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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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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. ;-)
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."
Ed Burkhead
http://edburkhead.com
ed -at- edburkhead???.com (change -at- to @ and remove "???")
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