Prajadhipok; The Original Thai Fighter

January 27, 2023

I wrote an article recently on the Paribatra bomber, Thailand’s first indigenously designed and built aircraft. This rather obscure aircraft was a little tricky to research as there is not a lot out there on it, certainly in English.

But there is a veritable encyclopaedia of information available on the Paribatra in comparison to the aircraft I am covering today, which was Thailand’s second indigenous design.

The Prajadhipok – the first Thai fighter.


I cover the reasoning for Thailand (or rather the Kingdom of Siam as it then was) deciding to design and build their own aircraft more fully in the previous article, so check that out for more information. But to give a brief summary, in 1922 the Thai’s decided to standardise their air force on two primary types, the Breguet 14 two-seat bomber and reconnaissance aircraft, and the Nieuport Delage NiD 29C.1 fighter. Both of these were subsequently put into licensed production by the Kingdom of Siam, using local materials for construction wherever possible.

But when the supplier of the French-made engines that both types used suddenly jacked up the prices, the Thai’s decided to come up with alternatives. Thus in 1928 the Prajadhipok was created, named in honour of the King of Siam, and which the Siam Air Service it was classified as the Fighter Type 5

The aircraft was of conventional design, an equal span single-seat biplane that was powered by – I believe – a BMW VI water-cooled engine. This would have been a rather new product at the time, only going into production in 1926. But as it was not French and produced around 600hp, it would have seemed a pretty good choice.

As said, very little details seem to exist on this aircraft, and I can’t be even sure that it was ever armed, despite being classified as a fighter. Indeed, it was definitely an experimental type more for testing what the indigenous Thai builders could create. Because unlike the Paribatra, which did at least see some limited production, the Prajadhipok was only ever the single example.

The primary reason for this seems to have been that, despite the greater horsepower available in comparison to the NiD 29C.1 fighters whose Hispano engines only produced 320hp, the Prajadhipok had basically the same performance. This means that, though the figure isn’t confirmed, the Prajadhipok would have had a top speed of around 150mph (241km/h).

So, it wouldn’t have been a particular good idea to put into production an aircraft that offers basically the same performance as what the Thai’s had already, which was already starting to be outclassed.

Plus the Kingdom of Siam was about to undergo a rather fraught time politically. In 1932 a coup saw the King lose his absolute power and a constitutional monarchy instituted. This didn’t proceed entirely smoothly and there were several years of disruption, ultimately with King abdicating in 1935 and going into exile.

Notable that was the same year that the Siam military decided on a replacement for the NiD 29C’s, adopting Curtiss Hawk IIIs and acquiring a licence to build them.

That seems to have been pretty much the end of the Prajadhipok fighter, which assumably was scrapped as both obsolete and an unfortunate reminder of its exiled namesake. Now the closest thing to it is a replica that now exists in the Royal Thai Air Force Museum in Bangkok.


Worthy of a Prince; The Royal Siamese Air Service Paribatra (Paribatrara)

Kurt Tank’s First Fighter; The Rohrbach Ro IX ROFIX

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