enginehistory.org

[jrussell]

Does anyone know why the change was made from a four valve head ( in the "A" series ) to a three valve head ( in the "D" series) ? Is there any reference available which covers the development of the DB series engines? Thanks in advance for any info.
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It runs best just before it blows!

[rhaus]

I am not that familiar with this engine, but my guess is this must have been a change from 2 intake / 2 exhaust valves to 2 intake / 1 exhaust valve....if so, the likely reason would be the difficulty of cooling the "bridge area" between the two exhaust valves (given the close proximity to each other in the head) Providing ample cooling in this zone would have been a challenge and failure to do so would have lead to detonation, valve and seat failures, etc.

sincerely,
rh

[jrussell]

I have received information that the "D" series did not convert to a three valve setup. Supposedly, the mis-informatiom is a result of a defective translation from a Finnish authored book. I am trying to ascertain the what the correct facts are, but given the scarcity of specific detail information, it is difficult. It seems that not that many aircraft guys are intrested in this level of detail on the modification history of the 605 series!
_________________
It runs best just before it blows!

[jjuutinen]

JRussell, I think you meant the Czech JaPo booklet on the 109K, if you are the same person who asked this on Luftwaffe Experten MB.

The 605D did have 4-valve head, as did the rest of the 605 series.

The sad truth is that there are no good books on the development of the 605 (nor for other German piston engines). One may hope that e.g. Olivier Lefebvre (he is the one known as Butch2K) finds time to do one!

[rinkol]

[gryan]

I read somewhere that prototype coupled DB engines caught fire! What was the cause of this trouble? Was it solved?

Regards

Gerald

[rinkol]

Re. question on coupled engines.

The coupled engines seem to have had issues with both the engine design and their installation.

Engine Design issues:

- oil return pump is said to have been too large and have had a tendency to cause the oil to foam at altitude due to creating a vacuum
- inverted arrangement meant that leaking oil or fuel had a good chance of coming into contact with the exhaust manifold
- DB601F and early DB 605 engines had reliability problems when operated at rated output (I'm suggesting that the basic engine designs (at least in their early production form) used to construct the coupled engines were not well suited for use in a bomber given the need for a lengthy climb to cruise altitude). Heinkel, in his book, seems to support this by claiming that the valves tended to quickly foul.

Installation issues

- no firewall in He 177
- insufficient space around engine to allow access to plumbing and wiring (this contributed to leaks of fuel and oil) In later He 177s, the engine mounts were lengthened to help address this issue)
- airflow around the engine may have been insufficient for cooling (note that the Bf 109G had small air scoops added to the cowling to help cool critical components)

Interestingly, the He 119, which was the first aircraft to use the DB coupled engines doesn't seem to have been as badly affected as the He 177. This may have been due to a combination of factors (the DB 601A used as the basis for the early coupled engines was more reliable than most of the later DB engines to start out with, there may have been more space for the engine, and the lighter aircraft would not have required as lengthy a climb to operating altitude).

One issue with the twin engine configuration of the He 177 is that if one of the coupled engines had to be shut down, the other engine had to be operated at high power to maintain flight; a situation that would not help its reliability.

I have the impression that the worst engine reliability problems were eventually resolved, though careful operation was still needed.

Robert