MILAVIA Forum

Aviation Hobby => Flying => Topic started by: Viggen on October 16, 2006, 06:08:50 PM

Title: Physics of flight?
Post by: Viggen on October 16, 2006, 06:08:50 PM
There is a question that is troubling my little mind... We all know how a wing works and that it produces lift. But if the aircraft is flying upside down, then the wing must produce downforce instead of lift. Now how is it possible for aircraft to fly upside down?? Is it the forward motion from the engine/engines, or what is the effect/physic that makes this possible??

Can someone explain this in laymans terms, so i can understand it.  :)
Title: Re: Physics of flight?
Post by: Gripen on October 17, 2006, 08:20:44 AM
i thought that the air going over the wings and the speed from the engine kept the plane flying normally, so upside down would be the same?

the engines are still propelling it, which makes the wind go over the wings, so wouldnt it be the same, just a little more touchy if you aimed the nose down,  the plane would basically fall!

i dont know
im not aeronautical engineer
Title: Re: Physics of flight?
Post by: Webmaster on October 17, 2006, 07:02:27 PM
Ok, let me start with saying that I am not an aerospace engineer either, nor a pilot. Not sure if there is an easy answer. But don't forget the control inputs and pitch level, it's not just a matter of wing profile. Even when you are flying right side up, you have to balance your pitch to your speed by using the trim. Your lift is reduced by having the inverted wing, but it's not completely converted into a downforce, the wing still creates lift only with lesser effect, which may not be enough to keep you flying unless you adjust your pitch and speed. Because you adjust the pitch of your aircraft, you can still generate enough lift to keep flying, depending on your speed and aircraft characteristics of course. In fighter jets, the wings are flatter, speed contributes more to lift than the wing profile, and the computer will make adjustments for you.

I think we need an aerospace engineer on this forum to provide some better drawings and explanations  :(

Title: Re: Physics of flight?
Post by: Viggen on October 17, 2006, 07:54:52 PM
Ok. So what i have understood, its basicly down to the forward motion/speed of the aircraft that makes it possible.  Why this idea entered my mind was mostly because of racingcars. Their wings produce alot of downforce, enough to drive upside down through a tunnel when they reach speeds over 290 Km/h. It just hit me that you should get lift here instead of downforce if you are driving upside down.  ???

There is big diffrences between wings on a formula one car versus airplanes, but the ground concept they build wings on is the same. If if im not completly wrong and way out there. ;)
Title: Re: Physics of flight?
Post by: Webmaster on October 18, 2006, 02:40:12 PM
It just hit me that you should get lift here instead of downforce if you are driving upside down.  ???

Yeah, but they are upside down, so that lift is downforce onto the ceiling...
Title: Re: Physics of flight?
Post by: Viggen on October 19, 2006, 12:10:35 AM
Not if its upside down, because of the shape of the wing....Ahhhh!! This drives me nuts....  :o Guess im just to stupid to understand this. hehe, no wonder im unemployed at the moment.  ;D
Title: Re: Physics of flight?
Post by: Webmaster on October 19, 2006, 01:25:28 AM
They got wings to push the car down, so when it is inverted, it pushed them up... the force then sticks the cars to the ceiling of the tunnel instead of the road....

Unemployed? So you should have time to fnish the Viggen section,  >:D Hehe, sorry, that's too bad man. Maybe work abroad is an option, like Finland or Norway?
Title: Re: Physics of flight?
Post by: Gripen on October 19, 2006, 12:02:19 PM
hey you could make you own Military Aviation Forum thing, and be the WM of that

a little competition never hurt no one!
Title: Re: Physics of flight?
Post by: Viggen on October 19, 2006, 01:54:23 PM
Maybe i just need to to get back to school...
Title: Re: Physics of flight?
Post by: Viggen on October 19, 2006, 10:11:09 PM
I asked a friend of mine who fly planes about this today. Guess what???  Our dear webmaster was right again, i got the same answer from my friend.  The wing will still produce lift if you are upside down, you will just need to adjust the power, give it more throttle and rudder input (dive).  It is not just the shape of the wing that makes it possible, it is all combined.  :)

No more sleepless nights for me... Thanks to you two rascals!  :D

Title: Re: Physics of flight?
Post by: Gripen on October 20, 2006, 07:54:40 AM
Question: Whose the rascals

And random thing: dont let the wings fall off otherwise you are sooooo f****d!!!
Title: Re: Physics of flight?
Post by: Webmaster on October 20, 2006, 06:59:15 PM
I asked a friend of mine who fly planes about this today. Guess what???  Our dear webmaster was right again, i got the same answer from my friend.  The wing will still produce lift if you are upside down, you will just need to adjust the power, give it more throttle and rudder input (dive).  It is not just the shape of the wing that makes it possible, it is all combined.  :)

No more sleepless nights for me... Thanks to you two rascals!  :D

Right, and I now see some problem in both answers, of course it's not the rudder (yaw moving), but the stick (pitch) and this controls not the ailerons I have drawn on the wings, but the elevators on the horizontal tail planes or the entire tail planes and/or canards on some aircraft. You might have to use the rudder in propellor driven aircraft though, to compensate for the drift because of the power up.
Title: Re: Physics of flight?
Post by: Goose on October 21, 2006, 08:19:07 PM
Ok I am a pilot and an engineer and the answer is semi correct. The wing will produce lift no matter what aspect it is in as long as there is laminar airflow over it. Now this is due to Bernouli's principle which states that the rates of flow must be equal. For it to be equal the flow traveling over the curved (upper) surface of a wing has to travel faster to cover the longer distance. Due to the higher speed the pressure is less. This is what lift is the 'Pressure Differential' between the two surfaces.

An inverted wing still produces this force but it no longer cancels the weight of the aircraft or generates an upward force. It is combined with weight now to pull the aircraft down. Normally you can counter a downward pull by increasing power and/or pitching up. In this case you cannot counter by increasing power since that will increase the pressure differential and increase the downward pull. Ergo you must pitch the nose upward. What this means is inverted a pilot must push the stick forward to deflect the Horizontal tail planes downward. This will force the tail down and the nose up. That is how you maintain your altitude when inverted. Additionally from vectors since the force is now at an angle to counter the vectors you will need to increase your forward thrust by increasing the power output of your engine.

Hope I was helpful. 
Title: Re: Physics of flight?
Post by: Viggen on October 21, 2006, 09:56:17 PM
Of course you were helpful and i thank you for that explicit answer.  :)

He also mentioned alfa-angel (but in swedish) or is that the same as angel of attack?
Title: Re: Physics of flight?
Post by: Goose on October 22, 2006, 07:07:06 PM
He is talking about the 'Angle of Attack' of a wing. That is the angle of the wing to the relative airflow. A wing stops flying, 'Stalls,' at an angle not a speed. When the wing reaches this angle the point of pressure is to far forward along the wing and the flow breaks down from laminar to turbulent. When this happens the pressure differential no longer exist and there is no lift.
Title: Re: Physics of flight?
Post by: Viggen on October 23, 2006, 12:37:27 AM
Thanks again,  it was really helpful.  :) :) :)
Title: Re: Physics of flight?
Post by: Raptor on March 01, 2007, 06:26:47 AM
Ok. I finally figured it out. Thanks to my Aerospace Engineer Uncle who lent me that book. But this helped some. Thanks.