CFI oral intel

"Michael Ash" wrote in message
...
In rec.aviation.student gatt wrote:
A question the examiner asked him: "You're flying cross-country and
trimmed at 110 knots. You die, and the engine quits. At what airspeed
will the aircraft strike the ground?"

In addition to all the other factors discussed, your airspeed will be
slightly lower than what you had trimmed due to the weight of your soul
departing the aircraft.

OK, so I don't really believe that, but I'd love to see what the guy would
say if you told him that answer!


Your airspeed may also be slightly lower due to the weight of the fuel that
has departed the aircraft (through the engine)

Everyone who has replied has made one significant and incorrect assumption.
I would have replied, "Really really fast, yellow arc at least, perhaps at
or above Vne depending on the aircraft."

Why? Because all posts have made the (probably) incorrect assumption that
the aircraft somehow fly wings-levels to its demise. That just won't
happen. Forget dihedral, that won't stop it going into a spiral. Another
factor worth considering is that when the pilot dies, there is a really good
chance that the pilot will fall forward and possibly push on the yoke. With
a side stick, this will probably cause a bank as the pilot pulls sideways on
the stick.

Anyway, my point is, is that since no wings leveler or autopilot was
mentioned, it is almost guaranteed that the aircraft would enter a spiral
and trim speed does not apply in a spiral.

Hilton


"gatt" wrote in message
. ..

One of the folks around the hangar took his CFI practical last week. He
had his AGI so they threw out all of the Fundamentals of Instruction stuff
entirely during the oral.

A question the examiner asked him: "You're flying cross-country and
trimmed at 110 knots. You die, and the engine quits. At what airspeed will
the aircraft strike the ground?"

Another was, "You're turning final and you enter a cross-control stall. Is
it better to be in a slip, or a skid?"

-c

Hilton wrote:
Everyone who has replied has made one significant and incorrect assumption.
I would have replied, "Really really fast, yellow arc at least, perhaps at
or above Vne depending on the aircraft."

Why? Because all posts have made the (probably) incorrect assumption that
the aircraft somehow fly wings-levels to its demise. That just won't
happen. Forget dihedral, that won't stop it going into a spiral. Another
factor worth considering is that when the pilot dies, there is a really good
chance that the pilot will fall forward and possibly push on the yoke. With
a side stick, this will probably cause a bank as the pilot pulls sideways on
the stick.

Anyway, my point is, is that since no wings leveler or autopilot was
mentioned, it is almost guaranteed that the aircraft would enter a spiral
and trim speed does not apply in a spiral.

Hilton


"gatt" wrote in message
. ..
One of the folks around the hangar took his CFI practical last week. He
had his AGI so they threw out all of the Fundamentals of Instruction stuff
entirely during the oral.

A question the examiner asked him: "You're flying cross-country and
trimmed at 110 knots. You die, and the engine quits. At what airspeed will
the aircraft strike the ground?"

Another was, "You're turning final and you enter a cross-control stall. Is
it better to be in a slip, or a skid?"

-c


Really getting nitty here Hilton :-)

With the engine dead, and assuming good rigging, there is no specific
reason to assume a spiral. The initial question specified the engine
"quit". Again, assuming proper trim and no aerodynamic forces to induce
bank, the aircraft for all practical purposes anyway, can be assumed a
straight path into the ground.

Take out the proper trim and an idling engine and perhaps you have a
case for a spiral. Also, few aircraft are rigged perfectly so that also
could be a factor for a spiral.

Other than these things being present and considering the "spirit" of
the question, trim speed would be the answer for ground impact in my
opinion.

--
Dudley Henriques

In article ,
Dudley Henriques wrote:
Really getting nitty here Hilton :-)

With the engine dead, and assuming good rigging, there is no specific
reason to assume a spiral. The initial question specified the engine
"quit". Again, assuming proper trim and no aerodynamic forces to induce
bank, the aircraft for all practical purposes anyway, can be assumed a
straight path into the ground.

Take out the proper trim and an idling engine and perhaps you have a
case for a spiral. Also, few aircraft are rigged perfectly so that also
could be a factor for a spiral.

Turbulence would increase the likelihood of a spiral departure from
level flight, wouldn't it?

Other than these things being present and considering the "spirit" of
the question, trim speed would be the answer for ground impact in my
opinion.

Steve Hix wrote:
In article ,
Dudley Henriques wrote:
Really getting nitty here Hilton :-)

With the engine dead, and assuming good rigging, there is no specific
reason to assume a spiral. The initial question specified the engine
"quit". Again, assuming proper trim and no aerodynamic forces to induce
bank, the aircraft for all practical purposes anyway, can be assumed a
straight path into the ground.

Take out the proper trim and an idling engine and perhaps you have a
case for a spiral. Also, few aircraft are rigged perfectly so that also
could be a factor for a spiral.

Turbulence would increase the likelihood of a spiral departure from
level flight, wouldn't it?

Other than these things being present and considering the "spirit" of
the question, trim speed would be the answer for ground impact in my
opinion.
Yes. Anything that changed the basic balance equation that was in effect
when the trim was set would do that.

--
Dudley Henriques

On May 30, 3:36*am, "Hilton" wrote:
Why? *Because all posts have made the (probably) incorrect assumption that
the aircraft somehow fly wings-levels to its demise. *That just won't
happen. *Forget dihedral, that won't stop it going into a spiral.

You're right, of course. The only way that will happen is with
artificial stability augmentation (a single axis autopilot). With a
two axis autopilot the plane will hit at stall speed. It may or may
not be wings level, depending on the stall characteristics.

See, this is what made the question such a good one. It allows lots
of room to explore different aspects of aerodynamic stability.

