# Mk.XIV Bombsight



## Zipper730 (Jul 31, 2017)

Did the Mk.XIV use a gyroscopic system, or other means to determine airspeed, ground-speed, altitude, drift?


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## wuzak (Jul 31, 2017)

Mark XIV Bomb Sight - Computing History


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## wuzak (Jul 31, 2017)

Bombsight, Gyro Unit Sighting Head Mk XIV (AIR 318)


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## Old Wizard (Aug 1, 2017)




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## Zipper730 (Aug 4, 2017)

I'm confused: If it used a gyro, how is it that

1. The gyro never toppled as on the Norden?
2. The sight remained in operation long after the Norden?


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## wuzak (Aug 4, 2017)

Zipper730 said:


> I'm confused: If it used a gyro, how is it that
> 
> 1. The gyro never toppled as on the Norden?
> 2. The sight remained in operation long after the Norden?



1. It was a better design?
2. Britain was broke after WW2

Alternative answer for 2 is that the Norden sight was limited in that it required a long, stable run up to target, after which it was theoretically superior in accuracy than the Mk XIV. The Mk XIV could be set in a fraction of the time and after manoeuvring. 

The time the Norden took to set and needed to fly straight and level was, probably, too long in WW2. Post WW2 with jets coming into service the time was way too long. 

Also, how accurately do you need to drop nukes?

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## stona (Aug 4, 2017)

wuzak said:


> The time the Norden took to set and needed to fly straight and level was, probably, too long in WW2. Post WW2 with jets coming into service the time was way too long.
> 
> Also, how accurately do you need to drop nukes?



Optical sights become redundant when dropping ordnance at speeds, from altitudes and at ranges which mean the aimer can't see the aiming point. 
I know the Mk XIV remained in service into the 1960s but there must have been other radar sights by this time.
Cheers
Steve


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## Greyman (Aug 4, 2017)

The gyros in the XIV would topple if you exceeded a 60 deg bank or a 40 deg dive.

Re-erection of the gyros took about 15 minutes.


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## Zipper730 (Aug 4, 2017)

wuzak said:


> It was a better design?


It was better in terms of the ability to stabilize after 5-10 seconds, and could tolerate greater bank/dive angles; at 12000-16000 feet it was similar to the Norden, above 20,000 feet it's accuracy was considerably less.


> Britain was broke after WW2


That would explain something!


> Also, how accurately do you need to drop nukes?


That probably did affect the decision making process, except the problem is that dropping nukes becomes really undesirable when other nations have them that aren't your friends, and both you and they are willing to use them.


stona said:


> Optical sights become redundant when dropping ordnance at speeds, from altitudes and at ranges which mean the aimer can't see the aiming point.


Wait, if I recall correctly, the distance to the horizon is

312.6 statute miles / 271.6 nmi at 65000 ft

287.5 statute miles / 249.8 nmi at 55000 ft
274.1 statute miles / 238.2 nmi at 50000 ft

260.1 statute miles / 226 nmi at 45000 ft

245.2 statute miles / 213.1 nmi at 40000 ft

229.3 statute miles / 199.3 nmi at 35000 ft

222.7 statute miles / 193.5 nmi at 33000 ft

217.5 statute miles / 189 nmi at 31500 ft

201.7 statute miles / 175 nmi at 27000 ft

193.8 statute miles / 160.4 nmi at 25000 ft

181.8 statute miles / 157.98 nmi at 22000 ft

168.9 statute miles / 146.8 nmi at 19000 ft

150.1 statute miles / 130.4 nmi at 15000 ft
That's quite some distance even at 65000 feet...



Greyman said:


> The gyros in the XIV would topple if you exceeded a 60 deg bank or a 40 deg dive.


So, it would topple, just took more to do it? The Norden if I recall was limited to 18-degree banks and, eventually, dive-angles from what I was told of 18-degrees.


> Re-erection of the gyros took about 15 minutes.


How long did it take to re-erect the Norden?


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## stona (Aug 5, 2017)

Zipper730 said:


> Wait, if I recall correctly, the distance to the horizon is
> 
> 312.6 statute miles / 271.6 nmi at 65000 ft
> 
> ...



They needed to see and 'track' the target, not the horizon.

