[Robo.]

Originally Posted by klem

The control movement for the two-pitch prop went through a mid-stage where the pitch moved (not flipped) from one setting to the other and with slow and careful movement you could actually select a rpm between the two extremes. It would of course alter with changes in power and airspeed so the pilot had to be the rpm 'governor' and adjust it but you could hold a general rpm setting that way. The result was that the general performance of the aircraft, managed that way, was almost as good as the Rotol version but it took some management. I suspect in combat it was shoved to fully fine and left there. Apparently (I've lost the link) it became an officially recommeded method of managing the aircraft for better performance. Unfortunately in CoD it flips between the two. The A2A simulations spitfire models it correctly.

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.

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.)

Originally Posted by klem

I see very little change in the boost with the cutout plug pulled and that is only when I give the prop and/or throttle a little twitch which seems to "wake it up" but that could be my imagination. I do seem to be able to overtake my buddies when its pulled unless our e-states were different so I'm really not sure if its doing anything. There was a long thread about just that point but it didn't come to any amicable conclusion.

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'.

Originally Posted by klem

I have had engine faiure with the plug pulled for a long time (was it 10 mins + ??) with no overtemp indications.

Confirmed, same here

Originally Posted by klem

Actually I'm a bit mystified because we can get the full +6.25lbs on full throttle without the boost override. In the MkI pilot's notes that's the max for take-off, 6.25lbs @ 3000rpm (3 mins max), max climbing +6.25lbs @ 2600 rpm (30mins max), emergency +6.25lbs@ 3000 rpm (5 mins max) max cruising +4.5lbs @ 2600rpm. (The 100 octane combat rating was +12lbs but lets stay on track with 87 octane.)

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.

Originally Posted by klem

I wouldnt trust those climbing figures in CoD, I'm sure I've wrecked my engine in less than 30 minutes.

They're fairly realistic and more forgiving from my experience, 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.

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

Originally Posted by klem

Now this report on the Merlin III
http://www.wwiiaircraftperformance.o...in3-rating.jpg
seems to relate to the 87 octane performance because it has above take-off, climb and cruise figures but there is also a combat power rating of +12lbs. Is this what should be available with the plug pulled? I have found no other sources to indicate this is so but why would it be listed there?

+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.

Originally Posted by klem

Other bits and pieces suggest an uncontrolled Merlin would overboost to +17lbs and that the 100 octane engine modification was made specifically to keep the MP down to +12lbs so that obviously wasn't occurring on the 87 octane engine which had to be modified for it. In fact I have found nothing to suggest the plug needs to be pulled to get +6.25lbs, no mention of a 'normal' full throttle MP versus plug pulled MP, nor any mention of the plugs use in combat for 87 octane.

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.