How Low to Spin??

Kirk Stant wrote:
(Mark James Boyd) wrote in message news:412b9c97

Think about it for a minute. If you're going 50 knots in one direction,
and then one-half second later the nose of the glider is 180 degrees
pointed the other way, does this mean you are doing 50 knots in the other
direction? That's some G's, and I don't feel them in a spin.

And what do you mean by doing "a
complete 180 during the spin ...and is now to some degree flying
backwards." That isn't a spin, it's a frisbee! As far as G's, if you
enter a spin at low speed (not accelerated), you can't pull any G's -
as the plane unloads and goes down there is actually a decrease in
G's!

Some aircraft have a very nose low spin (Blanik), others have a much
flatter spin (Katana). The Katana, which spins very flat on the horizon,
is going North at 30 knots. I stall it and spin. Over the course of
a second, the nose is now pointed South. Is the Katana moving
South with an airspeed of 30 knots? No, it is not. This is
part of the reason why, during the first turn or two, the
pitch oscillates more violently than in a fully developed spin.

Because of momentum, the airspeed from front to back of the
wings is less during the South pointed nose part of the spin than
during the entry of North.

And yes, this is a frisbee. At least for the first 180 anyway...

This is why aircraft oscillate pitch up and down for a few turns before
stabilizing in a spin. For the first few turns, the aircraft momentum
is still slogging through the air.

I don't have a spin text handy, but I would think the oscillation is
more due to angular momentum and changing AOA as the glider rotates
around it's pitch and roll axes than from "flying backwards".

Yes, and part of this changing AOA is due to momentum in the
Northerly direction.

Even with an aft CG, any glider is fully controllable up to the spin -
it's recovering that would be interesting.

True, true. The more aft the CG, the more controllability.

It's pretty hard to get the CG that far aft (it can be done,
especially if you are light, but any sort of preflight should find it)

Ms. Campbell is the Hawaii state altitude record holder. She
worked at Dillingham as a CFI. She told me during a ground session
she was in an uncontrolled spin for more than 5,000 feet at one point,
with a passenger, before recovering.
She said after landing, she weighed the glider and the CG
was well aft of what was on the 10+ year old "official" form.
And her new calculated CG for that flight was well aft of limits.

In my experience, the older the calculation, the further back
the actual CG is from it. Dirt and crap on the long lever arm
of the tail do a lot more than crap in the short nose.

and if discovered the plane is still fully controllable - unlike a too
far forward CG that can lead to a heavy landing. Just my opinion, but
I bet there have been very few spin accidents caused by aft CGs (CG
out of the aft limit, not just at the aft limit).

Except for that 1 in 10 case, I'd guess aft CG is just a contributing
factor, not a cause. But I'd like to see data. When I hear of
a winch launch by an experienced pilot during the first
flight of the season, ending in a fatality, I have to wonder if
he took something out of the nose, or put something in the
tail, and so his stick pressure feel and initial trim setting
were off... Of the stall spin fatalities on record, I'd
bet most, if not all, had CG further back than the 60-70%
forward that Eric described...

Sounds like trying to turn via ground references down low - a big
no-no

This is required to fly a rectangular pattern with wind correction,
and still part of the PTS...

and probably the real reason for low altitude "stall-spin"
accidents.

Clearly true. If one weren't trying to land on a particular
bit of ground, and the world was just one big flat runway,
I'm certain landing accidents would be more rare.

The classic spin entry from a shallow bank is uninteresting.
I won't be jamming in the rudder for a skid at some obviously
low speed close to the ground. I think the focus on the classic case
is niave and dangerous. Yes, it's easy to teach and demonstrate,
but it ignores too much. The more complex, less discussed
spin entry is the one in the accident reports: tight pattern,
higher speed, steep bank, lots of inside rudder, pilot focussed on
keeping the yaw string straight, quite a bit of opposite aileron
in the steep bank, in vertigo, pulling stick back to tighten up the
turn, and then wham! I'll look back through the accident reports, but
the ones I recall, and the B-52 and the DG spin I saw on video, involved
stabilized, 30-45 deg bank turns before each of the spins. In each,
it looked like the craft was overbanking, and the pilot put in more
opposite aileron and more elevator and WHAM! Instant spin...

Again, you are describing a pilot who has no clue how to fly his
glider.

Hard to quiz them, the dead are VERY quiet...

A stabilized steep turn doesn't call for a lot of inside
rudder.

Many of the 10 reports seem to indicate the spirals/spins happened
during the roll, not the turn. High roll rates require a lot of
rudder (and then rudder release), used quite precisely.

And I am a bit confused by your reference to vertigo -
again, this is avoidable (don't stare at the ground, no rapid head
movements, etc) and should be taught.

