Introduction -- Basic Limitations of the AIM-9B Missile against a Non-Maneuvering Target
Basic Limitations of the Disturbed Sight and 20 mm Cannon
To adequately employ the disturbed sight and the 20mm cannon, we must understand the limitations of this equipment in any tactical situation. The operating range of the ASG-17 disturbed sight is from 600 to 6000 feet. It will compute the proper prediction angle for a target throughout that range, from the ground up to 50,000 feet and from zero to nine G, if the pilot can track the target properly. However, it is improbable that a pilot would be able to deliver a lethal burst of fire at a range greater than 3,000 feet because of the difficulty in tracking beyond that range.
To accurately predict the lead requirement, any disturbed sight requires the following basic information: range and target angular velocity. In the disturbed sight, range is provided by the ranging radar, and target angular velocity information is acquired by tracking the target aircraft. Since the pilot is forced to turn his aircraft at a certain rate, this rate of turn is a representation of target motion and is directly proportional to target speed. The angular velocity of the attacking aircraft is set into the sight through gyro action. The information is then married to the input from the radar and the proper prediction angle is computed by placing an electrical restraint (stiffness current) on the gyros. At long ranges, little restraint is applied, while at short ranges a great amount of restraint is applied. At ranges beyond 3,000 feet, little restraint is applied, thus producing a tracking index which is quite loose and difficult to control. Since the pilot’s responses are not precise enough, results are usually poor, even though the equipment may be working properly.
Another limitation is the cone of dispersion of the 20mm cannon. For the M-39, harmonization criteria specifies that 80% of all rounds fired must impact in a 4-mil cone. As we increase firing range, bullet density will be decreased by a function of the square (if range doubles, bullet density quarters). At 3,000 feet, bullet density will be decreased to 1 ∕ 9 that at 1,000 feet. As a result, an attacker must fire over a longer time span in order to deliver a lethal burst. At the same time, he must track a target smaller in perspective. Since it is extremely difficult to track with the disturbed sight at ranges greater than 3,000 feet, and the 20mm cone of dispersion causes loss of effective bullet density at this range, we consider our maximum range for the disturbed sight/20mm cannon as 3,000 feet.
Introduction -- Basic Limitations of the AIM-9B Missile against a Non-Maneuvering Target