Japanese Zero vs Spitfire vs FW 190

[MiTasol]

By Pacific standards the distance from Henderson field to where they shot Yamamoto down and back is quite short, about half the distance the Rabaul A6Ms flew to attack Henderson field.
By European standards this was a long flight.

 

[GrauGeist]

The straight line distance was about 400 miles, but the intercept route was planned to head out over water to avoid being detected, so the route was about 1,000 miles round trip, plus enough fuel factored for combat.

 

[Shortround6]

You don't suppose there's a relationship between this and the fact that Allisons could handle oversquare (high MP, low RPM) much more smoothly than Merlins, thus giving them superior long range cruise efficiency? (Guadalcanal->Yamamoto->Gaudalcanal)
Try that in a Spit.

British were advising using 1800 rpm for Cruising In a Spit V with a Merlin 45. Depending on the boost used at 1800rpm this could give the same speed as 2650rpm at a lower boost.

One reason the P-38s could cruise at low rpm and high boost (whatever that actually means) was the turbos could deliver positive pressure to the carb inlets even if not much.
Try using high boost and low rpm in a P-39 or P-40. How much boost can you get from the engine supercharger if the engine is turning 1600-1800 rpm?

Spitfire V cruise could be 250 ASI at 10,000ft using + 3 3/4lbs at 2000rpm burning 42 imp gallons/hr or + 2lbs at 2650rpm burning 47 imp gal/hr.

For really long range over water the Allison could run at lower RPM than the Merlin but cruise speeds are going to closer to 200mph than anything most pilots wanted to use over enemy territory.

 

[Peter Gunn]

True, but the Yamamoto mission was close to sea level all the way, not to mention cruising at 200 over the Pacific (any altitude) was NOT like cruising at 200 over continental Europe.

 

[ThomasP]

Does anyone have any actual official test/comparison data for the idea that the Allison could run at lower rpm significantly more satisfactorily than the Merlin - hopefully something that explains the problem/difference. The reason I ask is that I have not been able find any officially stated reasons for any significant difference, only anecdotal statements and suppositions.

As far as I know, based on what I know about engines and have been able to find out about the Allison and Merlin, the only reasons that might have made a difference are the type of spark plug used and the compression ratio.

1. Some spark plugs are more prone to fouling than others.
2. Engines with higher compression ratios are generally less prone to fouling of the spark plugs.

No.1 is ~solved by changing the type of spark plug (which was done a few times for various reasons - on both makes of engine). I can not imagine that the various responsible agencies did not think of this and implement a change if needed.
No.2 is ~solved by opening up the throttles to higher rpm and boost periodically during the flight (which is listed in the flight manuals for both makes of engines, although it does seem that it is mentioned less frequently re the Allison.). The higher compression ratio of the Allison would have slowed down/decreased (to a small but possibly significant degree) the fouling process caused by the high TEL content fuels used at the time.

I realize the above is somewhat general, but it should apply regardless of engine type.

Otherwise, I have read in most of the manuals for Merlin powered AC that it was often problematic when running below 1800 rpm, but this was due to the generator not being able to charge the batteries at lower rpm. I have read of this problem with Allison installations as well, although not as often.

I confused. + + + =

 

[pbehn]

Does anyone have any actual official test/comparison data for the idea that the Allison could run at lower rpm significantly more satisfactorily than the Merlin - hopefully something that explains the problem/difference. The reason I ask is that I have not been able find any officially stated reasons for any significant difference, only anecdotal statements and suppositions.

As far as I know, based on what I know about engines and have been able to find out about the Allison and Merlin, the only reasons that might have made a difference are the type of spark plug used and the compression ratio.

1. Some spark plugs are more prone to fouling than others.
2. Engines with higher compression ratios are generally less prone to fouling of the spark plugs.

No.1 is ~solved by changing the type of spark plug (which was done a few times for various reasons - on both makes of engine). I can not imagine that the various responsible agencies did not think of this and implement a change if needed.
No.2 is ~solved by opening up the throttles to higher rpm and boost periodically during the flight (which is listed in the flight manuals for both makes of engines, although it does seem that it is mentioned less frequently re the Allison.). The higher compression ratio of the Allison would have slowed down/decreased (to a small but possibly significant degree) the fouling process caused by the high TEL content fuels used at the time.

I realize the above is somewhat general, but it should apply regardless of engine type.

