I think that somebody should ban ATPL students from attempting to impress us with their most recent readings from textbooks.

😉

Nobody is trying to impress anyone Trinny, this is a misconception on your part, Ollie asked the question, and one can only answer what one has been taught, period, maybe your infinite wisdom can shed some light on why Bernoulli’s equal transit theory is still being taught at all levels if it is indeed proven to be flawed?

No need to apologise, lift is lift regardless of what type of airfoil 🙂

Ollie

(just to make Trinny whince & puke some more) A symmetrical airfoil flies because of positive Alpha, if you present the symmetrical airfoil to the relative airflow at a positive alpha you can see that the overflowing air has to travel further thus speeding up, airfoils produce negative pressure above and below the wing, it’s just that the pressure falls more above it.

Fantastic shots Si, do you mind if I save a couple of the Embraers for my own personal use? (desktop etc)

chorn I think you are getting confusesd, are you sure you completely understand stability? that being, positive static & dynamic stability, negative static & dynamic stability & neutral static & dynamic stability? and all three in the 3 axis of aircraft movement, Lateral, Longitudinal & Directional?

Then how does a plane come down from FL390 in 3 and half minutes or so? This is roughly 200 km/h… If spin weren´ t stable, you would expect some sort of recovery over 3 and a half minutes…

I’m not sure how you could expect a recovery from a spin if your example aircraft was unstable as you stated, I think an aircraft in a spin is generally holding neutral dynamic stability, (which is an unstable state?) and that basically means the spin is not getting any worse or better (hence the neutral) and it stays in this state until an input from the pilot, be it a rudder deflection in the opposite direction to the yaw which corrects it and straightens the aircraft

What about Tu-154? Attempted to climb over a thunderstorm near or above ceiling, then something like an attempt to turn or a gust provided the upset… It did not right itself in a couple of turns (and inside the thundercloud they were attempting to avoid to start with) – it continued all the way to the ground. Or so the explanation of the Pulkovo Airlines crash goes.

The TU154 is not a training aircraft, WD means your average Piper or Cessna (I assume), when you start talking about T tailed & swept wing aircraft you are in a different ball game, T tails are prone to “Deep” stall, which is virtually irrecoverable, the tail is blanketed by the wing wash which destroys the laminar flow making control authority near impossible, and swept winged aircraft are prone to tip stall, where the tips stall first, this moves the wing CP forward rapidly which gives a pitch up moment making the stall far worse

There’s a good post on Prune at the moment in the FLight Istructor’s forum regarding the theory of lift, I think they could be discussing the same thing Blue?

happy birthday gary
dam hes still younger than me
dave

But everyone’s younger than you 😉

Happy birthday Arm for Sunday 🙂

That’s very nice of the kids, but shouldn’t you be able to get him the explanation Dean? 😉

Moggy

HAHA, they could probably explain it better than I can 😉

Yes, that was interesting… but it did not clarify well where the yawing couple comes from.

The yawing moment can come from a number of sources, the by-product of roll is yaw (adverse aileron yaw) and the by-product of yaw is roll, it could be from a catastrophic failure of an engine (does’t have to be this severe), also BR is right, the down going wing has a greater AoA in the spin but it will have passed critical alpha, causing more drag, as long as the AoA exceeds critical alpha you will get autorotation and a wing drop even more (different to spin, autorotation can cause a spin), hence why aileron is not used to stop autorotation or a spin, the down going aileron will increase the camber thus increasing it past critical alpha even more making the situation alot worse.
With any turning moment you need a force to keep the aircraft in the turn, this is where centrepetal force comes into play.

In which frame of reference is the less stalled wing going up? I suspect that the whole airframe, including the less-stalled wing, is going down, very fast, in a spin…

Of course, but a less stalled wing, will be the right side of critical alpha compared to the more stalled wing, thus giving greater lift than the other, this will cause one wing to be “higher” than the other, just the same as any aircraft in a rolling moment, to turn left the right wing must be “up going” & the left wing “down going”

The question in the first post was why spin is a stable state – so referring to fully developed spin. After all, a logical way of looking what happens in incipient autorotation is to look at what happens at fully developed spin, and figure out what happens in between.

Whiskey D answered this for you

chorn just as a matter of interest, where are you getting your information from?, and purely for information purposes do you know the difference between autorotation and spinning?

Dean