Friday Official Update, July 20, 2012

[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

[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

[MD_Marx]

Originally Posted by Wolf_Rider

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

Thanks for this very interesting item - I haven't looked at the article yet, but you might need to consider a few more variables before identifying a value for Cd for the bomb.

1. Bombing altitude. If you are bombing below the height needed to attain terminal velocity, the bomb won't attain it, and the Cd value will need to be computed from a theoretical velocity.

2. The Cd of falling objects will generally increase to a point where the object has shock waves generated from it at near-sonic bomb velocities. As the bomb goes sonic/trans-sonic the Cd will probably drop slightly.

3. The Germans did an awful lot of aerodynamic research during the war, and I would be surprised if the likes of Schlichting et al did not provide a pretty comprehensive Cd-Velocity envelope for specific bombs, or a more generic CD-velocity profile for use in general calculations?

4. My own interest in this has been from determining the theoretical 'effective' range of WW2 aircraft cannon/mg, in which the highest velocity (and drag) is established at the muzzle and thereafter decays through sub-sonic drag. For my calculations, I found a very interesting article on the net by a team of Indian researchers who managed to investigate and tabulate the trans & sub-sonic CD values of a fired test cannon shell. I appreciate that the bomb is probably more aerodynamic than the shell, but the CD - Velocity characteristic will be similar.

5. Air density - or static pressure - is generally a function of altitiude but of course changes due to atmospheric conditions. If my memory serves, air density can be calculated from P/RT where P is the pressure at altitude (which will vary as the bomb descends), the gas constant R for air and the absolute temperature. No-one can predict precise values from the (discomfort) of a bomb-sight, but these values should be reasonably accurate.

Hopefully I can now take off my annorak, as it's getting rather warm in the UK

Marx

[TomcatViP]

Originally Posted by MD_Marx

As the bomb goes sonic/trans-sonic the Cd will probably drop slightly.

[...]

my annorak, as it's getting rather warm in the UK

Marx

Wait wait... transonic drag is much higher than subsonic. This why it is called the Mach wall.

[Wolf_Rider]

Originally Posted by MD_Marx

Thanks for this very interesting item - I haven't looked at the article yet, but you might need to consider a few more variables before identifying a value for Cd for the bomb.

1. Bombing altitude. If you are bombing below the height needed to attain terminal velocity, the bomb won't attain it, and the Cd value will need to be computed from a theoretical velocity.

Though I didn't write that up, it does suggest that the calculations required are not a simple feat

and I guess that's why (the yanks, at least, in the later stages and the PTO) went back to iron sight "guestimating" , dive and skip bombing for low level raids?