1. Title of the invention
Retractable Landing Aid for mini/micro UAV.
2. Field of invention
This retractable landing aid is extremely light and offer protection to the payloads and airframe of unmanned vehicles (micro and mini class UAV) during recovery.
3. Use of invention
This invention will be useful for micro and mini UAV for recovering during landing as it offers minimum drag, minimum weight, minimum complexity and good amount of protection to payloads and airframe of UAV which would be otherwise susceptible to damage due to belly landing on airframe.
4. Prior art
Current practices involves recovery of UAV by one or combination of these methods viz:
1. Conventional take off and landing: This method of recovery requires runway for launching and
recovery of Unmanned aircraft similar to fighter and passenger aircraft. Mostly used for larger UAVs
with All-Up-Weight of more than 400 kg approx.
Eg: Tactical UAVs (Searcher- IAI, Isreal);
MALE UAV (Heron - IAI, Isreal; Predator - General Atomics, USA; Hermes - Elbit, Isreal;
HALE UAV (Global Hawk - Northrup Grummen, USA).
2. