Stalls and Thoughts

Bob F. wrote:
WrongO againO. The "coffin corner" is an altitude (point on a chart
where the stall speed and Mach come together) with a max power setting.
If you go faster, you get mach buffet. If you go to slow, you stall.
If you reduce power setting, you stall. If you nose over to recover,
you mach buffet. With your example I can see why you're confused.

I'm not confused and neither are you. :-))

The coffin corner YOU are describing can be found in the flight envelope
of the U2 (as well as other airplanes) at high altitude cruise. The
coffin corner I'm describing can be found on a dragged in approach AT
LOW ALTITUDE with the aircraft behind where the flight test community
defines the area of reverse command; that being below the airspeed for
maximum endurance. The corner is reached as you get the airplane low
enough on the approach where the sink rate can't be stopped with power
as maximum is already applied. The ONLY way out of the corner is to
reduce angle of attack. If the proximity between the aircraft and the
ground won't allow that angle of attack reduction, you hve what we call
the "coffin corner".

--
Dudley Henriques

The term "coffin corner" has the term "critical mach" in the formula. I've
never been at critical mach at such a low altitude. A little to fast for an
approach. So now you're telling me that the term "coffin corner" has been
high jacked to mean something different. Wouldn't be the first time!

--
BobF.
"Dudley Henriques" wrote in message
...
Bob F. wrote:
WrongO againO. The "coffin corner" is an altitude (point on a chart
where the stall speed and Mach come together) with a max power setting.
If you go faster, you get mach buffet. If you go to slow, you stall.
If you reduce power setting, you stall. If you nose over to recover, you
mach buffet. With your example I can see why you're confused.

I'm not confused and neither are you. :-))

The coffin corner YOU are describing can be found in the flight envelope
of the U2 (as well as other airplanes) at high altitude cruise. The coffin
corner I'm describing can be found on a dragged in approach AT LOW
ALTITUDE with the aircraft behind where the flight test community defines
the area of reverse command; that being below the airspeed for maximum
endurance. The corner is reached as you get the airplane low enough on the
approach where the sink rate can't be stopped with power as maximum is
already applied. The ONLY way out of the corner is to reduce angle of
attack. If the proximity between the aircraft and the ground won't allow
that angle of attack reduction, you hve what we call the "coffin corner".

--
Dudley Henriques

Bob F. wrote:
The term "coffin corner" has the term "critical mach" in the formula.
I've never been at critical mach at such a low altitude. A little to
fast for an approach. So now you're telling me that the term "coffin
corner" has been high jacked to mean something different. Wouldn't be
the first time!

Yes, that is exactly right. In the engineering sense I as well as you,
have always heard he term used in the sense you are using it.
In the world of high performance singles, especially in the figher
community, terms are often "stolen" or used in conversation so often
that they eventually become generic in the industry.
The term "Coffin Corner" as relates to "dragging it in" has been a
mainstay in our industry since the 50's. The F100 crash at Edwards
in 56 solidified the term to posterity. A young pilot named Barty Brooks
augured in when his nose wheel malfunctioned. He got so far behind the
curve on approach he couldn't lower the nose to recover the sink. The
subsequent crash has been used to demonstrate area of reverse command
issues t both the Naval and Air Force Test Pilot Schools for as long as
I can remember.
Actually, the other use of the term as well had it's origins within the
test community as do most terms like "coffin corner" :-)
Both are correct. I'm sure Bertie will eventually pop in and remind us
both of the blind men feeling the elephant. I agree with him
actually.That one's becoming one of my favorite Usenet analogies :-))

--
Dudley Henriques

Well, the bit of the envelope you're talking about is the low end of the
speed envelope fro every airplane. The coffin corner really only applies to
high alt/high speed transonic airplanes. When you climb up above transition
and reach th ealtitude where the airplane is mach limited the rules
changed.
I've attached a diagram of a typical flight envelope showing the constant
indicated max/min speeds up to transition where they taper in. The point in
dashded lines at the top is the point Bob was talking about where both
happen at the same time. To maintain a margin a max altitude dictated by a
G is determined. Going to fast or sow or pulling too much G at or near max
will result in a buffet and loss of lift, just for starters.





I've just reposted this because I've gotten some e-mail complaining that
the attachment didn't come through. I'll repost that in
alt.binaries.pictures.aviation


Bertie

Bertie the Bunyip wrote:
Well, the bit of the envelope you're talking about is the low end of the
speed envelope fro every airplane. The coffin corner really only applies to
high alt/high speed transonic airplanes. When you climb up above transition
and reach th ealtitude where the airplane is mach limited the rules
changed.
I've attached a diagram of a typical flight envelope showing the constant
indicated max/min speeds up to transition where they taper in. The point in
dashded lines at the top is the point Bob was talking about where both
happen at the same time. To maintain a margin a max altitude dictated by a
G is determined. Going to fast or sow or pulling too much G at or near max
will result in a buffet and loss of lift, just for starters.





I've just reposted this because I've gotten some e-mail complaining that
the attachment didn't come through. I'll repost that in
alt.binaries.pictures.aviation


Bertie
If you read my post first mentioning "coffin corner", you will notice I
used it as an adjective to describe a "condition" found t the extreme
end of the back side of the power curve; this being the "condition"
where low altitude and no more power available necessitate a reduction
in angle of attack to stop a developing sink rate; a very dangerous
situation on any approach.
It should be obvious that I never meant to convey that the term "coffin
corner" didn't refer to it's classic definition for high altitude
critical mach vs stall condition.
I will not get into a shouting match with Usenet advasiaries who wish to
convey I have no idea what coffin corner is as defined in the
aeronautical engineering sense.
Good God, I've even heard coffin corner used to define
the warnings block on an approach plate!

--
Dudley Henriques