Underwater Reconnaissance Gliders and Acoustic Identification Module

213

1. 1

   Pitch battery sled

   Motion

   Slides fore and aft

   Travel / range

   ±35 mm

   What it does

   Shifts the centre of gravity to pitch the nose up or down

   Driven by

   Small motor → lead screw → nut on the carriage; motor encoder for position, limit switches at both ends

2. 2

   Buoyancy-engine piston

   Motion

   Strokes fore and aft

   Travel / range

   76 mm stroke

   What it does

   Takes on or expels water to change buoyancy; being in the nose it also helps pitch

   Driven by

   Gear motor → spur gears → ball screw

3. 3

   Rudder

   Motion

   Swings left and right on its shaft

   Travel / range

   Deflection set by the servo chosen

   What it does

   Steers the heading (turn left or right)

   Driven by

   Oil-filled, pressure-compensated servo driving the rudder shaft directly

See them move

Loading motion frames…

1. 01Pitch battery slides ±35 mm (the bend of the power-cable U-loop follows at half the distance)
2. 02Buoyancy piston strokes (76 mm)
3. 03Rudder swings left and right (schematic ±20°)

Play

1. 01

   Power cable

   Exits the top of the battery: a Ø7 mm high-flex silicone cable (2 power cores + battery-management data), laid as a horizontal U-loop above the battery with a 20 mm bend radius (about 6× the cable diameter).

2. 02

   Why it does not break

   One leg is clamped to the battery and moves with it; the other is clamped to a fixed tray. When the battery travels ±35 mm the bend of the U moves only half as far (±17.5 mm) – the cable rolls rather than being pulled or kinked.

3. 03

   Connector and fuse

   A disconnect at the fixed end (the battery comes out without cutting wires), followed by an inline fuse; a trunk cable runs along the hull crown through the payload section to the power board in the aft hull.

4. 04

   What moves it

   A small motor under the sled turns a lead screw; the nut carries the carriage and battery fore and aft. An encoder on the motor rear counts turns, converted to battery position.

5. 05

   How it knows the end of travel

   A flag on the starboard edge of the carriage passes two slot-type optical switches. At power-up the sled drives to the forward switch to zero itself; at ±32 mm a switch trips and the motor stops before the mechanical end (±35 mm).

1. 01

   Where 484 cm³ comes from

   Piston area π × 45² ≈ 6,362 mm², times the 76 mm stroke ≈ 484 cm³, about one mug.

2. 02

   What ±2.4 N means

   484 cm³ of seawater weighs about 0.50 kg (4.9 N). Ballast makes the vehicle neutral with the piston at mid-stroke, so half a stroke in makes it 2.4 N heavy and half a stroke out 2.4 N light: only ±0.37% of the 65.8 L displacement. Those 2.4 N give a glide angle of about 18° at 0.26 m/s horizontal; one 150 m profile takes about 1.1 h and covers about 0.9 km.

3. 03

   Why a rolling diaphragm

   One side of the cylinder is seawater, the other the dry hull. An O-ring slides along the bore; over 66 days and about 1,440 cycles it wears, sticks and seeps. A rolling diaphragm is a fabric-reinforced rubber membrane clamped at the cylinder mouth and attached to the piston; as the piston moves it rolls along the bore instead of sliding, with almost no friction. Sea pressure always exceeds the internal pressure, so the membrane stays pressed onto the piston; the pressure load is carried by the piston, screw and end cap, and the membrane only seals.

4. 04

   Why a ball screw with reduction

   The piston pushes out against water pressure: about 1.5 MPa and 9.6 kN at 150 m; about 2.0 MPa and 12.8 kN (nearly 1.3 t) at the 200 m design target. A gear motor turns the ball screw through a spur-gear pair; the nut sits in the piston and turns rotation into a high-force linear stroke.

5. 05

   How much energy

   Pushing the full stroke out at 150 m takes about 1.5 MPa × 484 cm³ ≈ 729 J of work; at an efficiency of 0.45 that is about 1,621 J (0.45 Wh) of electricity, about 2 min at 15 W, or 17% of each cycle's energy; most of the rest is the hotel load of sensors and recording.

6. 06

   It also helps with pitch

   The cylinder sits in the nose, about 825 mm from the centre of buoyancy: taking on water makes the nose heavy so it pitches down for the dive, and pushing water out lifts it for the climb. On its own it gives about ±19° statically; the moving battery trims the rest.

7. 07

   Why G2 and G3 don't use it

   The piston load scales with depth: at G2's 1000 m target the same piston would carry about 64 kN, making the screw and end cap heavy, so the deep designs pump oil into an external bladder with a high-pressure pump. A piston engine suits shallow water: simple, efficient and cheap.

8. 08

   Still to verify

   Coastal seawater density can range from 1.020 to 1.028 kg/L, a buoyancy difference of about 0.53 kg, more than the ±0.25 kg of adjustment, so measure density and re-ballast for each operating area. The 0.45 efficiency is an assumption; bench-test the screw, gears and motor under a 2 MPa load. Confirm the diaphragm's pressure rating, seawater compatibility, flex life and gap against the maker's specification.

1. 01

   Where the forward force comes from

   Resolve the 2.4 N of net buoyancy along the 18° path: the forward component 2.4 × sin 18° ≈ 0.75 N balances drag, and the remaining 2.3 N is carried by wing lift. At about 0.27 m/s the equivalent propulsive power is only about 0.2 W. The energy comes from the battery: the roughly 1,621 J spent pushing water out at the bottom is like towing a sailplane up a hill.

2. 02

   The wing works both ways

   The wing section is symmetric. Diving, the nose is about 12° down on an 18° path, an angle of attack of about +5.7°; climbing, the nose is up and the angle of attack becomes −5.7°, so lift flips direction and still turns buoyancy into forward speed.

3. 03

   Pitch: moving the battery

   The 12.9 kg pitch battery rides a lead-screw sled ±35 mm, giving about ±37° of pitch; the nose cylinder adds about ±19° as it takes on water (nose heavy) or pushes it out (nose light). The flight computer keeps trimming the battery against the attitude sensor to hold the path angle.

4. 04

   Roll: passively stable

   The centre of gravity is about 8.9 mm below the centre of buoyancy, so like a roly-poly toy it rights itself and needs no active roll control.

5. 05

   Heading: rudder

   The rudder behind the antenna fin is driven directly by an oil-filled, pressure-compensated servo. Water flowing over it pushes the tail aside when it deflects and the nose turns, just like a boat rudder, so it can steer whenever it is gliding. Heading comes from the attitude and heading sensor with a magnetometer, mounted at the rear of the aft section about 1 m from the moving battery to limit magnetic interference.

6. 06

   Position: dead reckoning plus surface fixes

   GNSS doesn't work underwater, so position is dead-reckoned from heading, depth rate and estimated speed; about every 3.3 h (about 2.8 km) it surfaces for a GNSS fix, sends data by satellite and receives new waypoints. The gap between the estimate and the fix is mostly current; once the depth-averaged current is estimated the vehicle crabs into it (the dashed line on the right is the track pushed off by current). A 1° heading error gives about 48 m of error; an uncorrected 0.10 m/s current about 1,194 m, reduced to about 239 m once the current is estimated.

7. 07

   Weak points

   Horizontal speed is about 0.26 m/s, so a faster current simply carries it along; it also cannot hold position or fly at constant altitude, which needs thrusters (see G3).

Operating modes

With no thrusters, G1 only flies buoyancy-driven profiles. Any mode whose capability is not yet proven stays disabled.

Control architecture

How many dives between two surface fixes

If the pressure sensors drift slowly, the vehicle is deeper than it thinks. The planner sizes the depth margin from the time between the last fix and the bottom of the dive, and only admits as many dives as keep it within the 200 m design depth and clear of the seabed. The chart shows an example with 0.005 m/s vertical current.

These are conditional suggestions from a synthetic model; the 0.005 m/s vertical current is an example, not a measurement.