From the first measurable point in 1972 to today, the Wankel rotary never once out-improved the piston engine it was meant to replace: 5–6%/yr against a rising 10–13%. The method calls losers as clearly as winners.
The data series opens in 1972, as GM's programme was at full speed. The verdict predates every cheque that followed.
Smooth, compact, few moving parts, on paper the piston engine's obvious successor. The industry begins to believe.
Dozens of manufacturers buy Wankel licences: Curtiss-Wright, Mercedes-Benz, Toyota and General Motors among them. The strongest consensus any alternative engine has ever drawn.
NSU's rotary flagship suffers mass early-life rotor-seal failures. Warranty claims bleed the company.
Financially drained, NSU is folded into Volkswagen's Audi. The rotary claims its first company before the data series even opens.
In November 1970 GM licenses the Wankel, roughly $400M in today's money, and president Ed Cole projects production in three years. The first platform reading lands two years later.
Rotary fuel consumption becomes untenable; GM shelves the programme as Cole retires; Mercedes cancels the C111 line. The rate had never moved.
Engineering heroics, including a Le Mans win in 1991, against a rate that never budges. RX-8 production ends in 2012, closing 45 years of rotary manufacture.
The rotary returns in Mazda's MX-30 R-EV, not driving the wheels, but as a small onboard generator. A supporting role was all the rate ever supported.
The rotary attracted more manufacturers than any alternative engine in history. The arguments were real. The rate never was.
Mechanical elegance reads like destiny. But elegance is not a learning curve: apex seals, chamber shape, fuel economy and emissions never entered a fast improvement loop, and the flat rate proved it, year after year.
When Mercedes, Toyota, GM and Curtiss-Wright all pay for the same technology, dissent feels reckless. Consensus was the filing count. The rate disagreed with all of them at once.
Rotaries won races, including Le Mans 1991. Race wins prove peak performance on one day, not the compounding of cost and performance that decides markets.
We forecast the improvement rate from two citation metrics, cycle time and knowledge flow. Both were visible the whole time.
The rotary's cycle time sat near twenty years for half a century, each invention generation took a generation. Its knowledge flow never crossed 0.3: later work simply did not build on it. Compare the piston engine, unglamorous and compounding, its cycle time tightening decade after decade. The verdict was never close.
Provenance. Every patent carries a filing date, so the record can be replayed: every improvement rate on this page uses only the patents that were public at the time. No hindsight enters the series. Chart data: GetFocus platform exports, August 2026. The historical facts below come from the public record.
Bring us one live technology decision. Within 48 hours you get a free preliminary Decision Brief: a first-pass radar, improvement rates and suggested triggers.