How Low to Spin??

Andy Blackburn wrote:
I guess the question comes down to energy management.
At one extreme, if you come in low and slow on a long
final you run the risk of not being able to extend
your touchdown point should an obstacle become apparent.
At the opposite extreme, a short, high and fast approach
runs the risk of running too long on touchdown, even
with full spoilers.

In between, I suppose there is "high and slow" (perhaps the "normal"
pattern), and "low and fast" (what you seem to be using). I am curious
about how you decided "low and fast" was the best choice: conversations
with other pilots, testing both methods on fields (maybe with a
motorglider?), or ...?


I've opted for being a bit faster in the pattern to
keep some extra margin for wind gusts and to allow
more margin for moments of distraction turning base
or final.

What are you flying "a bit faster" than? The glider handbook
recommendation? The club instructor's opinion? Or just what you used to use?

To keep total energy under control, this
means flying a bit lower pattern. Flying 70 knots instead
of 60 knots means about 50' lower in the pattern for
the same total energy. Obviously you'd start to slow
down before getting to treetops or other obstacles.

What glider are you flying? 60 knots in calm air already sounds "a bit
faster" than most gliders would have to fly. Where is the yellow
triangle on your airspeed indicator?

How much wind would it take before you'd use _more_ than 70 knots? My
glider has the yellow triangle at 50 knots, and normally I wouldn't use
70 knots on final unless the wind was over 30 knots.



In a 'standard' approach you have to lose about 20
knots from final approach to touchdown. I need lose
30 knots, which means starting that process a few seconds
sooner. The flatter glidepath on short final means
that you are, for a brief period, at a lower angle
to your final touchdown point, so you do get a peek
at potential obstacles.

This "fast and low" approach sounds like something easily done at the
home airport, but would be tricky to do right going into a field you've
never seen before. Have you used this method at airports and into fields
you've been landed at before?

I can't say that this has ever
directly benefitted me, but I do know of cases where
pilots have been too slow on final, with bad results.

And there have been cases where pilots have been too fast on final, with
bad results.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

With the big spoilers on modern gliders, there's not much risk in
adding 10 extra knots, and while your argument that it adds an
increased cushion before stall is unarguable, I guess the measure of
value comes in whether that reduced risk is a justified departure from
the "correct" pattern airspeed. I'm with Mark... it deserves some more
discussion.

BTW, as I noted in another thread, spins are not caused by lack of
airspeed, but uncoordinated use of the controls -- at least in modern
sailplanes. Two things must happen to enter a spin: 1) you must
stall, and 2) you must fail to apply sufficient rudder during your
attempt to pick up the low wing with aileron. That is, the sailplane
is designed with enough rudder to stop autorotation, even with full
deflection of the aileron throughout the stall break.

As demonstrated by my thread last fall, a Ventus 2 won't spin if the
controls remain coordinated (half stick/half rudder... full
stick/rudder). It enters a controlable spiral, instead. However, half
rudder and full stick (or half stick and no rudder) would induce a
spin if the stick is held full back throughout the stall break.

Avoiding the stall is the first most important step, but thorough
training of the appropriate response during an inadvertent stall is a
close, close second. And I could even argue that it's more important,
since once you've stalled by accident, the outcome is determined by
how well you've been trained to recover (that is, it becomes the
failsafe for your stall avoidance error).

Though I'm not a fan of axiomatic training, there's some value in
remembering that you can stall at any attitude and any speed. If you
wear that axiom on your sleeve, then you'd be best served by
understanding and practicing superlative stall recovery technique in
addition to practicing stall avoidance.

That so many capable pilots have stall/spun in relatively docile
aircraft indicates to me that there is a training gap. We are clearly
handling the controls diffently at low altitudes. Why? If we can agree
that this is the case, then adding speed is good insurance. But it
doesn't address the cause.

Andy, apologies for being the pedant. I'm spitting this stuff out at
60 words per minute, so I'm not giving much thought to "balance."