I commonly induce vertigo in students to demonstrate unusual attitude
recovery. Although easiest to induce by rapid head movements,
I can also induce it with nothing more than a rapid, perfectly
coordinated roll into a steep bank, and then a rapid coordinated
roll to level flight. I've done this with pilots from 10-30,000 hours.
In all of them, if I cover all the instruments on a nice dark night
with foggles on, they get vertigo. Not staring at the ground and
avoiding rapid head movements is a start, but is an incomplete
solution...rapid roll rates and dramatic G changes are another
factor.

When I fly gliders, I have to remind myself to fly at least a 1/4 mile
out pattern. I normally fly a power plane (day VFR only) with a 5:1
glide ratio, and a tight pattern, with steeper banks and
faster roll rates at higher airspeed. I don't do this when
in a glider approaching an unmarked landout field with mountains and
no horizon around.

If a pilot continually gets
vertigo in steep turns (and I have some really good friends who do,
unfortunately) they need to seriously consider the ramifications of it
and fly accordingly!

I see we are agreeing again
--

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

Mark James Boyd wrote:

Some aircraft have a very nose low spin (Blanik), others have a much
flatter spin (Katana). The Katana, which spins very flat on the horizon,
is going North at 30 knots. I stall it and spin. Over the course of
a second, the nose is now pointed South.

Why do you think it takes only one second? Even a aerobatic glider can't
reverse direction that quickly - that would be such a violent manuever.
Think about it: a 60 knot change in one second takes over 3 gs, and a
spin entry produces nothing like that.

Try timing a spin entry sometime with stopwatch or a recorder on board.

Is the Katana moving
South with an airspeed of 30 knots? No, it is not.

It's probably still got about 30 knots airspeed (do they really stall at
such a low speed?), but because it is pointed down, the southerly
component is less than 30 knots.

snip

Except for that 1 in 10 case, I'd guess aft CG is just a contributing
factor, not a cause. But I'd like to see data. When I hear of
a winch launch by an experienced pilot during the first
flight of the season, ending in a fatality, I have to wonder if
he took something out of the nose, or put something in the
tail, and so his stick pressure feel and initial trim setting
were off... Of the stall spin fatalities on record, I'd
bet most, if not all, had CG further back than the 60-70%
forward that Eric described...

Just to be clear here, the convention is: 0% is at the front of the
range; 100% is at the aft end of the range. It sounds like you have it
backwards.

--
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Eric Greenwell
Washington State
USA

Eric Greenwell wrote:

Just to be clear here, the convention is: 0% is at the front of the
range; 100% is at the aft end of the range. It sounds like you have it
backwards.

My mistake. I wasn't expecting you to have flown
aircraft in such an aft CG range, and inverted it in my mind.

Really. So the aircraft were in the aft 1/3 of the range?
And still wouldn't stall at 45 deg bank? Interesting...

I believe you, I'd just like to see this myself as well.

As far as stalls in a steep bank, without uncoordinated
inputs, I've noticed many aircraft roll wings level,
just like the GFH and AFH (and Marc, it seems) say...

One thing I haven't tried that I recall is banking into
a turn and then just failing to take rudder out
while rolling level at a high rate (all while at low
airspeed). This should get a nice spin entry too...

Maybe there are spin fatalities in this category too...steep
bank close to the ground, more elevator to tighten the
turn to final, then an attempt at a quick roll to level wings...
--

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

Mark James Boyd wrote:

Eric Greenwell wrote:

Just to be clear here, the convention is: 0% is at the front of the
range; 100% is at the aft end of the range. It sounds like you have it
backwards.


My mistake. I wasn't expecting you to have flown
aircraft in such an aft CG range, and inverted it in my mind.

Really. So the aircraft were in the aft 1/3 of the range?
And still wouldn't stall at 45 deg bank? Interesting...

70% is a common CG location, because (for many/most gliders, especially
the newer they are) the glider handles pleasantly, recovers easily from
spins, and is close to the optimum CG for cross-country performance.


I believe you, I'd just like to see this myself as well.

The limit on elevator "authority" isn't so much the force it can
generate (except at the most forward positions) but more the angle of
attack reduction on the elevator that occurs in steep turns. I'm sure
the bank angle you can stall at is higher with a more aft CG, but in the
commonly used 60-80% range, you do run out of elevator in the steeper turns.

--
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Eric Greenwell
Washington State
USA

(Mark James Boyd) wrote in message news:412ce2c4$1@darkstar...

Some aircraft have a very nose low spin (Blanik), others have a much
flatter spin (Katana). The Katana, which spins very flat on the horizon,
is going North at 30 knots. I stall it and spin. Over the course of
a second, the nose is now pointed South. Is the Katana moving
South with an airspeed of 30 knots? No, it is not. This is
part of the reason why, during the first turn or two, the
pitch oscillates more violently than in a fully developed spin.

