DeanAllen
Topic Author
Posts: 1
Joined: Wed Jul 31, 2019 8:50 am

### Inverted flight, Coanda and Bernoulli princes

I have a simple question.
I watched this video https://youtu.be/OCh4svEfDmE explaining how the airplane wing works with the Coanda and Bernoulli princes.
I know that the airfoil is made so that the airflow lifts the plane. But in an inverted flight situation should the plane drop? Now the wing pushes towards the ground. How then does inverted flight exist?
Perhaps by activating ground spoilers you could have a lift in inverted flight?

Starlionblue
Posts: 19314
Joined: Fri Feb 27, 2004 9:54 pm

### Re: Inverted flight, Coanda and Bernoulli princes

The video shows airliner airfoils. Airliners don't typically fly inverted. Due to airfoil shape and other reasons, airliners are not very good at sustained inverted flight.

Airfoils for aircraft that routinely fly inverted, e.g. aerobatic aircraft, are typically symmetrical or close to it. All lift is derived from angle of attack, not the shape of the airfoil. At 0 AoA, a symmetrical airfoil has zero lift. The airfoil must be angled relative to airflow to produce lift. Whether this angle is positive for upright flight or negative for inverted flight doesn't matter. In comparison, an airliner airfoil is cambered and asymmetrical, and it does produce lift at 0 AoA.

This is a model of an aerobatic aircraft, showing symmetrical airfoil. As you can see, if the aircraft is upside down, the airfoil shape is the same due to symmetry. By flying with a negative AoA inverted flight can be maintained. If you watch airshow videos carefully, you'll see that in straight and level inverted flight, the nose of the aircraft is pointed slightly skywards, same as in normal flight.

NASA has excellent simulation tools that allow you to play around with airfoil shapes and angles of attack. https://www.grc.nasa.gov/WWW/K-12/airplane/foil3.html
Last edited by Starlionblue on Wed Jul 31, 2019 10:52 am, edited 1 time in total.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

flyingturtle
Posts: 5613
Joined: Mon Oct 31, 2011 1:39 pm

### Re: Inverted flight, Coanda and Bernoulli princes

Simply, by deflecting enough air downwards (towards the ground).

It would even work with a wooden board as a wing. No spoilers needed at all. But for normal flight, it's horribly inefficient.
Reading accident reports is what calms me down

Woodreau
Posts: 1776
Joined: Mon Sep 24, 2001 6:44 am

### Re: Inverted flight, Coanda and Bernoulli princes

From an old unusual attitude recovery training video “you do not have the pitch authority to maintain 1g inverted flight....” (in an airliner). Capt Warren VanderBurgh

https://youtu.be/35Zy_rl8WuM
https://youtu.be/WfNBmZy1Yuc
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.

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