André Chapelon

André Chapelon was a French locomotive engineer who pioneered the adoption of thermodynamics and gas/fluid flow theories in the design of steam locomotives.  Even though he first demonstrated the astonishing performance improvements that could be attained by relatively simple application of these theories as early as 1926, his work was largely ignored by his more eminent contemporaries.  One (partial) exception was Gresley’s experimental use of Chapelon’s Kylchap exhaust system on a small number of his then new A4 Pacifics, one of which (Mallard) proceeded to claim the world’s speed record for steam traction in 1938.

Chapelon produced very few new locomotive designs, most of his masterpieces being rebuilds of existing (and often poor-performing) machines. The performance enhancements he incorporated into his rebuilds mainly focussed on increasing steam superheat temperatures, enlarging and streamlining of steam passages and improving exhaust systems.  In addition he often included improvements to boilers, fireboxes, valve gear and other components.

The most famous examples of his work are probably his 240P Class (at the time regarded as the most thermally efficiency locomotives in the world) and his 242A1 (having, at the time, the highest power-weight ratio of all steam locos in the world).  Perhaps the most interesting (and daring) of his designs was the experimental 6 cylinder 2-10-0 160A1 which demonstrated astonishingly high power outputs at low speeds.

It was not until the mid-1950s that British engineers began adopting a few of Chapelon’s basic prinicples that resulted in an Indian Summer of spectacular (by previous standards) steam workings. However it was by then too late to stave off the ascendency of diesel traction or prevent the demise of steam.  Only Livio Dante Porta, in far-off Argentina, picked up Chapelon’s torch and single-handedly continued the developement of steam traction into the 21st Century.

Perhaps one reason why Chapelon’s work was not more widely known is that he did not write in English. Of his many written works, only his “La Locomotive a Vapour” was translated into English by George Carpenter and published (in 2000) by Camden Miniature Steam.

In 1972 an excellent English language biography “Chapelon – Genius of French Steam” was published by Ian Allan.

Sadly very few Chapelon locomotives survived into the preservation era.

The photo at the top of this page was supplied by Alain Cassagnau of AAATV Midi-Pyrénées, a society dedicated to the restoration of Chapelon’s 241-P-9 locomotive.  The photograph was taken in 1976 at Guîtres (near Bordeaux) where the 241-P-9 was stored, during an event to celebrate Chapelon’s achievements.  This was the last time the locomotive was in steam.

M. Cassagnau who hosts his own steam website at, was present at the 1976 steaming of 241-P-9 and saw Chapelon there.  He recalls that Chapelon was clearly not happy at the event as witnessed by the expression on his face in the above photo.  M. Cassagnau records that:

“… during his farewell address, recalling the “glory days” of French railways, Chapelon was not happy. Everybody knew that his best locomotives had been scrapped, and that SNCF had kept the 241-P series. But why scrap the best machines? Because after the war the French governement wanted to show France as a strong and progressive nation, so a political decision was taken to get rid of steam traction as quickly as possible.

However Chapelon’s 242-A-1 had demonstrated such high power outputs that it created political embarrassment, so SNCF demanded that Chapelon build a new machine that excluded his best steam technology. Thus the 241-P series became Chapelon’s newest creation, but not his best.  Chapelon claimed that new steam technologies could be outperform electric traction until 1980 when he planned that the last steam locomotives should be built and which would remain in operation until 2010.  By then the performance of electric traction would be markedly superior to that of steam.”

M. Cassagnau adds that:

“As described above, just after the war Chapelon was regarded as ‘dangerous’. But how to ‘destroy’ him?  The method was simple: during the war, Chapelon hadn’t stopped his research, so he was officialy attacked for having demonstrated a “passive attitude in front of the enemy”.  As a result, by way of punishment, he was demoted from his senior engineering position.

All that I say is revealed in 1992 through the work of the National Center of Scientific Research (CNRS) France’s most prestigeous research institute), and serves to explain why Chapelon was not happy in front of a preserved 241-P.  CNRS’s work is described in a paper titled “Centenaire A. Chapelon – Evolution scientifique et technique de la conception des machines à vapeur” (Centenary of A. Chapelon – the Scientific Evolution of the Steam Locomotive”) by B. Escudié, J. Payen, J. Ramuni, which was presented at the Colloque National du CNRS (CNRS National Conference) in September 1992.”