Browse Prior Art Database

Attitude Sensing and Control for Helicopters

IP.com Disclosure Number: IPCOM000114204D
Original Publication Date: 1994-Nov-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 105K

Publishing Venue

IBM

Related People

Gibbs, T: AUTHOR [+2]

Abstract

Landing a helicopter in a confined space is a difficult task for a pilot. It is further compounded when the landing surface is moving in an undefined and variable manner, as when landing on the deck of a ship, for example.

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Attitude Sensing and Control for Helicopters

      Landing a helicopter in a confined space is a difficult task
for a pilot.  It is further compounded when the landing surface is
moving in an undefined and variable manner, as when landing on the
deck of a ship, for example.

      For accurate control of the helicopter during descent the pilot
needs to know the height and attitude of the deck relative to his
aircraft.

      The height is usually given to him by dual redundant radio
altimeters, but these are not sufficiently accurate in the later
stages of descent (below 10 metres).  More importantly they also do
not give an indication of relative attitude (roll) to the landing
surface.

      The relative attitude of the deck is not available visually
because of the pilot's field of view when he is in position for
descent.  Generally a pilot will position the helicopter to one side
of the moving ship and get a feel for the relative motion and then
quickly move into position and put down swiftly.   This is hazardous
and not always predictable.  At night the dangers are increased.

      These problems are substantially reduced by the use of a high
frequency radio transmitter and dual receivers as a means of
detecting the height and positional attitude of the helicopter above
the landing platform (Fig. 1).

      By transmitting a pulse, and then measuring the relative time
delay before reception of the reflected pulse by the two receivers,
mounted on each of the two sponsons, it is possible to calculate the
height of each sponson from the reflecting medium (Fig. 2).

      Comparing these heights provides a measure of the attitude of
the aircraft relative to the deck.

      In a relatively simple system the heights are displayed
visually to the pilot.  Alternatively by the use of suitable scaling
algorithms and correcting signals they could be fed to the Automatic
Flight Control System and thus make the helicopter roll in sympathy
with the ship, automatically, during the landing phase.

      Figs. 3 and 4 show the system in detail.  A master 1 Ghz
oscillator 1 is scaled down in a divider 2 to 8Mhz and used as a
reference for a transmitted pulse with a pulse repetition frequency
(prf) of 8Mhz.  This gives a period, t, equal to 1/frequency,
equating to 125nS between pulses.   Radio waves travel at the speed
of light (3 x 108 metres/sec).  The dis...