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Radar Sights
03-24-2008, 10:08 AM
Post: #1
Radar Sights
I was wondering if we could put together what Radar Systems various Aircraft are using and how good they are and what we'll more likely than not see before the war ends.

"All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as self-evident."

Arthur Schopenhauer, German philosopher
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04-01-2008, 03:54 AM
Post: #2
 
F-86 A Sabre

A-1CM Gunsight: The early sights like the A-1 were 2 gyro sights; one deflection ; one elevation. They were rate gyros mounted in single plane of freedom gimbals. The principle is a bit complex, but basically, the amount of precess was measured for use in calculating a prediction lead. Range was either manual or automatic as selected by the pilot. The range data was transmitted to the sight where it was converted to a usable signal that exerted restraint on the gyros- low restraint at long ranges; high restraint in close.The amount of precession was modified by the range input. Basically, the sight solved for lead in the plane of target motion, gravity drop, and trajectory shift.

There was a choice of manual or radar ranging for the A-1 sight. For radar, lock was generally impossible at ranges under 1000 feet. The reticle was a 10 diamond system with a pipper center. The diamonds could be manually set for range. I believe the reticle was 16 mils min. and 150 mils max. In Radar ranging, when a lock was achieved, you got a lock on light and the reticle would increase in brightness. As for ground clutter, at low altitudes, most pilots would use manual ranging to eliminate the ground clutter problem
which could effect the radar ranging mode.

APG-30: The AN/APG-30 was the radar used for most of the jet day-fighters. It was used on later model F-84 straight-wings, the F-86 day fighters, the F-84F, and the F-100.
The radar is a simple X-band pulse set, with a fixed horn antenna. It doesn't scan, and radiates a signal that can basically be described as a 20 degree cone. The peak power is 5kw. I don't remember pulse width or prf, right at the moment. The radar controls and indicators consist of an On/Standby/Off switch, A switch to control the range gate, a dial to set the maximum range that the radar will sweep the range gate, and a button on the control stick to reject the current target. Indicators are a light that illuminates when the radar locks on, and a range indicator, either an analog dial next to or withing the sight itself, ir as a range bar on the sight reticle.

When the radar is active, it scans in range, sweeping the range gate from the minimum range, (225 yds/200m) to the maximum range seleced by the pilot. (up to 3000 yds/2700m). When an echo is returned, the range gate will stop sweeping and track that target, the lock-on light will illuminate, and the range meter will indicate the range. (Range information is also sent directly to the sight.) When the range gate is sweeping, the range indicator follows it, IIRC. This has the effect of locking the radar automatically on the nearest target. If this isn't the proper target, the pilot can press the Radar Reject button on the control stick to command the radar to sweep the range gate from that point, locking on th ethe next target further out, and so on. Ground return can be a problem, either when flying low enough that the scanned cone is touching the ground, or when diving. The range gate can be turned off, or the radar set to standby in these cases, and manual ranging used, just like a WW 2 gyro sight.

It sounds rather complicated, but all the pilot has to do is turn on the radar, set the range sweep, and, in most cases, let the radar lock on to whatever's in the sight combining glass. If it's not the target he wants, he pushes the button to get the next one. It's much simpler to operate, and more accurate than the "Size the Reticle to the Target" stadiametric system, which can be thrown off by in inaccurate estimate of the target's size, or the perspective of a high angle-off view.

F-86D Sabre Dog

E-4 FCS: The First F-86D-1 was fitted a Hughes E-3 fire-control system (FCS), followed by F-86D-5 with an E-4 FCS, with much longer range radar than the E-3. In operation, the pilot would be directed to the vicinity of a target by a "Ground-Control Intercept (GCI)" operator. At a range of about 50 kilometers (30 miles), the pilot would acquire the target with the aircraft's AN/APG-7 radar. The E-4 fire-control system, which integrated the radar with an AN/APA-84 electronic analog computer system, would provide a course to intercept the target. At the appropriate time, the E-4 would indicate that rockets should be fired as the two paths intersected, the F-86D streaking past the target from the side or front. The E-4 would also provide a warning if there were danger of a collision. The F-86D had a manual lead-computing gunsight as a backup.

In reality, dumping the workload normally handled by a pilot and a radar operator in a two-seat interceptor on a single man proved to be challenging. Despite the fact that the electronics were intended to take up much of the load, the F-86D was said to require the most training of any contemporary USAF plane, even more than the Boeing B-47 bomber. And the advanced technology used in the interceptor led to painful teething troubles.

F-86K

MG-4 FCS: The F-86K was a simplified version of the F-86D, developed as an export intercepter for the western allies under the Mutual Defense Assistence Program. The E-4 FCS of the Sabre Dog was felt to be unsuitable for an export a/c because it was complicated, not very reliable und top secret. So the F-86K sacrificed the collision-course intercept abilities of the Sabre Dog and reverted to less challenging tail-chase intercept. The MG-4 used the existing APG-7 of the -86D and could compute efficient tail-chase intercept trajectories.

F-86L Sabre Interceptor

SAGE: The F-86L was essentially a Sabre Dog incorporating a data-link capability for the Semi-Automatic Ground Environment (SAGE) air-intercept control system. The CGI system used with the F-86D had not proven entirely satisfactory. Communications between the ground controller and the pilot tended to be slow or confusing, and so something a little smarter was needed. SAGE, introduced in 1953, had been developed by the Lincoln Laboratory at the Massachusetts Institute of Technology (MIT) and used a big ground-based computer to assess target information obtained by ground radar, and relayed target data to the interceptor through an AN/ARR-39 datalink, automatically guiding the interceptor to the target while the targeting information was displayed to the pilot.

Well, this was the age of vacuum tubes and a SAGE computer was the largest, heaviest und most expensive computer ever built. Each one of the 24 installations in fact had two identical CPUs, one of which would be in standby mode and one of which would be running. Each one had about 60,000 vacuum tubes and weighed 250 tons.

and at last F3D Skyknight

APQ-35: The first two prototypes had been fitted with the older SCR-720 radar since the AN/APQ-35 hadn't been available at the time. The AN/APQ-35 actually consisted of two radars: (a) the AN/APS-21 search radar that could locate fighter-size targets at a range of 32 kilometers (20 miles) and (b): the AN/APS-26 targeting radar, with a range of 3.2 kilometers (2 miles). According to other sources "the SCR-720 radar could detect targets at up to 85 miles away", while the APQ-35 "was able to meet the requirement for detection at a range of 125 miles."

The AN/APS-21 could be used to locate a target, pass it over to the AN/APS-26 at close range for target tracking, and continue to scan for new targets. In the case of the Skyknight, descriptions of the AN/APQ-35 radar system are confusing and contrary, particularly since it actually consisted of two separate radars, the AN/APS-21 and AN/APS-26, working in conjunction. Range figures vary widely from source to source; as it turns out, radar range has to be specified relative to the size of a target, and not surprisingly a radar can pick up a heavy bomber from much farther away than it can pick up a fighter.
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