Hurricane engine questions

Hi,

1) Is the supercharger in the Hurricane automatic or manual please, I assume automatic as I can't find a key for it! Answered by Wiki, it is single stage.

2)The spec in the aircraft has climb as 2600rpm and +6 boost, I can never get over +4 without using WEP which just shoots it up. Am I missing something? (I am leaning the mixture correctly as far as I can see to get the maximum boost )

Thanks for any help.

Good question Chief! I'm standing by on this one.

It's automatic. Over 15,000ft or so it kicks in. (Edit: Probably less)

At what altitude are you only getting +4? Have you tried at sea level? As you get higher your boost will be lower due to lower outside air pressure. Boost is Manifold Pressure expressed in 'Atmospheres' instead of inches because the English are weird and like to make up units that nobody else uses. So outside pressure must be taken into account. The higher you go, the less boost you will see.

I have never been able to get it past +4 boost unless I engage the boost cut out, which then takes me straight to +8 boost.

I'll pay more attention, but I don't recall ever seeing it do anything except <= +4, or, by pulling the red button it jumps way past it (like Trooper117 says).

My confusion is that it says to use +6 for 'climb'. My experince is that I can get +4 at most 'early' altitudes, but not even +5, so +6 puzzles me.

All very good questions folks in my opinion.

The placards are copied directly from the real thing. I guess you can see where the issue might arise here...

Just took off from Croydon, first mission of a career, got no more than +4 (slighty less actually) full rich fuel, full throttle. (WEP boosts straight to +8.)

(Placard says takeoff should be +6 too and 2850 rpm)

Well I've just answered my supercharger question from WIki, the Merlin III has a single stage supercharger.

Could it be the guage is incorrectly drawn? See the second one on here that is said to be the 'classic BoB one?

http://www.raf-surplus.co.uk/main-panel-flight-instruments.php

WIki also said the Merlin III can go to +12 (yes I know it is Wiki but it is all I have from a quick search).

Some pictures here on a warthunder thread too (yes I know)

https://forum.warthunder.com/index....nd-hurricane-boost-pressure-gauge-issue/

This may be something for the devs to have a look at for a future fix, if that is needed.

Yup I'm going back to shooting down those pesky bombers, whatever the boost is!

Sorry, totally missed this bit of your post. Wiki said it was 'single stage but geared', which I figure is essentially the same thing as you're saying (I'm not an engineer). The end answer is 'no key required', thanks.

It was single stage, single speed. Gearing is a part of any supercharger -it's just an air compressor geared to the engine in such a way that it turns many times faster than the engine. Later models allowed you to switch between two gear ratios for better optimized performance at high and low altitudes. Some changed automatically at a specific altitude, others required the pilot to make the switch. Since the Merlin III had a single speed supercharger, it's neither automatic nor manual, as those terms don't apply to it. It's just there, geared into the engine, always compressing all the air that passes through the engine.

The Merlin III's supercharger could put out +6 PSI of boost up to about 18,000ft, after which it began to drop off. This is only if you are running at 3,000 RPM, if you are running less RPM, that means less compression from the supercharger and thus boost pressure dropping off at a lower altitude. At sea level, the supercharger could produce about +17 PSI, but the thottle valve limited boost pressure to +6 PSI. "Pulling the plug" essentially gave the throttle valve more travel and allowed up to +12 PSI. +12 PSI was possible up to about 10,000ft at 3,000 RPM after which it dropped toward +6 PSI at 18,000ft and so on.

The +8 PSI gauge is correct (there were several varieties) as the engine wasn't originally intended to be able to run more than +6 PSI. The +12 PSI setting was a stopgap feature made possible by the introduction of 100 octane fuel. The gauge wasn't changed to reflect the higher power settings until much later.

Ok thanks, so then back to my original question 2, how can I ever see +6 PSI?

It seems like you can't the way it's set up right now.

The correct boost gauge for Hurri/Spit in 'B of B' period should be the +16 version due the use of 100 octanes fuel allowing use +12 lbs of boost. IL-2: CloD has this wrong, because game was modeled for 84 octanes fuel, and after their... "release" players pressure result in add 100 octanes, but cockpits are not redone.

But since Merlin conversion for 100 octanes use was done "in the field", second line units (e.g. training units) can have the +8 gauge at time, an example is this Spitfire with the triangle indicating 100 octanes fuel and still with the +8 gauge.

https://www.youtube.com/watch?v=8HIFc9xpguc

Thanks. I've raised it in the technical section for them to look into it they wish.

Very interesting, the few BoB period photos I've seen all show the +8 PSI gauge. The aircraft in the video appears to be a 609 squadron machine just prior to or during the beginning of the BoB, so that one at least is a frontline aircraft. I'm not saying you are wrong, what you say makes sense. Do you have a period photos showing the 16 PSI gauge or some other source?