Chris OCallaghan wrote:

BTW, as I noted in another thread, spins are not caused by lack of
airspeed, but uncoordinated use of the controls -- at least in modern
sailplanes. Two things must happen to enter a spin: 1) you must
stall, and 2) you must fail to apply sufficient rudder during your
attempt to pick up the low wing with aileron. That is, the sailplane
is designed with enough rudder to stop autorotation, even with full
deflection of the aileron throughout the stall break.


Well, you have to precise what you are calling "uncoordinated use". I
remember an incipient spin in an ASH25 (can be considered as a modern
sailplane, although it existed well before I started gliding 9 years ago).
My mistake was only a to high nose up attitude while circling, which was
not obvious to me as it was my first flight in the aircraft (with an
instructor of course). Due to its high inertia, the sailplane was slowing
down very slowly to the speed corresponding to its attitude, and needed
while slowing down more and more action on controls to counter induced
roll and induced bank up to the point where I had almost full out stick
and a lot of inner rudder when the inner wing dropped. Of course the controls
were badly crossed, but some amount of cross control is normal in order
to counter induced roll and induced yaw, this is not an uncoordinated
flight, the yaw string is is the middle. The excess in cross control
was due to the fact that both induced effects increase when speed decrease,
not to a lack of coordination.

Another experience I had, which is also in contradiction with this opinion
(i.e. spin can only occur by lack of coordination) was when I was
preparing my instructor rating. As there was no other spinable glider
available, we had to demonstrate spin entry and recovery in a Fox, an
aerobatic glider. My instructor was Katona, a well known aerobatic
pilot, and he explained that in order to spin this glider I should
slow it down just very close to the stall and then have stick and rudder
to the same side. I objected that I had always be taught to push the
rudder to the side I want to spin ans the stick to the opposite side.
He said that in this case the Fox would do a flat spin, which is difficult
to exit and was not the objective of the present exercise.

Knowing your glider is the key. Open class ships are built to the
limits of acceptable flying characteristics, as is the case with
aerobatic aircraft (one reason they are typically certified
"experimental"). You must read and understand the flight manual,
noting the divergence from the norm, which is what I cited in this and
previous threads.

I suspect that many pilots are simply not used to the difference in
force required to displace the rudder equally with the aileron. A
tendency to underrudder at flying speed is common. Applying the same
"balance" near the stall would produce much less rudder force, which
means that the greatly increased and unbalanced aileron drag will
produce a skid, and the angular momentum required to start
autorotation.

Flying your glider at MCA and experimenting with various displacements
of the controls is a good exercise. Gentle turning stalls while using
coordinated aileron and rudder (not solely determined by the yaw
string but also by percentage of travel applied) to pick up the lower
wing will help you understand what your glider can and cannot do in
the stall.

In previous threads, we discussed intentionally spinning at pattern
altitudes to acclimate pilots to this "view." Such practices are
patently absurd. However, regular practice flying on the edge of the
stall while applying coordinated aileron and rudder should have real
(and much more valuable) benefits. Does your yaw string act differntly
at low speed? Are you able to accurately judge onset of the stall?
During a stall, are you applying sufficient rudder? We all make
assumptions that we will react correctly, but I'd guess that without
regular practice of the type I descibed above, we're probably not
flying as efficiently near the stall as we think. So if we get there
by accident, is it possible that we might not be aggrevating the
situation through improper control inputs?

BTW, recall that during my test flights, I was able to avoid a spin
while holding full back stick throughout the stall and ensuing spiral.
Simultaneous release of back pressure and coordinated use of aileron
and rudder is the key. Flying MCA and reacting this way to any sign of
an impending stall is the best training you can give yourself. Then
add 15 knots in the pattern to be sure you won't have to exercise
those skills.

