109 e3b against spitfire II

[CaptainDoggles]

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.

[Seadog]

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



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?

[TomcatViP]

Originally Posted by Seadog

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

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 ...

Originally Posted by Seadog

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) )

[Seadog]

Originally Posted by TomcatViP

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

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.

[TomcatViP]

Originally Posted by Seadog

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.

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)

[Viper2000]

Originally Posted by TomcatViP

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!

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.

[TomcatViP]

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

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

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 )

[Osprey]

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?

[Kongo-Otto]

Originally Posted by Osprey

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!!

[Kurfürst]

Originally Posted by Seadog

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?

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.