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wild.blue(at)verizon.net
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 Posted: Fri Apr 07, 2006 2:24 am Post subject: glide ratios |
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Remember, the airplane Bud was flying was "Furias," a Hawker Sea Fury with a
Pratt & Whitney R-4360 engine and a monster prop, so his technique may not
be entirely applicable to the airplanes we fly, but probably pretty close.
Here's what he did:
1. He pulled up (actually, he'd already pulled up--s.o.p. at the end of a
race heat--that's when he discovered the problem) to give himself altitude
to work with, time to think and to reduce airspeed;
2. Pulled the prop all the way to low rpm. Since we're talking
engine-driven geared superchargers in Furias and our airplanes, too, that
also substantially reduces manifold pressure. Yak-52's and Nanchangs don't
have much propeller governing authority and pretty skinny blades (usually),
so the effect may not be as great as with the 4360, but you will reduce
power;
3. Pulled some substantial G's to load the airplane and increase induced
drag, further reducing speed to allow landing gear and flap extension;
4. Landed on the longest runway available. Pulled the mixture on short
final. On Furias the resulting power-off, full flap glide angle is seriously
nose low, so don't get excited and pull the mixture until you are absolutely
sure you will make the field. If you've never made a power off, full flap
landing in your CJ or -52 you may be surprised at the pitch angle needed to
maintain speed. Worth practicing every now and again.
5. You and I might want to obtain clean shorts. Bud got a drink of water
and continued with business.
The airplane and engine were undamaged. In fact, the throttle linkage was
re-connected and the airplane continued racing. In retrospect, this all
seems pretty elementary. However, when you're doing more than 400mph in an
airplane with a few thousand horsepower under the cowling, it's a little
different than the emergency landings you practiced years ago in a Cessna
150. The guys--and gals--that race at Reno not only have serious cojones,
they've got to be on top of emergency procedures for their airplanes and
pretty fair with the stick and rudder. Chances for very serious malfunction
are way high.
I agree that flipping the mag switch on and off is probably not a good idea.
Imagine the inertia of the huge prop on a 4360, or even on a CJ or -52, and
the loads from instantaneous full power torque reversals. I remember seeing
pictures several years ago of a CJ that had a sudden in-flight engine
stoppage. The crankshaft was twisted a whole bunch by the prop inertia
(though it remained attached--splined shaft, YMMV, esp w/flanged shaft).
WWI rotary engines were low-horsepower, low-compression and though they had
lots of engine rotating mass, also very low propeller mass and the
crankshaft was firmly attached to the firewall, so no great opposing forces
to be absorbed like a "normal" airplane engine.
My guess is the reason we shut down with ignition (esp HS-6/A) and full
throttle advance is that pulling the mixture won't shut the fuel off
sufficiently to obtain clean shutdown--a function of carburetor design. A
little residual fuel could result in dieseling, kickback and engine damage.
Again, what works for one engine, even with similar systems, may not work
for another.
It's easy to say "just jump" if something goes south. The problem is
knowing exactly what's wrong, what your options are and the probable results
of each. Why throw away a perfectly good airplane--especially your own--if
there's a reasonable chance of saving it? Reno racers don't have ejection
seats (except you L-39 guys, Barry). More than one has been killed trying
to jump. Reminds me of the story a friend told me about flying -105's in
Viet Nam. He was one of the original Wild Weasels. As sometimes happened,
they took a little damage. While my friend was pondering the question, his
GIB said "Let's get outa this SOB!," so they did. No sooner had they
departed the airplane than it went kablooey. If the GIB hadn't spoken up,
since everything seemed to be working OK, he would've continued on and not
be around to tell the story today.
Sometimes it's easier to let the taxpayers deal with it. Not so easy if it
s your pride and joy and you're just not quite sure what's happening...
Jerry Painter
Wild Blue Aviation
425-876-0865
wild.blue(at)verizon.net
http://mysite.verizon.net/res0cs5r/index.html
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Rob Rowe
Joined: 10 Jan 2006
Posts: 124
Location: Berkshire, UK
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| Posted: Fri Apr 07, 2006 2:36 am Post subject: Re: glide ratios |
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| brian wrote: | | I still think you can modulate the power output with the fuel cut-off lever if you are careful. |
FWIW - a fellow -52 driver experimented with the fuel cut-off lever at ground idle a couple of years back.
To his surprise it idled for several minutes before cutting out due to the c. 1 litre fuel reserve sat in the downstream compensation tank (the yellow sphere on the firewall) ... so even at full throttle there could well be a (guesstimated) 15-20 seconds of full power available.
Equally on re-opening the fuel cut-off afterwards would require the fuel pump & compensation tank to be re-primed before the pressure carb would function again ... this might take some time (and manual intervention!).
So speculate that the power latency between fuel shut-off & restoration might not be conducive to the crisis at hand ... so maybe the mags are the more predictable control to use after all.
As an aside - my understanding is that the fuel cut-off lever linkage is engineered to shut off & is not to be relied upon to re-open again ... to be kept in mind even in an emergency.
Rob R
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ira.saligman(at)verizon.n
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| Posted: Fri Apr 07, 2006 3:16 am Post subject: glide ratios |
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Has anyone timed how long it takes from closing the Fuel Shut Off until the engine stops?
Ira Saligman
isaligman(at)saligman.com (isaligman(at)saligman.com)
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dsavarese(at)elmore.rr.co
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| Posted: Fri Apr 07, 2006 3:57 am Post subject: glide ratios |
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".....my understanding is that the fuel cut-off lever linkage is only
engineered to shut off & is not to be relied upon to re-open again."
I'd be very interested in hearing where you found that information Rob.
Dennis
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Valkyre1(at)comcast.net
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| Posted: Fri Apr 07, 2006 10:36 am Post subject: glide ratios |
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Thanks Cliff. Good Point. I knew that a 360hp engine had to have a downside somewhere. Other than that and the molecular changes inherent to aging metal, I can't think of a better previous owner than Jeff "Linedog" as far as treating my CJ6 well.
Guess I'll just have to review my options as well as do a very thorough pre flight at all times.
I've only had one negative experience in light airplanes with fuel controls. That was when I was instructing in a Cessna 150 and had the mixture control come out in my hand while shutting down. Of course it didn't shut down (no I didn't use my inhuman strength to yank the thing out). That was more of a humorous experience and at least I could get out, open the cowl and mechanically shut it down. Things do tend to loosen up what with all of the yanking, banking and vibration.
- Val
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Rob Rowe
Joined: 10 Jan 2006
Posts: 124
Location: Berkshire, UK
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| Posted: Fri Apr 07, 2006 11:41 am Post subject: Re: glide ratios |
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| dsavarese(at)elmore.rr.co wrote: | ".....my understanding is that the fuel cut-off lever linkage is only
engineered to shut off & is not to be relied upon to re-open again."
I'd be very interested in hearing where you found that information Rob.
Dennis
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Dennis
I amended my original web posting within a few minutes to remove the "only" as I realised it misconstrued a one-way operation by design, but guess web edits don't get cascaded into the email list.
While the YAK-52 fuel valve has a distinct binary operation which should snap on or off reliably, it's the control linkage that may not be so dependable when being "pushed" on versus being "pulled" shut.
This arose from a discussion I had with a Lithuanian engineer some 18 months ago when I was researching the fuel system's operation.
Rob R
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