Analysis of real life 109E performance for CloD

[Crumpp]

Spit Ia

FTH = 16500 ft
at 6.25psi, 2750rpm (rad open) engine fails after about 3 minutes. Just enough time to get stable 245mph IAS (with 3000rpm couldn't get this alt without engine death)

245mph IAS@16500ft = 323mph TAS = 520 kmh TAS

Oh dear, this is under even B6 plot speed (560kmh TAS at 16500ft).

What data are you looking at camber?

If it is this:

http://www.spitfireperformance.com/n3171.html

Then you are not at the same engine settings as this data. This data is 6.5lbs @ 3000 rpm at 16,500 feet.

Unfortunately we only have the one airplane and not Supermarines mean with a percentage variation.

If you look at this test:

Aeroplane and Armament Experimental Establishment
Boscombe Down
30 July 1940
Comparison of Performance of Rotol and DH Airscrews on Spitfire


Both the aircraft are similar externally and are fitted with bullet proof windscreen and armour plating over the tank, etc.

Aircraft R6774 is fitted with DH airscrew and N3171 with Rotol airscrew.

It will be noted that these aircraft are about 12 miles an hour down in speed against the previously tested K9793, but the relative comparison remains. This loss in speed is accounted for, by 6 miles an hour for the bullet proof windscreen and 6 miles an hour due to loss in engine power.

Level Speed miles per hour.


Aeroplane Altitude Feet


14000 16000 Max. speed 20000 22000
R6774 342 349 355 @ 17,800' 350 341
N3171 336 343 354 @ 18,900' 354 352



--------------------------------------------------------------------------------


The above tests were all carried out using 87 octane fuel with boost limited to +6.25 lbs./sq.in. Climb figures were achieved using the 2600 rpm 1/2 hour climb limit. By the Battle of Britain all operational squadrons had changed over to 100 octane fuel and the engine limits on the Spitfires had been increased to +12 lbs./sq.in. 3,000 rpm with 1/2 hour climb limit increased to 2850 - 3000 rpm. Royal Aircraft Establishment figures for a Spitfire I using +12 lbs/sq. in. boost are 314 mph at Sea Level and 359 mph at a full throttle height of 11,500 feet.

We don't have the entire report but we do have the poster's comments at the bottom. Throwing those out the window we get a little closer to our 2750 rpm.

BTW, running a propeller at a higher rpm on a hot day at high altitude does not mean the airplane will go faster. Usually it will go slower than it will at a lower rpm.

On that report, the data is only between 7% to 5% off from the reported figures at the lower rpm. We don't know the weights, so the data could be spot on or it might be off.

In order to make a definative statement we need:

1. Atmospheric conditions
2. Speed at same engine settings
3. weights of the aircraft

[camber]

Originally Posted by Crumpp

What data are you looking at camber?

The B6 data was that posted by B6 (1c representative) about the post-beta patch CloD performance in this thread (i.e. sim not historical data):

http://forum.1cpublishing.eu/showthread.php?t=31450

Originally Posted by Crumpp

If it is this:

http://www.spitfireperformance.com/n3171.html

Then you are not at the same engine settings as this data. This data is 6.5lbs @ 3000 rpm at 16,500 feet.

Agreed on the rpm. However the boost in the posted link for N3171 is stated as +6 1/4 psi nominal, and during the top speed test table it is listed as +6.1psi at 16500ft. The CloD Merlin failed within minutes at rpm> 2700 and FTH, and max available boost at or just below FTH is +6.2psi for the SpitI (and Spit II). So 2700rpm, +6.2psi was tested as CloD max practical height performance(BTW 3000rpm at same boost did not indicate any speed increase in the moments before the engine failed, rad open)

Originally Posted by Crumpp

On that report, the data is only between 7% to 5% off from the reported figures at the lower rpm. We don't know the weights, so the data could be spot on or it might be off.

In order to make a definative statement we need:

1. Atmospheric conditions
2. Speed at same engine settings
3. weights of the aircraft

I think an interesting issue is the difference in TAS we have calculated, me using a rather simple thumb rule (TAS = IAS + 2% increase per 1000ft), you with a more rigorous approach. Eg for Hurricane:

Rotol Hurri = 235mph IAS@15500 ft

My calculation (2% rough rule) gives 305mph TAS, your calc gives 286mph. Thanks for providing a more rigorous calculation.

I actually hadn't checked whether how the Hurri compares at height to the B6 data and RAE Hurri tests, I just did a quick offline Hurri sim test in response to a question from Kwiatek...sounds like from your analysis it is not too bad. Earlier I was referring to the Spit and 109 data which (for Spits) showed TAS at FTH being too low for both the B6 data (hence what 1c intended the patch to allow) and historical RAE tests. The 109 is pretty good at height according to my 2% rule calc (i.e about the average Messerchmitt guaranteed spec). It might drop under with your calc method, I guess an important consideration is what are the equations in the simulation of how IAS and TAS relate.

Cheers, camber

P.S I should note my IAS speeds at height are from offline, and Snapper has noted some oddities and discrepencies for the SpitII between online and offline

[Crumpp]

equations in the simulation

The equations in the sim should be the same.

The CloD Merlin failed within minutes at rpm> 2700 and FTH

What were your other settings? Radiators and how did you treat the engine before hand?

What rating did you climb and did you allow the temperature to recover after climbing?

Climbing is the hardest thing you do to an airplane engine.

Except that Full throttle = 3000 rpm and 6.25lb boost:

285 mph at 2700 vs 315mph at 3000rpm....

Do you understand the conversation Seadog? I really don't think so but rather feel the need to comment because you somehow believe I am a threat to your favorite gameshape.

My suggestion would be to learn about how aircraft perform and put your pointy tin foil hat aside.

[Seadog]

Originally Posted by Crumpp

285 mph at 2700 vs 315mph at 3000rpm....

Do you understand the conversation Seadog? I really don't think so but rather feel the need to comment because you somehow believe I am a threat to your favorite gameshape.

My suggestion would be to learn about how aircraft perform and put your pointy tin foil hat aside.

A) the poster made a point of stating that higher RPM led to engine failure, but this was the rated RPM for full power and this needs to be addressed for the game to properly simulate Merlin III engined aircraft.

B) Boost at height is related to engine RPM and there's no way that 2700 rpm at an altitude/pressure altitude of more that 16500 ft would permit 6.25lb boost to be attained - another flaw in the simulation. I am rather shocked that you don't know that.

Maybe you should have considered these points.

I know you admire the RR Merlin very much but you need a better understanding of it's capabilities.

[camber]

Originally Posted by Crumpp

The equations in the sim should be the same.

One certainly might hope so but perhaps not count on it

Originally Posted by Crumpp

What were your other settings? Radiators and how did you treat the engine before hand?

Radiators fully open, I polished the engine and swapped the rubber hoses for braided stainless steel

Originally Posted by Crumpp

What rating did you climb and did you allow the temperature to recover after climbing?

Climbing is the hardest thing you do to an airplane engine.

Climbed from sea level to FTH at 140mph IAS, full throttle, 6.2psi, 2700rpm. Full fuel and normal ammunition load. FTH@2700rpm detected via onset of boost drop from 6.2psi. Aircraft allowed to settle at close as possible to FTH@2700rpm and 0 fpm. Speed taken from guage in no cockpit view.

Your point is correct that cooling the engine (e.g by throttling back at FTH to give say 150mph IAS for a while, then accellerating to maximum speed) might make it possible to stay on 3000rpm for longer without engine failure. But 2700rpm to 3000 rpm at FTH gave no hint of speed increase prior to the engine failure.


Cheers, camber

[Robo.]

Originally Posted by Crumpp

285 mph at 2700 vs 315mph at 3000rpm....

My suggestion would be to learn about how aircraft perform and put your pointy tin foil hat aside.

Crumpp please have a go yourself, I am looking forward for your tests at FTH at full power.

[Crumpp]

Climbed from sea level to FTH at 140mph IAS, full throttle, 6.2psi, 2700rpm

That looks like a problem. According to the Operating Notes, Vy for the Spitfire Mk I is 185mph ASI below 12,000 feet, 179 mph ASI to 15,000 feet, and 169 mph ASI to 20,000 feet.

Climbing at such a reduced airspeed will limit the cooling of the engine at a very high manifold pressure and rpm.

If your oil temperature and coolant temperatures are high, you won't last as long at any overboosted condition.

Try climbing at the faster speed. You should get to altitude quicker and have a cooler engine.

But 2700rpm to 3000 rpm at FTH gave no hint of speed increase prior to the engine failure.

In reality it won't either so that actually sounds realistic. In fact, on a summer day, the aircraft will slow down instead of speeding up. That is why I was saying many folks will be mad if they realistically model density altitude effects.

Once the propeller tips begin to approach their mach limits, the ability of the propeller to make thrust diminishes. So you get less thrust the faster your propeller turns at high density altitudes.

[camber]

Originally Posted by Crumpp

That looks like a problem. According to the Operating Notes, Vy for the Spitfire Mk I is 185mph ASI below 12,000 feet, 179 mph ASI to 15,000 feet, and 169 mph ASI to 20,000 feet.

Climbing at such a reduced airspeed will limit the cooling of the engine at a very high manifold pressure and rpm.

If your oil temperature and coolant temperatures are high, you won't last as long at any overboosted condition.

Try climbing at the faster speed. You should get to altitude quicker and have a cooler engine.

True for a real MkI, but remember we are talking about a CloD Spitfire with modelling issues.

I tried climbing at 170mph IAS to 16500ft, +6.2psi 2700 rpm
Oil temp at 16500 feet 93'C, coolant 107'C
Itunes playlist: Kim Wilde 1980's pop diva
Throttle back to +2psi 5 mins for cooling, Oil 91'C, coolant 100'C
Then 3000rpm +6.2psi for max speed test.
Itunes Song: Kim Wilde "Kids in America"

What do you get under similar conditions? I don't want to give away all the flight tests, we need to encourage a cadre of high alt flight testers for CloD to get some data variability

Cheers, camber

[Crumpp]

we need to encourage a cadre of high alt flight testers

When am I supposed to fit that in?

[fruitbat]

Originally Posted by camber

True for a real MkI, but remember we are talking about a CloD Spitfire with modelling issues.

I tried climbing at 170mph IAS to 16500ft, +6.2psi 2700 rpm
Oil temp at 16500 feet 93'C, coolant 107'C
Itunes playlist: Kim Wilde 1980's pop diva
Throttle back to +2psi 5 mins for cooling, Oil 91'C, coolant 100'C
Then 3000rpm +6.2psi for max speed test.
Itunes Song: Kim Wilde "Kids in America"

What do you get under similar conditions? I don't want to give away all the flight tests, we need to encourage a cadre of high alt flight testers for CloD to get some data variability

Cheers, camber

Camber I see your problem.

Its a well known fact you will climb better with Elton John - Rocket Man.

Of course, you will bleed from your ears.....