Friday Official Update, July 20, 2012

[Blackdog_kt]

Thanks a lot Blacksix, that's wonderful.

I will probably have a more detailed report for the bombsight bugs in a few hours.

I have been discussing this a lot with some of the bomber pilots who fly on the ATAG server and one of them (Aus3620) has helped me a lot by running all the tests and making videos of the results.

We have found out that the Luftwaffe bombsights in the He-111 and Ju-88 track targets correctly. The player simply has to input his altitude and speed (i'm just waiting for a confirmation on if that speed is IAS or TAS).

What is wrong is the calculations for releasing the bombs. Even if you calibrate the sight correctly, the bombs always impact before the target.

To score hits the player has to convert IAS to TAS from the imperial table in the manual instead of the metric one. For example, if you are flying at 300km/h and 3000meters, you have to go to the imperial chart and input the number for 300mph and 3000feet (but just the number as it is, you don't convert it from mph to km/h).

Also, the altimeters seem to be under-reporting a bit and the way to account for this is to convert meters to yards. I don't know if this is simply a case of calibrating the altimeters, because when we spawn they are set at 1000mbar by default.

However, most people have found that with default weather this gives inaccurate altimeter readings. For example, one of the coastal RAF airfields has an elevation of 72ft but when you spawn there, the altimeter reads about 300ft.

If Ilya Shevchenko wants more information about this, i'll be glad to describe the issue to him in more detail via PM or email.
Thank you and thanks to all the players who helped me with this and took part in the exchange of knowledge and testing. We have learned a lot of technical details along the way and if we can help you fix the bombsights in time for the next patch, it will be great for all sim pilots.

Expect a more detailed report later in the day in a separate thread (i will post here a link to it).

[csThor]

It's not a mixup of metric and imperial units, it's simply that the "Rücktriftwinkel" calculation was forgotten to model. IIRC somebody posted a part of the bombsight manual here. It should appear if you use the german term in the search mask.

[Blackdog_kt]

Originally Posted by csThor

It's not a mixup of metric and imperial units, it's simply that the "Rücktriftwinkel" calculation was forgotten to model. IIRC somebody posted a part of the bombsight manual here. It should appear if you use the german term in the search mask.

Thanks for the tip. According to the search results, this is equivalent to the trail or terminal velocity setting.

As luck would have it, i've been recently reading about bombsights and wikipedia has some great articles about the British CSBS (the one we have on the Blenheim) and the Norden. The Lofte is very similar to the Norden in how it operates.

It never occurred to me that this setting is missing, because i thought it was handled automatically by the simulator.

Some things in our aircraft do get handled automatically. For example, leveling the bombsight or managing the hydraulic pump in the Blenheim, you don't have to do it because the sim does it for you, but it is modeled (just try to raise the Blenheim turret when you are on the ground, even if the engines are on...it's not possible because the hydraulic pump is set to power the gear and flaps). So i thought that the trail setting is automatic as well (it certainly is in the Blenheim).

So, let's see what this setting is. Bombs drop in more or less parabolic trajectories. They start roughly parallel to the aircraft (unless you're weird and your name is He-111, then they drop ass-first because the bay is vertical ) and progressively nose down while they fly due to air resistance and gravity (negative forward acceleration due to friction and positive downward acceleration due to gravity)

Each bomb type has its own trajectory, depending on aerodynamics of the casing and its weight/density.

Since bombs accelerate and nose down during their flight, it's easy to see that a bomb released at higher initial speed (the speed of the carrier aircraft) and lower altitudes will be more parallel to the ground upon impact, than one released at lower speed and/or higher altitude (the forward speed is easily countered by air resistance during its flight and it settles in a dive).

So, the higher you go the more chance of the bomb settling in an attitude where it has a lot of vertical and very little forward motion. And yes, if unaccounted for it will impact short.
Please behold technical schematic no.1, also known as "my awesome MSPaint skills, let me show you them"



What they did was calculate trajectories for the bomb types used by each bomber and added a function to the sights, so that bombardiers could select the correct one depending on their bombload (so probably mixed bombloads means mixed results because the bombs have different trajectories, while maybe the sight can only handle one preset at a time).

In some bombsights it was called trail (i don't know in what values they measured it), in some later RAF sights they would input the bomb's terminal velocity and now i learned that in the Lofte it was called Rücktriftwinkel and it compensated wind resistance through the drop.

What amazes me is how our friend Heinz realized this is missing, since there is no clear way to test for it. Eg, we would have to make our own bombing practice range in the FMB with objects at preset distances, to see that they impact short by specific distances each time.

For information on the matter:
http://forum.1cpublishing.eu/showthr...twinkel&page=5

I'm starting to think that this explanation is the most possible one. It would certainly explain why we need to do all kinds of weird unit conversions when bombing from high altitude, while people who bomb from low altitude say the sight works fine for them.


Finally, two more questions (now that Blacksix is taking notes ):

1) What's up with the R22 autopilot mode? It's supposed to hold the plane level with the horizon during the bomb run, but it seems that the engines don't have enough power to keep it from losing altitude at that angle of attack.
Certainly the 111 has trouble achieving its rated power settings, or the instruments read incorrect values (eg, full fine pitch at take-off and it barely goes up to 2100RPM).

2) Why do the bombs explode backwards (the last one to impact explodes first)?

Thanks everyone for your help and i'm hoping we see a fix for these issues in the next patch

[Damixu]

Originally Posted by Blackdog_kt

...
Also, the altimeters seem to be under-reporting a bit and the way to account for this is to convert meters to yards. I don't know if this is simply a case of calibrating the altimeters, because when we spawn they are set at 1000mbar by default.

