In article ,
"John Carrier" writes:
In use, did this radar provide a lead point in the HUD at which to aim??

Not a HUD, merely a gunsight. Lead computing gunsights adjust for bullet
trajectory based on gravity and aircraft load factor (G). The pilot could
adjust the sight for target range and (sometimes, usually?) wingspan of the
target aircraft (the better to estimate range by). Once engaged, you had a
sight that provided a correct lead solution for a particular range
(typically 800-1000 feet).

With radar input, the range setting is based on actual target range vice a
fixed input, thereby eliminating a variable in what is typically a highly
dynamic environment.

If I may amplify a bit, here - The sight itself wasn't all that much
different than any other gyro gunsight. The Gyro sights measured teh
precession of a pair of gyroscopes in the sight to measure the
azimuth/elevation rates when the pilot (or gunner, if it was a turret
installation) tracked the target, cross-referenced that with bullet
Time of Flight, which is affected mostly by range, but also by the
bullet's drag (deceleration after leaving the barrel), and a couple of
other factors (Jump, which is a fudge for the gun moving when the
bullet's fired) and gravity frop (again, propotional to time of
flight). The sight, using the range, jump, and bullet drop factors to
adjust the tension of springs hooked to the gyroscopes, would move the
piipper (Aiming Mark) to the spot calculated to be the correct lead
necessary to hit the target. As you can see, it's really imortant to
have the proper range (and range rate, in more sophisticated sights).
In WW 2, when the sights first came out, this was done using
stadiametric techniques. You dialled in the opponent's wingspan on
the sight, and, using a twist grip like a motorcycle throttle
(Actually on the throttle for fighters, or one of the sight grips for
bombers) adjusted a circular range reference reticle to fit the
wingspan of the target's image. Of course, if the target wasn't quite
head on, you had to fudge it a bit, to get it right. This means,
though, that your pilot or gunner is a busy guy, working the stick &
throttle to smoothly track a jinking target, or a target making a
Curve-of-Pursuit pass, where the range and elevation/azimuth rates are
changing all the time, and trying to be as smooth as possible while
tracking the target so that the sight settles down. The biggest
errors that occurred with the sights were range measurement and
tracking. In the late 1940s, teh Air Force and Navy decided that it
would be a good thing to use a small, non-scanning radar that only
tracked range to feed accurate range measurements to the sight. This
was the genisis of the AN/APG-5 and AN/APG-30 that ended up in all the
U.S. swept-wing jets that didn't have a bigger air-intercept radar.
Thae AN/APG-30 was a small pulse set, that swept a range gate
(it would only look for an echo for a small part of the time that a
pulse was going out & bouncing back, that correponded to a particular
range) out through its max range of 6,000', and would lock onto and
track the range of the nearest target in its field of view. (Well,
it's a little more complicated than that - there was a button on the
pilot's stick that would tell the radar to ignore the target it was
tracking and move out to the next one). This, whne it worked,
provided fairly smooth, accurate range measurements to the signt, and
allowed it to compute a better lead. With teh high closing speeds
that jet fighters had, and the large lead angles needed to track
crossing targets, it was a very useful item indeed.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster