Rolling a 172 - or not

In article ,
Robert Moore wrote:


No John, I didn't talk or write about...... I just quoted from the
acro.harvard.edu web site and William Kershner's fine book.
You may not have seen the picture from the Kershner book when you
wrote this, but write back when you have seen the barrel roll as
described by someone who is considered an authority in the field.

I've been shown two different ways to do a barrel roll.

The first was to pick a reference off one wingtip. Start pulling and
rolling toward the reference point. Once inverted you would be 90
degrees off original heading (pointed at the ref point). You continue
to roll and pull returning to the original heading.

The second way was to pick a reference point over the nose. Put the
nose slightly to one side of that point then roll and pull keeping the
nose the same distance from the reference point.

The first is the big loopy typy barrel roll - and a lot of fun to do.

The second is a much tighter roll without any loop.

--
Dale L. Falk

There is nothing - absolutely nothing - half so much worth doing
as simply messing around with airplanes.

http://home.gci.net/~sncdfalk/flying.html

Does the water spill because the aileron roll is *not*
a positive-G maneuver, or because the forces on it are not balanced
laterally or longitudinally? (I can't do the experiement because there's
nowhere to put the glass in the plane I fly).

If you can tie or tape a string with a small weight on the end to the
top of your canopy or windshield, you could use that.

Let's take a snapshot of the airplane at the moment it is inverted.

At that instant, (as at all other times), gravity is exerting a force
of 1 G on the airplane, down toward the earth--in other words "upward"
in relation to the airplane. What we normally call one negative G.

Now, as Einstein pointed out, "acceleration" is a force
indistinguishable from gravity. In this context, acceleration does
not mean "increasing speed," it means "changing direction." (As the
acceleration of a steep turn exerts Gs on the airplane.)

To counteract the one negative G now being exerted on the airplane by
gravity, plus a little more to make it a positive G maneuver, we must
have acceleration, of the sort experienced when pulling out of a dive
or in a loop--although not that much. That is, the nose of the
airplane must "rise"--in relation to the airplane-- to provide more
than 1G of positive acceleration.

If the stick is over to one side, but not pulled back, how is that
acceleration provided? I do not see the nose of the airplane "rise"
while I'm inverted in an aileron roll.

Or do it in a Cessna Aerobat -- which requires a positive G force to
keep the oil and fuel running. I can get the engine to stutter in a
second or two in a slow roll (more like a slowish roll in an Aerobat,

I've never flown an Aerobat, but if it aileron rolls as fast as an
SNJ, then the engine won't stutter simply because the maneuver doesn't
last long enough. No SNJ I've flown stutters even in a properly done
slow roll--in which the stick is moved *forward* to keep the nose up
(in relation to the horizon) while inverted.

vince norris

Place a glass of water atop the instrument
panel and execute a steep turn. It won't stay there,

It should!!! If not, you're not using the controls properly.
I teach my students to execute co-ordinated steep turns,
doesn't everyone do it that way???

The point is that it will likely move, not because there is a negative G
situation, but because it takes very little lateral G force to knock it off.

Seems to me it would take MORE lateral force to knock it off than
when the airplane is at rest on the ground, because in a coordinated
tight turn, or a loop, additional Gs are causing the glass to press
down harder on the surface.

vince norris

1. A 'barrel roll' is a roll where (if done properly) you as a
passenger, with your eyes closed, can not tell you did a roll. The
ball stays centered and if one 'G' is maintained,

I suspect there is more than one definition of a "barrel roll."

The ex-Air Force P-47 pilot I've flown with does a peculiar corkscrew
barrel roll that bears virtually no resemblance to the one I was
taught at Pensacola.

The barrel roll I was taught, and like to do, cannot be done at a
constant 1 G.

There is positive acceleration all the way around (see my post just
above), that is, the stick is back, and the nose keeps coming "up,"
all the way around.

(The ball is in the center all the way around, too, and a glass of
water will not spill.)

That positive acceleration means that more than 1 G is experienced
during those parts of the roll in which the airplane is essentially
upright.

vince norris

Big John wrote

Talk me through a loop doing a Barrel Roll. We must be using
different words or maneuvers?

John, have you looked at the barrel roll picture that I e-mailed
you and posted on alt.binaries.pictures.aviation?
If not, further discussion will be of no use.

Have you checked the "Willian Kershner" web site and read the
author's credentials?
If not, you just leave us wondering "who-the-hell" is Big John,
and what credence should we give to his unsupported assertions?
Mr. Kershner owns and operates an Aerobatic Flight School and
has authored the book, "The Basic Aerobatic Manual" which as he
points out, was an offshoot (with permission) of the manual he
helped write for Cessna Aircraft in 1969.

First let me try a different set of words for a GA barrel roll.

Here are William Kershner's words that accompanied the diagram of
the barrel roll in his The Flight Instructor's Manual in which he
devotes all of chapter 5 (66 pages) to aerobatic instruction.

Quote..............or should I say OCR'ed

THE BARREL ROLL
• Preparation. It's almost impossible to draw a barrel roll
on the chalkboard, but a model will give the desired results.
Have the trainee study the references.

•Explanation. The barrel roll is a precise maneuver in which
the airplane is rolled around an imaginary point 45° to
the original flight path. A positive-g level is maintained
throughout the maneuver, and the ball in the turn indicator
should stay in the middle.

You may wonder why the barrel roll is taught this late,
since it appears to be so simple. Well, it is a precise maneuver
requiring particular airplane attitudes at particular reference
points, which is difficult for the average trainee to do properly
at first.

This maneuver might be considered an exaggeration of the
wingover, but instead of starting to shallow the bank at the 90°
position, the pilot must steepen it continually until the airplane
has rolled 360° and is back on the original heading. The rate of
roll must be much greater than that used for the wingover
because the airplane must be in a vertical bank at 45° of turn,
and it must be inverted at 90° of turn. The roll and turn is
continued until the airplane is headed in the original direction with
the wings level. Compare the barrel roll in Fig. 23-12 with the same
view of the wingover in Fig. 20-7.

From behind the maneuver looks as though the airplane is being
flown around the outside of a barrel. This is a very good maneuver
for gaining confidence and keeping oriented while flying inverted in
balanced flight.
Good coordination is required to do the barrel roll properly and
the trainee will show an improvement in that area after a session of
barrel rolls.

The barrel roll is generally more difficult and precise than the
aileron roll, and he may have to work on this one awhile.

Why-
The barrel roll is one of the best maneuvers for improving
orientation.

Unlike the other acrobatic maneuvers covered thus far, the barrel
roll requires a constantly changing bank and pitch (with attendant
changing airspeed) and a radical change in heading (90°) while the
airplane is rolling. The average trainee probably will be looking at
the wing tip at a time when he should be checking the nose, or vice
versa.
When he is able to stay well oriented in the barrel roll, he is ready
to move on to the reverse Cuban eight or reverse cloverleaf.

How-
You might use the following explanation, or develop your own:
(1) Make sure the area is clear, then pick a reference on the
horizon off the wing tip as in the wingover and lazy eight.
(2) Set the throttle to low cruise rpm and ease the nose over to
pick-up about 10 K more than used for the wingover or set up
the airspeed used for a loop, whichever is higher. Power
adjustment should not be necessary during the maneuver. You
might have some of your sharper trainees apply full power as
the airplane approaches inverted and then remind them to
throttle back as the airspeed picks up in the last part of the
maneuver.
(3) Smoothly pull the nose up and start a coordinated climbing turn
(note that it will have to be at a much faster rate than was
used for the wingover) toward the reference point. (Assume that
at first the roll will be to the left.)
(4) When the nose is 45° from the original heading, it should be
at its highest pitch attitude and the left bank should be
vertical.
(5) When the nose is at 90° from the original heading, you should
be looking directly at the reference point that was originally
off the wing tipfrom a completely inverted position
(momentarily).
(6) When the airplane heading is again 45° from the original, the
bank is vertical but you will be in a right bank as far as the
ground is concerned; that is, the right wing is pointing
straight down at this instant of roll. The nose will be at its
lowest pitch attitude at this point.
(7) The roll is continued to wings-level flight as the nose is
raised back to the cruise attitude.

The maneuver must be symmetrical; the nose must go as far above the
horizon as below. The barrel roll requires definite checkpoints to
ensure that the airplane is at the correct attitude throughout. It is
interesting to note that if the barrel roll is to the left, all of
the airplane's path is to the left of the original line of flight and
the airplane's nose is always pointed to the left of the original
flight line (until it merges again at the completion of the
maneuver). The opposite occurs, naturally, for the barrel roll to the
right.

Another method of doing a barrel roll is to pick a reference on the
horizon, turn the airplane 45° to the reference point, and proceed to
make a wide roll around this real point. One disadvantage of this
method for the newcomer is that it depends on the pilot's own
judgment of how large the orbit around the point should be. For an
introduction to the maneuver, the first method is usually better, but
you may prefer the second and work out your own techniques of
instructing it.

Demonstration.
Try not to lose the reference point yourself while demonstrating
this one. You may find your explanation is not keeping up with the
airplane, which usually results in sputtering and stuttering while
the maneuver proceeds to its foregone conclusion -and then you have
to do a new demonstration. Don't worry, this will happen plenty of
times during your career of instructing aerobatics -when your mouth
can't keep up with your brain or the maneuver-and it can ease tension
if you react to it with humor.

Usually the trainee is surprised to see the same wing tip back on the
reference point and may confess that, like the first snap roll, the
earth and sky were blurred and he had no idea where the reference was
during the maneuver.

Practice.
You may rest assured the trainee will "lose" the reference point
during the first couple of barrel rolls. He'll usually stare over the
nose, seeingnothing but blue sky or ground and not really seeing the
point at all.

Common errors during barrel rolls include these:
1. Not pulling the nose high enough in the first 45° of the
maneuver, which means that the highest and lowest nose positions
are not symmetrical to the horizon.
2. Not maintaining a constant rate of roll. Usually things are fine
at the 45° position; the nose is at its highest pitch and the
bank is vertical.
As you approach the position of 90° of turn you will probably
find that he is not going to be completely inverted at that
point and will have to rush things a bit to make it. The usual
reason is that he did not maintain a constant rate of roll.
Remember that the nose is up and the airspeed is slower in this
segment of the maneuver, so the controls must be deflected more
to get the same rate. This is where coordination comes in. Watch
for it in particular.
3. Letting the nose drop after passing the 90° point; losing too
much altitude and gaining excess airspeed.
4. Failure to roll out on the original heading; having the wing tip
well ahead, or well behind, the reference when the maneuver is
completed.

Evaluation and Review.
Review each barrel roll briefly in the air, and have the trainee
use the model on the ground. This one can be hard to "see," so go
over it again as necessary after getting on the ground.

By the time a half-dozen barrel rolls have been practiced, the
average trainee should be oriented throughout the maneuver even
though he may still have minor problems of heading and symmetry.
After a dozen rolls he should be starting to work on a constant roll
rate and starting to ease his heading problems. After several
hundred, he may begin to be satisfied with his barrel rolls but will
realize that constant practice is required.

Unquote.................

But John...you really should look at that picture.

Bob

Dale wrote

The second way was to pick a reference point over the nose. Put
the nose slightly to one side of that point then roll and pull
keeping the nose the same distance from the reference point.

This is what Kershner has to say about the second method.

"Another method of doing a barrel roll is to pick a reference on the
horizon, turn the airplane 45° to the reference point, and proceed to
make a wide roll around this real point. One disadvantage of this
method for the newcomer is that it depends on the pilot's own
judgment of how large the orbit around the point should be. For an
introduction to the maneuver, the first method is usually better, but
you may prefer the second and work out your own techniques of
instructing it."

It should be noted that by using the 45 degree angle to the reference
point, one gets the same maneuver if done properly.

Bob Moore

In article ,
vincent p. norris wrote:

Does the water spill because the aileron roll is *not*
a positive-G maneuver, or because the forces on it are not balanced
laterally or longitudinally? (I can't do the experiement because there's
nowhere to put the glass in the plane I fly).

If you can tie or tape a string with a small weight on the end to the
top of your canopy or windshield, you could use that.

Indeed. And when you do that, you observe positive G's all the way
around an aileron roll (in the aircraft I fly, at least). I do a bit of
aerobatics photography, and I'm absolutely required to be able to
anticipate G forces to keep the camera from smashing into something else
(or myself).

Let's take a snapshot of the airplane at the moment it is inverted.

At that instant, (as at all other times), gravity is exerting a force
of 1 G on the airplane, down toward the earth--in other words "upward"
in relation to the airplane. What we normally call one negative G.

Now, as Einstein pointed out, "acceleration" is a force
indistinguishable from gravity. In this context, acceleration does
not mean "increasing speed," it means "changing direction." (As the
acceleration of a steep turn exerts Gs on the airplane.)

Indeed. And an aircraft in an aileron roll changes direction constantly
as it describes a ballistic corkscrew-like path (S&G).

To counteract the one negative G now being exerted on the airplane by
gravity, plus a little more to make it a positive G maneuver, we must
have acceleration, of the sort experienced when pulling out of a dive
or in a loop--although not that much.

Indeed.

That is, the nose of the
airplane must "rise"--in relation to the airplane-- to provide more
than 1G of positive acceleration.

Or the corkscrew motion of an aileron roll must provide enough "outward"
(normal) force to counteract the downward force of gravity. Which it
does.... We're not doing a slow roll here, so the longitudinal axis of
the aircraft describes a circle around the axis of the maneuver itself.
The maneuver starts with a pullup, and that pullup is never really lost.

If the stick is over to one side, but not pulled back, how is that
acceleration provided? I do not see the nose of the airplane "rise"
while I'm inverted in an aileron roll.

At the start of most aileron rolls the stick *is* pulled back -- to get
you to the magic 30 degree point with a small 2G pullup. Then by the top
of the roll the nose is trending down, with enough normal force from the
corkscrew motion to keep the G's positive. Once again, as described by
Szurovy & Goulian (quoted in the bits you snipped) and nearly every text
or reference I can find, and my own experience, a simple aileron roll is
one of the canonical positive G maneuvers (unlike the slow roll, which
can result in negative G's in many aircraft).

