DCS Spitfire Mk IX performance

[Yo-Yo]

What do you mean by "equal energy"? One would think the Spitfire would be more competitive with 25 lb to have an distinct advantage over all fighters in rate of climb. Also since the Spitfire would be the slowest out of all the fighters including the P-47D-30, ~337mph vs 345mph @ SL. Even with 25 lb boost the Bf-109K4 and Fw-190D9 would still be faster.

 

Energy means climb or/and acceleration. Surely, this parity ends in the region of high speed.

The reason of it is higher wing area fo the Spit that gives it great advantage in sustained and instant turns.

But it pays for this advantage.

[Hiromachi]

Hmmm hmmm, but I believe 109 K-4 actually has superior energy since its rate of climb is higher. At least thats what was found in game testing, you said yourself back in the older bug report thread that 23 m/s is very pessimistic for 109 K-4. Some folks claimed it to be 26+ m/s in game atm.

Based on the first post Spitfire IX makes 23.5 m/s at best.

So I might be understanding you wrong here, but it looks to me that Spit doesnt have equal energy.

[Friedrich-4B]

We need allied medium or heavy bombers to do much else right now. The focus on almost all of these planes were either defending or attacking the bomber stream. The spit was obvioulsy more of an air superiority dogfighter, but i'm not sure what role it had in '44.

 

Over Western Europe in 2 TAF, the L.F. IX's primary role was that of tactical fighter-bomber, although it was also being used as an air-superiority fighter.

 

Going back to Yo-Yo's original post:

 

The Spitfire development was started by obtaining a lot of original materials including wind tunnel tests, flight tests measurements, prop (we use wooden Rotol in the model) wind tunnel tests. Wind tunnel tests both for the prop and the airframe were performed for high Mach numbers as well.

So, the parts of the FM (airframe, prop, radiators) were carefully tuned separately to get the specified parameters of the real prototypes. Then, the blower of the existed V1650-7 engine was changed to fit Merlin 66 gear ratios, the automatic shift was set to new pressure.

 

As it was assembled together, we get the following results.

 

As a reference, Mk IX BS. 543 was used for level speed and climb rate, Mk IX MA. 648 was used for level speed. Additionally Mk VIII JF. 275 having the same wing and engine was used for both tests.

 

THe radiators shutter were open for the climb test and shut for the level speed tests as in the references.

 

The results from another report we have was not plotted at the diagrams because the climb rate was determined at +12 lbs/2850 rpm, and the level speed test at +18/3000 is very close to BS. 543.

 

As you can see, DCS Spitfire matches the references within the real tests tolerance in the whole range from 0 to 10-11 km. The higher altitudes differencies, as far as I can suggest, can be explained with various reasons. As one can see even real time tests have increasing differencies in that region.

 

But, frankly, I think not many people like to dogfight at these altitudes :).

 

So forum members can evaluate the cited reports for themselves, and in context, here are the figures for BS543, MA648 & etc

while here is the report for BS543, compared with BS551 powered by a Merlin 70.

 

As already noted:

 

I believe he [Yo-Yo] is just using those charts as a comparison for this example, I dont think he is using data from those aircraft for the FM, if that makes sense.

 

Yo-Yo has made it clear that his research covered far more than just the information shown in the reports on BS543 and MA648:

 

The Spitfire development was started by obtaining a lot of original materials including wind tunnel tests, flight tests measurements, prop (we use wooden Rotol in the model) wind tunnel tests. Wind tunnel tests both for the prop and the airframe were performed for high Mach numbers as well.

So, the parts of the FM (airframe, prop, radiators) were carefully tuned separately to get the specified parameters of the real prototypes. Then, the blower of the existed V1650-7 engine was changed to fit Merlin 66 gear ratios, the automatic shift was set to new pressure.

 

BS 543 also had an experimental propeller that was never serialized and achieved performance far in excess of ALL other Spitfire IXs/VIIIs tested...

 

Of course there is nothing wrong with using BS 543 and MA 648 as reference if you do not name Spitfire Mk IX. Name it a "an experimental Spitfire with an experimental propeller...

 

The propeller BS543 used did very little to influence the performance because, as shown in this original document the so-called experimental ("original") duralumin Rotol 10'9" diam. XH.54D RM-SS, produced inferior climb performance and conferred no appreciable difference in speed cf the "production" propeller, Mark R3/4F5/3, or the Hydulignum unit, XH54H/RM/SS.

 

As it is, DCS is modelling the Jablo (compressed wood) bladed Rotol type R.5/4F5/3 or similar, that was also a production unit.

Edited March 25, 2016 by Friedrich-4/B
spelling

[NineLine]

Hmmm hmmm, but I believe 109 K-4 actually has superior energy since its rate of climb is higher. At least thats what was found in game testing, you said yourself back in the older bug report thread that 23 m/s is very pessimistic for 109 K-4. Some folks claimed it to be 26+ m/s in game atm.

Based on the first post Spitfire IX makes 23.5 m/s at best.

So I might be understanding you wrong here, but it looks to me that Spit doesnt have equal energy.

 

If you only base it on rate of climb maybe, but there s many more aspects to consider than just climb. Where is the fun if all things were equal?

[Friedrich-4B]

For interest, this is how the A&AEE achieved their test results:

 

Edited March 25, 2016 by Friedrich-4/B

[Yo-Yo]

Hmmm hmmm, but I believe 109 K-4 actually has superior energy since its rate of climb is higher. At least thats what was found in game testing, you said yourself back in the older bug report thread that 23 m/s is very pessimistic for 109 K-4. Some folks claimed it to be 26+ m/s in game atm.

Based on the first post Spitfire IX makes 23.5 m/s at best.

So I might be understanding you wrong here, but it looks to me that Spit doesnt have equal energy.

 

I mean that k4 and MK IX are equal in energy gain regardless of 1-1.5 m/s difference (about 5% of the total gain), because this difference is noticable only in pure tests - at the constant predetermined speed, with strictly 1g load, etc.

 

In real dogfight, for example, this difference is so negligible that sometimes a good pilot in the Spitfire can see his constant energy advantage over medium K4 flyer.

Moreover, in loaded flight the energy balance can be more preferrable for Mk IX.

 

Only 15-20% of energy gain difference and more gives the feel of energy advantage.

[Talisman_VR]

404mph @ 21,000ft

 

 

I find this very interesting as it shows that multiple use of the 5 min combat setting could be expected in a single sortie and gives guidance regarding the subsequent effect on fuel consumption :thumbup:

 

Happy landings,

 

Talisman

[Kurfürst]

No, and I wrote why.

 

No, and I wrote why.

Look at the picture if I were not clear explaining the matter.

Are you happy now?

 

Well take a look at the graph on which I also added the full curves of JL 168, MA 310, JF 973 and the unknown serial no. IX LF measured by the NII VVS, they are all in close agreement.

 

Its quite clear that all the serially produced Spitfires ever tested all reach their full throttle heights in the region between ca 19 000 - 20 000 feet.

 

From your graph I can only see that your model simply ignores the results of serial production aircraft test results and reflects most closely the performance obtainable only with non-standard prototypes and experimental machines: BS 543 and MA 648.

 

Again, and I must stress this, since there seem to be a bit issue of miscommunication or parallel talk - the issue is not the top speed (such as the the lower top speeds typically obtained with serial production Spits compared to the optimistic condition prototype machines - such is very much expected with mass produced machines).

 

Of course always an easy solution to ignore the majority of real life test results and accept only those that fit in the model. If I take only the high values into account.... then the high values I get in my calculation will look normal. :music_whistling:

 

The issue isthat the altitude those speeds are reached: both BS 543 and MA 648 achieved their top speeds way, way higher (21-22k feet) than all the other machines with the same engine tested. Its actually even explained in detail in both flight test reports (for example MA 648 had experimental air intake - why take this as basis..?). The British testers made it very clear that these altitude results are very high and unusual for the type, yet for some reason, the current DCS Spit model achieves even greater altitudes... the issue will be even greater with climb rate as a result.

 

CONCLUSION: its extremely likely that the air intake efficiency is simply far too high in the current DCS model because its based on non-serial production results, that result a ca 2-3000 feet increase in the full throttle height realistically achievable by serial production machines.

[Yo-Yo]

Well take a look at the graph on which I also added the full curves of JL 168, MA 310, JF 973 and the unknown serial no. IX LF measured by the NII VVS, they are all in close agreement.

 

Its quite clear that all the serially produced Spitfires ever tested all reach their full throttle heights in the region between ca 19 000 - 20 000 feet.

 

From your graph I can only see that your model simply ignores the results of serial production aircraft test results and reflects most closely the performance obtainable only with non-standard prototypes and experimental machines: BS 543 and MA 648.

 

Again, and I must stress this, since there seem to be a bit issue of miscommunication or parallel talk - the issue is not the top speed (such as the the lower top speeds typically obtained with serial production Spits compared to the optimistic condition prototype machines - such is very much expected with mass produced machines).

 

Of course always an easy solution to ignore the majority of real life test results and accept only those that fit in the model. If I take only the high values into account.... then the high values I get in my calculation will look normal. :music_whistling:

 

The issue isthat the altitude those speeds are reached: both BS 543 and MA 648 achieved their top speeds way, way higher (21-22k feet) than all the other machines with the same engine tested. Its actually even explained in detail in both flight test reports (for example MA 648 had experimental air intake - why take this as basis..?). The British testers made it very clear that these altitude results are very high and unusual for the type, yet for some reason, the current DCS Spit model achieves even greater altitudes... the issue will be even greater with climb rate as a result.

 

CONCLUSION: its extremely likely that the air intake efficiency is simply far too high in the current DCS model because its based on non-serial production results, that result a ca 2-3000 feet increase in the full throttle height realistically achievable by serial production machines.

 

So, you think that previous document specification regards to an experimental plane?

In my turn I'd like to ask why do you prefer to refer to the results that obviously belong to the "tail" of statistical distribution?

By the way, I can add to this chart another British test reduced to the standard atmosphere using the same British method that shows even better results.

[MiloMorai]

If BS543 was an experimental and non standard, why was it issued to an operational squadron (403 Sqdn. 9-6-43) and failed to return from operations 22-8-43?

 

You have data for serial produced Spitfires Kurfurst?

[Kurfürst]

So, you think that previous document specification regards to an experimental plane?

 

What does it relate to then?

 

In my turn I'd like to ask why do you prefer to refer to the results that obviously belong to the "tail" of statistical distribution?

 

Since when? Can you qoute where I said this? All I say is that they need to be taken into account when assessing the subject, not ignored at a whim. What do you suggest then - ignore the all the results of test that were all made on planes in serial production standard, and by some weird logic, rely only on two planes tested, which even the test themselves say are not representative of the serial production standard?

 

I said in my first my first post that BS 310 sounds reasonable, since it agrees with

a) the nominal British specs for the IX LF and

b) it is actually falls between the highest figures achieved by the experimental machines and the results more typically achieved with serial production machines in the UK, in the USSR and in Australia.

 

There are 7 flight tested machines there on the graphs. 5 of them are serial production machines, and 2 of them are prototypes with usually high full throttle heights. You seem to be on the opinion that out of the 7 tests, its best to "forget" the 5 serial production machines and try to match the speeds of those two weird prototypes.

 

The British who tested them had a different view on this. The report on MA 648 says:

 

External equipment of the above four aircraft was similar with the exception that MA.648 had the new pattern of air intake.

 

It will seen that the above full throttle heights vary considerably. Differences in ram effect due to speed variations account to some extent for this; for instance if the speed of JL.165 were increased to that of MA.468 the full throttle height would be increased roughly 500 ft. The effect of difference in ram effect on the other aircraft would not exceed 150 feet.

