Question on WEP devices.

[Kweassa]

I need some info on what kind of WEP devices AH planes used in combat. For instance, I know 109G10 used MW50 Methanol-Water injection, or P-47s used water injection. From what I remember, P-51s had electric WEP, didn't they?

 But.. what did the Japanese planes such as Ki-61s and N1K2-Js use?? Or planes like F4U, F6F, La-7, Yak-9T?? Does the G6 we have here also use MW50, or do they use something else? What about 109F4s and G2s? Did they also use MW injections? Italian planes??

 I know this is an awful lot to ask. Please just enlighten me on some of WEP devices you know that are portrayed on AH..   Thx in advance.

[flakbait]

The type of WEP used in 109's depends on the model. I've read that the F models could mount GM-1 (nitrous oxide) as a Z option. I know that any G or later model could take either one. Fw-190's used MW50 (methanol & water: 50/50 mix), direct injection of C3 (97 octane fuel), or maybe GM-1 but I'm not too sure about it (GM-1 that is). Our Fw-190A and F use the direct injection boost, while the D9 and Ta-152 supposedly have MW50. But the Ta-152 is moving 20-25mph too slow at alt (26,250 ft) to be using MW-50, so I suspect something is up. I have no idea what type of boost system any of our 109's are fitted with. Our G6 and G10 can use either GM-1 or MW50.

Early F4U models, like our -1D, had water injection. I'm not sure about the F6F but I think it used the same system. I have no idea what type of WEP system the P-51 used, but you're right about the P-47. It did use water/alcohol injection from a 15 gallon tank behind the engine bulkhead. This was installed from the D-5-RE onward.

That's about what I know.


------------------------
Flakbait [Delta6]
Delta Six's Flight School
Put the P-61B in Aces High
"I wanted to go back for another 50 missions, but they ruled it out
because I had a case of malaria that kept recurring. So I had to stay
in the States and teach combat flying. I was shot down by a mosquito!"
Frank Hurlbut, P-38 pilot
 

[funkedup]

A few of the planes have water injection which allows higher manifold pressures to be sustained without detonation or overheating.  It is actually a water-methanol mixture but the methanol is just there as anti-freeze.  Luftwaffe called it MW 50 and the US called it Water Injection or ADI (Anti-Detonant Injection).

Water injection is used on:
Bf 109G-10
Fw 190D-9
Ta-152
P-47
F4U
F6F

There is also Nitrous Oxide (Luftwaffe called it GM-1) which boosted power above the rated altitude of the engine.  The only aircraft in AH with this system is the Ta 152H.

On all the other planes, WEP is just the use of manifold pressure (supercharger boost) or RPM beyond the normal levels.  But the amount of time for WEP operation was limited.  Some aircraft had a mechanism which limited the WEP duration but on most of them there was a time limit in the manual and it was up to the pilot to operate the engine accordingly.

Where did the time limits come from?  WEP operation could cause detonation and overheating.  If a pilot noticed either of these conditions he would (if he was smart) reduce power.  But many of the engines could be run at WEP power levels for hours and hours without overheating or failure.

In these cases the main limit on WEP time was engine overhaul intervals.  WEP operation caused the life (in hours) of some engine parts to be reduced from the life which could be achieved using normal power levels.  This means that the engine would need to be overhauled more frequently in order to keep engine failures at acceptable rates.

Overhauls and early engine failures are undesirable from an operational and logistical standpoint, so engineers determined a satisfactory rate of overhauls, and then determined what WEP time limit was required to maintain that rate of failures or overhauls.  That's where the WEP time limits generally come from.  

And the time limits are enforced in AH.  In real life a less responsible (or more endangered) pilot might exceed the WEP limit times.  But in AH we are not allowed to abuse our engines so.  The game automatically reduces power at the proscribed time.  So the game makes us all "by the book" pilots whether we like it or not.  

[ 12-02-2001: Message edited by: funkedup ]

[HoHun]

Hi Funked,

great summary on war emergency power!

I'd like to add that generally, the idea that MW50 was most useful below rated altitude and GM-1 was most useful at high altitude is correct.

However, MW50 boosted power by acting as anti-detonant and to a lesser extent by the charge-cooling effect of its evaporation. The anti-detonant effect couldn't be exploited above rated altitude since the supercharger didn't provide full rated manifold pressure there. The charge-cooling effect on the other hand was still beneficial, as the same volume of intake air at a lower temperature had a higher density and contained more oxygen. MW50 charge cooling was standard procedure for some of the Jumo 213E/F powered Focke-Wulf aircraft which did not feature an intercooling system. Even above rated altitude, MW50 was good for a power increase of a few percent.

