In wave, in blue hole at cloud level, hole closes, in IMC, then what?

On 4/9/2015 9:51 AM, Jonathan St. Cloud wrote:
I do have a comment about coming out of the cloud in a spin. How many
times have you tried to sustain a spin in your glider? I would do this
before I tried spinning out of a cloud. The reason is in some aircraft a
spin will turn into a spiral dive. They look the same but spin recovery
technique will not work recovering from a dive and the airspeed builds very
fast in a spiral dive. First time this happened to me was a real eye
opener, just because I have never considered the glider would transition
from spin to spiral dive. I did recognize it right away and recovered no
problem, but it got my attention as I had never considered this before. I
was in very clear smooth air with lots of altitude. I know the POH for an
ASG-29 says spins will turn into spiral dive in a few turns. Just know
what your gliders does. When practicing spins I do not remember ever
letting the spin go more than 2 revolutions, what if it takes 10
revolutions and on the 3rd revolution your glider spirals.

Good thread though with lots to think about.


Indeed...lotsa good stuff to contemplate, and ideally practice beforehand,
against the time you might (willingly or unwillingly) need to use any of it.

Spinning - what could possibly be surprising in a bird with an Approved Type
Certificate, rated for spins? Ignoring the certification fact that an explicit
number of turns was tested (usta be 3 in the U.S.), and if you go beyond that
you're now officially an unpaid test pilot, and ignoring the fact that spins
are sufficiently complex aerodynamically as to be still "inexactly
predictable" via computational methods, and nodding in the direction that
flight testing of spins and flutter are two things even professional test
pilots still pay Serious Respect to, many years ago I opted intentionally to
become an unpaid test pilot in my 1-26A (still airworthy today!), building my
skills and confidence by exploring spinning behavior. Over the course of a
summer, on days with about 10,000 vertical feet of spin-worthy airspace, I
incrementalized my way into extended spins in both directions...entries,
partial rotations, single turn spins, 2-turn spins, 3-turn spins, etc.

By the time I was up to 3-turn spins, it was becoming clear the ship had
distinctly different behaviors between left and right spins. One direction (I
forget which after all these years), the spin was "textbook classic" - nose
well down, spin rate constant, only full aft stick w. "the correct" (neutral?)
aileron and into-turn rudder convinced the ship to remain in the spin. Similar
control conditions the other direction showed considerable up-and-down
oscillation of the nose throughout each turn, in concert with variable spin
rate, slowing as the nose rose, and increasing again as it dropped. Had I not
seen before in college a US Navy film of A4 Skyhawk spin testing displaying
similar behavior, ALL of the varying-spin behavior would have been 100% new to
me (as a possibility, I mean), though I *was* also aware of the concept of
unrecoverable "flat spins."

Before I sold that 1-26, I'd convinced myself that example would spin "all day
long" the one direction in a stable, unchanging manner...at least up to 17
turns, which was the most I ever did. I also convinced myself it would NOT
ever remain in a stable spin the other direction, never being able to get more
than 5 turns from it before it staggered out from the nose-high condition.
Further, depending on how I positioned the ailerons (against the turn,
neutral, into the turn) the variable spin behavior ranged from "mostly an
'instant' uncoordinated spiral dive" through variable-over-time spinning
behavior followed ultimately transitioning into some form of uncoordinated
spiral dive. Arguably, in the absence of that knowledge, had I ever "needed to
spin through the clouds" I'd'a had a 50:50 chance of doing so in an intact
airframe.

I found it all very instructive and thought-provoking, one obvious conclusion
being not to expect consistent spin behavior just because a ship has an ATC
and is approved for spins! I'm not bashing the 1-26 or certification
procedures. The 1-26 is a wonderful ship for pilots of all skill levels,
allowing all manner of hamfistedness with relatively low risk to Joe
low-time-or-incautious Pilot. Certification procedures have necessarily
defined-before-the-fact conditions which must be met, and it's up to Joe
Pilot to decide how meaningful to him are those limits.

One other conclusion was, I really hoped/planned never to put myself into a
position where I seriously had to consider using my 1-26's spinning
capabilities to bail my butt out of cloud-coffin-corner! Flight in "wet waves"
to my way of cowardly thinking would be really tweaking the tiger's tail more
than I was ever comfortable with as a generic concept...though the devil is
always in the details, ground-to-cloud clearance and terrain beneath being two
obvious considerations...