 

The mean full throttle heights for BS.310, JL.165 and BS.543 are 9,200 ft. in MS gear and 20,300 ft. in FS gear, but the engine of BS.543 has full throttle heights far above average. Even then, the full throttle heights of MA.648 with the injection pump are above average by 200 ft. in MS gear and 800 ft. in FS gear. The new type intake on MA.648 is expected to reduce the full throttle heights by a small amount, so these figures may be rather pessimistic.

 

The improvement is attributed chiefly to the reduction in pressure losses occuring before the air enters the supercharger by the elimination of the choke and other obstructions of the normal carburettor.

 

Owing to large variations in the performance of the four aircraft tested it is not possible to obtain an accurate value for the improvement in performance but the above quoted figures for increase in full throttle height give an average increase of about 3 mph. around the full throttle height.

 

The only satisfactory way to obtain exact figures would be to repeat the tests with the normal carburettor substituted for the injection pump. When this was done on Spitfire VB W.3322 (Merln 46 S.U. Mark I injection pump), the increase in speed at full throttle was about 5 mph, and the improvement in full throttle height 1300 ft. The increase in full throttle height indicated by the present report therefore seems to be pessimistic.

 

By the way, I can add to this chart another British test reduced to the standard atmosphere using the same British method that shows even better results.

 

Is it another experimental plane that never saw service in this condition or a plane in serial production standard?

Edited March 26, 2016 by Kurfürst

[Yo-Yo]

What does it relate to then?

 

http://www.spitfireperformance.com/spitfire-lfix-ads.jpg

[Kurfürst]

Ok, so its a yellow spec sheet, got it. Well at least it confirms two things : a) the specs were understood for mean weight of 7106 kg (cc. Half ammo and fuel) and b) their overlay curve seem to confirm that they were a sort of mean avarage/crossing point between the prototype and BS310.

 

My conclusion seems to be correct then - its extremely likely that the air intake efficiency is simply far too high in the current DCS model because its based on a small sample on non-serial production results in which weight corrections may have bern also ignored, and that in the end results an artificially increased full throttle height and abnormal performance achieve well above full throttle height realistically achievable with the Spitfire Mk IX LF in standardized condition.

Edited March 26, 2016 by Kurfürst

[Friedrich-4B]

(for example MA 648 had experimental air intake - why take this as basis..?).

 

Actually, the so-called "experimental" air intake was the Vokes "universal system, as fitted on the vast majority of the L.F Mk. IXs, as well as to Mk VIIIs and IXs.

 

Edited March 29, 2016 by Friedrich-4/B
Reinstate image

[Kurfürst]

Actually, the so-called "experimental" air intake was the Vokes "universal system

 

Speculation (with a good measure of good will) without any evidence.

 

If it was fitted to the "vast majority" of Spitfires, why do they call it a "new type" in MARCH 1944 as opposed to the "standard" - in addition to that the Vokes air filter was around for years by that time already on Malta Spit Vs?

 

There is no evidence that the experimental air intake with larger dimensions and the S.U. fuel injection pump was ever fitted to operational Spitfires.

Edited March 26, 2016 by Kurfürst

[MiloMorai]

Because as your 16 years of research should have shown you this is the Vokes filter you are confusing with the one fitted to the Mk IX.

 

[Kurfürst]

I am sure someone is very confused, but its certainly not me.

[MiloMorai]

Yes you are as Vokes is a manufacturer of air filters and not just for airplanes.

 

The enlarged carburettor intake with built-in compact Vokes Aero-Vee universal dust filter was another feature introduced on the Mk. IX. It became standard only later during Mk. IX production, but was also retrofitted to many earlier machines.

 

[Friedrich-4B]

Speculation (with a good measure of good will) without any evidence.

 

If it was fitted to the "vast majority" of Spitfires, why do they call it a "new type" in MARCH 1944 as opposed to the "standard" - in addition to that the Vokes air filter was around for years by that time already on Malta Spit Vs?