I read somewhere that a CEP of 3,000 ft was considered acceptable by the USAF for air dropped nuclear weapons. Not really my thing the cold war, so I can't say where I read that 

Cheers

Steve


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## Tim Moore (Jul 4, 2018)

The Mark XIV or Sperry T-1 had two gyroscopes. One was in the computer, to adjust for climb and dive in the pitch axis, and the other was in the sighting head, to adjust for roll. The sighting head gyroscope was geared so that the mirror rotated at half of the bank angle. The computer gyro would topple at a dive exceeding 40 degrees, and the sighting head gyro would topple at a bank exceeding 60 degrees. It would take twenty minutes for them to erect. The Mark XIV was not superior to the Norden in accuracy, although it did have some advantages in that it could function in climbs, dives, and turns (although not skids). It also could be set up with as little as a ten second bomb run and evasive action could be take up until that point. The Norden continued in service, was used in the Korean war, and was kept in inventory until 1967-8. It was last used to drop acoustic sensors in the Vietnam War in 1967. However, it was rapidly replaced due to superior technology in the jet age. Here is a video of a Sperry T-1 that I have restored and is fully functional:

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## Tim Moore (Jul 4, 2018)

To further answer the original post's questions, airspeed was determined directly by pitot-static input. The wind speed and direction were calculated by the bombardier and input via two dials. The course information was input either by a remote compass or manually using a course knob; the computer calculated the drift angle from that information and the wind data.


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## Zipper730 (Jul 4, 2018)

Tim Moore said:


> The Mark XIV or Sperry T-1 had two gyroscopes. One was in the computer, to adjust for climb and dive in the pitch axis, and the other was in the sighting head, to adjust for roll. The sighting head gyroscope was geared so that the mirror rotated at half of the bank angle. The computer gyro would topple at a dive exceeding 40 degrees, and the sighting head gyro would topple at a bank exceeding 60 degrees. It would take twenty minutes for them to erect.


Was there a caging function? I remember hearing something about the corkscrew maneuver producing some rather steep dive and bank angles...


> The Mark XIV was not superior to the Norden in accuracy, although it did have some advantages in that it could function in climbs, dives, and turns (although not skids).


Isn't drift a skid of sort?


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## Tim Moore (Jul 4, 2018)

Both gyros have a caging knob. It rotates a pair of collars that lock the gyro in place. 
Drift correction is simply angling into the wind so that the ground track proceeds directly to the target, without being blown off course. It is straight and level flight, without turning once the heading is established, just that the nose of the plane is pointed into the wind. 
A skid is the result of turning with too much rudder input relative to the roll axis. This is an active turn that results in centrifugal forces pushing to the outside of the turn along its radius. A bomb released during a skid would be “flung” to the outside of the skid. 
At the beginning of my video “Norden Bombsight Tutorial” there is a demonstration of drift correction.


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## Zipper730 (Jul 4, 2018)

Tim Moore said:


> Both gyros have a caging knob.


Ok


> A skid is the result of turning with too much rudder input relative to the roll axis.


What I was trying to get at was if you were drifting while rolling, I figured the effect would be the same as a drift...


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## Tim Moore (Jul 4, 2018)

I would like to answer your question as best I can. As a pilot, and I don't know if you are or not, I might use terms differently. I certainly don't in any way want to be condescending, so forgive me if I appear so. 
A turn is a change in the heading. A coordinated turn uses equal bank or roll (aileron input) and yaw (rudder input). A slip is using too much roll, with the airplane "slipping" down the down wing. A "skid" is too much yaw, pushing the airplane laterally behind its center of gravity, similar to a rear wheel skid in a car. A bomb released during a skid will likewise be accelerated laterally, so you would not want to do that. In flying, there really is no reason to ever want to skid, but I assume it could happen during evasive action.
Drift, as used in the discussion of bombing, can be either a verb or a noun. To drift, or "drifting", means to depart the desired course, not a good thing. You can be in straight and level flight and still drift due to the wind blowing you off course. Stopping this process is frequently referred to as "killing the drift". This is done by turning the aircraft to a new heading that points the nose into the wind. The airplane is pointed in one direction, but has a different ground track or course. So, don't ever want to be "drifting" but you do want to have established a drift angle or "killed the drift". You would use a coordinated turn to turn to the new heading. There would be no slipping or skidding, but you wouldn't release the bomb until you had completed the process and established your new heading.
So "drifting", the "drift angle", and skidding are all different things. You could still drift off course while turning, of course, but that is not the same as a skid.
Drifting simply means deviating from the desired course, whether turning or straight and level, what the aircraft is doing with relation to the ground. Skidding is uncoordinated flight, with relation to how the aircraft is flying through the air. In theory, you could skid to a new heading and establish the correct drift angle. However, the combination of rolling/banking and drifting does not create a skid.

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