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wild.blue(at)verizon.net
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 Posted: Sun May 04, 2008 4:43 am Post subject: Samold, reminiscing |
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Y’all—
I remember years ago my dad was at Boeing working on the 727, trying to cram
high-lift devices into the wing and still leave space for landing gear and
fuel. Triple-slotted trailing-edge flaps and Krueger leading-edge flaps
gave the three-holer reasonable runway performance and expanded the
cruise/stall speed ratio. Spoilers for speed control on descent. Then
there was the SLC crash and subsequent fire (followed by crew bailout while
the pax burned criminal negligence). It took old-timers a while to figure
out how to manage energy/L/D on approach. All that induced drag required
lots of power to get ‘em to the threshold on a 3-degree glide slope. They
still wanted to use power to control glide path, too. No worky no mo
without that prop disc drag and long spool-up times. “Reverse-loading” was
de rigeur on Dougs and Connies, non? Or was it?
I guess we should be clear about the use of the term L/D in this context:
We’re really talking about energy management in variable
lift/drag/power/descent-angle configurations. Things like flaps and gear,
propeller disc (sometimes), parasite and induced drag all play a part in the
L/D/energy equation and resultant “glide” ratio, and so does power and speed
just like with the 727. Unlike most 727 approaches, we don't usually make
long, flat straight-ins at fixed airspeed with all the laundry out.
When I learned to fly most of us were still being taught to always make
power-off, fixed-speed approaches, using the “key” position (wherever that
was) to somehow educate our eyeballs to make “accuracy” spot landings. It
was a difficult thing to learn, slips were considered cheating, but we used
‘em anyway. 200+/0- feet tolerance for Private Pilot, 100+/0- feet for
Commercial, same as now. Landing short was (and is) death. Lots of fun in
2-control Ercoupes. Wolfgang Langewiesche was a test pilot for Erco and
that’s why he talks about slowing down to increase induced drag and steepen
the glide path in Stick and Rudder—its right in the old Ercoupe POH’s. Just
make sure you put the nose down at least 200AGL so you'll have energy to
generate the lift to stop the descent and make the
flare—Smackerooney-McFaddee, otherwise. Spot landing contests were big
deals at small-airport fly-ins—which were actually participatory aerial
activities and not just about watching aerobatics and fly-bys. Not many
people had heard of Curtis Pitts or Betty Skelton, even if Cox had a “Little
Stinker” model, or EAA for that matter. Only a rare few had T-6’s or Vultee
Vibrators, tres spensee. Cavalier was trying to sell P-51’s to various
militaries. Bob Hoover was God incarnate.
Emergency landings were just like “regular” landings. Only a few schools
used 172’s and they still made the same old fixed-speed 70mph approaches,
but had to make what seemed like multi-mile-finals to get ‘em down to the
ground. Some didn't even bother to use the flaps—oh, no, this is a big
airplane, very tricky, them flaps is dangerous. We only do that in great,
big Bonanzas or Navions (lovely old airplanes), but no, you can't fly one,
and multi-engine was for the high-buck crowd (I was just a kid, no dough not
hardly). We still see some of that happening today (and lots of schools
around here still use multi-engine airplanes for complex/high-performance
training, just like then), scary sometimes as always, though flap use
throughout the approach is pretty standard now. But lots still teach
fixed-speed approaches, 70mph/kts all the way from downwind to touchdown,
flaps extended and lots of power, 747 patterns, 150’s to Duchi. We’re
perfectly justified complaining about them taking up excess space and time,
plus the potential danger if it quits. But fact is, they seldom quit. Hard
sell. Gotta fit in, like it or no, safer that way.
I don't think I’m unusual in advocating power-on, variable-speed,
incremental-flap-extension (when possible, late extension if not
incremental) and/or slipping (on short final) approaches, using a
combination of pitch and power to control descent path and airspeed, whether
in J-3’s, 172’s or Yaks. Never had a Pitts but am kinda looking for an S-2A
or CAP-10 to play and teach (myself included) with. One of these first fine
days. I'd love to have an RV or another Yak/CJ, but po’ boy (sorry, Craig,
for stealing your line) that I am, its gotta make $$$. No experimentals
allowed, sigh. How do you (legally?) do it, Larry Salganek?
For better or worse (and I think mostly “better”), the “key” position isn't
talked about much any more. “New” airplanes like C-172’s and 150’s with
their big flaps are kind of like 727’s: if you want to use those
high-lift/high-drag devices anywhere other than short final you either have
to make very fast or very steep approaches and/or use power. Revolutionary
stuff, at least compared to T-crafts, Ercoupes and Luscombes. Single-engine
aircraft with performance like Yaks, CJ’s etc. are still mostly only used by
the military. And so we have “complex,” “high-performance” and
“powered-lift” (where can I get one?) ratings/endorsements and RPA events.
Big, bad, very scary.
Its easy to make the energy equivalent of a power-off, best L/D approach
(even the same flight path if you want), power-on, as long as you keep the
speed (energy) up, the pattern close-in (hose-nose curve if you like) and
incrementally reduce speed by reducing power and increasing drag to arrive
at “fence” speed on short final. Stabilize the approach path, vary the
speed. Doesn’t take a lot of skill to land on the “spot.” Keeping the
speed up gives lots of margin above the stall and the inertia to get you to
the runway while keeping you cool if the fan stops turning and you start to
sweat. Not steep, not slow, FAST. That’s what I like about Jim Bourke’s
“high-speed” 3-bladed speed-brake approach in his -54. You can’t use the
prop like that on many airplanes, but Yaks and CJ’s have pretty effective
flaps and slipping your Pitts will slow it right down, too.
I understand what you’re saying, Budd, I just think there’s a better way,
most of the time, and its hard to fit steep and short into the flow, maybe
that’s what you’re trying to explain, you don’t have to slip all the way, or
steep. Roger that. Maybe what I was doing when we flew your Pitts, slipping
steep, all the way from power reduction (off) to flare, wasn’t what you
wanted me to do then, either, but that’s what I thought you wanted. And it
was fun, even if I never mastered the roll-out. My aerobatical “skills”
aren’t much better now, either--haven’t had much opportunity to practice
(that’s my excuse and I’m sticking with it). Did you finish your hot rod?
High energy compensates for high drag and vice versa. No, you won’t get max
L/D at high(er) speed, but not so bad, usually (up the wing loading/gliders
full of water exception), and altitude is still your friend. 360 overheads
are lots of fun, but I really don’t understand fixed/low-speed power-off
360’s with steep banks. Why not keep the power on and the speed up? Is it
that tough to formate while varying speed? Yaks, CJ’s and RV’s have good
flaps, Pittses and even 3-control Aircoupes can generate lots of drag
slipping, no boards (?), yet, Doc.
Staying behind 70mph J-3’s on downwind or speeding it up to stay ahead of
bizjets are problems we just have to deal with, regardless.
Push-Pull: My ignoramus presumption is that at/near zero-thrust with
significant, rapid throttle up-down or speed changes, the lash in the
gearbox can generate lots of alternating big inertial loads, wear and tear
on the gears, shafts, bearings etc. Reverse-loading, per se, is not the
problem, it’s the back and forth. No? Plus, Big round engines have lots of
reciprocating and rotating mass (though I understand R-2800’s and maybe
others have 2800RPM redlines) to accelerate back and forth. Low compression
ratios and supercharging mean you can run at low RPM and high MAP and
maintain high MAP at altitude without stressing the engines, thereby
“driving the prop” and relieving inertial loads. The only way the prop can
drive the engine is “high” speed, high RPM (low pitch)/low MAP settings, i.e
, speed-brake operations. Eh?
So much for “facts” only, no old-wives tales, please etc. Sheesh.
Sometimes I discussed myself. Even more on my web site. Geez, I love this
flyin’ stuff, too, Pappy!
Jerry Painter
CFI, Chief (and only) Pilot, A&P, Permanent Latrine Orderly & c.
Wild Blue Aviation
425-876-0865
wild.blue(at)verizon.net
www.FlyWBA.com
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viperdoc(at)mindspring.co
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| Posted: Mon May 05, 2008 6:04 am Post subject: Samold, reminiscing |
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. Low compression ratios and supercharging mean you can run at low RPM and
high MAP and maintain high MAP at altitude without stressing the engines,
thereby
"driving the prop" and relieving inertial loads. The only way the prop can
drive the engine is "high" speed, high RPM (low pitch)/low MAP settings,
i.e, speed-brake operations. Eh?
Jerry Painter
CFI, Chief (and only) Pilot, A&P, Permanent Latrine Orderly & c.
Wild Blue Aviation
425-876-0865
wild.blue(at)verizon.net
www.FlyWBA.com
Great dissertation. So it all boils down to the last 6 sentences of the
email you sent out on Sat. correct?
We are loading up our engines when push the prop lever to 100% (or 80%) and
pull the MAP lever to 0 mmHG (idle) in an effort to slow the aircraft down.
So my initial statement that low pitch and low manifold pressure using the
prop as a speed brake was/is correct.
Not smash the dead horse to pulverized dust here but I think I have done so.
Doc
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