 

There is no evidence that the experimental air intake with larger dimensions...was ever fitted to operational Spitfires.

 

:doh: 16 years of so-called research and Kurfurst still doesn't know what air filters were fitted to L.F Mk. IXs? Note what MA648's report says:

 

The air intake was of a new type (meaning not "experimental"), designed to combine the temperate and tropical versions. In tropical conditions the normal air scoop beneath the engine cowling is blanked off by a movable shutter and the air is drawn through a filter from the engine bay. For these tests a blanking plate was fitted flush with the internal wall of the air intake, i.e. in the normal position for temperate use and the pilot's control was locked in the filter out position. No snowguard was fitted.

 

The "standard" air intake was this one:

 

 

as compared with the Vokes universal, as fitted to MA648 and production Spitfire L.F. IXs:

 

 

Extremely poor choice IMO since subsequent reports (see report BS 310 w. M70) and the BS 543 curves make it clear that the engine of the prototpye BS 543 was operating on too rich mixture, therefore it had an abnormally high full throttle height and improved low/medium performance at low medium altitude. Very higher altitude performance suffered somewhat.

 

Kurfurst is confusing two reports, that of BS310 w/Merlin 70 is here http://www.spitfireperformance.com/bs310.html

 

The report mentioning a rich mixture is http://www.spitfireperformance.com/bs543.html and it reads as follows:

 

5. Conclusions.

...Another point of note is that the performance of Spitfire IX BS.551, fitted with the improved high altitude Merlin 70 engine, has a lower ceiling by about 3000 feet than the standard Merlin 61 engined aircraft and subsequently the fall off in rate of climb and level speed is greater than would be anticipated. This rapid fall off is attributed to carburettor richness at altitude, and it is hoped that at a later date further tests with an adjusted carburettor may be made.

 

BS551, NOT BS543, was suffering from a fuel-rich mixture, that lowered the service ceiling and reduced the rate of climb. Nowhere, in any of the reports, is BS543 described as operating with a fuel-rich mixture.

 

If BS543 was an experimental and non standard, why was it issued to an operational squadron (403 Sqdn. 9-6-43) and failed to return from operations 22-8-43?

 

BS534's career: an ex-Spitfire VC converted to a Mk IX w/Merlin at R-R Hucknall, then to an L.F Mk IX:

 

BS543 IX 3534 R-R M61 FF 22-10-42 R-RH Cv IX M61 23-10-42 AFDU Duxford 8-11-42 AAEE 13-12-42 M66 (RM10SM) install comparison trials with BS534 and BS551 see BS534 for details CRD VA 22-2-43 403S 9-6-43 611S 10-6-43 AST 19-6-43 mods 485S 'OU-F' 6-7-43 Missing from sweep 22-8-43

Edited March 29, 2016 by Friedrich-4/B
Reinstate images (moved to new folder)

[Kurfürst]

Another wall of red herring and speculation, designed to sidetrack the thread and bury the evidence under a pile of rubbish.

 

The report on MA 648 says:

 

It will seen that the above full throttle heights vary considerably. Differences in ram effect due to speed variations account to some extent for this; for instance if the speed of JL.165 were increased to that of MA.648 the full throttle height would be increased roughly 500 ft. The effect of difference in ram effect on the other aircraft would not exceed 150 feet.

 

The mean full throttle heights for BS.310, JL.165 and BS.543 are 9,200 ft. in MS gear and 20,300 ft. in FS gear, but the engine of BS.543 has full throttle heights far above average. Even then, the full throttle heights of MA.648 with the injection pump are above average by 200 ft. in MS gear and 800 ft. in FS gear. The new type intake on MA.648 is expected to reduce the full throttle heights by a small amount, so these figures may be rather pessimistic.

 

The improvement is attributed chiefly to the reduction in pressure losses occuring before the air enters the supercharger by the elimination of the choke and other obstructions of the normal carburettor.

 

Owing to large variations in the performance of the four aircraft tested it is not possible to obtain an accurate value for the improvement in performance but the above quoted figures for increase in full throttle height give an average increase of about 3 mph. around the full throttle height.

