All,
The engine offset designed into the coupe engine mount, down and to the
right, serves the same purpose as it does on a "free flight" model
(pilotless) airplane. It almost eliminates the difference in control
settings between "high power" and "low power".
The coupe's higher wing loading (as compared to a Champ, J-3 or
Taylorcraft as examples) acts to minimize such effect, even as it
reduces our "glide ratio". Our "split rudders", or "H-tail", puts half
our rudder area on one side of the "propwash spiral" of air aft along
the fuselage and half on the other side.
With two-control or three-control I noticed little, if any, difference
between my usual 85-90 mph "cruise climb" and a flat out stabilized
cruise. On the other hand, when climbing at "best rate" or "best
angle"...i.e. high power and relatively low speed, the pilot just "does
what must be done". I don't recall ever noticing any difference, but
it's likely much less that other designs.
Regards,
WRB
--
On Mar 29, 2010, at 07:40, Jerry Eichenberger wrote:
Ed -
The need to apply right rudder in 3 control airplanes when operating
at higher angles of attack is primarily due to P factor.
P factor is the effect of the fact that at higher angles of attack,
the descending blade of the prop has more effective pitch than does
the ascending blade, creating thereby more thrust from the right side
of the prop disc (as viewed from the cockpit) than the left side of
the prop disc produces.
In European engines, most of which rotate backwards to American
engines, the pilot applies left rudder when in higher angles of
attack.
Jerry E.
-----Original Message-----
From: [email protected]
[mailto:[email protected]]on Behalf Of Ed Burkhead
Sent: Monday, March 29, 2010 7:07 AM
To: 'Hartmut Beil'; ety
Subject: RE: [ercoupe-tech] Funny Tales About Ercoupes
I wrote:
> Putting the vertical stabilizers outside the slipstream keeps
> the slipstream from causing trim changes when going from
> idle to full power.
Hartmut wrote:
> The Ercoupe had no rudder trim. So that could not have been the
reason.
Sure it could have been the reason. Planes are normally designed to
fly straight in cruise. In some planes, the vertical stabilizer has
a tiny cant, as if there were a tiny bit of right rudder. This
counters the spiral slipstream hitting the left side of the vertical
stabilizer and rudder and it’s tweaked to be just right in cruise.
At low airspeeds and high power, there’s more effect of the spiral
slipstream and this pushers the tail to the left, hence the pilot
applies right rudder to compensate.
Thus, these planes have a “trim” change in yaw from idle to full
power and need pilot controllable rudders to counter this.
In designing the Coupe, Fred Weick wanted to eliminate this
misbehavior. He did this by putting the vertical surfaces at the
ends of the horizontal stabilizer, outside of the slipstream.
This is effective for Fred’s purpose of a well behaved airplane. I
suspect it was nearly essential for development of a well behaved
two-control airplane.
Hartmut wrote:
> most of my information is from the book "The Ercoupe" by
> Stanley Thomas. Do you have the book? If not, I recommend
> reading it. Awesome details.
>
> Thomas also speaks about the small "stall strips" at the wing root,
> added not for stalling purposes, but for creating an extra air
burble
> in a slow flight configuration. That burbled air hits the elevator
> and is needed to keep elevator authority at slow speeds with a 13
> degree restriction. The tested prototypes had a lesser restriction
> on the elevator. [emphasis added – Ed]
Please recheck the bottom of page 47 of “The Ercoupe.” You’ll find
this: “Third, the loss of lift in the center of the wing reduced the
downwash on the tail, thus reducing the effectiveness of the elevator
in forcing the tail down and increasing the angle of attack.”
[emphasis added – Ed]
Hartmut wrote:
> That indicates that the split elevator is the ultimate design in
> Ercoupe elevators and should be added where ever possible.
Agreed. However, I don’t think it’s so important that I’d put it
ahead of other safety improvements. I can’t remember his exact
phrasing, but when I asked Fred what he thought of the split
elevator, he said it was effective in doing for the elevator what the
Coupe tail did for the vertical stabilizers and rudder – get it out
of the slipstream and reduce the effect of the slipstream on the
behavior of the plane as the power changes between idle and full
power. Fred said he didn’t think of it himself but he wished he had
and he was complimentary towards Sanders for thinking of it.
Ed
