Four Engined He 177 w/ Level-Headed Specs

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D Deleted member 68059

I was thinking about the He 100 and the surface-evaporative cooling system and I'm curious how the RLM came to the conclusion it could withstand battle damage early on?
 
The "Need for Speed" got into their head, letting them forget the negative aspects. Good for racer, terribly bad for a combat airplane.
 
Zipper730 said:
D Deleted member 68059

I was thinking about the He 100 and the surface-evaporative cooling system and I'm curious how the RLM came to the conclusion it could withstand battle damage early on?
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I dont have the RLM records for the dates when that aircraft was being developed.

However, I do have reports on the later Heinkel P-1076, and it was stated in there that the more fragile cooling system was judged to be
an acceptable compromise for a large increase in speed for the specific application of point-defence interceptors, as they had
a resoviour for a short period of operation on a continual-loss basis at very low engine power, which in the case of getting home to a local
airfield was judged to be plausible.
 
Snowygrouch said:
I dont have the RLM records for the dates when that aircraft was being developed.
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Understood. Do you know anybody who would?
I'm surprised it was considered acceptable for a long-ranged bomber however. It seemed nobody in the RLM seemed to even notice this as a problem (in regards to the He177).

BTW: Wasn't the P.1076 proposed in 1944?
 
Revisiting this post: I was thinking about something that was said by Snowygrouch (he's no longer a member) which had to do with the fact that the Germans tended not to use the degree of pressurization in their liquid cooled engines as Allied powers did. The Jumo 213 seemed to be the first to use a higher pressurization. When did this come online?
 

The Jumo 213 had a long gestation, and practically speaking it wasn't until 1944 that it started appearing in service aircraft. At which point there's little need for a long-range aircraft?

Maybe instead introduce the 4-engine He177 earlier by using Jumo 211 engines? Not convinced that bombing factories east of the Ural is useful, but had a functional and reliable He177 been available earlier, it could have been a nice step up from the FW 200 as a maritime patrol aircraft?
 
Makes sense, or at least the provision for either engine.
Not convinced that bombing factories east of the Ural is useful, but had a functional and reliable He177 been available earlier, it could have been a nice step up from the FW 200 as a maritime patrol aircraft?
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Truthfully, it would have been useful for either mission.

I'm not sure I mentioned this before, but there was something that interested me about the surface evaporative-cooling system that Heinkel used: As I understand it, the idea did involve jacking up the water pressure to some degree. I'm curious how it compared with pressurized glycol cooling systems used by allies.

While I could be wrong, one would assume the radiator would be the manufacturer's responsibility and Heinkel would presumably have the means to deal with systems run under some degree of pressure: I'm not sure what kind of designer Heinkel was (or the lead-designer on the He-177), and whether he was a person prone to consider back-up ideas, but it would be a solid compromise.

It is kind of funny that the Germans didn't realize surface cooling would be bad for a combat aircraft: After all, you can't armor it, and a well placed round causes you to lose the whole cooling circuit.
 

I haven't done any numbers, but it seems to me that a high pressure surface cooling system would be very heavy. A traditional radiator designed to withstand high pressure would also be heavy, but at least has the saving grace of being relatively compact.
 
According to this diagram, the pressure required for the water not to turn into steam at 130 degrees is of the order of 3 bars, if pumps etc. are added, we do not exceed the limit / safety values of ordinary home installations (10 bars) (though temperature is a much more critical component here - especially with today's plastic installations ). 130 degrees Celsius is the max temperature for Merlin's cooling system, so .... we don't know about special problems or excessive weight of cooling system.




And the Fw 190A and his BMW 801 had armoured surface cooling - albeit only for oil. Of course, this is not applicable for liquid-cooled engines.
 
Part of the problem with surface cooling is turning the high temp water (steam?) to lower temp water.
normal radiators use a lot of surface area (fins/tubes) condensed into a small space. Surface radiators spread the coolant out over a very large area requiring a lot very thin but strong metal sandwich.
We may be trading weight for drag. Lower drag at speed but more weight.
 

To nitpick, keep in mind the Brits were using a mixture of water and ethylene glycol, which changes that curve slightly. IIRC they were using 50/50, but switched to 70/30 (70% water, that is) shortly before the war. A 70/30 mix has a boiling point at ground-level pressure of around 104C. So that curve would be slightly shifted downwards.

My point about weight wasn't that the Merlin's cooling system was excessively heavy, but rather that a high pressure surface cooling system might well be. Turns out that a cylindrical geometry is very efficient at resisting pressure, and that is exactly what a "normal" radiator is; a bunch of small tubes (probably slightly flattened for better aerodynamics, though) where the fluid flows. Further, there are fins brazened to those tubes, providing even more surface area without having to be pressurized. In contrast with a surface cooling system you have big almost flat surfaces that have to be kept in shape, as presumably you don't want your wing shape to balloon out when you pressurize your cooling system. Keeping those flat surfaces rigid takes strength which means weight. And you don't have the fins giving extra surface area either.

Then you also have to take into account the effect of altitude. One of the advantages of the pressurized systems were that they kept the boiling point constant as the aircraft climbed. But it also means that the system has to be engineered to withstand a greater pressure difference than at ground level.

As for the FW 190A oil cooler, AFAIU it was a "normal" radiator, it was just covered from the frontal arc by an armored shield.
 
Actually, I was also surprised when I checked the pressure level, and how relatively low it is, I probably have the numbers from thirty years ago stuck in my head (related to steam turbines).
Of course, this (relatively) low pressure and relatively high temperature causes a lot of problems on the large surface needed for surface cooling.
Actually, it is interesting that the calculation is that all the additional weight of the radiator (because they have to be thicker/stronger than the normal casing) of all the valves, pipes, pumps, etc. is less of a problem than air drag.

The oil cooler on the Fw 190 can be said to be "normal" because it did not work under pressure (except for the pump), but with a reversible (in the letter s) air flow forced by fan, it is still special.

And I'm have to admit that I thought that the armoured part was also an integral part of the cooler wall, similar as on the MC 200 the copper tube was literally wrapped around the edge of the cowling. Actually, I like these kinds of discussions because you always find out and learn something new.

It is easy to mix up surface cooling and high pressure surface cooling and high pressure cooling, especially if English is not your native language. It's good that we haven't included steam cooling yet, like in the British Goshawk engine.
 
Zmauky said:
Actually, I was also surprised when I checked the pressure level, and how relatively low it is, I probably have the numbers from thirty years ago stuck in my head (related to steam turbines).
Click to expand...

Ah yes, of course a steam turbine will have much higher pressure and temperature, as there the water & steam is the working fluid of the entire engine, vs. just cooling. Trying to run a piston engine at significantly higher temperature (say, several hundred deg C?) in order to make the radiator even smaller sounds attractive, but to my knowledge has never been done successfully. I guess you run into problems with reducing detonation margins, and perhaps also issues with thermal expansion of components causing issues, and at some point the strength of the aluminum castings start to drop off. AFAIU air-cooled engines, which ran hotter than liquid cooled ones, typically had the redline for the cylinder head temperature in the 200-250C range.


I meant that the FW 190 oil cooler was a "normal" radiator in the sense that it consisted of a set of tubes, rather than a surface type cooler. You might well be right that the armor was part of the front wall of the cooler rather than a separate component; it would make sense to design it that way after all. And indeed there's no need to pressurize the oil cooler, as the boiling point of lubricating oil is sufficiently high that it's not an issue.
 
I'm possibly misunderstanding things here, but I figure if you can make a very strong structure, then you have the means to make either a surface-cooler or a conventional radiator, right?

Plus, on that note: What temperature did the belly-radiator on the He.100 use?
 
That is a shure bet .
For belly radiator
I'm not sure, but off the top of my head I think it was just the oil cooler (which wouldn't surprise me because the DB 601 is known to throw a higher percentage of excess heat into the oil than other engines)
 
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