A helpful community member sent me a copy of a Blenheim Mk.IV pilot's operating handbook. I'm probably being a bit paranoid, but since it is copyrighted material i'd rather not name him nor link it directly so that we don't draw any flak on the guy and the admins/forums. What i can do is copy the relevant parts here.
Controls and what's different between the real and the in-game Mk.IV:
Propellers:
The real Mk.IV has two-speed propellers. In the sim it has the correct propellers but the slider/control behaviour is wrong. We can move the prop pitch controls through their entire range of travel but it has no effect for the most part: setting it fully aft sets full coarse pitch, setting it to anything higher than that sets full fine pitch.
You can easily see this for yourself when sitting on the ground with the engines off, just pull the controls forward/aft a couple of times and watch how the propeller blades change their pitch.
In other words, there's absolutely no reason to set it about 50% of the way, it has no effect and it's still running full fine unless you pull the controls all the way back.
What the manual recommends:
Fine pitch for takeoff, climbing on one engine and approach for landing. Coarse pitch is to be used for all other phases of flight, unless the engines are throttled way back in which case fine pitch might be needed to prevent rough running/way too low RPM.
Mixture:
Mixture in the real one is semi-automatic. The mixture control positions on the throttle quadrant are labeled normal (for auto rich) and weak (for auto lean). In the sim we can again move the controls through the entire range of motion. I don't know if this means the mixture is semi-auto and it's just the top and bottom positions of the control that matter. It could be that the mixture is fully manually adjustable which would probably be wrong. There were two different types of carburetors fitted, but the manual doesn't state any of them being a manually operated type.
In any case, how mixture works is difficult to test in the sim because we don't have the kind of immediate feedback we can get with the propellers.
There is also a very strong possibility that it is modeled correctly with a strong attention to detail. The manual states "each mixture control lever has two
effective positions only", which could very well mean that it could move through the entire range with half of the lever's travel range corresponding to auto lean and the other half to auto rich.
The mixture controls in the sim are reversed as in every other RAF aircraft, not only in regards to animation but keymapping/controller usage as well: you need to press your "decrease mixture" key or pull your HOTAS sliders back to move it towards auto-rich.
What the manual recommends:
Use auto rich (labeled "normal" on the in-game throttle quadrant, levers aft) when running more than +1.5lbs of boost. Use auto lean (labeled "weak", levers forward) when running less than +1.5lbs of boost.
The mixture levers snap back to the normal/auto-rich position when closing the throttles to prevent rough running, just like in the Hurricane, but i don't remember if this is reflected in the sim.
Flaps, gear and hydraulics:
The hydraulics (flaps, gear and turret) are driven by a pump which is in turn driven by the port engine. If you lose or have to switch off the port engine you must set the flaps/gear controls to the desired position and then use (as in ,repeatedly click on) the emergency hand pump in the cockpit, situated to the right of the pilot's seat.
The engine driven hydraulic pump is not powerful enough to drive everything at once, it's either the turret or the flaps and gear. This explains why the turret refuses to move when the aircraft is on the ground, the sim models the correct procedure without input from the player. In reality they could even switch off the pump completely to prevent it from overheating.
Flaps in the real Mk.IV were adjustable. In the sim we only have fully retracted or fully extended flaps (much like the Spitfire), but it should probably work more like the Hurricane, with up, neutral and down positions so that you can set it to neutral mid-way through the extension sequence and get partial flap extension.
What the manual recommends:
Use 15 degrees of flaps when the outboard tanks are full for long range missions (14500lbs total weight), they are not essential for lighter load-outs (up to 12600lbs total weight).
This is why when turning on the autopilot/handing control to the AI you see them flipping like mad between flaps up and down, they are trying to get partial flaps. Until we get a revised flap control logic for the Blenheim, we can't use partial flaps in the sim.
Maximum speed with the gear down is 130mph IAS.
Cowl flaps:
During normal flight they allow enough air to pass through to cool the engines even when they are set to the fully closed position. They must be open for ground running to prevent overheating when there's no airflow to cool the engines. For climb, high speed (probably meaning high power settings) and flying in warm weather they should be partially open.
Keep closed as much as possible to minimize drag, unless the cylinder temperatures (the two instruments on the right cockpit wall above the fuel selector switches/wheels) are climbing above specified limits (to be given further on down, keep reading
)
Boost over-ride:
Similar to the boost cut-out in Spits and Hurris, the lever on the instrument panel to the right of the RPM gauges.
Used for takeoff when the aircraft is configured for long range flight and thus heavier (outboard tanks filled, 14500lbs total weight). When activated, it raises maximum available boost from +5 to +9lbs.
As you may have guessed this needs 100 octane fuel.
Important: Interestingly enough, since +9lbs is only to be used for takeoff when the outboard tanks are full,
only these outboard tanks carry 100 octane fuel.
This could even explain why some people have more trouble taking off than others. The default loadout has all tanks filled up. If the difference in octane ratings is modeled in the sim it's very important to execute the takeoff with the outboard tanks selected as this enables us to use the boost over-ride for an extra 4lbs of boost, then switch to the inboard tanks once the boost over-ride has been disabled and we are running normal boost values again.
Various controls:
There's a fuel dump switch for the outboard wing tanks to the left and behind the pilot, right there with the carb heat and pitch controls that are obscured by the pilot's seat. You can only jettison fuel from the outer tanks (which are only filled up for long range missions), so the suggested procedure is to use up the inboard tanks first.
I don't know if this is functional in the sim.
The third fuel selector is used for cross-feeding. If you need to shut down an engine you turn on this fuel selector and the remaining engine is fed from the tanks on both wings, so that you don't get an imbalanced airframe with more weight on the "dead engine" wing. In general, it should be left to the off position in most other circumstances.
Trim tabs should not be used to assist in maneuvering, especially dive recovery, as they can cause overstress of the airframe.
The brake lever could be locked in the "down" position, effectively functioning like a parking brake, pressing the lever again unlocked it. I don't know if this is reflected in the sim, it would be very useful if it was because we wouldn't have to keep the brakes pressed while warming up our engines.
I'll cut off here and supply the engine operating limits in the next post for ease of reading (this one's a wall of text as it is).