Spitfire prop pitch help

[reflected]

Hello,

I read throught the original pilots notes and I finally figured out how to manage the MKIIa's engine. However, I have trouble with the 2 pitch propeller of the MKIa. For landing and takeoff one has to set it to fine, otherwise it's coarse. But what about combat? What are the rpm/boost limitations?


Also, the naming is not accurate: Spitfire MKIa-s were equipped with constant speed prop from early july 1940. Still, ours have a 2 pitch one :( But then I don't understand what the difference between our MKI and MKIa is....:confused:



Thanks!

[IvanK]

Prop Pitch issues in the Spits are reasonably complicated the Devs are aware.

MKI in game is fitted with DH 2 Pitch prop correct visually and in game .... correct

MKIA is fitted with 2 pitch prop however 3D model shows ROTOL CS unit. ... Wrong
It should be fitted with DH CS prop. So same visual model as MKI but with CS operation.
In reality most MKI units were modified in the field from DH 2 pitch to a CS operation using a conversion kit so the visual appearance was the same as the 2 speed unit.


MKII is fitted with ROTOL CS unit and visual model and in game model ... Correct

Combat on 2 pitch prop ... I would go full fine but be careful with RPM limits. consider 3000 the max so if IAS increasing and RPM edging over 3000 then pull off Boost.

[Viper2000]

Technically AFAIK there was no real difference between the Mark I and the Mark Ia; the Ia nomenclature was applied retrospectively to avoid confusion with the small production batch of cannon-armed Mark Ib aircraft; thereafter the "a" wing was the first generation 8 Browning gun wing.

It's probably fair enough to use the Ia nomenclature to denote CS prop mod state, because by the time the Ib arrived and forced the invention of the Ia designation, most aircraft had probably been converted. However, I don't believe that the designation Ia would have represented any kind of guarantee that the prop was CS.

The Pilot's Notes issued with the CE lump all Spitfire I aircraft together, and include information about the cannon as well as information about both the Rotol and Dh propellers (which it implies are both CS). However, there are issues with these notes; the picture on the front shows an aeroplane fitted with a 5 bladed prop and an e wing. The internals of the Notes appear more authentic, but are dated May 1940, Revised December 1941 for section 1, and January 1942 for section 2.

The engine ratings in the notes are not entirely consistent.
On page F.S/3.:
ALL OUT
5 MINS LIMIT 3000 rpm | +6 1/4 | 120ºC coolant | 95ºC oil.
(reformatted for clarity due to board limitations)

However, on the next page, we have:


(v) The following limitations must also be observed:
At +6 1/4 lb/sq.in boost: Minimum r.p.m. 2,080

Diving: Maximum boostc +6 1/4 lb/sq.in.
Maximum r.p.m. 3,b00

3,000 r.p~m. may be exceeded only for
20 seconds with the throttle not less than
one third open
[...]
(vii) Combat concessions:
(a) When using 100 octane fuel, +12 lb./sq/in.
boost, obtained by operating the boost control
cut-out, may be used for short periods.
(b) Maximum r.p~m. below 20,000 feet (1/2 hr.limit):
2850'
Maximum r.p.m. above 20,000 feet (1/2 hr., limit):
3,000
Use of these concessions must be reported upon
landing and an entry made in the engine log book.
(Reproduced, complete with typographical errors; I assume that 3,b00 is supposed to be 3,600...)

It therefore isn't immediately clear what the real limits were intended to be, and the picture is doubtless clouded by the fact that the Mark I was hardly a first line aeroplane by 1942. Therefore, I suspect that the ratings may well have been reduced for use by second line units where life and reliability were more important than absolute performance.

In the sim as it presently stands, I would advise trying to keep the rpm close to 2600 if possible, and boost of +4 or less, since the Merlin seems very fragile (5 minutes or so at +8, which is the most I've managed to extract from a Spitfire) almost always causes an exhaust header failure, which is rather harsh. (High power running in the Hurricane isn't really a good idea at all given the questionable labelling of the mixture control.)

However, brief overspeeding of the engine shouldn't be a problem provided that the engine is driving the prop and not vice versa (hence the minimum throttle requirement). I believe that the limiting problem was the bearings, but I don't have the right books with me at the moment.

I have been rather perturbed by the erratic rpm indications; I hope and assume that this is just intended to represent instrument error (though I can't understand why the rpm should fluctuate so extremely); if it isn't then obviously there is a risk of accidental overspeed even when the mean rpm is considerably below the limit.

As for the Mark II, notes are available online:

http://www.zenoswarbirdvideos.com/Images/spit/Spit2Manual.pdf

They appear to be authentic, though it's hard to tell whether or not they have been revised. It is worth pointing out the Maximum continuous rpm of 2650, which is common to all other Merlins that I know of. I was therefore quite surprised that the Spitfire I notes quote 2600 rpm as the maximum continuous limit. Perhaps at some point next week I will be able to lay my hands on some other references in order to ascertain whether or not this was another typographical error...

[reflected]

Thanks for the info.

So the only difference now between the MKI and MKIa is a different animation?

I hope they'll fix it, and not by changing the animation but giving the MKIa a real CS prop.

[Sutts]

(Reproduced, complete with typographical errors; I assume that 3,b00 is supposed to be 3,600...)



I very much doubt they meant 3600 there. I'd say it's just a typo for 3000.

[reflected]

I very much doubt they meant 3600 there. I'd say it's just a typo for 3000.

No, it really is 3,600. Only for 20 seconds though. See here:

http://www.scribd.com/doc/4598146/Pilots-Notes-Supermarine-Spitfire-Mk-IIA-IIB-Merlin-XII-Engine

(looks like we don't have enough boost in our Spit? It talks about +9 for climbing, we only have +7! )

[Sutts]

No, it really is 3,600. Only for 20 seconds though. See here:

http://www.scribd.com/doc/4598146/Pilots-Notes-Supermarine-Spitfire-Mk-IIA-IIB-Merlin-XII-Engine

(looks like we don't have enough boost in our Spit? It talks about +9 for climbing, we only have +7! )

Thanks for that...I've learnt something.