Funny that Merlin Vs DB tell the opposite.

Seems you forgot one parameter : rpm and charging raise the strain and the temp with negative consequence on efficiency: try to win the 24h Le Mans race with a 2L engine and then jump in 7.0L 'vette ;)

To put it in perspective : there was no successful post war Merlin engined airliner. But lot of with P&W primitives big radials ;)

Sry but you are bypassing economics realities : the Industrial war machine was in such a strain at the end of WWII that minimal change in production were made where there was not strategical importance in order to downsize the level of investments. Many non-allied advanced tech were simply rejected in face of this.

Civil Aviation (the only one still interested in piston engine at the time) loose for long Injected eng, Fadec (without D and E ;)), canards foreplane etc.. Some of the very much "advanced" tech that was rushed back on the GA shelves as "new" products in the late 80's and 90's.

The conclusions you give does not convince me - Sry I am duplicating earlier comments of very good quality

rpm isn't especially interesting. Piston speed is generally a better metric.

Liquid cooled engines run colder than air cooled engines, and actually one of the main problems for the Merlin was over-cooling of the charge during cruising flight, which necessitated modification of the aftercooler to act as a heater to prevent the charge temperature falling below 40ºC.

The Merlin powered version of the DC-4, the Canadair Northstar was considerably faster than its radial engined equivalent. Noise was a problem initially due to the stub exhausts; the big radials tended to have collector rings; a crossover exhaust for the Merlin mitigated this to some extent. It wasn't an unsuccessful machine, but it wasn't ever going to capture the US market because it wasn't American.

As for perspective, how many DB powered airliners were there post WWII?

The Merlin wasn't successful as an airliner engine for many reasons - it hadn't be designed for that sort of duty for a start. It did rather better than the V-1710 though.

But perhaps the main reason for its "failure" as an airliner was that there just weren't suitable British airliners to bolt it onto. Lancastrian, York & Tudor could hardly compete with contemporary products from Lockheed & Douglas, because Britain had basically stopped airliner development in 1939 whilst the Americans had continued throughout the War (because they needed long-range transports anyway). They weren't about to put British engines onto their aeroplanes if they could possibly help it, so the considerable technical lead of the American airframers translated directly into market share for their engine manufacturers.

It's probably better to compare the Merlin's civil record with that of Hercules & Centaurus, which faced a similar airframe problem (though of course at this time Bristol had an aeroplane division as well, which provided them with a captive market for their engines).

In this context, the Merlin doesn't look so bad.

Post WWII, it was perfectly within the Allies' rights to confiscate any and all German IP that they were interested in. So they could have made Bosch fuel injectors and put them into their engines at no great cost. They chose not to.

As for post-war engine development, the US government funded considerable development work on the R-3350 turbocompound, and indeed also upon the R-4360, both of which found their way into airline service.

Britain funded development of the Napier Nomad, which was a more ambitious take on the turbocompound idea (I strongly suspect that this engine was cancelled due to failure to meet its quoted performance; I modelled it in considerable detail a couple of years ago, and I could never make the quoted component efficiencies add up to the quoted SFC...).

Direct injection makes a lot of sense for naturally aspirated engines, compression ignition engines, or engines which operate over a wide power range. It's less attractive for a big aero-engine because if you're operating at fixed power with a reasonable amount of supercharge you should be able to attain excellent mixture distribution, and so the pragmatic solution is to have single point injection into the eye of the supercharger - which is basically what everybody ended up doing.

Of course, these days people aren't designing big piston aero-engines anymore, and they aren't supercharging*, so DI makes sense.

*and turbochargers tend to be bought from turbocharger companies, which means that injection into the eye of the turbo-supercharger impeller isn't really an option because it would be too much of a nightmare to organise the development effort - who pays for what etc?

The supercharger is driven by the engine.

If you reduce the power consumed by the supercharger then you increase the brake horsepower and reduce the SFC.

Supercharger power consumption is just W*Cp*deltaT, ie W*deltaH.

Supercharger isentropic efficiency is

deltaH[actual]/deltaH[isentropic]

In the case of the Merlin, this figure was about 70%.

For isentropic, adiabatic compression,

T2 = T1(P2/P1)^(gamma/(gamma-1))

Hence it's trivial to calculate the isentropic deltaT, and deltaH.

DeltaT and deltaH both get smaller if we reduce T1.

Injecting fuel upstream of the supercharger reduces the temperature by about 25 K due to the latent heat of evaporation of the fuel.

This reduces the temperature rise across the supercharger, which is equivalent to increasing its adiabatic efficiency.

Clearly this confers an advantage to engines which inject fuel upstream of the supercharger. Given the considerable difficulty associated with increasing the aerodynamic efficiency of compressors, this advantage is not insignificant.

Mixture distribution is going to be very good provided that the charge temperature is sufficiently high for complete evaporation to be ensured. This will basically always be the case at high powers because deltaT is 100 K or more; indeed intercooling & aftercooling start to become necessary once you've got a lot of supercharge.

These advantages vanish at low non-dimensional power settings. Cars spend most of their time at very low non-dimensional power settings, and therefore DI wins hands down most of the time, especially if you go for CI, in which case it's almost no-contest.

In the end, the nature of all engineering trade studies is that the devil is in the detail. The optimum is a strong function of engine size and duty cycle, and we just don't build the sort of highly supercharged, high power spark ignition engines for which single point injection is attractive these days.

To use an analogy, old amplifiers used valves and therefore tended to have large transformers & rectifiers to produce the high DC voltages which allowed them to function. Most modern amplifiers are solid state, and they don't need those high voltages.

This doesn't mean that high DC voltages aren't still a good idea for valve amplifiers; I've got a pair of hundred watt half stacks sat next to me which run in excess of 400 V DC and sound great. But probably 99% of modern amplifiers for domestic use are solid state and so if you just ask "are high voltages a good idea for amplifiers" then the short answer is "probably not".

I suspect there is politics involved with that.

Quite.

To a lesser degree the same argument applies to British engines, given that the most successful airliner airframes were American in 1945. Therefore comparison between the Merlin and the R-2800, R-3350 or R-4360 in the civil market isn't really fair; it makes more sense to compare it with the Bristol Hercules or Centaurus, and if you perform that comparison then the Merlin doesn't look quite so much of a "failure" in the civil market anymore...

I like that ... Good point.

However this shld lead to a certain amount of "latency" with DI eng being more reactive upon power changes by the pilot

Regarding the Merlin as an airliner eng, it has proved unreliable as high power value were run only at high boost and then prove to be non-efficient (the cruise power has always been low); Add to the disastrous engineering of Britain's airliner projects tht seems to hve been hand-ended by gvrnmt officials (don't take me wrong France had to face the very same situation until legitimate firms could emerge out of the bundle in earlies 60's) and you'll end with a more pragmatic vision of the failure of the British industry in perspective of the US success stories like Boeing/Doug/Lockheed right after war end.

Humm hve we run OT (out of topic) again?

It was....

Both Daimler-Benz and BMW were forbidden from even being in the aviation market.

Post-war, both companies withdrew from anything to do with aviation and produced automobile engines instead. Both are industry leaders from the moment they entered the market and that leadership continues today.

They produced some of the best engines in the world.

And injecting fuel directly into the combustion chamber is even better, Viper. How hard is that to understand?

And that it is much more efficient to realize the power gains by directly injecting fuel into the combustion chamber than it is by dumping it into an intake manifold......

No, it is attractive and if we had the technology to do it on a cost effective basis, we would have done it. It is the ultimate fuel metering method for a piston engine in terms of power and efficiency. A single point injection simply cannot maintain a stoichiometric mixture in all the cylinders. That is why the EGT and CHT will always be different in each cylinder unless you have direct fuel injection.

In fact in the 1950's, we started doing it.....

In the R-4360C Wasp Major power-plant with CH 9 turbo-blower.....

http://www.flightglobal.com/pdfarchi...0-%200248.html

AFAIK they had to quit for 3 years. Thereafter they didn't get back into aerospace because they didn't have a market rather than anything else.

However, Daimler has quite a big stake in EADS, whilst BMW started a joint venture with RR to make turbofans in Germany from 1990, though now this is 100% owned by RR.

Why do you think it's better?

A supercharger is a pretty effective way to homogenise a mixture. The intake manifold is going to end up at roughly charge temperature, which for a Merlin at high power is going to be about 90ºC. You are very unlikely to see condensation of the fuel onto the manifold at that temperature. FAR will therefore be pretty constant from one end of the manifold to the other.

Charge distribution may well vary, which would modify CHT somewhat, but the same argument applies to air distribution.

FAR will become variable when supercharger delivery temperature is low, and this will affect acceleration behaviour, especially from low boost & revs. But aero-engines spend most of their time at fixed, relatively high, power settings, and so this sort of transient behaviour is far less of a problem for an aero-engine than for a car engine.

If you are supercharging then you'll win by injecting into the supercharger and thereby reducing supercharger work.

The supercharger is basically adiabatic if you're not injecting fuel or water into it. However, isentropic efficiency of superchargers tends to be much lower than the isentropic efficiency of the compression stroke of a piston engine.

In any case, you're always going to gain more by reducing temperature as early in the compression process as possible, because compressors (whether steady-flow or non-flow) produce temperature ratios in exchange for pressure ratios, whilst the absolute work required for the compression process is proportional to deltaH, i.e. Cp*deltaT.

If you reduce the starting temperature then you reduce the deltaT all the way down the chain, and the benefit multiplies. Therefore, if your fuel is liquid, you really want to inject it at or before the start of the compression process in order to maximise the thermodynamic benefit associated with its latent heat of evaporation.

Clearly for a naturally aspirated engine you might as well go for direct injection, especially if the number of cylinders is small.

The cylinders & pistons are very far from being adiabatic, but are very efficient at performing compression work. The limiting factor is the rate at which they can pass non-dimensional flow through their intake & exhaust valves at any given rpm. Hence supercharging; pre-compressing the air allows you to get more absolute mass flow rate into the fixed non-dimensional mass flow capacity of the piston engine. That's the objective of the exercise.

You use a steady flow machine upstream of the unsteady flow machine because unsteady flow machines are inherently bigger than steady flow machines, and therefore you can shrink the physical size of the engine in relation to its effective flow capacity.

That's only true for naturally aspirated engines.

EGT and CHT will be different anyway because that's life; holding FAR constant is great but it's not magic; airflow into the cylinder depends upon induction manifold design and engine speed. Induction manifold design is quite a complex business, and compromises are inevitable.

DI is very useful if you want to vary non-dimensional power setting over a wide range, but this isn't so important for an aero-engine, and so the higher design-point efficiency offered by injecting into the eye of the supercharger is a pretty compelling argument, before you even consider the cost, mass and complexity advantages.

Modern GA engines are going DI because they're going CI (in order to burn Jet-A and save money), and also because they don't have a lot of cylinders, which means that the cost of injectors is inherently less important.

The benefit comes from getting more work out of the turbocharger; if you cruise higher then the turbocharger has a bigger expansion ratio to work with and can therefore get more work out of the exhaust.

Charge temperature is limiting, and you'd obviously rather get your supercharger work from the turbine than the crankshaft. So you throw away the supercharger, but that means you need to either go to DI or else inject into the eye of the turbosupercharger impeller to homogenise the mixture.

The turbocharger came from GE, whilst the piston engine came from P&W.

Fuel injection into the turbocharger wasn't viable because of the fire risk, both in case of leaks between the hot and cold sides of the turbocharger, and because of the relatively long ducting from turbocharger to piston engine, which would otherwise have been full of stoichiometric mixture. But most importantly, it wasn't viable because it would have been almost impossible to start the engine unless the turbocharger was clutched to the crankshaft for that purpose, which in turn wasn't possible due to the physical separation between turbocharger and piston engine which was itself a consequence of the historical decision that GE would make turbochargers in isolation from the piston engine manufacturers.

The thermodynamic benefit comes from utilisation of exhaust enthalpy which would otherwise have gone to waste. However, there is an enthalpy loss equal to the sum of enthalpy drop across the aftercooler, and the cooling drag on the cold side thereof; if fuel had been injected upstream of the turbosupercharger, the compression process would have had a higher apparent isentropic efficiency, and the aftercooler would have had less work to do because the compressor delivery temperature would have been lower.

In essence, the benefit comes from improved matching/work balance rather than from going to DI itself. In other words, they wanted to throw away the supercharger to get more of their compressor work from the turbocharger, and this drove them to DI because they then didn't have a method to homogenise the mixture. So DI is a consequence rather than a cause.

That's an interesting take on direct injection, Viper.

I'd always assumed DI was first introduced to more reliably control mixture, eliminate pre-ignition and get a stratified charge in CI systems.

DI was indeed initially introduced to improve mixture control and avoid the various problems associated with carburettors.

In general, a single carburettor isn't likely to give good mixture distribution to a multi-cylinder naturally aspirated piston engine, because evaporation isn't completed before the charge reaches the intake manifold, and so you get a fairly complex multi-phase flow.

However, if you've got a supercharger between the carburettor and the intake manifold, things get a lot better because the supercharger homogenises the mixture and also increases its static temperature. This means that much more, if not all of, the fuel evaporates; diffusion is then very helpful in further homogenising the mixture. Furthermore, the flow is likely to warm the induction manifold sufficiently that fuel doesn't condense upon contact with it.

This means that supercharged engines which put the fuel into the airflow (whether via a carburettor or some kind of injection system) upstream of the supercharger will tend to deliver a pretty consistent FAR to all of their cylinders. This removes one of the main motivations for direct injection.

However, it must be stressed that this is something of a special case; take the supercharger away and FAR will vary considerably from cylinder to cylinder, whereas with DI you can set FAR quite accurately.

As an aside, WWII vintage technology would just meter the fuel into the cylinders, which is an open-loop approach. You'd still get FAR variations from cylinder to cylinder because although the fuel mass injected would be the same for all cylinders, the airflow would not.

A modern car engine would use an oxygen sensor to tune the fuel mass injected into the cylinder so as to maintain stoichiometry throughout the operating range of the engine; this is vital to the operation of 3-way catalysts. However, this sort of closed-loop approach requires computers, and it is primarily driven by emissions legislation rather than engine performance (power, SFC) considerations.

Without such constraints you'd run the engine leaner to improve SFC, or richer to improve power.

Fuel injection is very useful for CI engines because injection timing can be controlled in order to control the timing of the combustion event; it also allows the pressure profile of the combustion event to be controlled.

Limiting the peak cylinder pressure allows you to make the engine lighter.

With modern engines you can also just stop fuelling cylinders in order to reduce power. This is useful because the turn-down ratio of the injectors is limited if you want good atomisation; poor atomisation leads to reduced combustion efficiency and increased emissions (especially CO and UHC). The alternative is to use multiple injectors per cylinder, but that's a pain.

(If you really really want to then you can build a CI engine with a carburettor, but it's hard work, and it tends to be difficult to control combustion in a satisfactory manner, which hurts thermal efficiency and will tend to cause vibration due to considerable cycle-to-cycle variations in engine behaviour. You'll also find that the smoke limit is set by the richest cylinder, and smoke is a factor then this inevitably limits output.)

Anyway, DI is great for mixture control, but as with all aspects of engine design, it's an option within a tradespace, rather than an unmitigated upside.

If you're mostly interested in operating at a fixed design point then the advantages of DI may easily be outweighed by other options, especially if you're supercharging heavily. OTOH, if you're making a small engine for an economical passenger car today, it's very hard to beat a turbocharged CI engine with DI.

So I'm not suggesting that carburettors are magic; what I'm saying is that DI isn't magic either. Which is better depends upon your priorities, and the job you're trying to make your engine do.

In the very specific example of R-4360C, the primary goal was to get rid of the supercharger so that more useful work could be extracted from the exhaust via the turbocharger. The removal of the supercharger then drove the design towards DI. But it's not reasonable to say that DI is thermodynamically superior; the advantage comes from the improved utilisation of exhaust enthalpy, and DI is just a tool which allows this to be done. Indeed, had it been possible to inject fuel upstream of the turbosupercharger's impeller, superior performance would have been attained.

So DI is analogous to a bridge in this case; the economic benefit comes from the traffic which the bridge carries, rather than the bridge itself, and life would have been easier & cheaper if there had been no need to build a bridge in the first place.

But I must stress again that I'm talking about big aero-engines with high degrees of supercharge here; very different conclusions would be reached if the engine in question was designed to power a car, or even a significantly smaller aeroplane.

It is better Viper. An intake manifold cannot precisely meter fuel to the cylinders irregardless of having supercharger on it or not.

Have you ever flow an piston engine aircraft with individual EGT/CHT? The CHT and EGT will be vastly different if the fuel metering system is not direct injection.

Each cylinder is being meter a different amount of fuel. That means power loss just in the thermal differences!

Not to mention that none of them are a stoichiometric mixture. Add to that, it is impossible to optimize the timing advance. All of your cylinders are developing different power levels and none of them are optimal.

There is no why to precisely control how much fuel goes to each cylinder in an intake manifold.

With direct injection, you can not only optimize timing advance to the power curve, you can maintain a stoichiometric mixture. The thermal losses are eliminated because your CHT/EGT's are the same.

Add to that, the fuel cools the combustion chamber much more efficiently than cold air.

A simple illustration of that basic principle.

1006 J/kgC

460 J/kgC

2100 J/kgC

To change the temperature of a mass of 1 Kg of each by 2 degrees….

Air = 1006 J/kgC * 1kg* 2 C = 2012J
Fuel = 2100J/kgC*1kg*2 C = 4200J
Steel = 460J/kgC * 1kg * 2 C = 920J

Our 4200J of fuel energy goes to cool the 15C air…

4200J * 1kg /1006J/kgC = Change in T = 4.17 C

15C - 4.17C = 10.83C

Now let us dump our fuel on the hot steel of our combustion chamber.

4200J * 1kg / 420J/kgC = Change in T = 10 C

15C - 10C = 5C

5 degrees Celsius is much colder than 10 degrees Celsius.

That is correct.

A supercharger is a intake system has nothing to do with the fuel metering.

Every supercharged engine has to have a fuel metering system. The Merlin for example uses a carburetor. It has a supercharger but fuel is metered by the carburetor.

Read the article you posted. Rolls Royce does not make the argument a carburetor with a supercharger is better, they argue their engines are not as inefficient as people think when compared to the direct injection used by the Germans.

The only drawback to Direct Injection is complexity and expense.

Nice article on direct injection:

http://books.google.com/books?id=byE...page&q&f=false

Go back to the paper given by Lovesey which I posted earlier.

Engine shaft power is proportional to mass flow rate.

Mass flow rate, W, is given by

W=0.422*Ncylinders*(Pcharge-(1/6)*Pexhaust)/Tcharge

Charge temperature & pressure are measured in the intake manifold. In this equation, W is in lb/minute; piston engines are tiny.

You will note that Lovesey cites a 7% improvement in supercharger pressure ratio from injecting fuel into the eye of the supercharger.

This is very significant given the pretty awful isentropic efficiency of the supercharger.

You can go through the data, and calculate the supercharger work from the efficiency curves in Figure 11.

You can calculate the actual engine air consumption iteratively by assuming that the FAR is about 1/12 at high power. Hence, given the SFC curve and the full throttle power vs altitude curve, you can use the fuel flow to calculated the total rate of charge consumption.

You can use the total rate of charge consumption to calculate the supercharge power consumption as a function of inlet temperature. You must of course add this supercharger power consumption to the brake power in order to calculate the shaft power, because it is the shaft power, not the brake power, which is directly proportional to fuel flow.

This means that you'll need to iterate in order to achieve convergence.

Try this with and without fuel injection into the eye of the supercharger, which may be modelled as a 25 K temperature reduction exchanged for a 1/12 mass flow rate increase.

Because the supercharger work is W*Cp*deltaT, you will find that injecting fuel into the eye of the supercharger results in a considerable reduction in the supercharger power required for any given boost pressure, which naturally improves brake power and brake SFC.

Your argument regarding cylinder temperature is spurious because the engine has a cooling system to maintain CHT, and because the reduction in induction manifold temperature results in a considerable reduction in the charge temperature during the compression stroke because compression through a fixed volume ratio results in a fixed temperature ratio rather than a fixed absolute temperature increment.

This means that there is less compression work.

Peak cycle temperature is essentially fixed by dissociation, and therefore the reduction in charge temperature translates directly into an increase in BMEP.

Alternatively, you could hold constant charge temperature and reduce the size of the aftercooler. Either way, you're still getting a benefit from the latent heat of evaporation of the fuel; but this benefit is greater overall when the fuel is injected into the eye of the supercharger.

Arguments about stoichiometry as less important for an aero-engine at high power than for a car engine because you're not bothered about emissions (at least in this period). Therefore you run the whole thing rich of peak.

Cylinder to cylinder variation in FAR will be small so long as the induction manifold temperature is kept reasonably high; this may be seen from the discussion about lead fouling towards the end of Lovesey's paper; charge distribution is good down to intake manifold temperatures of about 35ºC.

Cylinder to cylinder charge consumption will vary due to intake manifold aerodynamics.

But this actually means that if you go for 1940s DI you'll get a variation in FAR from cylinder to cylinder because the injection system would give each cylinder equal fuel irrespective of its actual air consumption. Modern engines would use an oxygen sensor in the exhaust to maintain stoichiometry. However, this would preclude operations rich of stoichiometric, so the benefit is to BSFC and emissions rather than to absolute power.

I have flown a Citabria with modern after-market engine instrumentation. Obviously the CHTs vary because it's air cooled; you're never going to get the back cylinders as cool as the front ones. Likewise, mixture distribution will always be questionable for a naturally aspirated engine, even on a hot day in South Carolina.

That sort of engine would obviously benefit from DI; and in the modern world, the philosophy is to turbo-normalise if altitude performance is wanted. The convenience of maintaining a fixed engine operating point independent of altitude is considerable. Modern compressors are very much more efficient than those from the 1940s, and therefore there is less compressor work to save in the first place. Additionally, with substantial exhaust energy being dumped out of the waste-gate, there is obviously less motivation to reduce compressor work. So there are a variety of factors driving modern engines towards DI.

This does not mean that single point injection upstream of a supercharger does not have advantages, especially if you have a high degree of supercharge.

Modern piston engines simply have different design goals than the high-powered piston aero-engines of the 1940s.

Pretty redundant if you ask me, if you are already using a variable speed supercharger adjusted already for supercharging needs, as DB did with its barometrically controlled hydraulic clutch.. the supercharger wasn't making less waste, it made almost no waste at all.

Correct me if I am wrong, but injecting fuel into the supercharger eye reduces charge temperature, delaying detonation point. Direct fuel injection does the same (in the combustion chamber), but later, and with better fuel effiency, no risk of backfires, and no negative G problems. High octane fuel is a pretty expensive agent for charge cooling..

You're confusing throttling losses, which are avoided by varying supercharger speed, with the aerodynamic losses associated with the supercharger's design, which are not.

The aerodynamic losses increase the temperature rise associated with a given pressure rise, which increases the work required.

Because compression through a given pressure ratio tends to produce a given temperature ratio, you reduce the absolute deltaT by reducing the initial temperature, all other factors remaining constant. This reduces compressor work, which is equivalent to an increase in compressor efficiency.

You obviously get a greater benefit from cooling the working fluid at the start of the compression process.

Eg

Start at 288 K. Cool by 25 K. T = 263 K. Compress through a temperature ratio of 1.5, and then further through a temperature ratio of 2. Temperature = 263*1.5*2 = 789 K. Delta T from start = 501 K.

Compare with:

Start at 288 K. Compress through temperature ratio 1.5, cool by 25 K and then compress through temperature ratio of 2. Final temperature is then 814 K, so delta T is 526 K.

Thus, compressor work differs by 5% or so in this example.

This is the reason for the reduction in the isentropic efficiency associated with a given polytropic efficiency as compressor pressure ratio increases.

Injecting into the eye of the supercharger is no more efficient than a carburetor at fuel metering.

You are still getting the compression from a supercharger and directly cooling the combustion chamber with direct fuel injection.

I am sorry Viper but it does not change the fact you cannot precisely meter the fuel thru an intake, either.


http://www.onsemi.com/site/pdf/PSDE_0411.pdf

Of course it's better than a carburettor; you're not reliant upon venturi suction to get the fuel into the airflow; you're positively chucking it in with a pump.This will provide considerably better matching across the flow range.

Because you're injecting fuel under pressure, you can positively atomise it, achieving a considerably lower Sauter mean diameter of fuel droplets than is possible with a simple carburettor, which means that it will evaporate much faster. This means that more of the temperature drop happens earlier in the compression process, which increases the overall efficiency bonus.

Once the fuel has evaporated, the mixture distribution problem goes away.

This is inherently less efficient. It's relatively simple thermodynamics.

Fuel metering is not a particular problem. You measure the flow through the intake, and inject fuel in proportion thereto. It's much easier to get this measurement & injection process right at a single point than it is to get it right at 12 points.

Fuel distribution may be a problem at low manifold temperatures where the fuel fails to evaporate fully, but that is a separate problem.

You seem to be mostly hung up on fuel metering issues, which certainly exist for naturally aspirated engines with carburettors, especially away from their design point.

However, fuel metering is not especially important at high power if you don't care about emissions. You run rich of stoichiometric, and fuel flows say +/- 5% won't make a great deal of difference to power output. Obviously the SFC is pretty bad at that point; you can clearly see this on the SFC curve in Lovesey's paper.

Mixture distribution is not a problem at high induction manifold temperature.

The reductions in supercharger work and intercooler size are far more important than the slight increase in fuel mass fraction which you might suffer from the need to keep the leanest cylinder sufficiently rich to avoid detonation. The cost of a single point system is far lower than a multi-point system, and the fuel pressure required is lower than for true direct injection. (Port injection is a pretty horrid compromise which only makes sense if the alternative is a carburettor which would produce bad mixture distribution.)

For a supercharged spark-ignition aero-engine, operating at a fixed non-dimensional power setting, provided that you've got enough induction manifold temperature to avoid condensation, the mixture distribution will be good and the single point system wins.

Multi-point FI is an expensive solution to mixture distribution problems. It is great for naturally aspirated engines, and probably pragmatic for turbo-normalised engines, especially if the engine manufacturer isn't responsible for the turbocharger.

But if you're using a mechanical supercharger and will mostly operate the with reasonably high induction manifold temperatures, then there's no great mixture distribution problem unless your induction manifold is horrible, so multi-point injection offers limited benefit, whilst single point injection into the eye of the supercharger reduces supercharger drive power requirements. So single point injection is a pretty obvious choice.

Now, if you're designing a sports car engine, you might supercharge it to get high power, but most of the time it would operate at very low non dimensional power settings, so mixture distribution would be a major problem with single point injection, and therefore you'd probably go for multi-point FI.

But that's because the sports car engine isn't really designed for high performance. It's designed to make an expensive noise and very occasionally provide bursts of acceleration to impress the girl in the passenger seat. Most of the time it's practically ticking over, and so you're much more bothered about part-load characteristics than would be the case for an aero-engine. You're also trying to meet modern emissions regulations, which means that you're paranoid about stoichiometry so that you don't poison your catalyst. It's a totally different world, with different trades and different drivers.

I hve to disagree loudly with the above comment. It's the worst thing to do ;) Having a fat diesel with a body kit is what impress the girl nowadays :(

http://www.slideshare.net/rjperforma...rj-performance

It works in any engine to increase power and performance over any other fuel metering system no matter if the intake is supercharged or not.

http://www.steerbythrottle.com/hccyong/files/DFI.pdf

http://cars.about.com/od/thingsyoune...tinjection.htm

A good primer article on Direct Injection. It explains very well the difference between the various types of fuel injection and why Direct Injection is the ultimate fuel metering system for power and performance.

http://www.driverside.com/auto-libra..._injection-350

Here is a good article that explains the German Direct injection systems in easily understandable terms:

http://www.motorcycleproject.com/mot...xt/inject.html

The German systems were far from perfect but they certainly did their job and allowed them to level the playing field in terms of aircraft engine performance.

IIRC, the British and United States did a combined effort to develop a Direct Injection engine that was used in a tank at the end of the war.

Viper, direct injection is a fuel metering system. Supercharging is an intake system and does not have a thing to do with fuel metering.

It is two completely separate things you want to combine.

You point to the thermal benefits of introducing the fuel ahead of the supercharger instead of downstream of it. I agree it is there when compared to introducing fuel downstream of the supercharger in your INTAKE SYSTEM.

Got it but that does not make it more thermally more efficient that directly injecting the fuel in the combustion chamber. You are not looking at the heat capacity but are stuck on upstream vs downstream fuel introduction for your intake.

As Rolls Royce points out, direct injection is much more efficient than metering your fuel downstream or anywhere in the intake system. Just because that small part of the intake system becomes more efficient vs introducing fuel downstream does not make the whole system more efficient.

A simple illustration of that basic principle.

1006 J/kgC – Specific Heat Capacity of Normal Air

460 J/kgC – Specific Heat Capacity of Steel

2100 J/kgC – Specific Heat Capacity of Gasoline

To change the temperature of a mass of 1 Kg of each by 2 degrees….

Air = 1006 J/kgC * 1kg* 2 C = 2012J
Fuel = 2100J/kgC*1kg*2 C = 4200J
Steel = 460J/kgC * 1kg * 2 C = 920J

Our 4200J of fuel energy goes to cool the 15C air…

4200J * 1kg /1006J/kgC = Change in T = 4.17 C

15C - 4.17C = 10.83C

Why do you think direct injection is the ultimate fuel metering technology and so desirable to have in an engine? If was not for the complexity and expense, all engines would be direct injected because it is the most efficient system mankind knows of at the present for metering fuel.

Rolls Royce also shows in the article you posted their system is not as efficient as directly injecting fuel into the combustion chamber combined with your supercharged intake.


Why? YOU STILL MUST HAVE A FUEL METERING SYSTEM ON YOUR ENGINE. Introducing the fuel ahead of the supercharger does not eliminate the basic problem of NON DIRECT INJECTED FUEL METERING SYSTEM, uneven fuel mixtures found by introducing fuel ANYWHERE in the intake system.

;)

The only way to eliminate that is too directly inject fuel into the combustion chamber.

Direct injection engines with a supercharger STILL benefit from that supercharger intake system.

Yes and you are correct in that metering fuel anywhere in the intake system is not going to give you the power gains compared to injecting precisely metered fuel directly into the combustion chamber.

The drawbacks to direct injection are the expense and complexity. The BMW801 series used 14 high pressure fuel pumps and consisted of more parts than the entire rest of the engine.

The supercharger technology of the allies combined with better fuels restored the balance.

You cannot point to Direct Injection technology and say it was decisive and gave the German engines better performance over the allied ones anymore than you can point to better fuel quality and supercharger technology of the allies as being better than the German engines.

In the air war over Europe, all sides developed their engines and fielded 2000 hp plus designs by the wars end. The implications made a few folks that fuel technology was decisive are not correct when one takes in the whole picture. Fuel quality and supercharger technology simply maintained the balance with fuel metering technology as well as superior chemical engineering.

That any of these engines were routinely operated outside of their published guidelines is another ludicrous idea hatched in the gaming world but that is another subject.

:)

Air is a mixture of gasses which have different molecular weights. But you wouldn't expect that the issues you allude to above would modify the composition of air going into the cylinders.

If the fuel has evaporated, and is in a gaseous phase, which is perfectly reasonable if the induction manifold temperature is high, the exact same argument applies; inertial separation of species within the gaseous mixture is unlikely because the forces are insufficient to overcome the diffusive tendency of the gas.

If the fuel is still liquid in the intake manifold then mixture distribution will be bad. This is often the case with naturally aspirated engines because the induction manifold temperature is essentially ambient.

The benefit of single point injection into the eye of the supercharger is that it improves the effective isentropic efficiency of the supercharger, and thus reduces supercharger work, increasing the brake horsepower output of the engine when compared with multi-point injection into the cylinders or ports.

I'm getting pretty tired of trying to explain this relatively simple concept.

Here's a nice big paper. It's got a lot of interesting stuff in it, but the bit that is germane to this discussion is the analysis of the effects of water injection upon compressor performance. It doesn't matter whether you're injecting fuel or water, the latent heat reduces the temperature rise through the compressor, which is analogous to an increase in compressor efficiency.

Happy reading.

In one of Viper's earlier points he argues that if you don't care about emissions and purposely run a bit rich, then minor variations in fuel/air ratio will not cause problems. Temperatures on the downstream side of the supercharger ought to be plenty high enough to cause evaporation of the fuel droplets, particularly if you aren't intercooling.

On a turbocharged, intercooled engine I'd wager that direct injection would be superior since the turbo is already much more thermodynamically efficient than a supercharger. But on a supercharged engine where the supercharger can pull as much as 30% of the crankshaft's power it's a sound engineering decision to try to increase that efficiency foremost.

Now this is hilarious coming from Barbi when all he can produce is,

"The proposed changes to units equipped with Bf 109 were as follows:

OKL, Lw.-Führüngstab, Nr. 937/45 gKdos.(op) 20.03.45"

(it is not an original document either)

unit - on hand - serviceable - type
"I./JG 27 - 29 - 13 - Bf 109 K
III./JG 27 - 19 - 15 - Bf 109 K and some 109 Gs
III./JG 53 - 40 - 24 - Bf 109 K and some 109 Gs
IV./JG 53 - 54 - 27 - Bf 109 K and some 109 Gs"

for the use of 1.98ata boost on 109K-4s.

Just have to love that double standard. :lol:

The proof is in the pudding. The Merlin III/12lb boost was producing much more power than equivalent DB601 engines:

http://www.spitfireperformance.com/spit1-109e-eng.jpg

From what I can gather on the web, the DB601 also had a 100 hr TBO versus 240 for the Merlin. Does anyone have other figures?

This is true but only because of the higher boost level ..... hence a slightly more shaft power consuming s/c (the RAF had to build a high alt engine with lower cubic inches)... hence ...
this diag depict Merlin without s/c (test on grd) and a DB with SC!

But it is true that Merlin had a superior TBO although I am not sure what the value were for the BoB period

By the way with this curve I am not sure that the FC would hve selected "your Merlin" as the max power requirement was for high alt (at the time 20kfeet (my own guess) )

Pls stay focused on facts and BoB period - Thx

So what figures do you propose for HP?

240 hrs was the BofB TBO figure for the Merlin. It was raised progressively to about 350 hrs by 1945, for combat aircraft.

Great ! but don't forget the Mass flow : Lowered Heat + increased Mass Flow = higher efficiency

I think you summed it up.

I understand your (strong) point). Don't forget the stochio ratio (1 to 8 (?)) that even the above result.

Sry for the red thumb down... I hve really no idea how it came here

Just pointing out the double standard that Barbi uses.

Everywhere I look it's a 1150/75 value ON the Spitfire. What ever we think logic would ask for a lower value than the latter XX that is well documented (see my post for the Merlin XX on the Hurri)

TBO for DB 601A-1 was 200 hours. RR TBOs were understood as a figure that 1/3 of the engines could satisfy, and if a single cause of failiure did not amount to more than 2/3 of the cases IIRC.

There's no sign of "proposed" in the original document. See for details: http://www.kurfurst.org/Engine/Boost...arance198.html

Nope; it's plotting BHP.

I'm pretty certain that I've posted the RM1 rating from Harvey-Bailey several times now, which gives the rating at 1310 bhp at 9000', +12 psi.

I really don't understand why you keep trying to "de-rate" the Merlin. There's no shortage of source material on the subject (you can cross check the power output of the Merlin III against figure 6 in Lovesey's paper for example), and in any case, given that we also have no shortage of data about the performance of the Spitfire & Hurricane, even if you managed to persuade 1c that the Merlin made less power than was actually the case, that would just mean that they had to artificially reduce airframe drag to match the known speed and climb performance.

The result of that would be that the RAF would have an unrealistic advantage in shallow dives against the Luftwaffe. Frankly, if I was one of the "make my plane better irrespective of realism" crowd, I'd rather have less drag than more horsepower, because B&Z is a rather more effective strategy than T&B.

It may well be that http://www.wwiiaircraftperformance.org/ doesn't post the best performance data for Axis aeroplanes, but I haven't seen any evidence to suggest that the source material it contains is fabricated. I might not necessarily agree with some of the interpretation, but that's irrelevant given that most people here just repost the source material and debate it, rather than reposting the gloss from the site.

BTW, if anything, the +12 FTH of 9000' is an underestimate because it doesn't include intake ram AFAIK.

If you cross-check the Merlin 66 horsepower chart which includes 400 mph intake ram against the RM10SM rating in Harvey-Bailey, you'll find that the MS gear +18 FTH from the rating is 5750', whereas the chart gives an FTH of over 9000'. Likewise, the rating specifies the FTH in FS gear as 16000', whereas the chart shows an FTH of about 20000'.

You can cross-check the ram pressure rise against the FTH by using a standard atmosphere calculator like this one if you feel that way inclined.

So actually the power comparison is unrealistic in as much as it's based upon the Merlin's static FTH. In reality, at about 300 mph you'd see an increase in FTH of a couple of thousand feet.

You can easily cross-check this if you look at airframe speed vs altitude diagrams; max TAS is achieved at the rammed FTH for whatever boost they're using, and this is invariably higher than the FTH for the engine rating quoted in Harvey-Bailey.

I don't know what the basis of the DB601 power curve is, so I can't comment on whether or not it includes intake ram.

Reference:
Harvey-Bailey, A. (1995) The Merlin in Perspective - the combat years. 4th edition. Derby: Rolls-Royce Heritage Trust.

Those are your words I posted Barbi. I don't see any original document in the link.

You are picking what suit better to your thesis and once again put a layer of complicated arguments to dissimulate this fact.

You are right there is the intake ram effect. Just like exhaust gazes propulsive effect ... and a lot of drag with the cooling system that did not take into account the boundary layer drag even at a late stage in the war.

It does not mean that you can add all the Power gains RR refer in its doc and then say that the merlin had the a total of BHP equal to the cumulative effect measured on the test bed.

Note that the intake ram effect went as a benefit only after a major redesign witch hve to be dated :rolleyes:

The diag you show is difficult to interpret as it it shown put out of any contest. And we are talking abt early war tech not late achieved Merlin boost. In 1944/45 the war for the Spit has switch from high alt air interception to low level mud fighting and interdiction witch favor over-boosting. (we also know that those level of boost proved unreliable and were lowered on the field - the griff engine being put forward has the 2K HP piston eng - Oh... and yes there is the Merlin Hornet but... wait is that not an evidence that DH has superior engineering capacities in term of aero when Supermarine despite strong gov support only produced contestable design ?)

In term of FM and drag for the spit, just catch the six of a 109 in the game and follow him in her maneuver for a min. If you are not laughing after 30 sec and still need to be convinced, pls take a similar ride in the Excellent Hurri we hve for now.

So no drag reduction! My humble opinion wld bend me in the direction of some change toward the set of modeling eq that might not apply to a 300mph fighters (in fact modelizing the Spit wing as a trapezoidal wing of similar wing surface/wing root chord and thickness wld lead to better accurate results without changing the overall FM engine). But this is pure guess as I don't know anything abt CoD FM engine :-P

So, to resume my self : you can't take a pce of this or that and build a convenient result

For example if you build your opinion on the spit only reading my posts here you'll conclude that the spit was an antique machine unsuitable for fighting even if this is not what I am thinking.

I repeat myself : The spit/Merlin were great design but with some major flaw that a simple look at history puts in perspective (search the web for a Elliptical winged B2 or floating carburetor PT6 turboprop or a Malcom Hooded BlackBird ;) )

Can't believe Kurfurst is still peddling out these BS arguments still? Ordinarily I wouldn't care a jot but he's doing his best to get what he wants and ruin any chance of a more realistic FM.

What could his agenda be?

History revisionism and or Historical Denialism!!

Viper,

It does not work that way.....

If you have flown an aircraft with individual Exhaust Gas Temperature Gauges and Cylinder Head Temperature gauges you would know their is a wide variance in the temperatures with any fuel metering system that introduces fuel to the intake.

100 degrees or more is considered normal variance........

Why? The fuel mixture is different for each of the cylinders.

There is no such thing as a direct injection aircraft engine in General Aviation. All fuel injection is single point injection much like the Allied designs of WWII.

In a direct injection engine, there is almost no variation in CHT or EGT between the cylinders.

It is that temperature variation that robs a single point fuel metering system of power.

http://www.costaricaaviation.com/fli...tions_rev1.pdf

Crumpp,

At first, thx for all the excellent references you are giving on many of your post.

I understand you point on DI vs SPI (single point injection). DI has clearly many advantage and was the panacea at the time.

Viper care much abt theory and given that you run at cte regime and that the ducting are of equal length after the s/c (what is not feasible) the SPI has clearly an edge in terms of practical answer.

DI however as you has pointed out offer much more advantage on reality grounds and this clearly can be seen in ehaust temp even in today cars (Ask GrandPa about engine backslash and loud bang with carburetor engined cars before the 80's GTI went out) ;)

Coming back on the BoB, I believed that RR had however an advantage with the s/c being inline with the engine witch simplified the routing of the air with a relative symmetry (the DB has some prob and a slight differences btw raws of left and right cylinder due to the s/c being on the port side ). This tend to makes the RR simpler ... and what is simpler is much easier to improve : a strong point for any strategical war item ;)

As a pilot, slick aircraft are problematic when it comes to maneuvering. They are good for cross country performance but poor in maneuverability. That is why you don't see many slick aerobatic platforms.

Drag with appropriate power gives a pilot precise speed control allowing him to reach and maintain his aircraft's design performance speeds quickly.

As a pilot, there is nothing worse than having too much speed and not being able to get rid of it when you need the airplane to maneuver or require maximum performance from it.

You are most welcome. Thanks for your contributions to the discussion too.

The technological advantage of DI allowed the German designs to be equal to despite strategic material shortages.

Maintaining equality with inferior materials came at a high cost though.

Exactly. The main drawback of Direct Injection is the expense and complexity. Germany is just a little smaller than the state of Montana in terms of square miles and had a strategic material shortage even before the war began.

For a resource poor country of that size to take on most of the civilized world in an all out war of attrition, complex and expensive is something to be avoided.

Actually pairs of these things fly over my head every day...

CHT is dominated by cooling; EGT is dominated by stoichiometry. CHT variations are an inevitably fact of life for air-cooled engines.

A perfectly reasonable statement if and only if you are comparing identical intake conditions.

He's not saying that EGT and CHT are equal, he's saying that across the cylinders CHT won't vary much, and neither will EGT.

I was responding to this:

...

Correct. Thank you.

What I am saying is obvious for anyone who has flown a piston engine aircraft with individual CHT/EGT. You can see the power robbing temperature differences of introducing fuel anywhere in the intake system.

Only by metering fuel with a direct injection system will the cylinders have equal EGT's and CHT's across the engine.

I did not know the DA-42 diesels were direct injection. It figures, diesel is the easiest type of engine to direct inject.

You misunderstood it.

Of course EGT is not going to equal CHT in an individual cylinder, that is a silly concept. Only in direct injection will the EGT and CHT be equal across the cylinders of your engine.

Fuel introduced in the intake will cause the cylinders to draw different mixture ratios as the firing order is cycled. The different fuel mixture ratio will cause each cylinder to have a different CHT and EGT from the other cylinders in the engine. This is a very common known fact for pilots as you see it every time you fly so you don't get worried when one cylinder has a temperature 100 degrees lower than another cylinder. That is just a by product of introducing fuel into the intake system instead of directly injecting it in the cylinders so the mixture can precisely metered.

In many ways it's tougher because the pressures are higher. However, the alternatives are worse, so injection becomes the route of least resistance sooner.

Diesels are some the first engines to be successfully directly injected. DI eliminated the need for a complicated pre-mix chamber and the mechanical gearing required to control the mixture.

You don't have to worry about getting fuel and spark to the chamber at the right time, just the fuel.

Any fuel metering system that introduces fuel into the intake system cuts down on the efficiency of that intake just by being there.

Sure the fuel cools the charge but the airflow volume is restricted by the fuel metering device. Carburetors, whether float, SU, or TBI restrict the airflow volume.

With Direct Injection, the intake can be designed free from the volume and flow obstruction of a fuel metering system component.

It was not solved in the "Spitfire II" the problem of negative G?

Oh, i see. Thanks for the clarification cheesehawk!

Regards

It was a lady's orifice....err idea

http://en.wikipedia.org/wiki/Miss_Shilling's_orifice

A stop gap "fix" to the neg G cut out came in March 1941 with the fitting of the famous "Miss Shillings orifice" developed by Miss Tilly Shilling this was superseded by true negative G carbs fitted from 1943 onwards.

+1

It is possible that the devs have made a mistake by putting the "Spitfire IIa" when it should be the "Spitfire Ia" ROTOL? ´Cause I see no performance difference between one and another, except for the best use of prop.
So i believe that the "Spitfire IIa" IS really an Spitfire Ia with rotol with an grammatical mistake.

Here's part of the engine config from the I, Ia and IIa

Spitfire I

Spitfire Ia

Spitfire IIa

Looks like it's got the Rotol to me. Whether it's working properly in game is another matter.

I flew in the new vers of the Spit that came with the last patch and what ever the version (flew on Syndicate server) it has ridiculous FM. This thing can loop on it self (and certainly inside the roomy space of my Hurri cockpit) and create E or inverse the gravity field like no other in any Hollywood movies. And I am not referring to the cockpit view that hide nothing to the rear just like some popular Brazilian underwear :rolleyes:

So what ever it is a I, I Rotol or a IIa ... IT'S NOT A SPIT !

:confused: What was it called in the game? AFAIK Syndicate only has Spitfire Marks 1 and 1a available to fly, and these spitfires match well with the 109.

yes if you are looking at the nbr (speed, climb and bla bla bla). But when you start to shake that tail, bank and turn it's industrial ironing vs Moscow Ballets :(

I actually have no idea what any of that means. But I don't have trouble shooting down spitfires online unless it's the MkII variant which outclasses the 109 quite easily in almost every aspect.

As for the MkI and MkIa, the 109 can outclimb them at almost any altitude, and is faster in level flight at high altitudes.

+1

You're probably right, I've never really tried it so I didn't want to say one way or the other.

http://en.wikipedia.org/wiki/Aircraf...n#cite_note-27

The above is a link to a source that has something to say under the heading of 100 octane fuel. Below is an extract. Is this seen as a reliable source?

A meeting was held on 16 March 1939 to consider the question of when the 100 octane fuel should be introduced to general use for all RAF aircraft, and what squadrons, number and type, were to be supplied. The decision taken was that there would be an initial delivery to 16 fighter and two twin-engined bomber squadrons by September 1940.[27] However, this was based on a pre-war assumption that US supplies would be denied to Britain in wartime, which would limit the numbers of front-line units able to use the fuel. On the outbreak of war this problem disappeared; production of the new fuel in the US, and in other parts of the world, increased more quickly than expected with the adoption of new refining techniques. As a result 100 octane fuel was able to be issued to all front-line Fighter Command aircraft from early 1940.[28] [nb 1]

Happy landings,

Talisman

You're not seriously asking if wikipedia is a reliable source are you?

Witch one inspire you most in term of agility ?

Note that IMHO the 109's FM are great as are those of the Hurri.

Are you asking which RAF fighter I feel is more agile? Hard to say, probably the spitfire.

The 109 FM is not particularly accurate IMO. It's undermodeled (probably the RAF fighters are as well, and yes that includes the spit)

Humm did you not see the pictures of the ballerina (aka the spit) and the iron (aka the 109) ? :shock:

Regarding the 109 FM it's not under modeled. I feel them like perfect (ok ok it lack a lot of buffeting, dyn stalls etc ..) but those are way ahead of the previous IL2 series.

