Me-261 Engine Exhaust routing

[GrumpyOldCrewChief]

OK, folks, here comes a real esoteric request. I have been researching this question for a loooong time, and have not found a definitive answer. The The Me-261 was powered by the legendarily wretched (underdeveloped, arguably) DB paired motor units. On most of the aircraft that shared the use of this style motor, the inboard banks of cylinders exited their exhausts out of the cowling downwards, under the center of the motor. Some paired the manifolds into a single output manifold, some did not. But on the Adolfine, the struts and wheels for the MLG were placed right in line with that "usual" location. That situation would lead to all kinds of problems. I have not found a reliable reference anywhere that shows where that center pair of cylinder banks dumped their exhaust. Technically, there is no reason not to run a manifold to any other location, just to get it safely out of the cowling, but simplicity and lightness are Holy Grails in any aircraft design. Most drawings, I realize, are somebody's "best guess", and so can't be relied on. None of the photos I have layed eyes on so far show any clear detail of the underside of the engines. (see samples) Anybody got any real information? I already have all kinds of speculation. After all, I am a grumpy old crew chief, and an A&P mechanic...

 

[wuzak]

Is that an exhaust pipe on the left hand engine, right on the edge of the picture?

It starts inwards before curving down vertically.

 

[vikingBerserker]

Pic from the same shoot, just a little clearer

From FalkeEins - the Luftwaffe blog: Messerschmitt Me 261

How was it handled on the HE 177? I cannot get a clear shot of it either.

 

[Crimea_River]

Is that an exhaust pipe on the left hand engine, right on the edge of the picture?

It starts inwards before curving down vertically.

I would suggest that is a coolant line.

 

[wuzak]

I found this image on Heinkel He 177 - Wikipedia and tried to brighten it a bit.

The outer banks have exhausts that go down to the sides.

I think the inner exhausts go in behind the bottom fairing.

 

[GrauGeist]

I would suggest that is a coolant line.

I agree.

On the 261's engine nacelles, there was a deep recess in the bottom cowling between the engines. I have never seen a clear enough photo to prove it, but the DBs were installed at an angle, which meant the inner exhaust banks would be close to each other, which leads me to suspect that the deep recess in the cowling was there for the exhaust.
Otherwise, it wouldn't make sense to have that deep recess there in the first place, as it would have been less man-hours to make a smooth cowling that radiused clean between the two coolers.

Here's the best photo I can find at present, that shows that deep recess between the engines.

 

[wuzak]

GG, it looks you have found the answer.

A front view of the DB 610 shows the exhaust layout.

Category:Daimler-Benz DB 610 - Wikimedia Commons

 

[GrauGeist]

Here's a couple of images showing the DB606 engine.

Front view:

Rear view:

Still digging around to see if I can find a better view of the cowling. I think the best view I've seen was V2 after it's landing incident at Lechfeld, but most of the images I've seen are too small (size-wise) and/or poor resolution.

 

[GrumpyOldCrewChief]

This is all well-travelled materiel. The paired DB units were filthy engines, both in leaks, and exhaust. The main wheel fairing that shows prominently in one of the photos shows plenty of evidence of oil leak streaming, but NO traces of exhaust staining. Also, the deep trough between the banks is partially an illusion. Most of that is actually the space between the oil cooler fairings. It does seem odd to use two separate coolers, instead of one larger one, but since the single coolers were already engineered and built, why reinvent the wheel? A frequent happening for low-volume items. It would make sense to place the exhaust in this location, as suggested, but it also would not. I remain unconvinced. I have not liked ANY of this evidence to date. We are back into opinions, again, and that is not where I want to be!

 

[GrumpyOldCrewChief]

I found this image on Heinkel He 177 - Wikipedia and tried to brighten it a bit.

View attachment 519823

The outer banks have exhausts that go down to the sides.

I think the inner exhausts go in behind the bottom fairing.

Yes. This is one application that paired the separate banks into a single manifold. It was also designed from the outset as flame-dampening unit. It is a large, and conspicuous assembly.

 

[GrumpyOldCrewChief]

The exhaust on the DB-610 museum example pictured is not representative of any particular installation. They are most probably test stand items. This view also illustrates that there is no space for a deep recess between the inner cylinder banks. Every aircraft installation solves its problems differently. The prominent collector under the He-177 installation is not even suggested under the Me-261. But there was no need for flame damping, either. Another "doppelmotor" installation that has vexed me for this center exhaust is the He-119. It used both -606 and -610 in it's various Versuch editions. How exactly was it solved earlier, with Heinkel? It is difficult to model what you do not know...

 

[GrauGeist]

We have to take into consideration several things.

First of all, just about all DB606 and DB610 installations had the center exhaust exiting at the centerline.

Secondly, behind the firewall of the engine nacelle was the wing spar and maingear joint assembly, which also included the pivot for 90° rotation as it retracted. This really would leave no room for an exhaust duct.

And finally, re-routing the exhaust from the inside banks to another location but leaving the outer banks unhindered, would create uneven back-pressure during the combustion cycle which would result in performance issues.

One final observation: if the inner bank's exhaust was re-routed, the cowling would have a clean radius covering all that, but instead, there is that deep recess, which would be in the way of any sort of exhaust manifold.

 

[GrumpyOldCrewChief]

Yes, all good points. Not lost or disregarded. But not conclusive, either. The lower cowling is relatively smooth, between the valve train fairing covers and the oil cooler fairings. There is no room for depth. The inner faces of the cooler fairings would be getting something from exhaust staining, if both banks dumped out there. But, again, no evidence of what should be prominent staining anywhere in that area.

 

[GrauGeist]

From what I understand, the three aircraft (V1, V2 and V3) were not extensively flown, two were damaged by bombing raids at I believe Lechfeld, where they sat derelict until war's end.

From the photos I've seen, there doesn't seem to be much in the way of exhaust tracking from the outboard exhaust on the various ships.

So it looks like some further digging into the mystery is at hand!

 

[wuzak]

Off topic, but I just found this recognition training film for the He 177.