# Gyro Gunsights



## Zipper730 (Feb 16, 2019)

I understand that they use a gyro to sense the movement of the aircraft, but what I'm uncertain about is how they avoid tumbling the site during aggressive maneuvers...


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## XBe02Drvr (Feb 16, 2019)

Zipper730 said:


> I understand that they use a gyro to sense the movement of the aircraft, but what I'm uncertain about is how they avoid tumbling the site during aggressive maneuvers...


Ever hear of a 3-axis gimbal? That's how it's done. Because you're not attaching an instrument panel indicator directly to the gyro itself, you don't have to "anchor" it or restrict its travel in any way. With no gimbal limits for it to bang into, there's nothing to make it tumble.
The alignment of the gyro is sensed by either electrical contacts or capacitive sensors on the gimbal rings and sent to the processor, a primitive analog computer, along with accelerometer values in all three axis relative to the alignment of the guns (for lead calculation), and range/closing velocity from the radar (if so equipped) for trajectory calculation. It's all FM (F--king Magic)!
Cheers,
Wes


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## Airframes (Feb 16, 2019)

In addition, the British GSG (and the licence-built American version, the K-14), had a 'standard' reflector graticule alongside the gyro 'pipper' graticule, for use if the gyro did tumble, or couldn't 'track' during extreme conditions, hence the twin projector lenses seen on top of the sight body.


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## Zipper730 (Feb 16, 2019)

XBe02Drvr said:


> Ever hear of a 3-axis gimbal?


I have heard of it, but I don't know much about it. That said, why didn't they fit every combat aircraft with these types of systems? Many of the USAF bombers such as the B-52 and B-58 were capable of executing turns over 2g, but their bomb/nav gyros would tumble silly if they went past that. I know the B-58 had all sorts of problems with the gyros getting tumbled when a pilot did a light-weight takeoff and did a climb with a series of aileron rolls (he was trying to show some F-4 drivers that they can do cool maneuvers too).

The attitude direction indicator on aircraft (first reference to this was around 1954) had a gyro that would go through a controlled precession when you went past 80-degrees up or down, and that would also be a decent feature too since such aircraft usually do not reach dive angles anywhere near that steep, and the B-52's bomb/nav systems eventually incorporated some sort of "auto-cage" feature. I'm not sure exactly when but I do remember a mention being made during the Christmas day raids that the displays would suddenly show large black areas as the gyro would cage attempting to shake off all the missiles coming their way.


> The alignment of the gyro is sensed by either electrical contacts or capacitive sensors on the gimbal rings and sent to the processor, a primitive analog computer, along with accelerometer values in all three axis relative to the alignment of the guns (for lead calculation), and range/closing velocity from the radar (if so equipped) for trajectory calculation.


So the movement of the rings is interpreted as an electrical-input? Don't those systems suffer from gimbal-lock?



Airframes said:


> In addition, the British GSG (and the licence-built American version, the K-14), had a 'standard' reflector graticule alongside the gyro 'pipper' graticule, for use if the gyro did tumble, or couldn't 'track' during extreme conditions, hence the twin projector lenses seen on top of the sight body.


So if one went apeshit, the other would look normal?


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## XBe02Drvr (Feb 16, 2019)

Airframes said:


> the British GSG (and the licence-built American version, the K-14)


Is there anything aeronautical (or nautical) that the Brits didn't think of first?
I read recently that the Philadelphia shipwright whose diagonal bracing made the Constitution class frigates so hard to sink in the war of 1812 actually pirated the idea from the Brits. They hadn't successfully used it in their own ships because they didn't have the right wood (live oak) to make it work properly.
Cheers,
Wes


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## Zipper730 (Feb 16, 2019)

XBe02Drvr said:


> I read recently that the Philadelphia shipwright whose diagonal bracing made the Constitution class frigates so hard to sink in the war of 1812 actually pirated the idea from the Brits.


That is interestingly the same principle as the geodetic construction


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## XBe02Drvr (Feb 16, 2019)

Zipper730 said:


> I have heard of it, but I don't know much about it. That said, why didn't they fit every combat aircraft with these types of systems?


A 3-axis remote, electrically sensed gyro system was complicated, expensive, and troublesome in the early days of the technology, and not felt to be necessary in the high altitude level bomber regime in which cold war nuclear bombers were designed to operate. You young folks have very little concept of what things were like before transistors, integrated circuits, and digital technology came along.


Zipper730 said:


> The attitude direction indicator on aircraft (first reference to this was around 1954) had a gyro that would go through a controlled precession when you went past 80-degrees up or down


When you're talking a panel mounted Attitude Indicator with an integral gyro, you by definition have a gyro with constraints on its freedom of motion. The physical attachment that transmits the gyro's motion to the indicator on the face of the instrument limits the gyro's freedom of motion in 3 axis, so there will be gimbal limits. When the gyro hits those limits it will tumble. Later aircraft that have full 3 axis attitude indicators do it with remote electric gyros. As the technology has advanced, the relative cost as gone down and reliability improved.


Zipper730 said:


> So the movement of the rings is interpreted as an electrical-input? Don't those systems suffer from gimbal-lock?


Free to tilt in all three axis, what's to cause gimbal lock??
Cheers,
Wes


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## XBe02Drvr (Feb 16, 2019)

Zipper730 said:


> That is interestingly the same principle as the geodetic construction


Yeah, but I think it predated the Wellington by a bit.
If you're ever in Boston, check out USS Constitution. She's still in commission and has a regular active duty Navy crew. If you ask real nice and they're not too busy, you MAY get someone to take you down in the hold (not part of the tour) and show you the braces. She got drydocked a couple years ago and all of that hull structure got refurbished. Maybe if you're lucky you'll get a knowledgeable sailor who can explain such terms as "hogging of the hull", "broadside weight of metal", "fearnought screens" and "brass monkey"
Cheers,
Wes


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## Zipper730 (Feb 16, 2019)

XBe02Drvr said:


> A 3-axis remote, electrically sensed gyro system was complicated, expensive, and troublesome in the early days of the technology, and not felt to be necessary in the high altitude level bomber regime in which cold war nuclear bombers were designed to operate. You young folks have very little concept of what things were like before transistors, integrated circuits, and digital technology came along.


I probably do, but I'm curious about something in particular...

Aren't star-tracking systems also complicated, as well as doppler based radar-systems, as well as a navigation system that acts like a Euler Pendulum (the idea was conceptually like a pendulum that extends right down to the middle of the earth, except using gyros and gearing systems instead to duplicate this effect for most intents and purposes)? The B-58 had all these things...


> When you're talking a panel mounted Attitude Indicator with an integral gyro, you by definition have a gyro with constraints on its freedom of motion.


This would be the older ADI's?


> Later aircraft that have full 3 axis attitude indicators do it with remote electric gyros.


That's the ADI I described right?


> Free to tilt in all three axis, what's to cause gimbal lock??


Gimbal lock - Wikipedia


> Yeah, but I think it predated the Wellington by a bit.


I would say by more than a bit...

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## XBe02Drvr (Feb 16, 2019)

Thanks


Zipper730 said:


> Aren't star-tracking systems also complicated, as well as doppler based radar-systems, as well as a navigation system that acts like a Euler Pendulum (the idea was conceptually like a pendulum that extends right down to the middle of the earth, except using gyros and gearing systems instead to duplicate this effect for most intents and purposes)? The B-58 had all these things...


Ayup, and it had finite weight, capacity, and cost constraints as well. Give 'em half a chance, and engineers will stuff your flying machine so full of gadgets it won't fly. If you're going to drop your nuke from 50,000 feet at Mach 2, an all-axis AI isn't probably your greatest need.


Free to tilt in all three axis, what's to cause gimbal lock??

Gimbal lock - Wikipedia

Well, you live and you learn! So that's what that extra gimbal with its little servomotor was for. Thanks for the enlightenment.
Cheers,
Wes

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## Zipper730 (Feb 16, 2019)

XBe02Drvr said:


> Ayup, and it had finite weight, capacity, and cost constraints as well.


