Mercedes D.III or D.IIIa ?

Aquilius · 12 November 2016, 08:53 AM

Gentlemen,

is it possible to decide the definitive engine type by its serial number?

In question is the Daimler Mercedes engine 356421.

This was the engine August Euler used as powerplant for his late prototypes D.R.5, D.5, D.7 & D.10 in 1917/1918. The triplane D.R.5 is told to have been completed in April 1917. But the actual engine he might have received little later.
At various places this engine is referred to as D.III or D.IIIa.

Could this have been the improved 180 hp Mercdes D.IIIa already?
Does someone eventually has a list of D.III/D.IIIa serials or does know where this is to find?

Thanks for any comments.

Aquilius

MickMcGrath · 16 November 2016, 10:43 AM

No replies from the experts , you really need Dave Watts, but this is what I have got:......

Daimler Mercedes engine 356421

This quoted number does not match any Mercedes motor number.

The Mercedes D.III series had a three part number:
1) Bau Nr, in three digits, which was the block/ batch construction number.
2) Motor Number, in one or two digits, which was the order of the motor in the block /batch of 100 motors.

Both these numbers were stamped on the port side of the crankcase along with a six months guarantee date.

3) Another motor number, the actual motor number, in five digits, which was stamped on a data plate also on the port side of the motor.

Your number has six digits and so does not match any of these, but.................

If the last digit "1" of your serial number is any kind of typo and we cut it off then we have 35642 which is a valid Mercedes motor number.
Now we have M.N. 35642 which was an actual motor of Bau Nummer block approximately B.N 71x and thus a Mercedes D.IIIa manufactured in the Fall of 1917, the first D.IIIa motors being approximately Bau Nummer 61x and accepted Summer 1917.

Incidentally, the photo's of the Euler Dr.II and D.III(?) in Gray and Thetford, definitely show D.IIIa motors with the large, vertical air pump and rear-mounted rocker gear.

I hope this helps.

Aquilius · 16 November 2016, 01:10 PM

Thanks Mick. Your input is most welcomed!

I already noticed Mercedes motor numbers had 5 digits only.

If the number is 35462 actually, it might be in the range of a 180 hp D.IIIa, of which Dave Watts has restored an example numbered 37400.

The record I have is from a written copy of the Euler company catalogue.
Will try to get a look on the original document.

I just wondered why Euler had developed fighter prototypes in Summer 1918 with an old D.III engine. And a powerplant of 160 hp doesn't seem to be appropriate in that time, compared to other contemporary developements.
Just Euler used the same Mercedes engine for the above mentioned fighter types. What is to make out from pictures, he too might have used the very same airframe and only changed the wing configuration. That is proven for the D.R.5 triplane / D.5 biplane and likewise might have happend with the D.7 / D.10 biplanes.

If Euler received this Mercedes in Spring 1917 - it could have been an older 160 hp D.III. But probably this was a brand new 180 hp D.IIIa?

Thanks a lot for your hint to the air pump & cam shaft arrangement!

I hadn't noticed the difference here. It does make the story much more reasonable to me.

Cheers

Aquilius

rsanz · 16 November 2016, 01:48 PM

Quote:

Originally Posted by Aquilius

Gentlemen,

is it possible to decide the definitive engine type by its serial number?

In question is the Daimler Mercedes engine 356421.

This was the engine August Euler used as powerplant for his late prototypes D.R.5, D.5, D.7 & D.10 in 1917/1918. The triplane D.R.5 is told to have been completed in April 1917. But the actual engine he might have received little later.
At various places this engine is referred to as D.III or D.IIIa.

Could this have been the improved 180 hp Mercdes D.IIIa already?
Does someone eventually has a list of D.III/D.IIIa serials or does know where this is to find?

Thanks for any comments.

Aquilius

Is there a photo of any of these prototypes that shows the style of air pump at the front of the engine? That would be one way to discriminate between a D.III & D.IIIa.

Aquilius · 16 November 2016, 02:29 PM

Here are some pics from the SDASM. I do not have them much better.
(There are no verified pictures known of the D.7 or D.10.)

Euler D.R. 5 (company designation) - supposedly built in April 1917.

Euler D. 5 (company designation) - same fuse with new wings built in May 1918.

If I got it right, they are powered by a 180 hp Mercedes D.IIIa.

Cheers

Aquilius

rsanz · 16 November 2016, 08:03 PM

Quote:

Originally Posted by Aquilius

If I got it right, they are powered by a 180 hp Mercedes D.IIIa.

Cheers

Aquilius

D.IIIa would be my interpretation too based on what looks like the fat air pump at the front in those photos.

Ransom E. Olds · 16 November 2016, 08:40 PM

I think that the first image at least depicts the earlier type engine with the rocker boxes straddling the camshaft between the valves for a given cylinder rather than the later type with each box set just to the rear of the pair of valves it activates. I think this is one of the points Mick has made and perhaps it's best to google up good images of early and late Mercedes D.III series engines to see what I'm trying to describe in mere words. Ransom

Laserlloyd · 17 November 2016, 06:09 AM

I will contact Dave to let him know about this thread.

Lloyd...

Aquilius · 17 November 2016, 08:10 AM

Thanks Lloyd.

To further complicate matters, I read D.IIIa production only started in June 1917.

But there should have been an early D.IIIa variant built since February 1917, which had flat cylinders - opposed to concave ones with the D.III.
This engine was rated about 170 hp. Daimler designations "F1466a" or "DF 170" (Daimler Flugmotor 170 PS).

The final production D.IIIa had domed cylinders to further increase compression and reached 180 hp.

If that is true and Euler received his engine in Spring 1917 already, he must have gotten an early D.IIIa, which is to rate as a 170 hp Mercedes D.IIIa.

Is there a source for that?

Regards

Aquilius

Maxim08 · 17 November 2016, 12:02 PM

Aquilius, a few tidbits about the DMG engines. As previously noted, D IIIa production started in June of 1917. While named the D IIIa, it was a low compression motor. It wasn't until the D IIIau that we have high compression in the 'a' engine.

It is note worthy that there are early and late model D III engines. Early engines have the air pump located at the rear of the engine sitting on top of the camshaft housing, just ahead of the decompression gear. Later engines moved the pump to the front as in the later 'a' engine. BTW, horizontal and vertical air pumps are interchangeable and no guarantee of identifying a specific model. Better to focus on the rocker boxes as noted by Mick.

I have a March 1917 production D III rated at 170hp due to high compression pistons. It is unit #31802 this number is stamped into the upper crankcase on the opposite side from the BN number ie the starboard side. While DMG produced about 12,000 D III / DIIIa engines, I would doubt that they built ~4,000 units between March '17 and June '17. I suspect that the engine you refer to is the later 'a' model.

The two engines in the photos certainly look like D IIIa motors.

I hope some of this helps,

Regards
John