Helicopter Jump Navigation?

[MightyGem]

Anybody know what it is??
http://www.pprune.org/rotorheads/545950-mysterious-function-helicopter-flight-computer.html

[ALTAM]

It is an ASW function for navigation between dipping positions for ASW helicopters. A dipping position is the the helo hovers and lowers the sonar. The AFCS or auto pilot flies the aircraft from flight at 200 ft 100 knts to the hover.

Before Helios had radar, Wessex mk 1 the computer was used to work out transit headings and times from dipping posn to dipping post.

[John Eacott]

ALTAM,

Except that this Dalton was back in the Whirlwind/Wessex HAS1 days when the transit height was 150ft and the dip height was 30ft, and 100 knots was a speed to be dreamed of ;)

Sea King upped the transit and hover height, but the Wessex HAS3 doppler plot aligned with the radar made the Dalton obsolete.

[MightyGem]

So, how did you use it?

[ALTAM]

I understand that it was a bit fiddly, but I never had to use it as I only flew in Wessex 3 and Sea King 2 and 5 with doppler driven true motion radar. However, some of my instructors on 750 SQN used them in the 1960s and told their stories.

With the wind set on the Dalton, work out the range and bearing to the next dip posn. Then use the side shown, slide and wiz wheel to work out the transit heading and the ground speed. The calculator on the back of the Dalton would give you the flight time. The curves on the slide would automatically calculate the transition down and up distances as well as the turning circles. These would depend upon the wind speed.

I understand that it worked quite well as long as you had an accurate wind, and the pilot flew to the numbers. Essentially, the AFCS would fly the aircraft from the hover to the transit height 135 ft 90 knts, the pilot would turn onto the transit heading and the Obs would start the watch. When the time was reached, the Obs would call mark dip, and the pilot would turn into wind and engage the AFCS and transition down program.

The sonar was a searchlight beam unlike the 90 degree beam that I used in the Wx 3 and Sea King so I suspect that it was a bit hit and miss. Also, insert the Napier Gazelle engine with its susceptibility to 7th stage compressor failure it must have been fairly sporting.