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  #101  
Old June 5th 08, 05:30 PM posted to rec.aviation.piloting,rec.aviation.student
gatt[_5_]
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Posts: 156
Default CFI oral intel

Michael Ash wrote:

The original question specified "trimmed at 110 knots" which implies that
the autopilot is not engaged.


Correct. The question was asked about two weeks ago by the examiner in
an initial CFI oral. The simple answer that worked was "about 110
knots." I talked to the guy who passed the checkride yesterday. If he
had tried to give a more complicated answer and he was incorrect on
anything he said, he'd have been digging his own hole.

Instead, the examiner moved on and said "I'm a student and I was
supposed to study and prepare for pylon 8's but I didn't do my assigned
homework, so teach me from the beginning."

(My wife's pragmatic response would have been "Come back when you've
completed your assigned homework.")

Fortunately he had a lesson plan prepared on p-8's.

-c

Ads
  #102  
Old June 5th 08, 08:19 PM posted to rec.aviation.piloting,rec.aviation.student
Michael[_1_]
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Posts: 185
Default CFI oral intel

On Jun 4, 10:42*am, Dudley Henriques wrote:
Below is a very well done white paper on stability by Russel Williams
that addresses much of what we have been discussing.


The link does not work, and I can't find it through google. Do you
have another link?

The long and short of it in my opinion is that positive lateral
stability is present in GA airplanes


As lond as you mean static stability, then yes - weak positive lateral
stability is present in most non-aerobatic (and a few aerobatic) GA
airplanes as long as the displacement from wings-level is small.

and they will tend to recover from
the sideslip coupling.


Again, as long as the displacement is small and the lateral trim is
near-perfect.

Your key point addresses potential disturbances
that can indeed exceed this recovery tendency.
I agree totally with you that such a disturbance can exceed positive
stability tendencies if strong enough.


And I guess my point is that in most cases, these disturbances will be
strong enough, especially in an airplane that can cruise 110 kt. I
think this is something easy enough to prove in most cases. For those
playing along on the home game, try this next time you fly. Do this on
the smoothest possible day you can get.

Set up the plane in cruise at 110 kt. Trim it out as well as you can,
both in pitch, and, if aileron and/or rudder trim is available, in
roll as well. My guess is that most airplanes that can cruise 110 kt
will have aileron or rudder trim available - I can't off the top of my
head think of any certificated exceptions to this (I am sure there is
one).

Let go of the controls. All of them - hands off the yoke/stick and
feet off the rudders - and just sit there. Note how long it takes to
exceed 25 degrees of bank or change heading by 90 degrees.

If in 15 minutes that doesn't happen, smoothly bring the throttle to
idle to simulate fuel exhaustion. Let the plane descend 2000 ft or so
(use carb heat if appropriate). Now see if you are still within 25
degrees of wings level. The reason this matters - generally the
engine is offset just enough that at cruise, you should need no
rudder. On takeoff the left-turning (for CW engines) tendencies are
increased, so you need some right rudder. On a power-off descent, you
need some left rudder. Yaw and roll are coupled. So even if you were
in perfect lateral trim before you went to idle, you're not anymore.

Now I'm willing to bet that at least 9 out of 10 people who try this
will find that the plane won't fly level for 15 minutes without pilot
input, and of the few that do, the engine coming back to idle will
change the yaw enough that more than half the rest will enter a
spiral.

Michael
  #103  
Old June 5th 08, 09:01 PM posted to rec.aviation.piloting,rec.aviation.student
K l e i n[_2_]
external usenet poster
 
Posts: 18
Default CFI oral intel

On Jun 5, 1:19 pm, Michael wrote:
On Jun 4, 10:42 am, Dudley Henriques wrote:

Below is a very well done white paper on stability by Russel Williams
that addresses much of what we have been discussing.


The link does not work, and I can't find it through google. Do you
have another link?

The long and short of it in my opinion is that positive lateral
stability is present in GA airplanes


As lond as you mean static stability, then yes - weak positive lateral
stability is present in most non-aerobatic (and a few aerobatic) GA
airplanes as long as the displacement from wings-level is small.

and they will tend to recover from
the sideslip coupling.


Again, as long as the displacement is small and the lateral trim is
near-perfect.

Your key point addresses potential disturbances
that can indeed exceed this recovery tendency.
I agree totally with you that such a disturbance can exceed positive
stability tendencies if strong enough.


And I guess my point is that in most cases, these disturbances will be
strong enough, especially in an airplane that can cruise 110 kt. I
think this is something easy enough to prove in most cases. For those
playing along on the home game, try this next time you fly. Do this on
the smoothest possible day you can get.

Set up the plane in cruise at 110 kt. Trim it out as well as you can,
both in pitch, and, if aileron and/or rudder trim is available, in
roll as well. My guess is that most airplanes that can cruise 110 kt
will have aileron or rudder trim available - I can't off the top of my
head think of any certificated exceptions to this (I am sure there is
one).

Let go of the controls. All of them - hands off the yoke/stick and
feet off the rudders - and just sit there. Note how long it takes to
exceed 25 degrees of bank or change heading by 90 degrees.

If in 15 minutes that doesn't happen, smoothly bring the throttle to
idle to simulate fuel exhaustion. Let the plane descend 2000 ft or so
(use carb heat if appropriate). Now see if you are still within 25
degrees of wings level. The reason this matters - generally the
engine is offset just enough that at cruise, you should need no
rudder. On takeoff the left-turning (for CW engines) tendencies are
increased, so you need some right rudder. On a power-off descent, you
need some left rudder. Yaw and roll are coupled. So even if you were
in perfect lateral trim before you went to idle, you're not anymore.

Now I'm willing to bet that at least 9 out of 10 people who try this
will find that the plane won't fly level for 15 minutes without pilot
input, and of the few that do, the engine coming back to idle will
change the yaw enough that more than half the rest will enter a
spiral.

Michael


If this worked reliably, it would be taught as a standard technique
for inadvertant VFR into IFR excursions. Hey, just throttle to idle,
hands off and wait for VFR to appear. But....this is not what is
taught. Wonder why???

This is curiously close to a technique for spin recovery that is
taught for certain aerobatic airplanes such as the Pitts and the
Extra, called Muller-Beggs. In this method, if you find yourself in a
spin and you can't figure out what to do, then throttle to idle, hands
off the stick and full rudder to counter the apparent yaw you see
directly out the front, wait patiently for the spin to stop, then
neutralize rudder and recover from the dive. This does NOT work for
all aerobatic aircraft. One I'm personally familiar with that does
not work is the Yak-54.

K l e i n
  #104  
Old June 5th 08, 09:16 PM posted to rec.aviation.piloting,rec.aviation.student
Hilton
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Posts: 118
Default CFI oral intel

Michael Ash wrote:
Hilton wrote:
Michael Ash wrote:
In a steady *spiral* dive the wing loading will be determined by your
bank
angle.


Can you prove that? (mathematically or non-mathematically)


If it's steady, i.e. constant speed, then the loading will be equal to the
arccosine of the bank angle, because you need to generate 1 gee straight
up to counterbalance gravity. This is the same situation as a level turn,
and the math and vectors should be discussed in any introductory book on
flying.


Your 'proof' above is almost correct for *level* flight (it ignores attitude
etc, but I don't want to knit pick), however, it is not appropriate at all
in a spiral even if the aircraft is at a constant speed. In a spiral, there
is a non-zero component of vertical drag, therefore less vertical lift is
required. However, your lift vector is now at an angle to the vertical.
You cannot ignore these. Therefore the wing loading is also a function of
the coefficient of drag, and perhaps other things, but clearly not only
determined by your bank angle.

Hilton


  #105  
Old June 6th 08, 02:54 AM posted to rec.aviation.piloting,rec.aviation.student
Michael Ash
external usenet poster
 
Posts: 309
Default CFI oral intel

In rec.aviation.student K l e i n wrote:
If this worked reliably, it would be taught as a standard technique
for inadvertant VFR into IFR excursions. Hey, just throttle to idle,
hands off and wait for VFR to appear. But....this is not what is
taught. Wonder why???


One reason that comes to mind is that you have no guarantee that the
ceiling under your IMC condition is high enough to allow for recovery.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon
  #106  
Old June 6th 08, 03:05 AM posted to rec.aviation.piloting,rec.aviation.student
Bertie the Bunyip[_25_]
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Posts: 3,735
Default CFI oral intel

Michael Ash wrote in news:1212717258.920305
@web1.segnet.com:

In rec.aviation.student K l e i n wrote:
If this worked reliably, it would be taught as a standard technique
for inadvertant VFR into IFR excursions. Hey, just throttle to idle,
hands off and wait for VFR to appear. But....this is not what is
taught. Wonder why???


One reason that comes to mind is that you have no guarantee that the
ceiling under your IMC condition is high enough to allow for recovery.


Well, "inadvertant flight into IMC" is almost always a push on regardless
scenario where the pilot gets lower and lower, often in inhospitable
terrain, so it'd be kind of useless in that anyway.


Bertie
  #107  
Old June 6th 08, 03:19 AM posted to rec.aviation.piloting,rec.aviation.student
Jay Maynard
external usenet poster
 
Posts: 521
Default CFI oral intel

On 2008-06-06, Michael Ash wrote:
In rec.aviation.student K l e i n wrote:
If this worked reliably, it would be taught as a standard technique
for inadvertant VFR into IFR excursions. Hey, just throttle to idle,
hands off and wait for VFR to appear. But....this is not what is
taught. Wonder why???

One reason that comes to mind is that you have no guarantee that the
ceiling under your IMC condition is high enough to allow for recovery.


....especially if there's cumulo-granite or cumulo-steel inside.
--
Jay Maynard, K5ZC http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
Fairmont, MN (FRM) (Yes, that's me!)
AMD Zodiac CH601XLi N55ZC (ordered 17 March, delivery 10 June)
  #108  
Old June 6th 08, 03:26 AM posted to rec.aviation.piloting,rec.aviation.student
Michael Ash
external usenet poster
 
Posts: 309
Default CFI oral intel

In rec.aviation.student Jay Maynard wrote:
On 2008-06-06, Michael Ash wrote:
In rec.aviation.student K l e i n wrote:
If this worked reliably, it would be taught as a standard technique
for inadvertant VFR into IFR excursions. Hey, just throttle to idle,
hands off and wait for VFR to appear. But....this is not what is
taught. Wonder why???

One reason that comes to mind is that you have no guarantee that the
ceiling under your IMC condition is high enough to allow for recovery.


...especially if there's cumulo-granite or cumulo-steel inside.


Just so.

Reading my own post it occurs to me that "IMC condition" is one of those
redundant uses of acronyms, like "ATM machine" or "PIN number". My
apologies for any annoyance this may have caused.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon
  #109  
Old June 6th 08, 03:05 PM posted to rec.aviation.piloting,rec.aviation.student
Michael[_1_]
external usenet poster
 
Posts: 185
Default CFI oral intel

On Jun 5, 4:01*pm, K l e i n wrote:
If this worked reliably, it would be taught as a standard technique
for inadvertant VFR into IFR excursions. *Hey, just throttle to idle,
hands off and wait for VFR to appear. *But....this is not what is
taught. *Wonder why???


Well, two reasons. One, because there is no guarantee that you will
reach stability in a bank without exceeding Vne (and in fact in many
airplanes you will not - wings or tail will come off). Two, because
recovery from a spiral dive actually takes a fair amount of altitude,
and trying to do it quickly will likely break something as you will be
well above Va.

This is curiously close to a technique for spin recovery that is
taught for certain aerobatic airplanes such as the Pitts and the
Extra, called Muller-Beggs.


Well, OK - but it's not a technique at all. It is simply a
demostration that the airplane will not remain wings level at trim
speed without pilot input for very long, expecially in the event of
engine failure. Quite the contrary, an active recovery will most
likely be necessary.

If the demostration is wrong, then the plane WILL remain wings level
(the way a ram-air parachute will). Now THAT would be useful for
inadvertent IMC encounters. Just tell people to let go of the
controls, and the plane will fly out of it. In fact, that is exactly
what parachutists do if they inadvertently encounter a cloud.

Michael
 




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