Honestly, how many of you really practice stall recognition and
recovery as a regular flight proficiency routine? I typically only fly
on the cusp of a stall for several seconds each flight: as I take off
(I get impatient) and just before I touch down. That's not a whole lot
of opportunity to experience a critically important flight regime.

Over my quota for the week. I'll check in next week.

OC



Robert Ehrlich wrote in message ...
Chris OCallaghan wrote:

BTW, as I noted in another thread, spins are not caused by lack of
airspeed, but uncoordinated use of the controls -- at least in modern
sailplanes. Two things must happen to enter a spin: 1) you must
stall, and 2) you must fail to apply sufficient rudder during your
attempt to pick up the low wing with aileron. That is, the sailplane
is designed with enough rudder to stop autorotation, even with full
deflection of the aileron throughout the stall break.


Well, you have to precise what you are calling "uncoordinated use". I
remember an incipient spin in an ASH25 (can be considered as a modern
sailplane, although it existed well before I started gliding 9 years ago).
My mistake was only a to high nose up attitude while circling, which was
not obvious to me as it was my first flight in the aircraft (with an
instructor of course). Due to its high inertia, the sailplane was slowing
down very slowly to the speed corresponding to its attitude, and needed
while slowing down more and more action on controls to counter induced
roll and induced bank up to the point where I had almost full out stick
and a lot of inner rudder when the inner wing dropped. Of course the controls
were badly crossed, but some amount of cross control is normal in order
to counter induced roll and induced yaw, this is not an uncoordinated
flight, the yaw string is is the middle. The excess in cross control
was due to the fact that both induced effects increase when speed decrease,
not to a lack of coordination.

Another experience I had, which is also in contradiction with this opinion
(i.e. spin can only occur by lack of coordination) was when I was
preparing my instructor rating. As there was no other spinable glider
available, we had to demonstrate spin entry and recovery in a Fox, an
aerobatic glider. My instructor was Katona, a well known aerobatic
pilot, and he explained that in order to spin this glider I should
slow it down just very close to the stall and then have stick and rudder
to the same side. I objected that I had always be taught to push the
rudder to the side I want to spin ans the stick to the opposite side.
He said that in this case the Fox would do a flat spin, which is difficult
to exit and was not the objective of the present exercise.

Robert Ehrlich wrote:

BTW, as I noted in another thread, spins are not caused by lack of
airspeed, but uncoordinated use of the controls -- at least in modern

Well, you have to precise what you are calling "uncoordinated use". I
remember an incipient spin in an ASH25 (can be considered as a modern
sailplane, although it existed well before I started gliding 9 years ago).

Of course the controls
were badly crossed, but some amount of cross control is normal in order
to counter induced roll and induced yaw, this is not an uncoordinated
flight, the yaw string is is the middle.

As I mentioned earlier, as the bank angle increases, and the
wingspan increases, the AOA of the inner and outer wing
can differ by several degrees with the yawstring centered.

I think we calculated for 18m wingspan and 30 deg bank, something
like 3 degrees, and 6 degrees for 50 deg bank. But hey, this
is just a newsgroup, please do the math yourself and tell us what
you get.

It was a bit complex to calculate. Radius of circle for inner vs.
outer wingtip, stall speed and sink rate and... I don't remember
all the details, but it seemed painful...

Eric and Marc (?) I think made good points that at steeper
banks stalls are hard to muster. So perhaps the 10-30 deg banks
are really what we are discussing...
--

------------+
Mark Boyd
Avenal, California, USA

Derek Piggott has written as follows:

"I think lots of people still think that pro-spin controls means having a
lot of rudder or aileron on and don't realise that the important thing is
the stick position. If the stick is well back, spinable machines spin:
without the stick being back they don't spin.

"I don't need to tell you that many other gliders will spin a turn or two if
the stick is kept back on the stop, the c.g. is well aft and a wing drops,
even if the aileron and rudder are still central."

