Spitfire 1 is faster than spit 5 at low alts?

[1K3]

i saw a page somewhere that spitfire 1 with +12 boost/100 oct fuel can reach 310+ on deck, that's faster than spit 5 a deck!

[milian]

That is correct, a Spit Ia should be somewhere around 310 to 312 at +12, a Spit V would be around 303 to 305 at +12lb.  From what I gather, when production switched from the Spit I to the Spit II, there was an increase in drag.  There was an increase in drag from the Spit I to the Spit Ia with the addition of the external armored windscreen, mirror, bubble canopy, arials and other equipment.  The top speed of the Spit I is around 365 at 18 to 20kft, the Spit Ia is around 355 at alt.  The Spit II and Spit V were able to reach 372 to 375 at altitude due to improved supercharger.  But at low altitudes the Spit II and Spit V had more drag than the Spit Ia.  Spit Va, upgraded from Spit Ia suffered the same.  I don't have exact figures on engine performance, but it may be that the Merlin XII and Merlin 45 produces less horsepower than the Merlin III due to more horsepower being consumed by the larger supercharger, but this is just a guess on my part.  Later model Spit Vs were faster with +16lb boost Merlin 45/46 and +18 lb boost on the Spit LF V with the Merlin 45M, 50M and 55M engines.

oh, one other thing . . . it appears that the 372/375mph Spit II/SpitV used a 2 pitch prop, and that those Spits with the CS Rotol were only capable of 365 at altitude.

[justin_g]

Engine power for Spitfire Mk I and Mk V:

Spitfire Mk I: Merlin III @ +12lbs has 1185hp at sea level, and 1310hp at 9,000ft. At +6.5lbs power is 880hp at sea level, and 1030hp at 16,000ft.

Spitfire Mk V: Merlin 45 @ +9lbs has 1185hp at 20,000ft - and at sea level of course it would be less than this(probably about 1000hp). At +16lbs power was 1440hp iirc.

[1K3]

are u for real that spit 1 is faster than spit 5 at lo alt? also in BoB scenarios the balance of power will shift directly to spit 1 vs the 109E. spit 1 will dominate 109E in speed + climb + turn.

i always thought that spit 1 and 109 E were equal advesaries and would be sad to see it gone if balance of power shifts directly on one of these planes:(

[Knegel]

Hi,

the 12lb boost was WEP, so the Vmax of the Spit1a with 12lb booth is a theoretical value. The 12lb boot was similar dangerus for the MerlinIII like the take off power of the DB601a (1175PS), they did clear this power cause they did need it.
So in general the SpitV was the faster plane all over.

The Me109E had its combat power (920PS SL, around 990PS up to around 6000m depending to the ram effect), the 5min Power (990PS SL, around 1050PS up to around 6000m) and it has the 1min power (1100PS SL, 1175PS 2000m) .

The german Vmax values (around 460 SL, 550km/h 4500-6000m) of the 109E1/E3 are made with combat power.

If the Spit1a get the 12lb boost, the 109E would need the 1min take off power too, but AH would need to simulate a damaged engine after short time!

Greetings, Knegel

[Kurfürst]

There is nothing that surprising in that, the Spit V had "high altitude" Merlin with a bigger supercharger, which would drain more power at lower alts than the Merlin III.

As for the 109E, the yugoslavian manual for the E-3 with DB 601Aa shows 500 kph speed at SL, and 575kph at altitude. That would still fell short of the E-4/N and E-7/N, which had DB 601N engines running on 100 octane fuel for even higher outputs, but there chief merit was the improved altitude performance. They saw service from June 1940.

[Kurfürst]

... and to add, the SpitV is of course much faster than the MkI at altitude, ie. a good 600 kph vs. the 560ish speed of the BoB-era MkI with windscreen, etc.

[MiloMorai]

Originally posted by Kurfürst
There is nothing that surprising in that, the Spit V had "high altitude" Merlin with a bigger supercharger, which would drain more power at lower alts than the Merlin III.

What was bigger about the Spit V's supercharger? Spit Vs were fitted with Merlin 40 and 50 series engines, both having 2 speed, single stage superchargers just like on the earlier models of Merlin.

[Squire]

More drag, lets start with that. The 1940 Spit IAs (and later) had a "bubble canopy", a mirror, an armored windscreen, and an ariel (for the radio) as standard equipment. Radioless fighters were maybe big in Russia? I have no idea, the RAF kinda liked them.

The first Spit Vs were engine conversions from Spit IBs and Spit IAs, and the equipment was otherwise the same.

What increased drag there was from a Spit VB resulted from the 20mm cannon in the wings, where the Spit VA had no cannons.

The rest of the differences are attributed to the full throttle height differences between the Merlin III and the Merlin 45/46 series.

Also, you have to compare apples to apples. The BoB Spit I, Spit II and 1941 Spit V (early) all ran at either +9 (normal full throttle), or +12 lbs boost ( 5min wep on 100 octane). So you have to compare them that way.

There was not a big difference in the sea level speeds of the 3 types running at +12 lbs "flat out", the speed differences were minor, the biggest advantage a Spit V had was in #1 rate of climb and #2 service ceiling. Both considered important by the end of the BoB.

The Spit V Merlin 46 had the slightly larger impeller blower, compared to the Merlin 45. Both versions were @250 hp more than the Merlin IIIs, at least in 1941.

...Prop type, snow guard, armament and specific engine type would give slight differences in top speed of the various Mk Vs.

[Kurfürst]

Both M45 and M3 had single speed superchargers, not two speed ones. its evident from the perf graphs, theres no stage between boosts.

AFAIK the Merlin 45 was based on the improved Merlin XX which had a two speed supercharger they snipped off one speed and arrived with a kinda bast*rd with moderatly improved altitude performance. But, the improved supercharger is quite obvious in view of the relative altitude performance of the MkI vs V. Driving a supercharger more hard always costs some performance down low, so its a tradeoff.

[Knegel]

Originally posted by Squire
More drag, lets start with that. The 1940 Spit IAs (and later) had a "bubble canopy", a mirror, an armored windscreen, and an ariel (for the radio) as standard equipment. Radioless fighters were maybe big in Russia? I have no idea, the RAF kinda liked them.

The first Spit Vs were engine conversions from Spit IBs and Spit IAs, and the equipment was otherwise the same.

What increased drag there was from a Spit VB resulted from the 20mm cannon in the wings, where the Spit VA had no cannons.

The rest of the differences are attributed to the full throttle height differences between the Merlin III and the Merlin 45/46 series.

Also, you have to compare apples to apples. The BoB Spit I, Spit II and 1941 Spit V (early) all ran at either +9 (normal full throttle), or +12 lbs boost ( 5min wep on 100 octane). So you have to compare them that way.

There was not a big difference in the sea level speeds of the 3 types running at +12 lbs "flat out", the speed differences were minor, the biggest advantage a Spit V had was in #1 rate of climb and #2 service ceiling. Both considered important by the end of the BoB.

The Spit V Merlin 46 had the slightly larger impeller blower, compared to the Merlin 45. Both versions were @250 hp more than the Merlin IIIs, at least in 1941.

...Prop type, snow guard, armament and specific engine type would give slight differences in top speed of the various Mk Vs.

Hi,

dont ask me where was the different but somewhere i did read that the Spit1a had already less drag than the Spit2a. Weight and therefor a greater needed aoa is probably one aspect.

Afaik, the Spit1a (merlinIII) dont had a 9lb boost and the 12lb boost was a 1-3min emergency boost, not as reliable as the 12lb in the SpitV!

Greetings,  Knegel

[Squire]

+6 to +12  for a Spit IA Merlin III
+9 to +12 for a Spit IIA Merlin XII
+9 to +12 for a Spit V (1941).

5 minutes wep became "policy", the pilots were encouraged to not "overdo it" to not be too hard on the engines, so a "5 min limit" was standardised later. You could run them past that. Originally they just said "for short periods"
Spit I:

http://www.spitfireperformance.com/ap1590b.jpg

Spit II:

http://www.spitfireperformance.com/spit2pnfs3.jpg

5 min emergency boost became the norm for almost all Spits during WW2, but it was a recommendation to increase engine life, thats all.

[Crumpp]

Absolutely true Squire.  IIRC, one Spitfire ran for 45 minutes at (+25).

Pretty much standard practice for all Air Forces in WWII to endurance test the engines and to limit them for maintenance reasons.

Depending on the system used, the BMW801D2 was limited to 10-minute periods at 1.58ata/1.65ata using Erhöhte Notleistung.  However it ran for 31 hours 57 minutes on a Bench at that manifold pressure with no difficulties.

The same engine was then installed on an aircraft and flown over multiple test flights for a total additional time of 48 hours on Erhöhte Notleistung.  That is equal to running the same motor around 450 times on WEP.

FW-190 pilots in operational Geschwaders nevertheless still had to inform the maintenance crew each time they used it.  Operationally the motor was inspected after each use.

Almost exactly like the P51 manual says to do:



All the best,

Crumpp

[Angus]

Hey Crumpp.
True true. I once quoted an incident where the pilot in a tough spot had to make a run, - he ran on panic boost for some 30 minutes. The engine was opened up for checking, - completely undamaged. This was in the Med somewhere, - 1943 I think.

[Squire]

"Absolutely true Squire. IIRC, one Spitfire ran for 45 minutes at (+25)."

Thats it then, I want mine to be able to do that!!!  

Ah well, a guy can dream I guess... as I think I mentioned in another post we dont get called into the COs office in AH for burning out our powerplants, thus the "auto cutoff" feature.

Even in IL-2, where they model engine damage from over use of max power, it does not really prevent wide abuse im sure. I mean, hey, at the end of the mission you get a brand new plane, unlike RL, where the mechanics gasp at what you have done to it over 10 missions.