Right, where do I start... - Page 2

Chock · 12-19-07, 07:41 PM

Well, the only ever prop fighter plane I've flown in real life was a two-seater Spitfire (and that was only once, cos it cost me a lot of money to do it - and the guy didn't let me try landing it, although I did do the approach, don't blame him!), so I can't speak for any other fighter plane from real experience, after that it's been Chipmunks, Cessnas and stuff like that for me, and these days I only fly gliders. But I suspect that behaviour you describe is fairly accurate, as whacking the power on with a big powerful engine in a prop plane does two major things which would cause that issue, the first is 'p factor' which is basically asymmetric thrust caused by the fact that the angle of attack of the prop blades becomes different for the blades as they go around in a circle, making the thrust line go off to one side, the other is the airflow spiraling back down the fuselage as it is thrown back from the propeller and striking one side of the tailfin more than the other, shifting the tail around. Thus you get a massive yaw.

I imagine that would be a problem on the Polikarpov, because it has a short tailboom, and if that started swinging it would be difficult for the rudder to overcome things since the short tailboom would mean it has rudder authority that might be limited in extreme circumstances.

If both of these issues (p factor and asymmetric thrust hitting the tailfin) affected things in the same direction, then you're going to get a big swing on, and in some aeroplanes where the centre of gravity is quite far back, that can cause problems if you don't stop it early, because then you'll be fighting the momentum of the rear fuselage swinging (this is the chief cause of ground loops). The issue was a big problem on the Messerschmitt bf109 when it had full fuel on board, because it had the fuel tank behind the pilot's seat (putting the centre of gravity well back), and is one of the main reasons for all the ones that got lost in take-off accidents, as they would get a swing on and still be slow, making the rudder ineffective because of the lack of airflow over it at low speeds. Then the landing gear would break off because it was basically held on with sticky tape and a couple of tiny bolts on the bf109 :-)

The other issue is when you get a big yaw on, the fuselage effectively blocks the airflow to the inner part of the wing on the side you are yawing towards, because your momentum will still be carrying you forward and for a few seconds, that means you'll be flying sideways, and if that happens when you're right above the stall speed, one of your wings is suddenly not going to have enough lift to keep flying, and that means you'll go into a spin, as one wing keeps flying and the other gives up, hence you spin like a sycamore leaf dropping down from a tree. That's why you apply rudder to come out of a spin rather than aileron, because you have to yaw the 'dead' wing back into the airflow.

Incidentally, all this stuff is actually a lot easier to handle in a real aeroplane than it is in a simulated one, because you get much more feedback from the thing and you tend to not push things as much in a real plane anyway, because if things go tits up on a real one, you die. Although I must admit, I do really love spinning in the real thing, it's the best fairground ride you'll ever go on :-) That's why I prefer gliders, they are usually stressed for quite a lot of G.

Chock

FIREWALL · 12-19-07, 08:43 PM

Thx Dowly

I guess I'll have to look more closely at them.

Boy this stuff can get confuseing.

Steel_Tomb · 12-22-07, 06:22 AM

YOU'VE FLOWN A SPIT!?!?!?! I'M GREEN WITH ENVY!

It would my DREAM come true to fly a spit, hell I'd settle for just sitting in one!

Chock · 12-22-07, 01:30 PM

As far as I know, all the (two seater) Spits in the UK, with the possible exception of Caroline Grace's, are not certified for public transport, but there are moves to try and change this, so if you really want a trip in one, make your view known here:

http://www.flights4all.com/challenge10k.asp

This is a problem for a lot of airfields actually, although some places I know do get around the rules by offering 'trial lessons', which technically are not pleasure flights, but it's bending the rules a bit!

Incidentally, you'd be looking at well over a grand for a short flight.

Chock

12-19-07, 07:41 PM	#16
Chock Sea Lord Join Date: May 2005 Location: Under a thermal layer in chilly Olde England Posts: 1,842 Downloads: 0 Uploads: 0	Well, the only ever prop fighter plane I've flown in real life was a two-seater Spitfire (and that was only once, cos it cost me a lot of money to do it - and the guy didn't let me try landing it, although I did do the approach, don't blame him!), so I can't speak for any other fighter plane from real experience, after that it's been Chipmunks, Cessnas and stuff like that for me, and these days I only fly gliders. But I suspect that behaviour you describe is fairly accurate, as whacking the power on with a big powerful engine in a prop plane does two major things which would cause that issue, the first is 'p factor' which is basically asymmetric thrust caused by the fact that the angle of attack of the prop blades becomes different for the blades as they go around in a circle, making the thrust line go off to one side, the other is the airflow spiraling back down the fuselage as it is thrown back from the propeller and striking one side of the tailfin more than the other, shifting the tail around. Thus you get a massive yaw. I imagine that would be a problem on the Polikarpov, because it has a short tailboom, and if that started swinging it would be difficult for the rudder to overcome things since the short tailboom would mean it has rudder authority that might be limited in extreme circumstances. If both of these issues (p factor and asymmetric thrust hitting the tailfin) affected things in the same direction, then you're going to get a big swing on, and in some aeroplanes where the centre of gravity is quite far back, that can cause problems if you don't stop it early, because then you'll be fighting the momentum of the rear fuselage swinging (this is the chief cause of ground loops). The issue was a big problem on the Messerschmitt bf109 when it had full fuel on board, because it had the fuel tank behind the pilot's seat (putting the centre of gravity well back), and is one of the main reasons for all the ones that got lost in take-off accidents, as they would get a swing on and still be slow, making the rudder ineffective because of the lack of airflow over it at low speeds. Then the landing gear would break off because it was basically held on with sticky tape and a couple of tiny bolts on the bf109 :-) The other issue is when you get a big yaw on, the fuselage effectively blocks the airflow to the inner part of the wing on the side you are yawing towards, because your momentum will still be carrying you forward and for a few seconds, that means you'll be flying sideways, and if that happens when you're right above the stall speed, one of your wings is suddenly not going to have enough lift to keep flying, and that means you'll go into a spin, as one wing keeps flying and the other gives up, hence you spin like a sycamore leaf dropping down from a tree. That's why you apply rudder to come out of a spin rather than aileron, because you have to yaw the 'dead' wing back into the airflow. Incidentally, all this stuff is actually a lot easier to handle in a real aeroplane than it is in a simulated one, because you get much more feedback from the thing and you tend to not push things as much in a real plane anyway, because if things go tits up on a real one, you die. Although I must admit, I do really love spinning in the real thing, it's the best fairground ride you'll ever go on :-) That's why I prefer gliders, they are usually stressed for quite a lot of G. Chock __________________ Last edited by Chock; 12-19-07 at 07:52 PM.

12-19-07, 08:43 PM	#17
FIREWALL Eternal Patrol Join Date: Mar 2006 Location: CATALINA IS. SO . CAL USA Posts: 10,108 Downloads: 511 Uploads: 0	Thx Dowly I guess I'll have to look more closely at them. Boy this stuff can get confuseing. __________________ RIP FIREWALL I Play GWX. Silent Hunter Who ???

12-22-07, 06:22 AM	#18
Steel_Tomb Ace of the Deep Join Date: Mar 2007 Location: Cambridgeshire - UK Posts: 1,128 Downloads: 0 Uploads: 0	YOU'VE FLOWN A SPIT!?!?!?! I'M GREEN WITH ENVY! It would my DREAM come true to fly a spit, hell I'd settle for just sitting in one! __________________ _______________________________________________ System Spec: Intel Core 2 Duo 2.4Ghz \| 4Gb Corsair XMS2 Dominator DDR2 PC-2 6400 RAM \| XFX GeForce 8800GTS 640mb PCI-E \| Creative X-fi sound card \| 250Gb HDD \| *Rest In Peace Dave, you will be missed.*

12-22-07, 01:30 PM	#19
Chock Sea Lord Join Date: May 2005 Location: Under a thermal layer in chilly Olde England Posts: 1,842 Downloads: 0 Uploads: 0	As far as I know, all the (two seater) Spits in the UK, with the possible exception of Caroline Grace's, are not certified for public transport, but there are moves to try and change this, so if you really want a trip in one, make your view known here: http://www.flights4all.com/challenge10k.asp This is a problem for a lot of airfields actually, although some places I know do get around the rules by offering 'trial lessons', which technically are not pleasure flights, but it's bending the rules a bit! Incidentally, you'd be looking at well over a grand for a short flight. Chock __________________