However, most people have found that with default weather this gives inaccurate altimeter readings. For example, one of the coastal RAF airfields has an elevation of 72ft but when you spawn there, the altimeter reads about 300ft.
..

The most logical way of modeling atmospheric conditions is to model standard atmospheric conditions which is 1013 mbar/hPa at sea level and I assume 1C has done it in this sim.

In order to get correct altitude the pilot should dial in correct atmospheric pressure to altitmeter. If you keep default 1000 mbar setting you get 13 mbar error which is 13 x 27 ft (8m) near seal level = 251 feet/104 meters. The error will increase when flying altitude increases. (1 hPa difference = Alt 2,5 km = 11 m, 5,5 km = 16m, 10 km = 26 m) Naturally you also must take in account the ground level at airfield and add it to the altimeter.

Just my 2 cents if this might be some cause of problems you have discovered...

[Wolf_Rider]

Originally Posted by Blackdog_kt

In some bombsights it was called trail (i don't know in what values they measured it), in some later RAF sights they would input the bomb's terminal velocity and now i learned that in the Lofte it was called Rücktriftwinkel and it compensated wind resistance through the drop.

What amazes me is how our friend Heinz realized this is missing, since there is no clear way to test for it. Eg, we would have to make our own bombing practice range in the FMB with objects at preset distances, to see that they impact short by specific distances each time.

Determine the weight of the falling object. The easiest way to do this is usually to measure this quantity directly. You can also estimate weight if you know the construction materials and dimensions.

2
Calculate the frontal area of the falling object. The frontal area is the apparent area facing in the direction of falling. You can determine this area by measuring the outline of the object from that orientation. For example, if the falling object were a cone, the tip of the cone would point straight downward, and the frontal area would appear to be a circle equal to the area of the circular base of the cone.

3
Determine the drag coefficient of the falling object. You can usually avoid having to calculate the drag coefficient yourself by looking up an approximate value in a reference book or on the Internet. If you need a highly precise value, you should consult with an engineer.

4
Determine the gas density of the medium through which the object will be falling. If the medium is the air, then you should know that air density decreases with altitude, which means that the object's terminal velocity will decrease as it gets closer to the ground (where the gas is denser and pushes back harder, providing stronger braking power). Thus you can calculate terminal velocity at any one altitude using simple mathematics, but to calculate the change in the terminal velocity over a long-distance fall, you will require the use of calculus or empirical approximations. Air density also changes with the weather; there is no uniform density value for a given altitude. To get the most accurate measurements of air density, you will need to multiply average air density values by local weather condition offsets. Atmospheric information is available in the United States from the National Weather Service, a service of the National Oceanic and Atmospheric Administration.

5
Calculate terminal velocity at a given altitude with this equation: Terminal V = sqrt ((2 x (Object Weight)) / ((Frontal Area) x (Drag Coeff.) x (Gas Density))).

In plain English, the terminal velocity of the object is equal to the square root of the quotient of twice the object's weight over the product of the object's frontal area, its drag coefficient, and the gas density of the medium through which the object is falling.



Read more: How to Calculate Terminal Velocity | eHow.com http://www.ehow.com/how_6134922_calc...#ixzz21SPSlnUQ

[Kwiatek]

Originally Posted by BlackSix

I'll get some your questions in this thread and give them to Ilya today or tomorrow.

Black Six plz ask about FM&performacne both British and German planes.

Beacuse actually situation is very bad.

RAF fighters both Spitfire and Hurricanes had wrong power engine settings, had wrong performance - way too slow - at emergency +12 lbs power rating they could reach speed RL planes had at only + 6 lbs power rating. Also British planes can't used power ratings from manual - or if used engine broke after very short time.

Other hand 109 is still too slow at slow speed - ab. 20 kph, slats open too late ( at too low speed and or too high angle of attack), had strange stall characterisctic ( should be more gentle) and had too sensivity rudder.

[5./JG27.Farber]

Originally Posted by Kwiatek

Black Six plz ask about FM&performacne both British and German planes.

Beacuse actually situation is very bad.

RAF fighters both Spitfire and Hurricanes had wrong power engine settings, had wrong performance - way too slow - at emergency +12 lbs power rating they could reach speed RL planes had at only + 6 lbs power rating. Also British planes can't used power ratings from manual - or if used engine broke after very short time.

Other hand 109 is still too slow at slow speed - ab. 20 kph, slats open too late ( at too low speed and or too high angle of attack), had strange stall characterisctic ( should be more gentle) and had too sensivity rudder.

Dont forget the roll rates

[ATAG_Doc]

<br />
<br />
Black Six plz ask about FM&performacne both British and German planes. <br />
<br />
Beacuse actually situation is very bad.<br />
<br />
RAF fighters both Spitfire and Hurricanes had wrong power engine settings, had wrong performance - way too slow - at emergency +12 lbs power rating they could reach speed RL planes had at only + 6 lbs power rating. Also British planes can't used power ratings from manual - or if used engine broke after very short time.<br />
<br />
Other hand 109 is still too slow at slow speed - ab. 20 kph, slats open too late ( at too low speed and or too high angle of attack), had strange stall characterisctic ( should be more gentle) and had too sensivity rudder.

And service ceilings and way off as well.

Sent from my SCH-R910 using Tapatalk 2

[ATAG_Snapper]

Originally Posted by 5./JG27.Farber

Dont forget the roll rates

Nor you! LOL

http://www.il2bugtracker.com/issues/232

[MegOhm]

Blackdog....Your and ATAGs efforts are much appreciated...I look forward to engaging the bomber formations!!!!

<S>