Author Topic: Spifire Performance Questions (Read 891 times)

Nashwan · « **on:** June 04, 2000, 01:42:00 PM »

I've been looking at the test reports on the Spitfire IX at http://www.fourthfightergroup.com/eagles/spittest.html and comparing them with the figures Ruy Horta posted. It's left me with more questions than answers.
1. Someone (pongo?) has claimed on several occasions the AH IX is too fast, by approx 10mph. Could this be accounted for by the extra boost (18 rather than 15lb), or can't maximum boost be used at higher alts?
2. Is the usually quoted 408mph speed for the Spit based on a plane running 15lb boost? The test at fourthfightergoup was carried out before the evaluation against the 190, although in a different plane. If 18lb boost had been available earlier, wouldn't they have at least noted in the test vs the 190 that the Spit was down on power?
Basically what I am asking is have HTC got it right after all, and the Spit is supposed to do more than 408?

juzz · « **Reply #1 on:** June 05, 2000, 02:25:00 AM »

Basically; the Spitfire F Mk IX is not supposed to do more than 408mph. The highest speed I have ever seen quoted for a Mk IX was for a prototype HF(BS551): 415.5mph at 27,800ft.

Btw: IMO the AFDU Fw 190A-3 vs Spitfire Mk V/IX test is a bad source for performance figures of those planes, since none of the planes were performing at full capacity.

Citabria · « **Reply #2 on:** June 05, 2000, 03:22:00 AM »

It is suspicious that the spitfire IX still does not have climb and speed data for the AH web page.

I suspect the AH spit F IX is powered by a merlin 63 or 63a since it represents a late war mk F IX with e type armament

im sure its not a spit IX LF with a merlin 66 either though, since our spit IX tops out its max speed at high altitude while the LF IX supercharger is tuned for low alt.

however the merlins 45,60,61,63,66,70 were all the same engine with different blower configurations and altitude ratings from what i have read so im more confused now than when i first read into it.

but i think a spit LF IX (unofficially known as spit IXB)would be an excellent varient to add to the sim as it is a low alt fighter (22k top speed then coughs) and over 4000 LF IX w merlin 66 were built while 1200 F IX (unofficially Spit IXA)were built w 61, 63, 63a engine setup.

also it seems that the fuel octain was only a factor in permitting higher boost settings for short periods: ie 25lb bvoost for 5 min w a spit lf ix to get a speed of 360mph at sea level however alt performance was not spectacular in the test.

LF IX w 25lb 5 min boost will make the spitfire a little more competitive at lower altitudes with the likes of a yak9, la5, n1k2 fw190 and other low alt birds.(i know scary thought of being outrun and out turned by a spitfire)

[This message has been edited by Citabria (edited 06-05-2000).]

Pongo · « **Reply #3 on:** June 05, 2000, 08:51:00 AM »

If I ever claimed the spit was too fast I was talking out of my...
I dont know how fast it was supposed to be.
In my experiace in the game my FW is a bit faster then the spit IX at mid to low alt.
I thought that was accurate.

------------------
"Stupids are like flies. they are everywere, but are easy to kill"
RAM

Vermillion · « **Reply #4 on:** June 05, 2000, 10:13:00 AM »

Nashwan, it was probably Me (or maybe Juzz).

I haven't tested the Spit IX in 1.02, but in previous versions the Spit IX in AH could do between 420-425mph TAS at around 27,000ft and maintain that up to about 32,000ft, before its speed began to fall off.

I have never done the climb tests for this plane.

Now supposedly, we have the standard F model Spit IX. And most of the data I have seen for F models, is the same as the data from the 4th FG website link you posted. In other words 405 mph (+ or - 5 mph) at 27,000ft.

No clue on what boost settings were used in the tests, but I would be suprised if more than a single test quoted a top speed from an aircraft that wasn't using max throttle settings.

The arguement isn't just that it is too fast, but that it maintains that speed thru too high an altitude range.

The only tests or data from Spit IX's that I have seen that exceeded that 405mph (+- 5mph) were HF models (which does about 420 at 28,000ft), and or high octane fuel or other special variants.

But I am far from a Spitfire expert, and I am only recounting what I have learned from others.

------------------
Vermillion
**MOL**, Men of Leisure
"Real Men fly Radials, Nancy Boys fly Spitfires"

funked · « **Reply #5 on:** June 05, 2000, 11:09:00 AM »

I just tested it at 28,000 and I get 420 mph with WEP on. The AFDU data (on MW's page) show 409 mph at this altitude. This is above the critical altitude so I don't think the boost limit would apply. I think we know why Pyro doesn't have the Spit IX chart up. Or else we have a later model, or else the boost limit is more important than I think.

[This message has been edited by funked (edited 06-05-2000).]

wells · « **Reply #6 on:** June 05, 2000, 11:51:00 AM »

Interesting that the LF IX with 150 octane fuel couldn't break 400 mph, while the other LF IX's were able to (without 150 octane?). While the critical height for 25 lbs boost would be lower, the Merlin 66 should put out the same power at 20k as with 100 octane.

jmccaul · « **Reply #7 on:** June 05, 2000, 01:36:00 PM »

Here some operating data for the merlin 61,63, 66 and 70

jmccaul · « **Reply #8 on:** June 05, 2000, 01:41:00 PM »

I've also got another page from this manual which talks abotu having a similar system to the 190 where rpm and MAP aren't set seperatly but controlled with just the throttle (it doesn't say this excplicitly so i may have completly mis-inturpreted the text). They call it "interconnected throttle and proppellor controls".

It is in the spit 9,11 and 16 and unfortunatly doesn't specify which aircraft were fitted with this.

Nashwan · « **Reply #9 on:** June 05, 2000, 01:58:00 PM »

The reason I now doubt the 408mph figure is because of a quote from Jeffery Quill regarding Spitfire testing. It's on the Fourth Fighter Group page.
"As time went on Boscombe Down came increasingly to accept the firms figures, making only spot checks themselves, in order to save wear and tear on the prototypes. In other words Boscombe Down provided the offical seal of approval, though many of the performance figures quoted in their reports were in fact measured by Supermarine's experimental flight test unit at Worthy Point, later at Hight Point. The A and AEE made their own judgements on the aircraft's handling and other qualities."
If this is the case, and the figures come from an early production model, then it is perfectly possible that +18lb boost was not cleared at that time, and all performance figures were taken at +15. That would explain why it was not noted that the Spit was running below power in the test v the Fw190.
The performance figures for the SPit are quoted from a test dated April 42, well before the introduction of the Spit, and before the combat trial against the 190.
What I don't know, and what I hoped someone could give me a definitive answer on, is wether the higher boost would increase performance at altitudde, because as has been pointed out, +25lb boost doesn't seem to increase speed at altitude.
Pongo, looks like it was Vermillion that commented on the top speed being to high. Sorry but my memory isn't what it should be.

juzz · « **Reply #10 on:** June 05, 2000, 10:49:00 PM »

Me too! Me too!

The (new) highest speed I have seen for a Mk IX with a Merlin 61 is 417mph at 28,800ft. The plane was R6700(Mk I conv.), during propellor trials in April '42. At 35,000ft speed was 404mph. Another Spitfire Mk IX, BS310 recorded 413mph at 28,000ft during engine comparison trials in Oct '43.

Trust me, the Spitfire Mk IX is too fast.

The LF Mk IX with 150 octane fuel certainly did break 400mph. JL165 was a Mk V converted to LF Mk IX(Merlin 66). A comparison was made with BS543, also a Mk V converted to LF Mk IX.

At +18lbs boost. JL165 BS543
Max climb, radiators open.
MS gear......... 4200 4700
FS gear......... 3500 3850
Max level speed, radiators shut.
MS gear......... 364 384
FS gear......... 388 407

At +25lbs boost. JL165
Max climb, radiators shut.
FS gear......... 5100
Max level speed, radiators shut.
MS gear......... 374
FS gear......... 409

Unfortunately no altitudes are given. BUT:

JF275, a Mk VIII(Merlin 66). +25lbs boost.

362mph at sea level.
MS gear 374mph at 2,800ft.
FS gear 409mph at 14,000ft.
5,580fpm at sea level.
FS gear 5,100fpm at 11,000ft.

Now thar be an uberspit!

Interconnected propellor and throttle controls were used with the Merlin 66 afaik.

[This message has been edited by juzz (edited 06-05-2000).]