Hi Bart, Ed
In a January 18, 2009, email to Maynard Smith, I stated:
"...with the trim set for "cruise" the trim tab is "high" (although
neutral) and
therefore with full "up" elevator there is greater effect from the
limited
movement available for flare and speed scrubbing. That would further
reduce touchdown speed a bit and perhaps offer a worthwhile
improvement in response of the 415-D (with only 9º up elevator
available).
Since the above is in reference to touchdown after the yoke has been
moved
fully rearward, it seems obvious that the effect on "minimum speed"
would also
affect the indicated speed at which the stall occurs.
With specific reference to the Ercoupe design, consider flying rule
#63a:
If the Ercoupe departs controlled flight, cut the throttle to
approximately
1700 RPM and release the controls. In other than significant
turbulence,
it should level out (steady itself side to side) trimable to
approximately a 200
FPM descent.
The pilot may then climb or descent by adjusting throttle and trim for
a forward
speed of around 70 MPH and, if the bird is rigged correctly, know
(preferably
from prior VFR verification) that a heading can be selected and
maintained with
gentle (one finger) left-right input without risking the dreaded
"graveyard spiral".
≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈
The above speeds, etc. are from memory...determine what your indicated
air speed is
under stated conditions. Here's some basic checks on if your plane is
properly rigged:
Per Ercoupe Service Memorandum No. 19 (crank style trim on instrument
panel thru
Serial No. 1622 trims entire elevator...no movable trim tab as
originally manufactured):
Item, 6-7: "Flight check should show a glide speed of 68-70 MPH with
trim unit
set at "nose up".
Item 7-3: "Change elevator trailing edge to function as a fixed trim
tab, to obtain
proper glide speed."
[see also Ercoupe Service Memorandum No. 35, Item 14]
Per Ercoupe Service Memorandum No. 25 (applicable to lever style trim
on left inner
fuselage) on 415-C Serial No. 1623 up, AND "Airliner Quadrant" trim
mounted at
center bottom of the instrument panel on all 415-D and 415-CD (as
manufactured...
WITHOUT SPLIT ELEVATOR):
"With the trim crank handle full back ["nose up"-WRB]...a glide, power
off, at 58
mph and a 55 mph climb with power on." [should result]
[see also Ercoupe Service Memorandum No. 35, Item 14]
Per Ercoupe Service Memorandum No. 35 (applicable to lever style trim
on left inner
fuselage) on 415-C Serial No. 1623 up, AND "Airliner Quadrant" trim
mounted at
center bottom of the instrument panel on all 415-D and 415-CD (as
manufactured...
WITHOUT SPLIT ELEVATOR):
Item 15: "Effective about Ercoupe No. 3882, the elevator trailing
edge has been
bent downward 3º on production aircraft. It was found that this
modification makes
it easier to bring the airplane within to (sic) the desired glide
characteristics."
Per Ercoupe Service Memorandum No. 38 (applicable to lever style trim
on left inner
fuselage) on 415-C Serial No. 1623 up, AND "Airliner Quadrant" trim
mounted at
center bottom of the instrument panel on all 415-D and 415-CD (as
manufactured...
WITHOUT SPLIT ELEVATOR):
Item 11.b.(3) Note: "...with the trim crank handle full back ["nose
up" position], the
airplane is trimmed for a power-off glide at 65-75 MPH and a full
power climb of
60-70 MPH."
It is presumed that these later values take precedence over those in
ESM-25.
Per Ercoupe Service Memorandum No. 35A (applicable to "Airliner
Quadrant" trim
mounted at center bottom of the instrument panel or to all 415 series
airframes to which
a split elevator has been installed:
Item 4a: "Bend the fixed trailing edge of the left panel of the
elevator down 11-1/2º".
[WRB note-this adjustment could cause "right wing drop" after
stall!]
Item 4b: "Power off minimum airspeed" is 60 M.P.H." [when "lower
speed warning
cushion spring is encountered...if IAS below, shorten; if
above, lengthen]
Regards,
William R. Bayne
.____|-(o)-|____.
(Copyright 2009)
--
On Aug 15, 2009, at 10:01, Ed Burkhead wrote:
Bart accidentally sent this to me, only. (Y'all be sure to send to the
forum, ercoupe-t...@... and not ercoupe-tech-ow...@...)
I can see that there could be a slight difference in minimum speed due
to
trim tab position, Bart, but that's way bigger an effect than I would
expect! Has anyone else ever measured this?
Bart wrote:
You can get the stall speed to change depending on where the elevator
trim
is set. With
power off and the trim in approximately cruise position, the stall, or
"mush" occurs in my
airplane at just below 50 mph. If I trim for landing(nose up trim)the
mush occurs at a little
above 50 mph. If I trim full nose down, a stall occurs at a little
below
45 mph with a gentle
stall buffet but no "break". If you roll in some aileron during a
stall
in this configuration,
you get the buffet then a slight break with some apparent rotation
which
looks like a spin,
but it is not a spin. It's a spiral, and you can stop it by just
rolling
wings level and relaxing
back pressure.
Which leads me to overall flying rule #63. If the aircraft departs
controlled flight, neutralize
the controls until you see something you recognize, then recover.
Bart
------------------------------------
Yahoo! Groups Links
