From: Jerry Painter
Date: 5/1/2008 7:44:25 AM
Subject: L/D
This is an interesting discussion. Let's see if I can make some waves, just
for fun.
You can follow the same flight path power on/off flaps up/down etc. by
simply varying speed and drag. Power, speed, drag and flight path are all
interdependent variables--the Fab Four in the L/D equation. T-Crafts,
Cherokees, CJ's, -52's, 747's et al. I have to say I've never quite
understood what makes folks think that when you enter the pattern the
airplane suddenly becomes more likely to have an engine failure than while
en route, ergo power-off approaches, but that's another discussion. I fly
over mountains/water all the time. Yes, I understand that first power
reduction is the mostly likely time for engine failure, so take your time
about that, but we're talking approaches. I dare say "nobody," wannabees or
otherwise, "normally" makes power-off approaches in typical military or
civilian trainer, fighter or transport aircraft, feet wet or dry, recip or
turbine, though I'm sure there are exceptions (emergency/practice), but, hey
I'm just a civilian. The X-15 had a near 1:1 l/d, I expect the Shuttle isn
t much better, most of the approach is less than that. In any case, there's
no point in slowing to best L/D or pulling the power off until you've got
the runway made, X-15 or otherwise--we're not talking timed approaches are
we? The only time speed really matters is on touchdown. Budd is absolutely
right about the need to fit into the flow, like it or not--cutting others
off isn't just bad manners, its dangerous. At the home drome, KAWO, on those
occasional sunny and even usual rainy days we have to mix it up with various
civilian single/multi/turbines, helicopters (what makes them want to
land/autorotate on the runways and taxiways inquiring minds want to know,
SSH is--for the better--gone, but, apparently, not forgotten), gliders,
ultralights, RV 360 gaggles, overlapping patterns left, right, parallel and
diagonal plus the odd P-47, Me-109 (thank you, Paul Allen), Apha Jet/L-39
and usual bizjets, practice ILS against the flow with missed right through
the downwind (tho not in the procedure). And once in a while the Navy drops
by in a P-3 for good measure, tho no B-1's or -2's, yet.
Constant speed power-off 60mph approaches in your J-3 or power-off manhole
cover in your Pitts ainna gonna cut it for spacing, 360 or otherwise, no
hurry for combat turnaround. Plus, as Barry says, if you're making a 60
degree bank be sure you keep the speed up because the stall just went to 1.
4Vso. The only good thing about a 45 degree bank in the pattern is max rate
of turn for altitude lost, so its good for that (absolutely necessary?) 180
back to the patch, but the stall goes up to 1.2Vso, so keep the speed up
then, too. And mid-airs ain't no fun, neither.
The ILS is 3 degrees (20:1) for good reason, but not many of us can do it
power-off. Emergencies ain't standard procedure.
Jerry Painter
CFI, A&P, Chief pilot, airport bum, permanent latrine orderly & c.
Wild Blue Aviation
425-876-0865
Wild Blue Aviation