 

The only satisfactory way to obtain exact figures would be to repeat the tests with the normal carburettor substituted for the injection pump. When this was done on Spitfire VB W.3322 (Merln 46 S.U. Mark I injection pump), the increase in speed at full throttle was about 5 mph, and the improvement in full throttle height 1300 ft. The increase in full throttle height indicated by the present report therefore seems to be pessimistic.

 

 

BS 543 report notes:

 

The powers of the RM-9SM and the Merlin 66 engines in F.S. gear should be identical, since the high speed supercharger gear ratio is the same. It will be seen that on the climb, the performance and boost pressures were similar, within the limits of experimental error, but in level flight above the full throttle height the Merlin 66 engine was developing about 1 lb/sq.inch higher boost pressure than the 9 SM engine, with a consequent higher full throttle height and improved performance. This discrepancy must be due to variations in the manufacture of the engines and possibly of the air intakes, but it should be borne in mind that any small differences in performance of a high compression ratio supercharger or of the intake will be more noticeable at high speeds because of the increase in the dynamic head.

 

Thus:

 

(i) The British considered the full throttle height of BS 543 abnormal, hinting at production differences

(ii) The same report also report carburrator richness problems with BS 551, but BS 543 also shows the exact same abberation, very noticable in the curves (far too good low/medium performance, sudden drop as altitude increases - mixture is too rich)

(iii) BOTH BS 543 and BS 551 trials were repeated later ;)

(iv) MA 648 had a new type of S.U. carburetor, which in previous trials resulted in 1300 feet improvement in FTH.

(iv) Despite this, BS 543 had higher FTH than MA 648, even with the Bendix carburator.

(v) Considering how much trouble carburetors gave , one just wonders if it really worth sticking to them

(vi) Since several members took such an interest in this new type of intake, and claim that is was widely used in fact, we should note that MA 648 report says that: "The new type intake on MA.648 is expected to reduce the full throttle heights by a small amount" and that the FTH on the early serial production aircraft must be far too optimistic then.

[Friedrich-4B]

Another wall of red herring and speculation, designed to sidetrack the thread and bury the evidence under a pile of rubbish.

 

Apparently the new design of air intake wasn't fitted to either MA648 or the serial production L.F Mk. IXs, nor was BS543 a fully operational L.F. Mk. IX, while Kurfurst's claim that BS543 had a rich mixture was definitely confirmed (based on Kurfurst's speculation about how the power curve looks, and nothing else.)

 

(iii) BOTH BS 543 and BS 551 trials were repeated later ;)

 

So when will Kurfurst show us these later tests and results? To help, here is the list of tests carried out on the Mk IX, from Morgan and Shacklady:

 

 

Clearly more misinformation by Kurfurst; the trials carried out by BS543 or BS551 were not "repeated later"...the closest was BS310 by Vickers-Armstrong in December '42. ;)

 

(iv) MA 648 had a new type of S.U. carburetor, which in previous trials resulted in 1300 feet improvement in FTH.

 

No doubt Kurfurst has the results of his "previous trials" of the S.U., seeing as he also knows of other tests conducted using BS543 & 551?

 

As it was, the increases in FTH by MA648 were

200 ft. in MS gear and 800 ft. in FS gear.

 

(iv) Despite this, BS 543 had higher FTH than MA 648, even with the Bendix carburator.

 

For interest, here's an article on how the Bendix injection carb worked, and the engines it was used on.

 

back to the report, for what it's worth:

 

Owing to large variations in the performance of the four aircraft tested it is not possible to obtain an accurate value for the improvement in performance but the above quoted figures for increase in full throttle height give an average increase of about 3 mph. around the full throttle height.

 

Wow! An average increase of 3 mph because of a higher FTH (ie: about .75% difference)! (Note: this was mainly because JL165's performance was some 16 mph below-par, as is noted here.).