GM-1 (nitrous oxide) injection provided much more power than MW50. The beauty of the system was that no matter how much power the engine still provided, GM-1 would boost it by a constant horse power number regardless of altitude and air pressure. Nitrous oxide was injected in liquid form into the supercharger air intake, just like MW50, and the rate at which it was injected was directly proportional to the horse power gain. German aircraft typically featured two different injector nozzles that could be used independendly or simultaneously, so that they had three stages of "special emergency power", as WEP modes employing special power augmentation systems were called.

GM-1 would yield its full power even at sea level, provided the engine was strong enough to take it. With a power gain of several hundreds of horse power, the pistons or the connecting rods weren't necessarily strong enough to do so! Accordingly, a minimum altitude had to be observed for each GM-1 stage - which might yield 150 HP/300 HP/450 HP respectively, for example.

However, even when the engine took the power, boosting it from 1800 HP at low altitude to 2250 HP was a gain of just 25%. GM-1 was much more useful at higher altitudes where engine power might be down to just 900 HP - a 450 HP increase would mean a 50% power boost there! That's the reason GM-1 was really intended for high-altitude operations - it gave the engine unparalelled power in the extremely thin air above 35000 ft.

By the way, it was also possible to inject liquid oxygen in the same way as nitrous oxide was used. Liquid oxygen injection was experimentally used both with the early Me 109G aircraft as well as with high-altitude Spitfires. It seems also to have been used occasionally as substitute for GM-1 when Luftwaffe units had supply problems late in the war.

The Ta 152H when fully equipped featured both MW50 and GM-1 injection, and could use both at the same time. That illustrates quite nicely that one only worked below and the other only above rated altitude :-)

Regards,

Henning (HoHun)

[HoHun]

Hi again,

>That illustrates quite nicely that one only worked below and the other only above rated altitude :-)

Of course, what I meant to say was it illustrates that:

- it is not the case!

that one only worked below and the other only above rated altitude :-)

Regards,

Henning (HoHun)

[funkedup]

Understood, thanks.  

[Kweassa]

So does this mean.. um..

 or 109G-10 has both GM-1 boost AND MW50?

 ... ??

[R4M]

no, Kweassa, the 109G10 carries only MW50.


HoHun, the GM1,as you said, could be used at any altitude. However I think that the reason if was used only over the rated altitude of the engines was a very good one even while teorically its advantages were usable at any altitude...

the GM1 is N2O. The laugh gas,as they call it  . Injected into the engine that gas gives a surplus of Oxigen while,at the same time, acting as antidetonant.

The final result is that the engine has a extra income of oxigen, wich is added to the normal ammount the supercharger forces into the engine. That means that you can pull more manifold pressure than with the supercharger air only. The antidetonant effect gives you the chance to pull a higher manifold pressure than usual, too.

However this advantage is more sensible at high altitudes for varions reasons.

1-Evidently at altitudes over the rated alt of the engine, the oxigen forced into the engine by the supercharger is simply not enough to keep the power up. WIth GM-1 you are adding much needed air and so the pilot could get more power from the engine.

2-At lower altitudes, the limit is the manifold pressure limit for the engine itself. Even counting with the antidetonant properties of the GM-1 system,a pilot couldn't pull all the power he could teorically (because he ran the risk to break the engine).  In fact you'd be wasting the N2O. AT high altitudes your engine gasps for air, so the GM-1 is a very useful addition. At lower altitudes, where the engine has more than enough air, there is no use for the surplus oxigen.

I'm not sure about it, but I think that the MW50 was a more effective cooler and antidetonant than the GM-1, allowing for higher manifold pressures without detonation. (in fact I have no damned idea of why does the MW50 or GM1 act as antidetonants, but well..  ).

 The downside of the MW50 is that it carries no oxigen surplus, so at high altitudes you can't run the engines at high manifold pressures because the lack of oxigen. So at those altitudes the MW50 would be unnecesary (as it was used just to allow the engine to run at very high MAN pressures) and gives no advantage at all.

Another advantage of the MW50 over the Gm1 was that the N2O, being a gas, was more complicated to handle than the MW50, wich was a liquid. The only real downside of the MW50 was its absolute lack of utility over the rated altitude of the engine.

[Seeker]

I'd like to ask a question regarding No2 equipped engines...

Was there any coupling of boost to prop pitch?

It may sound a strange one, but I know from auto engines that Nox has most effect in the lower rev range, that's to say it realy boosts torque, not horsepower (they're very closely related, but not exactly the same).

If you want to run a Nox car, you'd use it mostly for acceleration (at the risk of twisting half-shafts), not maxmimum speed. Is this practise carried through to areo mechanics too? If it was, I'd expect a pilot to hit the laugh gas while increasing prop pitch at the same time to utilise the extra power generated.

Just curious..

[Staga]

Power=Torque(Nm)*Speed(rpm)/9551
Torque(Nm)=Power*9551/Speed rpm

So when DB605 gaved 1800hp@2800rpm:
1800hp*9551/2800rpm=6140Nm. (<-Can it be that high???)

Anyway one carmanufacturer said that when customers want more power they actually want more torque  

[niklas]

Originally posted by Seeker:
I'd like to ask a question regarding No2 equipped engines...

Itīs N2O afaik not NO2

niklas

[Seeker]

That was it, Niklas?

You made me check in here to see you corrrected my spilnining?

Or course it's N20, unless it's NOx.

Now, what does it do to torke throughout the rev range of an engine? At which point in the tawk curve is it best introduced? I've a small amount of expericence with NOx installations on large American V8's, but as far as I know, aero engines are designed for constant speed application, and I'm interested in how that changes things.

It's something to torque about, is all.

[Starbird]

It sounds like N2O was used to give the engine more O than its supercharger could pull in.

Give an eninge more oxygen, you get a bigger bang when it ignites, the piston then pushes back harder than it would without the extra oxygen.

Now, all of the aircraft in this sim use a constant pitch prop. When the prop lever is full forward, the prop will keep a constant max rpm (usually around 3000).

The prop will change pitch on its own to keep that set rpm. If you kick in the N20, and get the pistons firing harder, they're going to increase in RPM. The prop doesn't want that, so its going to increase its pitch to keep a constant RPM.

This incresed pitch will move more air, giving you better thrust for a higher top speed, or better climb. Whatever you want to do with it.

I hope I explained that correctly.  

[HoHun]

Hi R4M,

>the GM1 is N2O. The laugh gas,as they call it . Injected into the engine that gas gives a surplus of Oxigen while,at the same time, acting as antidetonant.

You're right, I didn't mention that nitrous oxide acts as an oxidizer.

>2-At lower altitudes, the limit is the manifold pressure limit for the engine itself. Even counting with the antidetonant properties of the GM-1 system,a pilot couldn't pull all the power he could teorically (because he ran the risk to break the engine).

To be more accurate, the engine was limited in power by its ability to withstand the resulting internal forces. If you're implying that the manifold pressure limit isn't necessarily the same as the maximum manifold pressure attainable from normal supercharger use, we're actually in agreement here.

>So at those altitudes the MW50 would be unnecesary (as it was used just to allow the engine to run at very high MAN pressures) and gives no advantage at all.

Actually, even above rated altitude, MW50 still had a charge-cooling effect and was historically used to overcome the Jumo 213E-engined Fw 190D's lack of an intercooler.

>Another advantage of the MW50 over the Gm1 was that the N2O, being a gas, was more complicated to handle than the MW50, wich was a liquid.

You're right for ambient temperature and pressure :-)

However, nitrous oxide was really stored as a liquid in the German aircraft and evaporated only after being sprayed into the supercharger air intake. The German fighters usually had a large 85 L pressure vessel in the aft fuselage for the nitrous oxide. Since it was stored in liquid form, it was necessary to pressurize the nitrous oxide tank employing compressed air to force it out of the tank and into the lines leading to the engine. (The Me 109E-?/Z variants used four smaller steel vessels instead of one larger one.)

This equipment was quite a bit more heavy and bulky than the MW50 equipment: The same fuselage space that accompanied 85 L of nitrous oxide in a pressure vessel would hold 115 L of MW50 in a conventional tank.

Regards,

Henning (HoHun)

[HoHun]

Hi Seeker,

>Was there any coupling of boost to prop pitch?

Good question! Since the Me 109's engine controls were similar to those of US engines, I expect the pilot set the correct values manually. For the otherwise fully-automatic Fw 190A, I have no idea. However ...

>It may sound a strange one, but I know from auto engines that Nox has most effect in the lower rev range, that's to say it realy boosts torque, not horsepower (they're very closely related, but not exactly the same).

I think that when we're talking about aircraft with a constant-speed propeller, they're actually equivalent. A constant speed propeller could be regarded as a continuously variable transmission in automotive terms :-)

It's interesting to see that nevertheless, revolutions were reduced when using nitrous oxide injection. I think the reason is different from automotive applications, though: At the high altitudes where nitrous oxide was most beneficial, propeller efficiency would drop due to the tips achieving high mach numbers.

With conventional fuel, the supercharger had to be kept at full speed to deliver oxygen for the combustion, but I'd speculate that with nitrous oxide injection, it paid off to slightly reduce revolutions so that the speed-independend nitrous oxide-induced horse powers could exploited more efficiently, leading to more thrust power even at slightly decreased crankshaft power.

Regards,

Henning (HoHun)