Lee H. Marzke on 20 Jul 2017 16:24:46 -0700

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Re: [PLUG] Waaaaay Off Topic: Thunderstorm Movement

----- Original Message -----
> From: "Rich Freeman" <r-plug@thefreemanclan.net>
> To: "Philadelphia Linux User's Group Discussion List" <plug@lists.phillylinux.org>
> Sent: Wednesday, July 19, 2017 9:30:31 PM
> Subject: Re: [PLUG] Waaaaay Off Topic: Thunderstorm Movement

> 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).

If your 4 point harness is tight, it's not so noticeable,  except that the
first time inverted your feet fall off the pedals !    and of course you have
significant forward stick pressure.  The Decathlon has a symmetrical  airfoil so
inverted flight is not less efficient, but the trim is set for normal flight so
you have to contract that trim.   Normal,  non-aerobatic airplanes may be less efficient inverted
because the airfoil IS optimized for normal flight.

>> 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).

Yes, Most airplanes are designed and certified for anti-spin and will come out themselves.

Most gliders do not have drag buckets under the ailerons to contract
adverse yaw,  and also don't have wing turbulators or stall strips or even wing washout.
So with long wings and HUGE adverse yaw they typically spin very easily.
The Blanik L-33 single seat will often snap roll right at stall as nearly
the entire wing stalls at once.   The L-13/23 is very docile ,however and enters
a spin so slowly from crossed-controls that you may not notice.  This is why
you need to spin each glider that you fly.

My club's check-out in the single seat L-33 required you stall / spin the
aircraft while the instructor signing you off watches from the ground.  My
first stall was nearly a spin as wing dropped and even with instant opposite
rudder, I still had a 70deg bank before it recovered.   ( You recover
from Wing drops or incipient spins with rudder - not aileron - as the
wing is stalled and ailerons don't work or can make it worse )

> 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.

Piper Warrior's have even less pronounced transition to stall because of the
wing washout, and stall strips near the fuselage cause the inboard section of the wing
to stall way before the tip and you seldom drop a wing or fully stall unless provoked.

If you pull back the yolk with power on, and don't release the back pressure the
Warrior will sometimes drop the nose and recover itself and start porpoising
with 2 second period - and precise rudder inputs can keep you level.

This is the old military style 'full oscillation stall' , and if done improperly
can result in a spin entry - so don't try at home without a CFI  and/or
spin training.

Instructors  need to be prepared for students delayed recovery from a stall
and other errors.

Jets flying very high in thin air have their stall speed increase, and
it can get close the the MMO or Maximum Mach number.  This short range of
safe speeds is called the coffin corner.   In the U2 spy plane at it's
ceiling I've heard the difference from Stall speed to Mach buffet is
only 5 kts, and the autopilot must fly it as it's too sensitive for mistakes.

>> 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.

In this case the Spoilers were DEPLOYED during the start of the TO run,
and the actual glider checklist calls for them to be forward, closed and locked
for take-off, so there must be some other reason like overabundance of caution
about climbing above the tug on the take-off roll.

Negative flaps are used at high cruise speed to align the fuselage more with
the relative wind and reduce drag.  We had one ship ( Janus-B 40:1 glass ) that
had these and it felt like downshifting gears when you went used neg flaps at 120K.

> 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.

Note that L-13/23 has a single 1" diameter PIN about a foot long though the main spar
that holds each wing on , and another short 1/4" pin at the drag spar that keeps the wing
from swinging for/aft.   Think about that when you do a loop.

This is to allow easy disassembly for the trailer after landing out. Our club didn't allow
aerobatics, but we did spins and steep wing-overs.

> 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...)

I also want to get back into flying after a long recess.   I've been into
most airports in this area as I was a part-time CFI at west chester ( koqn.net )
for a few years.

When I get a stable job and get back into flying it I'll have to call you up. My
CFI(s) are current , but nothing else at this point,  though for the heck of
it,  I took a BFR  with the Chief instructor a few months ago and passed in 1.2 hours with no stick
time in the past 10 years, likely to all my towing and glider flying experience.

The most unusual approach in this area is Butter Valley Golf Course,  which
has a  ridge and trees ~400ft above runway on base leg so for a short field landing you need to
be almost touching the tree tops on left base in order to be on the TLAR
(that looks about right) path down final.  I took many students here prior to
their check-ride, and if they could do it here,  any normal short/soft approach
was easy.

I landed the Warrior once at the Private Glider club in Beltzville, LeHighton PA, 1500ft
Grass on a hilltop.  But the Warrior can barely get out of there - on a
warm day on grass with 1 person I was only 20ft over the fence at the
departure end.  No other obstacles.   Do anything  even slightly wrong on the
short/soft take-off and you have problems.

> --
> Rich
> ___________________________________________________________________________
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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 
Philadelphia Linux Users Group         --        http://www.phillylinux.org
Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce
General Discussion  --   http://lists.phillylinux.org/mailman/listinfo/plug