D. R. Pobjoy was an RAF captain and the designer of these small radial engines with little power for the cylinders they had. These engines were all of the same size and had the same displacement: 77 mm bore by 87 stroke, in total 2,835 cc. Except the 130 hp engine.

-In a curious way, they are the only ones (not counting the rare Gnome rotary and some other) that, being radial, had a frontal superimposed gearbox to raise the propeller shaft and reduce its rotation.

“Pobjoy P, rear view”

“Pobjoy P, side view”

-Around 1928 he tested his first engine, the "P" model, with 7 cylinders and only 60 hp. It was built at George Parnall's factory. Later it reached 67 hp.

-Around 1930 he founded "Pobjoy Airmotors Ltd." in Cheshire. The first engine to leave the factory was the "R" model. Followed by the Cataract and the Niagara.

-A separate mention is the unknown but existing "Cascade", curiously ungeared. It is covered at the end of this chapter.

-Below we see a P engine in a photograph showing its real aspect.

“Pobjoy P”

-This company went through various name designations. Starting with that of D.R. Pobjoy its designer and builder of the original engine and who shortly thereafter founded Pobjoy Aircraft Motors in Surrey.

-Later it became Pobjoy Airmotors Ltd and then Pobjoy Airmotors and Aircraft Ltd, in Kent.

-The first engine, the P or rather the P-1, we show below in two photographs, highlighting the rear-view one with the intake manifold assembly and we can see that the carburetor is heated by an exhaust pipe from a cylinder .

-In the front-view photo, the gearbox box has a smooth surface, later it would become tighter, with thinner and lighter walls and therefore, with external ribs.

“Two views of the Pobjoy P-1”

-They produced the R, Niagara, Cataract and the little known Cascade models.

“Cataract cross-section”

-It is interesting to observe the formidable crankshaft and the one that had a flywheel or damper in the front just behind the gearbox.

“Pobjoy R ad”

-The Pobjoy R ad is from 1933.

-From Pobjoy has now appeared an engine called "Aurora" and whose information is on file at the Nasm with the reference (BP-500000-01). It seems that it is a 7 cylinder radial as well.

-The R gave the brand fame and consistency so they were able to develop the models that followed. It gave 75 hp at 3,000 rpm (crankshaft) and 80 hp at 3,300 rpm.

-All rpms were reduced from 0.47 to 1 for the propeller.

“Pobjoy R, side view”

“Pobjoy R, installed”

-Apart from the installed one in the photograph, another engine can be admired at the Rectimo facilities, in Chambery, France: a perfectly cared-for Pobjoy R.

“Pobjoy R in Chambery”

-The most surprising thing about this particular engine is the “spider-shaped" rear intake manifold.

“Pobjoy R, rear view”

-The “Caratact” was very similar to the R. It has already been said that the displacement is the same in all of these engines. It had at least three versions: the Cataract I (Mark I), from 1934 that gave 80 hp. The II gave 84 hp at 3,200 rpm and 90 hp at 3,500 rpm.

“Cataract, 80 hp”

-The Cataract Mark III version appeared in 1936 and delivered 98 hp.

-That same year another line of Pobjoy engines came out, the “Niagara” with 3,200 rpm.

Starting with the Niagara Mark I that gave 84 hp at 3,200 rpm and the Mark II and III that gave 85 hp. The Mark IV gave 98 hp.

“Niagara giving 90 hp at 1,645 propeller rpm”

"Niagara with another front fairing"

“Niagara Mark V”

-Curiously we see three types of fairing and grills offered by Pobjoy.

-The Niagara Mark V displaced somewhat more and gave 130 hp. It was from the year 1937.

“Opened side hoods” (PiP)

-The side hoods opened as in cars.

-An unknown engine of the brand has been the “Cascade”, based on the Cataract. It had no gearbox, as we see in the figure below in which the propeller comes out through the center of the engine and a cover is placed on the supposed gear box.

“Pobjoy Cascade”

-The Cascade gave 65 hp at 2,600 rpm and 70 hp at 2,850 rpm. As it was not geared, the propeller rpm was the same as that of the crankshaft. It was from the year 1929.

From Appendix 6: Around 1926 Capt D.R. Pobjoy designed the first Pobjoy that would lead to the P.1. By 1928 it had already passed the Type Qualification Test of the English Air Ministry.

-From the Flight magazine of the time we provide two views with different propellers of this model that also appears in the main text.

“Pobjoy P.1 on test benches” (PiP)

-The 7 cylinders and the superimposed gearbox, give these engines an unmistakable appearance. Precisely thanks to the gearbox they deliver more power due to the high speed of the engine of about 3,000 or 3,300 rpm.

-Below two views of Pobjoy R from 1930.

-Author's note= Note that this engine is not an “R” but a P.1. The information we received was not correct, but it remains here for the studiers.

“Pobjoy P.1 and not “R”

-Observing the rear we see that the carburetor is situated in a common place in the center where the intake ducts come out.

-There is a small impeller that, spinning at speed, distributes the mixture equally - against the effect of gravity on each droplet of gasoline - that would tend to enrich the lower cylinders.

-In addition, a branch of the exhaust runs around this point to avoid icing.

From Appendix 12: Differences between a classic Pobjoy with overlapping gearbox and the “Cascade” with ungeared direct output.

“Difference between a classic Pobjoy and a Cascade”

“Pobjoy 50 hp on a Handley Page”

-Below we provide an interesting exploded view of the crankset with pistons and another one with a formidable gearbox, precisely with the type of gear patented by Citroën, and with a proportionally large size.

"Difficult clarity of detail of the alternative mechanism"

-New Flugsport photo of the Pobjoy engine for the hp-Cranwell aircraft. It gave 60 hp.

“Pobjoy on test bench and schematics” (PiP)