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  #91  
Old June 4th 08, 04:41 PM 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
:

In rec.aviation.student Gezellig wrote:
Michael Ash pretended :
In rec.aviation.student Gezellig wrote:
On Fri, 30 May 2008 01:20:04 -0500, Michael Ash wrote:

Joking aside, if your straps were loose enough that you could
slump forward, that *would* affect your CG which would in turn
affect your trimmed airspeed.

There's another issue that I just thought of that I don't think
anyone has mentioned yet, though. Won't you get into a graveyard
(bad terminology for this scenario, as you're already dead)
spiral? After all, if you could stay straight and level just by
taking your hands off the controls you wouldn't need to fear IMC
with no gyroscopic instruments. So it seems that if you start high
enough, the correct answer to this question would be whatever the
terminal velocity of your fuselage is without its wings. Am I
off base here?

You fly until gassless, stall, nose down, then descend too rapidly,
striking the ground with the wings ripped off. Works for me.


You don't stall, because when the engine quits the airplane will
start to descend, maintaining approximately the original airspeed.


At what point do you expect to lose the wings via "the correct answer
to this question would be whatever the terminal velocity of your
fuselage is without its wings."?


If you enter a spiral dive as I surmised, the wings fall off either
when you exceed Vne or when you exceed the maximum loading the wings
can support, whichever comes first. However it would seem that whether
this happens or not will depend on the airplane in question.


Well, the wings won't come off as you exceed VNE. You have a good 10% on
top of that before anything will happen.
Something nasty will at the load limit, though. Not the published one,
of course, but at 50% over that. At the published load limit you are
guarunteed that the airplane will not permanently deform. 50% over that
you're guaunteed it will remain in one piece. Over that you're on your
own. It;s not quite as tidy as all that, though and with most light
planes it's probably flutter that's going to pull it apart and that will
probably be brought on by a combination of load and speed. This is not
to say it's safe to operate at or near the red line or load limit.
It isn't.



Bertie


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  #92  
Old June 4th 08, 04:46 PM posted to rec.aviation.piloting,rec.aviation.student
Bertie the Bunyip[_25_]
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Posts: 3,735
Default CFI oral intel

Michael wrote in
:

On May 30, 6:25*pm, Dudley Henriques wrote:
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.


The positive static stability, when present, is slight. More to the
point, it is only slightly positive around the zero point. Once an
excursion in roll gets past a few degrees, the stability is negative
(for a while) and the new stability point is in a significant bank (or
non-existent).

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.


And that's the point. Dynamic stability is generally mildly negative,
and once a slight displacement from zero occurs, the restoring force
from the mild positive static stability starts a very mild oscillation
that will eventually take you outside the area of positive static
stability. Once that occurs, dynamic stability is indeed no longer
important.

Even a plane with comparatively good lateral stability will eventually
wind up in a spiral once something like turbulence disturbs it. In
some cases it won't happen - combine a very stable plane with very
smooth air, and it might fly wings level for a long time. It has
happened. Also note that the stability improves with lower weight
(this is true of the longitudinal axis as well - that's why the
allowable cg range on most light airplanes is wider at lower weights)
so we do have these stories of planes without pilots flying just fine
for hours.

I recall one particular sad incident where a Pilatus Porter dropping
jumpers lost the yoke - it literally came off in the pilot's hands.
The pilot elected to bail out (which was, IMO, the wrong call - a
plane can be landed with rudder, throttle, and trim). His parachute
malfunctioned, and the pilot died. The plane eventually ran out of
fuel and 'landed' in a field. After a few minor repairs, it was flown
out.

These things do happen, but they are the exception. Under most normal
conditions, the combination of neutral or weakly positive static
stability and negative dynamic stability in the lateral axis will
eventually put the plane into a spiral.

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.


Sure - but that source will be found in the normal turbulence found on
most days. There are also additional factors.

