hang glider for military application

June 11, 2010

FACULTY OF ENGINEERING

SCHOOL OF MECHANICAL ENGINEERING

MECHENG 4108 AIRCRAFT DESIGN

AIRCRAFT DESIGN PROJECT

HANG GLIDER FOR M ILITARY APPLICATION

AUTHORS:

Jia Yao CUI - 1160900

Garland HU - 1163062

Tuyen NGUYEN - 1147028

Joshua NORTHEAST - 1161924

Jake PHOENIX - 1161542

Quoc Hung TRAN - 1160835

Hang Glider Design 2010

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Executive Summary

This report details the design of a hang glider for military applications. It was decided

that the hang glider is to be used to drop paratroopers at their landing zone without

endangering the aircraft.

A classic approach was used to design the hang glider and feasibility studies and

statistical analysis was used in development of our hang glider design. These allowed

us to approximate the size of our hang glider allowing detailed models to be generated.

The hang glider has the capability to be dropped out of a slowly travelling aircraft at

3000 metres and allow the pilot to be safely transported to the ground with a glide

ratio of approximately 1:15. The mission profile was constructed such that the hang

glider was launched from the aircraft then descended to landing.


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Disclaimer

The content of this report is entirely the work of the following students from the

University of Adelaide. Any content obtained from other sources has been referenced

accordingly.

Jia Yao Cui

Date:

Garland HU

Date:

Tuyen Nguyen

Date:

Joshua NORTHEAST

Date:

Jake Phoenix

Date:

Quoc Hung Tran

Date:


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Table of Contents

1. Introduction............................................................................................................1

2. Literature Review and Market Evaluation.............................................................4

2.1. Literature Review............................................................................................4

2.2. Market Review ................................................................................................6

2.2.1. Wills Wing...............................................................................................7

2.2.2. Airborne C4 .............................................................................................7

2.2.3. Avian JAVA.............................................................................................8

2.2.4. Moyes Light Speed RS ............................................................................9

3. Design Specifications...........................................................................................10

3.1. Technical Task ..............................................................................................10

3.1.1. Standard Requirements ..........................................................................11

3.1.2. Technical Level of the Product ..............................................................11

3.1.3. Performance Parameters ........................................................................11

3.1.4. Economical Parameters..........................................................................14

3.1.5. Power Plant Type and Requirements.....................................................14

3.1.6. Main System Parameters........................................................................14

3.1.7. Special Systems and Miscellaneous....................................................15

3.1.8. Reliability and Maintainability ..............................................................16

3.1.9. Unification Level ...................................................................................16

3.2. Statistical Analysis ........................................................................................16

3.2.1. Statistics of Civilian Application Hang Gliders.....................................16

3.2.2. Statistics of Parachutes ..........................................................................20

3.3. Mission Profile ..............................................................................................21

3.4. Weight Estimation.........................................................................................21


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3.5. Sensitivity Analysis.......................................................................................22

3.5.1. Sensitivity to Empty Weight..................................................................23

3.5.2. Sensitivity to Payload Weight................................................................23

3.6. Aircraft Sizing...............................................................................................24

3.6.1. Sizing Parameters...................................................................................24

3.6.2. Design Point...........................................................................................26

4. Preliminary Design ..............................................................................................27

4.1. Concept Design Number 1 ............................................................................31

4.2. Concept Design Number 2 ............................................................................36

5. Weight Balance and Stability Analysis................................................................39

5.1. Static Margin .................................................................................................40

6. Aerodynamic Analysis.........................................................................................42

6.1. Lift distribution .............................................................................................42

6.2. L/D Determination ........................................................................................42

6.3. Fineness Ratio and Drag of Structure ...........................................................43

7. Performance Analysis ..........................................................................................45

8. Three View Drawings ..........................................................................................46

9. References............................................................................................................47

Appendix A – Something.............................................................................................49

Appendix B – Sensitivity Analysis Calculations .........................................................50


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List of Figures

Figure 1-1 - Paratroopers ...............................................................................................1

Figure 1-2 - Airborne Troops.........................................................................................2

Figure 1-3 - Gryphon Attack Glider ..............................................................................2

Figure 2-1 - The Gryphon Parachute System ................................................................5

Figure 3-1 - Empty Weight Technology Diagram.......................................................17

Figure 3-2 - Aspect Ratio Technology Diagram..........................................................19

Figure 3-3 - Wing Span Technology Diagram ............................................................20

Figure 3-4 - Mission Profile.........................................................................................21

Figure 4-1 - Hand Sketch of Glider Configuration......................................................28

Figure 4-2 - Sketch of pilot configuration on conventional hang glider......................30

Figure 4-3 - Air flow over forward swept wing and backwards swept wing (Wilson

2008) ............................................................................................................................31

Figure 4-4 - Concept Design Number 1.......................................................................33

Figure 4-5 - Detailed sketches of concept 1.................................................................34

Figure 4-6 - Parachute Deployment.............................................................................35

Figure 4-7 - Image of vertical tail used for stabilization (Marshall Brain 2008).........36

Figure 4-8 - Vertical tail concept design......................................................................37

Figure 4-9 - Detailed Sketch of Vertical Tail ..............................................................38

Figure 5-1 - CG Envelope............................................................................................40

Figure 6-1 - Technology Diagram of Glide Ratio .......................................................43

Figure 6-2 - Drag Coefficient of Cylindrical Bodies in Axial Flow...........................44


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List of Tables

Table 2-1 - Wills Wing T2 Hang Glider (Wills Wing 2009).........................................7

Table 2-2 - Airborne C4 Hang Glider Specifications (Airborne 2004) .........................7

Table 2-3 - Avian Java Hang Glider Data (Avian 2010) ...............................................8

Table 2-4 - Moyes LightSpeed RS data (Moyes 2005) .................................................9

Table 3-1 - Summary of Performance Parameters.......................................................12

Table 5-1 - Weight Breakdown of the Hang Glider Subsystems.................................39

Table 8-1 - Compliance with performance parameters................................................45


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1. Introduction

Airborne forces are military units of light infantry that can be deployed and

transported via aircraft. With this aerial deployment method, they can be ‘dropped’

behind enemy lines without alerting enemy troops. The basic premise of this

technique is that the units can be deployed with such speed and fast enough that a

cohesive defence cannot be mounted against them immediately, thus giving a tactical

advantage. Typically, airborne forces are able to land with parachutes from aircrafts

as shown in Figure 1-1, or transported by helicopters as shown in Figure 1-2; however,

both methods have their various limitations. Hang gliders could provide a viable

alternative to these methods, as they could efficiently complete such a mission, and

offer a range of advantages over the methods currently used.

Figure 1-1 - Paratroopers


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Figure 1-2 - Airborne Troops

Hang gliders are light, unpowered aircrafts that are typically foot-launched from

higher ground to glide through the air, supported by aerodynamic lift from various

sources. Hang gliders have a main frame which is constructed out of lightweight

materials, typically an aluminium alloy or a composite. This frame supports the wing,

which can be either flexible, and made of fabric, or rigid, and made of epoxy and

carbon fibre materials. Given their ability to glide silently, this technology could be

used to replace the parachutes to provide stealth transportation via aerial deployment

at a large distance from the destination. Currently, the military has begun

investigating several designs for such hang gliders, an example being SPERCO’s

Gryphon Attack Glider shown in Figure 1-3

Figure 1-3 - Gryphon Attack Glider


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Prior to undertaking an extensive design process, existing hang glider concepts were

compared, the different configurations were examined, and the most viable option

was selected. The aerodynamic and stability qualities and overall performance of the

vehicle was investigated, before a final design was proposed and supported by

engineering drawings. The manufacturing and testing of the final design was not

assessed, as this is a paper based exercise and such detail is considered beyond the

scope of the project.


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2. Literature Review and Market Evaluation

2.1. Literature Review

To conceptually design a hang glider for military operations an analysis was

conducted into current hang glider models. This involves a literature review of texts

and reference books regarding this topic. This will provide us with a greater

understanding of the types and configurations of hang gliders enabling us to correctly

size a hang glider to be used in military applications.

The military performs aerial insertions by the use of helicopters and parachutes.

Helicopters are traditionally used for these operations as they can drop personnel at

their landing zone (LZ) accurately without risk to the personnel. However if the LZ is

in a hostile area the helicopter there is a risk the helicopter can be shot down.

Parachuting is another way to drop personnel at their LZ there is however a larger risk

to the safety of the persons because they slowly glide to the ground and are required

to land in open areas like fields which provide minimal cover. There are three types of

parachuting missions Low Altitude, Low Opening (LALO) jumps, High Altitude,

Low Opening (HALO) jumps and High Altitude, High Opening (HAHO) jumps.

LALO jumps are a method of aerial insertion where the parachutist leaves the aircraft

at a low altitude of approximately 500 to 2000ft with their parachute opening as they

exit the aircraft. This has the advantage of being able to drop a large number of

parachutists quickly into a large LZ. This reduces the time the parachutist is visible

ensuring they remain safer (White, 1992) however the aircraft must be travelling

slowly and at low altitude making it exposed to surface to air missile (SAM) sites.

HALO jumps are a method of delivering equipment, supplies and personnel from a

transport aircraft at high altitude to a LZ by free fall parachute insertion. The


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parachutist will require an oxygen supply as they exits the transport aircraft at an

altitude of between 25,000ft and 90,000 ft but will open their parachute at a

approximately 2500ft. The transport aircraft are required to reach this altitude to pass

above the SAM defences. The parachutist will also not be detected by radar by a

combination of a high vertical velocity and minimal metallic on the persons. Drops

conducted using this method is typically conducted at night and it ensures that the

parachutists reach the LZ close together.

HAHO jumps are used to deliver personnel to a LZ using a transport aircraft. HAHO

drops are used when the parachutist needs to be dropped into a hostile environment.

During a HAHO jump a parachutist is dropped between 25,000 ft to 90,000ft opening

their parachute 8 to 10 seconds after exiting the transport aircraft. The parachutist will

then glide with a glide ratio of approximately 1 to 3.5 to their LZ. This technique was

employed during the gulf war where SAS teams could leave the transport aircraft

outside of hostile areas gliding silently and landing inside enemy territory.

Figure 2-1 - The Gryphon Parachute System

Wing Suits are suits used to increase the surface area of a human to create more lift

during a parachute jump. These have been known to decrease the velocity of the

parachutist by up to 40 km/h. A form of this has been applied in the SPELCO

Gryphon parachute system see Figure 2-1.This was developed to bring soldiers to

their LZ without exposing the transport to anti-aircraft fire and maintaining the

surprise. The gryphon parachute system weighs only 13kg, has a 1.8m wing with


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control surfaces. It enables a pilot to be dropped out of a plane at altitude then glide

with a glide ratio of 1 to 5 to their LZ (SPELCO, 2010). This design differs from ours

as they still require a parachute for a safe landing. Therefore a larger aspect ratio is

required to provide a slower descent speed and land the hang gliders pilot safely.

