Hi Daniel,
Your interest is appreciated.
You're absolutely right that people who try to fly an Ercoupe like
other aircraft always blame the design when things go badly. While
only the uninformed will believe them, this include those (a majority?)
in the pilot "community" that presume all criticism of the Ercoupe
valid without proof. Consider the source.
I can't give you actual "high sink rate" numbers because it's been so
long since I checked it...1,000+ FPM comes to mind. If the
opportunity presents in the next week or so, I'll get back to you on
this. The "best glide to land without power" sink rate is the opposite
extreme of the overall range available.
The "glide to land" option in an Ercoupe is what it is. If the engine
quits and you have no "real" information, assume a 10"1 glide ratio at
which the plane will travel 10,000' forward with every thousand feet
of altitude lost. Do you REALLY want to wait until your engine quits
to check out this assumption?
Monitor a 70 MPH glide on a straight course from 4,000' to 2,000' with
a traffic observer, your altimeter and a watch (or stopwatch). Don't
forget to "blip" the throttle every 30 seconds or so to verify the
engine is running and not just windmilling. NEVER go below 2,000 AGL
when practicing! The only difference in the final 2,000' is "ground
effect" and the strength with which one's sphincter progressively grips
the upholstery when landing without power off-airport.
If it takes you 3 minutes 15 seconds (3.25 minutes) to lose that 2,000'
and your airspeed indicator is accurate, at 70 MPH ground speed on a
calm day and "standard day conditions" you would travel 6,160' in one
minute (70 MPH x 5280' feet per mile divided by 60 for FPM traveled
horizontally). If 70 MPH IS your "best glide speed" for maximum range
and it doesn't take you MORE than 3.25 minutes to lose that 2,000' of
altitude, what does this mean?
It means in 3.25 minutes you would travel 3.8 miles (20,020' divided
by 5,280') while descending at an average rate of 615 FPM! (2,000'
divided by 3.25) It means that if you slow that plane down below 70
MPH without power, the rate of descent will INCREASE, so don't even
think about doing that. It means you MUST sustain that 70 MPH trimmed
glide all the way down, flaring to slow just only before touchdown
(trading excess speed in the flare to reduce excessive sink).
Touchdown off-airport at a rate of descent of about 300 FPM with
immediate brake application (unless ground is soft) should minimize
ground roll-out and potential damage.
Check your Airspeed indicator against your GPS for accuracy at 70 MPH.
Vary the trimmed speed up and down seeking the least sink rate and then
see how much the sink rate increases to gain another 5 MPH forward
speed. You need to cover ground at a good rate as well as stay aloft.
If the 3.25 minutes is not optimum for your plane, redo the
calculation(s).
While I have a prewar Ercoupe brochure that claims a landing "ground
run" of 200' possible on pavement, you will need no less than 500' so
as to clear a 5' fence, flare and stop before hitting something; 1,000'
or 1,500' if possible. Pace off 1,000' at your airport and mark it.
Make an overhead pass at 2,000' AGL and mark your windshield with tape
either side such that you know what that 1,000' looks like from that
height. You will want to evaluate a potential landing site while above
2,000' AGL without livestock, power lines, ponds, gullies, crops,
furrows, trees, fences, gates, signs and vehicles. Learn and stay
familiar with what these things look like from that high. Learn the
clues of wind direction at ground level from that height. No clues =
light winds and longer ground roll. Strong wind lowers touchdown speed
and ground roll the more directly you can land into it.
Go up again on a calm day having picked two landmarks 3.8 miles (or
whatever) apart. Set up a glide to commence at 4,000' AGL from above
one towards the other (GPS is the best way to judge this). Once the 70
MPH glide at idle is established toward the second landmark, put a
piece of tape on the windshield such that the tape is "on the landmark"
when you resume your "normal" sitting position. A 12" wide line either
side of the windshield centerpost marking this "line of sight"line
inside your windscreen will reveal to you in a slow 360º turn the limit
of your glide range (if the wind were calm) FROM ANY ALTITUDE within
which to pick a landing site while trimmed for a steady 70 MPH with the
throttle at idle. If other directions do not look more promising,
gliding downwind will allow you slightly increased range within which
to select a landing site.
As to numbers, which of your instruments is more reliable? Trick
question. A VSI indication is a momentary "snapshot" of what is
happening at a given moment. The Altimeter is slow, but remarkably
accurate representation of what is happening over a longer period of
time. So let the airspeed and trim control the rate of descent until
just before touchdown, then using Airspeed, eyes and seat of the pants
govern your final control inputs (in that priority).
Best regards,
William R. Bayne
.____|-(o)-|____.
(Copyright 2010)
--
On Jan 1, 2010, at 22:04, Daniel Arditi wrote:
William,
I carefully read your mail about the Coupe 'glide
ratio', and found it very interesting. I consider this topic really
important because it is related with security.
There is one thing I would like to know, and is the sink rate in
numbers (for example in feet/minute), when the Coupe is gliding like a
refrigerator as all pilots say (you referred as 'alarming' rate of
descent).
I heared several times this comparison with a refrigerator, but this
is the first time I hear it the way you expressed, and it sounds
marvelous (I am referring to the phrase "In computer lingo, this isn't
a bug, it's a feature! Learn to use it.").
I think it has to do with something basic, but important, as to know
the plane we are flying. Just that. The plane is, as it is. It is in
our hands and mind the capacity of understanding it, how it behaves in
different conditions, configurations, and that is not free. We have to
invest some time to know how 'the machine' works and fully understand
it.
Thank you very much in advance for all your help.
Happy 2010 to all of you !
Daniel Arditi
Ercoupe Argentina.
