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From: Ed Burkhead [mailto:[EMAIL PROTECTED]
Sent: Thursday, June 15, 2006 9:05 AM
To: [EMAIL PROTECTED]; Cflyin
Subject: [COUPERS-FLYIN] Ercoupes - a "short" history (long message)
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> -----Original
Message-----
> From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]
> Sent: Wednesday, June 14, 2006 11:05
PM
> To: [EMAIL PROTECTED]
> Subject: X Wind
Concerns
>
> Ed,
>
> Now that I have had some time to
research Ercoupes, I realize they
> have no rudder pedals. Are the rudders tied into
the ailerons?
>
> I would like more information on the
design considerations as this was
> in conception. It goes against all I've been told
to believe.
>
> Someone was out of the box on this one, hmmm,
curiouser and curiouser.
>
> You have a nice website and community, it seems
like a sickness. :)
>
> Dave Bohannon
>
Dave,
Here's a short history even though it makes a long
e-mail message. This is from memory and I might have slipped on some
details, especially in the exact time line. But I think it's pretty
accurate.
In the late 1920s-early 1930s, Fred Weick was senior
researcher at the NACA full size wind tunnel, the one big enough to take entire
aircraft.
A burning issue at the time was stall-spin
accidents.
As part of his research, Fred went to the National Air
Races and had as many pilots as possible take him up and do stalls and spins in
lots of different aircraft. (Given the state of the art of aircraft in
those days, this seems heroically brave or stupid to me. But he survived
and got a lot of information.)
They continued to research stalls and spins and came to
clearly understand them.
In the mid-1930s, Fred and a number of the other NACA
engineers decided to build a test-bed aircraft. They built the W-1 (W for
Weick), a high wing, tricycle gear aircraft which they flew, tested and
modified. Some experiments involved linked ailerons and rudders and they
proved the efficacy and safety of the concept.
Along the way, Fred developed the swiveling nose gear (a new concept at the time) and owned the patent. (I suspect he flew free on all the airlines because of his patent - he certainly flew more than his apparent wealth would explain. Or, maybe he was just richer than he showed.) The military and major aircraft manufacturers came to evaluate, then incorporated the tri-gear into their warplanes.
>>>First point. This is not a
free swivel, as in the Grumman Yankee/Traveler/Tiger series. It is canted
back, but still attached to the
yoke.
In the later 1930s, Fred left NACA to join Engineering Research Corporation (ERCO), the leading maker of automated equipment to manufacture aircraft. ERCO 's owner, Henry (I think) Berliner, wanted to build a light aircraft and he hired Fred Weick to be the chief designer.
>>>Henry Berliner squares with my memory
also.
In the period of about 1938-1940, Fred and assistants
designed the Ercoupe, trying to make it a "safe aircraft." The design goal
was ease of flying and an aircraft that wouldn't turn and bite the
pilot.
One aspect was effective development of the linked ailerons and rudders.
>>>The Wrights Brothers did this on their
first ships as well.
Another aspect was that the aircraft shouldn't have trim
changes or behavioral changes from idle to full power, as much as
possible.
The H tail resulted as they found that almost eliminated the spiraling airstream's effect on the vertical tail surfaces (the majority of what people mistakenly call P-factor). The actual P-factor remains and was countered by canting the engine to the right and down. Calculations and tests showed that canting the engine improved full power climb behavior but made virtually zero effect on cruise.
>>>A point here. Thrust differential in
single-engine airplanes is not present when the air stream enters the
prop disk orthogonally. When the disk is tilted by a climb attitude,
the descending blade has a higher angle of attach. Hence, more
thrust. This is also present on every engine of twins, et
al.
The design of the "stall" behavior was extensively
researched. The wing's joint with the fuselage, the shape of the fairing
between them, the short pinch of metal at the leading edge of the wing root all
combine to make the stall begin at the wing root and fan out from
there.
The up-elevator travel was limited to prevent fully
developed stalls. Working in combination with the turbulent air from the
wing root stall, the Ercoupe earned FAA approval that it is "characteristically
incapable of spinning."
