Rolling a 172 - or not

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

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

In article , Big John wrote:
From these figures you can see that it would be touch and go if you
rolled the bird inverted. Of course the figures given are not ultimate
so might only bend things a little )

But you'd have to really blow an aileron roll to pull enough negative
G to even reach the limit, let alone exceed it. So I dispute the
assertion that 99 times out of 100, you'd overstress a C172 doing
an aileron roll!

In article , Big John wrote:
On a 172,. I'd do a barrel roll in the bird but not a slow roll or
aileron roll .Either would over stress the bird 99 times out of a
hundred.


--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"

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

In article , vincent p norris wrote:
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.

Correct me if I'm wrong (I've not had access to an aerobatic plane for
over a year) but the way I was taught to do them at least, you're
following essentially a ballistic trajectory whilst doing the roll,
so feel zero G as you go through inverted. That's what it felt like
to me at least - I never hung on the straps during an aileron roll
either.

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"

Correct me if I'm wrong (I've not had access to an aerobatic plane for
over a year) but the way I was taught to do them at least, you're
following essentially a ballistic trajectory whilst doing the roll,
so feel zero G as you go through inverted. That's what it felt like
to me at least - I never hung on the straps during an aileron roll
either.

I can't "correct" you, Dylan; I agree with you.

vince norris