SG178643A1

SG178643A1 - Tow hook, system and method for launching an unmanned aerial vehicle

Info

Publication number: SG178643A1
Application number: SG2010063212A
Authority: SG
Inventors: Yio Hock Tan; Keen Ian Chan
Original assignee: Singapore Technologies Aerospace Ltd
Priority date: 2010-08-31
Filing date: 2010-08-31
Publication date: 2012-03-29
Also published as: WO2012030300A1

Abstract

TOW HOOK, SYSTEM AND METHOD FOR LAUNCHINGEmbodiments of the present invention provide a tow hook for use inlaunching an unmanned aerial vehicle (UAV), the tow hook comprising: a firstend capable of releasably engaging a wing of the UAV, a second end capableof being connected to a tow line; and a rigid member connecting the first endto the second end to extend a connection point said tow line below said wingtowards a center of gravity of said UAV. Additional embodiments provide fora system and method for launching a UAV using the tow hook.Figure 520

Description

TOW HOOK, SYSTEM AND METHOD FOR LAUNCHING AN

UNMANNED AERIAL VEHICLE

FIELD OF INVENTION

The present invention relates broadly to a tow hook that may be used to launch an unmanned aerial vehicle (UAV), and to a system and method of launching a UAV using the tow hook.

BACKGROUND

Unmanned Aerial Vehicles (UAVs) are lightweight aircraft that are remotely controlied and which may be used for various purposes. Currently,

UAVs are launched either by hand (for very light-weight UAVs}, or using a bungee cord attached to the UAV to provide a forward thrust sufficient to render the UAV airborne. A first-generation bungee launch system (also known as a hi-start launch) uses a length of an elastic material, e.g. rubber, which provides the necessary pulling force fo launch the UAV. in some of these systems, a non-elastic, lightweight tow line is used to provide safety and additional altitude. One end of the tow line is releasably connected to the

UAV using various types of connectors, while the other end is coupied to the elastic material. These systems may also include a picket or stake to secure the remaining end of the elastic material to the ground,

Typically, in the first-generation bungee launch system, a single hook is attached to the underside of the fuselage at or near the center of gravity (CG) towards the front of the fuselage. The hook is releasably connected to the tow line using for example, a meta! ring. A human launcher is usually required to physically hold the UAV off of the ground before launch.

It has been noted that the first-generation single-hook bungee launch system is unstable and unreliable, especially during gusty, variable and strong crosswind conditions. In addition, the first-generation bungee launch system requires a human launcher to hold the UAV, and is thus prone 0 human error. Furthermore, for larger UAVs, it can be difficult for a person to hold the UAV against the force of the bungee. in other bungee launch systems, a ramp is used to mount the UAV before launch, thereby eliminating the need for a human launcher. However, as with the first-generation bungee launch system, this system still uses a single hook. Therefore, launch reliability remains iow as the UAV fends io sway left or right during gusty or sudden crosswind conditions, leading to failed launches and potentially to damaged aircraft.

In an effort to overcome this deficiency, an effort was made {o attach a hook to the end of either wing. Figure 1 illustrates a schematic side view of a portion of one such prior art UAV, designated generally as reference numeral 10. The UAV 10 includes a wing 20. A pair of tow hooks 30 (only one shown) are attached to an underside 22 of the wing 20. The UAV 10 has a center of gravity 40 that is located well below the underside 22 of the wing 20.

The hooks 30 are thus separated from the center of gravity 40 by a distance

Z.. The UAV 30 resis on a launch ramp (not shown). A bungee (not shown) is attached to each of the hooks 30. The bungee then provides a launch force in a direction shown with arrow 47. However, since the UAV 10 is sitting on the launch ramp, it is actually launched in a direction shown with arrow 45. The difference between these directions is shown as an angle ©.

This design showed some success in alleviating the problem of aircraft sway during variable or gusty wind conditions. Unfortunately, since the center of gravity 40 of the UAV 10 is much lower than the position of the hooks 30 on the lower surface 22 of the wing 20, the UAV 10 tends fo pitch downward (i.e. nose-dive) as soon as it is launched. This can result in a failed launch and possible damage to sensitive instruments disposed at the 3C nose of the UAV 10.

A need therefore exists to provide a system and method for launching a UAV that seeks to address at least one of the above probiems.

SUMMARY

One aspect of the present invention provides a tow hook for use in launching an unmanned aerial vehicle (UAV}, the tow hook comprising: a first end capable of releasably engaging a wing of the UAV, a second end capable of being connected to a tow ling; and a rigid member connecting the first end fo the second end fo extend a connection point of said tow line below said wing towards a cenier of gravity of said UAV. in alternate embodiments, the tow hook may also include a second member coupled to said rigid member, said second member may be configured to engage a surface of said wing such that when force is applied {o said second end, said second member engages said surface of said wing to minimize twisting of said tow hook during launch. In further embodiments, said first end may further comprise a loop configured to engage a pin attached to said wing, said pin comprising a strut having a first end connected to and extending from said wing, said pin being bent at an angle such that a second end extends towards a rear of said wing such that said loop engages said second end of said pin. The angle may be at least 90 degrees such that said loop slides off of said pin once said UAV is launched.

In some embodiments, a weight of said tow hecok may be adjusted fo faciiitate disengagement of said tow hook from said pin once said UAV launch is completed. In further embodiments, a length of the rigid member may be adjusted to provide for a launch angle of said UAV of between 25 and 35 degrees from the horizontal.

An alternate aspect of the present invention provides a bungee launch system for a UAV, the system comprising: a first tow hook as defined in any one of the preceding claims, said first tow hook being slidingly engaged to the pin attached a right wing of said UAV; a second tow hook as defined in any one of the preceding claims, said second tow hook being slidingly engaged to the pin attached to a left wing of said UAV, an elastic member comprising a first end and a second end; a first tow line comprising a first end connected to said second end of said first tow hook, and a second end coupled to said first end of the elastic member; a second tow line comprising a first end connected to said second end of said second tow hook, and a second end coupled fo said first end of the elastic member; wherein before launch, the elastic member is substantially elongated in a forward axial direction of the

UAV, and then released to launch said UAV.

In alternate embodiments, the system may further include a launch ramp configured to receive and support said UAV and to hold said UAV prior to launch. The launch ramp may further include a support frame capabie of being fixed to the ground; and a pair of spaced apart launch rails configured to receive a fuselage of said UAV; wherein said pair of spaced apart launch rails are elevated from the horizontal.

A further aspect of the present invention provides a bungee launch method for launching a UAV, the method comprising the steps of: providing a first tow hook as defined in any one of claims 1-8; providing a second tow hook as defined in any one of claims 1-8; providing an elastic member comprising a first end and a second end; providing a first tow line; connecting a first end of said first tow line to said second end of said first tow hook; connecting a second end of said first tow line fo said first end of the elastic member; providing a second tow line; connecting a first end of said second tow line to said second end of said second tow hook; connecting a second end of said second tow line to said first end of the elastic member; stretching said elastic member while holding said UAV in a fixed position; and releasing said elastic member to launch said UAV. in alternate embodiments, the method may further include a step for adjusting a length of the rigid member to provide for a launch angle of said

UAV of between 25 and 35 degrees from the horizontal.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be betfer understood and readily apparent to one of ordinary skill in the art from the following written description, by way of exampie only, and in conjunction with the drawings, in which:

Figure 1 shows a side plan view of a portion of a prior art UAV fitted with 5 pins attached to the wings of the UAV,

Figure 2 illustrates a front plan view of a UAV fitted with tow hooks according to one embodiment of the present invention;

Figure 3 shows a perspective view of the UAV of Figure 2 with the tow hooks attached to the pins;

Figure 4 shows a close-up perspective side view of a portion of the UAV of Figures 2 and 3 showing the tow hook attached to the aircraft pin;

Figure © iliustrates a close-up perspective front view of the tow hook attached to the aircraft pin as shown in Figure 4;

Figure 6 illustrates a side pian view of the UAV fitted with the tow hooks of

Figures 2-5,

Figure 7 illustrates a top plan view of one embodiment of a ramp launch system that may be used with the tow hooks and UAV of Figures 2-6,

Figure 8 illustrates a side plan view of the ramp launch system of Figure 7;

Figure 8 illustrates a top perspective view of one embodiment of a launch ramp that may be used with the ramp launch system of Figures 6 and 7; and

Figure 10 shows a side plan view of a UAV wing fitted with the tow hooks of Figures 2-8.

DETAILED DESCRIPTION

Figure 2 illustrates a front plan view of a UAV 100 fitted with tow hooks 150a, 150b according to one embodiment of the present invention. Figure 3 shows a front perspective view of the UAV 100 fitted with pins 110a, 110b attached to the wings 120a, 120b of the UAV 100 for receiving tow hooks according to one example embodiment. Figure 3 shows a perspective view of the UAV 100 of

Figure 2 with the tow hooks 150a, 150b attached to pins 110a, 110b. Figure 4 shows a ciose-up perspective side view of one tow hook 150a attached to the pin 110a according to the embodiment shown in Figures 2 and 3. Figure 5 iilustrates a close-up perspective front view of the tow hook 150a attached to the aircraft pin 110a as shown in Figures 2-4. Figure 6 illustrates a side plan view of the UAV 100 fitted with the tow hooks 150b (150a not shown) of Figures 2-5. 12 With continuing reference to Figures 2-6, the UAV 100 includes a fuselage 102, a support strut 106 mounted on the fuselage 102, a tail 104 (Figure 6) mounted on the support strut 106, and left and right wing sections 120a, 120b mounted on the support strut 106. it is understood that various types and configurations of the

UAV 100 may be used with the exemplary tow nooks 150. For example, the wing 120 may be a unitary wing mounted onto the support strut 106. Similarly, other mounting arrangements for the wing 120 onto the fuselage 102 may also be used with various embodiments of the tow hook 150, as will be described below. The

UAV 100 also includes a propeller 108 (Figure 6) driven by a motor (not shown).

Similar to a conventional aircraft, the wings 120a, 120b extend from either side of the support strut 106. The wings 120a, 120b may have an airfoil cross-section 122 about a vertical plane, shown as the "z” axis 101 (see Figure 6). In the example embodiment, the cross-section 122 of the wings 120a, 120b is constant.

However, it should be appreciated that the wings 120a, 120b can have a varying cross-section in alternate embodiments, e.g. narrowing outwardly from the fuselage 102. It is thus understood that various types and designs of UAVs 100 may be used with the tow hook system described herein.

As will be understood by a person skilled in the art, the fuselage 102 provides a housing for essential componenis of the UAV 100, e.g. battery, surveillance equipment, etc. These essential/optional components provide most of the weight of the UAV 100. The significance of the weight of the UAV 100 as it relates to the present embodiments will be discussed below with reference to Figure 10. In the example embodiment, the fuselage 102 may be substantially cylindrical along an axial direction with respect to the UAV 100 (i.e. x-axis). in addition, a centre of gravity of the UAV is disposed at a relatively low position, e.g. at a point below the wing 120. This will be discussed in more detail below with respect to Figure 8.

The following discussion will focus on a single wing 120a, tow hook 150a, and pin 110a. However, it is understood that the description provided applies equally to the wing 120b, tow hook 150b, and pin 110b. As best shown in Figures 4 and &, the tow hook 150a may include a first end 154 capable of reieasably engaging the wing 120a of the UAV 100 and a second end 156 extending below the wing 120a. The second end 156 may include various means to provide a connection to a tow line (not shown). Ii is understood that various means for releasably engaging the wing 120a of the UAV 120 with the tow hook 150a, and of attaching the tow line to the tow hooks 150a, 150b, may be used. The tow hook 150a also includes a rigid member 152 connecting the first end 154 to the second end 156 to exiend a point of force exerted by a tow line (Figures 7-8) below the wing 120a. This will be discussed in more detail below. in a preferred embodiment, the wing 120a includes a pin 110a mounted on an underside 124 of the wing 120a. The pin 110a may include a strut 112 having a first end 114 connected to and extending from the wing 120a. The pin 110a may be connected to the wing 120a using, by way of example and not limitation, welding, brazing, various types of fasteners, epoxies and the like.

The strut 112 may be bent at an angle such that a2 second end 116 extends towards a rear portion 125 of the wing 120a. The pins 110a, 110b may be similar to the pins 30 of the prior art embodiment illustrated in Figure 1.

Alternately, the pins 110a, 110b may be specially configured for use with the tow hooks 150a, 150b.

in this preferred embodiment, the first end 154 of the tow hook 150a may be shaped as a loop or cylinder such thai the loop or cylinder releasably engages the second end 116 of the strut 112. lt is understood that various other shapes and/or release mechanisms may be used. Similarly, the second end 156 of the tow hook 150a may include a ring 158 for altaching the tow line. It is understood that various devices may be used on the second end 156 to effect this attachment. in a further preferred embodiment, the tow hook 150a may include a second member 160 coupled to the rigid member 152. The second member 160 may also have a pad 166 on an end 164 thereof. The second member 160 and pad 166 provide stability to the tow hook 150za to prevent twisting of the tow hook 150a during launch of the UAV 100. It is understood that the rigid member 152 and second member 160 may be formed as a unitary piece of material made from, by way of example and not limitation, a metal such as ’ aluminum. It is understood that the specific geometry of the tow hook 150, including but not limited to the angles that the rigid member 152 and second member 160 form with respect to each other, may be adjusted as desired. All such embodiments are deemed to fall within the scope of the appended claims.

It is also understood that the discussion above appiies equally to both tow hooks 150a, 150b. in a preferred embodiment, the tow hooks 150a, 150b may be designed for specific use on a right and left wing 120a, 120b, respectively. In this embodiment, the tow hooks 150a, 150b may thus be symmetrical with respect to each other to provide for a right and a left tow hook 150a, 150b. However other geometries, including non-symmetrical right and left tow hooks 150a, 150b may also be used.

Additionally, in a preferred embodiment the tow hooks 150a, 150b should have a sufficient weight to allow them to slide off of the strut 112 once the

UAV 100 has been launched. In a preferred embodiment, the tow hooks 150a, 150b may be made from Aluminum 7075. When made from aluminium 7075, the tow hooks 150a, 150k may weigh approximately 26 grams.

However, other light weight materials which are not easily deformed (bent),

and having different weights, may also be used.

Figure 7 illustrates a top pian view of one embodiment of a bungee ramp launch system 200 that may be used with the tow hooks 150a, 150b and UAV 100 of

Figures 2-6. Figure 8 illustrates a side plan view of the ramp launch system 200 of Figure 7. Figure © illustrates a top perspective view of one embodiment of a launch ramp 280 that may be used with the ramp launch system 200 of Figures 6 and 7. Figure 10 shows a side plan view of the UAV wing 120a fitted with the tow hook 150a of Figures 2-6.

With reference to Figures 7-10, the launch system 200 may include a launch ramp 280 designed toc support the UAV 100 prior to launch. The bungee launch sysiem 200 may also include an elongate elastic member 230 which provides the forward thrust required to launch the UAV 100 from the launch ramp 280.

The bungee launch system 200 may further include a first tow line 210 having a first end 212 connected fo the second end 156 of the first fow hook 150a, and a second end 214 coupled to a first end 232 of the elastic member 230.

The bungee launch system 200 may also inciude a second tow line 220 having a first end 222 connected to the second end 156 of the second tow hook 150b, and a second end 224 coupled to the first end 232 of the elastic member 230. As will be discussed in more detail below, the elastic member 230 may then be substantially elongated in a forward axial direction of the

UAV 100 and secured to the ground 235 at a second end 234 using, by way of example and not limitation, one or more pickets 237.

In a preferred embodiment of the system 200, a stopper 238 may be employed to effect the connection between the first end 232 of the elastic member 230, the second end 214 of the first tow line 210, and the second end 224 of the second tow line 220. In other embodiments, each of the first and second tow lines 210, 220 may extend to the ground 235 and pickets 237. In these embodiments, the stopper 238 may also be used to provide a division point for the first and second tow lines 210, 220. The two tow lines 210, 220 then form an angle 221 as measured on the inclined plane. This will be discussed in more detail below with reference to Figure 10.

The stopper 238 may be made from, by way of example and not limitation, a plastic material. Other materials may aiso be used. It is understood that various arrangements of the elastic member 230 and first and second tow iines 210, 220 may be used with the embodiments of the system 200 as described.

The elastic member 230 may be made from, by way of example and not limitation, a mandrel dipped bungee rubber. Mandrei dipped bungee rubber generally maintains a modulus of elasticity that is relatively flat with respect to displacement, even at high elongations past 400%. Mandrel-dipped rubber is also able to store significantly larger amounts of potential energy without placing larger stresses on the airframe during launch. It is understood that other types of bungee material may also be used. in some embodiments of the launch system 200, a safety system 250 may be employed to prevent premature reiease of the UAV 100. The safety system 250 may include a quick release mechanism 252 and a quick refease line 254.

This will be described in more detail below.

Figure © illustrates a top perspective view of one embodiment of a ramp 280 that may be used as part of the bungee launch system 200 employing the tow hooks 150a, 150b and the UAV 100 of Figures 2-8. The ramp 280 may include a first support section 282 and a second support section 284 fixed to a pair of launch rails 286, 288. The ramp 280 may also include a pitch and roll bubble type level indicator 285 which may be used to level the ramp 280 prior to receiving and launching the UAV 100. The ramp 280 may also inciude a wing support mechanism 290 which provides stability fo the wing 120 of the UAV 100 prior to taunch. The ramp 280 may further include one or more pickets 192 to secure the ramp 280 to the ground 235. lt is understood that other devices and/or methods for securing the ramp 280 fo the ground 235 may also be used. in a preferred embodiment, the ramp 280 may be made from, by way of example and not limitation, aluminium 68061. When made from aluminium 6061, the ramp 280 may weigh less than 1 kg. in alternate embodiments, the ramp 280 may be constructed from any light weight andior rust proof material. Additionally, it is understood that various ramp designs may be used with the embodiments of the tow hook 150a, 150b described above without departing from the scope of the appended claims.

In operation, the UAV 100 may be placed on the ramp 280, and secured with the wing support mechanism 290. A bungee launch system, such as the bungee launch system 200, including the tow hooks 150a, 150b, may then be used to faunch the UAV 100. As shown in Figure 1G, using the tow hooks 150a, 150b provides several advantages over the prior art when launching the UAV 100.

Figure 10 illustrates the wing 120a of the UAV 100 with the pin 110a extending below the lower surface 122 of the wing 120a. The tow hook 150a is coupled to the pin 110a, as described above. As with the UAV 10 shown in Figure 1, the

UAV 100 has a center of gravity 139 that is much lower than the pin 110a.

However, by using the two hook 150a, the effective moment produced when launching the UAV 100 is greatly reduced. This is explained in more detail beiow.

As discussed in the Background section with reference to Figure 1, the UAV 10 has a center of gravity 40 that is much lower than the position of the hooks 30. If, for example, an acceleration of 5g is desired to launch the UAV 10, and the UAV 10 weighs approximately 5kg, the force required to accelerate the UAV 10 may be calculated using Equation 1 below:

Force = Mass X acceleration (1)

For this example, the force required is approximately 245 Newtons. The tension in the bungee (not shown) would then need to be 24.5 kg. Unfortunately, when using prior art launching methods, this leads fo a large nose down pitching moment being applied to the UAV 10. With reference to Figures 1 and 10, this pitching moment may be calculated using Formula 2 below:

M =(Fcosacosf)z,-2 where M is the moment, F is the Force calculated from Equation 1 above, the angie a is shown as reference numeral 221 in Figure 7, the angle 6 is shown in

Figure 1, and z1 is shown in both Figures 1 and 10 as different distances. Thus the nose-down pitching moment exerted by each bungee rubber is determined from the product of 2 terms: the component of the tension force in the direction of jaunch and, the moment arm distance z, from the CG fo the force component of (1), measured perpendicular to the direction of launch. The first term is determined from the magnitude of the tension force F and two independent angles specifying its 3D orientation. In this instance the angles « and 6 are known as discussed above. In the prior art as shown in Figure 1, the bungee rubber was attached at a large z, from the CG 40. With F=10kafor 981 N, a = 20°, 6 = 20° and z; = 0.1m, and using Equation 2, the moment may be calculated as 17.3 Nm.

However, using the embodiments of the tow hook 150 as shown in Figures 2-10 extends the connection point for the bungee rubber below the wing towards the center of gravity of the UAV. The distance z, is thus greatly reduced (Fig 10). By way of exampie and not limitation, in this embodiment the distance of z; may be 0.03m, which results in a 70% reduction in AM to 5.2 Nm. This reduction may be very effective in reducing the pitch down moment associated with the force of the launch, thus providing a successful launch. [i is understood that the various dimensions and calculation provided above are for the purpose of illustration only. Various angles, UAV weights, bungee force, and CG displacement distance z,, efc. may be used depending on the specific application. In some embodiments, the displacement distance z; may actually be below the center of gravity 139, thus providing an upward moment during launch. lf is understood that all such applications of the embodiments and formulas discussed above are deemed to fall within the scope of the appended claims. in a preferred embodiment, the length of the iow hook 150 may be determined based on the measured value of from the aircraft's centre of gravity. The value of 0.03m was determined from flight tests fo be optimal for the specific embodiment of UAV provided as an example illustration. As many high-wing mini-UAVs are of the same basic geometry as the expel embodiment, the value of 0.03m for z, may also be a reasonable guideline for initial positioning of the bungee rubber for this category of mini UAVs. Based on the teachings provided herein, some actual flight testing may be required to more precisely refine the 2; value to be optimal for the respective aircraft.

The embodiments of the tow hooks described above provide several advantages over the prior art. Extending the point of force exerted by the tow line below the wing reduces the downward torque applied to the UAV during launch. The tendency of the UAV to pitch nose-down may thus be greatly reduced or even eliminated. In some embodiments, an upward torque may actually be applied to the UAV. . tt will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

Claims

1. A tow hook for use in launching an unmanned aerial vehicle (UAV), the tow hook comprising: a first end capable of releasably engaging a wing of the UAV, a second end capable of being connected to a tow line; and a rigid member connecting the first end {fo the second end to extend a connection point of said tow line below said wing towards a center of gravity of said UAV.

2. The tow hook of claim 1, further comprising: a second member coupied to said rigid member, said second member configured to engage a surface of said wing such that when force is applied to said second end, said second member engages said surface of said wing to minimize twisting of said tow hook during launch,

3. The tow hook of claims 1 or 2, wherein: said first end further comprises a loop configured fo engage a pin attached to said wing, said pin comprising a strut having a first end connected to and extending from said wing, said pin being bent at an angle such that a second end extends towards a rear of said wing such that said loop engages said second end of said pin. 4, The tow hook of claim 3, wherein said angle is at least 90 degrees such that said loop slides off of said pin once said UAV is launched.

5. The tow hook of any one of the previous claims, wherein a weight of said tow hook is adjusted fo facilitate disengagement of said tow hook from said pin once said UAV launch is completed.

8. The tow hook of any one of the previous claims, wherein a length of the rigid member is adjusted to provide for a launch angle of said UAV of between 25 and 35 degrees from the horizontal.

7. The tow hook for claim 6, wherein said length is approximately 0.03 meters above said center of gravity.

gE. A bungee launch system for a UAV, the system comprising: a first tow hook as defined in any one of the preceding claims, said first tow hook being slidingly engaged to the pin attached a right wing of said UAV; a second tow hook as defined in any one of the preceding claims, said second tow hook being slidingly engaged to the pin attached to a left wing of said UAV; an elasiic member comprising a first end and a second end; a first tow line comprising a first end connected to said second end of said first tow hook, and a second end coupled to said first end of the ejastic member; a second tow line comprising 2 first end connected to said second end of said second tow hook, and a second end coupled to said first end of the aelasiic member; wherein before iaunch, the elastic member is substantially elongated in a forward axial direction of the UAV, and then released to jaunch said UAV.

9. The system of claim 8, further comprising: a launch ramp configured to receive and support said UAV and to hold said UAV prior fo launch.

10. The system of claim 9, wherein said launch ramp further comprises; a support frame capable of being fixed to the ground; and a pair of spaced apart launch rails configured to receive a fuselage of said UAV; wherein said pair of spaced apart launch rails are elevated from the horizontal.

11. A bungee launch method for launching a UAV. the method comprising the steps of: providing a first tow hook as defined in any one of claims 1-7; providing a second tow hook as defined in any one of claims 1-7;

providing an elastic member comprising a first end and a second end, providing a first tow line; connecting a first end of said first tow line to said second end of said first tow hook; connecting a second end of said first tow line to said first end of the elastic member, providing a second fow line; connecting a first end of said second tow line to said second end of said second {ow hook; connecting a second end of said second tow line to said first end of the elastic member; stretching said elastic member while holding said UAV in a fixed position, and releasing said elastic member to launch said UAV.

12. The method of claim 11, further comprising adjusting a length of the rigid member to provide for a launch angle of said UAV of between 25 and 35 degrees from the horizontal.