Level Bombing: Tests and results with 1.08.18956

[Blackdog_kt]

Let me just transfer here what i was discussing on the ATAG forum, for the benefit of all sim pilots who fly the He-111 and the Ju-88.

I'm just describing a simple airstart mission that i used for testing, flying the Ju-88 in a bomb run with the autopilot in R22 mode (the level attitude hold mode). Bonus track file at the end of the post

I did some more tests just now. I made an airstart mission in the FMB with 35% fuel (i think that's what i set it to) and a full bomb load (both bays full of SC50s and four SC250s externally). Apparently, with 75% pitch (2100 RPM) and 80% throttle (about 1.3 Ata with the superchargers at high gear), it almost stabilizes.

The spawn is at 5km but until i can set trims and everything from the default values, i'm down to 4k or so. Then, engaging R22 while at a somewhat high speed (320-340km/h IAS) results in the aircraft stabilizing in a slight descent of about 1m/sec. This can be accounted for easily by periodically looking at the instruments and adjusting bombsight altitude every 20-30 meters of lost altitude. A ballpark value for ground speed at that altitude and IAS is 370-380km/h (i didn't use tables, just engaged automation and played around with it until the sight stabilized in the vertical axis).

The interesting thing is that i also found how to account for drift. In my first run i was a bit out of trim when i engaged the autopilot but instead of correcting it, i thought i might see how drift works and well, it works just fine

What you do is move the bombsight sideways (controls: bombsight left/right) in the direction of the drift, not opposite to it. The idea is that the crosshairs should point where the bombs will impact. If you adjust for drift in this way, at some point you will see that with automation engaged the sideways motion of the sight is negated.

So it's a two step process really: adjust speed value to get a static sight picture in the vertical axis (target doesn't drift above or below crosshairs), then adjust drift value to get a static picture in the horizontal axis(target doesn't drift left or right of the crosshairs). It's very easy to judge, because we have the sight lines, just see if a ground feature near the lines moves parallel to them (correct drift) or tends to cross them (needs adjustment).

After all these adjustments are done, your aiming point (the crosshairs center) will have of course drifted off target. You can then command some slight turns with the autopilot in R22 mode to align the crosshairs with what you want to hit. This is your final correction.

After all is done, you should go back to the pilot's seat and adjust for the dropping altitude every 20-30 meters lost, switch to bombsight view and confirm the sight still tracks correctly.

At some point between 30 and 40 degrees of bombsight angle, the bombs release.

In my tests i used a series release with a spread of 1 meter. This creates a much bigger spread due to the bombs drifting, which is more pronounced the higher the altitude you drop from. A spread of 1 meter worked well for the airfield i was targeting.

I also found out why some people report backwards exploding bombs. The bombs are correctly modeled with regards to their different densities. All bombs fall with the same acceleration in a vacuum, but through the air the denser/heavier bombs have an advantage because they can penetrate the air easier. This is the same reason that gliders carry water ballast: a lighter glider climbs better in a thermal, but a heavier glider can attain higher airspeeds. So, glider pilots load water ballast and they have a jettison valve to dump some of it if they need more climb rate at the expense of forward speed.

What happens in the sim is the same thing. I think it's the forward bomb bay that drops first, then the rear bay and then the externals (SC250s). Well, the SC250s overtake the lighter bombs and finally impact at about the same time as the SC50s from the forward bay, while the SC50s from the rear bay impact last. This creates the effect of a backwards moving string of explosions, but it's not a bug.

It would be a bug if we released a stick of the same type of bombs (eg, only the internal SC50s in the 88, or 8 SC250s in the 111) and we saw the explosions moving backwards. However, in my tests i observed that bombs of the same type (the SC50s in the bomb bays) which drop at similar speeds, correctly explode in the sequence of impact.

All in all, i'm very very pleased with my findings, huge thumbs up to 1C for their work in this.

You can see some of what i'm talking about in the attached track file.

Get the track file from the link below, just unzip into Documents\1C SoftClub\il-2 sturmovik cliffs of dover\records

Then, you can load the track from inside the sim and observe how the bombs drop and how the lighter ones lag behind the heavier ones.