Design
1. Describe the design considerations for the actuation of the control surfaces of an
agile, medium range, axially symmetric air vehicle
- High Bandwidth and responsiveness– actuator must follow rapid guidance
commands to avoid phase lag and overshoot
- Compact and lightweight design – minimise mass and volume
- Sufficient onboard, with good efficiency
- Actuator electronics shielded – to avoid interference between seeker and
guidance electronics
- sufficient torque - to overcome the aerodynamic forces and hinge moments
- Environmental hardening – use components that are resistance to moisture,
dust, salt-fog and operate in high range of temperatures and altitude
- Reliability and ruggedness - Dual actuators/electronics, vibration-rated
bearings etc as per MIL-STD to ensure operation through launch and flight.
2. Explain why solid rocket motors are normally preferred to turbojets for supersonic
airframes.
- Solid rocket motors have an excellent T/W ratio and can maintain its speed at a
constant level easily
- Doesn’t need an initial speed (ramjets), constant airflow (turbojet)
- Can generate very high instantaneous thrust – important for high-g maneuverers
- Can design the propellant’s surface area to provide different thrust profiles
- Works at all atmospheres – independent of ambient pressure and speed thus
wide operating envelope
3. Explain the four types of control surface deflections used to control a canard-
controller ‘+’ type axially symmetric airframe.
FOR + type
Roll control (δp) - Differential canard deflection on the starboard vs. port
foreplanes (one up, one down) creates opposing lift-moments, rolling the
vehicle about its longitudinal axis.
Pitch control (δq) - Symmetric deflection of canards on left and right side
produces a nose-up or nose-down pitching moment about the lateral axis.
Yaw control (δr) - Symmetric deflection of canards on top and bottom
produces a left or right pitching moment about the vertical axis?
Drag modulation (δX) - Collective spoiler action—deflecting all canards
partially into the flow—increases overall drag without deliberate
roll/pitch/yaw moments
, 4. Difference between + vs x config
- + config: Simplest control mechanism, similar to conventional control surfaces, low
drag at trim, less static stability
- X config: Complex but less problems with roll stability, less drag and aerodynamic
efficiency, good for launch platform integration
5. What are the advantages and disadvantages of canard-controlled and fin-
controlled axially symmetric airframes? How do these factors affect the design of a
guidance-control system for such an airframe?
Canard control Fins Control
Pros: Pros:
- Good lift/latax control for moderate AoA - efficient packaging of subsystem,
- Good manoeuvrability - low hinge moment
- low induced roll moment
Cons: - good efficiency at high AoA
- shed vortices influence the fins, - used with guidance vanes in rocket
inducing roll moment. plume
- Stall at high AoA, use fixed canard Cons:
- Poor lift/latax control for stable
airframes
6. Explain how the shape of the propellant in a solid rocket motor can be designed
to produce different thrust profiles for the rocket
- Burn rate proportional to surface area of propellent
- Constant Thrust, Regressive Thrust, Progressive Thrust, Boost-sustain, Boost-
sustain-boost.
1. Describe the design considerations for the actuation of the control surfaces of an
agile, medium range, axially symmetric air vehicle
- High Bandwidth and responsiveness– actuator must follow rapid guidance
commands to avoid phase lag and overshoot
- Compact and lightweight design – minimise mass and volume
- Sufficient onboard, with good efficiency
- Actuator electronics shielded – to avoid interference between seeker and
guidance electronics
- sufficient torque - to overcome the aerodynamic forces and hinge moments
- Environmental hardening – use components that are resistance to moisture,
dust, salt-fog and operate in high range of temperatures and altitude
- Reliability and ruggedness - Dual actuators/electronics, vibration-rated
bearings etc as per MIL-STD to ensure operation through launch and flight.
2. Explain why solid rocket motors are normally preferred to turbojets for supersonic
airframes.
- Solid rocket motors have an excellent T/W ratio and can maintain its speed at a
constant level easily
- Doesn’t need an initial speed (ramjets), constant airflow (turbojet)
- Can generate very high instantaneous thrust – important for high-g maneuverers
- Can design the propellant’s surface area to provide different thrust profiles
- Works at all atmospheres – independent of ambient pressure and speed thus
wide operating envelope
3. Explain the four types of control surface deflections used to control a canard-
controller ‘+’ type axially symmetric airframe.
FOR + type
Roll control (δp) - Differential canard deflection on the starboard vs. port
foreplanes (one up, one down) creates opposing lift-moments, rolling the
vehicle about its longitudinal axis.
Pitch control (δq) - Symmetric deflection of canards on left and right side
produces a nose-up or nose-down pitching moment about the lateral axis.
Yaw control (δr) - Symmetric deflection of canards on top and bottom
produces a left or right pitching moment about the vertical axis?
Drag modulation (δX) - Collective spoiler action—deflecting all canards
partially into the flow—increases overall drag without deliberate
roll/pitch/yaw moments
, 4. Difference between + vs x config
- + config: Simplest control mechanism, similar to conventional control surfaces, low
drag at trim, less static stability
- X config: Complex but less problems with roll stability, less drag and aerodynamic
efficiency, good for launch platform integration
5. What are the advantages and disadvantages of canard-controlled and fin-
controlled axially symmetric airframes? How do these factors affect the design of a
guidance-control system for such an airframe?
Canard control Fins Control
Pros: Pros:
- Good lift/latax control for moderate AoA - efficient packaging of subsystem,
- Good manoeuvrability - low hinge moment
- low induced roll moment
Cons: - good efficiency at high AoA
- shed vortices influence the fins, - used with guidance vanes in rocket
inducing roll moment. plume
- Stall at high AoA, use fixed canard Cons:
- Poor lift/latax control for stable
airframes
6. Explain how the shape of the propellant in a solid rocket motor can be designed
to produce different thrust profiles for the rocket
- Burn rate proportional to surface area of propellent
- Constant Thrust, Regressive Thrust, Progressive Thrust, Boost-sustain, Boost-
sustain-boost.
