Alternate Engines

[kool kitty89]

This is for both engines that could/should have been developed (or developed further) and aircraft that should have used different engines (either exclusively used or as an alternate to suplement supply) This could be for performance, practicality, or other reasons.

There could be cases where engines were tested in the a/c but never adopted, but should have, were proposed but never tested, or were not proposed at all.

In the case of engine development, it should at least have been built and tested, or be a reasonably sound development of an existing engine.

This is for any country. With the timeframe ranging from anything from late inter-war period to the end of the war.

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I have a number of engines and aircraft in mind, but the first I want to bring up is the Fw 187 powered by Jumo 211 engines.


There have been several disscussions on the Fw 187, but not any mention of the consideration of using these engines. While performance would be somewhat less than if using comperable DB-601 engines, it would still be far better than with the Jumo 210 engines it ended up with.

Assuming it was developed in the proper single-seater format the a/c was designed for it could have been a capable a/c and would not compete for the Bf 109 for engines. (though it would compete with the He 111, Ju 88, and Ju 87)

If the Bf 110 was dropped (which did take a decen amount of the DB production) Messersmitt could also focus on development of the Bf 109 and other designs. (later the Me 262) And as to the Bf 110's most sucessful use, as a nightfighter, which the Fw 187 really wasn't cut out for, the Ju 88 would have been able to make up for it.

 

[Marshall_Stack]

What about developing a version of the Allison V-1710 with an internal two stage- two speed blower for high altitude work? I know that this wasn't developed because of the USAAF's preference for external turbosuperchargers but it would have been nice if the P-39 and P-40 could have had a better performance. Maybe they could have seen what Roll-Royce was doing with their high altitude Merlin.

 

[kool kitty89]

Well Allison did develop an auxillery supercharger stage. It was similar in configuration to the 2-stage superchargers used on the P&W R-1830 and R-2800 engines. These were most notably used on the P-63 series of fighters. (albeit early models lacked an intercooler, though some were fitted with water injection, like on the P-63C)


Adapting the Allison to a 2-speed supercharger may have been more difficult than the seperate 2-stage supercharger. (which was mounted in the excessories section and driven by a fluid coupling iirc)


What I do wonder though is why they didn't develop a single-stage single speed supercharged version that would compare to the Merlin 45 and similar series. (which used a single speed supercharger -basicly a merlin 20 series supercharger minus the low speed gear)

The best they seemed to manage with the single speed supercharger was with models using the higher 9.6:1 blower (supercharger) speed, opposed to the earlier 8.8:1, This offered significantly better medium altitude performance, but was still a bit short of the Merlin 45's altitude performance.
This included most notably the V-1710-81(P-40M/N, P-51A), 85(P-39N/Q), 83(late block P-39M's), 99(P-40N), 115(P-40N).

 

[kool kitty89]

How about the Curtiss V-1570?
Unlike the contemporary RR Kestrel and Jumo 210 it had a considerably higher displacement, and thus further potential room for development. (although the Kestrel did develop into the Peregrine)

With an improved supercharger, increased rpm, and necessary strengthening. A version in the 1000 hp range would likely have been avaiable before the V-1710.
Perhaps they could have focused on improved supercharging, development being moved over to Wright after merging and possibly using simiar 2-speed supercharger as those of the R-1820.

 

[red admiral]

The high altitude Napier Sabre versions with two-stage three-speed superchargers and high boost. More power at altitude than you can possibly cool.

There were a couple of Rolls-Royce studies looking at reducing the size of engines in the late war period but keeping power the same. 2500hp from a 10.6L engine about half the size of the Griffon but weight quite similar.

 

[kool kitty89]

Wouldn't such small displacement engines (the RR ones) have exceedingly high fuel consumption at those power levels? Also, wouldn't the maximum economical cruise power (lean mix) still be relatively low?

 

[kool kitty89]

How about a Fw 190 with a DB-605 engine?

 

[Marshall_Stack]

Well Allison did develop an auxillery supercharger stage. It was similar in configuration to the 2-stage superchargers used on the P&W R-1830 and R-2800 engines. These were most notably used on the P-63 series of fighters. (albeit early models lacked an intercooler, though some were fitted with water injection, like on the P-63C)


I realize that Allison had created this configuration with the external supercharger, but from what I have read, the USAAF had problems with these in the later model F-82s and these were slower than the earlier F-82s using the Merlins.

It would have been interesting if Allison could have developed the V-1710-127 further. From what I have read, the temperature from the turbocompounding was extremely high and the metallurgy capable of handling these temperatures were not available at this time. Here is an excerpt from Wikipedia about the engine..

"The most powerful factory variant was the V-1710-127, designed to produce 2,900 hp (2,200 kW) at low altitude and 1,550 hp (1,160 kW) at 29,000 feet (8,800 m). This engine was static tested at 2,800 hp (2,100 kW) and was planned for installation in an XP-63H aircraft. The end of the war ended this development, so this promising experiment never flew. The extra power of this version was derived from using exhaust turbines, not to drive a turbosupercharger, but to return that energy to turning the crankshaft. This was called a "turbo-compound" arrangement."

 

[kool kitty89]

I think the engines used for the P-82's were a particularly bad choyce, those versions in general were troublesome. IIRC the preceding series of V-1710's with similar capabilitied ( with the fully developed supercharger with intercooler) were considerably more reliable. I'm not sure of the changes between these lines that caused the problems. ( I believe it was the G and H series, but I have to find that differed article again)


The early 2-stage versions, as were used operationally by the P-63A and C durring the war) were quite reiliable from what I've read, though they lacked intercoolers which limited performance, though as mentioned previously the P-63C's engine had water injection and this boosted the WEP from 1,500 to 1,800 hp. (in low supercharger gear)
High alt performance was inferior to the V-1650-3 though. It was somewhat closer to the lower altitude V-1650-7.

Something to note is that the auxillery supercharger was driven by a fluid coupling, and not gears, similar to the DB-601/605's supercharger. So the power curves were fairly smooth and performance charts will also reflect this. (apearing similar to turbocharged a/c's curves due to the lack of sharp performance peaks resulting from geared supercharger)

http://www.wwiiaircraftperformance.org/p-38/fighter-comp-chart.jpg

 

[kool kitty89]

I'm still wondering why a single stange single-speed Allison similar to the Merlin 45 series wasn't developed. (inless the integral supercharger, which had remained virtually the same throughout the line, was simply not large enough to be used efficiently in that manner. Opposed to the Merlin's supercharger which I believe was upgraded in the 20 series, along with 2-speed gearing and remained virtually the same on the simplified single-speed 45 series)




On a different note, how about the Hs 129 with some decent ~1,000 hp class radials. Either the 14N, BMW 123, or Bramo 323.


Or Gloster's F.5/34 design with a Pegasus XVIII engine. (possibly a Hurcules later on)

 

[red admiral]

I think one of the problems with the Allison's superchargers was that they weren't as efficient so they robbed more power from the engine in addition to giving greater charge heating. The changes to the Merlin XX supercharger from the Merlin I/II were slight with better efficiencies being gained from matching the impeller and diffuser and straightening the air intake into a smoother curve.

The two-stage V-1710s used the same clutch arrangement as Pratt Whitney so one stage could be disengaged at low altitude. I never really saw the point in this as it would give poorer performance alongside higher weight and complexity. The -127 turbocompound suffered from many problems with the turbine, mostly being heat related issues. Its not really a simple case of just gearing the turbine to the crankshaft either which I imagine caused more problems.

 

[Marshall_Stack]

Can anyone chime in on Japanese engines? My knowledge is limited on this subject (my disclaimer) but it seems that the Japanese radial engines were pretty low power (to go with their light aircraft) and didn't develop more powerful engines (in the 2,000 hp range) until late in the war. Is this correct?

I know that they didn't too well with their license of the DB engines that powered their "Tony" aircraft because they kept overheating. It seems that this could have been a more formidable fighter (self-sealing tanks and armor) if they didn't have the maintenance nightmares. When they couple this airframe with a radial engine that had a good fighter (Ki-100) but was too little too late.

 

[kool kitty89]

There's a thread for that in the Engines forum: http://www.ww2aircraft.net/forum/engines/japanese-piston-engines-8450.html

And a website on engine performance from said thread: Translated version of http://www.warbirds.jp/kakuki/sanko/en_japan.htm


Also there's the Mitsubishi Kasei - Wikipedia, the free encyclopedia which was a prominant engine early-war with fairly high power output.

 

[renrich]

The R2800 in Navy fighters had a two speed two stage supercharger. The Merlin in the P51 also had a two speed two stage supercharger. The Merlin's supercharger switched automatically from low blower to high blower according to altitude. The Navy's R2800s had to be switched manually. Why was that? Seems like it added to the pilot's work load.

 

[kool kitty89]

The merlin's 2-stage supercharger was different (and the RR vs Packard superchargers differed somewhat too, though the configuration was similar).

WIth the P&W engines an auxillery supercharger with 3 settings (neutral, low speed, and high speed) with neutral bypassing the auxillery stage and going straight to the single stage single speed supercharger.

In the merlin the 2 supercharger stages were driven together by a common shaft with 2 speetings (similar to the simpler single-stage 2-speed supercharger). So both stages were driven at the same speed. (in the case of the RR merlin, the added supercharger stage utilized the impeller from the Vulture, I believe Packard used a Wright design) I think the intercooler set-ups were a bit different too.

 

[kool kitty89]

admiral,

Was the supercharger impeller of the Merlin XX any larger than that of the I/II/III?

Generall, a larger centrifugal compressor at a lower speed is more efficient than a smaller one at higher speed (delivering similar pressure and mass flow) correct?

 

[kool kitty89]

Also, would you agree that introducing 2-speed gearing for the V-1710's single speed supercharger would be impractical due to the compact location?

And would it have been dificult to improve the efficiency of the Allison's supercharger in this configuration.


Compare the Merlin III

and the contemporary V-1710-33

(note that's an early model with the long nosed epiciclic reduction gearing intended to improved streamlining, later abandoned in favor of a simpler and considerably stronger spur gear arrangement, hence the change on the P-40's nose)



Aand a better angle of the supercharger.

The integral "engine supercharger" remained virtually the same throughout the V-1710's life didn't it? With some changers in the speed (gearing ratio) and some utilizing updraft carbs.


The supercharger also apears to be significantly smaller than that of the single-staged merlin.

(also the Merlin XX doesn't seem to have any noticable change in size with the added 2-speed gearing)

 

[kool kitty89]

On a different note I've been looking more into the Curtiss V-1570. It doesn't seem to have used a supercharger. (besided some turbocharger intallations)

It does apear to be a fairly modern sesign though (for the time) with 4 valves per cylinder and a pressurized cooling system. (of course using a cast block, championed by the D-12 and inspiring the development of the Rolls Royce Kestrel)


Funding seems to have been cut in 1932:

Curtiss V-1570 Conqueror

Although the Conqueror accounted for 2/3 of the Army's purchases of of large engines as late as 1932, the Conqueror marked the beginning of the end for Curtiss aircraft engines. Tests in 1931 showed glycol leaks and, with a declining interest in liquid-cooling, funding was cut a year later.

It seems like a faily promising design with more development potential than the contemporary Kestrel or Jumo 210. (at 25.7L)


Perhaps with further development (probably taken over by Wright once they merged) supercharging, increased rpm, and the necessary structural improvements it may have proven to be a compeditive engine at the start of the war.




Similrly, how about further development of the Bristol Pegasus. Fairly large in diameter, but faily light weight. Seeing the problems and unreliability it of the Taurus it may have been better to continue development of the Pegasus as it was in the same power class and was much more reliable and already quite matured. As the amount of work devoted to further development of the Pegasus woud likely be consierably less than development of the problematic Taurus, development of the Hercules and Centaurus may have been speeded up as well.

 

[red admiral]

The Merlin also had automatic boost control so the pilot didn't have to go adjusting it himself during combat.

I'm not aware of any difference in supercharger diameter between the I/II/III series and the XX series but there were a few changes in geometry. Hooker's biography has some details in one of the early chapters.

Efficiency is hard to quantify exactly. The power consumption, i.e. how much power is robbed from the engine, is proportional to diameter^5 and rpm^3 so smaller and faster is better. But you've got to take into account the stresses in the impeller as well which depend more on rpm than diameter.

I imagine it would be possible to incorporate a two-speed gear into the V-1710 but can't really say without looking at the insides. It wouldn't take up too much space.

I quite fancy a double Pegasus which would be a similar size to the Centaurus with similar power levels. This did almost exist in the Alfa-Romeo 135/136 which gave 2400hp maximum in the late 30s with 100-oct fuel and 1600hp on 87-oct.

 

[kool kitty89]

Perhaps this would be good for a seperate thread in the engines forum, but But perhaps Bristol would have been better foregoing the sleeve-valve engines entirely and continued developing their traditional designs. (perhaps introducing fuel injection -of course the Pheonix had direct injection, but that's a different story)

Particularly as they used overhead cams with 4-valves per cylinder, somthing almost no one else was doing with radial engines.



Edit: just added this: http://www.ww2aircraft.net/forum/engines/bristol-radial-engine-development-14674.html#post391220