vtol aircraft comparision

Vertical Take Off & Landing

(VTOL)

Aircraft --

A Comparison

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

Methods of Transition for

Various V/STOL Concepts

VTOL Concepts

PURE HELICOPTER

ADVANTAGES

• 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)

Add a Third Fixed Thruster (Propulsive Thruster)

or

Use Vectored Thrust

SOLUTION:

Need to Get Propulsion from Someplace Other than Main Rotor

THERE ARE MAJOR PROBLEMS WITH

ADDING A WING

Main Rotor Needs Aircraft to

be Nose Down to Get Propulsion

Velocity

Thrust

Wing "Lift"

(Download)

Wing Needs Aircraft to

be Nose Up to Get Lift

Velocity

Thrust

Wing Lift

COMPOUND HELICOPTER (Fixed Thruster)

ADVANTAGES

• Good Hover/Loiter Efficiency

• Low Downwash

• Faster Than Pure Helicopter

• Good Maneuverability -- All Speeds

• Attitude Independent of

Speed/Acceleration


• Reverse Prop Thrust -- All Speeds

DISADVANTAGES

• Low Cruise Efficiency (Range)


• High Vibration Environment

• Increased Empty Weight


COMPOUND HELICOPTER (Advancing Blade Concept)

ADVANTAGES


• Low Downwash




Speed/Acceleration


• No Anti-Torque Rotor Required

• Reverse Prop Thrust -- All Speeds

DISADVANTAGES






COMPOUND HELICOPTER (Vectored Thruster - Open Prop)

ADVANTAGES


• Low Downwash


• Good Maneuverability

(Except Conversion)

• Reverse Prop Thrust at High Speed

DISADVANTAGES


• Conversion (Limited Agility)

• Attitude Depends on Acceleration at

Low Speed

• Unprotected Vectored Thruster




• Complexity

(1 Fixed + 1 Vectored Thruster)

COMPOUND HELICOPTER (Vectored Thruster - Ducted Prop)

ADVANTAGES


• Low Downwash



(Except Conversion)

• Reverse Prop Thrust at High Speed

• Ground Safety/Damage

(Ducted Prop)

DISADVANTAGES


• Conversion (Limited Agility)

• Limited / Unsymmetrical Yaw Control

• Attitude Depends on Acceleration at

Low Speed



• Complexity

(1 Fixed + 1 Vectored Thruster)

CANARD ROTOR WING

ADVANTAGES


• Low Downwash

• Potential for High Subsonic Cruise


(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)

TILT ROTOR

ADVANTAGES


• Moderate Downwash

• Good Max Speed

• Good Cruise Efficiency (Range)



Speed/Acceleration

• Ground Safety/Damage

(No Tail Rotor)

DISADVANTAGES

• Greater Operating Width

• Conversion (Benign)


• Moderate Vibration Environment


• Complexity (2 Vectored Thrusters)

TILT WING

ADVANTAGES

• Fair Hover/Loiter Efficiency

• Faster Than Tilt Rotor


• Good High Speed Maneuverability


Speed/Acceleration


DISADVANTAGES

• Marginal Downwash

• Conversion (Limited Corridor)



• Complexity

(1 Fixed + 2 Vectored Thrusters)

TILTING DUCTED FANS

ADVANTAGES

• Enclosed Thrusters (Safety)


DISADVANTAGES

• Low Hover/Loiter Efficiency

• Limited Low Speed Maneuverability


• High Empty Weight

• Complexity

(1 Fixed + 2 Vectored Thrusters)

FAN-IN-WING

ADVANTAGES

• High Max Speed



Speed/Acceleration

• Good RCS (High Speed Mode)

• Low Vibration Environment

DISADVANTAGES

• Low Hover/Loiter Efficiency

• High Downwash / Temperature



• High Empty Weight

• Complexity (3 Vectored Thrusters)

VECTORED JET LIFT

ADVANTAGES

• Highest Max Speed

• Highest Cruise Efficiency (Range)

• Excellent High Speed Maneuverability


Speed/Acceleration


• Low Vibration Environment

• Moderate Empty Weight

DISADVANTAGES

• Poor Hover/Loiter Efficiency

• Extreme Downwash / Temperature


• Conversion (Benign)

• Rotating Component RCS (Forward)

• Jet Exhaust IR

• Complexity (1 Thruster + 8 Nozzles)

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, . . . ?

VTOL Concept Helicopter Compound Compound Compound Compound Tilt Rotor Tilt WingCanard Rotor

WingFan-in-Wing Jet Lift

Features (Tail Rotor +

Aux Prop)

(Advancing

Blade Concept)

(Vectrd Thrst -

Open Prop)

(Vectrd Thrst -

Ducted Prop)

ExamplesAH-64,

RAH-66AH-56 Sikorsky XH-59

Sikorsky

AAFSSPiasecki VTDP

XV-3, XV-15,

V-22

CL-84, TW-68,

XC-142Boeing CRW

XV-5, Grum-

man ACASAV-8B

Hover / Loiter / Ground Ops

Efficiency (Endurance) Best Good Good Good Good Good Fair Low Low Poor

Downwash / Temperature Low Low Low Low Low Moderate Marginal Marginal High Extreme

Ground Ops Protection Optional Open Prop No Anti-Torque Open Prop Ducted Prop --- Optional No Anti-Torque --- Jet Exhaust

Cruise / Dash

Max Speed (Dash) Low > Helicopter > Helicopter > Helicopter > Helicopter Good > Tilt Rotor High High Highest

Cruise Efficiency (Range) Lowest Low Low Low Low Good Good Good Good Highest

Maneuverability / Agility

Low Speed Good Good Good Good Good Good Fair Limited Limited Limited

High Speed Limited Good Good Good Good Good Good Good Good Excellent

Conversion --- --- --- Limited Agility Limited Agility Benign Lmtd Corridor Lmtd Corridor Lmtd Corridor Benign

Attitude vs Accel (Low Speed) Coupled Independent Coupled Coupled Coupled Independent Independent Independent Independent Independent

Reverse Thrust Capability --- All Speeds --- High Speed High Speed --- High Speed --- --- ---

Yaw Control Symmetrical Symmetrical Symmetrical SymmetricalLimited /

UnsymmetricalSymmetrical Symmetrical

Limited in Low

SpeedSymmetrical Symmetrical

Survivability

RCS (Low Speed Mode) Rotating Blade Rotating Blade Rotating Blade Rotating Blade Rotating Blade Rotating Blade Rotating Blade Rotating Blade Doors / Louvers Short Inlet

RCS (High Speed Mode) Rotating Blade Rotating Blade Rotating Blade Rotating Blade Rotating Blade Rotating Blade Rotating Blade Good Good Short Inlet

IR (Engine Exhaust) Lowest Power Low Power Low Power Low Power Low Power Low Power Medium Power High Power High Power Short Exhaust

Cost / Supportability

Vibration Environment Highest High Very High High High Moderate --- Moderate Low Low

Empty Weight Low Increased Increased Increased Increased Increased Increased Increased High Moderate

Complexity

(Min # of Thrusters)2 Fixed 3 Fixed 2 Fixed

1 Fixed +

1 Vectored

1 Fixed +

1 Vectored2 Vectored

1 Fixed +

2 Vectored

Convertib le

Engine3 Vectored

1 Thruster +

8 Nozzles

Key to Table: Advantage Neutral Disadvantage

Comparison of Different Types of V/STOL Platforms

vtol aircraft comparision

Documents

high speed

disadvantageslow

helicopter

reverse prop

speeds attitude

ducted prop

vectored thruster

tilt rotor