I still don't buy your explanation. A spin is a combination of roll,
pitch, and yaw, all happening at the same time. As a result, the
actual flight path (motion of the CG through space) is hard to see,
especially from inside the cockpit, but conservation of momentum
cannot be violated. From 30 knots, the first half turn/half roll
(which probably takes a bit more than one second, I would think) will
corkscrew the nose down and around, but you are not flying backward!
And until you are established is a steady spin, you will get pitch
motion due to the inclination of the spin axis to the horizon. Once
you are established in the spin, with your CG motion basically
straight down, the spin is usually pretty stabilized (with the usual
exceptions, including Maverick's F-14 spinning out to sea after
departing over the desert - I would have loved to have seen that for
real!)

It's normal for a power plane to spin flatter than a glider - more
weight in the nose (and probably tail) makes for more inertial weight
tending to level the fuselage.

Because of momentum, the airspeed from front to back of the
wings is less during the South pointed nose part of the spin than
during the entry of North.

Still a bad analogy, in my opinion. Think of the snap roll example -
at what point do you stop "rolling" and start "frisbeeing"? You
don't, your flightpath just curves more downward as you initiate the
spin slower.

It sure would be fun to take up a nice spinning glider (a 2-32 for
example), instument it, then take turns trying to make each other
sick!

And yes, this is a frisbee. At least for the first 180 anyway...

Nope. Although, look up Zurakowski Cartwheel - some testpilot used to
do 540 degree rotation hammerheads in a Gloster Meteor, long before
the current airshow acts started doing it in monster Pitts (which I
think are about as interesting to watch as a radio controlled model).
Not a stalled maneuver, though.

Ms. Campbell is the Hawaii state altitude record holder. She
worked at Dillingham as a CFI. She told me during a ground session
she was in an uncontrolled spin for more than 5,000 feet at one point,
with a passenger, before recovering.
She said after landing, she weighed the glider and the CG
was well aft of what was on the 10+ year old "official" form.
And her new calculated CG for that flight was well aft of limits.

Must have been in a 2-32. G

In my experience, the older the calculation, the further back
the actual CG is from it. Dirt and crap on the long lever arm
of the tail do a lot more than crap in the short nose.

Broken glass ships have the same problem with weight in the tail...
G-103s are notorious for it. Othewise, instruments, batteries,
cheeseburgers, and beer tend to move the CG forward.

Except for that 1 in 10 case, I'd guess aft CG is just a contributing
factor, not a cause. But I'd like to see data. When I hear of
a winch launch by an experienced pilot during the first
flight of the season, ending in a fatality, I have to wonder if
he took something out of the nose, or put something in the
tail, and so his stick pressure feel and initial trim setting
were off... Of the stall spin fatalities on record, I'd
bet most, if not all, had CG further back than the 60-70%
forward that Eric described...

Again, the aft CG doesn't cause the spin, it just make it easier to
initiate, and maybe harder to recover. You still have to exceed the
stalling AOA, regardless of CG location. Winch launching is probably
a lot safer overall than aerotowing (from my limited experience in
Germany), with fewer potential gotcha's - plus it's really hard to
kill the winch operator (unless you crash on the winch, of course).

Sounds like trying to turn via ground references down low - a big
no-no

This is required to fly a rectangular pattern with wind correction,
and still part of the PTS...

Not the same as max performance low altitude turning (thermalling),
which are definitely NOT ground reference maneuvers. Pattern turns,
on the otherhand, should always have enough airspeed to be safe - so
are not really "max performance" turns, and are usually no more than
90 - 100 degrees (unless you prefer the 180 degree one turn to final
approach, which I do).

Clearly true. If one weren't trying to land on a particular
bit of ground, and the world was just one big flat runway,
I'm certain landing accidents would be more rare.
Hard to quiz them, the dead are VERY quiet...

Well, most glider landing accidents only break the glider, or maybe a
bush or two - and the reasons are usually pretty consistent. The main
thread seems to be a certain rigidity in the pattern, reliance on
ground references and the altimeter for turns, and failure to engage
brain and remember to fly the plane.

Many of the 10 reports seem to indicate the spirals/spins happened
during the roll, not the turn. High roll rates require a lot of
rudder (and then rudder release), used quite precisely.

Again, AOA is the key. By itself, high roll rates shouldn't lead to a
spin. There is a situation where it can: Initiate a rapid roll after
a push-over from a steep climb to below stall speed. More of a winch
launch cable break scenario, and hard to duplicate while just flying
around, as it requires a transient airspeed below 1-G stall speed
(but at less than 1-G, so not stalled) then increasing the angle of
attack coupled with a lot of aileron. I've tried to get there in my
glider but haven't been sucessful yet.

I commonly induce vertigo in students to demonstrate unusual attitude
recovery. Although easiest to induce by rapid head movements,
I can also induce it with nothing more than a rapid, perfectly
coordinated roll into a steep bank, and then a rapid coordinated
roll to level flight. I've done this with pilots from 10-30,000 hours.
In all of them, if I cover all the instruments on a nice dark night
with foggles on, they get vertigo. Not staring at the ground and
avoiding rapid head movements is a start, but is an incomplete
solution...rapid roll rates and dramatic G changes are another
factor.

Not necessarily - the key is the lack of outside references, coupled
with moving the head too much so as to confuse the inner ear. Then
again, it is also person dependent - some people are very susceptible
to vertigo (and get sick during acro, or just thermalling), I think of
them as inner-ear dependent. Their bodies believe their inner ears,
not their eyes - not good in a plane. Other people are eye-dependent,
and could care less what their inner ear is saying, as long as they
have a good visual reference. I'm in the latter group, I can thermal
all day long and do acro and feel fine, but I have had the leans in
formation in cloud - interesting when you pop out and your internal
gyros cage up!

When I fly gliders, I have to remind myself to fly at least a 1/4 mile
out pattern. I normally fly a power plane (day VFR only) with a 5:1
glide ratio, and a tight pattern, with steeper banks and
faster roll rates at higher airspeed. I don't do this when
in a glider approaching an unmarked landout field with mountains and
no horizon around.

I fly my pattern based on where I want to touch down, and adjust the
pattern accoding to my altitude and the wind. I prefer low, tight,
fast patterns, so I can see what I'm getting into during a landout!
It helps that my glider can get rid of a lot of energy fast when I
need to.

I see we are agreeing again

On the whole, just a different interpretation of the same facts.

Kirk

Kirk Stant wrote:


I fly my pattern based on where I want to touch down, and adjust the
pattern accoding to my altitude and the wind. I prefer low, tight,
fast patterns, so I can see what I'm getting into during a landout!

And if you don't like what you are getting into, how do you avoid if you
are low and tight? Even a high, large pattern will eventually have you
as close to the "what you are getting into", but in the mean time, you
have a lot more time to look things over and change your mind.

I don't think I like the idea of a fast landout, either.

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

Eric Greenwell
Washington State
USA

Slightly off topic but the following is pretty good reading, IMHO.

pdf:

http://home.comcast.net/~verhulst/GB...erLandings.pdf

If you prefer html:

http://home.comcast.net/~verhulst/GB...r_landings.htm


Tony V.


--

Even popularity can be overdone. In Rome, along at first, you are
full of regrets that Michelangelo died; but by and by you only regret
that you didn't see him do it.

Mark Twain

Tony Verhulst wrote:
Slightly off topic but the following is pretty good reading, IMHO.

http://home.comcast.net/~verhulst/GB...r_landings.htm

It really points out one of the largest differences between
power and glider flight: the increased need for no altimeter
approaches.

The Airplane Flying Handbook (AFH) suggests rectangular field engine failure
landouts just for this reason (to
eliminate the problem, just fly further on base).

I must say, however, that I vaguely recall that other countries don't
fly rectangles, but a V and then a 45 deg turn onto final.
Is this true? It seems like a better way to avoid looking
back over the shoulder for the touchdown spot...


--

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

I must say, however, that I vaguely recall that other countries don't
fly rectangles, but a V and then a 45 deg turn onto final.
Is this true? It seems like a better way to avoid looking
back over the shoulder for the touchdown spot...


--

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

Not in this country (UK). But I was taught to do a 45 degree approach at
Minden.

--
Mike Lindsay

Eric Greenwell wrote in message ...

And if you don't like what you are getting into, how do you avoid if you
are low and tight? Even a high, large pattern will eventually have you
as close to the "what you are getting into", but in the mean time, you
have a lot more time to look things over and change your mind.

I don't think I like the idea of a fast landout, either.

Eric, what I want is to have the best look at the potential landout
field before actually landing on it. That means picking the field
early, looking at it carefully while making a last attempt to climb
out (if possible, then setting up a pattern close enough to be able to
see terrain details and pick the exact point to touch down at. That
usually means being downwind at about 500' or so, and that means being
pretty close in.

By fast, I mean about 60 to 70 knots (depending on wind, etc) in my
LS6 dry. That is plenty enough for aggresive turning if necessary to
adjust my pattern, and to float over a last minute fence, but slow
enough that with full divebrakes I can quickly slow down on short
final for a low energy tail first landing.

And I practice this often at my home field, using different runways
when possible to get used to different patterns. And it has worked on
my actual landouts, when necessary (obviously not a good idea when
landing at a big controlled field - that requires a totally different
pattern technique!).

I shudder when I watch 2-33s flying wide bomber patterns, downwind at
1000', and flying long finals. It may be FAA approved textbook, but I
think it is bad technique. I like the BGA's idea of the angled base
leg, which approaches my preferred military-style one turn to final
pattern.

Hope this clarifies things a bit.

Kirk