Pom pom with director Mk IV vs Bofors 40mm with Mk 51

[dunmunro]

Well, a circular screen of an HVT would have the screening ships often less than 2,500 yds apart, so well within 2500 yds and attacker would often be trying to fly between the screening ships.

The Pom-poms can't open fire if screening ships would be hit. IIRC, the screens were meant to be beyond the SD range.

[wmh829386]

1) The layer and trainer's sights were aligned with the COFAS so it would be obvious to the CO and the layer and trainer if they were following the wrong target.
2) In later models the COFAS was linked to power control to allow the CO to track the target via the COFAS to ensure that everyone was following the same target; in fact I suspect the GRU joystick would then control the director.

We have to remember that the targets are typically making low deflection attacks directly towards the ship and fire would not be opened before the predicted range was about 2500 yds; at that range, as long as the sights are centred on the target the spread in the pom-pom mount barrels would ensure that the target was within the cone of fire.

The problem is that most RN AA action reports haven't been published and so we're only seeing a tiny proportion what transpired. I know that KGV and Howe reported favourably on type 282/MkIV director control in 1944/45.

Are there any sources on the 4 man (excluding radar and RF I assume) Mk IV director mount that you and Friedman (In his book on naval AA) refers to?

The only pictures/diagram I can found all has the three rate followers for range, lateral rate and vertical rate.

[wmh829386]

1) The layer and trainer's sights were aligned with the COFAS so it would be obvious to the CO and the layer and trainer if they were following the wrong target.
2) In later models the COFAS was linked to power control to allow the CO to track the target via the COFAS to ensure that everyone was following the same target; in fact I suspect the GRU joystick would then control the director.

We have to remember that the targets are typically making low deflection attacks directly towards the ship and fire would not be opened before the predicted range was about 2500 yds; at that range, as long as the sights are centred on the target the spread in the pom-pom mount barrels would ensure that the target was within the cone of fire.

The problem is that most RN AA action reports haven't been published and so we're only seeing a tiny proportion what transpired. I know that KGV and Howe reported favourably on type 282/MkIV director control in 1944/45.

1) True, just that unlike one man control, CO still have to tell the trainer and layer verbally. Obviously one man control is favoured in situations with low warning time (such as kamikaze)

2) I actually haven't found anything information regarding the COFAS on the MkIV Pom-pom director. All the pictures I have since looks like the a telescopic sight for the CO, rather than the typical open ring sight for the Mk II or Mk III

[wmh829386]

A torpedo bomber would not be flying directly at the ship. There was quite a lot of lead involved.

Yes some deflection, but nothing like that required to engage the same aircraft attacking a different ship.

I don't thing a low deflection shot is easy... most aircrafts' side profile is about 5 to 10 times large than front profile.

If there is a chance of getting a good lead, a deflection shot is much more likely to hit for TB and Glide bomber lining up for an attack

And I guess both pom-pom and Bofors with directors could do that in their respective SD ammon range reasonablly well with good crews.

[dunmunro]

1) The layer and trainer's sights were aligned with the COFAS so it would be obvious to the CO and the layer and trainer if they were following the wrong target.
2) In later models the COFAS was linked to power control to allow the CO to track the target via the COFAS to ensure that everyone was following the same target; in fact I suspect the GRU joystick would then control the director.

We have to remember that the targets are typically making low deflection attacks directly towards the ship and fire would not be opened before the predicted range was about 2500 yds; at that range, as long as the sights are centred on the target the spread in the pom-pom mount barrels would ensure that the target was within the cone of fire.

The problem is that most RN AA action reports haven't been published and so we're only seeing a tiny proportion what transpired. I know that KGV and Howe reported favourably on type 282/MkIV director control in 1944/45.

1) True, just that unlike one man control, CO still have to tell the trainer and layer verbally. Obviously one man control is favoured in situations with low warning time (such as kamikaze)

2) I actually haven't found anything information regarding the COFAS on the MkIV Pom-pom director. All the pictures I have since looks like the a telescopic sight for the CO, rather than the typical open ring sight for the Mk II or Mk III

I think the COFAS is partially hidden in drawings by the Type 282 radar; in the attached image I have marked it with an arrow.