Or do it in a Cessna Aerobat -- which requires a positive G force to
keep the oil and fuel running. I can get the engine to stutter in a
second or two in a slow roll (more like a slowish roll in an Aerobat,

I've never flown an Aerobat, but if it aileron rolls as fast as an
SNJ, then the engine won't stutter simply because the maneuver doesn't
last long enough.

*Nothing* in an Aerobat is fast :-). But in fact, since the aileron roll
(as described by S & G, again...) is a positive G maneuver, you can do
it without worrying about the fuel feed (or the oil). You can certainly
screw up an aileron roll and get non-postive G's (as I've discovered
:-)), but it takes extra effort (or forgetting to keep the ailerons
fully deflected...).

No SNJ I've flown stutters even in a properly done
slow roll--in which the stick is moved *forward* to keep the nose up
(in relation to the horizon) while inverted.

Which, if done as slowly as I do them, will result in non-positive
G's... it takes only a second or two to make the Aerobat stutter.

Hamish

Scott Lowrey wrote:
If I'm crusing along at 100 KIAS in a 172 in clear air and I roll left
while maintaining neutral rudder, what will happen if I don't
neutralize the ailerons?


WOW. I was away for several days and I think I'd see two replies to my
post before I left.

Thanks for all the replies - you guys are easy to get going but never
boring... well, usually never. :+)

Anyway, I thought about Vne being a problem later. Seems like the right
thing to do (after drinking my cup of water, tying a string to the
panel, plugging the fuel vents, and hoping I have enough oil) would be
to nose up a bit prior to the roll and push forward while inverted.

I know this isn't the plane for this kind of maneuver and I have no
intention of trying it. Sure would like to do some acro someday,
though. Maybe when I save enough to by that Stearman I've always wanted.

-Scott

Bob

Read Kershner's life story. Note that he left Moffett and crapped out
of the Navy the year I arrived at Moffett to fly All Weather Jet
Fighters (VF-23).

The Navy was just transitioning from Prop Fighters (F4U like he flew
in West Pac, etc) and one of my tasks was to give them the experience
of Air Force Jet Fighter operations including energy management which
was very important in those first generation jet fighters..

Reading his description of life events it seems he pushes the envelope
some like Zzzzom.

I see nothing he has done to warrant your placing so high on a
pedestal. He gives credit to only one document where he lifted some
data/technique. I also detect the wording of other manuals I have seen
through the years that he didn't give credit to.

Of course it may be just how many ways you can say loop?

He says he flies one or two students a month.That's not enough to
maintain proficiency or write from a current background.

You keep asking for my credentials. What do you want, my Military Form
5 where every flight I make in 28+ years is listed. There is at least
one or more pages per month depending on activity and totals well over
350 pages and about 2 1/2 - 3 inches thick weighing 3-4 pounds.

Or my formal education of BS with work on a MS.

Or the Patent number of my patents?

I'm married and have four grown daughters with three grand children
and three great grand children.

I'm over 21 and legal to buy 'booze' so drink Vodka on the rocks.

My GA Flight Logs are pretty thin as I didn't log a lot of the time
because I wasn't trying to build to any number of hours since I had
over 6500 in heavy iron.

It looks like there are several different ideas about acrobatic flyng
on this thread. I've expounded on mine so others can list their way
and I'll set back and might learn somethng??? One is never too old to
learn it is said.

I don't suffer fools but can be moved by facts.

Fly safe and keep the ball in the center unless you are slipping the
excess altitude off on final or landing in a cross wind.


Big John



On Sun, 09 Nov 2003 23:12:40 GMT, Robert Moore
wrote:

Big John wrote

My reference is years and years of doing acrobatics and teaching
same in both conventional aircraft and jets.

Check-out Mr. William Kershner at:

http://www.kershnerflightmanuals.com/

Bob

On Mon, 10 Nov 2003 02:02:01 GMT, Robert Moore
wrote:

----clip----

But John...you really should look at that picture.

----clip----

OK. I reconfigured my computer and subscribed to
"alt.binaries.pictures.avation" and down loaded the last 50 posts and
don't find anything from you.

I'll go back and download everything from day one to look for your
picture and then blow away the other thousands I down loaded.

Since I know what a barrel roll is and how to do same and have done
then for many many years, why should l look at a picture you drew and
if done as described by your expert I seriously doubt if anyone could
fly ???

I think I'll let you experts have the floor to do with as you choose.

I'm scheduled for a kidney x-ray tomorrow and need to go in refreshed.
(No muzzle loaders tonight - we used to call them booze berries G)

Big John