Henschel Hs 130 HZ supercharger system

[Stuka_Hunter]

Greetings

Recently I read some things about superchargers on airplanes and came across the HZ system used on E version of the Henschel Hs 130 reconaissance airplane. I have never before seen such a system on any airplane.

From the info available I figured out that HZ system was used as a replacement for normal superchargers used on two piston engines Hs 130 used. HZ placed a single big supercharger in the fuselage belly and was driven by the third piston engine.

The big air intake for the HZ system is clearly visible on this picture.

My question is why was the HZ system used anyway? Are there any advantages over the normal superchargers?

 

[Jemiba]

A drawing of the so-called "HZ Anlage" you can find here
https://www.secretprojects.co.uk/forum/index.php/topic,5921.msg152624.html#msg152624

And that system was actually used on another aircraft before, on a Zeppelin-Staaken R.VI bomber around
the year 1917, you can find some information here
http://www.luftfahrtmuseum-hannover.de/images/wehrmann/Henschel%20Hs%20130.pdf
and in a book written by Dietrich Eckardt "Gas Turbine Powerhouse: The Development of the Power Generation Gas Turbine",
partially available via Google books https://books.google.de/books?id=awvpBQAAQBAJ&pg=PA58&lpg=PA58&dq=henschel+%22hs+130e%22&source=bl&ots=1d1sDeffWX&sig=ep80T4ML9LcSRwAdaLfj4SEqtO0&hl=de&sa=X&ved=0ahUKEwiB8K2n3f3aAhUCxqYKHSbTCY84ChDoAQg1MAU#v=onepage&q=henschel%20%22hs%20130e%22&f=false

Raison d'être quite simply was in both cases the attempt to reach altitudes, which promised impunity against defenders,
even at the price of drastically reduced military payload, which probably would have made this arrangement viable only
for recce aircraft, or high altitued fighters ... if the enemy would have reached such altitudes first !

 

[Hobbes]

The advantage would be a bit more power available at the props without replacing the engines with more powerful types. Automotive superchargers on large car engines consume in the region of 50-100 kW.

 

[iverson]

Raison d'être quite simply was in both cases the attempt to reach altitudes, which promised impunity against defenders,
even at the price of drastically reduced military payload, which probably would have made this arrangement viable only
for recce aircraft, or high altitued fighters ... if the enemy would have reached such altitudes first !

This arrangement was, in fact, considered for bombers, including the Avro 684 Stratospheric Bomber and the Aerocentre NC.150.

I suspect that the separate engine approach was attractive because it it made the supercharger and the supercharged engines separate development problems that could be solved in isolation. Driving a supercharger from the engine it supercharged required complex gearing and/or hydraulic couplings that took time and effort to develop. So HZ looked like a quick way of getting the extreme high-altitude performance required for the specialized reconnaissance mission without putting in the sustained engineering effort other solutions would demand.

Unfortunately, as so often happens, HZ turned out to have complexities and problems of its own. The bugs were never quite worked out, and turbochargers became more attractive, in spite of the associated development challenges.

Of course, the turbocharger is itself a sort of separate engine for driving a supercharger. But it has far fewer components, is lighter and less bulky than a piston engine, and runs off of the exhaust gas of the main, piston engine. It's only problem is heat. Junkers successfully used turbochargers with its two-stroke diesel aeroengines. But diesel exhaust is significantly cooler than gasoline engine exhaust. So Germany did not manage to get turbochargers working reliably before the end of the war.

 

[Arjen]

Two other aircraft types of the period to feature a supercharger driven by a separate engine:

- The two Petlyakov Pe-8 prototypes, as well as the first five production aircraft, were powered by four Mikulin M-34 engines, with a Mikulin M-100 mounted behind the cockpit to drive a supercharger for the other four engines. The installation proved to be cumbersome - all of the early aircraft were re-engined with Mikulin M-35 engines which drove their own superchargers.
First flight of a Pe-8 prototype was in 1936.

- Dornier built three Do 217P prototypes (V1, V2, V3) and three Do 217P-0 pre-production aircraft. Each was powered by two DB 603B engines, with a fuselage-mounted DB 605T driving a supercharger. First flight of Do 217P V1 in 1942.

 

[rinkol]

The use of a separate engine to power the first stage of a two stage supercharger arrangement does have the advantage that it is an easy way of obtaining variable speed operation for the first stage; the engine driving this stage can be throttled to provide the reduced boost appropriate for low altitude operation.

I've wondered for some time what the reason(s) were for the poor reliability of the HZ Anlage. I suppose that the general unreliability of the early DB 603 engines would not have helped, but think there must have been other problems.

It might be noted that there are some fairly obvious disadvantages:

1. The considerable amount of space in the fuselage taken up by the engine driving the first stage supercharger;
2. High cost;
3. High fuel consumption;
4. High weight.

 

[iverson]

The use of a separate engine to power the first stage of a two stage supercharger arrangement does have the advantage that it is an easy way of obtaining variable speed operation for the first stage; the engine driving this stage can be throttled to provide the reduced boost appropriate for low altitude operation.

I've wondered for some time what the reason(s) were for the poor reliability of the HZ Anlage. I suppose that the general unreliability of the early DB 603 engines would not have helped, but think there must have been other problems.

It might be noted that there are some fairly obvious disadvantages:

1. The considerable amount of space in the fuselage taken up by the engine driving the first stage supercharger;
2. High cost;
3. High fuel consumption;
4. High weight.

HZ was a complicated arrangement, so that alone could have caused problems. More engines means more likelihood of a fault, and the failure of one engine--particularly the boost engine--would have a disproportionate effect compared a similar failure in a conventional, multiengine type.

Extreme altitude operation would also have been a challenge in any case. Coordinating mixture control, throttle position, and boost was a challenge for simpler, more widely deployed systems like the turbocharger. Compressor and intercooler design would be challenging. Finally the extensive plumbing itself might have caused problems. Any pressure variations due to geometry,leaking joints, or damage would have made mixture and boost control at the engine even more problematic.

Such issues could probably be worked out given enough development. But HZ was closely tailored to the configuration of a single, highly specialized aircraft. My guess is that the engineering effort required to get it working couldn't be justified in wartime, especially when competing technologies like nitrous oxide injection, conventional superchargers, and turbochargers could be applied to a wider range of aircraft types.

I've attached a drawing of the aircraft that I did some years back.