Dynamic stalling of delta wing a/c (wrt MiG 21)

Hello,

I was reading on the net that the MiG-21 is a high demand no-nonsense
a/c, and tends to lose control (without the warning buffets as
experienced bu other a/c)
quite easily (during high speed turns??). Is this a MiG-21 phenom, or
do other Delta wing aircraft also have such inhernt control problems?


Googling brought out the following...
**********************
classic delta-wing aerodynamics problems:

1) vortex bursting
2) dynamic stall
3) falling-leaf mode" of asymmetric deep stall??


Dynamic stall is where you keep raising angle of attack really fast -
and
the lift keeps increasing - and then the wings stall. And stay stalled
when the angle of attack comes down - past zero, down into a dive....
************************

quote(From Wng. Cdr Suresh's article on Bharat-Rakshak Monitor):
-------------------------------------------------------------------------------
It is the docility of the aircraft that not only generates a good bit
of
confidence but also encourages forays into exceeding the limits of the
stipulated flight envelope. In air combat manoeuvres, many
inexperienced
pilots have got into trouble without realising it. At high angles of
attack, the induced drag increases sharply and unless the angle of
attack
is quickly reduced, the aircraft develops a high rate of descent,
which
cannot be arrested with the power available (even with reheat). Added
to
this, there is no protest from the aircraft like severe judder, wing
rocking. etc, prevalent in other types of aircraft. This gives a
feeling
of well-being and a number of pilots did not recognise the danger in
time
to take recovery action or eject
-------------------------------------------------------------------------------



A search has not yielded anything on dynamic stalling and other
problems of the MiG-21 other than in passing. Can anyone point me out
to a source on the net, or any specific paper/book which deals with
issues of Dynamic stalling of aircraft in general and delta winged a/c
in particular? Have any studies been done on other Deltas (Mirage
family, F-102/104) ?

And what in your view will explain the aerodynamic limitations of the
MiG-21?

Thanks,
Lars

I flew the F102 about 1500 hours and did just about everything that
can be done in that aircraft. (only did one one-turn spin, though; it
was accidental, and recovery was standard and quick). The F102 had
about 740 sq ft of wing and clean weighed about 28000 for takeoff.
(38#/sqft!) The aircraft could be flown down to 90 knots controllably
in what looked like level flight but starting just below about 115 you
were descending and the only way to break the descent and accelerate
was by decreasing the angle of attack. Tough if you're close to the
ground. At 115 KIAS you were close to 30 degrees AOA and at the limit
of one-G flight in full afterburner. At 90 KIAS you were going down at
over 6000 FPM. Here is where a lot of transitioning pilots got in
trouble; they'd fly a 360 overhead (VFR) pattern, get too slow on
final (lulled into complacency by the ease of control) realize at last
they were going to land short and now go to full military power to
either reach the runway or go-around, and pull back on the stick 'to
reduce the descent rate', thus increasing the AOA and the induced drag
to horrific levels. Afterburner might have allowed them to fly out of
trouble but being new and 'unadvised' they would be loath to call for
it until too late. Result - prang. The B58 had sinmilar problems even
with experienced pilots. (Paris Air Show - 2X). FWIW there were NO
stall warnings whatsoever in the F102. The airplane felt good and
solid all the way down the airpseed scale. The caveat in the Flight
Manual was that if aileron was used to control wing drop at 90 KIAS
the airplane could/would spin. It felt just as solid at 115 as it did
at 500. As for the MiG21 - I do not know the airplane but do know it
has a much higher wing loading than the F102 (its rotation speed is
about 50 knots faster (F102 clean - ISTR 144) and I presume the final
approach speed is about the same amount greater. 150 on final was
plenty for the Deuce; at about 135 or so you were close to dragging
the tail end, but it was still under fine control. So the MiG is a hot
airplane on takeoff and landing. It has to have lots of energy to
execute hard turns in any flight plane, including a Split-Ess. Any
delta will shed energy under high G so quickly it will catch
'unadvised' pilots by surprise. A demo maneuver for transitioning
pilots was to roll the TF trainer (tub - side by side ugly mother)
inverted at 30 degrees noseup and 250 KIAS at 25,000 and
simultaneously light AB and suck back the stick to 5G and execute a
Split Ess from 25,000. Result - level flight at 22,000 and 225-250.
Done at 3,000 AGL with an F100 on your tail resulted in shucking the
Hun. They dared not try to follow you. I suspect a lot of MiGs were
lost in air-to ground weapons deliveries begun at too low an energy
level. Also - what are the MiG's spin/departure characteristics? The
original 21 was a lightweight bird - the last models are pretty heavy
even clean. And then there is always - how current are the pilots? How
good is the maintenance? There was a negative comment in AVWeek
recently on the 21's engine maintenance. Obviously critical on a
single engined aircraft.
My two cents worth as an ex-F102A pilot/maintenance test/flight
examiner - Walt BJ

Had the pleasure to fight the F-106's (a deuce with decent T/W) during
College Dart at Tyndall. Great machine aerodynamically, had a turn (one
usually) that would water your eyes ... it was easy to lure the ADC guys
into that bat-turn and the subsequent low energy state (delta wings begin to
generate significant drag at high AOA). But there was ONE guy ....

R / John

"Walt BJ" wrote in message
om...
I flew the F102 about 1500 hours and did just about everything that
can be done in that aircraft. (only did one one-turn spin, though; it
was accidental, and recovery was standard and quick). The F102 had
about 740 sq ft of wing and clean weighed about 28000 for takeoff.
(38#/sqft!) The aircraft could be flown down to 90 knots controllably
in what looked like level flight but starting just below about 115 you
were descending and the only way to break the descent and accelerate
was by decreasing the angle of attack. Tough if you're close to the
ground. At 115 KIAS you were close to 30 degrees AOA and at the limit
of one-G flight in full afterburner. At 90 KIAS you were going down at
over 6000 FPM. Here is where a lot of transitioning pilots got in
trouble; they'd fly a 360 overhead (VFR) pattern, get too slow on
final (lulled into complacency by the ease of control) realize at last
they were going to land short and now go to full military power to
either reach the runway or go-around, and pull back on the stick 'to
reduce the descent rate', thus increasing the AOA and the induced drag
to horrific levels. Afterburner might have allowed them to fly out of
trouble but being new and 'unadvised' they would be loath to call for
it until too late. Result - prang. The B58 had sinmilar problems even
with experienced pilots. (Paris Air Show - 2X). FWIW there were NO
stall warnings whatsoever in the F102. The airplane felt good and
solid all the way down the airpseed scale. The caveat in the Flight
Manual was that if aileron was used to control wing drop at 90 KIAS
the airplane could/would spin. It felt just as solid at 115 as it did
at 500. As for the MiG21 - I do not know the airplane but do know it
has a much higher wing loading than the F102 (its rotation speed is
about 50 knots faster (F102 clean - ISTR 144) and I presume the final
approach speed is about the same amount greater. 150 on final was
plenty for the Deuce; at about 135 or so you were close to dragging
the tail end, but it was still under fine control. So the MiG is a hot
airplane on takeoff and landing. It has to have lots of energy to
execute hard turns in any flight plane, including a Split-Ess. Any
delta will shed energy under high G so quickly it will catch
'unadvised' pilots by surprise. A demo maneuver for transitioning
pilots was to roll the TF trainer (tub - side by side ugly mother)
inverted at 30 degrees noseup and 250 KIAS at 25,000 and
simultaneously light AB and suck back the stick to 5G and execute a
Split Ess from 25,000. Result - level flight at 22,000 and 225-250.
Done at 3,000 AGL with an F100 on your tail resulted in shucking the
Hun. They dared not try to follow you. I suspect a lot of MiGs were
lost in air-to ground weapons deliveries begun at too low an energy
level. Also - what are the MiG's spin/departure characteristics? The
original 21 was a lightweight bird - the last models are pretty heavy
even clean. And then there is always - how current are the pilots? How
good is the maintenance? There was a negative comment in AVWeek
recently on the 21's engine maintenance. Obviously critical on a
single engined aircraft.
My two cents worth as an ex-F102A pilot/maintenance test/flight
examiner - Walt BJ

T38's the same way Walt. (I'm assuming you went through in T-Birds instead
of 38's, but if you've flown the Talon, please forgive my unnecessary input
here :-)

Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/CFI
Retired

Guess what we need is a definition of 'dynamic stalling'. Would that
be what I know as an 'accelerated stall'; i.e. one due to pulling too
many Gs for the plane's energy? When effected by an over-enthusiastic
pilot (ham-fisted plumber) some airplanes can depart (F4) while others
at certain speed regimes can dig in and overshoot desired G levels by
a sizeable margin (F4, transsonic)
Walt BJ

"Walt BJ" wrote in message
. ..
Guess what we need is a definition of 'dynamic stalling'. Would that
be what I know as an 'accelerated stall'; i.e. one due to pulling too
many Gs for the plane's energy? When effected by an over-enthusiastic
pilot (ham-fisted plumber) some airplanes can depart (F4) while others
at certain speed regimes can dig in and overshoot desired G levels by
a sizeable margin (F4, transsonic)
Walt BJ

Not exactly Walt. Dynamic stall is directly associated with boundary layer
burst due to pitch rate coupled with amplitude, and additional factors
involving behavior at high angle of attack. It's a highly complicated
subject, and it goes much deeper than simple accelerated stall which is any
stall developed at 1 g.
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/CFI
Retired

"drake" wrote in message
om...
Hello,

I was reading on the net that the MiG-21 is a high demand no-nonsense
a/c, and tends to lose control (without the warning buffets as
experienced bu other a/c)
quite easily (during high speed turns??). Is this a MiG-21 phenom, or
do other Delta wing aircraft also have such inhernt control problems?


The Gloster Javelin was prone to deep stall as the wing could
block airflow over the tail at high angles of attack and render
the aircraft uncontrollable

Keith

"Dudley Henriques" wrote in message
ink.net...

"Walt BJ" wrote in message
. ..
Guess what we need is a definition of 'dynamic stalling'. Would that
be what I know as an 'accelerated stall'; i.e. one due to pulling too
many Gs for the plane's energy? When effected by an over-enthusiastic
pilot (ham-fisted plumber) some airplanes can depart (F4) while others
at certain speed regimes can dig in and overshoot desired G levels by
a sizeable margin (F4, transsonic)
Walt BJ

Not exactly Walt. Dynamic stall is directly associated with boundary layer
burst due to pitch rate coupled with amplitude, and additional factors
involving behavior at high angle of attack. It's a highly complicated
subject, and it goes much deeper than simple accelerated stall which is
any
stall developed at

Flow seperation.

Flow seperation.

Separation

Dan, U. S. Air Force, retired

Flow seperation.

Separation

Dan, U. S. Air Force, retired

You won't believe this Dan, but I was going to do this exact post and
decided at the last second not to :-))))
Dudley


Dudley, our resident EE/PE, rocket scientist, aerodynamicist, physicist, test
pilot, political scientist etc tends to make spelling mistakes when he's
excited.

I guess when you are perfect and an expert on everything you are allowed a few
little mistakes.

Dan, U. S. Air Force, retired