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Rolling a 172 - or not



 
 
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  #1  
Old November 11th 03, 01:39 AM
vincent p. norris
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Or the corkscrew motion of an aileron roll must provide enough "outward"
(normal) force to counteract the downward force of gravity.


I think I understand what you're saying, Hamish. It may depend on the
airplane. An SNJ doesn't "corkscrew" very much. It would hardly be
enough to provide positive G in excess of 1.0.

The maneuver starts with a pullup...


It does start with a slight pullup, but then then back-prssure on the
stick is released, to produce what approximates a zero-G situation.
(Don't you do that in an Aerobat?)

I thnk the best description of an aileron roll is to call it a zero-G
maneuver. Not *exactly* zero, to the tenth decimal place, but close to
zero all the way around.

and that pullup is never really lost


I don't understand that. I need to use some right rudder after
passing the half-way point of a left aileron roll, or I'll end up
with the nose pointing down about 20 degrees.

(unlike the slow roll, which can result in negative G's in many aircraft).


I don't understand that, either. You're saying there are airplanes
that can perform a slow roll without experiencing negative Gs?

vince norris
  #2  
Old November 11th 03, 03:29 AM
Hamish Reid
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In article ,
vincent p. norris wrote:

Or the corkscrew motion of an aileron roll must provide enough "outward"
(normal) force to counteract the downward force of gravity.


I think I understand what you're saying, Hamish. It may depend on the
airplane. An SNJ doesn't "corkscrew" very much. It would hardly be
enough to provide positive G in excess of 1.0.


Well, the *whole point* of a textbook aileron roll is to maintain
positive G's -- not 1+ G's, but *positive* -- all the way through the
maneuver, regardless of whether you do it in a Pitts or a puny Aerobat
(the Pitts is a lot more, erm, exciting in this respect :-)).

The maneuver starts with a pullup...


It does start with a slight pullup, but then then back-prssure on the
stick is released, to produce what approximates a zero-G situation.
(Don't you do that in an Aerobat?)


The textbook aileron roll in an Aerobat starts with a shallow dive to
120 KIAS, then a smart pullup to 30 degrees pitch, then a quick
simultaneous full-over on the ailerons and neutralization of the
elevator until pullout. Apply rudder as appropriate... The Pitts is
pretty much the same, but at least with the constant speed prop you
don't have to spend so much time obsessing about the throttle.

I thnk the best description of an aileron roll is to call it a zero-G
maneuver. Not *exactly* zero, to the tenth decimal place, but close to
zero all the way around.


In no plane I've ever done an aileron roll in is the G force "close to
zero all the way around". In fact, it's close to 2G's at two points in
the maneuver (pullup and pullout), and it's probably around .5 to 1 G
over the top.

and that pullup is never really lost


I don't understand that. I need to use some right rudder after
passing the half-way point of a left aileron roll, or I'll end up
with the nose pointing down about 20 degrees.


Remember, half way around your altitude is still quite a bit higher than
it was when you started the maneuver....

(unlike the slow roll, which can result in negative G's in many aircraft).


I don't understand that, either. You're saying there are airplanes
that can perform a slow roll without experiencing negative Gs?


No I'm saying that true textbook slow rolls result in negative G's (and
are nearly impossible in an Aerobat, but never mind...).

Hamish
  #3  
Old November 12th 03, 02:10 AM
vincent p. norris
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An SNJ doesn't "corkscrew" very much. It would hardly be
enough to provide positive G in excess of 1.0.


Well, the *whole point* of a textbook aileron roll is to maintain
positive G's -- not 1+ G's, but *positive* -- all the way through the
maneuver....


Sorry, I didn't express myself well. I meant "It would hardly be
enough to provide positive G in excess of 1.0, enough to negate the
negative 1 G caused by gravity, plus a bit more to make it a positive
G maneuver."

BTW, I looked again at a tape of Tex Johnston's rolls, going and
coming. I cannot detect any "corkscrewing."

regardless of whether you do it in a Pitts or a puny Aerobat
(the Pitts is a lot more, erm, exciting in this respect :-)).


I'm sure it is. I've had a little time in a friend's Starduster 2
but never had the pleasure of flying a Pitts.

It does start with a slight pullup, but then then back-prssure on the
stick is released, to produce what approximates a zero-G situation.
(Don't you do that in an Aerobat?)


The textbook aileron roll in an Aerobat starts with a shallow dive to
120 KIAS, then a smart pullup to 30 degrees pitch, then a quick
simultaneous full-over on the ailerons and neutralization of the
elevator until pullout. Apply rudder as appropriate...


I would agree with that, except I neutralize the elevator THEN begin
the roll.

I don't think of the pullup as part of the maneurver, but as
"preparation" for it.

In fact, it's close to 2G's at two points in
the maneuver (pullup and pullout), and it's probably around .5 to 1 G
over the top.


I don't think of the pullup as part of the maneurver, but as
"preparation" for it. I don't pull up that sharply, and if I have to
"pull out" at the end, I figure I didn't do it right.

If by "over the top" you mean when 180 degrees inverted, I find that
very hard to imagine, based solely on my experience. (I've never
flown an airplane with a G-meter.) I don't hang on the seat belt, as
in a slow roll, but I feel a bit "weightless." I don't seem to be
pushing down (up?) on the seat very hard.

Remember, half way around your altitude is still quite a bit higher than
it was when you started the maneuver....


Yes, I think the airplane follows something like a "ballistic curve"
during the maeuver. Certainly, it gets dang little vertical lift as
it rolls past the 90 degree and 270 degree points.

Despite the fact that the nose is pointed up slightly, the airplane is
essentially "falling" and thus it, and whatever is in it, is
experiencing zero Gs. (One G from gravity, counteracted by one G from
the accelleration.)

vince norris
  #4  
Old November 12th 03, 02:49 AM
Hamish Reid
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In article ,
vincent p. norris wrote:

An SNJ doesn't "corkscrew" very much. It would hardly be
enough to provide positive G in excess of 1.0.


Well, the *whole point* of a textbook aileron roll is to maintain
positive G's -- not 1+ G's, but *positive* -- all the way through the
maneuver....


Sorry, I didn't express myself well. I meant "It would hardly be
enough to provide positive G in excess of 1.0, enough to negate the
negative 1 G caused by gravity, plus a bit more to make it a positive
G maneuver."


This is a little frustrating -- the standard aileron roll is done to
cause continuous positive G's. That's an *aim* of aileron rolls. And the
net G forces don't have to be more than 1, just enough to cause *net*
positive G forces on the pilot 9and engine, etc.). That's the
*definition* of a positive G maneuver.

This started when you stated that aileron rolls don't cause positive G's
all the way around, -- and that's just wrong, unless by "aileron roll"
you mean something different from what the IAC, various texts, etc., all
mean by the term.

BTW, I looked again at a tape of Tex Johnston's rolls, going and
coming. I cannot detect any "corkscrewing."


I can't comment on that except to say the corkscrewing is not always
obvious, especially from the ground... (I've never seen the videos, if
you're talking about the Dash-80 "barrell roll").

regardless of whether you do it in a Pitts or a puny Aerobat
(the Pitts is a lot more, erm, exciting in this respect :-)).


I'm sure it is. I've had a little time in a friend's Starduster 2
but never had the pleasure of flying a Pitts.

It does start with a slight pullup, but then then back-prssure on the
stick is released, to produce what approximates a zero-G situation.
(Don't you do that in an Aerobat?)


The textbook aileron roll in an Aerobat starts with a shallow dive to
120 KIAS, then a smart pullup to 30 degrees pitch, then a quick
simultaneous full-over on the ailerons and neutralization of the
elevator until pullout. Apply rudder as appropriate...


I would agree with that, except I neutralize the elevator THEN begin
the roll.


Well, I'm lucky if I can get it all done at the same time :-).

I don't think of the pullup as part of the maneurver, but as
"preparation" for it.


It's a necessary part of achieving that ballistic corkscrew motion --
and (speaking from dumb experience) if you don't do the pullup properly,
you can end up in something more akin to a split-S or a nasty dive off
the end of the "roll", and / or a great deal of lost altitude.

In fact, it's close to 2G's at two points in
the maneuver (pullup and pullout), and it's probably around .5 to 1 G
over the top.


I don't think of the pullup as part of the maneurver, but as
"preparation" for it. I don't pull up that sharply, and if I have to
"pull out" at the end, I figure I didn't do it right.


Well, the standard aileron roll typically has you pointing down at the
ground at much the same pitch at the 360 degree point that you started
the roll from (as a consequence of the corkscrew motion), so if you
don't do the pullup, you find yourself gaining speed very rapidly...

If by "over the top" you mean when 180 degrees inverted, I find that
very hard to imagine, based solely on my experience. (I've never
flown an airplane with a G-meter.) I don't hang on the seat belt, as
in a slow roll, but I feel a bit "weightless." I don't seem to be
pushing down (up?) on the seat very hard.


For it to be a positive G maneuver, you don't have to be pushed down
very hard. Most people probably think it's negative G's when in fact
it's just reduced G's. Negative G's mean, yes, you're pressing up
against the straps....

Remember, half way around your altitude is still quite a bit higher than
it was when you started the maneuver....


Yes, I think the airplane follows something like a "ballistic curve"
during the maeuver.


Indeed -- the ballistic corkscrew curve is part of the definition of the
aileron roll I gave from Szurovy and Goulian earlier in this thread.
It's that motion that makes it a positive G maneuever. If, like me on a
typical day, you screw up and use the elevator or rudder wrongly, you
can certainly make it a negative G maneuver, but it stops being a real
aileron roll at that point (and starts becoming a cause for quick
roll-out-of-trouble action :-)).

Certainly, it gets dang little vertical lift as
it rolls past the 90 degree and 270 degree points.


It's not really supposed to.

Despite the fact that the nose is pointed up slightly, the airplane is
essentially "falling" and thus it, and whatever is in it, is
experiencing zero Gs. (One G from gravity, counteracted by one G from
the accelleration.)


No, the plane is experiencing *positive* G's in a decent aileron roll.
It's already starting to dive off the top at this point. Or should be,
if you're doing it right...

Hamish
  #5  
Old November 14th 03, 04:22 AM
vincent p. norris
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Sorry, I didn't express myself well. I meant "It would hardly be
enough to provide positive G in excess of 1.0, enough to negate the
negative 1 G caused by gravity, plus a bit more to make it a positive
G maneuver."


This is a little frustrating -- the standard aileron roll is done to
cause continuous positive G's. That's an *aim* of aileron rolls.


I'm not trying to frustrate you, Hamish, but I don't agree with that.

I don't know if the aileron roll has any "purpose" or "aim" except to
have a little fun, and perhaps impress people who don't know how easy
and undemanding it is. It also puts minimum stress on the airplane.

Although an aileron roll can be done well, or badly, it's not a
precision maneuver. It wasn't even taught in navy flight training when
I went through. We learned to do slow rolls and barrel rolls to very
precise, very exacting, criteria, because it was *hard* to do them
that well, for a young pilot, and thus they developed our
stick-and-rudder skills.

And the net G forces don't have to be more than 1, just enough to cause *net*
positive G forces on the pilot 9and engine, etc.). That's the
*definition* of a positive G maneuver.


That's what I said, above. But if an airplane is in inverted flight,
it takes at least 1.000001 positive Gs caused by acceleration to
overcome the negative G caused by gravity and produce a G sum that is
positive.

This started when you stated that aileron rolls don't cause positive G's
all the way around,


IIRC, I responded to a posting that said it was a "one G" maneuver,
which is what I disagreed with. Perhaps my memory is faulty on that
score.

I can't comment on that except to say the corkscrewing is not always
obvious, especially from the ground...


Seems to me that enough corkscrewing to produce at least 1 G of
accelleration when the airplane is inverted would be noticeable.
Think about what it takes to produce one G of acceleration in other
maneuvers.

(I've never seen the videos, if you're talking about the Dash-80

"barrell roll").

Yes, that's the one. I've read Tex Johnston's book, and know it is
described there as a "barrel roll" and a "one G" maneuver. I strongly
suspect that wording was provided by the "ghost writer" who thought it
would sound impressive to the reading audience.

Whether one accepts the definition of a barrel roll supplied by Bob
Moore, a fellow naval aviator, or by, IIRC, "Big John," which is
radically different, each one produces very noticeable "corkscrewing"
and thus cannot be a one G maneuver.

The textbook aileron roll in an Aerobat starts with a shallow dive to
120 KIAS, then a smart pullup to 30 degrees pitch, then a quick
simultaneous full-over on the ailerons and neutralization of the
elevator until pullout. Apply rudder as appropriate...


I would agree with that, except I neutralize the elevator THEN begin
the roll.


Well, I'm lucky if I can get it all done at the same time :-).


OK, I'll accept that; in any case, the stick is "unloaded" while the
airplane is rolling.

I don't think of the pullup as part of the maneurver, but as
"preparation" for it.


It's a necessary part of achieving that ballistic corkscrew motion --


In an Aerobat, I suppose it is necessary. In a more powerful
airplane, it is not. For example, an airplane capable of a steep
climb can nose over toward level flight and when his nose reaches the
desired point above the horizon, do an aileron roll. In fact, he can
do an aileron roll going straight up.

Similarly, low-powered airplanes, including the SNJ, generally need
to lower the nose to pick up a little speed to begin a loop. But that
is not part of the maneuver; more pwerful airplanes can do a loop
without lowering the nose, and it is perfectly correct loop.

Indeed -- the ballistic corkscrew curve


That sounds like a contradiction. As I understand it, "ballistic"
refers to the trajectory of a shell after it leaves the muzzle of a
cannon, say, and is affected (in theory) only by gravity but in
actuality by air resistance, etc. It does not, so far as I know,
"corkscrew."

I believe the "Vomit Comet" describes a ballistic curve to produce a
weightless condition for budding astronoauts. No corkscrewing is
involved.

Certainly, it gets dang little vertical lift as
it rolls past the 90 degree and 270 degree points.