In the Colorado Rockies (site of most of my soaring), we pretty much never
have to be concerned with wet waves of the sort relatively common in the
eastern U.S. mountains (where I grew up and got into soaring). Nevertheless
the most ice I ever picked up was when I fell out the bottom of a "somewhat
wet" Rockies' wave into a mild band of rotor-cu, beneath/ahead of which I'd
climbed to get into the wave. Being in a 90-degree flapped ship, in a known
location with known ground-to-cloud clearances, I was mostly aggravated at
losing the wave (I was sidling XC, and non-wave flight would slow my
progress). I simply put on flaps and resigned myself to having to re-thermal
my way back into the wave once I dropped below the cloudband. As I recall, the
clouds were ~2k feet thick, and in the time I was in them, I picked up about
an inch of rime ice on the main wing leading edge (and presumably on the
all-flying stabilator, though flying qualities weren't obviously affected).
The accretion rate thoroughly impressed me. Once in the (above freezing)
clear, it sublimated/slid off about as rapidly as it had accreted.
(Considerably chastened, I re-thought that day's XC plan!)

Bob W.

On 4/9/2015 8:51 AM, son_of_flubber wrote:

Snip...
WRT turbulence in the cloud deck layer, my understanding is that the air in
that layer is smooth since the cloud is formed by the laminar flow of air.
The cloud forms where it hit the high pressure isobar and dissipates at the
low pressure isobar. Basically smooth air, no convection... Am I wrong
about this?

I used to think those things too, but my eyeball/butt experiences are Mother
Nature is more nuanced. I've climbed in waves' laminar flow up the faces of
what appeared to be the upwind face of 100% convective cumulus clouds...no
hint of nearby laminar flow in the structure of the clouds; no pileus caps in
sight. One day curiosity got the better of me and (being off the airways and
no other gliders then being aloft) I sidled over to where I poked a wing into
the "cumulus cloud"...still no turbulence. The (presumably) thermic lift
beneath the clouds had been pleasantly smooth, too, though until I climbed
into the laminar portion, only the alignment of the lift/cloud band gave any
visual hint wave was likely abundant. I wanted to go "hard IFR" out of sheer
curiosity, but didn't (sigh...).

Conversely, I've been in lenticular-marked waves and encountered
eyeball-rattling turbulence thousands of feet above the rotor band and
thousands of feet below the lennies. First time it happened I thought I'd
encountered wake turbulence and did a 180 to see if I was going to be on the
news later. No traffic ever seen. Later in that particular wave, and higher,
more - worse, sustained - turbulence. Again no obvious missed traffic. I opted
to land in order to better research and process the day's new-to-me experiences...

Since then, my working conclusion about laminar flow is "not always!" even if
solidly ensconced in a vertically deep wave. Three-dimensional effects can be
significant, as in when winds at varying altitudes vary in (laminar)
direction. Contemplating rocky streams helped me visualize this sort of thing.

Bob W.

On 4/9/2015 9:11 AM, Dan Marotta wrote:
Snip...
Circumstances vary but, when I'm trying to get down from wave, I fly slow
and draggy rather than fast and clean (near Vne). That way, when I hit the
rotor (out west it's often in clear air) it won't be such a bad
experience.

I'll second Dan's methodology. Assuming the glider's nose is pointed downwind
when rotor is encountered, you'll get the double whammy of "whatever the
glider speed is" encounter with a rotor, with wind speed added to the glider's
airspeed...somewhat analogous to trying to land downwind. Flying from Boulder,
CO, my preferred method of descending through possibly gnarly rotor was to
remain in laminar flow until just upwind of the airport - which puts you above
the plains, not the mountains - and descend at low speed, nose into the wind.
- - - - - -


BTW, having all my wave experience in Colorado and New Mexico, your
description of eastern wave sounds intimidating!

Heh. A long-ago Christmas present of a wet New Zealand wave (the Taierari
[sp?] Pet) intimidates me every time I look at it!

Bob W.

On Thu, 09 Apr 2015 07:27:44 -0700, JayM wrote:

I have H201 SN 81 and it will do a beautiful benign spiral! I've had
"hands off" for 15-20 minutes when descending from altitude.
Love the Libelle!

Thanks for the info. I'll definitely check that out next time I fly.

Curiosity: my Libelle was one of two that the GSA (UK forces soaring
association) bought in early 1970. The other one went to the 1970 World
Champs at Marfa. Is that your Libelle? What trim setting do you prefer
for a benign spiral?


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

I've never spun a glider more than about one or so turns and I've read
that most gliders will not stay in a spin by themselves. They tend to
transition to a spiral which, in cloud, without instruments and
training, will likely result in a broken glider. Recall that, in a
spin, the indicated airspeed will stabilize near the stall speed. I'd
suggest you try spinning your glider in gentle air and trying to lose a
thousand feet or more while in the spin. That is, if you really think
it's a viable maneuver.

On 4/9/2015 9:42 AM, wrote:
With the understanding that a spin is a 1-G maneuver, and responding to the original post, with sufficient clear air below and after slowing down, are there any comments about leaving the cloud using an intentional spin?

--
Dan Marotta

It would be interesting to compare descent rate between a fully
developed spin (if you can keep your glider in the spin) and a dirty
glider at low airspeed (brakes, gear, flaps (if you have them), and
speed around 40 KIAS, headed into the wind).

On 4/9/2015 9:53 AM, son_of_flubber wrote:
On Thursday, April 9, 2015 at 11:31:55 AM UTC-4, wrote:
Assuming slowing down first, and with known good VMC below the clouds, are there any comments about coming out of IMC using an intentional spin? (understanding that maximum load during spins is 1-G)
Compared to the benign spiral, a deliberate spin has the advantage of being faster, so there is less time to drift downwind. Especially appealing if you're above the valley floor when you start the spin.

I know pilots who use the spin to descend through strong wave lift in VFR and they comment on how long it took them to descend to the desired altitude. So it may take a lot of turns to get down.

--
Dan Marotta

On Friday, April 10, 2015 at 7:12:24 AM UTC-7, Dan Marotta wrote:
It would be interesting to compare descent rate between a fully
developed spin (if you can keep your glider in the spin) and a dirty
glider at low airspeed (brakes, gear, flaps (if you have them), and
speed around 40 KIAS, headed into the wind).

On 4/9/2015 9:53 AM, son_of_flubber wrote:
On Thursday, April 9, 2015 at 11:31:55 AM UTC-4, wrote:
Assuming slowing down first, and with known good VMC below the clouds, are there any comments about coming out of IMC using an intentional spin? (understanding that maximum load during spins is 1-G)
Compared to the benign spiral, a deliberate spin has the advantage of being faster, so there is less time to drift downwind. Especially appealing if you're above the valley floor when you start the spin.

I know pilots who use the spin to descend through strong wave lift in VFR and they comment on how long it took them to descend to the desired altitude. So it may take a lot of turns to get down.

--
Dan Marotta

A dirty glider flying fast will sink much faster than slow. Because all the dirt is parasitic, which goes up proportional to IAS^2. So dirty glider at 60 knots has 2.2x the (parasitic) drag compared to 40 knots.

Great point! That old V^^2 term, eh?

On 4/10/2015 8:17 AM, jfitch wrote:
On Friday, April 10, 2015 at 7:12:24 AM UTC-7, Dan Marotta wrote:
It would be interesting to compare descent rate between a fully
developed spin (if you can keep your glider in the spin) and a dirty
glider at low airspeed (brakes, gear, flaps (if you have them), and
speed around 40 KIAS, headed into the wind).

On 4/9/2015 9:53 AM, son_of_flubber wrote:
On Thursday, April 9, 2015 at 11:31:55 AM UTC-4, wrote:
Assuming slowing down first, and with known good VMC below the clouds, are there any comments about coming out of IMC using an intentional spin? (understanding that maximum load during spins is 1-G)
Compared to the benign spiral, a deliberate spin has the advantage of being faster, so there is less time to drift downwind. Especially appealing if you're above the valley floor when you start the spin.

I know pilots who use the spin to descend through strong wave lift in VFR and they comment on how long it took them to descend to the desired altitude. So it may take a lot of turns to get down.
--
Dan Marotta
A dirty glider flying fast will sink much faster than slow. Because all the dirt is parasitic, which goes up proportional to IAS^2. So dirty glider at 60 knots has 2.2x the (parasitic) drag compared to 40 knots.

--
Dan Marotta

Indeed better fly fast, say up to 100 knots, with full spoilers and gear down, but not with positive/landing flaps at this speed!
You will be going down at well over 1000 fpm.

Ramy

On Fri, 10 Apr 2015 08:08:09 -0600, Dan Marotta wrote:

I've never spun a glider more than about one or so turns and I've read
that most gliders will not stay in a spin by themselves. They tend to
transition to a spiral which, in cloud, without instruments and
training, will likely result in a broken glider. Recall that, in a
spin, the indicated airspeed will stabilize near the stall speed. I'd
suggest you try spinning your glider in gentle air and trying to lose a
thousand feet or more while in the spin. That is, if you really think
it's a viable maneuver.

Always reading the POH before trying prolonged spins would seem to be a
good idea. Two different behaviours I do know:

- an SZD Junior has three different behaviours depending on pilot weight
* it auto-recovers after 2.5 turns with a light pilot
* maintains the spin with a medium weight pilot
* may go flat after several turns with a heavy pilot
I'm quite light: I can confirm that they self-recover after 2.5 turns
at my weight (72-75kg + parachute) even with the controls fully
crossed. I don't remember the transition points or (for heavy pilots)
how many turns they take to go flat, so if you fly one, read that
part of the pilot's manual before spinning it.

- ASK-21s tend to oscillate after around 3 turns (reported by Edwards test
pilots after the USAF Academy asked them to check the ASK-21 spin
characteristics).
Accession Number : ADA213513
Title : Schleicher ASK - 21 Glider (TG-9) Stall and Spin.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |