"Interesting" wind yesterday

On Tue, 8 Mar 2005 17:24:46 -0500, "Morgans"
wrote:


"Mike Rapoport" wrote

I always thought that the "coffin corner" was where stall speed met the
Mach
limit. I didn't think that it even applied to non-jet aircraft.

Mike

No, I think the post above yours got it pretty much right..Vne is
significant, in that it demonstrates itself by nasty things like flutter, or
control reversal. Pull back on the stick to maneuver, or slow down, and
stall, or at least buffet like hell.

It is true, however, that it is pretty tough for a non jet aircraft to get
to the coffin corner. The Exxon tiger (can't think of the guy's name) that
has been trying to get the piston altitude record, has said that he is
really close to getting into coffin corner.

Another "coffin corner" I have heard discussed is the convergence of
Vne and Vs as altitude increases. I think it went something like
this:

1. Vne is a TAS, so its IAS decreases with increasing altitude.
Vs is an IAS, so as IAS, it remains the same with increasing
altitude.
Therefore, Vne, in IAS converges with Vs in IAS as
altitude increases.
2. Seen the other way, the TAS of Vs increases with altitude,
converging with the fixed TAS of Vne.

Or something like that I guess.

"Morgans" wrote
No, I think the post above yours got it pretty much right..Vne is
significant, in that it demonstrates itself by nasty things like
flutter, or control reversal.

Nope! Mike got it right.


"Jim" wrote
Another "coffin corner" I have heard discussed is the convergence of
Vne and Vs as altitude increases.

Nope! Mike got it right.

Coffin corner
From Wikipedia
Coffin corner is a dangerous portion of the flight envelope that must be
carefully approached by high altitude high subsonic speed aircraft, such
as the Lockheed U-2 aircraft.
Mach Limit
A subsonic aircraft must not exceed its Mach limit, some fraction of the
speed of sound near, but not at 1.0. At the low air densities encountered
at high altitude the speed of sound is lower. Exceeding the Mach limit
can cause loss of control and/or structural failure.
Stall Limit
At high altitudes the low density air is less capable of supporting the
aircraft and so the stall speed increases (as expressed in true air
speed).
The Corner
At some limiting altitude these speeds converge, and the aircraft cannot
be flown, as a slight pitch down will cause the Mach limit to be exceeded
while a slight pitch up will cause an aircraft stall with a subsequent
pitch down.


I've been to "coffin corner" in a Navy T2-V and very near to it in a
Boeing 707 and neither time was I close to Vne..Critical Mach
Number..yes, but not Vne.


Bob Moore
ATP B-707 B-727

"Morgans" wrote in message
...

"Mike Rapoport" wrote

I always thought that the "coffin corner" was where stall speed met the
Mach
limit. I didn't think that it even applied to non-jet aircraft.

Mike

No, I think the post above yours got it pretty much right..Vne is
significant, in that it demonstrates itself by nasty things like flutter,
or
control reversal. Pull back on the stick to maneuver, or slow down, and
stall, or at least buffet like hell.

It is true, however, that it is pretty tough for a non jet aircraft to get
to the coffin corner. The Exxon tiger (can't think of the guy's name)
that
has been trying to get the piston altitude record, has said that he is
really close to getting into coffin corner.
--
Jim in NC



I've never heard of Vne being related to TAS, only IAS. It makes no sense
to me. Could you provide a reference?

Mike
MU-2

What is a coffin-corner and how does one get into it in the pattern?

The "coffin-corner" is where you end up when the wind is blowing you
out from the runway on your base-to-final turn.

Your instinct is to tighten the turn in an effort to keep the runway
aligned, and maybe help it along with some rudder. This can be
disastrous at slow speeds while close to the ground, since a stall/spin
can develop quickly, and you won't have sufficient altitude to recover.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Coffin Corner, Deadmans Corner: The turn from base leg to final leg on a
landing approach. If the pilot has overflown the runway centerline and
attempts to roll back to the runway centerline adverse yaw will tend to
point the nose of the airplane in the opposite direction of the turn, a
natural reaction will be to use rudder to point the nose at the runway.
When this doesn't work the pilot may increase the bank in the same
direction. As the airspeed decays, the he incorrectly applies more rudder
in the direction of the turn creating a slow rolling uncoordinated skidding
turn close to the ground. Roll combined with Yaw in the direction of the
roll with airspeed dropping is a great recipe for a spin. The fact that
this situation is close to the ground makes the spin nearly unrecoverable.

Jim

Jim Burns wrote:

....
natural reaction will be to use rudder to point the nose at the runway.
....

I've never understood this whole turn to final hype, and I've never
understood why such a reaction should be natural. All my instructors
kept hammering into my head: When in the circuit, never fly below the
yellow triangle (plus half the wind) and always be sure to fly
coordinated. That's what I've been doing since then, and I've never had
any problems.

Stefan

Ahh.. you said the magic word... "circuit" and (just guessing the .ch) that
I can assume you are not from the US, please correct me if I'm wrong.

The FAA does not require spin training for private or commercial pilots but
instead puts emphasis on stall/spin awareness. One of the primary areas
being the base to final turn because you are low, slow and if uncoordinated,
in trouble. It's stressed on every written exam and in every oral exam that
I've had. They stress what a quartering tailwind can do to you while on
base leg, how it can blow you past the extended runway centerline and how
incorrect corrections can get a pilot in trouble. I've seen students
incorrectly use rudder to try to "get back" to the centerline, it is
something that an instructor has to be aware of, stay on top of, and like
you say, keep pounding it into the student because the student simply
forgets. The closer your pattern is to the runway, the angle created
becomes greater and at the same time creates an "urgent" situation for the
student. He now is faced with a discussion. This is where an instructor
must teach the student not to feel committed to the approach and to perform
a go around.

Now, here's one for you.... yellow triangle? airspeed marker?

Jim - CFII

Jim Burns wrote:

Ahh.. you said the magic word... "circuit" and (just guessing the .ch) that
I can assume you are not from the US, please correct me if I'm wrong.

No, you're absolutely correct. But believe me, the aerodynamics work
excatly the same on this side of the pond!

being the base to final turn because you are low, slow and if uncoordinated,
in trouble.

That's the point: Low, yes, but you are *never* slow and uncoordinated
at this point. Never. *This* has become my primary "natural" reaction.
But then, I've learnt how to use a rudder at day one.

Now, here's one for you.... yellow triangle? airspeed marker?

Doesn't this exist in the USA? Yellow triangle on the airspeed
indicator: Recommended minimum approach speed. (Something like 1.3 Vs at
MTOW and landing configuration or some such.) Drop below this at the
checkride, and you are invited to show up for a second try.

Stefan

("Jay Honeck" wrote)
Gotta love the Midwest in late winter!


We're calling it early spring. There was a memo.

Actually, we've had a 7 year run of pretty mild winters in the Twin Cities
beginning in 1998. Two years ago it reached 75F on St. Patrick's Day.

(1996 was brutal!!! - 40F/C for the first time ever in the Twin Cities)


Montblack

(1996 was brutal!!! - 40F/C for the first time ever in the Twin Cities)


Montblack

Ah.... a little Merlot would make it feel all warm and toasty!

Jim