If my elevator cable broke, I would probably be too busy cleaning my drawers to even think about a trim crank!
--- In [email protected], "William R. Bayne" <ercog...@...> wrote: > > > Ed, > > ESB 19 was written about the "later" crank style trim on the > instrument panel that spring-loaded the elevator. There was no > "aerodynamic" (separate articulating) trim tab on THAT elevator. In > item 1. ERCO states that Ercoupes up to Serial 212 with the elevator > disconnected would trim "at a speed of approximately 130 MPH, which > is obviously too high for a safe landing". It then explains that the > "new" system (213-1622) activates the elevator DIRECTLY...and will > therefore provide an additional means of control in case of failure > of the elevator linkage." With this trim system still functional in > event of elevator control failure the pilot could still trim for a 70 > MPH glide. > > The "aerodynamic trim tab" system installed on Ercoupes 1623 up thru > 415-CD production was even more independent of the elevator control > system. Later ESM 55A was issued to install the 415-SK286 "fail > safe" springs and a stop for the trim tab. Should the trim control/ > cable break, the springs returned the trim tab to the stop, and the > stop was to be installed such that its lower surface was parallel > with the top of the elevator upper skin top surface. > > Your observation is "right on", in that with the trim fully forward > (nose down) the tab is against the stop and, per ESM No. 38, 11.b. > (3): "the ship should be trimmed for high speed flying at 115-125 > MPH. With the trim crank handle full back, the airplane is trimmed > for a power off glide at 65-75 MPH and a full power climb of 60-70 > MPH." So, with the elevator disconnected, this was the rang of > airspeeds remaining available through operation of the "aerodynamic > trim tab" system. > > For those whose birds do not demonstrate these characteristics, refer > them to ESM No.35, item 15: "Effective about Ercoupe No. 3882, the > elevator trailing edge has been bent downward 3ยบ on production > aircraft. It was found that this modification makes it easier to > bring the airplane within...desired glide characteristics." > > ERCO did similar tweaking on the split elevator installations. Such > "adjustments" are common (and necessary) for "free > flight" (uncontrolled) model airplanes. Another such "trick" adopted > by Fred Weick was our engine mount right thrust and downthrust angles > (to compensate for "P Factor" and pitch changes between power on and > power off). > > I hope this eases your mind on this issue. > > William R. Bayne > .____|-(0)-|____. > (copyright 2010) > > -- > > On Aug 30, 2010, at 18:35, Ed Burkhead wrote: > > > > > > > > > > > On 2010-08-30 4:02 PM, William R. Bayne wrote: > >> > >> Don's trim system is discussed at length in Ercoupe Service > >> Memorandum No. 19 of 4/26/46 (date from ESM No. 38). It says: > >> "...the natural trim speed in a glide with the controls and trim > >> device disconnected is now approximately 70 mph, a speed at which > >> the airplane can be maneuvered to a satisfactory landing by > >> throttle alone". > > > > > > That statement concerns me. > > > > When the aerodynamic trim tab is in line with the upper surface of > > the elevator, the trim speed on my Coupe was well in excess of 110 > > mph - not 70 mph. So, how could the natural trim be 70 mph with no > > aerodynamic trim tab and no control cables? > > > > To trim any Coupe I've seen to 60 or less mph, the aerodynamic trim > > tab must be quite a bit down, on the order of 40-60 degrees down. > > The downward trim tab raises the elevator. The raised elevator > > pushes down the tail and increases the angle of attack of the wings > > which gives you the correct trim for low airspeeds. > > > > Something is not tracking in the discussion of what happens with no > > control cables and no aerodynamic trim tab, it seems to me. > > > > Ed > > > > > > >
