INS alignment on aircraft carrier

[7fortyfive]

Hi, was just wondering if anybody knew how an INS on an aircraft carrier could be aligned... considering that the carrier must be constantly moving...

Cheers

[KM-H]

7:45

The usual practice is to slave the aircraft INS to the ships inertial reference. This can be acheived using a cable linking the two systems, or an RF link between the aircraft and the ship.

Modern INS (ring laser) systems linked with GPS can also perform an 'in-motion alignment' including in-flight.

The old mechanical systems are the hardest to manage since you are actually aligning the gimbal rings to orient the platform before the accelerometers are correctly aligned to sense motion.

Very simple but I hope that helps

KM-H

[Genghis the Engineer]

I was once told that an early British system required the portable aircraft gyro platform to be slaved to the ships system then physically carried to the aircraft (presumably then to have the aircraft system slaved to it) - which of course would then wish to stay absolutely upright whilst some poor sod was trying to carry it down narrow companionways and up ladders on a rolling ship.

G

[Intruder]

If the cable or data link is not available, ship's position, course, & speed; plus the spotting angle of the airplane (angle between ship centerline and aircraft centerline) can be input to the system. These manual alignments are notoriously rough, though, and are prone to dump once airborne in older systems.

[John Farley]

7.45

KM-H has given you all I suspect you need to appreciate how it is done these days.

This may well get moved to the Nostalgia board, but in the old days (early 1970's) the RAF Harriers had an analogue inertial nav system. With this came a portable Ferranti platform on a cart that was put on the deck in front of your jet and you did things with the HUD to align the aircraft and the cart datums so that the cart could tell the aircraft kit how it should align. But it was never really successful in that the quality of alignment was inferior to what you could achieve parked on land.

[7fortyfive]

Great... thanks for helping out guys.. interesting to hear how they used to do it in the old days too...

Cheers

[Mr Proachpoint]

Ghengis and John F,

The systems you describe must be a product of the best of the most twisted design minds of the following companies
Rolls-Royce
Lucas
BSA
Hobson
Napier.

Was the testing achieved in an adapted AVRO Manchester powered by the more reliable and available RR Crecy on a floating rubber runway in the town of Slough?

MAPt

[KM-H]

Gengis,

The stuff of urban legend!! It is actually EXTREMELY unwise to physically move a spun-up IN without power on. This is because although the gyros are still spinning, there is no power to drive the platform gimbal motors to re-level/re-orient the platform. The gyros can precess without opposition and damage the gimbals by moving quite violently.

In the bay we never moved an IN until 5 mins or so after switching off.

John Farley,

I shiver at the memory; the system was called FINRAE if I remember correctly (Ferranti IN Rapid Alignment Equipment???)
Necessary to align the IN in RAF Harriers when aboard ship (on the way to the Falklands). Usually resulted in poor quality aligns that could dump at any motion detected.

regards,

KM-H

[wrenchbender]

20 years ago in the Canadian Forces, to align the compass system in a Sea King at sea, we ran a cable out to the Flight Deck that slaved the aircraft compass to the ship's system.

[Blacksheep]

Folks may scoff at that strange, quirky, historical Harrier INS but when it was first introduced there weren't any other fast jets that could operate out of forward locations with no runway. In fact, there still aren't. The idea was simple enough - flying out of forward areas right up with the infantry, Harriers needed to operate with minimum ground support, only what could be flown in by the mighty (?) Westland Wessex. So no heavy fuel bowsers, GPUs or crew busses etc. Aircraft sat there under their camo nets, cold and dead until needed in a hurry. Rather than wait twenty minutes for the contemporary "steam driven INS" to align itself before the aircraft could fly, the INS could be aligned as fast as a pilot could get aboard by using a portable inertial unit. This was kept running and aligned in the support tent (for detachments that actually had the luxury of a tent). Technology has moved on and the system now seems quaint and silly, but at the time it was considered a pretty nifty idea. RAF Harriers were not, of course ever intended to go to sea in a carrier. No wonder they had problems on a heaving rolling moving deck. So, whose brilliant idea was to do away with the Sea Harriers in the first place? Probably the same people who later took the credit for the success of the Falklands campaign (Succesful from a British viewpoint that is)... :suspect:

[John Farley]

KM-H

Yep, FINRAE it was. I did not go into any more detail in case somebody enqured - 'On a point of detail was your association with FINRAE something of which you are proud or ashamed?'

Regards

JF

[KM-H]

JF

Errr - Proud (I actually got two jets to align)!!

Annoyed - when the damn (note use of polite language) thing didn't work and you're trying to launch the jet.

KM-H

[timzsta]

I was 'Freddie' on a FA2 squadron 00-02. In the old days of FRS1 there were 2 ways of aligning NAVHARS as it was then. Freddie could pass ships position, course and speed on telebrief and then the pilot would enter aircrafts heading ( true bearing the nose pointing whilst on deck based on info given by the engineers out on deck). Alternatively if telebriefs was U/S the bridge would pass the info the flight deck and somebody would walk around with the information on a board and show it to each aircraft (which I am sure worked a treat at night...)

In the present days of FA2 the IN/GPS is a bit more snazzy and clever and the information above is passed over a usually more reliable telebrief and the INGPS does its stuff with a little less hassle i suspect. If I remember rightly it is clever enough to work out the aircraft heading whilst parked on deck and sense the ships course and speed with the aid of GPS. Perhaps on current FA2 pilot can enlighten us.

When it all went really peashaped 'Freddie' could be asked for vectors and a talkdown back to 'mum'.

[Bumz_Rush]

at least it is these days.....

can not vouch for fighter types, but in my all singing all dancing Gulfstream 550, recently delivered from Microsoft......we can align in flight at 500 kts....and that is down hill with the wind behind....
however, should the C/A/D not work in flight, you carry all your snags until WOW, then they all clear......but thats another story...Bumz.

[Genghis the Engineer]

Ah, but try landing it on a ship.

G :O