True


> If you're going to drop your nuke from 50,000 feet at Mach 2, an all-axis AI isn't probably your greatest need.


Actually the B-58 seemed to be capable of exceeding the Mach 2.0 specified speed, it seemed at least capable of hitting Mach 2.4, and some implied it could get pretty close to Mach 3 (nuts as it sounds) for short bursts.

The honeycomb skin played a role in reducing temperature build-up
It's smoother than regular aircraft skin, as it lacks rivets
The greater depth and volume might have some thermal-tolerance effects (that or internal surface area -- I remember reading about the Silbervogel using a type of sinterized aluminum foam and it could take 1000C, and the closest analogue is a honeycomb)

There was an SST proposal revolving around a B-58 design
The wings were largely lifted off the B-58 with the exception of the outboard wing (it had an engine pod on the tip)
The fuselage was totally different in design as it had a cabin and a side-by-side cockpit, most of the nose was different except (possibly) the tip, the tailfin might have been similar, but it had a tailplane and different engines (4 x J58) and pods.
The construction of the aircraft was presumably the same (honeycomb steel leading & trailing-edges, honeycomb-aluminum skin for the rest)
Cruising speed was to be Mach 2.4...

The maximum airspeed the B-58 was rated for was around 600 knots -- I'm not sure what they typically would be cruising around at, but since the plane wasn't power limited, and temperature being the ultimate limit, that would probably get you up around Mach 3.
As for all-axis AI -- what does artificial intelligence have anything to do with a four-gimbal system?


> Well, you live and you learn! So that's what that extra gimbal with its little servomotor was for.


The servo-motor basically kept the reticle always pointing ahead?


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## XBe02Drvr (Feb 16, 2019)

Zipper730 said:


> All axis AI? What does artificial intelligence have to do with this?


 😂 😂
Ha ha! Attitude Indicator, not Artificial Intelligence! Get your head out of the 21st, we're talking the 20th here.
Cheers,
Wes

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## Airframes (Feb 16, 2019)

Yes, if the gyro sight went t*ts up, then the normal, reflector sight graticule, always illuminated alongside it, could then be used. Of course, the pilot then had to calculate the 'angle off' for deflection himself.

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## Zipper730 (Feb 18, 2019)

XBe02Drvr said:


> Attitude Indicator, not Artificial Intelligence! Get your head out of the 21st, we're talking the 20th here.


Most people use ADI as the term for attitude-indicator. I was kind of thrown for a loop lol



Airframes said:


> Yes, if the gyro sight went t*ts up, then the normal, reflector sight graticule, always illuminated alongside it, could then be used. Of course, the pilot then had to calculate the 'angle off' for deflection himself.


Okay, that makes sense


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## XBe02Drvr (Feb 18, 2019)

Zipper730 said:


> Most people use ADI as the term for attitude-indicator. I was kind of thrown for a loop lol


Again, get your head out of the 21st century. The modern day *Attitude Direction Indicator *was still in the future back in the mid 20th century when gyro gunsights appeared on the scene. The incorporation of magnetic *Directional* information into the *Attitude Indicator* came later to create the *Attitude Direction Indicator, *or* ADI.*
Cheers,
Wes

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## Brooke (Feb 21, 2019)

Zipper730 said:


> I understand that they use a gyro to sense the movement of the aircraft, but what I'm uncertain about is how they avoid tumbling the site during aggressive maneuvers...



The gyro gunsight is NOT gimbled but rather constrained with springs. As the plane with the gyro sight turns to follow a target that puts a force on the gyro which then moves in a direction 90 degrees from the force and 90 degrees from the spin axis. Causing the image in the gunsight to lead the target. There are a number of factors that control the scale factor, i.e. how fast the image moves relative to the movement of the chase plane and these need to be properly set in order for the sight to show the correct lead.
Navy Mk. 18 Gun Sight

There are many aircraft uses for gyroscopes and each application has its own specifics.
Gyroscopes

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## PAulo PPI (Feb 22, 2019)

Zipper730 said:


> I understand that they use a gyro to sense the movement of the aircraft, but what I'm uncertain about is how they avoid tumbling the site during aggressive maneuvers...





