Investigating the stall......

[grade_3]

(Notwe: Please excuse any spelling erros, my keyboard is playing silly buggers atm http://www.pprune.org/ubb/NonCGI/frown.gif )


In Short, why does a wing stall?

My understanding of a stall:

"In a stall, the seperation point of the airstream moves forward, leading to an increased turbulent airflow over the wing and also a reduction in the lift produced by the wing."


Why does the airflow seperate from the aerofoil beyond the Critical AoA?


My current understanding of why the stall occurs is:

The airflow behind the seperation point moves *forward* along the wing towards the seperation point due to the pressure gradient on the upper surface of the wing.

So,....Is the pressure gradient over the upper surface of the wing the cause of the seperation point moving forward with an increase in AoA?


Awaiting the answer with baited breath.....

Cheers,


Grade_3

[John Farley]

So,....Is the pressure gradient over the upper surface of the wing the cause of the seperation point moving forward with an increase in AoA?


Yes

Its called an adverse pressure gradient in the trade because the air flowing rearwards over the top surface is meeting air at an ever increasing pressure (ie the stuff that has curled round the trailing edge from underneath and starts moving forwards from the trailing edge) which causes lower pressure flow to separate so that it can take the easy route over the top.

Bye

[Foyl]

CASA's latest Flight Safety magazine has an article all about stalling. It's at
http://www.casa.gov.au/fsa/index.htm

Hope this helps.

[before landing check list]

Actually the seperation starts foreward and progresses aft. And on most aircraft, inboard then out. Just remember when doing them keep ball centered and DON'T use aileron to lift a wing. Also a airplane can be stalled at ANY airspeed and ANY attitude. To recover point the nose in the direction the aircraft is going(most cases down but not always) to reduce angle of attack. Also adding power and lowering flaps will reduce AOA.
Good flying
j

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What can you conceive more silly and extravagant than to suppose a man racking his brains, and studying night and day how to fly?

— William Law, 'A Serious Call to a Devout and Holly Life XI,' 1728

[This message has been edited by before landing check list (edited 05 November 2000).]

[John Farley]

Oh dear

Now I shall have to go and ask all those tufts that I flew on so many wings why they did not know this.

Silly tufts.

[before landing check list]

never trust a tuft

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How could they possibly be Japanese planes?

— Admiral Husband E. Kimmel

Believe me, Germany is unable to wage war.

— Former British Prime Minister David LLoyd George, 1 August, 1934.

[Skycop]

John,

Have you just "come out" as the founder member of the "Tufty Club"?

Perhaps it's due to variation in the Coriolis effect in different hemispheres.

It just goes to prove the old adage that you should never trust a wing that goes the same way the navigator points.

[Skycop]

Pre Landers,

As JF was merely the test pilot of the Hawker P1127, the predecessor of your AV8A/B,

He (and his tufts) probably wouldn't know much about slow flight, would he? I have just now ripped up my RAF Central Flying School notes and placed them on the embers of my Guy Fawkes night bonfire as they must be incorrect.

OOPS?

[John Farley]

Pre landers

There’s no answer to that!

(OK I know – you were just checking to see if anybody reads your posts)

Skycop

I’m glad I’ve quit or I might be tempted to call myself Tufty Golden Balls Flight Leader – then there would be no end to it. Since you mention the AV-8B I got a tad over two hours gliding in one of those back in 1982. No sweat though ‘cos it was all over the lake bed at Edwards. Thinking about it, perhaps that’s why the tufts pointed the wrong way - after all they were probably confused by a civilian Brit flying a USMC jet on a USN flight test programme at the US Airforce flight test centre.

Sorry Danny, off thread again.

[Skycop]

JF,

Interesting, please tell us more! The two hours must have been built up over quite a few flights. Our squadron picked up quite a few Harrier pilots following birdstrikes in the early 1980s. Most of them agreed that it glid like a manhole cover due to the large intake drag and preferred to make their aquaintance with Messrs Martin and Baker's finest aviation appliances..

[John Farley]

Skycop

Nothing more really. About 40 plus separate episodes of 3-4 mins each, standard egine development stuff. The B with a 230 sq ft plastic wing did handle better in the flare -you could afford to hold off to say 150/160 kts whereas the old 200 sq ft metal (SHAR) wing would not really fly mitout donk below say 170. You needed a reasonable quality of touchdown to avoid bouncing which would have been bad news. The lake bed was so FLAT that was easy. That is what is so important. An ordinary runway (like Boscombe) has so many ups and downs that the wing lift just after touchdown (bicycle gear - so u cant get rid of alpha after touchdown would v likely toss you back in the air before you could slow down. Not that we needed to do many lake bed landings (other than practice and qual exercises) as the Pegasus is a great relighter. You must remember when it stopped it was nearly always because we had deliberately surged it to establish the manoeuvre envelope so there was no reason to feel it would not light again when it had cooled down a tad.

Bye