Even if the pilot coordinates perfectly, and string and ball remain exactly
central, a gust or turbulence may cause enough asymmetry to start a wing
drop. Gustiness, gradient, shear and turbulence are particularly likely
close to the ground.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.


"Chris OCallaghan" wrote in message
om...

snip

BTW, as I noted in another thread, spins are not caused by lack of
airspeed, but uncoordinated use of the controls -- at least in modern
sailplanes. Two things must happen to enter a spin: 1) you must
stall, and 2) you must fail to apply sufficient rudder during your
attempt to pick up the low wing with aileron. That is, the sailplane
is designed with enough rudder to stop autorotation, even with full
deflection of the aileron throughout the stall break.

snip

Bill,

Can't say I agree, but at least from my point of view, you are erring
on the side of safety.

Here is a simple argument that I have backed up with experiment in
many types of gliders. An aircraft that is capable of spinning during
a stall while aileron and rudder are held neutral (and within
published cg limits) is inherently unsafe. This means that such a
glider flown into a strong, turbulent wind gradient 50 feet above the
ground is likely to autorotate. Since recovery from an insipient spin
requires much more altitude than a straight ahead stall, there is a
very good chance that such a glider would see very few flights before
being retired.

I have proven to myself many times that stalling a glider without
abusing the controls results not in a spin but a spiral dive. While we
can all point to experiences of having a wing drop and losing control
in a stall, I doubt very seriously that any of us were holding
coordinated controls throughout the stall break. It takes a very
determined effort not to move the stick throughout the stall and
self-recovery.

Here's another argument. The vertical stabilizer provides a great deal
of yaw stability, even at very low speeds. To start autorotation, you
need a source of drag at the tip greater than the normal differential
to be expected resulting from span effect in a turn. That we don't
kill ourselves everytime the glider approaches stall is testament to
the stability provided by the tail. That we occasionally do screw
gliders into the ground makes me think that the cause lies more in the
way we are applying the controls under stress than any inherent
tendency of the glider snap into a spin at the least external
provocation. Yes, outside factors can influence how the glider flies,
but I think they do more damage by causing pilots to react in
unacceptable ways.

Go back and read through my reports on control use during stall in my
Ventus. What it drives home in my mind is that spins are the result of
control abuse. You're right, don't stall land you won't spin. But it's
just as right to say that a stall needn't develop into a spin so long
as the controls are not abused.

That's nonsense. Spin/autrotation is all about one wing (partially) stalled,
and the other not. It's not about drag.

--
Bert Willing

ASW20 "TW"


"Chris OCallaghan" a écrit dans le message de
m...

Here's another argument. The vertical stabilizer provides a great deal
of yaw stability, even at very low speeds. To start autorotation, you
need a source of drag at the tip greater than the normal differential
to be expected resulting from span effect in a turn. That we don't

At 21:54 29 August 2004, Eric Greenwell wrote:
I am curious
about how you decided 'low and fast' was the best choice:
conversations with other pilots, testing both methods
on fields (maybe with a
motorglider?), or ...?

After seeing too many friends die in stall/spin accidents
- it's purely a consequence of my own paranoia with
flying too slow in the pattern.

What are you flying 'a bit faster' than? The glider
handbook
recommendation?

Yes.

What glider are you flying?

ASW-27B

This 'fast and low' approach sounds like something
easily done at the
home airport, but would be tricky to do right going
into a field you've
never seen before. Have you used this method at airports
and into fields
you've been landed at before?

Yes.

Andy Blackburn wrote:

At 21:54 29 August 2004, Eric Greenwell wrote:

I am curious
about how you decided 'low and fast' was the best choice:

conversations with other pilots, testing both methods

on fields (maybe with a
motorglider?), or ...?


After seeing too many friends die in stall/spin accidents
- it's purely a consequence of my own paranoia with
flying too slow in the pattern.

I can see how the "fast" part can help, but not the "low" part. Being
low doesn't seem like an asset if you are worried about stalls and spins.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA