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kNOWON
02-01-2004, 07:02 AM
Greetings,

What allowance is made for 'gravity drop' when firing rockets?

I ask this question because the drop of the missile over range is much much greater than that of bullets. Should the aiming point for rockets not be the bottom of the graticule and not the center dot?

My reason for asking is that the MkIII gyro gunsight (GGS) used on British fighters in WW2 had two adjustable scales. The first was for setting the Range, this was operated by rotating the throttle grip (Not pushing it forward and back which was the engine control). The second was the Span setting on the sight itself. This the pilot set to the span of the enemy ac.

The pilot could see two graticules, one, on the left I think, was a circle with a central dot, this was the boresight of the guns. the second graticule was a set of 6 small diamonds and a central dot set in a circle whose diameter was adjusted by movement of either the range control or the span setting. This second graticule was gyro stablised and was the aiming point for the pilot.

Now, when the pilot wished to fire rockets he set his Span control to an index point marked 'RP'. This set the 6 graticule diamonds such that a pair of them were then at the 12 o'clock and 6 o'clock positions. He then used the BOTTOM diamond as the aiming mark! This had the effect of raising the point of aim to allow for the greater rate of drop of the missile due to gravity.

Is this gravity drop affect simulated in IL2?

Now I know many will say that the gunsights used in IL2 are not gyro controlled but nevertheless the effect is not dependent on the sight it's a matter of physics.

Incidently for those who might be interested the gunsight portrayed in the British fighters in European Air War is the MkIII Reflector Gunsight. As far as I can remember this no span or range setting. The circle represented a typical span of a fighter and when the wingtips touched the edge if the circle you were in range!

For the inquisitive or technically minded here is how the M3 GGS diamonds were achieved.

A small lamp, 24v 5w, was set behind two disks. One disk had a central hole and 6 straight radial slots cut in it similar to the spokes in a wheel. This was the Span disk and could be rotated by the pilot using the Span control on the GGS body. The second (Range)disk also had a small central hole and 6 slots however in this case the slots were curved. The resulting apprature through which the light shone was thus a rough diamond shape. Movement of the either disk had the effect of moving the diamonds in or out although the movement of the range disk also rotated the diamonds about the circumference of the circle slightly.
The resulting image of the diamonds was then reflected from a rotating mirror and thence through a lens, which focused it to infinity, and then onto the reflector glass, which was set at 45, degrees through which the pilot sighted. The mirror was so fixed (by means of a Hooks coupling)that it had a small degree of movement in two planes. he shaft on which the coupling was was rotated by means of a belt drive. Also on this shaft was a hemispherical copper drum which rotated within the influence of 3 magnetic fields. The strenght one of these fields was controlled by the setting of the Range control another by the span control and the third by an altitude unit which allowed for changes in air density dur to height. The resultant magnetic field determined the degree of 'Stifness' of the mirror assemble and thus the amount of gyroscopic precession obtained when the aircraft and the GGS were moved. The precession delflected the mirror and moved the graticule to show the correct 'Aim off'

The reflector glass could by adjusted within small limits when carrying out harmonisation of the sight with the guns.

An earlier sight the Mk1 reflector is often seen in the turrets of British bombers most noticably in shots of rear turrets. The reflector glass shield body looks somewhat like an inverted U.

Remembering all this brought back many happy memories. I joined the Royal Air Force as a boy in 1949!!!

Patrick M

kNOWON
02-01-2004, 07:02 AM
Greetings,

What allowance is made for 'gravity drop' when firing rockets?

I ask this question because the drop of the missile over range is much much greater than that of bullets. Should the aiming point for rockets not be the bottom of the graticule and not the center dot?

My reason for asking is that the MkIII gyro gunsight (GGS) used on British fighters in WW2 had two adjustable scales. The first was for setting the Range, this was operated by rotating the throttle grip (Not pushing it forward and back which was the engine control). The second was the Span setting on the sight itself. This the pilot set to the span of the enemy ac.

The pilot could see two graticules, one, on the left I think, was a circle with a central dot, this was the boresight of the guns. the second graticule was a set of 6 small diamonds and a central dot set in a circle whose diameter was adjusted by movement of either the range control or the span setting. This second graticule was gyro stablised and was the aiming point for the pilot.

Now, when the pilot wished to fire rockets he set his Span control to an index point marked 'RP'. This set the 6 graticule diamonds such that a pair of them were then at the 12 o'clock and 6 o'clock positions. He then used the BOTTOM diamond as the aiming mark! This had the effect of raising the point of aim to allow for the greater rate of drop of the missile due to gravity.

Is this gravity drop affect simulated in IL2?

Now I know many will say that the gunsights used in IL2 are not gyro controlled but nevertheless the effect is not dependent on the sight it's a matter of physics.

Incidently for those who might be interested the gunsight portrayed in the British fighters in European Air War is the MkIII Reflector Gunsight. As far as I can remember this no span or range setting. The circle represented a typical span of a fighter and when the wingtips touched the edge if the circle you were in range!

For the inquisitive or technically minded here is how the M3 GGS diamonds were achieved.

A small lamp, 24v 5w, was set behind two disks. One disk had a central hole and 6 straight radial slots cut in it similar to the spokes in a wheel. This was the Span disk and could be rotated by the pilot using the Span control on the GGS body. The second (Range)disk also had a small central hole and 6 slots however in this case the slots were curved. The resulting apprature through which the light shone was thus a rough diamond shape. Movement of the either disk had the effect of moving the diamonds in or out although the movement of the range disk also rotated the diamonds about the circumference of the circle slightly.
The resulting image of the diamonds was then reflected from a rotating mirror and thence through a lens, which focused it to infinity, and then onto the reflector glass, which was set at 45, degrees through which the pilot sighted. The mirror was so fixed (by means of a Hooks coupling)that it had a small degree of movement in two planes. he shaft on which the coupling was was rotated by means of a belt drive. Also on this shaft was a hemispherical copper drum which rotated within the influence of 3 magnetic fields. The strenght one of these fields was controlled by the setting of the Range control another by the span control and the third by an altitude unit which allowed for changes in air density dur to height. The resultant magnetic field determined the degree of 'Stifness' of the mirror assemble and thus the amount of gyroscopic precession obtained when the aircraft and the GGS were moved. The precession delflected the mirror and moved the graticule to show the correct 'Aim off'

The reflector glass could by adjusted within small limits when carrying out harmonisation of the sight with the guns.

An earlier sight the Mk1 reflector is often seen in the turrets of British bombers most noticably in shots of rear turrets. The reflector glass shield body looks somewhat like an inverted U.

Remembering all this brought back many happy memories. I joined the Royal Air Force as a boy in 1949!!!

Patrick M

AirBot
02-01-2004, 08:31 AM
Yes, FB does simulate drop both for bullets and for rockets. (With rockets obviously dropping much faster.)
This is easily seen when shooting rockets at a target from anything but the closest ranges. You'll find you have to compensate for the drop if you want to hit the target directly.

Oh yeah, and thanks for the lesson on sights. http://ubbxforums.ubi.com/infopop/emoticons/icon_biggrin.gif