lokokkee

Was watching TV documentary on racing cars, with claims that the wings generate enough downforce to keep the car going upside down in a tunnel. Can someone pl. explain how can planes fly upside down when the wings will be generating downforce instead of lift? By negating the lift, the thing should literally fall out of the sky.

Katana

You're Malaysian. You should've learnt this for your SPM..

Its more to do with balancing the forces and bernouilli stuff..

mj

http://www.smithsonianmag.si.edu/smi...und_nov96.html

so there!

lokokkee

Katana, I got a '1' for physics for my school cert. exam almost 40 yrs ago (no SPM those days) and theory of flight was not in the syllabus. Bernoulli's effect explains lift when the wing is upright, not upside down. MJ, to counter negative lift, the wing will have to generate the necessary upforce by striking the airflow at a sufficiently high angle of attack, but won't this create additional drag and slows the plane down, requiring more thrust from the engine to overcome? So it is literally brute force of the engine that is keeping the plane in the air and only planes with more powerful engines can do this, not your everyday Cessna trainer?

Pavlo

turn a wing upside down and move the ailerons down (up relative to the wing).

also some wing profiles are symetrical, and rely on an angle of attack, so when upside down, you can use the rear flap things to give enough angle on the wing to give lift.

astraboy

More angle of incidence than attack. A symmetrical wing will produce lift either way up it just depends on the incidence. Most wings have a small amount of positive incidence these days. What incidence is is if you hold the fuselage level then the wing will be at a positive incidence of around 4 degrees or so. So to fly inverted the pilot rolls the aircraft then moves the elevator "down" so the aircraft is trying to go down, but is in fact going up cos its inverted. This decreases the incidence to a point where the the wing is generating lift from its symmetrical planform but the wrong way up.
Clever eh?
astraboy.

RaZe-=Buzz=-

and where did you copy that from?

Dave T-S

If you invert your everyday Cessna 172 or similar, the wings will drop off due to not being to stand negative G loadings, but that's another issue

P1Fanatic

Crashed and burned the first time did you dave?

P1 Enthusiast

Dunno but it works, simply put looks in the mirror of the P1 and you see the spoiler acting very effectively as an upside down wing, you can see the kevlar strip moving whilst producing the downforce.

Also, whilst inverting a plane you are changing the AoIncidence to compensate for camber in the wing not functioning as intended.

Pavlo

Elevators! I knew they had a name. Attack/Incidence? I assume that they are opposite, and that attack is angled down (for down force) and incidence is up (for lift).

carl

Depends how you do it. You should be able to do a 1g barrel roll which will result in no negative g-loadings. There's a guy who does this with a glass of water standing on the 'dashboard' or whatever it's called. It's also why Spitfires rolled into combat, because they were carburetted and the carbs would stop working with neg g-loadings (floats went and sat at the top of the float chambers). Me109s were fuel-injected.

kenb@manx

Angle of Incidence is the angle at which the wing is attached to the fuselage. Angle of Attack is the angle at which the airflow flows over the wing. Typically on a modern aircraft this will be about 3 degress in cruise and go up to about 15 degress for slow speed handling before the airflow stall occurs. This angle can be increased by leading edge flaps and slats and trailing edge flaps. This is all subsonic of course, when approaching mach 1 there are a new set of forces (eg control reversal) to deal with. Which is nice.
Inverted flight also causes difficulty for fuel systems as well as aerodynamics and should not really be attempted in civil aircraft, unless it's the whispering death jet (Airbus aircarft) which will perform this operation without pilot input. Thats computers for you.

ken

carl

Transsonic control reversal is a myth perpetuated by a film with James Stewart in it. However, once the shock wave gets to the control surfaces it can cause them to flap, which isn't pleasant. That's why supersonic aircraft try to spend as little time as possible in the transsonic zone.

Katana

*MUST.RESIST.OLD.JOKES.*

Anyway Bernouilli is still there, not obvious of course. As you're plane is inverted, notice how its pointed slightly upwards towards the sky? As long as the velocity of the air above the plane (or under it if its upside down) is higher than below the plane, lift is produced..

Tiggs

at what point during all this do you give the finger to the mig pilot?

T

kenb@manx

Carl,
just read the thread re your transonic quote but am off out now. Will follow this up when I get in. Talk to you later m8.

ken

lokokkee

I was assuming a 'normal' wing with the airfoil section, not one of those supersonic ultra-thin symmetrical thingy, that is generating a lifting force equal to the weight of the plane, say W, to hold it up in normal flight. So if this is reversed, you will now have a downforce of 2W pulling it out of the sky. In constant speed horizontal flying, the thrust of the engine will be equal to the drag in the horizontal axis, while the weight of the plane is held up by lift generated by the wings. If in inverted flight, lift is produced by changing the angle of attack, this will drastically increase the drag, requiring more thrust.

Now we come to the relevant part, how much of the downforce produced by the Scoob's rear wing is due to 'angle of attack' read increased drag, and how much is negative lift due to the inverted airfoil section of the wing. In racing, it is a compromise between straight line speed and road holding when setting up the rear wing. So if your car can go upside down in a tunnel, it may not be winning too many races.

dsmith

Somebody planning to go giveing the wink to some totty in a citroen (or is it a renault ? :rolleyes)

roadrunner

Dave TS - find that hard to believe. I have been up in Cessna 172 with an aerobatic licence. I performed a spiral dive from 6,000ft . The wings didn't fall off but the damn gyro toppled so we had to go back and land

[Edited by roadrunner - 8/20/2002 8:01:49 PM]

johnfelstead

you dont need an engine to do aerobatics. I used to fly gliders every weekend when i was 16 and spent many a flight upside down, doing stall turns, barrel rolls etc. Bloody good fun!

As long as the wing profile can produce more lift than 1G inverted you can fly upside down for ever, even in a glider, the thermal effect still works. It's damn hard on your thighs though and tends to start cutting blood supply off to your legs.

The wing profile you use on race cars is very dependant on the speed range you are trying to optimise. Drag increases as a square of speed, so on circuits with long straights it pays to use low drag, low downforce wings. The analagy of being able to drive through a tunnel upside down isnt the same as flying an aircraft, as the force (negative lift) is still in the one direction relative to the vehicle the wing is attached to, i.e towards the floor of the car. In an aircraft you are reversing the lift relative to the aircraft as you roll. You tend to compensate for all this automatically after a while, just like you do when starting a turn, where you raise the nose slightly to compensate for the loss in lift.

astraboy

<and where did you copy that from? >
My six years at college spent studying aircraft engineering
astraboy.

Katana

So I take it that you had to repeat three years of it then as the course is only a three year one.

kenb@manx

Carl,
Further to yesterday.
Indeed it is correct to say that control reversal does not take place. See I admit when I'm wrong . Had to get my ancient college notes out for high speed aircraft! You'll probabaly know then that the shock wave forms initailly on the part of the areofoil that has the fastest moving air and works its way backwards as speed increasses. At the 'shock stall' the boundary layer of static air behind the shock wave thickens and you indeed (as you say) get buffeting causing aileron vibration known as 'buzz'. Now this is the bit where I got mixed up: Because of the turbulent airflow seperation over the control surface, you need to apply a greater deflection to the control surface to achieve roll or pitch.
So thanks for making me look at my study notes after all these years!



Ken