Author Topic: SpitfireV speed at +12lbs. (Read 5079 times)

gwshaw · « **Reply #60 on:** February 21, 2004, 09:26:15 AM »

Gripen,

I have read the same thing, and I did mention the larger carb on the Merlin. But I don't see that being responsible for 4250 ft or 4550 ft of additional alitude vs the F3R.

Another data point on the Merlin II/III: the Fairey Battle had a full throttle height of 13,000 ft @ 241 mph or 15,000 ft @ 250 mph depending on what source I look at. That is 1250 or 3250 ft below the rated altitude for the engine.

Since you have "Vees", take a look at the Merlin/Allison comparisons on page 322 and 329.

Compare the Merlin XX and the V-1650-1 on page 322. Yes, the 1650-1 had a smaller carb, but the Merlin XX figures are considerably more MAP, at a much higher altitude, but lower power.

Same blower setup, but note the different figures:

Merlin XX low - 1260 hp @ 12,250 ft & 58.6 in Hg
V-1650-1 low - 1385 hp @ 8000 ft & 54.3 in Hg

Merlin XX high - 1175 hp @ 21,000 ft & 62.6 in Hg
V-1650-1 high - 1250 hp @ 15,600 ft & 54.3 in Hg

The same manifold pressure will always put out more power the higher the altitude due to the lower temps. Higher MAP & higher altitude should be putting out much HIGHER power than the Packard, not lower.

Something on the order 1520 hp @ 12,250 ft in low blower after taking both temperature and increased MAP into account. Hi blower should be somewhere around 1470 hp @ 21,000 ft, not 1175.

Packard figures are flaky, note the next page gives values of 1235 hp @ 12,000 ft and 1130 hp @ 19,000. Unfortunately it doesn't give MAP, it just says mil power.

Next, take a look at page 329 and compare the Merlin 61 and the V-1650-3.

First off, the Merlin 61 figures look too high for +15 psi (60.5 in Hg) boost. They look more like +18 psi (66.6 in Hg).

Despite having a smaller blower diameter, 11.5 in vs 12.0 in, the Merlin 61 has a slightly higher low blower rated altitude than the V-1650-3, 12,000 ft vs 11,800 ft. That may just be the difference between 60.5 in Hg and 61 in Hg, I haven't crunched the numbers. But again, it puts out 40 less hp at 12,000 ft than the V-1650-3 puts out at 11,800 ft.

More importantly, look at high blower for both engines. In this case the Merlin 61 puts out 40 more hp, 1000 ft higher despite having both a smaller blower diameter and a lower blower gear ratio, 8.03:1 vs 8.095:1.

As I said earlier, I'm not sure what is going on with the RR engines, but they are frustratingly inconsistent compared to the US engines that I am sure are unrammed. I have been doing some simple calculations on them and ram seems to be the most consistent explanation.

Greg Shaw

gripen · « **Reply #61 on:** February 21, 2004, 03:53:29 PM »

HoHun,
Check the AA.878 test results. In the climb test (3000rpm) you can see that at the unrammed +9 lbs FTH (16000ft) tested plane could still do +9,8 lbs (FTH being about 17000ft with RAM, speed around 200mph TAS) and in the speed test it could do +12,7 lbs at 16k (FTH being 19900ft with RAM, speed about 360mph). These all are logical ie with RAM the FTHs were higher than unrammed FTH for +9lbs.

Then check +16 lbs FTHs. In the speed test the result is again logical ie rammed FTH is about 2000ft (or over 3000ft) higher than unrammed FTH 11000ft (or 9250ft depending on source). But in the climb test the rammed FTH is only 8800ft ie 2200 (or 500ft) lower than unrammed FTH. Note that in the case of the W.3228 (Merlin 50M +18 lbs) reached FTHs in climb and speed tests are higher than unrammed FTH (2750ft).

gshaw,
There can be many reasons why the FTHs tend to vary in the tests (filters, ice guards, poorly designed intake, bad example in the test, measuring errors, maybe too small intake for given MAP and so on). But if you look for example those A&AEE results in mw's pages you can see that in the vast majority of the cases the FTHs are far higher than unrammed FTH. And if you compare rammed FTHs between Mustang I (V-1710) and various Spitfires (Merlin) in those tests, you can again see that there really is notable difference in altitude performance and ability utilize RAM air; that is exactly the phenomena Whitney writes about. Of course you can pick up just one or two tests which happen to support you but that is not a very constructive way to analyze engines.