It's not really supposed to.


That's right.

Despite the fact that the nose is pointed up slightly, the airplane is
essentially "falling" and thus it, and whatever is in it, is
experiencing zero Gs. (One G from gravity, counteracted by one G from
the accelleration.)


No, the plane is experiencing *positive* G's in a decent aileron roll.
It's already starting to dive off the top at this point. Or should be,
if you're doing it right...


I'm afraid I disagree with that, too, Hamish. As I said eaarlier, if I
end up in a dive, I conclude I did it wrong.

I don't think we're ever going to agree about this, Hamish, so we
might as well just agree to disagree.

vince norris
  #6  
Old November 14th 03, 05:24 AM
Hamish Reid
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In article ,
vincent p. norris wrote:

[...]

And the net G forces don't have to be more than 1, just enough to cause
*net*
positive G forces on the pilot 9and engine, etc.). That's the
*definition* of a positive G maneuver.


That's what I said, above. But if an airplane is in inverted flight,
it takes at least 1.000001 positive Gs caused by acceleration to
overcome the negative G caused by gravity and produce a G sum that is
positive.

This started when you stated that aileron rolls don't cause positive G's
all the way around,


IIRC, I responded to a posting that said it was a "one G" maneuver,
which is what I disagreed with. Perhaps my memory is faulty on that
score.


Erm, well, we can stop right there, because that's what the problem
is... here's your article and my initial response (my stuff with the
single ""):

In article ,

vincent p. norris wrote:

Not if you maintain positive G all the way around (as in aileron

roll).

You don't have positive G all the way around in an aileron roll.


In a properly done aileron roll you certainly do...


To maintain positive G, you need a barrel roll.


Or an aileron roll. Were you thinking of a slow roll?



And later in the thread I also explicitly asked whether you meant a "1G
maneuver" rather than a "positive G" maneuver. In both cases you said no.

Oh well. I think I kinda suspected this -- if you'd actually said it
wasn't a *1 G* maneuver, I'd have agreed wholeheartedly. But to make the
blanket statement that you don't have positive G all the way around in
an aileron roll (or any aileron roll), well, that ain't right....

Hamish
  #7  
Old November 15th 03, 02:31 AM
vincent p. norris
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This started when you stated that aileron rolls don't cause positive G's
all the way around,


IIRC, I responded to a posting that said it was a "one G" maneuver,
which is what I disagreed with. Perhaps my memory is faulty on that
score.


Erm, well, we can stop right there, because that's what the problem
is... here's your article and my initial response (my stuff with the
single ""):

In article ,

vincent p. norris wrote:

Not if you maintain positive G all the way around (as in aileron

roll).

You don't have positive G all the way around in an aileron roll.


I believe that's essentially true.

As I said more recently,

But if an airplane is in inverted flight,
it takes at least 1.000001 positive Gs caused by acceleration to
overcome the negative G caused by gravity and produce a G sum that is
positive.


And I said that I have serious doubt there is enough "corkscrewing" in
the aileron rolls I've done, and seen others do, to produce more than
about 1 G. Maybe a bit less.

I would not suggest there are *noticeable* negative Gs, like a slow
roll; as I said, I don't hang on my seat belt. I think that halfway
through the roll, the airplane is *essentially* (i.e., for all
practical purposes) in a zero-G condition. I tried to say that
before, but perhaps I didn't say it well enough.

For that matter, when I "unload" the stick to begin the roll, I am
just about at zero Gs. I *attempt* to create a zero-G condition. I
believe that is the correct procedure. I'm sure I can't produce
exactly zero Gs every time, to several decimal places; no doubt I
sometimes produce a slight negative-G condition, sometimes a slight
positive-G condition.

Apparently you do not agree with that. I'm not suggesting you ought
to change the way you do aileron rolls, or think about them; I am
simply saying what I believe to be the case.

I've expressed my views several times, so I don't think there is much
to be gained by my repeating them again. We can just agree to
disagree.

Oh well. I think I kinda suspected this -- if you'd actually said it
wasn't a *1 G* maneuver, I'd have agreed wholeheartedly.


I imagine you would have. On that subject:

In a protracted discussion with a friend who is an aeronautical
engineer prof, specializing in aerodynamics, a year or so, in reaction
to an earlier thread on this newsgroup, we came to this conclusion:

"There is no such thing as a one-G maneuver."

An airplane flying straight and level, at constant speed, on a
smooth-air day, experiences one positive G.

ANY departure from that condition changes the G, either in amount, or
direction, or both.

Yet we often hear about "one G maneuvers." I think people use the
term to any maneuver that does not produce *palpable* G forces on
their bodies.

In that peculiar, inaccurate, sense, I suppose I would agree with the
statement that an aileron roll is a "one G maeuver."

vince norris
 




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