109 e3b against spitfire II

[Viper2000]

Originally Posted by TomcatViP

ViP

1. I am referring to the XX as it top off the III perf. . The XX is a well known referenced eng with plenty of raw data available and introduced latter in the war as an improved eng. Draw your own conclusion but I doubt pilot will have been happy to see their eng changed for the "less powerful" XX when they were asked to fly across the channel to bring the fight to the enmy.

So as you say that "very few XX took part in BoB" you are right on what I am pointing out

2. we hve started from a 6.5lb with an emergency boost of 12lb on a 87 oct

No - 87 octane limited the engine to +6.5. In this period, the boost control cutout was a safety feature to permit the pilot to manually control the throttle valves if the ABC failed. Fully opening the throttle at sea level static would give about +17 psi boost. This would be very bad for the engine.

Of course, in theory you could operate the cutout and then manually set the throttle to provide any arbitrary amount of boost that the supercharger was able to deliver at your altitude.

So a Spitfire or Hurricane pilot in 1938 could have overboosted their engine anywhere up to about +17 on 87 octane. But this would have rapidly damaged the engine and would have been completely against the instructions in the Pilot's Notes etc.

I have seen no evidence that anybody did this deliberately (though doubtless somebody did it by accident, because if it's possible to do something silly then somebody probably will). However, it was obviously known that +17 would result from operation of the cutout in its initial state because this is clearly set out in documents which I have cited in my thread on the subject of the effects of operating the boost control cutout in Spitfires & Hurricanes using 87 octane fuel.

Originally Posted by TomcatViP

and we were discussing abt a 100oct at 12lb

With 100 octane fuel, the engine could safely operate at +12. The boost control cutout system was then modified by drilling a bleed hole so that operating the cutout would now provide no more than +12 psi boost. This meant that the cutout could be used to provide a regulated level of emergency combat power instead of operating simply as a safety device.

The cutout could be wired "off" with thin wire, so that operation of the cutout would provide a tell-tale for the groundcrew. This was therefore a very elegant solution.

Originally Posted by TomcatViP

vs what I think is a Merlin 100oct topped a 9 (my Merlin argumentation based on the RR sources you know pretty well and based on Qualorific assumption (the amount of heat generated).

Climb power for the Merlin XX is +9 psi at 2850 rpm. This is the most likely source of your +9 figure.

Originally Posted by TomcatViP

Now if I read you well we shld hve a 17lb 100oct ?

Not at all. See above.

Originally Posted by TomcatViP

Humm will I hev to fear reading in the upcoming weeks about the Jet eng being available during BoB (see spitperf.com and blablabla) ?

3. You are mixing your argumentation with a lot of data that many young reader can't understand and that hve no meaning here. Just let make it clears MS gear refer to the charger's impeler de-multiplication (the speed at witch it turn related to the main crankshaft) that had to be kept bellow a certain speed for the efficiency of the overall boosting process.

MS = Medium Supercharge
FS = Full Supercharge

Supercharger efficiency depends upon where you are on the compressor map. You'd generally plot non dimensional flow vs pressure ratio and include constant speed lines.

What you find is that centrifugal impellers are pretty forgiving machines, and will operate over quite a wide range of flows and pressure ratios at any given speed without surging.

Really you only care about tip speed for 3 reasons:

• Structural strength
• Supercharger power consumption
• Charge temperature

So ideally you want to run the engine with a wide open throttle and turn the supercharger at the lowest speed at which it is able to deliver the pressure ratio required to give the boost you want at your current ambient conditions.

But this would be too complicated for 1940.

So you compromise.

The Merlin XX had a 2 speed supercharger drive gearbox, so 2 compromise speeds were available instead of 1 for the earlier engines. This allowed better overall performance, though it didn't have any direct impact upon peak power.

Originally Posted by TomcatViP

There is no link with the SHAP but only with the fighter speed and the alt of this perf. giving that the supercharger was designed for fighters on the base of procurement policy (by the way I read that the twin speed supercharger was patented by Farman and hev a hard time figuring in witch Farman's plane he wanted this installed ). Pls don't smoke the debate. Logic is at the reach of everyone (pls make the V hand sign reading this).

Farman patented the gearchange mechanism; RR just licensed the IP. IIRC there were a couple of other gear change mechanisms on the shelf, and some of the Packard engines may have used a different one for production reasons.

In any case, it was an IP licensing thing rather than a case of Farman having specifically produced technology with the Merlin in mind.

Originally Posted by TomcatViP

4.you alrdy stated about installed eng power that match only what I have here as an eng not fitted with a supercharger (the 1.3k+HP data) - maybe shld you look at your references.

Merlin without supercharger = Meteor. It would give something in the region of 650-850 bhp. It's quite hard to be concrete because Meteors were generally reconditioned (ie crashed, non-airworthy) Merlins and so they were never going to perform "as new".

Originally Posted by TomcatViP

By the way ~S! and thx to forgive me for my bad English grammar & spelling

~S