Rolling a 172 - or not

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?

Hamish

"Hamish Reid"

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?

I'm confused. Please describe a properly done aileron roll.

I have some glider acro training and lot's of RC model acro. I think of
axial rolls and barrel rolls. Both benefit from aileron, elevator and
rudder input. I've thought that aileron roles are synonymous with axial and
slow rolls synonymous with barrel rolls. But there is a lot of RC legacy
stuff in my understanding.

In article ,
"Maule Driver" wrote:

"Hamish Reid"

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?

I'm confused. Please describe a properly done aileron roll.

Check out http://acro.harvard.edu/ACRO/acro_figures.html#rolls for a
brief description.

I have some glider acro training and lot's of RC model acro. I think of
axial rolls and barrel rolls. Both benefit from aileron, elevator and
rudder input. I've thought that aileron roles are synonymous with axial and
slow rolls synonymous with barrel rolls.

Hmmm. Aileron rolls are closer to barrell rolls, slow rolls with axial
rolls. In fact, a slow roll is a roll around the longitudinal axis; an
aileron roll does not keep the longitudinal axis of the plane straight
ahead...

Hamish

"Maule Driver" wrote
I have some glider acro training and lot's of RC model acro. I
think of axial rolls and barrel rolls. Both benefit from
aileron, elevator and rudder input. I've thought that aileron
roles are synonymous with axial and slow rolls synonymous with
barrel rolls.

From the following web site about aerobatics:

http://acro.harvard.edu/IAC/faq_aerobatics.html

Aileron Rolls
Aileron rolls are flown with the rudder and elevator in the neutral
position during the roll. The aileron is fully deflected in the
direction of the roll. This is the easiest of the rolls to fly.
The aileron roll is started by pulling the nose up to 20 - 30 degrees
above the horizon. The elevator is then neutralized and the aileron
fully deflected in the direction of the roll. The controls are
maintained in that position till the roll is completed. After the
roll is completed the nose is usually 20 - 30 degrees below the
horizon.

The aileron roll is not a competition maneuver.


Slow Rolls
Slow rolls have to be flown normally on a straight line (exception is
the avalanche). The roll rate has to be constant and the longitudinal
axis of the plane has to go straight. This requires constantly
changing rudder and elevator control inputs throughout the roll.
Hesitation or point rolls include stops at certain roll angles. The
number on the base of the roll symbol describes the number of points
the roll would have if it were a 360 degree roll. Allowed are 2
point, 4 point and 8 point rolls. The fraction on the arrow of the
roll symbol describes what fraction of a full roll is to be executed.
If no points are specified, rolling is done without hesitations. If
no fraction is specified, a roll symbol that starts at the line
specifies a half roll (see description of the Immelman). A roll
symbol that crosses the line specifies a full roll (first figure).
The second figure shows the symbol for 2 points of a 4 point roll
(adding up to half a roll) from upright to inverted flight.

Snap Rolls
Snap or flick rolls also have to be flown normally on a straight
line. A snap roll is similar to a horizontal spin. It is an
autorotation with one wing stalled. In the regular snap, the plane
has to be stalled by applying positive g forces. In an outside snap,
the plane is stalled by applying negative g. In both cases rudder is
then used to start autorotation just like in a spin.

Barrel Roll
The Barrel Roll is a not competition maneuver. I The barrel roll is a
combination between a loop and a roll. You complete one loop while
completing one roll at the same time. The flight path during a barrel
roll has the shape of a horizontal cork screw. Imagine a big barrel,
with the airplanes wheels rolling along the inside of the barrel in a
cork screw path. During a barrel roll, the pilot experiences always
positive G's. The maximum is about 2.5 to 3 G, the minimum about 0.5
G.

Bob Moore

I get it and am smarter for it. Thanks.

My acro terminology is so rooted in RC flying from 30+ years ago, that I've
never realized how differently the terms are used in 'real' a/c.

In RC, the term aileron roll is commonly used for what is called a slow roll
here. It is a straight line roll and can happen very fast. Aileron and
elevator will produce a quite passable axial roll in a hot RC plane. Very
akin to what a full scale jet fighter might do. Pros like my brother will
use top rudder too.

A barrel roll in RC is typically done with rudder in a model without
ailerons. It looks like a full scale aileron roll. Less-than-hot
rudder/elevator only RC plance can do a passable barrel roll because of a
lot of dihedral. You don't even need the elevator if it is setup right.

And in a full scale glider, it's kind of hard to get all the way around a
pure aileron roll as described. You need to be pretty agressive with pitch
and rudder to do a passable 'aileron' roll. At least in my limited
experience.

"Robert Moore" wrote in message
...
"Maule Driver" wrote
I have some glider acro training and lot's of RC model acro. I
think of axial rolls and barrel rolls. Both benefit from
aileron, elevator and rudder input. I've thought that aileron
roles are synonymous with axial and slow rolls synonymous with
barrel rolls.

From the following web site about aerobatics:

http://acro.harvard.edu/IAC/faq_aerobatics.html

Aileron Rolls
Aileron rolls are flown with the rudder and elevator in the neutral
position during the roll. The aileron is fully deflected in the
direction of the roll. This is the easiest of the rolls to fly.
The aileron roll is started by pulling the nose up to 20 - 30 degrees
above the horizon. The elevator is then neutralized and the aileron
fully deflected in the direction of the roll. The controls are
maintained in that position till the roll is completed. After the
roll is completed the nose is usually 20 - 30 degrees below the
horizon.

The aileron roll is not a competition maneuver.


Slow Rolls
Slow rolls have to be flown normally on a straight line (exception is
the avalanche). The roll rate has to be constant and the longitudinal
axis of the plane has to go straight. This requires constantly
changing rudder and elevator control inputs throughout the roll.
Hesitation or point rolls include stops at certain roll angles. The
number on the base of the roll symbol describes the number of points
the roll would have if it were a 360 degree roll. Allowed are 2
point, 4 point and 8 point rolls. The fraction on the arrow of the
roll symbol describes what fraction of a full roll is to be executed.
If no points are specified, rolling is done without hesitations. If
no fraction is specified, a roll symbol that starts at the line
specifies a half roll (see description of the Immelman). A roll
symbol that crosses the line specifies a full roll (first figure).
The second figure shows the symbol for 2 points of a 4 point roll
(adding up to half a roll) from upright to inverted flight.

Snap Rolls
Snap or flick rolls also have to be flown normally on a straight
line. A snap roll is similar to a horizontal spin. It is an
autorotation with one wing stalled. In the regular snap, the plane
has to be stalled by applying positive g forces. In an outside snap,
the plane is stalled by applying negative g. In both cases rudder is
then used to start autorotation just like in a spin.

Barrel Roll
The Barrel Roll is a not competition maneuver. I The barrel roll is a
combination between a loop and a roll. You complete one loop while
completing one roll at the same time. The flight path during a barrel
roll has the shape of a horizontal cork screw. Imagine a big barrel,
with the airplanes wheels rolling along the inside of the barrel in a
cork screw path. During a barrel roll, the pilot experiences always
positive G's. The maximum is about 2.5 to 3 G, the minimum about 0.5
G.

Bob Moore

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

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

Were you thinking of a slow roll?

I know the diffference between a slow roll and an aileron roll.

If you think you maintain positive G in an aileron roll,

(1). Take along a bottle of water and a drinking glass next time you
fly.

(2). Fill the glass with water and place it atop the instrument
panel.

(3). Do an aileron roll.

vince norris

In article ,
vincent p. norris wrote:

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

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

Were you thinking of a slow roll?

I know the diffference between a slow roll and an aileron roll.

OK... but you contradict texts such as Szyurovy and Goulian, not to
mention basic experience.

If you think you maintain positive G in an aileron roll,

(1). Take along a bottle of water and a drinking glass next time you
fly.

(2). Fill the glass with water and place it atop the instrument
panel.

(3). Do an aileron roll.

And then what...? 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).

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,
but never mind :-)); not in a properly-done aileron roll. That's
because, unlike a slow roll (where at the 180 degree point we typically
get mild negative G's), we keep positive G's on the plane at all points
in the aileron roll.

Much of the whole point of an aileron roll is to maintain a positive G
force on the plane. It's the easiest and most pleasant (for passengers)
of the four main rolls. To quote S & G (p50 in my edition): "On its
ballistic, corkscrew-like flight path, the airframe continuously
experiences normal acceleration, maintaining light, positive G all the
way around the aileron roll". Not that I take much notice of texts, but
there it is....

You weren't thinking of a "1G" maneuver were you, rather than "positive
G"?

Hamish

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

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

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