Spinning (mis)concepts

At 14:48 30 January 2004, Todd Pattist wrote:
Pete Zeugma wrote:

Before
this I always thought that the blades did not appear
to be fully clear of the wing slot.

When blades are fully clear of the wing slot, you have
to be
certain that air loads will not flex them sufficiently
to
prevent them from re-entering the wing slot.

Dug out a photo i took on decent in the discus I fly
so you can see the extent of full travel of a schempp-hirth
airbrake. The blades are clear of the slot, as designed
to be.

http://uk.f2.pg.photos.yahoo.com/ph/...l?.dir=/glidin
g&.dnm=Save0018.jpg

link should work, hopefully!


I presume the
modification you made (if that's what it was) was in
accordance with factory recommendations. I know some
Grobs
had this problem, and the fix was to limit airbrake
throw
specifically to prevent the blades from clearing their
slots, thereby ensuring they could not lock the brakes
open.
Todd Pattist - 'WH' Ventus C
(Remove DONTSPAMME from address to email reply.)

At 03:30 30 January 2004, Eric Greenwell wrote:
Nyal Williams wrote:

Getting down fast! I was getting ready to enter the
wave window at Mt. Mitchell, NC, and the cold suddenly
told me my bladder was about to let go. Full divebrakes
in a slipping turn got me on the runway in time, but
I had to jump out and run to a ditch beside the runway;
at 75 yards, the FBO toilet was just too far away.

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.

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. :-)

I don't have the time right now, but anyone care to hazard a few lines
of discussion on the increase in induced drag during a slip and
compare it with the high speed, high drag descent Cindy described?

It might start something like this:

During a slip, the effective span and aspect ratio of the wing and
elevator decrease substantially. Additionally, total lift required to
maintain a constant airspeed is much increased (without any increase
in g loading) due to the tilting of the lift vector. Therefore, a much
higher angle of attack is required to maintain a given (low) airspeed,
one which might be employed to accomplish a steep approach into a very
short field.

Different circumstances, of course. But it would be interesting to see
someone develop this. Frankly, I don't think I've ever seen an
analysis of a slip that properly weighs the effects of induced drag.

Just out of interest, Cindy, according your data, which creates the
steepest approach (min L/D) (as opposed to greatest sink rate)? Yes,
we're likely to get some discussion on TV airbrakes, but we'll just
have to suffer through that.

In article ,
Chris OCallaghan wrote:
I don't have the time right now, but anyone care to hazard a few lines
of discussion on the increase in induced drag during a slip and
compare it with the high speed, high drag descent Cindy described?

It might start something like this:

During a slip, the effective span and aspect ratio of the wing and
elevator decrease substantially. Additionally, total lift required to
maintain a constant airspeed is much increased (without any increase
in g loading) due to the tilting of the lift vector. Therefore, a much
higher angle of attack is required to maintain a given (low) airspeed,
one which might be employed to accomplish a steep approach into a very
short field.

Different circumstances, of course. But it would be interesting to see
someone develop this. Frankly, I don't think I've ever seen an
analysis of a slip that properly weighs the effects of induced drag.

Just out of interest, Cindy, according your data, which creates the
steepest approach (min L/D) (as opposed to greatest sink rate)? Yes,
we're likely to get some discussion on TV airbrakes, but we'll just
have to suffer through that.

Well, the 2-33 manual says in a full slip that something like
45 to 50mph gives the most efficient slip.

I wonder if this means most amount of altitude loss
for distance travelled, or highest sink rate per
minute. I'd believe the first, but have trouble
believing the second.

And if it really is just best altitude loss for
distance of glide, then wind effects could change
the correct speed significantly...

Cindy, perhaps you would address that bit of nonsense in the Private Pilot
Practical Test Standards about no-spoiler accuracy landings. (I've always
thought it was there in order to make the PTS 2-33 specific.)

Bill Daniels

"Caracole" wrote in message
om...
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.

"Bill Daniels" wrote in message ...
Cindy, perhaps you would address that bit of nonsense in the Private Pilot
Practical Test Standards about no-spoiler accuracy landings. (I've always
thought it was there in order to make the PTS 2-33 specific.)

