Rolling a 172 - or not

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