MK 18 Gyro Gunsight

[mdbuehler]

Having a bit of fun with this, so figured I'd make a few posts to both show how this cool little guy works, and save anybody after me the time of sorting it out again.

I picked up a MK 18 gyro lead computing sight off of ebay a week ago (been playing alot of IL2 and wanted something cool for the living room ). Still has the Navy inspection tag signed and stamped attached, its quite cool! I wanted something from WWII, and this worked out perfect as the Catalina's used them (one of my faves) as well as planes all the way up to the F-86 (had an uncle that flew those).

The smaller cylinder on the rear is an electric motor, and the larger is the gyro. The colored rocks in the clear plastic case are silica, that is connected to a breather inside the sight to absorb any moisture that gets inside, and to change color when it does (I'm guessing to pink ). The labeled metal top ver the glass seems as much a warning as a sunshade. I didn't notice this on the K-14s I looked at. Two circular lenses on the top project two seperate images onto the angled glass, then looking at it with two open eyes (or I was watching to much Avatar) it combines them into one in a rather old school 3d kind of way. The effect doesn't show up when I take pictures.

The small hatch on the front opens up, and there are two light bulbs (one for each image) inside. You change these to whatever voltage your aircraft ran on, and some electrical magic on the inside ensures the motor spins at the same speed regaurdless. You can go from 14 to 22 volts.

The lever on the right raises and lowers a glare lense / sunglasses essentially for bight operating conditions.

The center dial is for choosing your targets wingspan (in feet). It will set the initial size of the "smart" portion of the sight, which projects on the right half of the looking glass. It consists of a circle shaped star looking projection:

On the bottom left of the unit is another turnable dial that would be attached to a rotatable selector on the throttle stick of the plane. This one also adjusts the size of the circle, but the pilot would use that while viewing a target to adjust the size so that it encircled the plane. In doing so, the sight now knows the distance the target is from you. It computes this as you twist the dial through a series of gears.

The left portion of the sight is a projected circle with a crosshair in the middle. This one is non-computing, I'm assuming a fallback of sort / one to use in heavy manuevers as the gyro side has to be turned off or it will be damaged (easy to see why in the later pics).

The lever on the left when pulled down, will mask the projected circle so all you see is the crosshair. Not sure of the purpose of that yet unless its just a preference thing.

I was lighting it up with a flashlight, which worked pretty good for the photos, but there wasn't any documentation anywhere for the pinout on the 10 pin attachement cable, and the left side projected sight didn't work at all, so I went ahead and popped the top off to check things out. I'll get those pics up later this weekend, as the insides are really interesting!

 

[Shinpachi]

I am very curious.
Thanks for sharing.

 

[Crimea_River]

Interesting!

 

[B-17engineer]

Sweet

 

[mdbuehler]

So with the back removed, looking in from the rear:

On the left is the lense / aperture that projects the star pattern. As you rotate the size selectors, it rotates the spiral patterned shroud over the lense, exposing the gap further up the spiral and covering the equalivalent inner area, which makes it grow in diamter.

On the right is the circle / crosshair, with the mask currently up so only the crosshair is projected through that hole, and the circle is blocked. The light bulbs are behind each of these illuminating through them, at a pair of mirrors located where your eyes are when looking at this photo. The image then bounces off those mirrors (which are the adjustable ones) and onto the angles mirror above the two apertures. In this photo the mirror is showing you the two lenses above it so its hard to tell thats actually a mirror there From there the image goes out the two top lenses (which you are seeing the reflection of) and into the angled top glass where you see it.

The three contacts in the bottom right corner provide power for the left and right bulbs, and the ground. They pick it up off contacts on the back plate where all the power comes in. In left to right order its Ground / Right Bulb / Left Bulb. The upper right hole on the outside is where the silica crystal box attaches, which feeds via a hose to that black partition segregating the two halves of the sight from each other.

 

[mdbuehler]

Now for the cool whirly bits!

On the left is the motor that drives the whole thing. Its connected to the gyro via a spring used as a belt (you can see a bit between the two mirrors). The left mirror is the fixed crosshair / circle sight's reflector. It can be fine tuned to center it up using the twist knobs located in the corners of the support plate. My mirror had fallen out on this one, which is why it didn't work. Happily, I found it wedged in the other side a bit later and was able to stick it back in

The right mirror does the magic. Its attached to the gyro unit, and is on a articulated / swively base so it can freely tip in any direction independant of the whole units orientation. When spun up, its just like a top wanting to keep its current orientation in space, and it will. That wouldn't be to usefull, so it has electromagnets that impart a force on it returning it to level after a second or so if you stop changing orientation in space.

 

[Airframes]

Nice stuff, and good pics too. You're right, the left side reticule is the stand-by sight, used when the gyro 'toppled' during hard manouvres, and was basically the same as previous, non-gyro reflector sights. The Mk18 is a direct duplicate of the Brirish MkII GSCGS.

 

[mdbuehler]

The magic of how it works seems to be this. Its spun up, your flying with 40' set on the target wingspan. A plane comes into range so you twist the throttle grip to match the projected sight to its wingspan. Now the sight knows the target distance via those gears and has compensated for bullet drop. You both go into an up left turn, so now you need to lead him. The gyro mirror resists this motion, so all the other mirrors actually move around it in space. Its now reflecting its image down to the right which translates after bouncing around the other mirrors to that difference from your current orientation inversed. So now its leading your target up and to the left, and the harder you pull up or turn left, the further up and left it will aim. Pretty cool!

Here's where the power comes in. The left three tabs correspond to the others in the main housing. Left light / Right light / Ground (for everything apparently). The squares are small connector boxes that terminate the incoming power lines and connect them to the leads for the motors and magnets. The first in that group is the positive lead for the motor, and the rest are the positive leads for the electromagnets. By applying 12 volts from a car battery or one of my RC planes to the main ground then any of the other leads, you can light up the lights (which burned out quickly lol) or fire up a magnet / spin up the gyro and mirror.

The mirror has enough range of motion to mash into the cage, so I'd guess this is why you had to park the gyro (not an option on the sight, must be a switch elsewhere that stopped the motor but left the magnets on). If you change direction quickly enough, it will hit the cage. While spinning, that wouldn't be pretty. With the magnets on but not spinning, the mirror will stay put and move with the rest of the sight.

As for the cabing pinout:

I got them, but some bad news from my voltmeter as they bleed over a bit so I think the insulation is going in the magnets (it also gets hot when run, and several don't work anymore). The motor works great and runs for hours though, and I have one good magnet so if I'm carefull it'll be OK and not 140 degrees

1. Main Ground
2. Magnet
3. Magnet
4. Motor
5. Magnet
6. Magnet
7. Magnet
8. Left Light
9. Right Light
10. Magnet

I may pull the gyro out at some point and give it a look, but for now I'll just be picking up some LED lights to replace the old burned out bulbs, and that will let me have it lit up at a lower voltage too The parts are cool, they're all covered in somebody's hand writing, numbered with random codes in pencil and marks made on the mirrors when it was getting balance out.

Neat little display piece, and now I finally get how it actually works. Time for more IL2

 

[Shinpachi]

I respect the inventor.
Thanks again for sharing, mdbuehler.

 

[Crimea_River]

Interesting stuff md.

 

[mdbuehler]

Last bit, as it now sits on my desk finsihed

I took apart the gyro even though I didn't need it to work, but was now curious. Its acutally working fine, magnets and all. The base of the gyro unit contains 4 electromagnets connected in series in two pairs.

