Hi Percy,
We know that the same trim crank and elevator are fitted to all
Ercoupes to Serial No. 1622.
The original trim system fitted to Serials 1 thru 122 acts directly
on the control column, so if elevator control input is lost anywhere
forward of the elevator to bellcrank pushrod assembly, Ercoupe Parts
Catalog, p. 30, Fig. 21, item 1, trim influence on the elevator is
also lost and it will assume a position consistent with a high speed
"cruise" trim setting at which a safe emergency landing is unlikely.
Per ESM 19, the revised trim system (Serial Nos. 123-1622)
incorporates a rear-mounted spring, Item 8, between the elevator
attachment (at the upper end of the elevator-to bellcrank pushrod,
Item 1), and the elevator arm (bellcrank), Item 43.
According to the Ercoupe Service Manual, page 27, "...with the trim
control crank...full up there should be no tension...on trim unit
cable when cable when spring is attached." That does NOT mean that
there is no tension on the elevator. The spring's "minimum" tension
is sufficient to keep the elevator in an "up" position against the
air flow pressure consistent with "nose up" trim position (and, thus,
tthe "fail-safe" position).
The revised trim system would remain fully functional should elevator
control be lost anywhere forward of the elevator arm (bellcrank),
Item 43. The panel-mounted crank tensions the fore-aft trim cable
(415-52268, not numbered but shown) so as to progressively stretch
the elevator spring and lower the elevator sufficiently to balance,
or trim in "cruise". It would be, therefore, the crank and cable
that pull down the elevator and not the spring.
I would observe that many Ercoupes have not had the rear cone
elevator arm assembly disassembled so as to clean up the shaft and
Oilite bushings. Our heim end bearings and rudder bellcrank bushings
have almost certainly received attention in the fifty plus years
since our birds came off the production line. I would presume that
the slightest stiffness (resistence) to the smooth operation of this
elevator arm assembly would make satisfactory (ability to hold a
desired setting) operation of this type of trim most difficult. It
might prove worth the effort to clean and re-lubricate (if not
replace Oilite bearings 415-52204-1 & 2.
Regards,
William R. Bayne
.____|-(o)-|____.
(copyright 2010)
On Aug 31, 2010, at 12:02, Percy Wood wrote:
Dear Bill, Ed, John, et al.
Found the discussion most useful. My first `coupe had the
"aerodynamic" trim, which consisted of a lever on the left side of
the cockpit and a wire going back to a movable tab on the back of
the elevator. My new-to-me Ercoupe has the "intermediate" system
of a crank, a cable, and a spring pulling down the elevator.
From this pilots perspective, the aerodynamic provided an
intuitive and stable system. With the crank, I am always trying to
balance the engine RPM and the trim setting. It would help if the
vernier throttle did not vibrate open as I cruised along, though!
Percy in SE Bama
