Sounds like the best of all of the explanations thus far. I think all of us
can get it now - No Aerobatics! But, for just plane fun and excitment nothing
beats a Coupe. I flew mine down to Hood River Oregon right next to Mt. Saint
Helens on Friday and it was Breath taking. Love my Coupe.. Jerry
----- Original Message -----
From: William R. Bayne
To: ety Ercoupe
Sent: Saturday, March 06, 2010 11:25 PM
Subject: Re: [ercoupe-tech] Re: NTSB probable cause...
Ed,
The ACS (Airworthiness Concern Sheet) from the Sebring crash was discussed in
great detail on Tech back in September.
Observers heard the engine winding up as if in a dive. NTSB evidence confirms
that the top spar cap failed under negative G force, and that the seat with
occupants was ejected from the airframe. (read the last paragraph through now
before proceeding further here...and yes, Bob Sanders wore a parachute while
testing Ercoupes!) A high speed low pass with a sudden pull-up would result in
positive spar loading. A "pull-up" is, however, consistent with accounts from
observers on the ground, none of whom mention seeing the seat and occupants
thrown from the cabin. The eyewitness accounts and the physical evidence do not
seem to match.
Speeds in excess of 130 mph require a dive. Considerable forward yoke
pressure is required and must be maintained. Let us speculate that the sudden
loss of some 400 lbs. of occupants and forward yoke pressure could cause a
structurally failed and unoccupied airframe to appear to "zoom", then turning
and physically disintegrating. The very sight of such a sudden "zoom" would
likely hold every watcher's absolute attention.
Just as the "art" of the magician relies, in no small part, on sufficient
distraction of the audience that they do not "see" all that goes on before
them, the departure of the occupants and seat as the flight path transitioned
from dive to zoom could have gone unobserved. We don't have a diagram of the
topography, the flight path in three dimensions or where each reporting
observer stood. Ejection of the occupants would have been unexpected, and no
observer mentioned seeing it . The human mind tends to dismiss that which our
eyes "see" if those images are radically unfamiliar.
Per my (certified) letter to the FAA's Roger Caldwell of 9/23/09, pages 5 & 6
(and email to Tech of that date):
On November 8, 1948, Bob Sanders of Sanders Aviation issued "Ercoupe
TakeOffs" #G3 entitled "Discouraging Aerobatics". This describes instances of
"wingtip failures" and other structural failures reported in "recent months"
and that "...wewere not surprised or alarmed since evidence presented strongly
indicates misuse of the Ercoupes involved." He explains that the 144 mph red
line "indicates themaximum speed for which the airplane is designed", pointing
that all airplanes havea similar restriction and that speeds above this "will
endanger the airplane and occupants inasmuch as excessive speed may induce wing
flutter or other unpredictable difficulties which will, in some cases, cause
immediate collapse of the structure". We have all seen reports of difficulties
of other popular make airplanes caused by pilots exceeding design limitations."
His last paragraph urges dealers to cooperate "in bringing to the attention of
all Ercoupe owners and pilots the seriousness of exceeding the air speed red
line and the inadvisability of doing aerobatics in the airplane since they may
easily exceed the speed or accelerations which can be safely borne by the
structure."
On December 1, 1948, W. L. Greene, then Chief Engineer of ERCO, wrote the CAA
Aircraft Components Branch, Airframe & Appliance Engineering Division(1-301)
following "several airplane accidents involving wing failure in flight". He
states that "We are of the opinion that the most probable cause...is aileron
flutter caused by a loose aileron control system. The wreckage of these
airplanes...all indicated...failure of the main wing spar was caused by a
negative lift load on the wing tip. This load could be applied in normal flight
on a smooth day by a substantial twisting of the wing to provide a negative
angle of attack of the tip. It...appears that a violent distortion of the wing
took place from some cause. The only obvious cause appears to be wing tip or
aileron flutter." In test flights investigating wing flutter, and with 9/16"
looseness in the control system "we obtained a violent wing flutter, or aileron
flutter, which caused the right aileron tobe torn from the hinge attachments
and leave the airplane at a speed of about 190 miles an hour...".
