Mysterious function on a (helicopter) Flight Computer

[Gallinazo]

Hello,

I present a question that has been bugging me now for 20 years. First, a picture (sorry, no attachment function on this forum, so it is dropbox, hope it works).

Photo on Dropbox (https://www.dropbox.com/s/e6navffrrq0zt8g/Mark4B.JPG)

The question; What is helicopter jump navigation?

I picked up this used flight computer at a sort of "airfield car boot sale" for one quid when I was in England. I was with a helicopter pilot when I bought it, but he looked caught out at my question (as pilots do) when asked something they think they should know but don't. It was with me throughout my PPL, and I did the same thing to each instructor again, until one finally made me buy an ARC-2 and "be done with that old thing" (I think it was a ploy to save future instructors the same embarrassment). With all the wonders of the age of information, I still cannot find out what it is. Can someone shed some light on it?

Of course, silence will indicate that I am still causing embarrassment with this thing! :)


https://www.dropbox.com/s/e6navffrrq0zt8g/Mark4B.JPG?dl=0

[4PON4PIN]

Just hazarding a guess, but on the Dalton Computer, (aka wizzwheel) the Nav used one side of the slide to determine the wind direction/speed for normal adjustments to course.
Some Transport a/c such as Andover, Argosy, Hercules, were designed to also drop stores and paratroops. When you're dropping stuff from an a/c the Nav needs to know the wind direction/speed on the ground and wind data at dropping height in order to determine a CARP (Calculated Air Release Point).
So I'm guessing that is the purpose of the "Helicopter Jump Navigation" side of the slide.
I would suggest you post this with our chums on ROTORHEADS Forum for certainty.

[moosp]

I have never seen that version of the Mk 4 in my long aviation life. A fascinating find.

The normal airspeed line up the centre must be associated with altitude, and the concentric rings could be associated with airspeed, as that is the only thing you could do to the knot in those days. Winds were much less accurate.

But jumping from a helicopter was of such a rarity in those days that I cannot imagine they went to the trouble of producing a special calculator just to calculate the correct speed to fly with a specific wind and altitude.

To me an interesting mystery...

[Ancient Mariner]

Try asking the manufacturer.
Per

London Name Plate (http://www.lnp.co.uk/EMail.htm)

[parabellum]

Was this thread moved to JB? Think it would do better in the Rotary Wing forum.

[handsfree]

This little clue from a search on google

... graduations from 20 to 120 and markings for helicopter jump navigation once used with the Wessex ...

E6BFlightComputer -RAF Computer Dead Reckoning Mk5A.

Your best bet is to post this in the military thread. Lots of ex-Wessex mates in there.

[Gallinazo]

Thank you for the replies.

I am just wondering from the suggestions if I should link this to the Rotor or Military sub-forums, now. I should think the Wessex pilots in the community would probably frequent both, so I will go with the Rotor Heads for better exposure. I have always had the same thought about the rarity of jumping from a helicopter, and thus the improbability of it being a dedicated function on a flight computer for that purpose alone. I don't know, however.

Hopefully we can get to the bottom of this, and how it is used, perhaps.

PS: I will send the manufacturer a note; hope they reply.

[Gallinazo]

Hello, rotor heads!

Please help me with my curiosity regarding a flight computer function, originally posted in the Jet Blast sub forum. Here's the link...

Specific Flight Computer Question (http://www.pprune.org/jet-blast/545913-specific-flight-computer-question.html#post8615432).

It seems to be an RAF flight computer, from the deductions on that thread. What is it and how is it used?

Thank you!

[Shawn Coyle]

If memory serves me right, (as I only heard about this in talk around the coffee pot at D Squadron, Boscombe Down and never did get to use this feature). jump navigation was used to reposition the anti-submarine warfare helicopter at a new position to use the dunking sonar. Problem for the crew was they had to raise the sonar, transition to forward flight into wind, then turn, and get to the new position and transition down and then lower the sonar. And do this at a new position that would hopefully be able to detect the submarine. In the middle of the night.

[John Eacott]

How to work out the entry point for marking dip, ie the 'gate' for commencing transition down. Obviously we had to start into wind at a distance from the hover point all of which became semi automated with the Wessex HAS3 and the radar/doppler plot. Before that the looker had to play all sorts of black magic down in the back to get the pilot to the top of descent, day or night, all weather.

We didn't know any better, Shawn ;)

http://www.eacott.com.au/gallery/d/6989-2/Mark4B.JPG

[Shawn Coyle]

John:
And you did pretty damn well with what you had.
Innovation!! You got to love it.

[CharlieOneSix]

Goodness, haven't seen that particular version of a Dalton computer since my Wessex 1 days in the mid 60's! Used by the Observer down the back to calculate where we would jump to next to contain the submarine based on the information from the sonar operator and his Type 194 sonar.

Everything depended on flying the jump pattern very accurately with regards to speeds, angles of bank etc. or you wouldn't end up where the Observer intended. Day or night the jump height was 125 feet on the Rad Alt. Hover height 30 feet Rad Alt, initially hover maintained on Doppler, then switched to a cable hover once the sonar set was in the water.

Not in the hover by 19,600 CRPM? - then go around using the last 300 CRPM to struggle away with 50 ft/min rate of climb. What memories of those hot sweaty windless days and nights in the Far East trying to keep the machine out of the oggin! Glad I don't have to do that any more!

[tottigol]

It used to be callea VECTAC, in which you were jumping over a dipping helo and getting vectored by its radar operator.
For everything else we used our superior SA.

[CharlieOneSix]

......and getting vectored by its radar operator.....

To misquote Monty Python...

Radar! You were lucky to have radar! Would ha' been a palace to us. We used to have shares in't pencil company for our navigation calculations, all four of us in this shuddering tin box of a Wessie 1, 'alf the electronics was u/s, and me and my co-pilot were all 'uddled together in one corner for fear of falling in't water.

And you try and tell the young people of today that ..... they won't believe you.

[Nigel Osborn]

With the Whirlwind 7 we had to hover by 40" as max power was 44" as it took 4" to fly away. I think our hover height was either 15ft or 20ft which we got off the cable, no doppler, rad alt or other modern aids, the main aid being the Mk 1 eye ball!
The looker had to really be on the ball & we had to fly exactly as he asked.:ok:

[Gallinazo]

Good grief, I have an ASW function flight computer? I somehow knew it had nothing to do with jumping out of helicopters. Thank you so much for the information, and not least, for the entertaining memories of the associated procedures!.

By any chance, does anyone remember an example of using it?

[John Eacott]

By any chance, does anyone remember an example of using it?

Far too complicated for the front seat, it was all we could do to manage a conventional Dalton and (maybe) a plotting board. The workings of such esoteric technological devices were jealously guarded by the lookers down in the darkness.

And they were welcome to them :p

Vectac: now there's a term that I'd forgotten, what fun that was on a dark and stormy night with a 100ft cloudbase and a Shackleton trying to understand the radio calls!