If you take any IL2 moded FM as a reference of course CoD planes have lower perfs but ... it's not related anyway to the CoD devs.

They hve done a tremendous work . ;-)

I have absolutely no idea what you are talking about.

The 109 and early spits don't get their historical performances. That is undermodeled. I'm not comparing it to IL2 or mods or anything.

Rgr that. No jokes btw cats and dogs

But I hve no prob with the 109 perfs. Perhaps at alt but there is no one flying there most of the time.

Hurri is just perfect.

Spits can still out turn a hurri (in fact it seems as it can turn inside the cockpit of the hawker, raise her nose faster than a 109 at any sped and stall only for a microsecond before being given back a positive vario. Oh and the max available power is always linked to max revs low pitch making that pit awfully noisy (I wld prefer rather be on the mower for an entire day than behind that propeller for an hour :rolleyes:).

Frankly everyone will gain having a more realistic Spit model with contested dogfights instead of this.

We'll have to agree to disagree, then. I don't find the spitfire Mk1 and 1a to be uber.

I remember, this an old story, it was changed in the first patch Il-2 Sturmovik: Cliffs of Dover: Patch 1.00.14072 -ARIL 15. "Completely removed overload assessment from carburetters. Rolls-Royce engines will now cut if overload is negative, and will not cut if it is positive. (old values were sneezing at .5G, and cut-out at .25 which we felt were dead on, but this apparently confused most of the players)".

They may not have written, that simply made the RAF planes easier :rolleyes: I don't know, how much this value now. Some topics started, but without a result.
Please keep the realism!
Realism or accessibility, what decision should be made?

This has been argued at length. The documented values taken from Instrumented aircraft are shown in the images below. These from documents from the national archives. The Devs have these values:

http://img59.imageshack.us/img59/5658/vegcutfile.jpg

http://img593.imageshack.us/img593/7585/vegcutfile2.jpg

So the first onset will occur at +0.1g

Spit under modeled as far as boost goes.

109 under modeled as far as top speed goes

There...that was easy

Plenty and plenty of posts on this matter and I'm sure the Devs know

->There is no prob with the speed. I'll try to post some vids.

->The boost story is highly controversial.

-> the carburetor behavior was difficult to handle. True. But we would hve ultimately learn how to do with that. Tht's what a simulator is all about - eg have a look at all the airliner simulator aficionados ! I hope we will see it back one day or another.

~S!

Hi. Based on a undated (? 1940-1941 who knows) sheet of paper, the Englishs was obtained this development in their all existed airplane? I guess to these modifications there is a more tangible source, when, into which airplane, where and who mounted it in? Could we see them?

Compared with this, as you wrote it in the topic (109s autoprop - did it ever existed?):
IvanK: "By general operational employment I am referring to general Squadron use, i.e. How many aircraft were equipped with it and at what date."

There were not enough to the German auto prop pitch, that were published a manual in 1939 (maybe from a joke it would be printed), and the german aug.-oct. 1940 somehow not part of the BOB era anymore...
I will be curious, there will be an automatics in the E-4, E-7 after these (Will be E-7 at all?). I hope so yes, otherwise this -beside all respect- is double standard.

You tried to climb above 8000 metres? Or you watched how fast the airplanes on 6000-7000 metres? The (edit: the 109 E-3...) top speed is ok on sea level... but the high altitude flying is totally wrong...

Effectively I was talking abt low to med alt speed. I will check the high alt perf with a quick test on my next flight.

Regarding your reply to IvanK : they do what they want, no ? It's upon to them to choose on which grd they make this sim credible (and I pay credit to them to be on that ground !)

Personally I found that the neg G carb cut out was a superb feature giving CoD a truly unique taste of credibility regarding effort made down to the details. This has been lacking before in several BoB era Sim since long !

I have for many years read about the cut out in spits by a lot diff and credible historians. I hve no doubt that the utmost majority of RAF planes were affected and that until really late (1942 ?).

Just want to say here (not to you Tom) that it's not because devs in some sort choose to share their enthusiasm with the community that it has to be a place for all sort of exigence. Man hve to be grateful for the possibility to put forward their case (opinion) but shld accept that their idea cld not be followed without any sort of justifications (and I know what I mean :rolleyes: !!).

The only moment that i had a cut out, was in a Spitfire Ia at 15000 feets when i started an vertical dive. Then the engine stopped completely, and when i pulled up it started again.

Theoretically yes, practically no. If the historical accuracy is important (they said this many times), and not only while it is appropriate for their side, it would not be allowed to do things like this then (to reduce serious but existing deficiencies on a subjective manner).

I write about it (among other things) :-P

yea we know :)

I was adding my input to the thread geezer... Thats the issues i have with both AC and have had from the first day playing this sim

Unfortunately nothing is done on this issue. However, a lot of good things (more realistic cut out behaviour of early Merlins removed) are tuned down ...

I don't know what the original cut out in your game was....

I do know that if you push the float up in a float carburetor, the flow of fuel stops.

While my airframe is aerobatic, my engine has a float carburetor. The mere suggestion of negative G's will cause the engine to spool down.

There is no way a float carburetor can perform a negative G loop. :rolleyes:

Err what exactly are you on about Tom? The first paragraph of the document is valid. This refers to the documented value of +0.1G that cut out effects commence. Thats the relevant bit ... the remaining bit of the document refers to a "proposed system" to reduce the effects. No one is suggesting anywhere that this "proposed system" be incorporated in CLOD. The document was provided for the sole purpose of providing a documented value of cut out (in terms of G) in original early Merlins .... i.e. those without any mods at all.

This is a single page of a two page document that is dated in the usual pattern in the signature block on the last page, the document date is 21/12/1940. The remaining documents in the file are dated 20/12/1940 and 21st February 1941.

What is the relevance of the 109 Auto Prop pitch statement ??

Well, the truth that I have to apologise, you're right, I responded to cheesehawk post, that myself did not check the things.
I was able to make a negative loop with the RAF types in the case that the CEM is turned off only...

Nothing.

The cut out was a 2 stage event. The 1st stage caused a momentary loss of power > a lean cut out. The 2cd stage of the cut out was the more serious cut out as the float floated the wrong way and openedthe inlet fully allowing full fuel pressure to the carb and thus flooding the engine > rich cut out.

i usually fly with the E1
Much better for me than the E3 [to much shaking when you fired the cannons
:)]
plus that i have more records with the E1..:-P

Really i can´t see any difference (in performance) between the Ia and the IIa, except for the Rotol constant pitch control, except of that, both of them has +6 lb, same speed, same climb rate, same maneuverability, same guns ... why most servers don´t allow to play with them?

Really?!? :confused:

you serious?

The fuel metering system does not change and the air/fuel ratio does not change very much.

That is the whole purpose of leaning the mixture to maintain that ratio as the density altitude gets higher.