Otherwise, I have read in most of the manuals for Merlin powered AC that it was often problematic when running below 1800 rpm, but this was due to the generator not being able to charge the batteries at lower rpm. I have read of this problem with Allison installations as well, although not as often.

I confused. + + + =

This was specifically stated in the quoted report in the thread, detailing RAF experience with the Mustang Mk I.

There are possibly other reasons. The Allisson and its supercharger were optimised for low altitudes so could be expected to run more smoothly at those altitudes. AFAIK the compression ratio is only a part of the story, the actual compression and therefore the pressure prior to ignition depends on other things too, like the whole turbo, supercharger, carburettor intercooler and manifold system.

 

[Shortround6]

I am not at all sure the Allison was "optimised for low altitudes".

yes it had lower altitude performance than the Merlin III and especially the Hooker modified single stage superchargers, But then so did every other aircraft engine in the world at the time (1939-41). The only Allison's I can think of that were optimized for low altitude were the ones in the A-36.

There were also a plethora of Merlins optimized for low altitudes. Anybody have any accounts of them running smoothly at low altitude?

 

[ThomasP]

Hey pbehn,

re "This was specifically stated in the quoted report in the thread, detailing RAF experience with the Mustang Mk I."

Can you point the post with the above quote out to me. Sorry, but I just went over the whole thread (admittedly somewhat quickly) and did not find anything providing any "official test/comparison data" or "officially stated reasons" for the disparity. Possibly I simply missed it, my eyes are tired tonight from driving all day.

As I said above, my post was somewhat general. However, the compression ratio for the Allison is 6.65:1, which gives the ~equivalent of +9.55 lbs boost (in terms of cylinder pressure) vs the Merlin's 6:1 compression ratio, and this is before we even look at any effects from the supercharger.

PS. Also, having a lower rated supercharger would not make the engine run smoother, at least not with WWII technology. The only effect that would have that might decrease stress on the engine parts would be if it resulted in a lower IHP. But as Shortround6 just posted, the Merlin supercharger was more efficient than the Allison (even before Hooker got involved) and that would mean that the 'cropped' impellers for the lower rated Merlins would have tipped the balance toward the Merlin.

 

[wuzak]

Some possible reasons that the V-1710 ran better at low altitudes:

Cam followers were rollers in the V-1710, solid on the Merlin. Maybe gives better consistency?
The V-1710 crankshaft was fitted with a torsional damper, the Merlin was not.
The V-1710 used an injection type carburettor, the Merlin did not until later in the war. The air flow at lower rpm may not have allowed for a consistent air : fuel mixture.

 

[taly01]

Does anyone have any actual official test/comparison data for the idea that the Allison could run at lower rpm significantly more satisfactorily than the Merlin -

Probably camshaft valve timing, eg. the Merlin had more of a high rpm racing heritage whereas the Allison came from an engine for dirigible airships (AFAIK).

 

[Shortround6]

Probably camshaft valve timing, eg. the Merlin had more of a high rpm racing heritage whereas the Allison came from an engine for dirigible airships (AFAIK).

The whole airship thing (or most of it) was funding.

Allison was trying to sell the engine to the army.
Army said, interesting but we have no money right now. The Navy does, perhaps they can fund development for a year or two while we try to get more money from congress.
Navy says we have no need/desire for liquid cooled airplane engines but we want to stop buying German engines for our dirigibles. We will buy a couple of prototype engines.
Allison figures a few engines sold is better than none and works on the airship engines.

Nobody was going to get rich building airship engines, there simply weren't enough airships being built. It helped keep the doors open and kept some employees working.
Sure enough, navy crashes a few airships and the whole airship program grinds to a halt.
Airship engine worked stopped in 1934-35, plenty of time to adjust the cam timing for aircraft.

The Allison started as a general purpose aircraft engine. Allison was happy to make special versions for special applications (any sales better than no sales).

 

[jaydawg73]

How good was Zero against famous Spitfire or German FW 190?

Can a Zero beat them any chance at all?

The zero was indeed a formidable platform that had superior performance to its adversaries. But, as the RAF found in the battle of france and the BoB, in the hands of a quick thinking pilot with a bit of experience tactics could be out to good use in order to outwit and ultimately defeat a superior platform. The 109 once put into a steep dive could not pull out, so RAF pilots would attempt to orchestrate a dogfight to get a 109 into such a situation. 109 pilots would attempt to avoid this, thereby straight away putting them at a tactical disadvantage even in a superior performing platform. The Hurricane and Spitfire could out turn a 109, so again RAF pilots would hold the 109 in a horizontal fight. Again the 109 pilot attempting to avoid this also put them at a tactical disadvantage, thereby putting your adversary on the defensive.

similarly in the Pacific area of operations, the Wildcat was far inferior and outclassed by the zero. But with tactics such as the 'Thatch Weave' manoeuvre by two wildcats it brought the fight to a level plane.

Today the USN FWS aka 'Top Gun' still utilise the thatch weave. I think it is accepted that as good and rugged a platform the F18 is in its different guises, it is outperformed and outclassed on many fronts by any potential adversaries. So the USN teaches its pilots to rely on tactics and manoeuvres. The F18 and stop on its tail and use its aerodynamics to bring the fight to its own terms against a faster and more ag platform.

In essence, the ability of a platform is only a part of the equation, in the hands of a well trained pilot that knows his platform inside out and knows the capabilities and vulnerability of his adversaries platform, that's what will decide the outcome of a duel in the skies..

JH

 

[PAT303]

The zero was indeed a formidable platform that had superior performance to its adversaries

At the expense of 200mph+ maneuverability, ruggedness, protection, communication and any hope of pilot survival. A Spitfire could have been made to the A6M's spec and totally outclassed it in speed, climb, turn and range but the Allied nations never compromised pilot safety and protection for performance.

 

[DerAdlerIstGelandet]

The zero was indeed a formidable platform that had superior performance to its adversaries.

Not quite…

The Zero being far superior is a myth, almost as bad as anything built by the Germans was a Wunderwaffe.

The Zero had superior performance initially at lower speeds. By 1943 it was being eclipsed by allied aircraft. Additionally, the Zero sacrificed armor and armament for that initial performance boost.

The Zero was a formidable aircraft throughout the entire wire, but lets not paint it as a far superior aircraft.

 

[BiffF15]

similarly in the Pacific area of operations, the Wildcat was far inferior and outclassed by the zero. But with tactics such as the 'Thatch Weave' manoeuvre by two wildcats it brought the fight to a level plane.

Today the USN FWS aka 'Top Gun' still utilise the thatch weave. I think it is accepted that as good and rugged a platform the F18 is in its different guises, it is outperformed and outclassed on many fronts by any potential adversaries. So the USN teaches its pilots to rely on tactics and manoeuvres. The F18 and stop on its tail and use its aerodynamics to bring the fight to its own terms against a faster and more ag platform.

In essence, the ability of a platform is only a part of the equation, in the hands of a well trained pilot that knows his platform inside out and knows the capabilities and vulnerability of his adversaries platform, that's what will decide the outcome of a duel in the skies..

JH

JayDawg,

Please expand on how or in what cases Top Gun uses the Thach Weave?

For reference:

 

[GrauGeist]

I think it is accepted that as good and rugged a platform the F18 is in its different guises, it is outperformed and outclassed on many fronts by any potential adversaries.

The F-18 is outclassed by any potential adversaries?

Surely that's not an F/A-18 we're talking about, is it?

 

[FLYBOYJ]

Today the USN FWS aka 'Top Gun' still utilise the thatch weave.

I don't think flying within VR in today's world you're going to have the ability to do a "Thatch Weave" so please provide your reference for that. Top Gun will teach energy maneuvers when the fight is within VR, but in today's world if you're fighting completely VR, you pissed away several million dollars worth of technology.

 

[DerAdlerIstGelandet]

The F-18 is outclassed by any potential adversaries?

Surely that's not an F/A-18 we're talking about, is it?

If it so outclassed, why is my company still building them, and why do we still have customers wanting it?

 

[GrauGeist]

If it so outclassed, why is my company still building them, and why do we still have customers wanting it?

Because they can do the "Thatch" Weave?

I just read that somewhere on the internet, so it must be true...

 

[buffnut453]

Because they can do the Thatch Weave?

Is that the same thing as a Thach Weave? Or perhaps it's a new form of baldness treatment for the discerning gentleman?



I wish to apologize for the above comment. I appear to be channeling my (sarcastic) inner pedant...AGAIN! Normal service will now resume!