Sure, an Ercoupe can stall - just do a hammerhead.
But the normal "stall" is really just flying at minimum flying speed. A
small portion of the wing root stalls and the burbling air combines with the
elevator up-limit to prevent the tail from being pushed down enough to stall the
majority of the wing.
Can a Coupe be forced into a spin? Maybe, for a
moment, But, even if you do a hammer-head stall and hold the yoke full back and
fully to the side, the Coupe won't stay in a spin - it'll recover in spite of
bad control inputs. (Try that in your average Spam Can, but wear a
parachute.)
Full aileron authority is maintained through a
"stall." With the yoke full back, you can crank the ailerons full left and
full right and be confident it won't have a stall break, let alone a spin.
(And, that thick airfoil gives some really amazing sink at low airspeeds.)
But you'd BETTER drop the nose well above the ground and get airspeed back if
you want to flare for a nice touchdown. Landing in that super-steep mush
tends to damage the landing gear and occasionally
more.
About 126 Ercoupes were made before WW2. After WW2, they made about 4500 very quickly till they overfilled their dealer channels. In the 1947-48 aviation bust, all the light aircraft manufacturers which did not have a 4-place or bigger in their lineup went out of business. ERCO dropped out of making aircraft.
>>>Actually, 110 made it off the line before
the aluminum supply was cut off. Two more were assembled from
spares. The government, in all it's wisdom, decided that
Luscombe deserved the metal; their plane was more like what the AAF and Navy was
flying!
But the Coupe didn't die. Saunders Aviation
finished selling the already produced aircraft, making some improvements.
The split elevator with a cutout in the middle lets the slipstream pass through
the cutout so there's no pitch change from idle to full power - a nice design
improvement.
In the 1950s, Ercoupes were made by Forney, in
Finally, Mooney bought the rights, put a standard tail
on the plane, made it stall and spinnable and sold it as a trainer, the Mooney
M-10 Cadet.
So, it was in production, off and on, from about 1940 to
about 1970.
Fred Weick, the designer, had expected to sell as many
Ercoupes WITH rudder pedals as without. But the marketing department
decided that 2-control was their gimmick. They advertised hard that the
Ercoupe could be flown by anybody (pretty nearly true) and made almost entirely
2-control aircraft.
Fred told me in 1991 that he thought that was a
mistake. In designing the plane to be safe, he greatly underestimated the
importance of good judgment on the part of the
pilot.
The poor pilots and pilots with poor judgment attracted
by the marketing program greatly hurt the Ercoupe's safety record. Looking
back, the design did do a good job of protecting people from mistakes but the
mistakes broke a lot of aircraft and killed some
people.
Aviation Consumer did an analysis of accidents in the 1980s. They found that in spite of all that, the Ercoupe had a safety record in the middle of the pack of light aircraft, near the C-172. The C-182 was the big winner.
>>>By the time you have the experience and
money for a 182, you tend to mess up
less!
But the Ercoupe really is an aircraft that must be flown with skill and good judgment. It rolls and turns like a little fighter plane but is still a safe design. Still, it must be flown by a skilled pilot with good judgment.
>>>Hell, ALL airplanes must be flown with
good judgment! The Ercoupe just kills in different ways. The two
main problems remain "flight into deteriorating conditions" and
"loss of power." The former is dummies don't know clouds/see night
coming, the latter is better called "running out of
gas."
But, if you're stupid and fly into 'inclement
meteorological conditions' then you can still come out in a spiral dive.
If you fly into the side of a hill while scud running, the Coupe can't protect
you any better than a Spam Can.
Coupes, with their personality and advanced design, have captured a lot of pilots hearts. We have a loyal group. Many pilots, when they lose their medical certificate, keep their Coupes a long time hoping they'll be able to fly it again. There are a lot of Coupes out there in barns, hangars and airport tie-downs waiting for their owners who hate the idea of selling them.
>>>I have discovered some of those
barns. There will be a page on ercoupe.org
soon.
After leaving ERCO, Fred Weick became a professor at
Texas A&M. He developed a proof-of-concept agricultural aircraft for
spraying, the Ag-1, which was designed to protect the pilot in
crashes.
When Fred became Chief Designer at Piper Aircraft in the
'50s, they developed the Pawnee based on the Ag-1.
Then Fred and his team developed the Cherokee and all
the subsequent Piper aircraft up till Fred's retirement in about
1967.
Fred came to our fly-ins regularly and it was a great treat to talk with him one-on-one. He and his wife, Dorothy, were such magnificently fine people we all loved them. Dorothy died in 1992 and Fred in 1993. I still miss them.
>>>I never met the man and regret it. I
did not get my Ercoupe until
1994.
You ask about the design considerations for the linked
aileron and rudder.
As the Wright Brothers proved, the only need for rudders on a flying aircraft is to overcome adverse yaw caused when a wing develops extra lift to be raised to start or end a bank. It doesn't matter whether it's wing-warping or ailerons that lift the wing, induced drag causes adverse yaw.
>>>Please see my review of Stick and Rudder on
ercoupe.org. It attempts to explain
this.
When you get a chance, get an Ercoupe owner to turn the yoke full left and right for you. You might have to have someone hold down the tail (pushing only on the bolts holding the tail on) to take the weight off the nosewheel.
>>>Oh, you meant on the ground...
:-)
In the Coupe, the ailerons were designed magnificently well. Their shape and differential action let them develop very little adverse yaw. The remaining adverse yaw is countered by the very small rudder surfaces. In fact, only one rudder is really used at a time. Full rudder deflection on a Coupe is 20° outward on one rudder and only 3° inward on the others - and the rudders are small.
>>>I was told by Don Jefferies that the rudder
peddles don't do much good because of the "tail volume" (area of the
rudder/vertical stabilizer times the distance from the
wing).
But it's enough to keep the plane in pretty good
coordination - better than most pilots manage.
The tricycle gear allows the landing to be done in the
crab, nose held high off the ground. When the mains touch, they are firm,
laterally, and the side loads turn the airplane to line up with the direction of
motion. The nose gear, when it touches, doesn't provide side loads because
the nose gear swivels on all aircraft - once the nose gear has turned, it just
rolls and does not provide side loads. So the aircraft
turns.
This is how Ercoupes, Boeing 707s, 747s, etc., Space
Shuttles, and more land. In the crab, letting the side loads on the main
gear rotate the aircraft. It's not a terrible jerk - if you had an egg in
a saucer in your lap, it wouldn't leave the saucer. (But I'd recommend
hard boiled eggs for the experiment. ;-) )
In a Coupe, you can land and take-off in crosswinds that
keep most pilots and planes on the ground - if you know how (and it's not hard
to learn). The demonstrated crosswind component for most models is 25
mph.
Most modern aircraft (except taildraggers) have little
need for rudder use. Some just have honking big vertical
stabilizers. Many have an interlinkage between the rudders and ailerons
though it's usually a soft one by a bungee or electronic fly-by-wire
now-a-days.
And then there are taildraggers whose "landing gear" is
really a take-off gear, putting the plane at the right attitude for takeoff on a
short, rough farm field. But their third wheel is on the wrong end and the
aircraft knows this and it is continually trying to turn around when on the
ground.
All in all, the Ercoupe was about 30 years ahead of its
time. And, even compared to many recent production aircraft, it is still
in the average range - 60 years after they were
built.
We love them. It is a sickness. ;-)
>>>My recreation chemical of choice is Av
gas. Not Jack Daniels, but I will on occasion...
:-)
You can get a lot more by reading the FAQ at http://ercoupe.org I'd also recommend "The Ercoupe" by Stan Thomas if you can find a copy. (There were about 700 unsold copies out there when the second publisher went out of business and went overseas for a job. We can't find them.) Also excellent (but a bit dry) is Fred Weick's autobiography, "From the Ground Up, Autobiography of an Aeronautical Engineer."
>>>I have both books and Highly
Recommend.
Ed Burkhead
http://edburkhead.com
ed -at- edburkhead???.com (change -at- to @ and remove "???")
>>>Percy (between Ercoupes) in NM, USA
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