First off, any side-by-side airplane with only one person on board is
going to be slightly out of balance laterally. Any plane with fuel
feed from a single wing tank, or a less-than-perfect 'both' feed
(which is most of them) will develop an imbalance. So what we need to
postulate is a plane that is tandem seating with a header tank (like
an old-style Champ or maybe a Cub) and then, on a really smooth day,
it might actually stay wings level.

If the aircraft has dihedral, it has positive static lateral
stability.


That's not necessarily the case. There can be other factors that
affect stability that would overcome a small amount of dihedral.
Remember that most airplanes have strong yaw stability, and that
weakens roll stability because yaw and roll are strongly coupled.

That's interesting. I never knew that. A pretty good primer on
stabilit

y 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.


I also like the site. The particular link includes much of what I
posted, including the assertion that most light planes left to
themselves will wind up in a spiral.

Of course as you mentioned elsewhere, this isn't the sort of
discussion you would have with the average FAA ops inspector. I knew
a couple who would have appreciated it in Houston. Neither one is
still with the FAA.


Yeah, sadly this is true. I'm just reading up to renew my instructor
cert and have been reading some of the circulars on the FAAs website.
Most of them are excellent, but I was just reading one about stalling
cross controlled, for instance and it's crap.. Having said that, I
suppose it's all good enough for basic private knowledge..
Fortunately, the examiner falls into the pragmatic category.

Bertie

  #93  
Old June 4th 08, 04:48 PM posted to rec.aviation.piloting,rec.aviation.student
Bertie the Bunyip[_25_]
external usenet poster
 
Posts: 3,735
Default CFI oral intel

BTW, just about any old ragbag will fly around like a free flight airplane
until they run out of gas. For that matter so will most cessnas and the
like.



Bertie
  #94  
Old June 4th 08, 09:17 PM posted to rec.aviation.piloting,rec.aviation.student
More_Flaps
external usenet poster
 
Posts: 217
Default CFI oral intel

On Jun 4, 9:38*pm, Michael Ash wrote:
In rec.aviation.student Gezellig wrote:





Michael Ash pretended :
In rec.aviation.student Gezellig wrote:
On Fri, 30 May 2008 01:20:04 -0500, Michael Ash wrote:


Joking aside, if your straps were loose enough that you could slump
forward, that *would* affect your CG which would in turn affect your
trimmed airspeed.


There's another issue that I just thought of that I don't think anyone has
mentioned yet, though. Won't you get into a graveyard (bad terminology for
this scenario, as you're already dead) spiral? After all, if you could
stay straight and level just by taking your hands off the controls you
wouldn't need to fear IMC with no gyroscopic instruments. So it seems that
if you start high enough, the correct answer to this question would be
whatever the terminal velocity of your fuselage is without its wings. Am I
off base here?


You fly until gassless, stall, nose down, then descend too rapidly,
striking the ground with the wings ripped off. Works for me.


You don't stall, because when the engine quits the airplane will start to
descend, maintaining approximately the original airspeed.


At what point do you expect to lose the wings via "the correct answer
to this question would be whatever the terminal velocity of your
fuselage is without its wings."?


If you enter a spiral dive as I surmised, the wings fall off either when
you exceed Vne or when you exceed the maximum loading the wings can
support, whichever comes first. However it would seem that whether this
happens or not will depend on the airplane in question.


If the plane is in a steady dive at 2x VNE what is the wing loading?
VNE may be set by srface instability (flutter) or perhaps engine
overspeed but is not set by wing loading -that is Va -at least that's
my understanding.

Cheers
  #95  
Old June 4th 08, 09:26 PM posted to rec.aviation.piloting,rec.aviation.student
Bertie the Bunyip[_25_]
external usenet poster
 
Posts: 3,735
Default CFI oral intel

More_Flaps wrote in
:

On Jun 4, 9:38*pm, Michael Ash wrote:
In rec.aviation.student Gezellig wrote:





Michael Ash pretended :
In rec.aviation.student Gezellig wrote:
On Fri, 30 May 2008 01:20:04 -0500, Michael Ash wrote:


Joking aside, if your straps were loose enough that you could
slump forward, that *would* affect your CG which would in turn
affect your trimmed airspeed.


There's another issue that I just thought of that I don't think
anyon

e has
mentioned yet, though. Won't you get into a graveyard (bad
terminolog

y for
this scenario, as you're already dead) spiral? After all, if you
coul

d
stay straight and level just by taking your hands off the
controls yo

u
wouldn't need to fear IMC with no gyroscopic instruments. So it
seems

that
if you start high enough, the correct answer to this question
would b

e
whatever the terminal velocity of your fuselage is without its
wings.

Am I
off base here?


You fly until gassless, stall, nose down, then descend too
rapidly, striking the ground with the wings ripped off. Works for
me.


You don't stall, because when the engine quits the airplane will
start

to
descend, maintaining approximately the original airspeed.


At what point do you expect to lose the wings via "the correct
answer to this question would be whatever the terminal velocity of
your fuselage is without its wings."?


If you enter a spiral dive as I surmised, the wings fall off either
when you exceed Vne or when you exceed the maximum loading the wings
can support, whichever comes first. However it would seem that
whether this happens or not will depend on the airplane in question.


If the plane is in a steady dive at 2x VNE what is the wing loading?
VNE may be set by srface instability (flutter) or perhaps engine
overspeed but is not set by wing loading -that is Va -at least that's
my understanding.


That's right, but the tendency to flutter is exacerbated by load. So, if
you're over redline and you're loading the wing, flutter will occur at a
lower speed than if that surface was unloaded. Flutter is all to do with
the elastic properties of the flight surface, so if it's loaded up
you're exciting the cycle.



Bertie

  #96  
Old June 4th 08, 11:26 PM posted to rec.aviation.piloting,rec.aviation.student
Hilton
external usenet poster
 
Posts: 118
Default CFI oral intel

Michael wrote:
I recall one particular sad incident where a Pilatus Porter dropping
jumpers lost the yoke - it literally came off in the pilot's hands.
The pilot elected to bail out (which was, IMO, the wrong call - a
plane can be landed with rudder, throttle, and trim). His parachute
malfunctioned, and the pilot died.


I'll file this under: "You know you're having a bad day when..."

Hilton


  #97  
Old June 5th 08, 04:11 AM posted to rec.aviation.piloting,rec.aviation.student
Gezellig[_2_]
external usenet poster
 
Posts: 45
Default CFI oral intel

on 6/4/2008, Dudley Henriques supposed :
http--soar.wichita.edu-dspace-bitstream-10057-754-1-t05045.pdf.webloc


Linky no worky


  #98  
Old June 5th 08, 04:33 AM posted to rec.aviation.piloting,rec.aviation.student
Michael Ash
external usenet poster
 
Posts: 309
Default CFI oral intel

In rec.aviation.student More_Flaps wrote:
If you enter a spiral dive as I surmised, the wings fall off either when
you exceed Vne or when you exceed the maximum loading the wings can
support, whichever comes first. However it would seem that whether this
happens or not will depend on the airplane in question.


If the plane is in a steady dive at 2x VNE what is the wing loading?
VNE may be set by srface instability (flutter) or perhaps engine
overspeed but is not set by wing loading -that is Va -at least that's
my understanding.


In a steady *spiral* dive the wing loading will be determined by your bank
angle. I think you may have misread my sentence; I did not mean to imply
that having the wings come off due to excess loading was in any way
related to Vne, it's just due to an ever-tightening spiral, if you
actually get into one and you reach the excess wing loading before you
reach excess speed.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon
  #99  
Old June 5th 08, 09:03 AM posted to rec.aviation.piloting,rec.aviation.student
Hilton
external usenet poster
 
Posts: 118
Default CFI oral intel

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)

Hilton


  #100  
Old June 5th 08, 09:40 AM posted to rec.aviation.piloting,rec.aviation.student
Michael Ash
external usenet poster
 
Posts: 309
Default CFI oral intel

In rec.aviation.student 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.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon
 




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