superstall

[Wizofoz]

I think in this case, incidence is meant as the angle between the chord-line and the longitudinal axis.

This is important if, as I suspect, they use the term "Super-stall" to mean what is also called "Deep stall".

This was a problem with some T-tailed aircraft (they lost a Trident in test flying due to it) as turbulent flow from a stalled wind would, at certain angles-of-attack, interfere with the tail and render the elevators ineffective, thus leaving the pilot with no way of recovering.

Changing the incidence of the wing would change the path of the turbulent flow, thus altering the tendency for this to happen.

[BOAC]

It was a 1-11.

Matt, thanks for transcribing that paragraph, although it leaves me slightly confused as to what DP was trying to say. Perhaps if he had inserted the italic words in the text it would have been clearer:

"Although the tail experiences an increasing negative incidence due to downwash with increase in attitude this increase is always 'beaten' by the decreasing negative incidence due to the physical change in attitude."

I guess the original quote by vish (assuming that DP was confused on definitions) is D P's way to lead up to the need to limit 'incidence' (AoA) by means of stick pushers? On its own it made no sense, since 'incidence' (AoA) is a 'valuable parameter' in any stall, is it not?

[Mr Optimistic]

could someone explain this to a non-pilot ?

Although the tail experiences an increasing negative incidence due to downwash with increase in attitude...


Is this saying that the flow behind the wing produces a 'downwash' (deflecting the free stream vector downwards I suppose) at the high tail at pre-stall aoa ( so that the tail is more or less always in perturbed air ?)

[bearfoil]

The Tail must push down at all flying speeds to keep the a/c flying level, and not nosediving. With a T-Tail, at Stall, the a/c can pitch down without this downforce. If the Tail Stalls, the Tail must be flown with a pull to arrest its Stall, then a normal recovery. Let's see, do I have this right? The Tail flies opposite the wing, the lifting surface is the top, not the bottom. Anyway, I rue the attempt to eliminate the use of a perfectly good aviation word (incidence), by combination with its trained for alter ego, AoA.

[rudderrudderrat]

Correct - the tail always exerts a down force to balance the c of g and the centre of pressure on the wings. (Speed Stability)

At high angle of attack, once the wing was stalled, airflow from that wing had less down wash and a more turbulent flow from the top of the wing, which destroyed the "lift" from the elevator of the T Tail which now sat inside that disturbed airflow.

The rear mounted heavy engines means there is a longer fuselage forward of the wing than behind, which hinders a natural recovery.

[bearfoil]

con-pilot has experience (alot) with the DC-8 and the B727, I'll defer to his experience; should we all?

[Mr Optimistic]

Although the tail experiences an increasing negative incidence due to downwash with i

but this quote implies pre-stall doesn't it ? At stall I guess the air is disorganised and there is no steady flow so aerodynamically the effect of the tail goes to zero. It was the quote I was interested in which implies that at any (pre-stall) aoa the flow over the high tail is canted downwards relative to freestream on account of the wing. Was just checking that was what was meant as it surprised me (perhaps through nothing more than ignorance).

Con-pilot ? Missed that.

[bearfoil]

The Tail's "downwash" is opposite the wing's downwash, eg, it is an 'upwash'. Like downflow on the wing reduces its AoA, up wash on the tail reduces its AoA.

[Mr Optimistic]

Ah, is that what was meant ?

My mistake, figured 'downwash' meant the condition of the airstream as it impinged upon the tail.

[bearfoil]

exactly!! See, that is what happens when unsuspecting aviators are subject to "one word fits all!" That is why the Tail is called a tail, even though it is a wing!!

[Mr Optimistic]

to add insult to injury

in my day we used 'incidence' for the cord line-free flow geometry (but not an aircraft application): quicker to write if nothing else.

[mattpilot]

I guess the original quote by vish (assuming that DP was confused on definitions) is D P's way to lead up to the need to limit 'incidence' (AoA) by means of stick pushers? On its own it made no sense, since 'incidence' (AoA) is a 'valuable parameter' in any stall, is it not?

I don't think its fair to say DP was confused by definitions. Throughout the book he uses the word 'incidence' to describe what most of us understand as the AoA. If one would read the 'language comparison' page (1 page before intro) and the 'glossary of terms' (pg 4) before reading the meat of the book, things would be much clearer. The 3rd edition was written in 1971, and with him being (or was) a certification pilot for the UK CAA (if i understood that right), i guess it is fair to say he used the proper terms that were known 'back in the days'.

But to be honest, i would of liked a '4th' edition myself that would make use of 'modern' terms when i read this book.

[bearfoil]

With the introduction of flight, travel acquired a third dimension, geometrically speaking. So to finalize this, and be clear, it is downwash that the tail experiences, only it is (seemingly) moving up!! Matt is right, each thread should begin with a glossary, "prior perusal prevents ****poor performance."

bear

[DozyWannabe]

Originally Posted by Wizofoz

(they lost a Trident in test flying due to it)

Originally Posted by BOAC

It was a 1-11.

Correct - BAC lost a 1-11 in testing, in an infamous accident that killed Mike Lithgow and his crew. BEA lost Trident G-ARPI in service due to premature droop retraction and subsequent stick pusher dump leading to deep stall.

[dixi188]

A Trident, G-ARPY, crashed on 3rd. June 1966 at Felthorpe after entering a deep stall and then a flat spin during a production test flight from Hatfield. The 4 crew died.

[BOAC]

Thanks dixi - and apologies to wiz for that error. I had forgotten that one.

[petitb]

DozyWannabe

"Correct - BAC lost a 1-11 in testing, in an infamous accident that killed Mike Lithgow and his crew".

-true, but why "infamous" ?

[Mr Optimistic]

maybe here ?

http://www.pprune.org/aviation-histo...-1963-a-2.html

[John Farley]

dixi188

I agree your info.

PY had done three successful stalls pusher ON but the fourth was done pusher OFF (I don't know why).

George Errington (40 years a tp) was among the crew although I believe he was a last minute addition.

[Brian Abraham]

Wiki cites "The use of the term "angle of incidence" to refer to the angle of attack occurs chiefly in British usage." and then gives reference to Kermode, A.C. (1972), Mechanics of Flight, Chapter 3.

Perhaps John Farley may be able to provide insight into this British usage. Sorry I don't have a copy of Kermode to see what he has to say.