200 hp Mercedes High Compression Engine

I was looking through Jane's Fighting Aicraft of WWI and in the back there is a section on engines. One of these was the 200-hp Mercedes high compression engine that had an altiude-compensating carbeurator. One was tested by the Brits. Jane's states that the test engine was taken from a Fokker D7 captured in June, 1918. It interesting to see the level of detail that was examined.

Anyway, my question is this. How many D7s had this engine? Was this an rare bird equipped with a prototype engine or was the 200 Merc fairly common?

I've seen so many books say that the Fokker D7F had a 185-hp BMW IIIa and this engine was highly sought after for its power at altitude. I wonder, if the 200hp Merc was common, why it wasn't even more sought after and I've never seen any reference to this engine installation.

[Dan_San_Abbott]

Paul:
The designations and horse power of the Mercedes D.III engines were:
160 Ps D.III never used on a Fok. D.VII.
170 Ps D.IIIa " " " "
180 Ps D.IIIau(umlaut u) most common on D.VIIs
200 Ps D.IIIauv(umlaut u) late production.
There was no special designation on the D.VII for these engines.
Clues for identification the various engines.
D.III, The air pump was mounted between the last cylinder and the cam shaft tower.
D.IIIa tall skinny air pump mounted in front of no1 cylinder.
D.IIIau fat air pump mount in front of no 1 cylinder.
D.IIIauv two cylinder air pump in front of no 1 cylinder and water jacketed intake manifolds.
Hope this is of help.
Blue skies,
Dan-San Abbott

[Lyle]

Amazingly, I believe the Rhinebeck crew is using one of these 200 hp Mercedes in their D.VII...the performance of this plane is astounding. Definitely worth a trip there during the season to see this one in action.
Lyle

[Ron_F]

Whats printed in Windsock special on the D7:

Mercedes D.IIIa 160-180hp;Mercedes D.IIIaü 180-200hp; BMW D.III 185hp. the BMW is what is sought after for its power at altitude.

I too have seen it described as DVIIF for the later built Fokker series. Windsock doesnt specify that the BMW D7s were called F. only squadron signals pub does.

DSA, hit and hold alt button and type 132 for ä and 129 for ü. it should be in the back of your microsoft windows and DOS book on keyboard characters.

fwiw,
Ron

[Dan_San_Abbott]

Paul & Ron:
The performance of the Mercedes D.IIIaüv 200Ps engine was the same as the BMWIIIa, however the BMWIIIa weighed 270kg while the D.IIIaüv weighed 310 kg. I understand that Daimler hired the BMW IIIa engineer to do the job. The Mercedes D.IIIaü is 180 Ps not 200 Ps and the engines are different. I am surprized that Dave Watts has not jumped into this discussion, He is very knowledgeable about Mercedes engines.
Dan-San Abbott

[Dan_San_Abbott]

Ron F:
All Fok.D.VII machines that had BMWIIIa engines installed at time of delivery were marked Fok.D.VIIF ----/18 on both sides of the fuselage. I can confirm this,I have a copy of the Fokker Flugzeugwerke acceptance lists. This identification was not used by Albatros or OAW to identify their BMWIIIa equipped Fok.D.VII aircraft. It can only be ascertained if the engine is visible.
Dan-San Abbott

Hi all,

Sorry for not jumping in sooner, been busy and probably will not be seeing the forum for another week due to travel.

In short Dan is pretty well on it. We have had some long threads on this subject that must be in the archive, where I dug into the subject quite thoroughly. Look under Mercedes or D.VIIF. I have done a lot of spread sheets on this and have something about ready for WW1 Aero.

Without consulting any references, I believe the BMW was simply a larger cubic displacement motor. You may recall all of the Göring letters I posted translations of, (with the help of Hannes), in which all Herman does is cry and complain about how he has to have more of the BMW motors. These letters are quite late in the war, so the higher compression Mercedes were available. In one of the posted letters, he states in effect his Jasta has been cut in half since half of his planes are BMW powered and half are Mercedes powered, and the higher performing BMW planes out climb the others so much in engaging the enemy, that the Jasta is reduced to "half strength".

Again without reference, I believe in the earlier posting I discussed that the D.IIIauv motors were never really in active service, as I recall the lion's share of these went to Fokker, and it was simply way to late for these motors to get in the planes and to the front.

Another point I went into was the fact that several of these later D.VIIs had old 160/170PS Mercedes motors rebuilt and "hopped-up" to "200PS" put into them that had served once before in a Albatros or some other airplane, without changing the air pump, so the exterior appearances of a motor don't always tell you what is in the inside of the motor. Proof of this is the 160 DIII motor that I helped to arrange for Frank Ryder that had been rebuilt in Aachen, and never had a chance to be reinstalled into another airplane. When this motor was disassembled it had the high compression pistons, etc., but still maintained the airpump at the rear of the motor! I still have the original 1918 rebuild tag from this motor.

We can get into this later more in depth, but check the archive, there should be some good meat to get your teeth into. Without reference, I believe you can't always use the air pump feature as a horsepower reference even on "fresh from the factory" motors. I have a spread sheet around here somewhere, where the changes in different motor parts has been bar graph charted and I seem to recall that the double opposed horizontal air pump is not a exact change that occured with "200PS". The thing to remember with these motors was that they were constantly improving many aspects of the motor, so the different parts were often being updated as production continued.

As Herman stated at altitude, the BMW powered D.VII left the Mercedes powered D.VII in its' dust, and at the end of the war, that's often where it was at.

Best,
Dave

[leo]

Does anyone have any information as to how these two AH engines compared with the 185 hp BMW and the 200 HP Mercedes. I have read that the Austro Daimler equipped Fokker D VII was faster and could out climb the 185 HP BMW. What did they weigh and how did they compare displacement wise?

leo

Dan and Dave,

How do I get into the archive to look at old threads?

Thanks for all you help.

Paul

Paul,

As far as looking up old threads, it looks like you go to the "front" page of the forum, and on the right side of the page you'll see a box and you go to forum "old threads" or ""thread archives" or something like that, and start paging back thru those. I know the Göring letters are from July of 1999. Maybe someone else can tell you if you can actually "search" the old threads.

In a couple of weeks I will be back, and can forward a lot of the postings which I personally kept. Send me a reminder then.

Best,
Dave

P.S. I recall that the Austro-Daimler Mercedes was a high displacement motor like the BMW. Don't have exact specs. at my finger tips.