Brooke said:


> The gyro gunsight is NOT gimbled but rather constrained with springs. As the plane with the gyro sight turns to follow a target that puts a force on the gyro which then moves in a direction 90 degrees from the force and 90 degrees from the spin axis. Causing the image in the gunsight to lead the target. There are a number of factors that control the scale factor, i.e. how fast the image moves relative to the movement of the chase plane and these need to be properly set in order for the sight to show the correct lead.
> Navy Mk. 18 Gun Sight
> 
> There are many aircraft uses for gyroscopes and each application has its own specifics.
> Gyroscopes



I had a Ferranti MK IV used in the Gloster Meteor and a K14 used in the F80. What actually turns is a small mirror. that reflects the piper and assorted diamonds that are varied by either the throtle or the the wigspan adjustment. This mirror is gimbled to the electric motor axis. In order to be able to see relected image of the piper and diamonds at eye level, I used some small foam pads to keep the mirror fixed in the correct position.


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## PAulo PPI (Feb 22, 2019)

PAulo PPI said:


> I had a Ferranti MK IV used in the Gloster Meteor and a K14 used in the F80. What actually turns is a small mirror. that reflects the piper and assorted diamonds that are varied by either the throtle or the the wigspan adjustment. This mirror is gimbled to the electric motor axis. In order to be able to see relected image of the piper and diamonds at eye level, I used some small foam pads to keep the mirror fixed in the correct position.


I just iluminated the sight lamp, not the electric motor.


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## PAulo PPI (Feb 23, 2019)

Zipper730 said:


> I have heard of it, but I don't know much about it. That said, why didn't they fit every combat aircraft with these types of systems? Many of the USAF bombers such as the B-52 and B-58 were capable of executing turns over 2g, but their bomb/nav gyros would tumble silly if they went past that. I know the B-58 had all sorts of problems with the gyros getting tumbled when a pilot did a light-weight takeoff and did a climb with a series of aileron rolls (he was trying to show some F-4 drivers that they can do cool maneuvers too).
> 
> The attitude direction indicator on aircraft (first reference to this was around 1954) had a gyro that would go through a controlled precession when you went past 80-degrees up or down, and that would also be a decent feature too since such aircraft usually do not reach dive angles anywhere near that steep, and the B-52's bomb/nav systems eventually incorporated some sort of "auto-cage" feature. I'm not sure exactly when but I do remember a mention being made during the Christmas day raids that the displays would suddenly show large black areas as the gyro would cage attempting to shake off all the missiles coming their way.
> So the movement of the rings is interpreted as an electrical-input? Don't those systems suffer from gimbal-lock?
> ...



I understand that the american K14 was an under license version of the brit GGS. But it introduced a very positive inovation, which was the possibility of introducing the necessary mil deflection so it could be used in dive bombing or rocket launch. Depending on the bombing angle, release altitude and speed, you could aim directly the target. I remeber that on a 45 degree angle, with bomb relase at 3 k feet at 350 kt, the delectin was around 60 mils.
One other observation, I also believe that the GSG was initially meant for use in the defensive guns of the RAF bombers. It was later adapted for use in th ighters. I also have one of the sights.

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## Greyman (Feb 23, 2019)

PAulo PPI said:


> I understand that the american K14 was an under license version of the brit GGS. But it introduced a very positive inovation, which was the possibility of introducing the necessary mil deflection so it could be used in dive bombing or rocket launch. ... One other observation, I also believe that the GSG was initially meant for use in the defensive guns of the RAF bombers. It was later adapted for use in th ighters. I also have one of the sights.



Yes the initial GGS design that made it to service was the Mk.IIc which was meant for gun turrets, the Mk.IId was the fighter sight. In USN service the Mk.IIc was the Mk.18 and the Mk.IIc was the Mk.21. After initial low enthusiasm the USAAF eventually came on board and adopted the Mk.IId/Mk.21 as the K-14.

