14 CFR Part 91: General Aviation
  Accident occurred Saturday, May 07, 2011 in Conroe, TX
  Aircraft: WOODWARD HAROLD L RAVIN 500, registration: N913RA
  Injuries: 2 Fatal.

  This is preliminary information, subject to change, and may
contain errors.  Any errors in this report will be corrected when
the final report  has been completed.

  On May 7, 2011, approximately 0855 central daylight time, a
Woodward  Ravin 500 experimental amateur built airplane, N913RA, impacted
  forested terrain shortly after takeoff from Lone Star Executive
  Airport (CXO), Conroe, Texas. Visual meteorological conditions
  prevailed at the time of the accident. The personal flight was
being  conducted under the provisions of 14 Code of Federal Regulations
  Part 91. The pilot and student pilot rated passenger were fatally
  injured. The flight was originating at the time of the accident and
  was en route to Temple, Texas, for the airplane to be displayed at
  an aviation event.

  According to CXO tower personnel, the pilot was cleared to depart
  runway 14 with a right turn on course. The airplane departed and as
  the pilot began his initial right turn he reported smoke in the
  cockpit. The pilot was cleared to land on any runway and giving the
  wind as being from 160 degrees at 8 knots. The airplane was
observed  to perform an approximate 240 degree right turn and
crossed back  over the departure runway before entering the left
downwind leg for  runway 14. While on the downwind leg of the
traffic pattern the  airplane was observed flying,
â<80<9Cslowâ<80<9D, wings level,  at an estimated altitude of 700
to 800 feet above the ground. While  approximately 4,500 feet along
the downwind leg the landing gear was  extended. Shortly thereafter,
the airplane started a descending left  turn towards the closer
runway 19. The airplane overshot the  extended centerline to runway
19 and the airplaneâ<80<99s bank  angle increased. The airplane
continued in the descending left turn  toward the runway until
approximately 300 feet above the ground. At  which point the
airplane appeared to â<80<9Cstallâ<80<9Dand  impacted into
forested terrain. A post impact fire ensued. Tower  personnel
reported that during the event they did not observe any  smoke or
flames coming from the airplane until impact.

  A pilot rated eyewitness located near the crash site reported
  hearing what he described as an engine that was
  â<80<9Cscreamingâ<80<9Dand varying in RPM. When he saw the
  airplane it was flying â<80<9Cvery slowâ<80<9Dat an estimated
  altitude of 300 to 500 feet above the ground. As the airplane made
a  high bank angle turn back towards the airport the witness
observed  the nose and left wing drop before the airplane went out
of sight.  Seconds later he heard it impact trees followed by an explosion.

  The airplane came to rest in an upright position about 1,600 feet
  out on the extended center line from the approach end of runway 19.
  The measured impact heading was 200 degrees magnetic.

  ------------------------------------------------------------
  Sounds like they will never know what happened.

  I am guessing. One possible scenario is the automotive clutch Bud
  used started slipping causing the smoke and the
  [WINDOWS-1252?]ââ?¬Å?screamingââ?¬Â  engine. The clutch disk
could wear  rather  rapidly due to normal high torque fluctuations
at high continuous power.

  IMHO the TBO on an automotive V8 in aircraft use should be 300 hours.
  Any piston engine can develop a crack in the critical parts leading
  to a hand grenade failure without warning. The main purpose of the
  TBO is to magnaflux the critical parts to detect cracks early
before  the engine explodes. Through years and millions upon
millions of  hours of experience and detail refinement the TBO on aircraft
  engines has increased to 2000 hours.

  The TBO on my C182 engine was 1500 hours. By adding another
  torsional damper on the crankshaft the TBO was increased to 2000
  hours. However unlike a piston engine in a car the aircraft crank
  and rods are made of the finest material possible. Only the best
  methods of manufacturing and finishing are used.

  Parts in an automotive V8 are made as cheaply as possible as the
  average required power is only about 40 HP despite a 400 HP rating.

  We are so lucky the Wankel rotary does not see the same kinds of
  reverse loading on the e-shaft and the rotor that are seen on a
  piston engine cranksaft and rods. Fatigue failures of the e-shaft
  and rotor are unheard of.

  Paul Lamar

  It sounds like the pilot might have stopped flying the airplane,
but  instead was trying to save it. My training was that in case of
fire,  you get the airplane on the ground immediately, as you really
don't  know what's burning. I can understand the smoke could have
been  incapacitating, so that might have been the issue, but if it
was the  clutch burning, it seems unlikely somehow.

