Thanks for the kudos, Ron
I just realized a few dots that I could have done a better job of
connecting.
My description of gently sinking to the runway at "minimum speed"
probably appears inconsistent with my acknowledgment that at altitude
flying at minimum speed will have the coupe "sinking like a stone".
Reality is what you observe at altitude. "Minimum speed" aloft defines
the lower limit of the coupe's "high sink rate" range and is where it
is at it's highest.
I don't recall the "crossover" point of coupe airspeed where the sink
rate begins to increase as speed is decreased, but it is probably near
80 mph. So I do not ascribe any advantage to flying an approach at 60
mph over flying it at 70 mph. From a pattern altitude 1000' above
ground level I set up my approach using an engine rpm that allows me to
descend 333' from downwind to base, 333' on base, and 333' on final.
Most will be utterly amazed if they try to do this sometime at idle
which, at many airports, would be dangerously inconsistent with the
wide patterns commonly flown today.
Ahhh, but what does one do when there is traffic, or at a tower airport
where they call your turns? Well, if you time how long it takes to fly
the approach described, you know your "time in descent". Fly a few
straight in approaches when there is no traffic and pick visual cues to
clue you when to begin your descent. Then fly your original pattern
again and you can see pretty much where what has to happen on any
approach flown in between those extremes. The visual "perspective"
will imprint sufficiently on your brain over time that you will be able
to do this at unfamiliar airports with only slightly more concentration
than at your home field.
When landing, you alter reality. ;<) From, say, 70MPH you are
"scrubing off" speed. That "excess" energy is being used instead of
engine power to keep the plane off the pavement and so the resulting
"sink rate" is, effectively, zero during the process. Once the forward
speed of the aircraft is thus reduced to "minimum speed" there is no
more "excess" energy and so at that speed the aircraft gently sinks to
a perfect landing.
Regards,
WRB
--
On Mar 15, 2010, at 12:25, Ronald Hynes wrote:
Bill, Your article here is long over due. It is the best and most
concise that I have ever read.
I would print it off in big letters, frame it and mount it on
my wall here. It applies to all aircraft types,such as the Piper Short
Wing types.
Ron Hynes
--- On Sun, 3/14/10, William R. Bayne <[email protected]>
wrote:
From: William R. Bayne <[email protected]>
Subject: Re: [ercoupe-tech] "Falling Out Of The Sky" at 72 mph
To: "ety" <[email protected]>
Received: Sunday, March 14, 2010, 11:43 PM
Jerry,
Your G model has (or should have) the "split elevator".
If the air speed indicator is accurate and if the plane is rigged
correctly it WILL NOT "fall out of the sky about 72 mph". That's
well above the "high sink rate" range. As a first step, I suggest
you take a GPS aloft, slow the bird to 73 mph indicated, and compare
the two readings. The Approved Flight Manual for Models 'E' & 'G' on
p. 11 showed a "true airspeed" of 60 mph when 56 mph was indicated,
70 mph when 67 was indicated and 80 when 78 was indicated.
Landing the various coupe models at the speeds Ed stated is not
rocket science, but it does presume an accurate air speed indicator
and proficiency in accomplishing an appropriate sequence of events.
In my own case, I had absolute confidence in the Ercoupe Instruction
Manual and "just did it"; but some are more comfortable having these
things demonstrated before they can proceed.
As a rule of thumb, the indicated airspeed is higher that the truth
below 100 mph and lower than the truth above. For all values above
"minimum speed" the error is 3 mph or less. That's not enough to get
anyone in trouble that has any "feel" whatsoever for the aircraft in
flight.
The "stall" in an Ercoupe should be a gentle drop of the nose to pick
up a few miles an hour and altitude loss should be minimal. If the
yoke is moved back too rapidly near the minimum speed, the resulting
"whip stall" is much more abrupt and more altitude is lost. This is
something best worked out at altitude and not just above the runway.
Should a low time pilot "balloon" (suddenly climb and find themselves
5-10 feet off the runway with little forward speed), immediate
application of full power restores lift to the wings with minimum
loss of altitude. Hesitation, however, will likely result in a hard
landing with possible damage.
Most of us have a WW II training base with long runways within flying
distance that is now municipally owned and operated. Go there and
make any necessary arrangements to practice slow flight and touch and
goes with plenty of hard surface available.
With a 5,000' runway, practice slow flight...holding the bird one
foot off the pavement at the slowest speed possible. Before the
coupe can "stall", it will sink. So long as you can keep the bird
from touching the runway surface with the yoke at a constant speed
you absolutely cannot stall while in "ground effect" at that speed.
Keep reducing that speed in two mph increments and eventually you
will be able to fly an approach arresting descent one foot off the
runway and fly the length of it without touching down.
Next time around, at that same constant speed move the yoke back a
bit. If the plane goes up, you weren't flying slow enough. If it
sinks to the runway surface, it will be your slowest, smoothest
landing ever. At the moment of touchdown, THAT is YOUR plane's
"minimum speed" occurring just when you want it to...at touchdown.
Jot it down for future reference.
If you go back up to pattern altitude and establish that "minimum
speed" you will probably find that you are sinking like a stone.
That's why the landing approach is not flown at that speed in an
Ercoupe. The G model has a power off stall speed of 56 mph. The low
speed warning cushion (spring) is supposed to be felt at 60 mph.
The 415-D Approved Flight Manual on p. 10 suggests an approach speed
of 75 mph and its power off stall speed is 58 mph. The manual for
the E & G models refers you to the Ercoupe instruction Manual, and it
suggests approaches be flown between 60 and 70 mph. At or near 1400#
the higher value is more appropriate.
Remember that 70 mph (true) is your "Best Rate of Climb" (see Climb
Data, p. 10 of the Approved Flight Manual for Models 'E' & 'G'). At
that speed, anytime you move the yoke back gently the energy of the
"excess speed" is converted into altitude and the plane's altitude
increases even as the forward speed decreases. Your speed for "Best
Angle of Climb" is even slower at full throttle. This is simply NOT
a speed range where you are tempting fate so long as you understand
how to trade speed for altitude and altitude for speed. This is a
fundamental skill all should practice, but If you are more
comfortable flying the approach at 80 mph, do so. The speed of the
approach is relatively unrelated to the speed at which touchdown
takes place.
Most find it easier to establish a "stabilized approach" (constant
airspeed and engine rpm while maintaining a relatively constant rate
of descent with the yoke) until just before touchdown. When you
cross the runway threshold at 5-10' up reduce power and SLOWLY move
the yoke back only as fast as does NOT make the bird climb. The idea
is to slowly increase drag with higher and higher angle of attack
holding the plane one foot off the pavement and when ALL the "excess
speed" is thus scrubbed off the plane will gently sink to a very
smooth landing. Unfortunately you may be using 4000'+ of runway to
do it.
Now do this again, establishing the one-foot-off slow flight.
Simultaneously close the throttle and move the yoke back to keep the
plane "balanced" at that one foot off. Once THAT coordination is
worked out, reduce engine rpm on final (if necessary) to cross the
"fence" at 70 mph. This should make it possible, with practice, to
land and make most second turnoffs WITHOUT BRAKES!
Minimum speed at the moment of touchdown is desirable because (1) the
plane can't lift off the runway again without power, (2) the wear on
the tires (the "chirp" at touchdown) is less because they have to
"spin up" only to the lower speed, and (3) brake puck and disk wear
is reduced so much that once the technique becomes "standard
operating procedure" for you there will likely be the need to land
fast and hot about once a month in order that the puck remove the
accumulated rust from disuse.
Operating a properly rigged Ercoupe in this manner is "stall proof"
except in high, gusty crosswinds. For high, gusty crosswinds, add
5-10 mph to your approach speed, but chop the power over the runway
threshhold at 5-10' up and do everything in the preceding paragraph
exactly the same from that point on. Having extra speed at or after
touchdown is a PROBLEM, not "insurance". Should a gust suddenly lift
the plane off the runway, immediate throttle restores lift to the
wings and returns to the pilot the option of go-around or a smooth
landing (remaining runway permitting).
Until this level of proficiency is developed (and more than a few
that will "instruct" in a coupe don't have it to pass on), your are
not master of the Ercoupe. Until you are master there is risk.
Maximum safety depends on owners or operators reducing that risk to
zero with appropriate priority.
Your metal wings reduce your useful load, but they have no meaningful
effect whatsoever on your approach speed or minimum (touchdown)
speed.
Hope this helps.
William R. Bayne
.____|-(o)-|____.
(Copyright 2010)
