1. Vertical Take Off & Landing
(VTOL)
Aircraft --
A Comparison

2. Lift / Propulsion / Control Approaches
For VTOL Aircraft (General)
For Shaft-Driven VTOL Aircraft, Need At Least Two Thrusters: l
Fixed Thrusters
> One Main, One Anti-Torque
> Two Equal Size (Opposite Rotation) l
Vectored Thrusters
> Thruster Tilting
> Exhaust Deflection

3. Methods of Transition for Various V/STOL Concepts

4. VTOL Concepts

5. PURE HELICOPTER ADVANTAGES DISADVANTAGES Most Efficient Hover/Loiter
Low Downwash
Good Low Speed Maneuverability
Symmetrical Yaw Control
Low Empty Weight
DISADVANTAGES
Low Max Speed
Lowest Cruise Efficiency (Range)
Limited High Speed Maneuverability
Attitude Depends on Speed/Acceleration
Rotating Component RCS
Highest Vibration Environment
Complexity (2 Fixed Thrusters)

6. THERE ARE MAJOR PROBLEMS WITH ADDING A WING
Wing Needs Aircraft to be Nose Up to Get Lift
Velocity
Thrust
Wing Lift
Main Rotor Needs Aircraft to be Nose Down to Get Propulsion
Velocity
Thrust
Wing "Lift"
(Download)
Need to Get Propulsion from Someplace Other than Main Rotor
Add a Third Fixed Thruster (Propulsive Thruster) or
Use Vectored Thrust
SOLUTION:

7. COMPOUND HELICOPTER (Fixed Thruster) ADVANTAGES DISADVANTAGES
Good Hover/Loiter Efficiency
Low Downwash
Faster Than Pure Helicopter
Good Maneuverability -- All Speeds
Attitude Independent of Speed/Acceleration
Symmetrical Yaw Control
Reverse Prop Thrust -- All Speeds
DISADVANTAGES
Low Cruise Efficiency (Range)
Rotating Component RCS
High Vibration Environment
Increased Empty Weight
Complexity (3 Fixed Thrusters)

8. (Advancing Blade Concept)
COMPOUND HELICOPTER
(Advancing Blade Concept)
ADVANTAGES
Good Hover/Loiter Efficiency
Low Downwash
Faster Than Pure Helicopter
Good Maneuverability -- All Speeds
Attitude Independent of Speed/Acceleration
Symmetrical Yaw Control
No Anti-Torque Rotor Required
Reverse Prop Thrust -- All Speeds
DISADVANTAGES
Low Cruise Efficiency (Range)
Rotating Component RCS
High Vibration Environment
Increased Empty Weight
Complexity (3 Fixed Thrusters)

9. (Vectored Thruster - Open Prop)
COMPOUND HELICOPTER
(Vectored Thruster - Open Prop)
ADVANTAGES
Good Hover/Loiter Efficiency
Low Downwash
Faster Than Pure Helicopter
Good Maneuverability (Except Conversion)
Reverse Prop Thrust at High Speed
DISADVANTAGES
Low Cruise Efficiency (Range)
Conversion (Limited Agility)
Attitude Depends on Acceleration at Low Speed
Unprotected Vectored Thruster
Rotating Component RCS
High Vibration Environment
Increased Empty Weight
Complexity (1 Fixed + 1 Vectored Thruster)

10. (Vectored Thruster - Ducted Prop)
COMPOUND HELICOPTER
(Vectored Thruster - Ducted Prop)
ADVANTAGES
Good Hover/Loiter Efficiency
Low Downwash
Faster Than Pure Helicopter
Good Maneuverability (Except Conversion)
Reverse Prop Thrust at High Speed
Ground Safety/Damage (Ducted Prop)
DISADVANTAGES
Low Cruise Efficiency (Range)
Conversion (Limited Agility)
Limited / Unsymmetrical Yaw Control
Attitude Depends on Acceleration at Low Speed
Rotating Component RCS
High Vibration Environment
Complexity (1 Fixed + 1 Vectored Thruster)

11. CANARD ROTOR WING ADVANTAGES DISADVANTAGES
Good Hover/Loiter Efficiency
Low Downwash
Potential for High Subsonic Cruise
Good Maneuverability (Except in Conversion)
No Anti-Torque Rotor
Reduced RCS in High Speed Mode
Low Vibration Environment in High Speed Mode
DISADVANTAGES
Limited Maneuverability in Conversion
Power for Yaw Control Near Hover
Moderate Vibration Environment in Low Speed & Conversion Modes
Rotating Component RCS in Low Speed Mode
Complexity (Rotor Stopping & Convertible Engine)

12. TILT ROTOR ADVANTAGES DISADVANTAGES Good Hover/Loiter Efficiency
Moderate Downwash
Good Max Speed
Good Cruise Efficiency (Range)
Good Maneuverability -- All Speeds
Attitude Independent of Speed/Acceleration
Ground Safety/Damage (No Tail Rotor)
DISADVANTAGES
Greater Operating Width
Conversion (Benign)
Rotating Component RCS
Moderate Vibration Environment
Increased Empty Weight
Complexity (2 Vectored Thrusters)

13. TILT WING ADVANTAGES DISADVANTAGES Fair Hover/Loiter Efficiency
Faster Than Tilt Rotor
Good Cruise Efficiency (Range)
Good High Speed Maneuverability
Attitude Independent of Speed/Acceleration
Symmetrical Yaw Control
DISADVANTAGES
Marginal Downwash
Conversion (Limited Corridor)
Rotating Component RCS
Increased Empty Weight
Complexity (1 Fixed + 2 Vectored Thrusters)

14. TILTING DUCTED FANS ADVANTAGES DISADVANTAGES
Enclosed Thrusters (Safety)
Symmetrical Yaw Control
DISADVANTAGES
Low Hover/Loiter Efficiency
Limited Low Speed Maneuverability
Conversion (Limited Corridor)
High Empty Weight
Complexity (1 Fixed + 2 Vectored Thrusters)

15. FAN-IN-WING ADVANTAGES DISADVANTAGES High Max Speed
Good Cruise Efficiency (Range)
Attitude Independent of Speed/Acceleration
Good RCS (High Speed Mode)
Low Vibration Environment
DISADVANTAGES
Low Hover/Loiter Efficiency
High Downwash / Temperature
Limited Low Speed Maneuverability
Conversion (Limited Corridor)
High Empty Weight
Complexity (3 Vectored Thrusters)

16. VECTORED JET LIFT ADVANTAGES DISADVANTAGES Highest Max Speed
Highest Cruise Efficiency (Range)
Excellent High Speed Maneuverability
Attitude Independent of Speed/Acceleration
Symmetrical Yaw Control
Low Vibration Environment
Moderate Empty Weight
DISADVANTAGES
Poor Hover/Loiter Efficiency
Extreme Downwash / Temperature
Limited Low Speed Maneuverability
Conversion (Benign)
Rotating Component RCS (Forward)
Jet Exhaust IR
Complexity (1 Thruster + 8 Nozzles)

17. Summary
VTOL Aircraft Are Inherently More Complex Than Conventional Take-Off and Landing (CTOL) Aircraft
Mechanization Required to Change Direction of Thrust With Respect to Aircraft
Additional Controllers (e.g., Collective Stick, Conversion)
“Best VTOL Concept” Only Has Meaning in the Context of the Mission to be Performed
What Do You Need Most? Hover Time, Fast Cruise, Long Range, ?
What Do You Have Available? Runway, ?

18. Comparison of Different Types of V/STOL Platforms