snips....
cha-CHING...
There's a world of difference between hitting the ground
with the plane trimmed for best glide, & hitting it half way
through the first turn of a spin.
CE
I agree Charlie but who said you will necessarily stall spin
when the motor quits on the back side of the power curve. We are
only
talking a few MPH difference in the approach speed. Say 66 rather
than 70 MPH
I talked to an old pilot flying a Martin twin engine cargo plane
down in
Baja and he told me he always near stalled the airplane at a
comfortable
altitude to see exactly what the stall speed was so he could adjust
his
approach speed accordingly to minimize the landing distance. The
point
is the optimum approach speed is a strong function of your gross
weight.
If you stick to a fixed approach speed all of the time you may or
may
not be making and optimum approach. If your gross weight is high
you may stall spin out of a recommended approach if the engine
quits
as well. You just need to be aware of the possibility and be
prepared
to shove the nose over right now. If you are ten feet over the
trees there
is not much you can do in any case.
If I'm on final approach (particularly at only 10 ft over the
trees) and
the engine quits I'd much rather be at a best glide AoA than at a
behind
the power curve AoA. If you are going to be making max performance
landings
you should be looking at AoA, not airspeed. Too many variables as
you
mention that make airspeed too inexact for a max performance
(minimum
landing speed/distance) landing. Its like playing Russian roulette.
Add an
AoA instrument to your airplane. It eliminates the variables. A good
AoA
indicator is accurate regardless of weight, G-load, etc... The guys
who
define max performance landings (the US Navy) fly AoA, not airspeed.
And
even with AoA I'd fly a nose low, full flaps, slipping approach
rather than
a nose high behind the power curve approach.
Mike WIlls
Somehow I think we've gotten to an apples and oranges discussion here.
The power
curve is crossed when you reach an angle of attack that requires more
power to
maintain level flight. Let's take the 172 as an example. You can
reduce power
until you reach an airspeed of 65 kts and an engine speed of 1600 RPM
and maintain
altitude. If you wish to go slower AND maintain altitude you must add
power.
Voile, you are on the backside of the power curve. If you do not add
power you go
down. As my instructor used to say, "to land, you must first go down".
If you're
going into our tree lined, power lined, short field you must increase
sink rate to
carry the minimum forward energy over the fence (plus a safety margin).
If you use
55kts (5 kts slower than POH recommended short field approach speed )
you are at a
sink rate that puts you well below recommended glide slope, assuming our
field has a
VASI or PAPI to let you know. To get behind the power curve on approach
you would
have to take the 172 below the very bottom of the white arc on the
airspeed
indicator, in effect making your approach in a falling leaf stall, which
would, of
course, be nuts. I don't have the luxury of an AoA indicator in the club
172's.
Anyone eaves dropping on the cockpit when I'm on approach would hear the
same chant
every time, "airspeed, airspeed, airspeed."
Rick Girard
13B + LEZ
John Gibbons wrote:
VASIS and PAPI are set up for 3 degree ( a very few exceptions ) approach
angle, which is below a normal light aircraft approach which is around 5
degrees. In doing a short field approach you are steeper still, more like
seven. As such they do not provide much useful info in a 172 and I can't
think of any " short " fields that have them anyway. The bottom of the white
arc is Vso ( stall in the landing configuration ) which is well below 55k if
my memory serves me correctly, and is certainly not recommended on the
approach. The speed at which you can use the lowest power setting, yet still
maintain level flight is the top end of the back side of the power curve,
max. slow flight speed and best endurance speed ( around 70k ? ). If you fly
any slower than that you are on the back side of the power curve, period. It
doesn't matter wether you are accelerating, descending or whatever, you are
on the back side. Some a/c are very challenged at arresting the high rates
of descent in this configuration even at full power if the nose is up. If
you lose power or even partially lose power you are dead unless you have a
lot of alttitude to trade for airspeed, but whoops we're on approach and
don't have any of that. If you try full flap power off, or full slip power
off approaches with the nose down an engine failure will mean only that you
have to pull the a/c onto the taxiway. The 172 is not a good slipper at all,
even if you use full LEFT rudder, but is a much safer and more consistent
method than fooling around down low behind the curve. Sorry if I'm rambling
on here a bit, I'd guess though that a lot of people on this list are either
low time , low currency or both and as such would probably be better off
flying in the safest possible manner.
PS If you want to see a real slip, get a ride in a Glastar with a CCW
rotation prop and full RIGHT rudder, you have to hang on and look out the
side window.
Cheers,
John
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