Hi Bob,
The spring you describe is 415-52026, and should be 18" long. It
connects to one
of three holes in a generally triangular steel "link", said "link"
being connected to the
elevator arm with the same bolt as pushrod that activates the elevator.
When correctly adjusted, this spring should not interfere with trimming
an airframe for
hands off level flight between "cruise" (nose low) and "land" (nose
high) positions.
The range of elevator operation available without encountering the
effect of this spring
should be more than sufficient for normal flight. Its purpose is to
provide a "feel" for a
such rearward position of the yoke as should result in a power off 60
mph TAS glide.
This position is NOT the rearmost position of the yoke available for
flaring before
touchdown at absolute minimum speed, as by increasing the rearward
force on the
yoke considerable additional "up" elevator is available before reaching
the stop on the
control wheel shaft.
In normal "level" cruise flight, i.e. where the plane is neither
climbing nor descending
from a given altitude, the Ercoupe is in a subtle "nose down"
configuration which also
affords improved forward visibility. The design engine downthrust was
incorporated
to decrease the change in pitch between "power on" and "power off"
operation with
a propeller thrust line well above the centerline through the wing.
Lynn's reference to ESM 35A for proper rigging is 100% correct, but
many overlook
the last sentence of 4.a.1. directing that the left panel of the split
elevator is to be bent
down 11-1/2º. While this should have been done in production, a
replacement
elevator may have been fitted without this having been done, and such
an adjustment
is has considerable effect in achieving the desired flight
characteristics.
A similar requirement to bend the entire trailing edge of elevators on
415-C, D and CD
model Ercoupes downward 3º was found beneficial by Erco "to bring the
airplane within
the desired glide characteristics" per paragraph 15 of ESM 35, and was
accomplished
on Ercoupes effective about serial number 3882.
It does appear there is a lapse in our parts and Service Manuals as to
this spring.
Regards,
William R. Bayne
.____|-(o)-|____.
(Copyright 2009)
--
On Feb 18, 2009, at 18:55, [email protected] wrote:
Hey Bob: The best answer is contained in Ercoupe Service Memorandum
35A. It is a lower speed warning cushion. Apparently it was designed
to provide a power off warning to help prevent the pilot from getting
too slow in the landing approach in the model E,G and F Ercoupe. The
flight test adjustment procedure requires changing the length of the
spring to keep the power off airspeed at or slightly above 60 MPH with
the pitch control back to the point where the
spring causes additional force to be applied to the control.
(obviously with the trim in full nose up condition)
If you are getting a constant down pressure on the elevator, I
would suggest checking the rigging in accordance with Memorandum 35A.
The 46 415CD should not have this problem unless it has been
modified with the split elevator and lower speed warning cushion
spring.
Lynn Nelsen
In a message dated 2/18/2009 7:16:13 P.M. Eastern Standard Time,
[email protected] writes:
Group: Can anyone shed light on the purpose of a coiled spring 1/2"
x 14" which attaches to the elevator bellcrank and to the bottom of
the tail fuselage near the tiedown eyebolt? We have noted this
spring being used on a 415E Ercoupe and a '57 Forney. It is not
shown in either the repair manual or current Univair parts manual.
It functions to place constant down pressure on the elevator causing
a "nose down" orientation. Would the pilot have to overcome the
pressure of this spring to maintain level flight? Could this
conceivably be a modification to relieve the need for the engine to
be canted down at a 3-1/2 degree angle below the nominal thrust line,
in which case the aircraft would achieve hands off level flight?
Any help with this apparent mystery would be appreciated. Thanks.
Bob Blanchard
N94676 - 415CD
