[klem]

ggrrrrr, typed this all out once and then hit some keyboard combo that closed the tab

Anyway thanks for the reply.

Originally Posted by Robo.

Hi klem, I am perfectly aware of the propeller developement for early Merlin engines (and happy a2a flyer ), but I believe this was only the case with our Spitfire, not the Hurricane. Although sharing the same engine (Merlin III), the Spitfire Mk.I featuring DH propeller had this 'bicycle pump' prop pitch lever that made finding the RPM sweet spots between full coarse and full fine possible. The Hurricane Mk.I though had slightly different PP controls (lever instead of pump) and it seems the trick was not possible to fiddle with it. At least there is no evidence whatsoever that Hurri could go semi-CSP with a DH airscrew.

I must admit that I assumed the Hurricane lever would allow pitch tuning as I expected the lever to be easier to use than the plunger. I searched the web a loooong time and cannot found mention of it's use in the Hurricane
Anyway my advice to Graveyard Jimmy remains the same, ignore the DH5-20 until you're used to the Rotol then maybe try the more awkward DH5-20.

btw, my Spitfire info came from:
http://www.spitfireperformance.com/spit1vrs109e.html
"The Spitfire I Pilots Notes (A.P.1565A) states:
Airscrew control.- This aeroplane may be fitted with one of the following airscrew controls: (a) de Havilland two position (b) de Havilland constant speed, or (c) Rotol (35°) constant speed. If constant speed control is fitted the r.p.m. can be adjusted to remain as desired, but within the limits allowed by the airscrew pitch range. If the two position control is fitted on this aeroplane it can also be operated to give various airscrew pitch settings between fine and coarse; this is obtained by slowly moving the control between its range of movement until the desired r.p.m. are obtained. For example, if a full power climb is required, instead of pushing the control into fully coarse pitch as the r.p.m. rise after taking-off, the control should be moved slowly forward until the r.p.m. drop to the maximum permissible for climb (2,600) and then pulled slightly back; this will leave the airscrew pitch at the position which gives these r.p.m. until power begins to drop off with altitude. As the power drops off the r.p.m. can be maintained by again fining the airscrew pitch as required. This in effect will give a similar improvement in performance to that obtained by means of a constant speed airscrew. The operation of varying the airscrew pitch in this manner to suit different conditions of flight will be found quite simple after a little experiment."

That's why I tend to believe that DH props as such are modelled OK for both Spit and Hurri - if you remember, Spit used to be wrong prior to the last patch, they fixed that because we reported this issue and backed it up with evidence (merlin in perspective, Spit Mk.I manuals etc.)

The last patch put the Rotol onto the Spifire MkIa, it's not the DH5-20 anymore. The MkI is and is definitely wrong because it 'flips' pitch settings.

At this moment, the gain is only 0.02lbs. That is as per data someone pulled out of FM files apparently. It helps a little bit but you will overheat and you can blow your engine quicker than you say 'messerschmitt'.
........
The plug was there from the day one, but it's function was not WEP (that came in later) but simply what it said - overriding the boost control in case of a failure of the BC. No modification was needed for 100 octane fuel as such afik, the holes drilled were simply to use the existing BCC-O system as emergency power later on. What they did was look we can bypass that thing but we need to limit it to 12lbs because that's about as much as this Merlin can take. So they did. The limit was still 12lbs for either 6.25lbs rated Merlin III or for 9lbs rated Merlin XII (Mk.II Spit).

As you say, no plug needs to be pulled to get the 6.25lbs from Merlin III as that was it's nominal rating.
Normal full throttle MP was 6.25lbs, plug pulled MP was 12lbs - only possible with 100 octane fuel, hope that made sense

Agreed.

Normal full throttle MP was +6.25lbs (that's correct), plug pulled MP was +12lbs - only possible with 100 octane fuel.

The 2600rpm figure is probably on the conservative side even for RL, you can do 2850 with Rotol Hurricane in game with no problem and Merlin could take that in RL, too when necessary.

Full rating for Merlin III with 87 octanes was indeed lower e.g. 4lbs @ 2600rpm for climb ('30) vs. 6.25lbs @ 2600rpm for 100 octane powered one. The 6.25lbs @ 2600rpm combination is mentioned in some sources but that was the early non-CSP variant I suppose as 2600rpm is what you get with DH prop set at fine pitch at optimal climbing speed (called High power climb in manual). The only difference between 87 and 100 octane variants would be Boost, not RPM, obviously

With 100 octanes and BCC-O on, your Merlin III could do 12lbs @3000rpm.

They're fairly realistic and more forgiving from my experience

Hmmm..... not sure on one point. Pilots Notes state +6.25lbs/2600rpm for max climb. 2850 was a combat concession. Admittedly it seems to be written for the Rotol prop as there are a variety of rpms quoted for cruising but I don't know if the boost would have been lower for the DH5-20 in fine pitch (30.25') versus the Rotol (23'). Also, I believe it was still normally +6.25lbs climb for 100 octane on the Merlin III. The 100 octane concessions are stated separately (+12lbs max combat boost and weak mixture running rpm/boosts)

Hurricane Rotol:
Every machine I get is slightly different regarding overheating characteristics. I would say that the Hurricane is the only machine with some kind of FM variety modelled.

Yes we've noticed that. I am wondering if its to do with the early running engine management ("keep cool, stay cool?"). Could they be modelling engine wear? Airspeed also has a lot to do with it, faster=cooler. But it does 'feel' inconsistent.

Take off at full power - 6.25lbs and 3000rpm
climb at 6.25 and 2850rpm, rad fully open, watching temps
cruise as desired, usually 4lbs @ fairly low rpm (depending on altitude and water temp)

I never wrecked my engine at 2600rpm full MFP climb (rad open in climb mind you), not even at 2850rpm! I usually climb at 2700-2800rpm

That's combat concession you're using for climb. Hope you're reporting it to the groundcrew We have often screwed our engines at 2600rpm at max boost in the climb but we would have been pretty slow. +4lbs seems to be on the edge and +3lbs is fine. I think that heating model needs a little bit of tweaking. Can certainly cool it fast by dropping to 2200rpm.

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+12lbs boost was not available at all (impossible) with 87 octane fuel. That chart is almost certain about 100 octane (it's a later version obviously)
Merlin XII was rated at 9lbs @ 2850rpm for climb, just for comparsion.
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Agreed, that's probably the answer.