First pair are White + and Black -

Second pair are Red / Yellow and Red / Green

A third magnet rings the circular metal insert above the other four magents using Black for + and Black for -

The final electromagnet is a very large half circle coil right behind the mirror, with Black + and Black -

Final cable pinout for whomever else reads this off google later

1. Ground
2. Black
3. White
4. Red
5. Red / Yellow
6. Red / Blue
7. Red / Green
8. light
9. light
10. Grey

Something else obviously controls these all seperately, as increasing or decreasing voltage to any given set lets you adjust the 'center' position of the mirror. As I didn't have that I wired them all up in series, and at 12 volts they put out a decent strenght field and could center up the mirror. I applied 18 volts to the motor which got it good and revved up, so it all works!

To display it there was no plan to have it spinning, but I do want it lit. I secured the gyro mirror with two easily removable dropes of hot glue. I went to the auto store and swapped out the 12 volt bulbs I'd replaced the 22 volt bulbs with for a set of low voltage (9 volt) LEDs.

I wired this into a 500ma 9volt wall power supply, and it'll pretty much run forever now without all the heat from the regular bulbs. End result looks good:

Your eye combines the two image into one when you view it, and it all appears centered when you do.

And the reason for the ability to mask that circle? When using the computing side, you mask the circle on the fixed old-style side since you see both at once. They leave the crosshair there, as that is still the final destination of your bullet, and it lets you see the lead the computer is giving you.

Kind cool, I like it

 

[Shinpachi]

I have summarized your explanation on an image.
Pupil distance is trially fixed at 60mm.
Thanks

 

[GMaximus]

Having a bit of fun with this, so figured I'd make a few posts to both show how this cool little guy works, and save anybody after me the time of sorting it out again.

It's a great find for me, thank you sir!

There's one simple silly question that brought me here, it's about how it works : what type of LCOS sight it is? Historical (real-time) or predictor (director)? Does it show the point where your bullets will be if you pull the trigger now, or is it the point where your bullets would be right now if you pulled it a bit earlier?
So, is it 1 bullet TOF forward or backward?
The same question goes for K-14 and GGS Mk.II, as they share the same construction.

 

[Brooke]

Last bit, as it now sits on my desk finsihed

I took apart the gyro even though I didn't need it to work, but was now curious. Its acutally working fine, magnets and all. The base of the gyro unit contains 4 electromagnets connected in series in two pairs.

First pair are White + and Black -

Second pair are Red / Yellow and Red / Green

A third magnet rings the circular metal insert above the other four magents using Black for + and Black for -

The final electromagnet is a very large half circle coil right behind the mirror, with Black + and Black -

Final cable pinout for whomever else reads this off google later

1. Ground
2. Black
3. White
4. Red
5. Red / Yellow
6. Red / Blue
7. Red / Green
8. light
9. light
10. Grey

Something else obviously controls these all seperately, as increasing or decreasing voltage to any given set lets you adjust the 'center' position of the mirror. As I didn't have that I wired them all up in series, and at 12 volts they put out a decent strenght field and could center up the mirror. I applied 18 volts to the motor which got it good and revved up, so it all works!

To display it there was no plan to have it spinning, but I do want it lit. I secured the gyro mirror with two easily removable dropes of hot glue. I went to the auto store and swapped out the 12 volt bulbs I'd replaced the 22 volt bulbs with for a set of low voltage (9 volt) LEDs.

I wired this into a 500ma 9volt wall power supply, and it'll pretty much run forever now without all the heat from the regular bulbs. End result looks good:

Your eye combines the two image into one when you view it, and it all appears centered when you do.

And the reason for the ability to mask that circle? When using the computing side, you mask the circle on the fixed old-style side since you see both at once. They leave the crosshair there, as that is still the final destination of your bullet, and it lets you see the lead the computer is giving you.

Kind cool, I like it

Hi: This post does not match post #8. Maybe a wire color typo?
I expect to get one of these in today's mail.
I think I have found some patents for it and they are at:
Mk 20 Mod 4 Gun-Bomb Sight and <CTRL>F Mk18