Mercedes D111 and D111a

[Captain Fantastic]

What's the difference between the Mercedes D111 and D111a? Would it be noticeable in 1/32 scale? I mean, most of the inline engined fighters have their motors covered by a multitude of panels with only the top part exposed. On that basis, would a D111 pass for the D111a?

Cheers,

[StephenLawson]

The main differences above the cowling are the the placement of the rocker box covers from the side or profile view. Centered on the rocker springs on the D.III, and early D.IIIa. On the later D.IIIa and all subsequent models of the 1466a type motor they were place further back so the rocker springs were at the leading edge. Note the boxes were moved, not the rocker arms and springs. Often there is some concern about the air pump. The stand up vertical pump was seen on late D.III through early D.IIIaü types. These are generalized comments as your request asked about general types.

[Familyman]

I think that the early D.III engines had also the port side pipes made of copper the later types had them made of steel (or aluminum? some greyish metal anyway). When did this change happen exactly, I do not know.

Mikko

[Maxim08]

Captain Fantastic (like the name)

This link gives a brief rundown on the D family of engines.

Mercedes Engine History | The Vintage Aviator

Regards,
John

[Captain Fantastic]

Stephen Thank you for the summary. Sounds like there is enough difference to be noticeable. Any close up pics of the top section as you describe it?

Mikko thanks for the change in pipe material. That's something I didn't realise.

John I can't take credit for the name. It's been thrust upon me by my friends and besides, who am I to argue? Thanks for the link. Very interesting info there.

[Patrick]

Originally Posted by Familyman

I think that the early D.III engines had also the port side pipes made of copper the later types had them made of steel (or aluminum? some greyish metal anyway). When did this change happen exactly, I do not know.

Mikko

The pipes are the intake manifolds. To insulate them, they were wrapped in gray asbestos cord which was then wrapped with black cloth tape. Fading and dirt rapidly caused the tape to turn grey and sometimes it came off completely (or was not applied) showing the cord underneath. This insulation was not used on later versions of the engine that incorporated intake manifolds with water jackets.

Some good photos here:

Mercedes Engines

It's pretty easy to find clear pictures of the late-style rocker boxes with the arms mounted on the front surfaces. Pictures of the early-style rocker boxes with center mounted arms are rare. Check the archives of Flight magazine for the article in the May 23, 1918 edition on the Mercedes D.IV:

1918 | 0560 | Flight Archive

It used the same center-mount rocker arms as the early D.III. The D.IV article contains some good detail photos of this feature.

[Captain Fantastic]

Patrick, many thanks for the additional links and info. I'll study these carefully.