Spinning (mis)concepts

Assume you make a glider which is a big cylinder with a huge
hollow tube going through the middle. I lay it on its
side and put a clear plexiglass on the top part for the pilot to
see out of, and give him a seat inside. Then I put three yawstrings
on it: one on the plexiglass "canopy", one in the middle of the
center tube, and one on the bottom.

I drop this "glider bomb" and it heads straight down (maybe there's
a drogue chute). A gyro rotates the cylinder on the way down.
Assuming no surface friction and ignoring gyroscopic
precession for now, all three yaw strings, from the
pilot seat, show different things. If the cylinder is
rolling right, the "glider bomb pilot" sees the yawstring on
the canopy and instinctively wants to add right rudder.
The string in the center of pressure shows straight, and the
bottom string would make the pilot want to add left rudder.

None of this has anything to do with gravity, adverse yaw,
or the cylinder slipping or skidding.

I contest that there is an error caused on the yaw string
depending on the roll rate, airspeed, and the distance of the
yaw string above the center of pressure, and this will
always tell the pilot to add more rudder in the direction
of roll (assuming the yawstring is above the center of
pressure), i.e. skid.

The size and importance of this error is another
matter entirely :PPP

Well, the size and importance DOES matter because you are making such
a point of it. I think that I adequately proved that your last point
was, shall we say, pointless. The offset of the yaw string to the
center of the roll axis is much less than its displacement from the
CG, making your "errors" proportionally less. I think you ought to
pursue a more reasonable hypothesis; like TWA 800 was downed by a
stray Navy missle.

Tom

Aerodynamics 101.
Parasitic drag as a topic.
If you truly want down fast, a slip is not the most effective tool.
AS-K 21, full spoilers deployed and 90 knots airspeed will descend at
4000 fpm.
You are below both maneuvering and rough air speed.

Slipping turns are a useful tool. They should be understood.
So should parasitic drag. Try it at altitude. Carry a GNSS recorder
(GPS logger for us unruly Americans). Analyze the data later about
how much sink rate you manufacture.

Don't believe it? Come fly with us. Or watch from the ground if you
wish. It works for everything from 1-26s up to Nimbus 3s and all the
standard class stuff inbetween. There are no too-little or
ineffective spoilers, just mild differences in sink rates.
Now, the AS-W 12, that's a different story.....until they fitted a
fitful drogue chute. Or the Carbon Dragon.

Slipping on approach to landing (or anytime), pitch attitude is your
friend for airspeed control.

Cindy B
www.caracolesoaring.com



What speed did you use? Could you have just used full
spoilers and
spiralled down at 90 knots or so (or faster, if air
was smooth), and had
the same descent rate?
--
-----
change 'netto' to 'net' to email me directly

Eric Greenwell
Washington State
USA

80kts in an ASK-21, but who knows the accuracy of
an ASI in a slip? I was turning to the left with full
right rudder and the nose as far down as I dared; the
noise was tremendous.

Parasitic drag as a topic.
If you truly want down fast, a slip is not the most effective tool.
AS-K 21, full spoilers deployed and 90 knots airspeed will descend at
4000 fpm. You are below both maneuvering and rough air speed.

It works for everything from 1-26s up to Nimbus 3s and all the
standard class stuff inbetween. Now, the AS-W 12, that's a different story.....until they fitted a fitful drogue chute. Or the Carbon Dragon.

Slipping on approach to landing (or anytime), pitch attitude is your
friend for airspeed control.


A second enthusiastic for parasitic drag - and slipping turns.
Downwind abeam the touchdown spot at 7000 ft agl, full brakes, 90 kts
and you have to be careful to keep the pattern snug to avoid
undershooot (or changing configurations). Yields about a 3:1 L/D or a
glide similar to the space shuttle. The angles look pretty strange in
the steep turns but one adapts.

Slipping turns are the ticket in non-spoilered beasts (AS-W12 or
Pawnee). Both can be flown in near-90 degree banks with full top
rudder, pulling lots of G and plummeting like a stone. The "look'
from inside and outside the cockpit is a bit strange but one adapts.
One can blow the side windows out of Super Cubs and probably Pawnees
doing this in sub-zero Colorado WX at 14,000 ft in dawn wave sorties
(we will not discuss howe I know this). Hard on airframe of aircraft
and pilot alike. Parasitic drag descents are much better.

High-G, high bank angle slipping turns are very useful for burning
airspeed (energy) in the pattern as well but are very tiring if done
repeatedly. The turn allows one to load up the wing with high G's
making the slip markedly more effective. Similar to military overhead
break approaches with the slip thrown in for good measure.

