http://www.youtube.com/watch?v=mOQejYwM9tU&feature=user

The History channel did a nice documentary on Jim Mederer's 200 MPH
crash
in a turbo 3 rotor 900 HP 3rd gen RX7 at Bonneville. Don Sherman, a
former
student of mine and previous record holder, in a Racing Beat 2nd gen
Mazda RX7,
called and asked me to come up to Bonneville to have a look at the car.
Csaba
Csere also a former student of mine was also there.

My wife Robin and I flew up in my Cessna 182.

When I got there  Don was correctly concerned that the car had 200
pounds of
down force on the front wheels at 100 MPH and none on the rear.

The 200 Lbs at 100 MPH would translate to 800 Lbs at 200 MPH.

The animation shown in the History Channel animation with the nose
lifting was
therefor incorrect.

The nose would NOT lift with 800 pounds of down force. In fact, if you
look
closely, you can see the body deflected down around the front wheels at
speed.

The car would merely pivot around the front axle as soon as the required

traction caused the rear tires to lose lateral grip.  I suggested adding
some
down force on the rear by taping up the vestigial rear wing the stock
3rd gen
RX7 came with. Jim did not want to do it as the rules did not allow body

modifications. In hind site it would have been better to reduce the nose
lift to
near zero or slight lifting which would have provided the needed
directional
stability at 200 MPH.

This is because the center of gravity is located well behind the front
axle. Any
yaw disturbance what so ever would cause the car to spin out with down
force on
the nose and no disproportional amount of downforce on the rear. This is
true
for all rear drive cars regardless of the amount of down force on the
front
wheels. The traction from the rear tires is equal to the total drag on
the car
and then some additional for acceleration. There is only so much
traction from
the rear tires available. If all is used overcoming drag none is
available to
keep the rear end in line behind the front end. In the mean time there
is a
rolling friction drag vector from the front tires which aggravates the
situation.

That is exactly what happened.

Well, while we were out on the salt looking at the car a thunder storm
appeared
off to the north and we were told to leave the race cars where they were
and get
off the salt immediately. Fortunately I had landed at the airport and
not on the
salt as some pilots had. After the rain died down and the sun came out
Don and
some of his friends and photographer for Popular Science talked me into
taking
them aloft over the flooded race course for the purpose of taking
pictures. It
was a disaster. Race cars were knee deep in salt water. The best picture
made
the center fold of Pop Science magazine.

Robin and I flew back home and I calculated at what speed the spin would
occur
and what the yaw acceleration would be once it started. As I recall I
passed the
info to Jim but it might have been Don. I had previously worked for Greg

Breedlove on his American Motors sponsored wheel driven land speed
record attempt.

Robin tells me the actual run shown in the documentary came three weeks
later
after the salt dried out.

It is also interesting that the video did not mention that this car was
powered
by a turbo charged three rotor rotary engine. At the time 300 HP per
rotor was a
modest amount of HP. Current turbo 3 rotor Mazda engines are generating
over 400
HP per rotor and the end is not yet in site. As soon as some one figures
out how
to make a rotor out of light weight beryllium aluminum alloy, instead of
heavy
cast iron, the current 11,000 RPM red line will double to 22,000 RPM and
so too
the current 1200 max HP to 2400 max HP.

Please give this youtube video a five star rating as it encourages  more
people
look at it. The rotary needs all the PR it can get. We need these
extraordinarily durable and high power to weight ratio engines for our
airplanes.

Paul Lamar


Paul, Very nice thank you.  Kelvin

You are welcome Kelvin.

Paul Lamar

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