As usual there are errors in the books and those values for the merlin XX in the p.322 are wrong. The Merlin XX was rated by RR (source RR spec sheet):

1485hp/3000rpm/ 6000ft/+14 lbs (M.S.)
1490hp/3000rpm/12500ft/+16lbs (F.S.)

The Merlin 61 was never qualified for the +18 lbs boost (some tests were made) and overall it was a strange animal among two stage Merlins. Probably the efficiency of the Merlin 61 just peaked around the FTH while the V-1650-3 was a real high altitude engine which worked well above FTH. The Merlin Mustangs usually reached top speed well above FTH.

gripen

niklas · « **Reply #62 on:** February 22, 2004, 03:08:40 AM »

Just to add something to the V-1710. A very detailed german technical report about the C-15 often mentions that the production of this engine resembles to the car industry. That means, for production output and not for weight or other special requirements of an high performance aircraft engine.

Many parts, after being forged or casted, were left this way without fine finishing.

For example in the diffusor part of the charger, the air guiding channels were barely worked on (left rough).
Furthermore there spirale of the charger had a perpendicular connection to the outlet, which is also particular bad for an air flow.

The report mentions some data for th 1710-C15

1,345ata @ 4030m (military)
adiabatic pressure height H_ad: 6500m
charger wheel outer diameter: 160mm
v charger (outerdiameter): 331m/sek
adiabatic efficiency: q = (H_ad * g)/(v^2) = 0.582

niklas

VooDoo · « **Reply #63 on:** February 22, 2004, 06:53:01 AM »

Question about Spitfire Performance Testing site. Does it just down for now or Mike decided to move it to another place or he decided to shut it down from public ?

mw · « **Reply #64 on:** February 22, 2004, 08:46:33 AM »

Hi VooDoo: I've had some security problems that need to be resolved. Its down until I sort things out.

Angus · « **Reply #65 on:** February 22, 2004, 09:01:24 AM »

In what aircraft were these Allison engines used?
After all, wasn't the P38 the only Allison powered aircraft that performed well at altitudes over 15K?
Would really love to know more of the Allisons really.

gwshaw · « **Reply #66 on:** February 22, 2004, 09:39:23 AM »

Quote

Originally posted by Angus
In what aircraft were these Allison engines used?
After all, wasn't the P38 the only Allison powered aircraft that performed well at altitudes over 15K?
Would really love to know more of the Allisons really.

The C15 was primarily used in the early P-40 variants. It was never really fully developed, since the E/F series was the main emphasis. A little over 2500 built between Feb '40 and Aug '41. It remained in production long after the much superior F3R entered production in Jan '41, probably for UK use.

The P-38 had a separate turbo-supercharger that effectively provided SL+ pressure at the carburetor inlet up to the turbo's critical altitude, about 25,000 ft.

So the P-38 engines only had to provide boost over SL+ pressure. ie if the desired pressure was 45 in Hg they only had to provide a pressure ratio of about 1.5:1 regardless of altitude. Non turbo-supercharged engines had to provide a pressure ratio of about 2.7:1 to provide 45 in Hg at 15,000 ft, or about 4.1:1 to get 45 in Hg @ 25,000 ft.

Greg Shaw

gwshaw · « **Reply #67 on:** February 22, 2004, 12:10:10 PM »

Quote

Originally posted by niklas

1,345ata @ 4030m (military)
adiabatic pressure height H_ad: 6500m
charger wheel outer diameter: 160mm
v charger (outerdiameter): 331m/sek
adiabatic efficiency: q = (H_ad * g)/(v^2) = 0.582

niklas

Interesting, both the 1.345 ata @ 4030 m and the 6500 m adiabatic pressure height work out to a bit over 2.2:1 pressure ratio, pretty damn close to what I have calculated from "Vees for Victory."

Adiabatic efficiency formula is great, I'll have to add that to my collection.

q = (6500 * 9.8066)/(331 ^ 2) = .5818

I'll have to start doing some comparisons on other engines.

Greg Shaw

justin_g · « **Reply #68 on:** March 01, 2004, 12:15:32 PM »

You guys might find this stuff interesting

head on over to http://naca.larc.nasa.gov/ and search for "supercharger".