Propulsion

Question 1

What are general requirements a torpedo must fulfil to be successful?

Answer 1

• 150% speed of the target
• Endurance
• Stealth
• Depth of operation
• Safety

Question 2

Name and describe the perfect torpedo hull form for minimal drag? Why is this not practical for military applications?

Answer 2

Carmichaels Hull form
- Diameter increases gradually from nose to create laminar flow of water in boundary layer
- control surfaces kept aft
- high quality finish

-ves
- Difficult to stow & embark
- internal layout is complex (doesn’t support modular design
- Wasted space
- Transducer placement not ideal & a complex beam former is required

Question 3

how much more power is required to increase a torpedo speed from 20kt to 50kt?

Answer 3

Power = 1/2 x p.v3.A.c(d)
*where p is rho

50(^3)/20(^3) = 15.625 x more power

Question 4

What affects the choice of energy source for a torpedo and what choices are there?

Answer 4

factors
- energy required
- operating characteristics
- safety of fuel
- cost

options
- electric (primary and secondary)
- thermal (open and closed loop)

Question 5

what is the difference between a primary and secondary battery?

Answer 5

primary is non-rechargeable
Secondary is rechargeable
Primary has better energy density
Secondary is better for reuse and training purposes

Question 6

what propulsion system is fitted in a spearfish and what fuels does it employee?

Answer 6

Spearfish is open loop with a propulsor .
It uses a sundstrand gas turbine.

Question 7

what are the advantages and disadvantages of an open loop thermal propulsion system?

Answer 7

• propulsion system discharge must overcome the ambient pressure of seawater
• Noisy
• It may limit depth of operation as pressure prevents gas escaping and chokes the engine
• Otto fuel means tanks can be reused
• Less complex engineering
• Significant past experience

Question 8

What is the purpose of a bipropellant?

Answer 8

Bipropellant uses fuel and an oxidiser (second liquid before combustion)
- more efficient & energetic combustion process
- increased torpedo endurance & speed
- only 10% waste gas
- much quieter (less detectable wake)

Question 9

describe SCEPS and it’s attributes

Answer 9

Sulphur hexafluoride is sprayed over a lithium block to generate heat, boiling water through heat exchanger to generate steam which drives up propeller through gearbox

Diagram

Question 10

What is the main risk with HTP which causes us to believe it has been the source at least two major submarine accidents

Answer 10

The exothermic reaction
- High concentration of hydrogen peroxide to water
- In contact with a catalyst decomposes into high temperature mixture of steam and oxygen with no remaining liquid water

Question 11

How can the rotational energy generated be transferred to seawater and what is the most efficient way of doing so?

Answer 11

propellers and propulsors
- Single propeller
- Twin propeller
- Contra rotating propeller
- Propulsor

Propulsor is significantly quieter
more efficient and higher speeds.
The wake is broken up
there is a more even flow over the control surfaces.

Question 12

Describe the process by which Shkval torpedoes achieve supercavitation

Answer 12

Supercavitation is the engineering of a torpedo body which can travel inside a cavitation bubble of water vapour

Exploits the cavitation bubble formed above by forcing the cavitation bubble to expand around the body of the torpedo, therefore travelling in a gaseous atmosphere where viscous drag is reduced

natural cavitation occurs on the canted cavitation disc
Exhaust gases from motors are fed back through the body and ventilation ducts increasing the size of cavitation
Cavity surrounds the entire body of the torpedo

Question 13

what are the current main disadvantages with supercavitating weapons?

Answer 13

No directional variation (point and shoot)