I think the added functionality for rockets came from Ferranti. In May 1945 the Director of Armament Development in the UK sent over (among other GGS technical data) drawings for Mod.19 FE to the US. This Mod introduced the RP attachment and raised the sight to 'Mk.IId Series 2'. For what it's worth the new orientation of the graticule called for by Mod.19 was also introduced to the current Mk.IId Series 1 production, in case retrospective fitment of the RP attachment was called for.

*EDIT*: I also note the first photo you have there also has Mod.20 FE; which introduced the sliding sunscreen and brought the sight to 'Mk.IId Series 3'. Drawings for this were also supplied to the USA in May 1945.


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## PAulo PPI (Feb 24, 2019)

Greyman said:


> Yes the initial GGS design that made it to service was the Mk.IIc which was meant for gun turrets, the Mk.IId was the fighter sight. In USN service the Mk.IIc was the Mk.18 and the Mk.IIc was the Mk.21. After initial low enthusiasm the USAAF eventually came on board and adopted the Mk.IId/Mk.21 as the K-14.
> 
> I think the added functionality for rockets came from Ferranti. In May 1945 the Director of Armament Development in the UK sent over (among other GGS technical data) drawings for Mod.19 FE to the US. This Mod introduced the RP attachment and raised the sight to 'Mk.IId Series 2'. For what it's worth the new orientation of the graticule called for by Mod.19 was also introduced to the current Mk.IId Series 1 production, in case retrospective fitment of the RP attachment was called for.
> 
> *EDIT*: I also note the first photo you have there also has Mod.20 FE; which introduced the sliding sunscreen and brought the sight to 'Mk.IId Series 3'. Drawings for this were also supplied to the USA in May 1945.



I believe that in1945 the P51s in Iwo Jima were already using the K14 (I saw them using it in a ground strafing gun camera film, after scorting the B29s). 
About the RP in the MK IV Ferranti, it had a fixed deflection of about 17 mil (that is what I can still remember) and it was not adequate for the HVAR that we used. But we found that we could deflect the + on the the fixed recticle by turning a smal spring knob on the back of the sight and in this way could place the + in any deflection we needed (by using the gyro recticle as reference) , and thus, used the fixed recticle for aiming. After use, all we had to do was to level the + it with the piper on the gyro recticle (provided we were in absolute undisturbed level flight) for using with the guns. We prefered using the fixed recticle for strafing and used the gyro only for air to air gunnery.

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## Greyman (Feb 24, 2019)

I'm not sure when the K-14 first started being used operationally by the USAAF, but it was March 1944 at the latest. As with most other pieces of equipment there were many variations/modifications to the K-14 throughout its service life. So just like a Mk.IId, a K-14 in February 1946 could have quite a few differences with a K-14 in 1944.

Basically what I'm trying to say is that a mid-44 K-14 used by the 8th Air Force wouldn't look like the one in the photo.

Do you know if all of the early US sights were produced at Bendix? I found this interesting bit:

_At a conference in Washington last Tuesday, General Childlaw, Major Elliott and myself conferred with a delegation from the Navy regarding the possibility of the Army obtaining some Mark 18 sights from the Navy for conversion for fighter use. General Childlaw stated the case so well that the Navy reversed its former decision and we are now to get a major part of the present Navy production. The production bottleneck at Bendix has been broken and sights are now being produced in quantity. I am visiting the Eastman plant at Rochester tomorrow with a Naval officer from Washington and we will get the Eastman production line changed from the turret sights to fighter sights. It is expected that enough sights will be obtained to equip all of the P-51's and part of the P-47's in the European theater of operations. As soon as the first two sights are produced I am taking one of them out to the North American Plant at Inglewood so that they can engineer a kit which will be suitable for field installation. If everything goes well, some sights should be delivered in ETO within two months._

_..._

_The first sights which will be sent to the ETO will be "quick and dirty" modifications of the Navy sight. The gravity drop correction will not be used and no super elevation of the moving reticles will be made. A cleaned-up version will appear in about three months._


This was in a letter to a Colonel H.G. Bunker from a Captain N. R. Peterson, 7 February 1944.

