How is it possible to fly inverted???

[UnAnswerd]

I've heard of circumstances in which an aerobatic airplane can actually fly inverted. I would like to know how this is possible. It seems that if you flipped an airfoil upside down and moved it through the air, you'd still get the area of low pressure, only it would now be on the bottom and would actually be pulling the aircraft downward. One guess is that while inverted, they fly at a high angle of attack, and take advantage of "impact lift". However, we all know this type of lift is relatively inefficient, and results in a substantial amount of induced drag. In short, I wouldn't think you could hold a plane up with impact-lift alone. Any information would be appreciated.

 

[jergar999]

Oversimplified answer:

Most aerobatic aircraft have what are called semi-symmetrical airfoils where lift is developed primarily from angle of attack.

 

[banned username 2]

Oversimplified answer:

Most aerobatic aircraft have what are called semi-symmetrical airfoils where lift is developed primarily from angle of attack.

Actually most aerobatic aircraft have a fully symetrical airfoil, they work equally well inverted as right side up...

 

[Bluto]

UnAnswered, the idea of "impact lift" is misleading. For a better idea about how lift really works check out:

http://science.howstuffworks.com/airplane8.htm

 

[mattpilot]

... but the 707 did a barrel roll and it did not have symmetrical wings.


Regardless of the shape of an airfoil (not withstanding efficiency), an aircraft should be able to fly inverted.

How does it work? When going inverted, you need to push the stick forward (point the nose upward). This will give you a positive angle of attack in regard to the relative wind. The airflow ABOVE the wing will still be faster than the airflow BELOW (*) the wing , thus still producing lift which is opposing gravity. It works the same way when in normal flight. The airfoil design, however, will not be efficient and depending on the chamber of the wing, the critical AoA will be lower in inverted flight than it is in regular flight. For a symmetrical airfoil, the critical AoA will be the same.



(*) to clarify - When saying 'above', i mean pointing towards the sky. When saying 'below', i mean the side thats pointing to the ground.

 

[Northern Lights]

I thought that it was just PFM

 

[Thedude]

... but the 707 did a barrel roll and it did not have symmetrical wings.


Regardless of the shape of an airfoil (not withstanding efficiency), an aircraft should be able to fly inverted.

How does it work? When going inverted, you need to push the stick forward (point the nose upward). This will give you a positive angle of attack in regard to the relative wind. The airflow ABOVE the wing will still be faster than the airflow BELOW (*) the wing , thus still producing lift which is opposing gravity. It works the same way when in normal flight. The airfoil design, however, will not be efficient and depending on the chamber of the wing, the critical AoA will be lower in inverted flight than it is in regular flight. For a symmetrical airfoil, the critical AoA will be the same.

.

Wow ... time to go back in the hole ...the sky must be falling. This is know as junk science. The first couple of guys had it right, most aerobatic aircraft have a semi-symetrical airfoil. I assume that be flying inverted that means sustained (more then 10 secs) and straight and level. Any aircraft can go upside down but not for very long or maintain altitude. ie the 707 "rolling through inverted".

 

[mattpilot]

Wow ... time to go back in the hole ...the sky must be falling. This is know as junk science. The first couple of guys had it right, most aerobatic aircraft have a semi-symetrical airfoil. I assume that be flying inverted that means sustained (more then 10 secs) and straight and level. Any aircraft can go upside down but not for very long or maintain altitude. ie the 707 "rolling through inverted".

really?

Question - How does an aeroplane manage to fly upside-down, if
it normally gets its lift from the differential airflow above and below
its wings?
-----------------
AG -

You are half right. What produces lift is a combination of Bernoulli's
principal - causing a low pressure area above the upper surface of the
wing - and Newton's Third Law - a reaction to the air particles being
pushed down by the bottom of the wing cause the wing to move up. We
generally consider these two laws to contribute to lift.

The amount that each of these contributes to lift is a function of the
cross section of the airfoil and angle of attach - the angle between the
wing (actually the chord line of the wing) and the relative wing (the wind
that is made by the forward motion of the airfoil). Some airfoils have a
greater curvature (camber) on the upper surface of the wing making the
Bernoulli effect greater at lower angles of attack.

Getting to your question... an airfoil that is made to fly with a greater
curvature on the top can fly - though not as efficiently - inverted as
long as the angle of attack is established in the upward (opposite of
gravity) direction. Some airfoils are made symmetrical to allow them to
fly equally well right-side-up and up-side-down. Airliners are unlike
candidates for symmetrical airfoils, but nimble aerobatic aircraft often
feature these.

The short answer... angle of attack controls lift.

Several factors affect the lift obtained from an airfoil. Primarily they
are related to the differential speed of the air flowing over the
top of the wing vs the air flowing underneath the wing. The air on top
has to flow farther, thus it must flow faster and the air pressure on top
is lower, resulting in lift.

The difference in distance the air has to flow is controlled by the shape
of the airfoil and the angle of attack (i.e., the angle with
respect to the airflow. Airfoils are designed for a relatively shallow
angle of attack under normal flight conditions. When flying upside down a
high angle of attack will allow sufficient lift to fly.

They probably adjust the ailerons and flaps to increase lift as well.

Greg Bradburn

http://www.newton.dep.anl.gov/askasci/phy00/phy00640.htm

 

[mattpilot]

amazing thing is i typed the first part from memory (from my adv. aero class). After your post i went to google, typed in "inverted flight" and got that as the first link.

 

[Bluto]

TheDude,
It sounds like you are suggesting that an airplane with a normal cambered wing cannot maintain inverted flight, that is simply wrong. It's just a matter of angle of attack. Clearly, it would be less efficient than a symmetrical airfoil. If that's not what you were implying, I apologize.

 

[BSkin]

Simple answer, not going back to aerodynamics, any medium to high performance (jet or prop) small planes -- even some large -- can substain inverted flight (i.e. greater than 10 secs.). That is, provided their engine design allows it, meaning fuel and oil feed.

 

[AcroChik]

Symmetrical Airfoils And...

Never mind. I somehow totally missed and entire page on the topic I was going to address. DUH!

 

[FN FAL]

... but the 707 did a barrel roll and it did not have symmetrical wings.

Helicoptors do loops as well, but they don't unload their discs...inverted flight and an aircraft with it's attitude inverted relative to the earth are two different things.

 

[paulsalem]

Most of an airplanes lift comes from Newtons 3rd law. For every action there is an equal and opposite reaction. Airplanes stay aloft beacause it pushed down air, and air pushes back up on it. Bernullio has very little to do with it actually. It is kinda the same as skipping a stone across the surface of the water. Stone pushes down on the water surface, water pushes on the stone. Stone skips up. Pick up a copy of stick and rudder and read the first few pages of it. (if not the whole thing)


Bernulli is an oversimpified answer for student pilots. Its ashame most CFI's teach half truths.

 

[EagleRJ]

Almost any aircraft can do an aileron roll (like the 707 did), because a properly executed aileron roll maintains between zero and one positive G all the way around. This enables the wing to work as it was intended, even if it is a typical high-speed airfoil that is highly inefficient when inverted.

You may have seen the video of Bob Hoover pouring water into a glass while performing an aileron roll. For a larger aircraft, the limiting factor is typically roll rate- many larger aircraft roll quickly to 180 degrees, and then the roll rate during the rest of the recovery is S.......L.......O........W!
Most larger aircraft cannot sustain level flight inverted. I've tried with several types in the simulator, and the limiting factor is actually pitch authority. There is not enough forward stick available to achieve the angle of attack that the wing needs to maintain level inverted flight. Like others said, though, the fuel and oil systems probably wouldn't be able to handle sustained inverted flight anyway.

 

[mattpilot]

You wanna back that up? A instructor was teaching that in an aerodynamics class here and got fired. He was going against everyone in the aviation industry - well maybe except you.

There are formulas that calculate how much lift (in lbs) the wings are creating at certain airspeeds. = more than enough to keep the plane flying. And that doesn't even factor in newtons third.

Most of an airplanes lift comes from Newtons 3rd law. For every action there is an equal and opposite reaction. Airplanes stay aloft beacause it pushed down air, and air pushes back up on it. Bernullio has very little to do with it actually. It is kinda the same as skipping a stone across the surface of the water. Stone pushes down on the water surface, water pushes on the stone. Stone skips up. Pick up a copy of stick and rudder and read the first few pages of it. (if not the whole thing)


Bernulli is an oversimpified answer for student pilots. Its ashame most CFI's teach half truths.

 

[profile]

There is no "bernoulli vs newton". A look at the Bernoulli equations will quickly show you that they are all Newtonian equations modified to apply to aer/hydro dynamics.

Newtonian laws explain lift, and Bernoulli's equations allow the precise application of Newtonian physics so that you can get real answers. The wing is pushed up due to differential pressure (Newton's 2nd law), 3rd law doesn't really apply, contrary to what some have managed to get muddied up.

Again, lift is not "part Bernoulli and part Newton" or anything else. You can use Newton to explain lift, but you'll end up deriving Bernoulli's stuff in the process, if you actually do it right!

 

[VNugget]

Exactly what he said.



Arguing between "Bernoulli vs. Newton" is like arguing whether a car is propelled by torque or friction (between the tires and the road.)

 

[paulsalem]

There are formulas that calculate how much lift (in lbs) the wings are creating at certain airspeeds. = more than enough to keep the plane flying. And that doesn't even factor in newtons third.

The forumula uses, airspeed, wing area, air density, and Coffecient of Lift to determine amount of force applied to the wing.

A formula can not "factor in" newtons law. It only produces a number.

Netwons third law is what explains what happens to an object when a force is exerted on it.

If amount of force (produced by the wing in lbs, or newtons, or whatever unit you prefer) is equal to the amount of weight of the plane, then it will "fly"

 

[paulsalem]

The wing is pushed up due to differential pressure (Newton's 2nd law), 3rd law doesn't really apply, contrary to what some have managed to get muddied up.

How does a perfectly symmetrical wing produce lift without washing any air down?