The mixture is semi-automatic: levers in the normal range (from the middle and back) is auto-rich, levers in the weak range (from the middle and forward) is auto-lean.
This is exactly like it worked in the real one too, the levers move all the way but they only have two effective functions: for example, if you have the mixture levers 30% forward it's the same as having them 10% of the way forward, both of it corresponds to auto-rich.
What i do is warm up by applying throttle with my cowl flaps closed and the carb heat on (it seems to accelerate the oil temp increase). Also, don't forget to set rudder trim full left and have the mixture levers back so that it runs on auto-rich.
As soon as my oil temps hit 35-40 and my cylinder temps are 200 i fully open the cowl flaps, hold the brakes and advance throttles to +2 lbs boost.
I do this to clear the engines and get them to a sufficient temperature so that i can then advance throttles even more without having them choke and run rough. I also turn off carb heat (it reduces available power) and wait a few seconds for the mixture to re-adjust and the engines to stop shaking.
At that point i enable the boost cut out (this gives you up to +9 lbs boost at the cost of overheat so you cant' use it for too long), advance both throttles to +4 lbs boost or so (throttles about 60-65% of the way forward) release the brakes, select the starboard engine and gradually advance it to more than +5 lbs boost.
Initially it turns strongly to the right, even under full left rudder and rudder trim, but you can straighten it out without using the brakes: just use
short bursts of +9 lbs boost on the starboard engine. Don't leave it there as it will overheat and get damaged, just give it a burst or two to realign with the runway and then pull it back to +5 or so. Immediately pull it back if you get any shaking, this is your engine telling you it's about to blow a gasket but you can prevent it if you pull it back to +5.
During all this time the port engine is running steadily at +4 lbs boost or thereabouts.
By that time i'll be having some forward speed and planning ahead a little bit i will have turned a bit to the left of the centerline by means of throttling up the starboard engine, so that i have some time to react before it starts veering off to the right again.
At this point i select the port engine and gradually advance it to +5 lbs or more. I don't use +9 unless i'm doing what i described above to keep it straight, but i think it can easily take +7 or so (approximate value, as i'm not looking directly at the instruments while "dancing" on the engine controls). Throttle is roughly 90-95% of the way open at this point. The trick is to advance it gradually so that it can warm up (remember, we had the port one running lower boost to reduce the right turning tendency), just advance throttle in two stages to give it a couple of seconds to warm up during the process, instead of going full out at once and getting the "shakes".
This makes it want to turn right even more, but by this point i have enough forward speed to keep it pointing straight with the rudder.
At this point the hard part is over. I set both engines to +5 or a bit more, force the tail up with some down elevator and lift off at around 90-100mph.
I might give it a short burst of +9 lbs boost to get an initial breath of altitude while the gear retracts, then throttle back down to +5 and disable the boost cut-out (with the boost cut-out on maximum boost is +9, by disabling it maximum boost is +5).
I then set props to coarse pitch (pull the levers ALL the way back, anything above that corresponds to fine pitch) and trade that initial bit of altitude for speed, diving back down to get into the speed range where coarse pitch works well (at least 120mph).
From this point on i just monitor my temperatures and adjust cowl flaps as needed.
All flying apart from take off and landing is done with coarse pitch. Maximum cruising boost is +1.5 lbs for lean mixture (levers forward in the "weak" range) and +3.5lbs for rich mixture (levers back in the "normal" range). Maximum climb is +5 lbs for half an hour (i think it is half an hour, going from memory here), but when flying level +5 lbs is limited to mere minutes because the RPM gets too high. In other words, +5lbs in level flight is war emergency power.
All this is with four 250 lbs bombs and 60% fuel, which is more than enough to do a cross-channel raid from one of the airbases west of Dover to Calais and back.
The aircraft is a joy to fly once you get it up in the air (apart from the slightly annoying tendency to roll, you either fly with the rudder trimmed and have the roll to contend with, or you fly with improper rudder trim in a constant sideslip and get rid of the roll) and will easily cruise at 170-180 mph with zero to +1 boost, rich mixture cowl flaps mostly closed.
Comparing with a manual someone sent to me, there are a couple of things that need tuning in our in-game Blenheim.
First of all, all engines in the sim seem to be hard to overheat or even warm-up when idling on the ground, which seems a bit off for a situation where there's almost zero airflow. As for the Blenheim in particular, the manual recommends cowl flaps closed for takeoff because they provide enough airflow to keep the engines healthy as soon as some forward motion occurs. The in-game cowl flaps seem to be less forgiving than that.
So, the way it happens in the sim is that we warm-up with closed cowl flaps and open them for the takeoff, which seems to be the exact opposite of the real procedure: idle and warm-up with cowl flaps open because engines running while sitting on the ground overheat easily, then close the cowl flaps to accelerate faster as soon as the take off run starts and the airflow helps to keep them cool.
Second, the real Blenheim carries two kind of fuel. Start up, taxi, warm up and take off is done on the outboard tanks, cruise and return to base is done on the inboard ones. The sim correctly cycles the fuel cocks, the first time you click on them it selects outboard tanks and on the second click it selects inboard tanks, but i don't know if it models the different fuel.
What happened is that they added two extra fuel tanks to gain range, but the weight went up so they needed more boost for the take off. So, they modified the engines to run +9 lbs but this also needed 100 octane fuel. In the end, they decided to run 100 octane during take off from the outboard tanks and then run 87 octane during the rest of the flight from the inboard tanks. That's the reason for switching tanks after take off, once they throttled down.
I don't know if the sim models this, maybe this is why running +9 lbs in-game is only possible in short bursts.
Finally, the in-game flap controls are similar to the Spitfire (full up or full down), while in the real one they were more like the Hurricane: up, neutral, down.
In other words, in the real Blenheim it's possible to set partial flaps. Move the control to the "down" position to start lowering them, return it to the "neutral" position to stop them where they are.
The Blenheim manual in fact recommends 20 degrees of flaps when flying in long range profile (with the outboard tanks loaded).
Moreoever, the AI in the sim also uses partial flaps, but the way they do it is by rapidly cycling between the up and down commands (you can see this if you enable the autopilot and let it take off for you).
I've posted most of this stuf in another thread under the gameplay sub-section of the forums (
http://forum.1cpublishing.eu/showthread.php?t=23192) and i hope to have the most relevant portions of the manual copied over soon.
In any case, i bet the Blenheim will get its share of fine-tuning in the upcoming FM/DM improvements that Luthier announced for the next patch.
Until then, use differential thrust with short full throttle bursts to keep it straight like i described above. It's a joy to fly once you manage to take off
