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