CoD Spit Mk.I 100 oct vs. Real World Spit Mk.Ia +6 lbs

[NZtyphoon]

Originally Posted by winny

A quote from "Spitfire in combat" Dr. A. Price

'In Spring 1940, in a bid to further improve fighter performance, the RAF introduced 100 octane petrol in place of the 87 octane fuel previously used. In the case of the Merlin II and III engines fitted to Spitfires, this gave no improvement in performance at or above the engnes' full-throttle altitude of 16,500. Below that altitude however the new fuel gave a valuable increase in power. Supercharger boost could be increased from +6.5 lb to 12lb. That increased the Spitfires maximum speed by 25mph at sea level and 34 mph at 10,000 feet....

(he then goes through a list of modificatons that cost the Spitfire speed)

.....The maximum speed usually quoted for a Mk I is 362 mph @:18,500. But that figure reffered to K9787, the first production aircraft during it's initial performance tests in 1938 at an AUW of 5,819lb. By the summer of 1940 the maximum speed of a fully equipped Mark I was somewhat lower, about 350 mph at the same altitude'.

My personal opinion is that the in-game Mk I should be hitting around 350/360 mph depending on loadout @18,500 feet. It's also a shame that the same sort of info doesn't seem to exist for other types in the game.


EDIT: List of some of the modifications between K9787 and a BoB era Spit I that cost speed

73 lb's worth of pilot's armour
Bulletproof windscreen (cost around 6mph aerodynamically)
3mm armour plating for the upper fuel tank
IFF Aerials (cost another 2-3mph aerodynaically)

Total weight of above mods 335 lb.

The constant-speed propeller on N3171 made a big difference in take-off distances (225 vs 320 yards, 370 vs 490 to clear 50 ft screen) and rate of climb. N3171 was fitted with the windscreen, 3mm alloy sheet (not armour) over the fuel tank and domed canopy. Once fitted with armour and IFF the rate of climb would have gone down as would the top speed.

That aside the real problems still lie in CLOD performance below 10,000 ft using +12 lbs boost, which has not been modelled properly:


© ACE-OF-ACES INC. 2012

[ACE-OF-ACES]

Originally Posted by Redroach

with which weapon configuration(s) and with which ammo load(s) did the RL-tests take place?

A link is provided to the source of the real world test at my website, i.e.

www.flightsimtesting.com

There you will find the answer to all those questions and more.

[ACE-OF-ACES]

Originally Posted by camber

Perhaps I am not understanding the question fully,

Ok, lets see..

Originally Posted by camber

but all Spit Ia's at +6.25psi boost (full throttle) should go the same speed whether they are using 87 or 100 octane.

Agreed.. So far so good..

Originally Posted by camber

The Spit 1a 100 octane has the ability to use +12psi (using the modified boost cutout red tab)

Correct.. So far so good..

Originally Posted by camber

and go faster (provided it is below FTH for +12psi). There is an intermediate altitude range where the supercharger can give less than +12psi but more than +6 psi, above that 87 and 100 octane variants are equal.

Agreed.. That is what I was refering to when I said..

Originally Posted by ACE-OF-ACES

but isn't the real world +6 lbs. Spitfire using 87 octane? If so, shouldn't the in-game 100 octane (i.e. +12 lbs.) version be faster that the +6 lbs. below the FTH?

Originally Posted by camber

I assume your flight tests for the CoD Spit 1a 100 octane were using the +12psi boost?

Yes!

Originally Posted by camber

Did the engine blow up during tests?

Nope!

[ACE-OF-ACES]

Originally Posted by winny

The RL data for a mk I (if it's the data usually quoted, top speed 363mph) was taken from a Spitfire that was at least 300 lb lighter than a mkI in Battle of Britain trim. It was around 5,800 lb as opposed to 6,100 lb (ish). It was the eight gun version, didn't have the pilot armour, bullet proof windscreen ( reckoned to cost 3-4 mph) or the IFF aerial (again another 2-3 mph). The only reference I've seen to it is by Dr Alfred Price. He says in "Spitfire in combat" that the top speed was closer to 350 mph for a BoB era MkI. It's a bit vague, I know, but does highlight how difficult it is to get accuracy. He knows his Spits though..

On that note..

Differences in weight typically affect the ROC results much more than the TSPA results..

That is to say you may not notice a difference (percent difference would be small) in TSPA due to a little weight change, but, you will notice it in an ROC test.

[winny]

Originally Posted by NZtyphoon

The constant-speed propeller on N3171 made a big difference in take-off distances (225 vs 320 yards, 370 vs 490 to clear 50 ft screen) and rate of climb. N3171 was fitted with the windscreen, 3mm alloy sheet (not armour) over the fuel tank and domed canopy. Once fitted with armour and IFF the rate of climb would have gone down as would the top speed.

That aside the real problems still lie in CLOD performance below 10,000 ft using +12 lbs boost, which has not been modelled properly:


© ACE-OF-ACES INC. 2012

True, and when you take into account that the first production batch had a take-off run of 420 yards, there's a reduction of almost 200 yards. Rate of climb to 20,000 fell from 11 min 18 sec to 7 min 42 sec, and max speed increased by 4 mph simply from changing the prop. And yes, there seems to be a distinct lack of 'oomf' low down.

Sometimes I get the feeling that with Spitfire's there's too much information!
It's always the centre of attention. Never seen a 93 page thread on a hurricane or 109.

[ACE-OF-ACES]

Originally Posted by winny

Never seen a 93 page thread on a hurricane or 109.

Wait until I upload my 109 and 110 testing!

[Redroach]

Originally Posted by winny

The RL data for a mk I (if it's the data usually quoted, top speed 363mph) was taken from a Spitfire that was at least 300 lb lighter than a mkI in Battle of Britain trim. It was around 5,800 lb as opposed to 6,100 lb (ish). It was the eight gun version, didn't have the pilot armour, bullet proof windscreen ( reckoned to cost 3-4 mph) or the IFF aerial (again another 2-3 mph). The only reference I've seen to it is by Dr Alfred Price. He says in "Spitfire in combat" that the top speed was closer to 350 mph for a BoB era MkI. It's a bit vague, I know, but does highlight how difficult it is to get accuracy. He knows his Spits though..

okay, I just wanted to know. Thank you!

I'm still afraid of people being awful "test pilots" like those who were around at CoD Release... of that type who complained hard, over multiple forum pages, about why they can't achieve maximum rated speed at sea level (TAS was totally unknown, anyways). If the devs would have listened to that, we would be in even more trouble now.
But you guys seem to have done your "homework" resp. proper set-up and flight procedures (wind/no wind, REALLY straight and level, eliminate any yawing etc.), and then some (that website I was directed to looks really nice)!

[ACE-OF-ACES]

Originally Posted by Redroach

(that website I was directed to looks really nice)!

Thanks it is a work in progress but it is comming along! S!

[Crumpp]

It does not do any good to model an aircrafts speed, climb, and turn performance but not reproduce it's flying qualities.

You are not "simulating" anything.

[Robo.]

Originally Posted by Crumpp

It does not do any good to model an aircrafts speed, climb, and turn performance but not reproduce it's flying qualities.

You are not "simulating" anything.

But the correct speed, climb and turn performance are a good start to the ''simulation'' process, are they not?