Found some tips for the Blenny
Feb 22, 2015 19:14:32 GMT -5
Post by Blackwolf on Feb 22, 2015 19:14:32 GMT -5
As an addendum to the previous post, i think the Blenheim's mixture also behaves in a similar fashion to the Hurri and Spit, rich is back and forward is lean.
This is part of the confusion in the cross country quick mission if you stick with the default choice of the Blenheim, definitely one of the most challenging stock missions.
1) You have a definite crosswind pulling you to the right. I tested it with the Moth and it's weightless enough to swing around to the right with the engine stopped, weather-vaning into the wind.
2) You have the Blenheim's engine torque pulling the same way and if you try to run about half-throttle on the port engine and full throttle on the starboard engine to keep it straight, you end up with a longer take-off roll while one engine is running flat out and get some kind of failure on the starboard one, either a governor failure (if the oil is not sufficiently hot) or a blown oil gasket (if you keep running it at full).
3) All the while, you wonder why the damn thing won't get off the ground and when you restart the mission and accidentally look at the animated throttle quadrant you see the little letters telling you your mixture is set to full lean --> less power, more heat and failures
I managed to take-off fine (if still not managing to completely maintain runway alignment) after setting it to rich. Now my next challenge is taking off with four 250lb bombs loaded, which i still haven't managed. I think i'll follow the advice of someone over at the 1c forums, taxi to the other end of the runway, turn 180 and take off in that direction so the crosswind will be pulling opposite the props.
Another thing to note, it might be beneficial to exercise the props between high and low RPM to "recycle" the cold oil in the governor with warmed up oil...maybe this will help with the prop governor failures and RPMs jolting around.
Finally, turn on your carb heaters for the start up but turn them off before take-off. Heated air = rarified air, it is equivalent to running with the wrong mixture all over again but this time too rich.
This is part of the confusion in the cross country quick mission if you stick with the default choice of the Blenheim, definitely one of the most challenging stock missions.
1) You have a definite crosswind pulling you to the right. I tested it with the Moth and it's weightless enough to swing around to the right with the engine stopped, weather-vaning into the wind.
2) You have the Blenheim's engine torque pulling the same way and if you try to run about half-throttle on the port engine and full throttle on the starboard engine to keep it straight, you end up with a longer take-off roll while one engine is running flat out and get some kind of failure on the starboard one, either a governor failure (if the oil is not sufficiently hot) or a blown oil gasket (if you keep running it at full).
3) All the while, you wonder why the damn thing won't get off the ground and when you restart the mission and accidentally look at the animated throttle quadrant you see the little letters telling you your mixture is set to full lean --> less power, more heat and failures
I managed to take-off fine (if still not managing to completely maintain runway alignment) after setting it to rich. Now my next challenge is taking off with four 250lb bombs loaded, which i still haven't managed. I think i'll follow the advice of someone over at the 1c forums, taxi to the other end of the runway, turn 180 and take off in that direction so the crosswind will be pulling opposite the props.
Another thing to note, it might be beneficial to exercise the props between high and low RPM to "recycle" the cold oil in the governor with warmed up oil...maybe this will help with the prop governor failures and RPMs jolting around.
Finally, turn on your carb heaters for the start up but turn them off before take-off. Heated air = rarified air, it is equivalent to running with the wrong mixture all over again but this time too rich.
The Blenheim:
The Blenheim is another tricky one, because it seems way sensitive to temp effects and especially having the correct oil temps. If your oil is cold, the oil pressure in the prop governor gets high and you get a governor failure.
Engine run-up:
Make sure to cycle the props between low and high RPM before applying power for take-off, as this will cycle the oil inside the governor and get warmed up oil from the engine into the system. This is called exercising the prop and is done during the engine run-up, prior to take-off.
Just keep the props at fine pitch, step on the brakes, full back stick, apply throttle until you get 1000-1500 RPM or so (arbitrary numbers, just something that won't break the engine from overheating while sitting on the ground and there's no airflow to cool it...in reality all aircraft have a specified RPM for the run-up) and move the pitch controls all the way back and forth a couple of times.
How the props work and how the game interface displays it:
As for the actual props now, it only has two-stage props but to put it in coarse pitch (the low RPM position) you have to pull the pitch slider all the way to the back. Anything higher than that puts it into fine pitch/high RPM. Effectively, this means that it has a prop similar to the one found on the in-game Spit Mk.I, but it doesn't "snap" between the two extreme positions (top and bottom) on its own. The bottom of the slider is the coarse pitch position, the rest of the slider all the way to the top is the fine pitch position.
Carburetor heating:
It does have carb heat but i haven't found any instruments displaying carb temps, so you need to read up a bit more to be able to set it.
You can't just set it to max either as it will reduce power, running too much heating lessens the air density in the carbs, so it's like running with too rich a mixture and choking the engine.
I've had some success setting it by ear, i just increase carb heat until the engines sound like they are losing power (this means i found the critical spot), then i decrease it a notch or two to get it back into the proper operating range and the engines sound healthy again. Had no problems up at 8000ft with this method last time i tried it in the free flight mission.
This is similar to leaning in an aircraft with manual mixture controls, which brings us to...
Setting the mixture:
First of all, there are two correct mixture settings for each altitude. The economy mixture is the leanest you can go without losing engine power, but it won't allow you to run high boost settings because of detonation and overheating. The best power mixture setting is a bit richer, burns a bit more fuel, but lets you run higher boost.
In modern and even not so modern general aviation aircraft, there are easy ways to set this: exhaust gas temperature and/or fuel flow gauges let you judge where is the correct mixture for each altitude.
In the Blenheim however we don't have those toys and we can't see the exhausts either, so we can't lean based on the colour of the exhaust flames.
Fear not, because there is a way. If you have a fixed pitch or two stage prop (which essentially is like having a fixed pitch prop that you can change mid-flight for another one with a different pitch) you can easily judge the changes in power.
This happens because for a given prop angle of attack, the power delivered by the engine has a direct effect on RPM. If your prop pitch remains constant, any change of throttle will change the RPMs too. In a similar fashion, every change of mixture that makes the engine run better or worse will also have an effect on RPMs.
This can be observed in aircraft with fixed props like the Tiger Moth (just lean until you get the highest RPM without touching your throttle), two-stage props and it would also work in aircraft that use the luftwaffe propellers if they didn't have automatic mixture, because they too are manually set to a specific angle by the pilot. It wouldn't work in an aircraft with a constant speed prop, because the resulting RPM change would be mitigated and cancelled out by the propeller governor, giving no useful indication to the pilot.
So, how does all that help us with manual mixture controls?
First, lean the mixture until you hear the RPMs increase. To know if you can lean further, keep at it until you hear the RPMs drop. This marks the point where further leaning doesn't yield any benefits, in fact leaning too much causes the engine to overheat.
So, as soon as you find that spot you've discovered the bottom of the useful mixture range for your altitude.
Go ahead and bump up the mixture towards rich a notch or two until the RPMs rise again. This is the economy mixture setting we mentioned earlier.
If you add a couple more notches of rich mixture (but not so much that it chokes and starts decreasing the RPM again), you will be at the best power mixture setting. This one is the best power mixture setting and it's the top of the useful mixture range for your current altitude.
In short, the scale looks something like this:
too lean---economy---best power---too rich.
Going too lean or too rich will cause your RPMs to drop, so just move the mixture controls until you find the range of highest RPM: the bottom of the range is economy mixture and the top of the range is best power mixture.
In the case of the Blenheim however, the mixture is semi-automatic: half of the lever's travel range corresponds to automatic lean and the other half to automatic rich. This is exactly how it was in the real aircraft (i have a PDF copy of the pilot's manual describing this in detail), pulling the lever back beyond the middle of its movement range makes the automatic system set best power/rich mixture, pushing the lever forwad beyond the middle point makes the automatic system set best economy/lean mixture.
Also, just like in the Hurri, Spit and Tiger Moth, rich is backwards and lean is forward in regards to not only the animated cockpit controls, but also the info window sliders (the interface "HUD") and your actual, physical game controllers: you will need to press your "reduce mixture" key or pull your slider backwards to move towards richer mixture.
The Blenheim is another tricky one, because it seems way sensitive to temp effects and especially having the correct oil temps. If your oil is cold, the oil pressure in the prop governor gets high and you get a governor failure.
Engine run-up:
Make sure to cycle the props between low and high RPM before applying power for take-off, as this will cycle the oil inside the governor and get warmed up oil from the engine into the system. This is called exercising the prop and is done during the engine run-up, prior to take-off.
