Hi William, Thank you for the correction. It's good to know the elevator trim springs are not 'flight critical' as I had been told.
I'd be interested to hear what the actual experiences have been of others who have had a trim wire failure without the spring & trim stop. My Ercoupe is S/N 4669 and has the spring & stop installed on the elevator trim. I 'pumped up' my forearms pushing nose down for the flight home when the trim wire broke. Dan Hall N3968H ---- "William R. Bayne" <[email protected]> wrote: > > 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:
