Old Car Trivia #15

[dwasson]

The world-beating Porsche 917 wasn't initially successful. In fact many drivers called it the "Widowmaker" in light of it's high speed instability. Porsche engineers fixed the instability problem using the research of a reknowned aerodynamicist. In honor of this man, the fix was named for him.

What was the fixed 917 called?

[fastblackmerc]

The instability was cause by the long tail, I think. Was fixed by a guy with the last name that started with a K.... don't remember anything else.... now I'm really going to bed.

[DirtyDog]

the 917K for a guy who's last name started with a K.

[fastblackmerc]

917K was the short-tailed version.

[dwasson]

Y'all are getting there. Who was the guy who's name started with a 'K'?

[DirtyDog]

I found it "Kurtzheck".

[dwasson]

I found it "Kurtzheck".

Nope, there's another name. It was also used on a large selling American car.

[jgc61sr2002]

K= Kieser:D

[DirtyDog]

Here is what I found, notice the bananas.

The Breakthrough 'Kurtzheck' :banana2:
There would be a solution, though, this coming in the form of an open-topped 917, the prototype of the spyder Jo Siffert was then running in the Can-Am for Volkswagen of America, which was also brought along for comparison. Although mechanically the 917 spyder remained virtually unchanged from its coupe sibling, its bodywork was quite different, featuring a flat top whose shape rose towards its tail, much in the manner of the Can-Am cars of the day.

Memories about what happened in the test session vary depending on who is or isn't talking, but the fact of the matter is that when Wyer's mechanics revised the coupe's rearward sloping bodywork to match the profile of its open-topped counterpart, the four-second per lap advantage the spyder had enjoyed over the coupes disappeared completely. Ugly though the "ad hoc" modifications might have appeared, they worked. The coupe was transformed into a stable winner.

Interestingly, Piech chose to skip the session. If he had attended, one has to wonder whether or not he would have permitted the revisions to have been applied to the cars. However, once the modifications proved themselves, Piech adopted them wholeheartedly, even going so far as to fully develop the tail's final shape in the wind tunnel.


What emerged in December was the basic definitive wedge-shaped short tail 917K (for Kurtz) :banana2: featuring a "valley" down the revised decklid's center axis to provide rear vision for the driver. Also modified was the nose, the air and brake into being changed, as were the fenders whose lower surfaces were made thicker and beefier to eliminate the need for the previously used "tack-on" front dive planes which had proved so vulnerable during 1969. The only other modification made was to get rid of the side exiting exhausts, all the headers now leading to a pair of rear mounted collector pipes.

Here is what I found, notice the bananas.

[Breadfan]

John Horsmann


During tests in Zeltweg (http://en.wikipedia.org/wiki/Zeltweg), Wyer's engineer John Horsmann had the idea to increase downforce to the expense of drag.

Source: http://en.wikipedia.org/wiki/Porsche_917

[dwasson]

Well the guy I was thinking of was Wunibald Kamm. In the 30s he figured out that lowest drag occurs when the tail of the vehicle in question is cut off at 50% of the maximum cross section. Prior to Kamm's research, streamliner cars were teardrop shaped, with very long tails. The long tail 917 exhibited rear lift and would get very loose at high speed. When they shortened the tail, and created the 917K, these problems went away. In the books I've read about the 917, the engineers used the word Kammback to describe the 'K' model.

In the 70s, GM used Kammback as the name for the Vega stationwagon.

[DirtyDog]

Here is the finish of your quote.

During tests in Zeltweg, Wyer's engineer John Horsmann had the idea to increase downforce to the expense of drag. A new wedge-shaped tail was molded with aluminum sheets taped together. This worked well as the new short tail gave the 917 better stability. The new version was called 917 K (Kurzheck).

[Breadfan]

Yup had to look that one up, I would never have guessed that Vega name. :)

Thing that concerned me is that wikipedia is editable so I take the info there iwth a grain of salt...

[DirtyDog]

I just looked up "Kurz heck" in german to english dictionary it means "short Tail".