Jacobs Dr.1 - Allied Engines and Performance

Gents,

It is known that Josef Jacobs continued to fly a Dr.I until close to the end of the war. From what I have read, he actively encouraged the salvage of Allied rotary engines, which were supposedly worth a case of champagne each to the delivering party. Presumably, these engines found their way into Jacobs Dr.I.

My question is: has anyone done any speculative analysis on what performance improvement might havebeen achieved by the Dr.I upon installation of a 130hp Clerget.


Byron

[leo]

I don't know about the Clerget but in a past thread someone had figures for the installation of various Goebel and Siemen Halske engines. As I recall these engines gave minimal increases in performance. Perhaps it was because they weighed more.

[Taz]

Byron- The 130 hp Clerget was actually kind of a dog. Reliability problems, especially from license built versions, and did not perform as well as 110 hp Le Rhones. But probably better than the Dr.I's Oberursel, which degraded in power rapidly in service. Voss swapped his Oberursel for a Le Rhone as soon as he found one for F.I 103/17. Camels equipped with Clergets weighed about 50 lbs more than similar Le Rhone equipped Camels. The long stroke (I believe) 140 hp Clerget was a much better performing engine. From Sopwith Camel- King of Combat the time to climb numbers to 15,000 ft for equivalent Camels were:
130 hp Clerget 20 mins 40 secs
110 hp Le Rhone 17 mins 20 secs
140 hp Clerget 15 mins 45 secs

Terry Phillips
Taz

[StephenLawson]

Here is a bit of fun. From Cross & Cockade Intl.
Vol. 25 #2 1994 “Jasta 7 under Kobes Pt.I”
Vol. 25 #3 1994 “Jasta 7 under Kobes Pt.II”
Vol. 29 #2 1998 “Sketches and Descriptions-Kobes”

Originally Posted by Taz

Byron- The 130 hp Clerget was actually kind of a dog. Reliability problems, especially from license built versions, and did not perform as well as 110 hp Le Rhones. But probably better than the Dr.I's Oberursel, which degraded in power rapidly in service. Voss swapped his Oberursel for a Le Rhone as soon as he found one for F.I 103/17. Camels equipped with Clergets weighed about 50 lbs more than similar Le Rhone equipped Camels. The long stroke (I believe) 140 hp Clerget was a much better performing engine. From Sopwith Camel- King of Combat the time to climb numbers to 15,000 ft for equivalent Camels were:
130 hp Clerget 20 mins 40 secs
110 hp Le Rhone 17 mins 20 secs
140 hp Clerget 15 mins 45 secs

Terry Phillips
Taz

..... Thanks Taz. I fixed upon the 130hp Clerget in the belief that it was the most common powerplant in use at the time. But maybe not.



Byron

[Taz]

Byron- The Camel had a relatively long service life, was built in the thousands, and went through engine upgrades which helped it stay relatively viable until the war ended. The last upgrade fitted to the Camel was the 150 hp AR/BR-1, which greatly improved performance. The Fokker Dr.I soldiered on with the 110 hp Oberursel until effectively replaced by the D.VII. Engine upgrades might have helped extend its service life, but the three month delay in deliveries for the wing failures meant the D.VII was already in the pipeline. With only 320 airframes extant, an upgrade was not worth the effort. Raben and Jacobs both liked the Triplane and did good work with them at low and medium altitudes. It was a real pilot's airplane.

Terry Phillips
Taz

Originally Posted by Taz

Byron- The Camel had a relatively long service life, was built in the thousands, and went through engine upgrades which helped it stay relatively viable until the war ended. The last upgrade fitted to the Camel was the 150 hp AR/BR-1, which greatly improved performance. The Fokker Dr.I soldiered on with the 110 hp Oberursel until effectively replaced by the D.VII. Engine upgrades might have helped extend its service life, but the three month delay in deliveries for the wing failures meant the D.VII was already in the pipeline. With only 320 airframes extant, an upgrade was not worth the effort. Raben and Jacobs both liked the Triplane and did good work with them at low and medium altitudes. It was a real pilot's airplane.

Terry Phillips
Taz

Agree re Camel. IIRC, J M Bruce identified at least five different engines fitted to the Camel over its career. Also agree re Dr.I, in the sense that it had a very small production run and a very short career at the front, both probably ultimately the result of shortages of proper lubricating oil (castor oil) for the Oberursel rotary.

My real focus however is to understand what kind of performance Jacobs might have enjoyed in a Dr.I powered by a reliable captured 130 hp (or perhaps even 150 hp) rotary. IMO, an extra 20-40 hp would have given Jacobs an astounding climb rate at merdium altitudes. Assuming that the Oberursel produced an honest 110 hp at the crankshaft, a 150 hp engine could conceivably have increased the maximum speed of Jacobs' Dr.I to very near 120 mph. Supposedly, at least one captured Allied flyer remarked to Jacobs about the surprising speed of his Dr.I (See "In the Cockpit").

[Taz]

Byron- Should be fairly simple to figure out if not gigantically rigorous. Let me look at the difference in top speed between a Le Rhone Camel and a 140 hp Clerget Camel. Should give us a good idea what the proportional increase was. Can even add a little fudge factor for the superior performance of the Le Rhone over the Oberursel. The Clerget powered Camels were faster than the Le Rhone Camels. Can just assume Jacobs had a 140 hp Clerget.

Terry Phillips
Taz

[StephenLawson]

Jacobs focus was to keep a reliable rotary in his two Triplanes. While horse power was a bit higher than the Oberursel 120hp the other Fok.D.VII types (powered by the 180 -200hp Mercs.) in his unit had to stay throttled back for him to lead. He never commented except to say that it was important for him to keep the Triplanes operational. He never compared the two powerplants and their performance in his diary or his combat reports. His only comment about the Clergets was that he found them a satisfactory replacement.

[Taz]

Byron- Stephen is the world's authority on Jacobs and has published numerous articles on Jacobs based on his diaries and photo albums.

Will still look up the data tonight to give you some idea of the performance gain.

Terry Phillips
Taz