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Pigeon_
08-28-2009, 05:58 AM
After all this time playing IL-2, I'm still unsure as to how throttle and prop pitch relate to speed and fuel usage. Sure, there's a lot to read on this subject, but there's also a lot of disagreement. So, I decided to just find out for myself.

I set up a test flight in an A-20C with 15% of fuel and default weapons loadout, flying at an altitude of 3500 m (best altitude for top speed, according to IL-2 Compare v4.07m) at a speed of 450 Km/h. I used the A-20C because it has level stabilizer, so I couldn't mess up the data with inconsistent stick movements. I conducted the tests as follows: I start the mission and then immediately engage the level stabilizer and the second stage of the supercharger. After that I set throttle and prop pitch by keyboard. All of this is done as quickly as possible. I speed up the time and wait for the fuel to run out while the aircraft accelerates to top speed. Then I save the track.

Two measurements were made during every test flight: 1) top speed (true air speed as indicated by the speedometer in 'wonderwoman view'), and 2) duration of the flight until the fuel runs out. I measured the duration by viewing back the track and then looking at the time in the bottom right corner.

Here are the data I got so far:

A-20C at 3500m altitude, second supercharger stage engaged. 15% of fuel.
http://i143.photobucket.com/albums/r144/VX_StonedPigeon/IL2/A20c3500m.jpg

It seems that higher prop pitch settings leed to increased top speed, but at the cost of a dramatically reduced range.

I think more data is needed to draw real conclusions. I'll do more tests and see if I can make some sort of graph out of the gathered data. I'll update this thread when I got the results.


And, last, but not least... What do you guys think of this method of conducting flight tests?


Ps. I used kilometers in all my measurements because this gives the most precise results. Multiply by 0.621371192 for miles.

Pigeon_
08-28-2009, 05:58 AM
After all this time playing IL-2, I'm still unsure as to how throttle and prop pitch relate to speed and fuel usage. Sure, there's a lot to read on this subject, but there's also a lot of disagreement. So, I decided to just find out for myself.

I set up a test flight in an A-20C with 15% of fuel and default weapons loadout, flying at an altitude of 3500 m (best altitude for top speed, according to IL-2 Compare v4.07m) at a speed of 450 Km/h. I used the A-20C because it has level stabilizer, so I couldn't mess up the data with inconsistent stick movements. I conducted the tests as follows: I start the mission and then immediately engage the level stabilizer and the second stage of the supercharger. After that I set throttle and prop pitch by keyboard. All of this is done as quickly as possible. I speed up the time and wait for the fuel to run out while the aircraft accelerates to top speed. Then I save the track.

Two measurements were made during every test flight: 1) top speed (true air speed as indicated by the speedometer in 'wonderwoman view'), and 2) duration of the flight until the fuel runs out. I measured the duration by viewing back the track and then looking at the time in the bottom right corner.

Here are the data I got so far:

A-20C at 3500m altitude, second supercharger stage engaged. 15% of fuel.
http://i143.photobucket.com/albums/r144/VX_StonedPigeon/IL2/A20c3500m.jpg

It seems that higher prop pitch settings leed to increased top speed, but at the cost of a dramatically reduced range.

I think more data is needed to draw real conclusions. I'll do more tests and see if I can make some sort of graph out of the gathered data. I'll update this thread when I got the results.


And, last, but not least... What do you guys think of this method of conducting flight tests?


Ps. I used kilometers in all my measurements because this gives the most precise results. Multiply by 0.621371192 for miles.

DeerHunterUK
08-28-2009, 07:05 AM
I don't know if this will help you Pigeon. I've got the pilot notes for the Boston IV and the following settings are recommended for use with supercharger pos 2:

Max. Rich
RPM: 2050
Boost: 34
Cylr: 205
Oil temp max: 90
Oil temp desired: 50/70

Max. Weak
RPM: 2050
Boost: 31.5
Cylr: 205
Oil temp max: 90
Oil temp desired: 50/70

Viper2005_
08-28-2009, 07:09 AM
You'll do better with the autopilot because you can set up a perfectly consistent procedure. However, there may be some difficulty in tuning the PID gains for accelerated time. Therefore you might find it useful to use the autopilot programme to sequence other commands like the level stabiliser.

You'd probably want to cruise rather higher than 3.5 km. In fact, the A-20C's biggest advantage online is its ability to keep on climbing. It's quite practical to use it for bombing from up to about 10 km, even if you're carrying the 1000 kg bomb.

High altitude cruise with the level stabiliser will require trimming before the level stabiliser is engaged.

The other important factor is that you'd generally try to push the edge of overheat. As such it would be sensible to investigate 110% power and different combinations of prop pitch and radiator setting. This can make a big difference at high altitude.

julian265
08-28-2009, 07:19 AM
Your method is fine.

The results are as I would expect, from my own observations and testing.

Prop pitch governors are set such that "100%" pitch sets the engine at its peak power RPM... Hence you get maximum level speed at this setting.

I think the disagreement arises when people discuss maximum DIVE speed (or minimum deceleration from above maximum level speed), which some tests have shown to benefit from reduced pitch.

And then there are the people that say reducing pitch gives you the best level speed, but they're just special.

You can't really relate real engine operating settings with IL2 engines, they're just not modelled that accurately. Often real manifold pressure and RPM settings lead to reduced range, an overheating engine, or poor speed.

julian265
08-28-2009, 07:23 PM
I see my post has been eaten by the server. I'll try again.

Edit: oh, its there now. lol.

Also:
Some people have noticed that you get a burst in speed when you pull the pitch back (once), but don't realise that it's only an temporary effect that lasts a few seconds. This is best attributed to the momentum of the spinning engine internals and prop being passed on to the air, as the blade pitch coarsens. Once the engine speed has reduced to that selected, the effect is gone.

Pigeon_
08-29-2009, 10:13 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by julian265:
I see my post has been eaten by the server. I'll try again.

Edit: oh, its there now. lol.

Also:
Some people have noticed that you get a burst in speed when you pull the pitch back (once), but don't realise that it's only an temporary effect that lasts a few seconds. This is best attributed to the momentum of the spinning engine internals and prop being passed on to the air, as the blade pitch coarsens. Once the engine speed has reduced to that selected, the effect is gone. </div></BLOCKQUOTE>

Yes, I noticed that. It gives you a small increase in speed, but after this little time the speed drops down fast. I don't think it's very usefull in the long run...