On April 20, 1950, Norman A. Hubbard, D.E.R. 1-21 for ERCO wrote the
CAA,Attn.: Chief, Aircraft Division (1-565) relative to flight tests for C.A.A.
approval of the installation of the Trim-o-matic in Models E and G only. He
mentions "The recent accident during flight test of the Trim-o-matic
installation...occurred at about 180 mph calibrated air speed." The next week,
on April 27, 1950, Bob Sanders of Sanders Aviation issued "Ercoupe Take-Offs"
#P-7 entitled "TEST FLIGHT--1950 Ercoupe". This described the decision "to dive
the airplane to the higher speed.required to approve the...installation on
earlier airplanes, which were not limited against aerobatic maneuvers. In the
process of this dive, which went to 185 m.p.h., something happened to the
airplane causing it to nose down sharply, throwing me out of the airplane and
causing substantial damage to the airplane, which resulted in its
disintegration. ...initial and unofficial opinion is that the nose ribs of the
outer panels deflected, initiating the failure. The rapidity with which I was
thrown out, without any advance warning of failure...impels me to
again...discourage aerobatics which may encourage unskilled pilots to get into
speed ranges and attitudes which are dangerous to them and their airplanes."
Cordially,
William R. Bayne
.____|-(o)-|____.
(Copyright 2010)
--
On Mar 6, 2010, at 21:22, Ed Burkhead wrote:
But what CAUSED negative g-load sufficiently strong to break the spar in a
negative g manner and eject the seat/pilot/passenger out of the plane?
I cannot imagine a pilot with the experience and ratings listed doing a
barrel roll or pushing negative g's close to the ground, over civilization
(the golf course).
I could, maybe, understand a high speed low pass with a sudden pull-up.
I've seen this done perhaps a hundred times at various Coupe flyins. May I
say CLEARLY that I think this is a BAD IDEA.
Any plane with slop in its control system can get surprise control surface
flutter when it encounters an airspeed and load combination that allows a
resonant vibration to get going. I had that happen to me and am very, very
glad that I reacted correctly and almost instantly (turned the yoke to load
the aileron control system and pulled [with moderation] up to slow down).
I'm not any kind of genius pilot. In retrospect, I think I must have been
thinking about flutter and been alert for it as I did my power-glide to see
what 144 mph felt like - only that would explain how I diagnosed the
vibration and did the right thing so quickly.
You'd better believe I got my control system tightened up to specifications
after that and never again tried to power-glide up toward 144 mph!!!!
The NTSB probable cause report mentions nothing about flutter being involved
in the accident chain other than repeating the quote from the ATP pilot who
said he observed both ailerons fluttering. I wish they'd addressed this -
but, I suspect they just had nothing solid to go on.
To me, vibration sufficient to shake the rear windows out of the plane,
knock the inspection hole covers off the plane and shake PAINT CHIPS off the
plane might, just possibly, be important.
I'd urge everyone to do the checks necessary to see if your control systems
are within specs.
And, please, don't show off by doing a dive down to a high speed pass with
or without a sudden pull-up at the end.
JMHO
Ed Burkhead
-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of William R. Bayne
Sent: Saturday, March 06, 2010 8:14 PM
To: ety Ercoupe
Subject: Re: [ercoupe-tech] Re: NTSB probable cause...
Hi Craig,
You make an excellent point. They may well have MEANT that
"cross-sectional strength" was reduced by 10% using "design code"
practices.
But what they SAID was that the "cross-sectional AREA of the top spar
cap" was reduced by 10%! On that basis that I deemed the COMMENT
"utter nonsense". Professionals should express clear and accurate
findings in any accident report.
The NTSB seems to conclude that aerodynamic stresses substantially
exceeding applicable design criteria preceded the observed catastrophic
structural failure of subject wing and spar assembly such that even had
the "extra" hole not been drilled the structure would have likely
failed in much the same way with unchanged result. If the possible
reduction in "cross-sectional strength" from this one non-factory hole
was dwarfed by the structural design load safety factor, no one would
bother to "do the calculations".
Regards,
WRB
--
On Mar 6, 2010, at 14:39, craig wrote:
The 10% figure probably came from design codes. Any hole no matter
how small and the design codes say that you must at a MINIMUM deduct
10% of the structural strength of the metal. In any case if you drill
more holes you would have to do the calculations to determine how much
tensile strength remains.ie, drill enough holes and you could end up
with NO tensile strength left.