Traditional hang gliders have not been used for military operations because of the use

of both parachutes and helicopters. This being said, as hang gliders price decreases

and technology level increases hang gliders performance has grown. This is due to the

use of carbon fibre, light weight fabrics for the sails and aluminium. This has enabled

hang gliders to have longer glide times.

Aero towing which is a system where an ultra-light aircraft tows a hang glider aloft.

The hang glider is positioned on a rolling cart designed to support at the correct angle

of attack for take-off. It also stabilises the hang glider until its velocity is large enough

that lift-off occurs (Hang Gliding, 2010). This system is the only system in which a

hang glider is towed into to altitude then released.

2.2. Market Review

A market evaluation was conducted to gain knowledge of hang gliders used for

commercial operations. A summary of this information is found in the following

section.

There is potential for hang gliders to be used to replace parachutes in aerial incursions

into combat environments. This is because the hang gliders can be dropped off a

distance from their drop zone and glide in. Some hang gliders have a glide ratio of

approximately 15.

As the hang glider is being designed solely for the military, it has been assumed that

the pilots are highly trained and thus will be able to use advanced level hang gliders

and there are not any cost constraints as the military is government funded. Therefore

the analysed market will consist of advanced level, high performance hang gliders.


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2.2.1. Wills Wing

Wills Wing is an American hang glider manufacturer that produces hang gliders for

beginners through to advanced pilots. The Wills Wing T2 is an advanced level, high

performance hang glider with two models, a 144 and 154. The 154 has a larger wing

area, span, and aspect ratio allowing for an increase in pilot weight. The performance

parameters are equal however for each model. Table 2-1 shows the configuration of

the T2 hang glider.

Table 2-1 - Wills Wing T2 Hang Glider (Wills Wing 2009)

Specification T2 144 T2 154 Area (ft^2) 144 154 Span (ft) 32.3 33.5

Aspect Ratio 7.3 7.4 Glider Weight (lbs) 71 73

Hook-In Weight (lbs) 160-235 185-285 Optimum Body Weight (lbs) 140-180 180-200

Nose Angle (deg) 127-132 Double Surface (%) 92

USHPA Rating 4 Maximum Velocity for straight flight Vne (ft/s) 77.73

Maximum Velocity For Turbulent flight Va (ft/s) 67.47 Minimum Descent Rate Velocity Vms (ft/s) 30.8 Maximum Steady State Velocity Vd (ft/s) 102.67

2.2.2. Airborne C4

Airborne are an Australian micro light aircraft and hang glider manufacturer. The

airborne C4 is another advanced level, high performance hang glider with three

different models, the C4 13, 13.5 and 14. C4-13 has the smallest wing area, span and

aspect ratio. These values increase between the other models as is shown in Table 2-2.

Table 2-2 - Airborne C4 Hang Glider Specifications (Airborne 2004)

C4-13 C4-13.5 C4-14

Wing area 12.7m2 (137ft2) 13.5m2 (146ft2) 14.3m2 (154ft2) Wing span 9.6m (31.5ft) 10m (32.8ft) 10.4m (34.1ft)

Aspect ratio 7.3 7.4 7.6


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Nose angle 128-133º 128-133º 128-133º Double surface 93% 93% 93% Glider weight 33kg (73lb) 34kg (75lb) 36kg (79lb) Packed length 4.9m (16.1ft) 5.1m (16.7ft) 5.3m (17.3ft) Short packed 3.8m (12.5ft) 4m (13.1ft) 4.1m (13.5ft)

Rec. pilot hook in weight

55-80kg (121-176lb) 70-100kg (154-220lb) 85-120kg (187-265lb)

VNE (max velocity)

85km/h (53mph) 85km/h (53mph) 85km/h (53mph)

VA (max rough air velocity)

74km/h (46mph) 74km/h (46mph) 74km/h (46mph)

VD (max steady state velocity)

125km/h (78mph) 125km/h 978mph) 125km/h (78mph)

2.2.3. Avian JAVA

Avian are an English hang glider and paraglider manufacturer. Avian JAVA hang

gliders are sports hang gliders offering an excellent blend of performance, handling

whilst being light weight (Avian, 2010). There are two models of JAVA hang gliders

are available, the 140 and 155. The performance data for the JAVA hand gliders are

shown in Table 2-3.

Table 2-3 - Avian Java Hang Glider Data (Avian 2010)

JAVA 140 155 Wing span 9.2 m (30' 1") 10 m (32' 9") Wing area 13 m² (140ft ²) 14.4 m² (155ft²)

Aspect ratio 6.5 7 Min sink rate 0.86m.sec (170ft.min) 0.86m.sec (170ft.min)

Max. L/D ratio 13 13 Speed range* 15-70mph, 24-113

km/h 15-70 mph, 24-113 km/h

Pilot Clip in weight range 55kg - 85kg 70kg - 110kg Max. speed (VNE turbulent

air) 72kmh (45mph) 72kmh (45mph)

Max speed (VNE smooth air) 113kmh (70mph) 113kmh (70mph) Normal packed length 5.6m (18' 5") 5.9m (19' 4")

Breakdown length 4.3m (14' 1") 4.6m (15' 2") Glider weight rigged 27.5 kg (60 lbs) 29.5 kg (65 lbs) Glider weight in bag 29 kg (64 lbs) 31 kg (68 lbs)


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2.2.4. Moyes Light Speed RS

Moyes are another Australian hang glider manufacturer producing hang gliders

ranging from beginner models to high performance, advanced level models. The

Lightspeed RS has aluminium leading edges, carbon fibre cross bars and standard

aerofoil uprights. This reduces the glide weight and improves the hang gliders

handling characteristics. The RS comes in two models the RS 3.5 and RS 4. Their

performance characteristics can be seen in Error! Reference source not found.

Table 2-4 - Moyes LightSpeed RS data (Moyes 2005)

Litespeed RS 3.5 RS 4 Area 13.7 m2 (147 ft2) 14.1 m2 (152 ft2 Span 10.3 m (33.7 ft) 10.4 m (34.1 ft)

Nose Angle 130-132 degrees 130-132 degrees Aspect Ratio 7.7 7.7

Glider Weight * 33 kgs (73 lbs) 33.5 kgs (74 lbs) Optimal Pilot

Weight 72 kgs (159 lbs) 78 kgs (172 lbs)

Hook-In-Weight 68-109 kgs (150-240 lbs)

68-109 kgs (150-240 lbs)

VNE 85 kph (53 mph) 85 kph (53 mph) VA 74 kph (46 mph) 74 kph (46 mph)

Trim Speed 34 kph (21 mph) 34 kph (21 mph) Stall Speed *** 26 kph (16 mph) 26 kph (16 mph)

Maximum Speed 124 kph (77 mph) 124 kph (77 mph) Best Glide Speed 45 kph (28 mph) 45 kph (28 mph) Best Glide Angle 15:1 15:1 Glide Angle 10:1 74 kph (46 mph) 74 kph (46 mph)


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3. Design Specifications

The development of the hang glider concept requires numerous iterations of design

and calculations, defined by specifications required of the design. The following

sections discuss the process used for identifying problems and opportunities,

determining objectives, describing situations, and defining successful objectives in the

form of a technical task. A conceptual design configuration will then be proposed

based off preliminary sizing for weight and wing area, as well as sensitivity studies.

The resultant design is then brought together in the three view drawings.

3.1. Technical Task

The purpose of this design is to develop a paper based concept for a hang glider for

military applications as part of undergraduate studies in Aircraft Design at the

University of Adelaide. There are many different missions that a hang glider designed

for military applications can possibly fulfil depending on the parameters that the

glider is designed around. Some of the possible missions of a military hang glider

include the aerial transportation of military personnel, flybys, surveillance, cargo

drop-offs or a mobile weapons platform where the hang glider has on-board weapons

mounted for strafing targets in an attacking configuration. A hang glider however,

designed for any one of these applications would need to be optimised for that

mission alone and would require modifications to fulfil other missions.

Due to this, the scope of the project will be restricted to the design a hang glider with

the main interest of transporting military personnel. The vehicle is to be controllable

by one pilot/driver with sufficient military training, and also allow for the carrying of

sufficient equipment and baggage.


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3.1.1. Standard Requirements

The proposed hang glider design must conform to Hang Glider Manufacturers

Association (HGMA) standards. These standards are defined and enforced by private

hang glider manufacturers across the globe, and are beyond the usual aviation

standards. These HGMA standards cover everything required, such as load testing and

stability requirements. This legislation will not be discussed in detail as it is beyond

the scope of the course.

The design must also comply with the Federal Aviation Regulations (FAR), which are

rules prescribed by the Federal Aviation Administration governing all aviation

activities. In particular, FAR 91, which covers general operating and flight rules, FAR

103, which covers the airworthiness requirements of all ultra-light vehicles, and FAR

105, which covers the airworthiness requirements of parachute operations will be

relevant to this project.

3.1.2. Technical Level of the Product

The hang glider will be designed to offer an alternative to parachutes currently being

used by the American military to service paratroopers. Consequently, the mission

capabilities should be more advanced and superior to those that are provided by

parachutes. Potential benefits from this new technology include longer range,

increased stealth, higher deployment speed and possibly passenger comfort.

3.1.3. Performance Parameters


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The main performance parameters associated with the design of a military hang glider

will be largely determined by the type of mission it will be undertaking. In the case of

a military hang glider intended for the transportation of personnel, the typical

operating environment will be similar to that of a paratrooper. This includes self-

launch from an airplane at a relatively low altitude, gliding through the air at a steady

rate of descent and landing on the ground at the destination where space may be

limited. With this application and the associated operating environment in mind, the

performance parameters to be designed for have been specified below and

summarised Table 3-1.

Table 3-1 - Summary of Performance Parameters

Parameter Value

Crew Weight 100 kg

Glide Ratio 15.0

Deployment Altitude 3000 m

Landing Distance 20 m

Maximum Flight Speed 100 km/h

3.1.3.1. Crew Weight

The crew weight of the hang glider will be the combined total of the pilot and any

equipped gear such as a backpack with supplies, weaponry and communications

devices. Based on rules of thumb exercised in weight estimations of aircraft, it can be

assumed that the typical pilot will weigh 70 kilograms. In addition, the equipped gear

carried by the pilot can be estimated to weigh approximately 30 kilograms which

would provide a total crew weight of approximately 100 kilograms.

3.1.3.2. Glide Ratio

To take full advantage of the travel range benefits that can be gained in comparison to

parachutes, ideally the glide ratio should be as large as possible. Here, the large


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expected payload weight will be one of the limiting factors in the potential glide ratio.

Due to current technological limitations, the glide ratio that can realistically be

achieved is approximately 15. This indicates that for every metre of descent, the

glider will travel 15 metres forward.

3.1.3.3. Deployment Altitude

The deployment altitude for a military hang glider will need to be selected as a

compromise between more forward range being achieved and less time being spent

airborne where the hang glider is subject to detection or attacks. Research shows that

paratrooper jumps are executed at altitudes as low as 150 metres. There is also the

limitation of oxygen masks being required at altitudes greater than 2.5 kilometres

where there is insufficient oxygen for proper mental function. Therefore the

deployment altitude to be designed for will be in between these two figures at 1

kilometre.

The glide range will be dependent on the glide ratio and deployment altitude. For a

glide ratio of 15 and a deployment altitude of 1 kilometre as specified above, the

maximum range will be 15 kilometres. The range can also be decreased by the pilot

inducing drag on the glider as necessary to meet the requirements of the mission.

3.1.3.4. Landing Distance

Ideally the landing distance will preferably be uphill and into the wind so that the

glider is on the verge of stalling just as the pilot lands. This landing distance can be

estimated to be approximately 20 metres, but from an approach of up to few hundred

meters.


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3.1.4. Economical Parameters

3.1.4.1. Hang Glider Cost Estimation

To maintain the viability of using a hang glider as an alternative means of

transportation for airborne forces, the extra cost versus the benefits gained over the

usage of parachutes will need to be justified. Ideally the cost should be comparable to

a parachute, however due to the intricate mechanisms and materials involved in the

manufacture of a hang glider it is very likely that the cost would exceed this. There

may also be additional costs associated with the training of the pilots and maintenance

of the hang gliders.

As such, for military applications an initial purchase cost of $5,000 (AUD) per hang

glider is ideal and is comparable to the cost of a parachute. If this initial purchase cost

is exceeded then it will need to be well-justified accordingly.

3.1.5. Power Plant Type and Requirements

This hang glider will have no propulsion system of its own and therefore solely rely

on gliding to travel long distances. For stealth purposes, this will allow for silent

gliding to the destination. Thus the only type of power required for the function of the

hang glider will be sourced from the internal body strength of the pilot for the

purposes of towing the hang glider and directional control. If the pilot is able to

support the empty weight of the hang glider whilst carrying other required military

gear such as a backpack with supplies, weaponry and communications devices then

the power plant requirements are met.

3.1.6. Main System Parameters


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3.1.6.1. Landing Gear

The legs of the pilot are intended to be used as landing gear as is done with

conventional hang gliders. Therefore in the interest of maintaining a compact and

minimalistic design for ease of towing, no additional landing gear will need to be

considered.

3.1.6.2. Navigational Equipment

For any form of transport, navigation is of utmost importance. As with

conventional hang gliders, weight-shifting will be used as the method of attitude

control for the military hang glider. Suitable navigational equipment will include a

variometer, radio and GPS where the variometer will also provide the functions of

an altimeter to indicate altitude, airspeed, climb rate and sink rate. While gliding,

the variometer and GPS may not be easily accessible and will need to be mounted

in an easy viewing position such as the control bar. The radio unit will be voice-

activated via a headset worn by the pilot and therefore will not need to be

mounted onto the control bar.

3.1.7. Special Systems and Miscellaneous

As the hang glider is a form of transport used for soldier deployment, mounted

weapons are not necessary. Similarly, weapons would be incredibly difficult to utilize

for a hang glider pilot. Lastly, firing projectiles from a hang glider would greatly

affect the dynamics of its flight, possibly causing loss of control as well as giving

away the gliders position. For these reasons, the use of weapons will be limited to

ground combat and will not be considered in the design of this hang glider.


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3.1.8. Reliability and Maintainability

The glider must be able to satisfy all the requirements described by the in the 2006

HGMA Airworthiness Standards, which include flight and load testing. It is also to

follow a maintenance schedule as described by the HGMA.

All maintenance and services should be carried out by a certified aircraft mechanic

who is familiar with the vehicle.

3.1.9. Unification Level

The hang glider should be able to be safely and comfortably piloted without removing

the centre of gravity from the centreline during forward gliding. The chosen aerofoils

are limited to those available for current hang gliders.

In future iterations of the design, the hang glider could possibly be designed to carry

either an extra passenger or payload package such that the hang glider may be able to

be used as a “taxi”.

3.2. Statistical Analysis

3.2.1. Statistics of Civilian Application Hang Gliders

At present hang gliders are almost exclusively used for recreational or sporting

purposes. Thus far there have been no known military applications of hang gliders. In

turn, this limited the ability to compare relevant statistical data due to the absence of

such aircraft. Therefore the next most relevant statistical data to be investigated were

civilian application hang gliders.

A trade study of existing hang gliders was undertaken to gather the initial estimates of

the take-off and empty weights of the hang glider. Subsequently other parameters


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such as the aspect ratio and wing span could be estimated based on this initial guess of

the take-off weight to be utilised in the proposed design.

3.2.1.1. Empty Weight

The technology diagram shown in Figure 3-1 shows the statistical trend of how the

empty weight varies with take-off weight.

Figure 3-1 - Empty Weight Technology Diagram

A linear trendline was fitted to this data where the equation of this trendline defines

the A and B variables of Roskam’s equation shown below (Roskam, 1985).

where and which was derived from the trendline of the

technology diagram. Also note that the take-off weight of the hang glider was defined

earlier as the sum of the empty weight and the crew weight, such that:


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Solving Roskam’s equation and the equation for take-off weight simultaneously

calculates the takeoff and empty weights of our proposed design. These weights were

found to be:

3.2.1.2. Aspect Ratio


aspect ratio varies with take-off weight using a fitted linear trendline. On the basis of

a takeoff weight of 134.3 kg as calculated earlier, a aspect ratio of 7.253 metres was

estimated.


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Figure 3-2 - Aspect Ratio Technology Diagram

3.2.1.3. Wing Span


wing span varies with take-off weight using a fitted linear trendline. On the basis of a

takeoff weight of 134.3 kg as calculated earlier, a wing span of 10.62 metres was

estimated.


