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View Full Version : trying to understand a little bit of technological kit the germans were working on



tralkpha
04-05-2005, 02:57 PM
"The Madrid used an
infrared photocell mounted on the front of a steerable telescope
mirror, with small metal vanes placed in front of the cell in the
shape of a cross. By moving the mirror side to side (or up and down),
the vanes would block off more or less of the image of the target,
and the system continually moved the mirror in both directions
while attempting to find the direction that maximized the signal.
This kept the mirror pointed at the target. The missile's control
system then had the task of attempting to point the missile in the
same direction as the mirror. However the system was never actually
developed beyond a test-bench mockup."


"The Sidewinder improved on this in a number of ways. The first was
to replace the "steering" mirror with a system using a mirror that was
rotating around a shaft pointed out the front of the missile, with the
detector mounted in a fixed location in front of the mirror.
Instead of attempting to track the target in the mirror, the IR sensor
would see the target as brief flashes as the mirror lined up with the
target. By knowing where the flash was as the mirror spun, the
direction (radially) to the target was also known. In addition this
system could track the angle-off to the target in a clever manner.
If the target was further to the side of the field of view, the flash
seen in the detector would be shorter due to the mirror's higher
rate of motion at the outside."

I find the madrid quite difficult to understand.
The sidewinder i understand pretty well.
If anyone would be so kind as to offer some insight into understanding
how this device functioned i would be greatly appreciative.

tralkpha
04-05-2005, 02:57 PM
"The Madrid used an
infrared photocell mounted on the front of a steerable telescope
mirror, with small metal vanes placed in front of the cell in the
shape of a cross. By moving the mirror side to side (or up and down),
the vanes would block off more or less of the image of the target,
and the system continually moved the mirror in both directions
while attempting to find the direction that maximized the signal.
This kept the mirror pointed at the target. The missile's control
system then had the task of attempting to point the missile in the
same direction as the mirror. However the system was never actually
developed beyond a test-bench mockup."


"The Sidewinder improved on this in a number of ways. The first was
to replace the "steering" mirror with a system using a mirror that was
rotating around a shaft pointed out the front of the missile, with the
detector mounted in a fixed location in front of the mirror.
Instead of attempting to track the target in the mirror, the IR sensor
would see the target as brief flashes as the mirror lined up with the
target. By knowing where the flash was as the mirror spun, the
direction (radially) to the target was also known. In addition this
system could track the angle-off to the target in a clever manner.
If the target was further to the side of the field of view, the flash
seen in the detector would be shorter due to the mirror's higher
rate of motion at the outside."

I find the madrid quite difficult to understand.
The sidewinder i understand pretty well.
If anyone would be so kind as to offer some insight into understanding
how this device functioned i would be greatly appreciative.

JR_Greenhorn
04-06-2005, 12:59 AM
So basically, the Sidewinder operates digitally with polar coordinates [minimizes radial distance of samples from center]. Based upon the description posted, the Madrid may have operated in analog with cartesian coordinates (axes created by the vanes) [maximizes analog signal by minimizing with of the vane axes].

The "crosshair" vanes must work like a sundial; the further the object/target reflected in the mirror shifts away from the axis of the missle, the larger the shadows cast by the vanes. The photocell then, provides the strongest signal when the shadows are thinnest.

The other component of the guidance is the target itself. The description posted makes no mention of the frequency of the light that the photocell can detect (IR, visible, etc.). It also doesn't mention whether the missile does the illuminating or if ambient light does.

However, the device must be set up so that the signal from the photocell is strongest when the target is near its center (this is probably accomplished in the telescope's lenses).

Perhaps there were separate photocells--one to track the target with the mirror, and another to minimize the shadows cast by the vanes. I still don't fully understand how the mirror did its tracking, but the flight path correction based on the moving mirror is fairly clear.



Obviously there's some pieces missing somewhere; is more information availible?

Tully__
04-06-2005, 02:18 AM
@Greenhorn: in the first sentence it says the Madrid sytem uses infrared (IR).

@tralkpha: If my understanding of the description is correct, the sensor is aimed at the mirror and the vanes are at right angles to the mirror (ie: edge on to the incoming light/heat when the mirror is aimed at the target). As the mirror goes of target, two things occur to reduce light/heat seen by the sensor:
- the angle of the mirror reduces the light it can catch and reflect to the sensor; &
- the increasing angle of the vanes blocks light from the target reaching part of the mirror altogether.

A diagram:
http://members.optusnet.com.au/tully_78th/madrid.jpg

tralkpha
04-06-2005, 06:54 PM
Thanks alot guys http://forums.ubi.com/images/smilies/11.gif between the additional descriptions and the diagram I think I finally understand http://forums.ubi.com/images/smilies/16x16_smiley-surprised.gif

@Greenhorn: thats all the info I have on the Madrid, other than that it's development superseded the Enzian, which was remote controlled until close enough to the target for an onboard radar system to guide the missile.

JR_Greenhorn
04-06-2005, 10:49 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Tully__:
@Greenhorn: in the first sentence it says the Madrid sytem uses infrared (IR). <HR></BLOCKQUOTE>Who actually reads the first sentence of a paragraph anyway? (Apparently I read part of it, if I picked the name "Madrid" out of it... http://forums.ubi.com/groupee_common/emoticons/icon_rolleyes.gif)

Tully's diagram mostly matches what I had envisioned, even if I had problems describing it. I still wonder how the the mirror follows the heat source, that is, if it can measure decreasing signal, how does it now which direction to follow the target?

This is based on my understanding of the system on a lead-follow basis. The mirror follows the target. Subsequently, the missile follows the mirror by the signal changes created by the vanes. Perhaps the systems aren't as separate as I am thinking they are?

ITA_5SA_Tecnico
04-07-2005, 03:15 AM
In my opinion,the cell isn't a single sensor,but an array of four forming a "four quadrant" matrix like this:

|
cell1 | cell2
_ _ _ |_ _ _
|
cell3 | cell4
|
the direction of the target,is detected by comparing the signals of each sensor,in a way similar to this:

(cell1+cell2)-(cell3+cell4)=up/down
(cell1+cell4)-(cell2+cell3)=left/right

tralkpha
04-07-2005, 09:18 AM
As far as I understand it only one sensor is required. The mirror merely scans a pattern, notes the direction which recieved the most ir, and centers the next scan pattern in that direction. The missile merely points itself towards the center of the mirror's scan pattern.

The only remaining questions I have are probably unanswerable:
what was the search pattern, how many degrees off center did it sweep, and how long did one sweep take?
at what distance could it detect a given ir source?

On a side note it seems the missile would be so indiscriminate that you would have to keep all friendly fighters out of the area.

ITA_5SA_Tecnico
04-07-2005, 12:50 PM
I think the pattern was similar to RADAR.For the target identification,was a problem because it needs a sort of spectrum analysys,in a simple way if you know target's IR spectrum,you can use a optical filter in front of sensor,that is effective but under some conditions:

1)Is Effective only for one airplane or engine.
2)Target's IR level must be greater than no-target's.

PS Those are my speculation based on physics/optics,basic knowledge in electronics/optoelectronic,and hobby.