Practice at altitude and be very careful in the "know-it-all" phase of
the learning curve. The "pitch" angles in these maneuvers will bear
no resemblence to a conventional approach and if they do (when you
revert to the known and familiar angles and habits), you have a big
problem. :-)

At 02:54 31 January 2004, Adp wrote:

Except it isnt is it! Gliders require you to understand
fully things like adverse yaw, energy management, not
being able to power-on and go around. When you land
a glider, you only get one shot at it, what ever the
conditions happen to be thrown at you. How much time
do you spend thinking of where you are going to land
out when you are at 1500 feet above the ground in
your power plane? It has nothing what ever to do with
irrational prejudice.

This is one of the biggest nonsense myths in the soaring
community. It
amounts to an irrational prejudice towards power pilots
who transition to
gliders.
There is considerably greater difference between, say,
flying a Bonanza and
flying a Boeing 757 than flying any glider.
Gliders are incredibly easy to fly. Simply be aware
of the differences.
It really amounts to attitude. (In both senses of
the word.)
When flying a Bonanza, think Bonanza. When flying
a King Air, think King
Air. When flying a B-757, think 757. When flying
a F18, think F18. When
flying a glider, think glider. When flying a motor
glider, think glider.
It can't be much simpler.

Allan

'Mark James Boyd' wrote in message
news:401acc7c$1@darkstar...
Pete Zeugma wrote:

Ah, power planes, not gliders! Do you not think perhaps
we should be differentiating between rudder usage
in
power plane, and a glider? I started flying originally
in gliders, so I dont have any bad habits from power
flying, and when I fly powered aircraft, i cant help
but fly coordinated all the time. I know that power
pilots who make the transition to gliders quite often
make fundemental errors due to the power mindset when
sat in a glider. What do you think?

Absolutely there are subtle differences that get overlooked.
Primacy is a factor here. Use of spoilers, wheel
brake
not at the feet, no stall horn, can't use throttle
to
descend, actually seeing adverse yaw, etc. All these
were probably much harder to learn (unlearn) than
if
one started as a glider pilot first.

....Snip....

Todd Pattist wrote:

Robert Ehrlich wrote:

This terminology is or was source of a lot of discussions and
misconceptions also in France where 2 equivalent terms exists,
"glissade" for slip, "dérapage" for skid. So the team responsible
for deciding the method and terminology that should be used
by all glider instructors decided, after some discussion, that only
one term should be used, "dérapage" was the choosed one.
During a turn, a slip should be called "dérapage intérieur"
(inside skid), a skid "dérapage extérieur" (outside skid).
In straight line we speak of "dérapage à gauche" (skid toward
left side) or "dérapage à droite" (skid toward right side).
This has the advantage of uniformity, any case where the string
is not in the middle is called by the same name and the further
qualification (inside, outside, left, right) always indicate the
side from which the relative wind is coming and the string is going
away.

Thanks for posting this. It is fascinating to see something
familiar from a totally different perspective.

I admit to not really understanding the advantage of using
your integrated terminology. A "skid" is almost never
(ever?) an appropriate maneuver, so giving it a completely
different name from a "slip" allows immediate recognition
that we're talking about something that's inappropriate to
do. I would be more concerned that a student would be
confused between when it's OK to "dérapage" and when it's
not

One of the ideas behind this integrated terminology is that
neither skid nor slip is an appropriate maneuver in today's
gliders having powerful airbrakes, morever on some of them
the POH prohibits skids and/or slips.

Pete,

Unfortunately, you are wrong on this one. You can, in fact, use rudder
to change direction, much to the aerodynamicist's chagrin. It is very
inefficient, but by holding wings level and ruddering (a skid) you
create an inward pointing force caused by the fuselage (along with a
rearward componenet -- drag). It is this force that allows you to slip
by counteracting the turning force of the wing with an opposite force
from the fuselage. (Again, much to the chagrin of the aerodynamicist.)

You need rethink your model. Remember, things only go straight if in
equilibrium. An aircraft flying sideways through the air wings level
won't be in equilibrium, therefore either speed or direction must
change.

Pete Zeugma wrote in message ...
If you have zero bank, and apply rudder you will begin
a
flat turn.

Wrong! UTTERLY WRONG!!!! A rudder yaws the airframe,
it does not 'turn' or 'steer' the aircraft.

Your whole problem seems to be in compairing a glider
with a boat. They may both have rudders, but they both
do totally different things.

Next time you fly in your glider, line yourself up
with a straight feature. Apply some rudder to yaw the
glider, but keep the wings level. All you will do is
continue in a straight line, sideways on. (commonly
known as a side slip)

However, the rudder does has a secondary control effect,
which introduces a roll moment due to differences in
lift between the wings. (which is why the first thing
you do is apply full opposite rudder to counteract
the rotation in a spin)

It is the ailerons that instigate a turn, the rudder
is used in a coordinated manner to 1) check the adverse
yaw (secondary effect of ailerons), and 2) to align
the airframe correctly into the airflow.