Just keep the props at fine pitch, step on the brakes, full back stick, apply throttle until you get 1000-1500 RPM or so (arbitrary numbers, just something that won't break the engine from overheating while sitting on the ground and there's no airflow to cool it...in reality all aircraft have a specified RPM for the run-up) and move the pitch controls all the way back and forth a couple of times.
How the props work and how the game interface displays it:
As for the actual props now, it only has two-stage props but to put it in coarse pitch (the low RPM position) you have to pull the pitch slider all the way to the back. Anything higher than that puts it into fine pitch/high RPM. Effectively, this means that it has a prop similar to the one found on the in-game Spit Mk.I, but it doesn't "snap" between the two extreme positions (top and bottom) on its own. The bottom of the slider is the coarse pitch position, the rest of the slider all the way to the top is the fine pitch position.
Carburetor heating:
It does have carb heat but i haven't found any instruments displaying carb temps, so you need to read up a bit more to be able to set it.
You can't just set it to max either as it will reduce power, running too much heating lessens the air density in the carbs, so it's like running with too rich a mixture and choking the engine.
I've had some success setting it by ear, i just increase carb heat until the engines sound like they are losing power (this means i found the critical spot), then i decrease it a notch or two to get it back into the proper operating range and the engines sound healthy again. Had no problems up at 8000ft with this method last time i tried it in the free flight mission.
This is similar to leaning in an aircraft with manual mixture controls, which brings us to...
Setting the mixture:
First of all, there are two correct mixture settings for each altitude. The economy mixture is the leanest you can go without losing engine power, but it won't allow you to run high boost settings because of detonation and overheating. The best power mixture setting is a bit richer, burns a bit more fuel, but lets you run higher boost.
In modern and even not so modern general aviation aircraft, there are easy ways to set this: exhaust gas temperature and/or fuel flow gauges let you judge where is the correct mixture for each altitude.
In the Blenheim however we don't have those toys and we can't see the exhausts either, so we can't lean based on the colour of the exhaust flames.
Fear not, because there is a way. If you have a fixed pitch or two stage prop (which essentially is like having a fixed pitch prop that you can change mid-flight for another one with a different pitch) you can easily judge the changes in power.
This happens because for a given prop angle of attack, the power delivered by the engine has a direct effect on RPM. If your prop pitch remains constant, any change of throttle will change the RPMs too. In a similar fashion, every change of mixture that makes the engine run better or worse will also have an effect on RPMs.
This can be observed in aircraft with fixed props like the Tiger Moth (just lean until you get the highest RPM without touching your throttle), two-stage props and it would also work in aircraft that use the luftwaffe propellers if they didn't have automatic mixture, because they too are manually set to a specific angle by the pilot. It wouldn't work in an aircraft with a constant speed prop, because the resulting RPM change would be mitigated and cancelled out by the propeller governor, giving no useful indication to the pilot.
So, how does all that help us with manual mixture controls?
First, lean the mixture until you hear the RPMs increase. To know if you can lean further, keep at it until you hear the RPMs drop. This marks the point where further leaning doesn't yield any benefits, in fact leaning too much causes the engine to overheat.
So, as soon as you find that spot you've discovered the bottom of the useful mixture range for your altitude.
Go ahead and bump up the mixture towards rich a notch or two until the RPMs rise again. This is the economy mixture setting we mentioned earlier.
If you add a couple more notches of rich mixture (but not so much that it chokes and starts decreasing the RPM again), you will be at the best power mixture setting. This one is the best power mixture setting and it's the top of the useful mixture range for your current altitude.
In short, the scale looks something like this:
too lean---economy---best power---too rich.
Going too lean or too rich will cause your RPMs to drop, so just move the mixture controls until you find the range of highest RPM: the bottom of the range is economy mixture and the top of the range is best power mixture.
In the case of the Blenheim however, the mixture is semi-automatic: half of the lever's travel range corresponds to automatic lean and the other half to automatic rich. This is exactly how it was in the real aircraft (i have a PDF copy of the pilot's manual describing this in detail), pulling the lever back beyond the middle of its movement range makes the automatic system set best power/rich mixture, pushing the lever forwad beyond the middle point makes the automatic system set best economy/lean mixture.
Also, just like in the Hurri, Spit and Tiger Moth, rich is backwards and lean is forward in regards to not only the animated cockpit controls, but also the info window sliders (the interface "HUD") and your actual, physical game controllers: you will need to press your "reduce mixture" key or pull your slider backwards to move towards richer mixture.
A wall of text but some good info in there.