all my fellow aviators!
Can anybody please explain the principle behind inverted flight or what forces of flight are involved in inverted flying? Heard this question is asked frequently in Airline interviews.

al you need is some down elevator. more on flat bottom wings and if you have an Extra very little. Blows away the theory of lift on flat bottom wings.

Not sure if I'd like to fly for with an airline that is interested in inverted flight.

I'm pretty sure the physics are the same as for normal flight though! The air doesn't care if you're upside down.

Give an upside down wing enough angle of attack and or speed and it will create enough lift for level flight. The more the wing was designed for efficient upright flight, the more inefficient it'll be when inverted. Something with a symmetrical wing will be somewhat inefficient both upright and inverted, but chuck a big enough engine on the front and you can drag it through the sky making it do what you want. It's always a compromise. Just remember when inverted that some design features that are designed to reduce adverse yaw when upright will contribute to it when inverted. A Pitts needs a lot more rudder to balance an inverted turn than it does to balance an upright turn.

If this was asked in an airline interview, i certainly wouldn't be answering it but asking why on earth they would ask such a question.

I've had a little acrobatics experience on a CAP-10C and the manouvre that I most like is the inverted flight.

on that aircraft, you need to push decisely the stick forward to create a positive AoA when you're flying inverted.

and you feel the full weight on your shoulders pushing you to the Earth !

awesome experience !

It's probably asked in an airline interview to see if you have any understanding of aerodynamics. Someone who doesn't understand inverted flight probably doesn't fully appreciate the importance of angle of attack and g loading. If I were conducting an interview I'd be interested to know whether the applicant could tell me under what conditions you could be flying at 5 knots IAS and NOT have a stalled wing. It's all related, and all shows whether someone understands the stuff or just memorised some answers for an exam once upon a time. Given the topical nature of stalling in airliners at the moment, I'd like to know that the pilots I was hiring had an understanding of what the wings are doing.

AerocatS2A,

very good point of view ! :ok:

I taught a lot of aerobatics in the past. Enjoyed showing how to fly and recover from any situation by flying outside the envelope of normal airline flying. My first airline we even flew a B737 sim inverted over LAX just because it was fun. Not sure how the fuel would be picked up in a real 737 but the sim did just fine. My model airplane had a tube with a weight on the end of the fuel line to keep fuel flow while inverted. I kind of think Boeing didn't think that was necessary. The famous 707 roll at SEA when the test pilot showed what it could do was not a negative G roll or slow roll, it was more like a zero G aileron roll.

Or even a positive G aileron roll?

I learned them in a Chipmunk, and I'm sure it was positive all the way round. But maybe I just did them badly.

True about being at 5 knots and not stalled. The hammerhead stall is a full power vertical climb to just enough speed to get the rudder to pivot the aircraft and opposite aileron to keep from banking as it goes into a vertical dive. Very easy to do as you still have enough rudder control. Just don't wait too long. Tail slides can get quite sporty even though I will see them this week at the Reno Air Races. The angle of attack is not a stall angle, it is almost zero aoa but they still call it a hammerhead stall.

Think Newton's third law. Think angle of attack. Don't get hung up on Bernoulli and don't do what Tex Johnson did!

http://www.aviationpics.de/airshow/707buzz3.jpg

In truth this was a co-ordinated roll but Tex was flying a 707 upside down at one point without appreciable altitude loss.

If you really want to go into this look at the Kutta condition as well.

Kutta condition - Wikipedia, the free encyclopedia

I would call it a stall turn, understanding that it is a misnomer, as that is just what they're called over here. I thought the alternate name was a hamerhead turn, not a hamerhead stall. I think hammerhead turn is a good descriptive name for the manoeuvre.

Positive g aileron roll or an aileron roll performed badly? It all depends on what you are trying to achieve and who your audience is. I think I've done something like 4000 loops, all in the first few years of my career. The vast majority of them were probably quite egg shaped. Why? Because my audience was the passenger sitting in the front seat, not a judge sitting on the ground, and my goal was to make my manoeuvres smooth, positive, and enjoyable. An aileron roll with a touch of positive g is a good thing when your audience is the person sitting in the passenger seat, it doesn't matter that it won't get you points in an aerobatics competition.

I agree, the typical aileron roll you pull up about 30 degrees, neutralize elevator and roll ending back in level flight. Bob Hoover did his famous pouring a glass of water while rolling his Shrike so slight positive G's would be required to not mess up his tie. Bob used to come out to Flabob in Riverside, Ca. and see Art Scholl regularlly when I was teaching aerobatics for Art's school of Aerobatics. He would always land on one wheel as he always did at Reno at the races.

I will see Bob and Chuck Yeager this week at Reno. I flew Art's clipped wing cub to airshows for him and learned how to do aerobatics from a book, Roll around a Point. Art figured out I was teaching my self all the maneuvers so went up for an hour with me and let me instruct for him. Of course he was getting his Chipmunk then so he didn't use the cub any more. Art was an interesting man. He did the inverted spin for Top Gun but unfortunately was unable to recover and was killed. Notice the last credit at the end says This movie is dedicated to the memory of Art Scholl.

Another good interview question might be how does the addition of a movie camera to an aircraft affect the A/B ratio..... and what affect might that have on spin recovery..

A good question and one that might have exercised poor Art Scholl as he attempted to recover his Pitt's special from an inverted spin!

Art Scholl - Wikipedia, the free encyclopedia

… and anyway, a wing ( or an inverted –wing) are not creating lift differently from the way a water-ski is creating the force to lift the water-skier ….. just push down sufficiently quickly a sufficiently weight of water ! ! !
Theory about higher/lower pressure under/above a wing is just a mathematical explanation of a physical phenomenom, which just states that it is necessary to change sufficiently rapidly the direction of a sufficiently heavy flow of air (or water) in order to impart a lift force to the wing/waterski or whatever other body .

Art couldn't mount the camera close in for his inverted flat spin video in the Pitts because the video was to look like an F14 so that weight that far out was untested before. No view of the propeller would make it realistic. Probably the weight and centrifical force that far out on the wing caused the crash. Art's wife Judy was at Reno this year and spoke by the way. Great lady.

are not creating lift differently from the way a water-ski is creating the force to lift the water-skier ….. just push down sufficiently quickly a sufficiently weight of water

Actually not the case. If you run a search you will find posts and articles which demonstrate that simply deflecting air molecules from the bottom of the wing doesn't account for anything like the amount of lift the wing generates.

John
I simply highlighted the fact that lift is generated by ‘deflection’ , therefore ‘Deflecting’ is the correct word, independently of how/ who /what deflects whatever fluid. In order to ‘lift’ , a wing must deflect – no deflection, no lift – everybody must agree on that !

Obviously, the section of the wing generates a deflection of the flow in a different way from the water ski – in fact , there is no flow on the upper part of the water-ski !

The wing section can ‘deflect’ the fluid also with an apparently null ‘angle of attack’ (let me not elaborate further on ‘angle-of-attack, let’s keep it simple…), and in this is helped by pressure gradients, etc , something that the water-ski cannot do – as the water-ski can only impart a deflection with its lower part.

But, again, the key-word is ‘deflection’ ; and the inverted wing section can ‘lift’ only if it can ‘deflect’ (in whatever way it obtain this ‘deflection’).

Daniel

PS: If I’ll run a search on articles , I’ll probably reference myself !