I wish I could have heard what General Chidlaw said!

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## PAulo PPI (Feb 24, 2019)

Greyman said:


> I'm not sure when the K-14 first started being used operationally by the USAAF, but it was March 1944 at the latest. As with most other pieces of equipment there were many variations/modifications to the K-14 throughout its service life. So just like a Mk.IId, a K-14 in February 1946 could have quite a few differences with a K-14 in 1944.
> 
> Basically what I'm trying to say is that a mid-44 K-14 used by the 8th Air Force wouldn't look like the one in the photo.
> 
> ...



I really do not have the profound knowledge of the technical and historical aspects of the evolution of these gyro sights that you have. I'm learning with you.
One thing I had always questioned is where the Navy planned the use of the Mk 18 turret sights (this is also confusing because they had a MK 18 sight and a Mk18 system which comprised the whole turret components). I never read about the Naval Liberator ever needing defensive armament since their job was to sink UBoats. 
Maybe they had planned using them on the Privateer and post war PB aircraft. 
Very interesting to know that they thought of converting the MK18s for fighter use. It is one doubt I had, if the Hellcats, Corsairs and Bearcats ever had the K14 installed on them. I know that some P47s had them in the ETO but not in Italy where the ones operated by the Brazilian AF, and also the american ones of the 350 FG, still had the MK8 fixed recticle, also a heritage from the british Mk II (?) or something else used by the RAF (I find it very confusing the names of the english sights). In the collection I had, there were the odd MK 9, 10, 11 and 13 specially projected for usse in specific turrets (tail, waist, top and nose) of the american bombers and not position interchangeables. They had the pursuit curve of the atacker programed in such a way that the sight aimed at the atacker while the guns were pointig to where they should hit the target. I do not know if they were used operationally. And there was also a huge K4 that I simply gave away so large it was.


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## Greyman (Feb 24, 2019)

Yeah the fact that the company name and the service name get thrown around tends to confuse things.

Barr & Stroud GM2
Pilot's Reflector Gunsight Mk.II
(American Mark 8 sight based on this)

Barr & Stroud GJ3
Free Gun Reflector Sight Mk.III
(American Mark 9 sight based on this)


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## Maury Markowitz (Sep 9, 2021)

Zipper730 said:


> Aren't star-tracking systems also complicated,


Replying to a necro-thread here, but Google sent me here so...

Star trackers are very simple. They're basically a spinning disk in front of a light sensor. The disk contains a series of radial slots cut in it. When the slot aligns with the star there is a brief flash of light on the sensor.

The disk is being spun by a synchronous AC motor. When a flash is seen, the angle of the star relative to the seeker is represented by the phase of the signal.

And that's it. It's pretty much identical to early IR missiles with the practical exception that the telescope in front of the reticle is much more powerful, and that one has to have some external reference, typically an inertial platform, to provide the initial aiming during setup.

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## Brooke (Sep 9, 2021)

Zipper730 said:


> I understand that they use a gyro to sense the movement of the aircraft, but what I'm uncertain about is how they avoid tumbling the site during aggressive maneuvers...


The gyro is not in gimbals but rather is a "rate gyro". That's to say it only moves a small amount. See the patent drawings at: Navy Mk. 18 Gun Sight

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## J_P_C (Sep 9, 2021)

XBe02Drvr said:


> Is there anything aeronautical (or nautical) that the Brits didn't think of first?
> I read recently that the Philadelphia shipwright whose diagonal bracing made the Constitution class frigates so hard to sink in the war of 1812 actually pirated the idea from the Brits. They hadn't successfully used it in their own ships because they didn't have the right wood (live oak) to make it work properly.
> Cheers,
> Wes


yes - dynamically tuned mechanical gyros, roll on bearings, gull wings, jet engine, infrared detectors, flush rivets, nuclear propulsion, comprehensive unit system (metric), missiles, gunpowder, magnetic compass and many, many others. But definitely UK holds one of most notable places in technological civilization development.


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