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I’m calming down
now. Comments interspersed below.
Ed
Burkhead
http://edburkhead.com/
ed -at- edburkheadQQQ.com (change -at- and remove the
QQQ)
-----Original Message-----
From: Greg Bullough
[mailto:[EMAIL PROTECTED]
Sent: Thursday, July 08, 2004 1:06
PM
To: Ed Burkhead; Coupe-Tech
Subject: RE: [COUPERS-TECH] Model
C to D conversion paperwork
At 01:12 PM 7/8/2004, Ed Burkhead wrote:
Jeeze, Lynn, there’s no way the 13 – 9
degree change can make a 20 mph difference in touchdown speed. With my D,
the touchdown speed was around 53-55 mph compared to a C model’s 47-52 mph
touchdown with 13 degree up travel.
Anyone who can’t get their D model down well below 60 had better do some
airspeed indicator repairs.
> I don't agree with Ed.
[Ed - ] We agree on most
of this. Differences discussed
below.
> And I'm concerned that someone taking the
words at face-value might interpret
> it to suggest that they come 'over the
fence' in the 60's and thus bend a perfectly
> good airplane.
[Ed - ] I’d certainly
agree that you MUST fly approach at a speed that gives you
1. cushion against wind shear or gusts
2. reaction time in case of loss of power
3. energy for the flair
> The issue isn't whether the plane will
FLY at well below 60. The issue is whether there
> is enough elevator authority to FLARE at
that speed. And it is VITAL that you be able
> to flare if you are at a touch-down speed
which is that low, because you've been sinking
> like a stone at anything less than 70.
And arresting the sink in an Ercoupe with its
> under-cambered airfoil requires
proportionately more time and power and/or pitch down
> than most planes. At 65 it's
flying...sort of. Not particularly well.
>
> Below 70, you are definitely 'behind the
power curve.'
[Ed - ] We need to
discuss the common inaccuracies of the airspeed indicators. Lots of them give high readings. And, some planes may be rigged
improperly and actually have a higher minimum flying speed than other planes of
the same model.
It’s NECESSARY to
determine the minimum flying speed of that airplane.
It’s true that Coupes
have short Hershey-bar wings that develop their best glide ratio at a higher airspeed
than would a longer Cessna wing.
I asserted that an
approach speed of 1.3 times minimum flying speed is a good approach speed. By testing, I found that the best glide
ratio was in the ballpark of 75-80 mph.
It’s true that 70 or 65 is on the higher-sink end of the curve. But I found that I still had adequate
energy for a flair when I approached at 1.3 times minimum flying speed on my D
model.
I’d encourage everyone to
TEST their airplane, starting on a perfect day and at 1.5 times minimum and do
successive approaches till you get down to 1.3 times minimum. Make sure you determine what airspeed
gives you a proper approach speed for safety and a good cushion for the flair.
> I don't really look at the ASI between
flare and touch-down anyway...I look at the runway.
> My landings can be crappy enough without
burying my head in the cockpit, though I've done
> a few that have caused me to want to bury
it somewhere else.
[Ed - ] Agreed. But I often cross-checked my airspeed
when sliding down the final approach hill and then again just at touchdown.
My procedure was to fly
the approach with about 1.3 times minimum flying speed, flair smoothly 1-3 feet
above the ground, then hold it off, hold it off, hold it off till I hit the
stop and it settled the last one (1) foot to the ground.
> Ironically, in a 415D, your touch-down
speed may well be HIGHER if your final
> approach speed is too low, because you
won't have the elevator authority to bring
> the nose up to decelerate in ground
effect. You will thus sink it on, nose down
> or flat.
[Ed - ] Yes, you’ve GOT
to have extra speed to give you energy for the flair.
> Believe me, feeling the elevator hit the
stop while the nose is still pointed down
> and the descent rate is still around the
500FPM rate is truly a 'sinking' feeling.
> It has happened to me twice in some 400
hours of Ercoupe time. Once I managed
> a go-round and the other time a bit of
power changed it from a 'hard landing' to a
> 'firm arrival.' Thank god for Belleville
springs and well-serviced oleos!