 

Anyway, as has been pointed out several times, but completely ignored by Kurfurst, Yo-Yo did not just model the Spitfire IX's performance figures on a few reports off the internet - they are indicative of the results he got from independent modelling and testing.

 

The Spitfire development was started by obtaining a lot of original materials including wind tunnel tests, flight tests measurements, prop (we use wooden Rotol in the model) wind tunnel tests. Wind tunnel tests both for the prop and the airframe were performed for high Mach numbers as well.

So, the parts of the FM (airframe, prop, radiators) were carefully tuned separately to get the specified parameters of the real prototypes. Then, the blower of the existed V1650-7 engine was changed to fit Merlin 66 gear ratios, the automatic shift was set to new pressure.

 

Hopefully, once DCS's Spitfire IX does come out, Kurfurst will actually buy the product and provide us with a professional, well argued summary of exactly how the Spitfire should fly and perform, preferably using the same modelling techniques and the same information that Yo-Yo uses.

 

(vi) Since several members took such an interest in this new type of intake, and claim that is was widely used in fact...

 

This was the same intake that Kurfurst adamantly claimed didn't exist as a production item, even after 16 years of "research". :smilewink:

Edited March 29, 2016 by Friedrich-4/B
Grammatical correction

[MiloMorai]

Yo-Yo, what gunsight will the Mk IX have?

[Pilum]

Since it was some time ago I modelled the Spitfire Mk9 in my C++ simulation code I reviewed it and revised my figures at bit (circa 5 mph lower speed and circa 700 ft less critical altitude than the earlier estimate in post #73) but the latest estimate in the figure below still seems to tab pretty well with the DCS Mk 9 model.

 

Concerning the accuracy of the results I can only say that I have over the course of more than 10 years modelled circa 20 different aircraft in my C++ simulation and the nice thing once you have a good model is that usually the numbers tab pretty well with the IRL median values.

 

The funny thing is that on a technological level both Allied and Axis planes seem to be close in performance and once you have the basic data like power, weight, wing area, wing span, prop diameter, prop rpm, tip speeds etc. it turns out that there are not that big differences in key performance parameters such as propeller efficiency, ram recovery etc.

 

This is why I trust the 21,000 ft critical altitude figure I get from my simulations for the Merlin 66 powered Spitfire Mk9 because this is what you would expect to see from a decently designed ram intake and I can see no reason why the Brits should botch this up? In addition, the air intake pictures presented above look reassuring since they incorporate boundary layer separation so the pressure recovery should be in line with a state of the art intake from that time.

 

Anyway, when I plug in the power/altitude characteristics of the Merlin 66 into my code I get a full throttle critical altitude of 21,000 ft and a top speed of 410 mph which looks pretty close both to the DCS values and what looks like the IRL median figures as well.

 

Of course there are always the outliers or tail end data as Yo-Yo calls them but why on earth would you want to bring those to the table since they by definition are unrepresentative? That’s a rhetorical question by the way so I’m not expecting an answer…….:music_whistling:

[Hummingbird]

Still can't understand why they didn't choose to do the Mk.XIV instead... but I guess they were afraid it would be abit too dominant :P - Unless of course it was because VEAO announced their plans for this bird beforehand.

Edited March 27, 2016 by Hummingbird

[Friedrich-4B]

BS 543 report notes:

 

The powers of the RM-9SM and the Merlin 66 engines in F.S. gear should be identical, since the high speed supercharger gear ratio is the same. It will be seen that on the climb, the performance and boost pressures were similar, within the limits of experimental error, but in level flight above the full throttle height the Merlin 66 engine was developing about 1 lb/sq.inch higher boost pressure than the 9 SM engine, with a consequent higher full throttle height and improved performance. This discrepancy must be due to variations in the manufacture of the engines and possibly of the air intakes, but it should be borne in mind that any small differences in performance of a high compression ratio supercharger or of the intake will be more noticeable at high speeds because of the increase in the dynamic head.

 

All rather meaningless, because the RM-9SM prototype was dropped in favour of the Merlin 66 because of the latter's greater efficiency.