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Figure 3-3 - Wing Span Technology Diagram

3.2.2. Statistics of Parachutes

Parachutes do not utilize any form of propulsion system. Because of this, the design

take-off weight is simply the total weight of the parachute system and the pilot.

Similarly the empty weight is simply the total weight of the parachute and the

container in which it is packed. Therefore any technology diagram developed to

compare various existing parachutes would show a straight regression line with a

gradient of one, assuming the weight of the user or payload were kept consistent.

Comparing the parameters of different military application parachutes:

Parachute

Type

Maximum

Suspended

Weight (kg)

Parachute

Assembly

Weight (kg)

Diameter

(m)

Rate of

Descent @

90.72 kg

(m/s)

Forward

Speed @

90.72 kg

(m/s)

MC1-1C Round 136 13 10.67 4.27 3.66 – 4.27

MC1-1B Round 136 13 10.67 5.43 4.27


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SET-10 Round 159 13 10.67 3.62 3.58 – 4.47

T-10C Round 159 13 10.67 5.03 N/A

3.3. Mission Profile

The hang glider was designed with a mission profile in mind. Initially the hang glider,

along with the pilot, will be taxied to the desired launch altitude by a cargo aircraft

with a tailgate such as a CASA-212. A tailgate would be preferable as it would allow

the hang gliders to be deployed safely without obstructions. Upon reaching the

desired launch altitude and location, the hang glider pilot would then take-off by self-

launching from the tailgate opening of the aircraft. Controlled gliding to the desired

location would then occur until the landing point is reached, where thereafter the hang

glider may be taxied and packed away. The intended mission profile is depicted below

in Figure 3-4.

Figure 3-4 - Mission Profile

3.4. Weight Estimation

AS can be seen from this mission profile, at no point does the hang glider require or

consume fuel. Thus, the weight estimation taken earlier still applies, which gave the

following values for a crew weight of 100kg.

Descent

4

Take-off Taxi

2 3 1

Start-up

Landing Taxi

6 5 7

Shutdown


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3.5. Sensitivity Analysis

The relative effects on the take-off weight of changing the main parameters of the

hang glider can be determined by performing sensitivity analyses. Sensitivity analyses

can also be used to indicate which parameters limit or otherwise have little effect on

the overall design. In turn the final design and configuration can be devised with these

sensitivities in mind.

In the Technical Task, the initial weight was estimated based on the statistics of

existing hang gliders and a regression line with A and B constants was obtained.

These A and B constants, among others to be calculated, can in turn be used to

determine the sensitivities using formulae derived by Arjomandi 2010. The hand

calculations of the sensitivity analyses can be found in Appendix B.

The necessary constants that were used in the sensitivity analyses were calculated as

follows:

Note that A and B were the regression line constants that were derived in the

statistical analysis based on existing hang gliders. For the constant, D, there was no

payload weight as the gear of the pilot is considered a part of the crew weight such


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that D is simply equal to the crew weight. For the calculations of the constants C and

F, the mass fuel fraction Mff was equal to unity since the weight of the hang glider is

constant throughout the phases of the mission profile as there is no fuel being

consumed. Similarly the mass fractions of the reserve and unusable fuel, Mreserve and

MFunusable, were equal to zero since no fuel would be held onboard the hang glider.

3.5.1. Sensitivity to Empty Weight

The empty weight of the hang glider is the total weight minus the pilot and his gear. If

the empty of the hang glider were increased, the effect of this was determined as

below:

The sensitivity of the take-off weight to empty weight was found to be 5.142; hence

for every kilogram increase in the empty weight, the take-off weight is required to

increase by 5.142 kilograms.

3.5.2. Sensitivity to Payload Weight

If extra payload besides the pilot and his gear were to be included in the mission

specification, the effect of this was determined as below:


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The sensitivity of the take-off weight to payload weight was found to be 1.241; hence

for every kilogram of payload added, the take-off weight is required to increase by

1.241 kilograms. Thus the sensitivity of the take-off weight to the payload weight is

almost halved compared to the sensitivity to the empty weight. Therefore it appears

that the empty weight has a much larger effect than the payload weight on the design

of the hang glider.

3.6. Aircraft Sizing

The hang glider was sized according to FAR 103 and the HGMA standards. The

design requirements consisted of stall speed, glide ratio and landing distance. The

sizing process is explained in further detail below.

3.6.1. Sizing Parameters

3.6.1.1. Stall Speed

For stall speed requirements, it was noted that in a glide, weight must equal lift, which

yields:

Rearranging this equation indicates that wing loading at stall depends on stall velocity

and the coefficient of lift of the vehicle:


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At sea level, the density of air is given as 1.227 kg/m3. At a deployment altitude of

3000m, the density of air can be found as 0.90916 kg/m3. From our statistical analysis,

we found that the stall speed of hang gliders falls within 10-22 mph, or 4.47-9.834

ms1. If we assume to our maximum lift coefficient to be 1.7, which seems reasonable

according to our statistical analysis, we have a wing loading of at least 195.2 kg/m2 in

order to satisfy our conditions at stall.

3.6.1.2. Glide Ratio

This glider has a glide ratio requirement of 15. Whilst moving at a constant speed in

still air, the glide ratio is numerically equal to the lift to drag ratio, but it is not

necessarily equal during other manoeuvres.

During glide, vdown should be equivalent to the terminal velocity of the glider, as its

descent is being slowed by the glider acting as a parasheet. Thus, vdown can be

calculated as (NASA 2010):

where cD is the coefficient of drag of the vehicle downwards. According to Culp 2000,

this is approximately 0.75 for a hang glider or parasheet. Rearranging these two

equations gives a wing loading of:

Given that a maximum forward flight speed of 200km/h is a performance parameter,

we can calculate the wing loading to be 6.3 kg/m3 in order to satisfy our glide ratio

condition.


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3.6.1.3. Landing Distance

Wing loading during landing can be calculated as

Due to the higher angle of attack, and the heavy flare that pilot’s use, the stall speed at

landing is generally higher than that for level flight, and so can be assumed to be 10-

12 ms-1. The maximum lift coefficient is similarly different, and will be assumed to be

2.3.

From this, we have a wing loading of 146.9 kg/m3 order to satisfy our conditions at

landing.

3.6.2. Design Point

As our glider does not have a power loading, a matching diagram is not needed, and a

design point can be taken from our wing loadings, which yields:

Given a take-off weight of 134.3 kg, we can find that our wingspan must be 31 m2.


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4. Preliminary Design

The following conceptual designs are primarily based on existing configuration of the

present day recreational hang glider. From Figure 4-1 it can be seen that the main

structure of the hang glider consists of keel, cross bar and the leading edge tubes. The

leading edge tubes provide the sweep desired sweep angle, while both the keep and

crossbar provide structural rigidity laterally and longitudinally. These tubes make up

the structural frame of the hang glider. The keel is then connected to the control bar.

This control bar utilizes the weight of the pilot to encourage pitch and roll directional

changes. The control bar is connected to the cross bar via flying wires. In addition

there are also wires from the leading edge keel post and trailing edge keel post to aid

in controllability and stability. The wires are the actuators which promote

manoeuvrability.


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Figure 4-1 - Hand Sketch of Glider Configuration

The vertical structure is held via a vertical post known as the king post. The king post

translates directly above the control bar and protrudes above the sail. Connected to the


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king post is a network of wires used for landing. These landing wires help incorporate

pitch movements, aiding the landing controllability of the hang glider.

The incorporation of the pilot can be seen from Figure 4-2. The pilot is held by a

pouch which is situated just above the control for ease of access to the control panel.

The pouch is connected to a network of straps and safety harness all connected to the

king post. The pilot manoeuvres through the production of moment forces. The pilot

harnesses are directly connected to the king post, which results in the pilot being

structurally fixed. The pilot then uses the control bar (which is connected to the cross

bar through flying wires) to alter the sail angle and hence producing a moment arm to

change direction.


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Figure 4-2 - Sketch of pilot configuration on conventional hang glider


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The final component of the hang glider to be added to the system is the sail. The sail

sweeps over the leading edge tube and extends to the rear till the end of the keel. The

sail is primarily the wing of the aircraft. The sail is works very similar to the sail on a

sailing ship. The sail slows down air flow producing a pressure difference between the

top of the sail and the bottom of the sail. This pressure difference to some degree

produces lift. However, this lift component is less than the gravitational force pulling

the glider down. Hence the term glider theoretically means prolonged falling.

4.1. Concept Design Number 1

The first concept design of a military application hang glider can be seen from Figure

4-4. This design is focuses on increasing manoeuvrability of the hang glider for

military purposes. A closer detailed figure can be seen from Figure 4-5. From

previous experimental bombers designed during the Second World War, forward

swept wing configuration on fighter jets provided heightened manoeuvrability. The

forward swept configuration reversed the airflow along the wing; the airflow flows

from the wing tip to the wing root, the reversal of reverse swept wing configuration.

This forward swept wing prevented stall at the wing tips at higher angles of attack this

can be seen Figure 4-3. This design also incorporates a parachute which is used for

safety landing purposes Figure 4-6.

Figure 4-3 - Air flow over forward swept wing and backwards swept wing (Wilson 2008)


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The ability to prevent stall at higher angles of attack gives rise to heightened ability to

maneuver and the ability to control this maneuverability. Hence this design

incorporates the addition of ailerons at the wing tip. The control ailerons at the wing

tip will allow for heightened roll ability as the magnitude of the moment force is

highest at the wing tip. The wing tip control surfaces maybe controlled electronically

through an onboard computer which can be situated underneath the parachute. The

commands from the pilot to the control surfaces for this design may be very difficult.

The incorporation of electronic control adds extra weight to the hang glider, which

already struggles to induce significant lift. The additional weight from the

accompanying electronic control will reduce the glide range, resulting in a limited

mission profile.

The overall configuration of this design concept provides good ideas in terms of

designing a glider that is more focused on the military and the potential tasks involved.

The aspect of a forward swept wing with heightened manoeuvrability controls work

together to enhance the glider to be able to change direction; this application can be

used to infiltrate an area with skyscrapers which require high controllability to

manoeuvre. The disadvantages of this concept are the design of a control panel and

the electronic actuators required to control the ailerons require some sort of sensor

interaction. The pilot him/herself will not be able to continually adjust control

surfaces to stabilize the glider. As such, a feedback loop computer system is required

to monitor the control surfaces and this addition of electronic device results in extra

weight, which is highly undesirable.


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Figure 4-4 - Concept Design Number 1


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Figure 4-5 - Detailed sketches of concept 1


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Figure 4-6 - Parachute Deployment


Page | 36

4.2. Concept Design Number 2

From Figure 4-7 shows the incorporation of a vertical tail in the previous concept

design. The vertical tail is designed to reduce aerodynamic slip and provide stability

in the yaw direction of the glider. The vertical tail design will be directly attached to

the keel post. The keel post is the main structural post through the middle of the glider,

theoretically be able to sufficiently support the weight of the vertical wing

comfortably. This concept allows the potential of again, increasing stability of the

glider while still designing the glider to have a high degree of manoeuvrability.

Figure 4-7 - Image of vertical tail used for stabilization (Marshall Brain 2008)


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Figure 4-8 - Vertical tail concept design


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Figure 4-9 - Detailed Sketch of Vertical Tail


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5. Weight Balance and Stability Analysis

An aircraft’s balance and stability is largely governed by the location of its centre of

gravity (CG). For a hang glider in particular, the lateral stability is also important

along with the longitudinal stability since the roll mechanics of the hang glider is

controlled by the CG shifting performed by the pilot. In order to calculate the CG

location, the weight of each component or subsystem in the hang glider was required.

For this task the hang glider was divided into the following subsystems:

• Control bar

• Pilot and harness

• Frame (keel, leading edge tubes and cross bar)

In this analysis the weight of the fabric was neglected due to its small weight and as

its location is not fixed due to the flexing nature of the fabric. Furthermore, the CGs

of each subsystem was assumed to be co-located with their geometric centres. This

assumption is normally only applicable to objects of uniform density, however for a

preliminary CG analysis this will provide a good estimation that can be further refined

in the future if necessary. Due to the scarcity of statistical data regarding the

individual weights of hang glider components, the weights were estimated using

ProEngineer CAD software functions with material densities input.

Table 5-1 - Weight Breakdown of the Hang Glider Subsystems

Aircraft Subsystem Percentage of Take-off Weight

Frame Wframe 18.62

Control Bar Wbar 6.92

Pilot and Harness Wpilot 25.54

Using the weights and CG locations of each subsystem which are presented in Table

5-1, the aircraft’s actual CG with respect to each axis was determined using the

equations detailed below. For this hang glider, X denotes the longitudinal axis, Y

denotes the lateral axis and Z is the zenith axis.


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The CG envelope was then generated to determine the forward and aft ranges of

locations where the CG must lie in order to be stable, expressed in terms of a

percentage of the mean aerodynamic chord (MAC). These were calculated at the

different operating conditions that might occur in regular use. For a hang glider, there

would only be two points: empty weight, and takeoff weight. These are shown in

Figure 5-1.

Figure 5-1 - CG Envelope

5.1. Static Margin


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Static Margin (SM) is critical in the assessment of longitudinal stability, and is

defined as the distance between the neutral point and the centre of gravity position,

expressed as a percentage of the mean aerodynamic centre (MAC), as expressed in the

following equation:

The neutral point is defined as the point where the moment of the vehicle does not

vary with angle of attack.

Due to the centre of gravity travel associated with the vehicle and as recommended

for general aviation aircraft, static margin must be at least 10%. As can be found from

our CG analysis, we have a static margin greater than 10%, even at our most aft CG,

which is acceptable.


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5.2.

6. Aerodynamic Analysis

The following section will discuss the aerodynamic properties of the hang glider, in

particular, the lift distribution of the wing, the lift to drag ratio, and the fineness ratio.

6.1. Lift distribution

A necessary part of the conceptual design of the hang glider was to ensure that

sufficient lift could be produced by the wings in order for the aircraft to takeoff and

sustain flight. Abbot and von Doenhoff 1949 present a method of estimating the lift

distribution which describes the total lift generated by the airfoil.

where is aerodynamic twist, is effective lift curve slope, S is wing area, c is

chord and b is the wing span, is the aspect ratio and the L values are coefficients

found by Abbot and von Doenhoff.

From this, taper ratio and wing geometry can be selected to optimise the aerodynamic

efficiency of the vehicle.

6.2. L/D Determination

The lift to drag ratio of an aircraft provides a good indication of the aerodynamic

efficiency. This value is also numerically equivalent to the glide ratio of a glider, in

steady flight, which is a performance parameter that must be met.


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CFD analysis was undertaken on the model at the operating conditions specified. This

resulted in a maximum L/D ratio of 16. This compares favourably to other hang glider

designs, as shown in Figure 6-1.

Figure 6-1 - Technology Diagram of Glide Ratio

6.3. Fineness Ratio and Drag of Structure

The fineness ratio describes the overall shape of a streamlined body. Specifically, it is

the ratio of the length of the body to its maximum width, thus aircraft that would be

considered short and fat would have a low fineness ratio, whilst those that are long

and skinny have high fineness ratios. As our hang glider does not have a fuselage, the

fineness ratio has taken about the harness that the pilot would be in. The wires and

struts connecting this structure to the wings were ignored.

The length of the glider was 2.22m, with a width of 1.09m, which results in a fineness

ratio of 2.04. With a pilot in the harness, we can assume this structure to roughly be a

cylinder with a cone pointed into the airflow. If we use statistical data from Scott

2010, this will result in a structural drag coefficient of approximately 0.2.


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Figure 6-2 - Drag Coefficient of Cylindrical Bodies in Axial Flow


Page | 45

7. Performance Analysis

The vehicle was designed to meet the following criteria, as per the technical task, and

the compliance is detailed below in Table 7-1.

Table 7-1 - Compliance with performance parameters

Parameter Value Compliance

Crew Weight 100 kg Designed to carry an average adult

(70 kg) with 30 kg payload

Glide Ratio 15.0 Aerofoil easily achieves this lift to

drag ratio

Deployment Altitude 3000 m Designed to be dropped at this

altitude

Landing Distance 20 m Used in sizing the aircraft

Maximum Flight Speed 100 km/h Used in sizing the aircraft


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8. Three View Drawings


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9. References

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Appendix A – Detailed Drawings


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Appendix B – Sensitivity Analysis Calculations

(for a non-fuel aircraft)

(if no payload initially)

hang glider for military application

Documents