[Ed - ] Here’s my story
of how I learned about and got very sensitive about approach speed cushion:
http://ercoupe.org/coupeflyingstories/Gas-line-ice.htm
> With both of my 415Ds, I have found that
if I want to land very short I can come
> over the fence at 72, having brought the
nose uncomfortably high and held around
> 1300 RPM +/- 100 to arrest the sink (the
power makes the elevator work better
> and also arrests sink). However, in that
situation, if the power goes away, the
> plane settles to the ground immediately.
That means that if the engine died, I'd
> be short and probably land hard. I found
this trick to be easier on N2906H
> with it's vernier throttle, than on
N99387 with a quadrant. Two quarter turns
> on the 'tap' was the 'land now' signal
:-)
[Ed - ] Here, we’ve got a
difference in technique. I tended
to fly my approach with 1500 rpm till I turned final when I’d be pulling off
the power. I tried to plan it so by
about 1/3rd of the way down final I was back to idle. Thus, there’s no worry about engine
failure on final. I was taught
that if the engine failed anytime before turning final, I was to turn directly
toward the touch-down point. That’s
the way I practiced it.
By flying at 1.3 times
minimum, in a Coupe that’s on the higher sink side of best glide. If I needed to glide farther, I knew I
could drop the nose a bit, pick up airspeed and INCREASE my glide. This works double when you’re
penetrating against a headwind.
If you’re already flying
at best glide ratio speed (about 1.4-1.5 times minimum), you can’t do ANYTHING
about stretching your glide. Not
ANYTHING. You’ve just got a choice
of where you’re going to land off the airport.
> I believe that the 415D has to be treated
like a high-performance airplane, perhaps
> most like a Bonanza. Stay well ahead of
the power curve down final, perform a
> round-out and flare with plenty of energy
in the airplane in order to guarantee
> effective pitch-up, and that you are in a
sink-free glide right into ground-effect.
> This introduces the risk of ballooning if
you flare too quickly... ...just get the
> nose up and 'don't let it land.' If
you do that, it will make you look brilliant.
[Ed - ] We’re mostly
agreed. You’ve got to maintain
energy for the flair. We still
have to settle whether you have to fly the approach at the best glide ratio
speed (about 1.4-1.5 minimum flying speed) or can you be safe at 1.3 times minimum.
The second issue is – I hate
to give mph numbers much because so many Coupe airspeed indicators are wrong. Whether the indicator is right or
wrong, it’s critical to determine the minimum flying speed of the airplane and
base all calculations on that number.
> Yes, that means coming 'over the fence'
perhaps a bit more quickly than
> necessary. However, the Ercoupe is so
light and slows down so quickly
> that unless you're on a 1000 foot strip,
you're still likely to be okay.
[Ed - ] Granted that a
Coupe can comfortably land hot on almost any local airport.
> The numbers I use on short final are:
>
> 80 - on a normal day. This gives me
plenty of cushion so sink isn't
> an
issue, and lets me choose at the last moment if I want to
>
paste it on or do a 'greaser.'
> 85 - if it's gusty or if N40's wind-shear
machine is cranking (This
> speed
causes me to float, but I prefer to sort all that out over
> a nice
runway, and I still don't use 2000 feet).
> 75 - if I want to keep it short (good for
well under 1000 feet)
> 72 - if I'm having some sort of
short-landing contest (have been as short as 400
>
with 5 knots of wind, 200 with 10)
[Ed - ] What is the
minimum flying speed on which these approach speeds are based?
>
> Once you're in ground effect, and nose
up, then you can mess about with trying
> to touch down as slowly as possible.
You're safe and virtually guaranteed a decent
> landing. Mess around at slow speed
anywhere at or above hangar height, and the
> outcome is in question....
[Ed - ] Yes. Right. I like to finish my flair within a yard
of the ground. Then no matter what
speed you actually touch down, you are well within the comfort range of the plane.
Final comment for runways
that are long enough:
If you come down the
approach at idle, then during the flair you can add just enough power to hear
the increase (about 200 rpm). As
always, the flair should be about 1-3 feet high. If you then put the nose of the plane on the landing lights
at the far end of the runway you are guaranteed a squeeker touchdown. You will be landing a bit faster than
with the yoke full back. But with
that touch of power, ground effect, moderate angle of attack, your sink rate is
so slow it’s almost impossible to thump it.
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