Michael

Michael wrote:
On May 30, 3:36 am, "Hilton" wrote:
Why? Because all posts have made the (probably) incorrect assumption that
the aircraft somehow fly wings-levels to its demise. That just won't
happen. Forget dihedral, that won't stop it going into a spiral.

You're right, of course. The only way that will happen is with
artificial stability augmentation (a single axis autopilot). With a
two axis autopilot the plane will hit at stall speed. It may or may
not be wings level, depending on the stall characteristics.

See, this is what made the question such a good one. It allows lots
of room to explore different aspects of aerodynamic stability.

Michael

I would respectfully disagree with you and Hilton on this one :-)There
should be no "of course" and no autopilot issues are involved in the
question that I can see.

The aircraft, if in trim at 110 kts will be trimmed for whatever angle
of attack is producing that airspeed. Unless there is something added to
the problem and assuming all factors normal with balance and stability
issues, what should be expected normally is a phugoid starting nose low
as the engine quits to recover the trim speed. I'm assuming no fuel
imbalance or rigging issues that could cause a bank input entry into the
problem.

So using just the aspects of the problem as presented;

Where the aircraft is along that phugoid and the exact airspeed to
expect at ground impact would depend on the altitude remaining and the
dampening properties present determining the decreasing phases of the
phugoid.

Just what is it that you are expecting to happen to cause the necessary
bank/lift imbalance to enter a nose low spiral?

--
Dudley Henriques

On May 30, 2:47*pm, Dudley Henriques wrote:
Just what is it that you are expecting to happen to cause the necessary
bank/lift imbalance to enter a nose low spiral?

Well, I am expecting normal behavior for a light airplane. Most light
airplanes have approximately neutral static and weakly negative
dynamic lateral (roll) stability. Thus, if left with no pilot input,
they will eventually roll into a turn. Maintaining AOA (which the
trim will do) will result in the increased airspeed.

Now the real question is why this is the case. Airplanes could be
built with positive dynamic lateral stability, and in fact ram-air
(square) parachutes (powered and unpowered) are built that way, which
is what makes it possible for them to be flown through clouds (absent
the legalities) with no gyros at all. However, airplanes are
generally not built that way. It's been tried before, and the results
were generally unsatisfactory.

Making the airplane too stable also made it too sluggish, and because
of the yaw-roll coupling involved gave it a really nasty ride in
turbulence.

A pretty good primer on stability issues can be found he

http://selair.selkirk.bc.ca/aerodyna...ity/Page5.html

Michael

Michael wrote:
On May 30, 2:47 pm, Dudley Henriques wrote:
Just what is it that you are expecting to happen to cause the necessary
bank/lift imbalance to enter a nose low spiral?

Well, I am expecting normal behavior for a light airplane. Most light
airplanes have approximately neutral static and weakly negative
dynamic lateral (roll) stability.

I would respectfully disagree. An Extra 300, as do most high performance
aerobatic airplanes has neutral static stability, but your vanilla
Cessna or Piper with dihedral is designed with positive static stability
in mind. Even a high wing Cessna like the 190 or 195 with little
dihedral has positive static stability due to wing position.
High performance airplanes like a Pitts or Extra have neutral static
stability.
As for dynamic stability, it really isn't much of a factor in lateral
stability. The ailerons if mass balanced around the hinge line by
weight, and if comparatively free in movement, usually assure that the
pure lateral movement is heavily damped. However, cross effects in yaw
displacement can result in lateral oscillations and Dutch Roll.

I totally agree that excessive dihedral is bad. It works against good
rolling qualities and as you say, makes for an overly stable aircraft.
It's for this reason that airplanes requiring a fast roll rate like the
Extra or a fighter for example, don't have excessive dihedral.






Thus, if left with no pilot input,
they will eventually roll into a turn.

Remember, we're dealing here with a dead engine. I'm still going to
stick with the spiel :-)) that says with a light GA airplane with
positive lateral stability built in with the normal dihedral found on
such airplanes and the engine dead, we're going to need a source for an
outside the system force strong enough to offset the countering dihedral
to any roll input to initiate the roll or yaw (or coupling if you wish)
that would end up with the aircraft banked enough to counter the
dihedral correcting it back into the normal phugoid I'm expecting.


Now the real question is why this is the case. Airplanes could be
built with positive dynamic lateral stability,

If the aircraft has dihedral, it has positive static lateral stability.
I don't see dynamic lateral stability as an issue here.




and in fact ram-air
(square) parachutes (powered and unpowered) are built that way, which
is what makes it possible for them to be flown through clouds (absent
the legalities) with no gyros at all.

That's interesting. I never knew that. I knew Steve Snyder quite well. I
believe Steve had something to do with the design of the square chute. I
know he designed the sentinel as well as a thousand other things related
to parachuting. Quite a guy. I miss him. He morted in his F86 a while back.





Making the airplane too stable also made it too sluggish, and because
of the yaw-roll coupling involved gave it a really nasty ride in
turbulence.

I completely agree.

A pretty good primer on stability issues can be found he

http://selair.selkirk.bc.ca/aerodyna...ity/Page5.html

I know the site. His stuff is generally very good. I do have some very
minor issues with his presentation on a few things.
DH

Michael


--
Dudley Henriques

On 2008-05-30, Michael wrote:
the legalities) with no gyros at all. However, airplanes are
generally not built that way. It's been tried before, and the results
were generally unsatisfactory.

Well, unless you consider a Champ unsatisfactory!
This one flew for two hours sans pilot, after it was hand propped with
the throttle wide open:

http://www.ntsb.gov/ntsb/brief.asp?e...28X02460&key=1

There was another one in similar circumstances which I think was is
Illinois, which flew until it ran out of fuel. I think that may have
been a Taylorcraft - it made what looked like a passable forced landing
into a cornfield.

--
From the sunny Isle of Man.
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