1. Development and Principles of Rocketry
Methods of Operation
Lecture Four

2. Forces on a Rocket When a rocket lifts off
there are 3 main forces acting on it.
Thrust and Drag are trying to ‘crush’ the rocket,
rather like pushing on opposite ends
of a drinks can.
and when these forces are at a maximum,
it is called “Max Q”.
DRAG
DRAG
Thrust
Weight
Drag
WEIGHT
THRUST
THRUST

3. Forces on a Rocket When a rocket lifts off
there are 3 main forces acting on it.
DRAG
Thrust
Weight
Drag
Depends on the amount of propellant
and oxidiser being burned.
Rocket weight plus the payload and fuels
equals total weight.
Depends on the aerodynamic shape
of the rocket and its velocity.
Remember –
when Thrust and Drag are at a maximum,
it is called “Max Q”.
WEIGHT
THRUST

4. Forces on a Rocket At Lift Off the rocket is stationary
DRAG
At Lift Off the rocket is stationary
Drag is zero because the rocket isn’t moving.
To lift the rocket,
thrust must be more than weight.
The thrust to weight ratio
of a launch vehicle is
Thrust divided by Weight
(normally in the range of 1.2 to 1.6)
WEIGHT
THRUST

5. Forces on a Rocket Once the rocket is moving
DRAG
Once the rocket is moving
Thrust must be greater than drag plus weight.
Drag increases as the rocket gains speed.
But weight decreases
as propellant is burned
and the acceleration increases.
WEIGHT
THRUST

6. Rocket Structure One common structure attaches all components
to a tubular frame
The frame comprises of -
Struts running the length of the body
Ribs running around the body
The Fairing protects the Payload
And the engines,
having moving parts,
are attached to the frame using support structures.
Support Structures
Ribs
Fairing
Struts
Engine
Payload

7. Rocket Structure Huge fuel tanks are required
One common structure attaches all components
to a tubular frame
Huge fuel tanks are required
to store the Liquid Hydrogen,
because Liquid Hydrogen has a very low density.
Support Structures
Ribs
Fairing
Struts
Engine
Payload
Fuel
Tank
Fuel
Tank

8. Rocket Structure Operation (usually Helium) “Blowdown System”
Fore
Tank
Aft
The fuel and oxidizer are stored in tanks
inside the rocket body.
Tanks are pressurized with an inert gas
(usually Helium)
to force the fuel and oxidizer towards
the engine.
This arrangement is called a
“Blowdown System”
Inert Gas
Propellant
Oxidiser
Engine

9. Like aircraft, rockets can roll, pitch and yaw.
Guidance
Like aircraft, rockets can roll, pitch and yaw.
The roll axis is about the direction of travel,
but the pitch & yaw axes are aligned with
the fins or any gyroscopes fitted to the rocket.
Fins are control surfaces,
aligned with the pitch and yaw axes,
and they are deflected to produce
aerodynamic forces.
The AIM-9 Sidewinder
used two sets of fins
to steer the missile.
FIN

10. Like aircraft, rockets can roll, pitch and yaw.
Guidance
Like aircraft, rockets can roll, pitch and yaw.
Robert Goddard inserted vanes
into the exhaust plume,
allowing the rocket to be steered
in both pitch and yaw.
Engineers then mounted
the whole engine on gimbals,
and tilted the complete motor
using hydraulics.
VANE
GIMBAL

11. Like aircraft, rockets can roll, pitch and yaw.
Guidance
Like aircraft, rockets can roll, pitch and yaw.
Another technique used on larger rockets
and for manoeuvring in space,
is to have small thrusters
fitted onto the rocket.
These are mounted on the craft
to give a sideways thrust.
THRUSTER

12. Action and Reaction the action produced by a rocket engine
In terms of Newton's Laws,
the action produced by a rocket engine
is caused by its fast exhaust flow.
Remember the balloon !
Engine efficiency
can therefore be improved
by using different propellants.
Reaction
The balloon moves in
the opposite direction
Action
Air leaves the balloon
at high velocity
Compressed
Gas

13. Engine Principles Rocket Engine Performance Thrust x duration of burn
We can compare propellant performance by determining
how much thrust can be obtained in 1 second,
by burning 1 kg of propellant.
We call this
“Specific Impulse”
which is a measure of the efficiency of the propellant.
Specific Impulse is defined as :-
Thrust x duration of burn
Weight of propellant burned

14. Check of Understanding
In terms of Newton's Laws,
the action produced by a rocket engine
is caused by its?
Reaction against the atmosphere
Ability to operate without atmospheric oxygen
Reaction against the pull of gravity
Fast exhaust flow

15. Check of Understanding
Which part of a launch vehicle
protects the payload?
The fairing
The skin
The motor case
The support structure

16. Check of Understanding
When a rocket is in flight,
as fuel is used the total weight falls
and acceleration is?
Reduced
Increased
Doubled
Not affected

17. Check of Understanding
Which of the following gases
is used to pressurise blow-down systems?
Oxygen
Helium
Hydrogen
Nitrogen

18. Check of Understanding
In a rocket engine what does the term
Specific Impulse quantify?
Acceleration
Efficiency
Energy
Power

19. Check of Understanding
A blow-down system works by:
Using gaseous propellant to force the oxidiser out of the tanks
Using gaseous oxidiser to force the propellant out of the tanks
Using pressurised inert gas to force the oxidser out of the tanks
Using pressurised inert gas to force the propellant out of the tanks

20. Check of Understanding
Huge fuel tanks are required for
Liquid Hydrogen because?
It has a very low density
It has a very high density
It boils at low temperatures
It freezes at low temperatures

21. Check of Understanding
The thrust to weight ratio
of a launch vehicle is normally in the range:
1.6 to 2.0
1.2 to 1.6
1.0 to 1.2
0.6 to 1.0

22. Check of Understanding
The point in a flight at which
the forces trying to crush a rocket
are at their greatest is called:
Lift Off
Max Q
Ignition
Burn Out

23. Development and Principles of Rocketry
End of Presentation