Hi Hartmut,
Comments interspersed below,
William R. Bayne
.____|-(o)-|____.
(Copyright 2010)
On Mar 17, 2010, at 17:26, Hartmut Beil wrote:
William.
I read in my FAA approved flight Manual 56 miles true air speed as
the lowest power off speed for 415-E and G models. This is meant for a
gross weight of 1400 pounds.
A 13 degree up elevator should get you down to 60 Miles in any Coupe.
Maybe less even. But not much. At least this is what the books are
saying.
I agree.
My split elevator stop holds the elevator 13 degrees up
OK, I believe you so far...
and when I let the plane settle to the speed it gives me then , I fly
60 -65 indicated.
OK, I would interpret your words "...let the plane settle to the speed
it gives me then..." as indicating that you are level, power off,
where you are approximately at 13º "up elevator" and at that point of
aft yoke travel beyond which which your "low speed warning cushion"
spring will make itself known. You are flying 4-9 mph above the stall
speed of 56 mph.
It seems evident that you have to pull the yoke further back (into the
"low speed warning cushion" range) in order to bring the plane to that
point in a power-off glide where you should get a mild jouncing or
buffeting at or about 3 mph above the minimum speed. In this I presume
minimum speed and stall speed to be identical.
What is your observed sink rate over this range?
That is the published approach speed for a Coupe. So all would be
good on final, but I would not be able to flare if I would not be able
to pull over the spring stop into a region where I can get still the
nose up.
Actually the the Ercoupe Instruction Manual (as referenced in the
Flight Manual for the 415-E and G) says, on p. 6: "A good airspeed
reading during the approach...is between 60 and 70 mph." As the ground
is approached the flight path is leveled off so as to reduce the
vertical velocity. At the same time the airplane is held off in the
conventional manner until it loses its flying speed."
At an approach speed between 60 and 70 mph you are still carrying the
excess flying speed of 4-9 mph before stall. Personally I favor the 70
mph (True Air Speed) approach, which would give me 14 mph excess flying
speed above stall. Once I flown my approach so as to be level one foot
above the runway at 60 mph, 65 mph or 70 mph, I can reduce power and
STILL slowly move the yoke back so as to reduce sink to zero. If I am
sufficiently skilled, I can do this at a rate that the plane stays
exactly one foot above the runway.
If I reduced power enough, at some point the excess energy thus used to
stay off the runway is gone and the plane gently sinks to touchdown. I
presumed, perhaps incorrectly, that this "touchdown speed" would
general correlate with "stall/minimum speed" at gross weight. I could
be wrong.
This is what the 20 degree up elevator gives you. You can pull wayy
beyond the limitations of the earlier models. Makes for better,
shorter landings.
Now imagine what a 9 degree elevator stop leaves you when you sail
engine off with 60 Miles or less to the runway. Little or nothing.
Per what I have written above, what "little" is available at 60 mph
should still be "enough" to flare the arrival level before touchdown.
Now you need to add power to get the prop wash push down the tail.
That seems not natural and requires planning. Airmanship. Not everyone
is able to do so. These folks will have a rather hard landing and
learn to come in fast.
I respectfully disagree. Power should not be necessary to land as I
have described.
Coming in fast is mostly ok, but when you have a short runway or
other not so favorable conditions, you may want to come in slower.
With the split elevator, you can do that.
To my knowledge there are no published figures for ground roll for the
415-C and CD at 1260 lbs., the 415-D at 1400 lbs. and the 415-E & G
with the split elevator at 1400 lbs. I certainly agree that the split
elevator may be able to get you down to 38 mph at touchdown...I just
have not personally experienced or witnessed that particular feat.
It is not about the stall speed. The stall speed is determined by
wing load. It is about being able to have elevator travel left beyond
the slow speed cushion.
When I pull the elevator full back, power off, the speed go down to
38, then the plane breaks. With power on and just me in the plane and
almost empty tanks, I see speeds around 30 until the stall breaks.
I'll take your word on all this.
You can not get into these low speeds with a 9 degree elevator
limitation.
Agreed. If you don't fly off a 1200' strip, though, of how much
practical use is the ability to touch down slower than 56 mph?
The spring stop that comes with the split elevator is there so you
don't get that low in speed inadvertently.
But you do have to enter that realm in a normal landing, and only the
pilot's "feel" separates "enough" from "too much".
The split elevator makes the Ercoupe more like the other airplanes
that you can stall if you want to, thus flare nicely in ground effect
at low speed
If I can keep the nose wheel off longer than the mains, I'm happy.
, but it still follows the safe design philosophy that you shall not
be able to stall the plane in a normal flight regime.
Could you word your point here another way? I do not understand.
So you keep having an elevator stop at 13 degrees, and then not.
Whoa! 13º "up" elevator in a 415-C or CD is NOT the same as 13º "up"
elevator in a 415-E or G. Per the Ercoupe Service Manual the elevator
area of earlier model Ercoupes is 9.6 sq. ft. Per the Forney Service
manual the elevator area is 7.5 sq. ft., or some 22% less. Accordingly
the response of the different models to yoke and elevator movement is
not directly comparable in the manner inferred.
Your choice how to fly it.
Agree 100%.
Hartmut
To: [email protected]
From: [email protected]
Date: Wed, 17 Mar 2010 16:48:48 -0500
Subject: Re: [ercoupe-tech] Re: split elevator
Ed,
The "Stall Speed" given as Item #1, p. 10 of the 415-D Manual is 58
mph (power off, with "up" elevator limited to 9º).
This is presumed as being at 1400 lbs. gross weight because data in
Items 2, 3 and 4 are "at 1400 lbs., gross weight". on this and p. 11.
The "Stall Speed" given on p. 10 of the 415-E & G Manual is 60 mph
(power off, with "up" elevator limited to 20º).
This is verified as being at 1400 lbs. gross weight on p. 11.
Since the 415-D does not have the "split elevator" and later models
do, I would presume that substitution of the "split elevator" reduces
"minimum speed" (or touchdown speed) at any given weight on comparable
airframes by (a mere) 2 mph.
Two strictly personal observations:
1. I prefer the "look" of the earlier elevator (with a trim
tab)
2. I HATE change in yoke "feel" with the "low speed warning
cushion" spring (and associated mental adjustment in the flare)
Any "cost to benefit" ratio calculated on above 2 mph difference would
make the "goodness" of this conversion all but impossible to justify.
What am I missing, here?
Regards,
William R. Bayne
.____|-(o)-|____.
(Copyright 2010)
--
On Mar 17, 2010, at 06:21, Ed Burkhead wrote:
I don’t think there are enough no-longer-needed split elevators
available to meet the demand.
Now, if someone were to set up an Ercoupe elevator conversion
“factory” with PMA authorization and convert a bunch of elevators, we
could improve the entire fleet.
Or, would it be (under current regulations) that each owner would
“fabricate” a replacement part him/herself, using a skilled mechanic
as his/her assistant?
But, then, demand also depends on cost. Back before you all caught on
to the goodness of the split elevator idea, I wanted one but couldn’t
justify the cost to benefit ratio.
Ed
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