  Matt-

  I agree but people that build airplanes have so much invested in
  them (more than money alone) they appear to be reluctant to crash
  land straight ahead as we were all told to do in case of engine
  failure on take off. Here is a map of the area and there does not
  appear to be many clear fields other than on the airport itself. In
  the case of rotary crashes at least two fatals were caused by the
  pilots attempting to turn back. In both cases there were suitable
  fields straight ahead. One rotary crash was caused by engine
seizure  after the loss of all oil pressure due to a split cheap oil
cooler  and the other an interruption in the fuel supply due to a poorly
  designed fuel plumbing system.

  IMHO there is another more subtle factor. One is naturally
reluctant  to do a 180 and land downwind on a controled airport or busy
  airport. We had an incident at SZP where a pilot  had an engine
  failure in a Bonanza and successfully made a 180 and landed down
  wind. He slammed it in so hard on the 2500 foot runway it bent the
  spar and broke the motor mounts totaling the airplane but he was
not  hurt. He skillfully ground looped it when it looked like he was
 going to run out of runway at thew other end. I was standing 50
feet  from the point of impact.

  I think people should practice 180's at altitude with the engine at
  idle. Just to get a feel of what the airplane will do. Note the
loss  of altitude.

  Paul Lamar

  --
  Persons close to the parties blame it on a bad oil line connection
  to the engine....not the clutch......FWIW.... Marc

  Why the "screaming" engine? Or did it sound like that all the time?

  Paul Lamar

  Re: Matt's comment about clutch burning unlikely. Yes unlikely, but
  possible.
  Hi-way haul trucks have got the brakes on fire coming down long
hills. I  worked on a Ford 1/2 ton that had stopped on the side of
the road.  Questioning  the driver/owner he said it slowed and
stopped going. The engine ran fine.  The  fellow said when he looked
under the truck there was fire underneath. When I  removed the
clutch cover, a couple of handfuls of clutch fiber came out. The
 flywheel, pressure plate, trans input shaft and the back of the crankshaft
  were blue from the heat of the slipping clutch. The trans input
and the  crank  just had small spots. The fire was the release fork
boot burning from the  radiated heat. Surfaced the flywheel and put
new clutch in. I also had to  replace the trans input bearing as
this fellow would shift into OD at 40MPH.  Ford dealer had replaced
the noisy brg 3 times previous. Only 45K miles on  the  truck. He
came back two weeks later to see if I had the clutch core. Said he
 was talking to his insurance agent and they figured the fire burnt the
  clutch
  out. There we go with the only thing more dangerous than a dumby,
 is a dumby  that thinks he is smart.

  Dale Davies

  Burning brakes happened to me when I was driving a semi as a teenager.

  Paul Lamar

Wouldn't the clutch gripping strength be stronger than the other
components in the drive train?  I'm thinking rev up and pop-the
clutch..  And the clutch clamping surface is quite a distance from
the center of the shaft, lowering the slipping force (torque) required.
In automotive use, clutches fail when they are slipped, or engaged
suddenly.  If the clutch is healthy to start with (not worn out from
miles or abuse), it won't slip.  I think your 1/2 ton truck customer
rode (left his foot on) the clutch pedal.  That's a quick way to wear
one out - abuse.

As a side note, I went hunting a while back with a friend..  We were
in his pickup, he was driving.  I have never ridden with anyone that
slipped the clutch as much as this guy..  I mean, probably half the
time we were accelerating, the clutch was slipping.  I could tell he
was doing it by watching his leg/foot..  I have no idea how long that
clutch lasted, but it couldn't have been many miles.

I guess the crash airplane might have had the clutch
linkage/hydraulics mis-adjusted so that it didn't allow the clutch to
provide its full clamping pressure..  That brings up a thought...
Maybe airplanes with clutches (or anything that could slip) should
have a tachometer on both the prop and the engine..  And a little
circuit that keeps track of the ratio between them.  And which sets
an alarm if there's any discrepancy between the engine and prop RPM -
 indicating slipping - which might not be immediately detectable to the
ear.

I understand that there may be torsional resonant loads at certain
RPM ranges, but I'd guess that they would threaten the prop shaft,
or output gear..  There's lots about this that I don't know - obviously.
Predicting the RPM at which resonant forces build doesn't seem to be
something that can be done by guessing or TLAR..  None the less, I
think the torsional loads would tear the center out of the clutch
before other failures, assuming proper engagement.

Matt-

Bud claimed the clutch damped the torsional pulses which implied it
had to slip.

Paul Lamar


Matt,

The 1/2 ton clutch probably did not get the clutch free play adjusted which
allowed it to start to slip. The dumby part. Have you ever passed a semi that
smelled like hot brakes? Probably the clutch if it is on fairly level road
over going up hill. Lots of them come into the shop with no free play, but
that is why they are there.

I think I read that the clutch in Bud's plane was of a centrifugal design that
engaged at a set RPM. Under take off power a slipping clutch would get
Chernobyl hot quickly. As the heat builds, the grip is reduced compounding the
problem.

Dale Davies