Bill Daniels


When I was more active instructing I used to give students simulated
airbrakes jammed full open and jammed closed (separate flights). I
expected them to demonstrate that they could complete the circuit and
landing. I released the malfunction on short final, or sooner if they
couldn't cope.

Isn't the PTS requirement to demonstate simulated jammed closed?


Andy

"Bill Daniels" wrote in message ...
Cindy, perhaps you would address that bit of nonsense in the Private Pilot
Practical Test Standards about no-spoiler accuracy landings. (I've always
thought it was there in order to make the PTS 2-33 specific.)

Bill Daniels

That would have to be "Schweizer specific" at the very least wouldn't
it, Bill? I was once forced by reason of a 2-32's spoilers being
frozen solidly closed to slip from 28,000 ft MSL near Pikes Peak to
land without them at old BFGP. (Not much of an accuracy landing
challenge there, of course, but my feet were pretty cold and I was
grateful for the rate of descent). FAA's aircraft registry lists at
least 1335 Schweizers having spoilers or divebrakes of similar
configuration, of which 2-33's of all varieties number only 375.

I'm embarassed to admit that I've also inadvertently jettisoned the
drag chute on a Salto on the base leg to a much smaller landing site
where I really could have used it, and an agressive slipping turn to
final made the difference between an otherwise certain overshoot and a
merely memorable pattern. Modern sailplanes don't ordinarily present
as much flat plate to the airstream and plummet from altitude quite as
dramatically as the Schweizers, but they all descend a bit more
steeply flying sideways and there are any number of reasons that extra
little increment of drag may be useful.

As training exercise, I'd argue that no-spoiler slipping patterns to
an accuracy landing can be uses to develop advanced levels of both
judgement and command of the aircraft in maneuvering with attention
focused largely outside the cockpit. In that sense, is demonstrating
proficiency in it any less "practical" a test item than some of the
ground reference maneuvers found in the airplane PTS?

"Eric Coleson" wrote in message
om...
"Bill Daniels" wrote in message
...
Cindy, perhaps you would address that bit of nonsense in the Private
Pilot
Practical Test Standards about no-spoiler accuracy landings. (I've
always
thought it was there in order to make the PTS 2-33 specific.)

Bill Daniels

That would have to be "Schweizer specific" at the very least wouldn't
it, Bill? I was once forced by reason of a 2-32's spoilers being
frozen solidly closed to slip from 28,000 ft MSL near Pikes Peak to
land without them at old BFGP. (Not much of an accuracy landing
challenge there, of course, but my feet were pretty cold and I was
grateful for the rate of descent). FAA's aircraft registry lists at
least 1335 Schweizers having spoilers or divebrakes of similar
configuration, of which 2-33's of all varieties number only 375.

I'm embarassed to admit that I've also inadvertently jettisoned the
drag chute on a Salto on the base leg to a much smaller landing site
where I really could have used it, and an agressive slipping turn to
final made the difference between an otherwise certain overshoot and a
merely memorable pattern. Modern sailplanes don't ordinarily present
as much flat plate to the airstream and plummet from altitude quite as
dramatically as the Schweizers, but they all descend a bit more
steeply flying sideways and there are any number of reasons that extra
little increment of drag may be useful.

As training exercise, I'd argue that no-spoiler slipping patterns to
an accuracy landing can be uses to develop advanced levels of both
judgement and command of the aircraft in maneuvering with attention
focused largely outside the cockpit. In that sense, is demonstrating
proficiency in it any less "practical" a test item than some of the
ground reference maneuvers found in the airplane PTS?

I've watched pilot attempt a no-spoiler approach in a Grob 103 and the only
way that a reasonably accurate landing could be done was to fly way too slow
for comfort because the 103 floats so far in ground effect. My Nimbus 2C
(No tail 'chute) floats so far that if the air brakes don't work, I'll need
several kilometers of runway to get stopped.

If you have a glider that exhibits a pronounced float in ground effect, I'd
advise against a no-spoiler approaches. I think this may be where accidents
due to training will be greater than those due to a real spoiler failure.

Bill Daniels