Jacobs Dr.1 - Allied Engines and Performance

[Taz]

Byron- Looks like a 140 hp Clerget or a BR.1 would give an increase of 10-15 mph over a 110 hp Le Rhone. Would push the Dr.I up to ~ 110-120 mph at sea level and 105-115 mph at 10,000'/3000 meters. Lots of extrapolating in there. Lose another 5-8 mph at 15,000'. Useful increase in performance.

Terry Phillips
Taz

In these speed discussions, are we talking true or indicated airspeeds? Which drags me to ask if they knew or understood true airspeed at all back then? Which leads me to ask, where is a good place to start if I wanted to study 2nd decade aeronautics/aerodynamics data?

[Taz]

Ridir- Beats me. TAS, I would imagine. We used KCAS when we flew. Took out indicator error. INS did TAS calculations. Do not know how they measured it in those days. Anemometers, it looks like. Do not remember seeing any pitot static systems.

Terry Phillips
Taz

Originally Posted by 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 comabt reports. His only comment about the Clergets was that he found them a satisfactory replacement.

..... Thank you for those details, Stephen. Taz has pointed out to me that you are the unofficial keeper of the Josef Jacobs memorial flame.

Originally Posted by Taz

Byron- Looks like a 140 hp Clerget or a BR.1 would give an increase of 10-15 mph over a 110 hp Le Rhone. Would push the Dr.I up to ~ 110-120 mph at sea level and 105-115 mph at 10,000'/3000 meters. Lots of extrapolating in there. Lose another 5-8 mph at 15,000'. Useful increase in performance.

Terry Phillips
Taz

..... That's what I was thinking. Basing my reasoning upon the dictum that drag increases as the square of the speed, assuming that the nominal HP ratings of the two engines you mention represented something close to their true output at the crank, and assuming that the props were the same or sufficiently similar in nature, I come up with about a 13 pct increase in level speed (+/- 115 mph @ SL)

I'll risk another semi-educated guess to the effect that initial climb rate could have improved by as much as 50 percent with a 140 hp engine.


Byron

[leo]

According to JM Bruce the Bentley engined Camel was un questionably faster, but the lower powered Camel climbed to 10,000 ft as fast and was faster to 15,000 ft. It also had a higher ceiling,

[StephenLawson]

Originally Posted by Byron

..... Thank you for those details, Stephen. Taz has pointed out to me that you are the unofficial keeper of the Josef Jacobs memorial flame.

The foundation I volunteer for does own about 1/3 of his aritfacts sold after his death. Fortunately for me these are mostly historical documents and I have been given the publishing rights. While he was a prolific writer technical aspects were the responsibility of his mechanics and riggers. For several years I have been searching for the bimonthly reports of Jagdstaffel Nr. 7. This had their equipment operational status reports to the Armee headquarters. His mechanic had to have some training in the engine type even if it was just practical hands on experience. The idea was Jacobs' to install the allied rotary but there is one indication that he had a discussion with his ground crew on the possibility of the installation before hand but none of that is a surprise. What I found interesting was the wine and Champagne was offered to unit commanders and not the front line troops. This ground crew were the one Jacobs relied on to keep him flying. There was a series of detailed interviews that Jacobs did for a a German national but these have not been available to anyone who is not a German national.

Originally Posted by StephenLawson

There was a series of detailed interviews that Jacobs did for a a German national but these have not been available to anyone who is not a German national.

..... That sounds rather foolish. Just a thought - could Achim Engels perhaps be persuaded to approach the possesor of these intereviews?



Byron

Originally Posted by leo

According to JM Bruce the Bentley engined Camel was un questionably faster, but the lower powered Camel climbed to 10,000 ft as fast and was faster to 15,000 ft. It also had a higher ceiling,

..... I've noticed that rotaries tended to fall off in performance with altitude to a greater degree than in-line engines. It is interesting that such a difference would exist between two different models of rotaries. Perhaps the induction system of the Bentley was less well suited to higher altitudes.



Byron

[Taz]

Byron, leo- There is some conflicting information even in the same book. Sopwith Camel: King of Fighters has about 15 sets of figures for time to climb and top speed. These vary quite a bit and some even quote specific tail numbers. All were probably real numbers, just varied because of different weather, different loads, different pilots, and different number of hours on the engine. About all we can do is extrapolate. Agree with leo on one point, the climb performance does not seem to have improved as much as one would think. This can be misleading depending on climb speed. The Le Rhone may have climbed best at 65 mph or so while the Clerget did so at 75 mph. This would put the Clerget Camel way ahead of the Le Rhone Camel at the end of the climb. The figures I took from the book show the 140 hp Clerget and Br.I outclimbing the Le Rhone in identical configurations, but not by much. J.M. Bruce may have compared a different set of numbers which showed otherwise. Lord knows he probably had every number ever quoted on British aircraft. The man was an encyclopedia.

Terry Phillips
Taz