All,
Per Ercoupe Service Memorandum No. 55A, only Ercoupes with serial
numbers 4869 ("E" Models and subsequent) were originally produced with
elevator trim stops and springs. The trim stop and spring was
"designed to prevent elevator flutter in the event that the elevator
trim tab actuating wire broke during flight".
SK 14 (about $15) is Univair's kit to add the elevator trim stops and
springs to earlier Ercoupes.
I would speculate, human inertia being one of the more common and
powerful forces existing, that more than half of the active fleet still
DOES NOT HAVE the trim stop and spring modification. While said
modification obviously adds a measure of safety in excess of it's
nominal cost, Ercoupes without it should NOT be considered "accidents
waiting to happen".
Understand that many Ercoupes were shipped from the factory in boxcars
after flight testing and reassembled by distributors prior to sale.
Kinking of the solid trim wire was not uncommon, and I would tend to
believe that many of the clots that kinked trim wire (always at the
same place) just straightened it...and the plane went to its new owner
with trim wire of considerably less than original design strength.
Accordingly, it is likely that many, many Ercoupes suffered breakage of
the trim wire WITHOUT trim stops and springs and the pilots lived to
tell the tale. Why? Because with the onset of an unusual noise or
"flight condition" our first instinct is to exercise caution...if we're
going fast, slow down ;<)
Every proficient pilot has a reasonable knowledge of the risks accepted
each time the wheels leave the ground. A new pilot's license is
sometimes called a "license to learn". In truth the recipient has
entered a race for as long as he lives....to acquire knowledge and
proficiency before circumstances thrust upon him the role of untutored
test pilot. Those who are uncomfortable with that concept should
seriously consider a more forgiving vocation or hobby than flying.
In the aforementioned context, if your plane has free play in the
controls, you should have measured (or had measured) said play and
verified said play does not exceed acceptable limits. With regard to
ailerons, the "good news" is that more free play is "acceptable" if the
original balance weights are still fitted. The "bad news" is that the
factory considered them a "maintenance problem" and a "flight hazard if
permitted to become loose...". Removal was "...not mandatory,
but...recommended..." and the ship became lighter by 3.5 lbs.
"Bottom line" is that flutter directly relates to speed. So long as
the plane is under control, even a nominal reduction in speed should
stop flutter. Immediate and significant power reduction is the most
intuitive action and will likely resolve the situation.
In southern California I once unexpectedly encountering an extremely
strong convective updraft flying parallel to mountainous terrain. From
an initial altitude of approximately 2000' MSA and AGL, cloud cover
above (height unknown), even after reducing power to idle my rate of
climb was still almost 2000 FPM.
Hindsight being 20-20, I should have raised the nose to make use of the
coupe's considerable low speed sink rate (as they say in
computers...that's not a "bug", that's a "feature".) Instead I shoved
the nose as far down as I could and held it at that angle that I would
not exceed 144 MPH. I also turned 90º away from rising terrain on my
left. Very soon I exited that updraft and things returned to "normal".
It's amazing when your adrenalin "pops" how much time you have to
choose and implement options.
My point is this...a broken trim wire under such condition could have
had two outcomes. With power already at idle, I don't remember what my
indicated airspeed was. I now realize that by raising the nose to drop
it further, flutter would not have been possible.
By lowering the nose, it is within the realm of possibility that the
increased speed might have overstressed a marginal trim wire. Sudden
and violent trim tab induced elevator flutter under such circumstances
might have torn the plane apart. That's the trouble with learning from
experience...you have to pass your "final exam" before you get the
knowledge!
Just as ERCO challenged anyone to show they could spin a properly
rigged Ercoupe and airworthy Ercoupe (no one ever collected), I do not
believe flutter possible from an unrestrained trim tab of either type
certificate dimension once forward speed is reduced below 70 mph IAS
(per an airspeed indicator of acceptable variation and accuracy).
Don't know if your air speed indicator meets that criteria? Go back to
the earlier paragraph beginning "Every proficient pilot has a
reasonable knowledge of the risks accepted each time the wheels leave
the ground."
I have every confidence that Dan would have found it quite possible to
"...continue on to a safe place to land" in the absence of the spring
and stop, although I don't doubt he's glad he wasn't forced to prove
it. ;<)
Best regards,
William R. Bayne
.____|-(o)-|____.
(Copyright 2008)
--
On Dec 27, 2008, at 20:59, <[email protected]> wrote:
Art,
Good point. The elevator trim tab wire failed in flight one time in
my Ercouope N3968H, and the spring made it merely uncomfortable to
continue on to a safe place to land.
If the spring(s) hadn't been there I may not have been so fortunate.
Dan Hall
N3968H
---- Art Langston <[email protected]> wrote:
