Lee H. Marzke on 20 Jul 2017 15:22:26 -0700

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Re: [PLUG] Waaaaay Off Topic: Thunderstorm Movement

From: "K.S. Bhaskar" <bhaskar@bhaskars.com>
To: "Philadelphia Linux User's Group Discussion List" <plug@lists.phillylinux.org>
Sent: Thursday, July 20, 2017 3:06:43 PM
Subject: Re: [PLUG] Waaaaay Off Topic: Thunderstorm Movement
Interesting thread that brings back memories. I did a few hundred glider flights in India circa 1970-75. The aircraft I flew included open-cockpit gliders (one a 1940s English design, the T-21B), and gliders with canopies, two Schweizers, 1-26 and 2-33. Every flight was winch-launched to 800-1,200 feet depending on wind, after which one had at most a couple of minutes to find a thermal before it was time to get into the landing pattern. Although I haven't done any myself, I do know that at one of the gliding clubs, just for kicks, they did a few car-tows, which got the aircraft perhaps 400 feet into the air before they had to drop the cable.
Nice,  I've only done auto-tow in the US at a ground launch certification camp weekend.

My club ( MIT soaring ) and I went to S.C. many years back and we earned our auto-tow (ground launch) ratings.   You need a long airport > 5000ft
and you can only climb up to about 1100ft AGL.     The interesting part is the S.C. operation left their ropes out in the grass all year
and they were UV damaged and actually broke every 2nd launch for real.   No need to simulate rope-break.  We got lots of
practice splicing Nylon rope with a fid.   The  airport had three 5000ft runways in a diamond shape and you could land anywhere, so it was completely safe.

The hardest thing to learn is that after a rope break you 1) pull the release (3) times to get rid of any extra rope on your end,  2) Simultaneously push
the nose over ( with NO bank ! ) until you obtain > 50kts,  then maneuver for landing.   If you try any maneuvering before 50K your just
asking for a stall/spin...

Now with the stick pushed forwards to get 0g , your stall speed also goes to zero, and you can maintain control well below
stall speed while the wings are unloaded.    ( Like aerobatic pilots doing hammerheads, the aircraft remains controllable below stall speed to near
0kts as long as the wings are not providing lift )      Most power pilots probability don't understand this. 

It was pretty much impossible to put any of those gliders into the proverbial deadly flat spin - you had to work the controls to get them to spin, and all it took to get out was just to release the controls (though of course, recovering by the book means putting the nose down). India in those days was almost entirely unrestricted airspace (and gliding in those days was subsidized by the Government, and cheap enough for even a college student to afford, the theory being that in the event of a war, there would be a pool of pilots who could be called on to serve).
I also flew gliders in college ( MIT Soaring ) as it was affordable and was the only undergraduate student to be a tow pilot for the club ( as was licensed at age 16 )
sometimes doing 20 tows in a day with breaks only for re-fueling.   I would often thermal on tow when an instructor or private ship was behind me, (not a student)
as the low powered tug didn't climb that well.   The L-19 was another story with it's 230HP it could climb like a rocket and with cowl flaps you could descend at high
airspeed without over-cooling the engine.  Plus,  you could TO and land on grass, unlike tricycle gear tugs with no prop clearance that were restricted to pavement.

The most expensive part of soaring here  in the US is the aero-tow,  and I've only heard of a few places here in the US with a winch or auto-tow , I visited Torry-pines CA long ago
where they had a winch launching over the Pacific cliffs and you could only fly ridge on the cliffs,  find a low altitude thermal, or do a 180 and land the other direction.   

One of my more memorable experiences was flying at the top of a thermal about 1,200 feet above Delhi - that meant the uplift the T-21B got from the thermal was matched with its own descent speed, and so it maintained a fixed altitude. A couple hundred feet above us were some kites (birds of prey), also at the top of the same thermal for them, playing with a long strip of paper tape. One of them would swoop down, grab it with its claws fly up with it for a bit, and drop it. Then another would do likewise. As they played, they kept calling to each other. I still remember it vividly 45 years later…
I've flown with many birds and with 1 or 2 other gliders in a thermal,  they don't fear you at all - just another big bird to them.
I've also flown at Sugarbush VT during wave season in a 1-26 at 70k into the wind climbing up to 14,000 MSL, with ground speed of 0 so your motionless over the ground
and you nearly freeze unless you have full winter parka, boots, etc.   I had no oxygen on board,  but had just been through the altitude training simulator
at Peese AFB that the club required for flight above 10,000 MSL so I knew the symptoms of Hypoxia.   

-- Bhaskar

On Wed, Jul 19, 2017 at 9:30 PM, Rich Freeman <r-plug@thefreemanclan.net> wrote:
On Wed, Jul 19, 2017 at 5:48 PM, Lee H. Marzke <lee@marzke.net> wrote:
> What I also wanted to do on my Decathlon aerobatic flight was inverted flight,  and to steer towards a point
> on the ground inverted, as I couldn't figure out how that worked.  In normal flight, When you bank right , the
> nose goes right, however it turns out when inverted, and you bank right, the nose goes left ! That
> screwed up my mind until figued it out.

I've done it on flight sims - it is pretty intuitive there.  I'm sure
it is less intuitive when you're hanging by your shoulder straps.  In
sims at least you tend to need a fair bit of "negative" pitch to
maintain level flight, probably because the wings aren't shaped for it
(I assume that there is a lot more induced drag as well, but I'm not
sure about that).

> The recommended emergency descent through a cloud layer without a
> gyro is to enter a spin ( which IS stable in most gliders ), and hold the spin until you break
> out of the bottom of the cloud, and then recover from the spin.   OK,  not sure I really want
> to do that maneuver.  I'm OK with spins when I can see but not in a cloud.

That is really interesting.  I'm pretty sure spins are stable in most
aircraft - that is why they're so deadly.  With most other undesired
situations the aircraft will return to normal flight if you just let
go of the controls assuming they're properly trimmed.  With a spin
that doesn't happen because it is stable (that is, when perturbed
slightly away from the spin the plane will want to re-enter the spin -
it takes firm/deliberate control inputs to get it out).

Of course, every plane is different.  When I was doing power off
stalls in the 172 I could barely tell that it had entered the stall
(horn hadn't quite gone off) but it was clear from the VSI, and it
barely took any effort to recover with very little altitude loss.
From what I understand something like an airliner is a whole different
beast in a stall.

> The handle on the far left in cockpit during TO roll are the spoilers.

Yeah, I've played around in gliders a bit in the sims as well.  I'm
sure it isn't quite the same but they do have spoilers and negative
flap settings, and ballast.  I guess they leave the spoiler off until
they take off to reduce the load on the gear.  I was thinking that the
guy sitting on the wing might over-load it, especially at the end, but
then I realized that during flight the load is actually upwards and if
anything he's probably balancing it out somewhat as he moves outwards.

Thanks for the video links - they were interesting, and the sound of
the variometer brought back memories!  I was surprised by some of the
maneuvers and looked up the L-23 manual, and it looks like it will
handle load factors around 6 - I guess without any fuel/etc they can
build them fairly strong.

Makes me want to go flying again, well, until I remember the landing
approach over the trees at KUKT which seems to always be rough.  (It
is much more pleasant at airports that have plenty of grass, like
Trenton/ABE/RDG.  Landing there is like putting it on easy mode...)

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"Between subtle shading and the absence of light lies the nuance of iqlusion..."  - Kryptos

Lee Marzke,  lee@marzke.net     http://marzke.net/lee/
IT Consultant, VMware, VCenter, SAN storage, infrastructure, SW CM

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