Mk4PPD1.jpg

(189.37 KiB) Not downloaded yet

[dunmunro]

A torpedo bomber would not be flying directly at the ship. There was quite a lot of lead involved.

Yes some deflection, but nothing like that required to engage the same aircraft attacking a different ship.

I don't thing a low deflection shot is easy... most aircrafts' side profile is about 5 to 10 times large than front profile.

If there is a chance of getting a good lead, a deflection shot is much more likely to hit for TB and Glide bomber lining up for an attack

And I guess both pom-pom and Bofors with directors could do that in their respective SD ammon range reasonablly well with good crews.

The problem with deflection shooting is the need for an accurate range and that's the the biggest issue with the MK51/Mk14 gyro gunsight, since is adjusted in 400yd increments, IIRC, and range is only crudely measured by fitting the aircraft's wingspan into a reticle. Obviously if you have multiple directors/gun mounts aiming at the same target there's a good chance that at least one director or mk14 equipped mount has the correct range to allow the gyro to compute the correct deflection. Type 282 radar was provided on the Mk4 PPD to give accurate and continuous ranging data.

A quad/octuple pom-pom is arranged to have a cone of fire and with a low deflection target you simply have to provide some superelevation to get the target into the cone of fire.

[wmh829386]

1) The layer and trainer's sights were aligned with the COFAS so it would be obvious to the CO and the layer and trainer if they were following the wrong target.
2) In later models the COFAS was linked to power control to allow the CO to track the target via the COFAS to ensure that everyone was following the same target; in fact I suspect the GRU joystick would then control the director.

We have to remember that the targets are typically making low deflection attacks directly towards the ship and fire would not be opened before the predicted range was about 2500 yds; at that range, as long as the sights are centred on the target the spread in the pom-pom mount barrels would ensure that the target was within the cone of fire.

The problem is that most RN AA action reports haven't been published and so we're only seeing a tiny proportion what transpired. I know that KGV and Howe reported favourably on type 282/MkIV director control in 1944/45.

1) True, just that unlike one man control, CO still have to tell the trainer and layer verbally. Obviously one man control is favoured in situations with low warning time (such as kamikaze)

2) I actually haven't found anything information regarding the COFAS on the MkIV Pom-pom director. All the pictures I have since looks like the a telescopic sight for the CO, rather than the typical open ring sight for the Mk II or Mk III

I think the COFAS is partially hidden in drawings by the Type 282 radar; in the attached image I have marked it with an arrow.

Mk4PPD1.jpg

The bes picture can find for a MkIV director from the front shows some kind of stabilised telescope, I have no idea how the CO can apply lead through that. I have a suspicion that the details are hidden away in some documentation that will never see the light of day...

[marcelo_malara]

The bes picture can find for a MkIV director from the front shows some kind of stabilised telescope, I have no idea how the CO can apply lead through that. I have a suspicion that the details are hidden away in some documentation that will never see the light of day...

Hi! In the Mk14-Mk51 the lead is applied by a moving reticle, the telescope/sight does not move beyond what is needed to follow the target. It can be that in the MkIV the lead is applied by the calculator by leading the guns respect to the sights.

A further comment. These gyro-based systems did not provide an exact calculation of the lead. For example the Mk14 assumes that the target plane is moving exactly across the LOS, it do not provide for the change of range during the TOF of the projectile. For that It MAY BE that firing to a plane that is attacking another ship would be more accurate that for a plane coming directly to the ship.

Regards

[wmh829386]

Hi! In the Mk14-Mk51 the lead is applied by a moving reticle, the telescope/sight does not move beyond what is needed to follow the target. It can be that in the MkIV the lead is applied by the calculator by leading the guns respect to the sights.

A further comment. These gyro-based systems did not provide an exact calculation of the lead. For example the Mk14 assumes that the target plane is moving exactly across the LOS, it do not provide for the change of range during the TOF of the projectile. For that It MAY BE that firing to a plane that is attacking another ship would be more accurate that for a plane coming directly to the ship.

Regards

1. Seems like the pom-pom director is more similar to a non-disturbed line of sight director as per Friedman.
This means that there isn't a reticle that provides a suggested aim off like a gyrosight, rather the correction from angular rates, range, are added directly to output of the director. But I cannot confirm the details.

2. Pom pom director has a measures range input, but the assumption for motion should be the same because of the absence of range rate input.
I am also not sure of superelevation is included for pom pom director.

[marcelo_malara]

1. Seems like the pom-pom director is more similar to a non-disturbed line of sight director as per Friedman.
This means that there isn't a reticle that provides a suggested aim off like a gyrosight, rather the correction from angular rates, range, are added directly to output of the director. But I cannot confirm the details.

2. Pom pom director has a measures range input, but the assumption for motion should be the same because of the absence of range rate input.
I am also not sure of superelevation is included for pom pom director.

1-I agree, the same I think is the case with the HA/LA director used in the Sumner/Gearing DD class (far from home, do not recall the exact Mk...)

[dunmunro]

Hi! In the Mk14-Mk51 the lead is applied by a moving reticle, the telescope/sight does not move beyond what is needed to follow the target. It can be that in the MkIV the lead is applied by the calculator by leading the guns respect to the sights.

A further comment. These gyro-based systems did not provide an exact calculation of the lead. For example the Mk14 assumes that the target plane is moving exactly across the LOS, it do not provide for the change of range during the TOF of the projectile. For that It MAY BE that firing to a plane that is attacking another ship would be more accurate that for a plane coming directly to the ship.

Regards

1. Seems like the pom-pom director is more similar to a non-disturbed line of sight director as per Friedman.
This means that there isn't a reticle that provides a suggested aim off like a gyrosight, rather the correction from angular rates, range, are added directly to output of the director. But I cannot confirm the details.

2. Pom pom director has a measures range input, but the assumption for motion should be the same because of the absence of range rate input.
I am also not sure of superelevation is included for pom pom director.

The COFAS has a reticle for eye-shooting aim off. The GRU sight required that the target be kept centred in the crosshair to allow the gyro to compute the target rate.

2) With continuous radar ranging the GRUB (computer could (and must) calculate true target motion otherwise radar ranging would actually make predicted target position more inaccurate,

[marcelo_malara]

2) With continuous radar ranging the GRUB (computer could (and must) calculate true target motion otherwise radar ranging would actually make predicted target position more inaccurate,

So you mean that if in the second sweep the radar detects the plane closer (or farther) to the ship the computer would calculate the true target trajectory instead of just assuming movement across the LOS?

Regards

[dunmunro]

2) With continuous radar ranging the GRUB (computer could (and must) calculate true target motion otherwise radar ranging would actually make predicted target position more inaccurate,

So you mean that if in the second sweep the radar detects the plane closer (or farther) to the ship the computer would calculate the true target trajectory instead of just assuming movement across the LOS?

Regards

Yes, If you have a continuous range to the target, via radar, then it's possible to accurately predict the target's location at the end of the projectile's TOF, but only if target motion is accurately modeled.

[marcelo_malara]

Yes, If you have a continuous range to the target, via radar, then it's possible to accurately predict the target's location at the end of the projectile's TOF, but only if target motion is accurately modeled.

I think that that is beyond the possibilities of the technology of the day. Somehow you have to record the first distance and bearing, and target elevation in degrees, and then take a second set of data, and compare to the first to determine airplane motion (velocity, course and rate of ascend/descend). Seems easy in these days of modern digital electronic computer, but do not think was possible in those day, when recording a variable meant moving a gear or bar a certain amount.

For this reason gyro prediction was invented, to measure relative motion assuming some simplifications to make it possible, automatic firing providing for inaccuracies of the system.

[dunmunro]

Yes, If you have a continuous range to the target, via radar, then it's possible to accurately predict the target's location at the end of the projectile's TOF, but only if target motion is accurately modeled.

I think that that is beyond the possibilities of the technology of the day. Somehow you have to record the first distance and bearing, and target elevation in degrees, and then take a second set of data, and compare to the first to determine airplane motion (velocity, course and rate of ascend/descend). Seems easy in these days of modern digital electronic computer, but do not think was possible in those day, when recording a variable meant moving a gear or bar a certain amount.

For this reason gyro prediction was invented, to measure relative motion assuming some simplifications to make it possible, automatic firing providing for inaccuracies of the system.

Tachymetric analog computers could predict target location accurately given accurate inputs; that was the whole point of it all. Where the computers failed was when the TOF was too long and the target's predicted location would no longer match it's actual location, due to target manoeuvring.