Roots type supercharger for WWII aircraft?

[gjs238]

Was a Roots type supercharger ever used or considered for aircraft engines, or were they all centrifugal?

[red admiral]

They were used by some. One that immediately springs to mind is for a Bugatti racing engine.

The centrifugal type is better suited to the specific speed range found in most engines though.

[jerryw]

Roots s/c's were used sparingly for aircraft engines during WW1 but they are bulky and not as suited as centifugal s/c's.
In WW2, the German HZ-Anlage arrangement used a central, fuselage-located Roots-type s/c to feed two wing mounted engines with compressed air for very high altitude work.
The first sentence in the caption next to the photo says, "This dual flow and two-stage main supercharger..... etc"
Has anyone got a cross-section of this big Roots s/c because I can't see how it can produce TWO stages of compression!

[danielp]

Jerry
the casing of the supercharger looks like a centrifigal instead of a roots type. wouldn't the casing be oblong like a gmc type blower which was a Roots? also they probably mean 2 stage by the fact that the center engine is the first stage and the second would be the superchargers on the main engines themselves. just a guess. dan p

[wombat40]

It is interesting to note that a Roots blower was borrowed from the US by Australia and fitted to a CA 13 Boomerang to enhance high altitude performance. The resulting aircraft, designated CA 14/14A differed most notably in a square tail, this design heralded the CA 15

[mad_max]

nver mind

[wombat40]

Originally Posted by mad_max

nver mind

Never mind?

[jerryw]

Below is a drawing of a German Argus As 10 V-8, aircooled engine fitted with a Roots-type supercharger.
Air to the engine can be obtained from below at atmospheric pressure or, with the valve closed, from the supercharger.

[vanir]

The mechanical difference between the two superchargers is the roots type uses vanes to pressurise the manifolding, whereas the centrifugal type uses an impeller to compress air within the casing (which in turn will pressurise the manifolding when it gets there).

The roots type is far more subject to heating due to friction, the vanes get very warm indeed and this type of supercharger is far less efficient for this reason. It transfers this heat to the intake air and has to work that much harder to pressurise the manifolding. The whole thing about aero engines is maximum mechanical efficiency to minimise weight. A roots type blower with similar effect to a comparable centrifugal will be much bulkier and heavier.

Centrifugal superchargers also heat up the air, but do it by compression rather than exchange. It is still more efficient when it comes to pressurising the manifold and this type of supercharger is probably easier to mount multiple gear drives on. But the pressure-heat can become a problem when you put more than one compressor in tandem, ie. multiple stage supercharging. You need big intercoolers and there we have that problem with aero engines again, they need to be light, very weight-efficient power producers.

One way to get around this is to use a centrifugal first stage with multiple gears and a roots type second stage. The first stage compresses the intake to the desired boost range, whilst the second stage or roots type blower simply keeps a positive pressure on the air intake system equivalent to sea level (or best performance altitude). Problem with this is you need intake cooling assistance at a variety of places on the engine, so this can become prohibitive in terms of weight and bulk.

The good thing about a roots type blower is they have a very gentle delivery of intake pressurisation itself by comparison to the centrifugal type (hence are fantastic torque producers). Where they mostly lose efficiency is in the maximum performance range. The thing to keep in mind about a roots type blower is they cause a lot of horsepower drag due to that friction I was talking about.

It is most desirable to have water injection at the intake of a roots type blower to cool the vanes and markedly improve operating efficency. Meanwhile it is all but necessary to have water injection at one or the other outlet of multiple stage centrifugal supercharging, or otherwise very effective intercooling.

The engine layout posted above is actually a very dramatic system where a DB605T motor (with complex looking dual stage supercharging) is used to feed pressurised air under high positive pressure to two 603 motors designed to accept this configuration. Mechanically it is the perfect supercharging system, as all horsepower drag from anciliary function and roots vane friction heat is effectively removed from the drive engines by using a third engine to drive them. The problem of course for aeronautical applications is the weight of the third engine, a small one would not be able to drive the intake requirements of the two DB603.

But before you poo-poo this idea, it was basically identical to the prelimenary ideas of Sir Frank Whittle which led to development of the centrifugal-turbine engine (centrifugal turbojet). The very next step is simply to turn the drive engines into heat/pressure turbines, simplify the compressor-engine and you're almost all the way to a turboprop.

[jerryw]

Some info from the patent record regarding the origin of the Roots Blower is given below.
The upper drawing is from the patent granted to Mr Philander H. Roots of Connersville, Indiana, USA in 1860 and it shows, almost completely, the Roots blower as we know it today.
P. H. Roots and his brother, Francis M. Roots went on to establish a manufacturing facility for this type of pump.
However, P. H. Roots did not invent the so called Roots blower. There are several other patents dated earlier which show the same kind of pump eg the lower drawing from a patent by Oliver Palmer of Buffalo, NY granted three years earlier in 1857.

[gjs238]

Originally Posted by jerryw

Roots s/c's were used sparingly for aircraft engines during WW1 but they are bulky and not as suited as centifugal s/c's.
In WW2, the German HZ-Anlage arrangement used a central, fuselage-located Roots-type s/c to feed two wing mounted engines with compressed air for very high altitude work.
The first sentence in the caption next to the photo says, "This dual flow and two-stage main supercharger..... etc"
Has anyone got a cross-section of this big Roots s/c because I can't see how it can produce TWO stages of compression!

Interesting system!
Two wing mounted engines, and a 3rd fuselage mounted engine whose sole purpose was to drive a huge supercharger.

Wikipedia article about this:
Henschel Hs 130 - Wikipedia, the free encyclopedia

[gjs238]

Originally Posted by jerryw

Below is a drawing of a German Argus As 10 V-8, aircooled engine fitted with a Roots-type supercharger.
Air to the engine can be obtained from below at atmospheric pressure or, with the valve closed, from the supercharger.

Nice post - just what I had in mind what I posed the question!

[gjs238]

Originally Posted by jerryw

Some info from the patent record regarding the origin of the Roots Blower is given below.
The upper drawing is from the patent granted to Mr Philander H. Roots of Connersville, Indiana, USA in 1860 and it shows, almost completely, the Roots blower as we know it today.
P. H. Roots and his brother, Francis M. Roots went on to establish a manufacturing facility for this type of pump.
However, P. H. Roots did not invent the so called Roots blower. There are several other patents dated earlier which show the same kind of pump eg the lower drawing from a patent by Oliver Palmer of Buffalo, NY granted three years earlier in 1857.

Guess I don't understand the patent process that well...
Why was Roots granted a patent in 1860 when there was already an existing patent for the same basic design dated 1857?
Was there sufficient difference in the two designs to warrant a second patent?

[jerryw]

You make a good point there, gjs238.
I come across this sort thing all the time in the patent record. In many cases it is difficult to see how one inventor could be granted a patent when an almost identical patent has been filed earlier!
Some of the differences must be subtle in the extreme.

[Gibbage]

It could be something as simple as one being for air, the other being for water. Also, in the mid 1800's, thats well before the digital age It may be a simple error in the patent office, or one hand not talking with the other. This has happened before, and the 1st patent always wins.