Please stop using language which inforces a belief
that the rudder is used to turn a glider in flight.
Your very action in doing so may well end up enforcing
that belief into a low airtime pilot reading these
posts and KILLING THEM!

At 14:24 02 February 2004, Chris Ocallaghan wrote:
Pete,


Every now and then, I like to keep my hand in with
sidesliping on finals. One airfield I fly at has a
real narrow tarmac strip, like 5 meters. When I am
in a nice balanced, wings level sideslip, how come
I maintain a striaght path all the way down to my reference
point where I kick it off to round out?



Unfortunately, you are wrong on this one. You can,
in fact, use rudder to change direction, much to the
aerodynamicist's
chagrin.

especially if you have and engine up front.

It is very
inefficient, but by holding wings level and ruddering
(a skid)

side slip actually

you
create an inward pointing force caused by the fuselage
(along with a
rearward componenet -- drag). It is this force that
allows you to slip
by counteracting the turning force of the wing with
an opposite force
from the fuselage. (Again, much to the chagrin of the
aerodynamicist.)

Please, expand on this 'force', from an aerodynamics
point of veiw. I'd love to know what law of physics
you have created this thrust vector from.


You need rethink your model. Remember, things only
go straight if in
equilibrium.

actually, all objects in motion exhibit a natual tendancy
to go in a straight line, unless an external force
is applied to upset that equilibrium. One of Mr Newtons
laws I think!

An aircraft flying sideways through the air wings level
won't be in equilibrium, therefore either speed or
direction
must change.

I did loads of sideways flying this weekend soaring
on our hill!
Wings level, straight line constant 60knots, crabbing
along at 40 odd degrees.

in order to keep the wings level while applying yaw,
you have to apply a roll moment to counter the secondary
roll moment caused by the yaw. This puts the aircraft
back into equilibrium by force. If you release the
aileron, the secondary roll moment caused by the yaw
will eventually bank the aircraft into a turn. Stick
an engine into the equation, and it all changes.

Pete Zeugma skrev den 2 Feb 2004
15:16:31 GMT:
you
create an inward pointing force caused by the fuselage
(along with a
rearward componenet -- drag). It is this force that
allows you to slip
by counteracting the turning force of the wing with
an opposite force
from the fuselage. (Again, much to the chagrin of the
aerodynamicist.)

Please, expand on this 'force', from an aerodynamics
point of veiw. I'd love to know what law of physics
you have created this thrust vector from.

The same laws which keep you in the air, in fact. When the fuselage is
going through the air at a beta angle (sideslip), it generates lateral
lift. That's what makes knife edge flight possible.

Chances are this effect is not very noticeable in a glass bird with the
streamlined fuselage, meaning that the bank angle required to keep the
glider travelling in a straight path might be marginal and not really
noticeable.

Cheers,
Fred

On Mon, 2 Feb 2004 15:16:31 UTC, Pete Zeugma
wrote:


: you
: create an inward pointing force caused by the fuselage
: (along with a
: rearward componenet -- drag).

: Please, expand on this 'force', from an aerodynamics
: point of veiw. I'd love to know what law of physics
: you have created this thrust vector from.

May I jump in? He's right, and it's dead easy, really. If the fuselage
is yawed to the right, the airflow comes from the left. Which tends to
push the big front big - the cockpit - to the right. And I'm an
aerodynamicist, amongst other things.

: in order to keep the wings level while applying yaw,
: you have to apply a roll moment to counter the secondary
: roll moment caused by the yaw. This puts the aircraft
: back into equilibrium by force. If you release the
: aileron, the secondary roll moment caused by the yaw
: will eventually bank the aircraft into a turn.

Whoops. I think you are confusing the effects of yawing and the
effects of being yawed. As you yaw, one wing moves faster than the
other and produces more lift, tending to roll the glider unless
prevented. But once you are yawed, this effect ends. There may be
other effects requiring use of aileron while yawed - sweep forward in
the wings, for example.

: Stick
: an engine into the equation, and it all changes.

Not very much changes, actually.

Ian

Todd,
Ever try to slip an Ercoupe?
No slip needed for crosswinds either.
And.. There's nothing quite like flying one over the city on a fine spring
evening with the window down.
Cheers!

Todd Pattist wrote in article
...
Robert Ehrlich wrote:

snip
I don't see how a POH could entirely prohibit slips - as you
could never land in a crosswind. :-)

Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)