Cantankerous wrote: ↑
04 Feb 2021 17:18
The He 280 and Me 262 had the turbojets slung under the wings, which was somehow a problem because it made plane a bit too heavy to fly faster than 530 miles per hour. Heinkel simply could have simply used the jet engine layout developed for the He 178 in a future jet fighter made from wood and fitted it with a more powerful version of the HeS 8, like the HeS 30, along with air intakes for the turbojet in the wing roots.
The Germans have a number of problems with jet engines in 1942 that they mostly resolved by 1944, but not entirely.
I'll start with how they were podded on the wings. This was done to avoid complex design of the intakes which would be necessary if you wanted smooth air flow from the inlet to the engine. Longer intake ducts were already known to cause a loss of engine performance so they were usually avoided in early jets. Putting the engines in nacelles on the wings was a quick way to get a minimal intake duct length and allowed for the possibility that one of several engines might end up on the plane.
Early jets usually needed a pair of engines in any case to produce enough thrust to carry the weight of the plane and a much larger quantity of fuel necessary for those thirsty engines to produce a viable range. This was an issue for the relatively small He 280 for example.
The problem with German turbojets in 1942 was none of the manufacturers had much experience with designing the compressor section. They all had issues with blade profiles, what sort of compressor was best, and so on. For the Germans, they were in a poorer state designing turbines than the US or Britain. Both of the later had large companies that specialized in steam turbine designs for ships that Germany really lacked. Yes, the Germans did build ship steam turbines but their industry was much more limited than companies like Vickers, GE, Westinghouse, and the like. This is why BMW turned to Brown Boveri in Switzerland for help. Brown was one of the largest steam turbine engineering firms in Europe--and they were accessable.
GE had the advantage they had been designing gas turbines in the form of turbochargers for almost two decades and had a huge library of blade profile designs available that would work for turbojets.
You see the Germans do the same sorts of experimentation the British and US did with gas turbines. Von Ohain at Henkel settled on a mixed design using a centrifugal compressor and one or more axial compressors for his engine. Counterrotating compressor stages were tried (they failed everywhere though). Griffith at Vickers (MetroVic) and then RR came up early with the idea that the blade profiles had to resemble wings and not be flat or simply curved. Stanford Moss at GE knew this from experimentation with turbochargers. BMW and Junkers went with axial designs. MetroVic went with an axial design while DeHaviland and RR were building centrifugal engines based on Whittle's designs.
The US went straight to axials while producing a centrifugal and improving it in the interim.
Thus, the overall situation was the Allies were in a better position to make more rapid development in jet engines than the Germans, particularly the US who could throw cubic dollars at the problem. The Germans first had to design an engine that would work at all. As noted, the BMW 003 ran on the bench fine in 1942. It didn't run fine on an airplane in a dynamic flight environment. That took BMW two more years of work to resolve. The Germans had the additional problem of lacking the resources to apply high temperature metals freely in their engine designs.
So, in 1942 the Germans simply don't have a jet engine they can put into production. The British do, but they dithered around for nearly a year and a half before finalizing production. The US had a "Duh!" moment seeing the Whittle engine but lost no time in putting it into production and getting into designing their own. It would be nearly two years for them to get mass production started though. That's a pretty short time to go from zero to turning out product in quantity.
In the 1940's nobody was going to get a jet that would exceed about 650 mph in flight in any case simply due to the lack of design knowledge on supersonic and even transonic aircraft. If you could get a jet into the high 500 mph range, you were golden up through about 1947. From there to the 50's breaking 600 mph was sufficient.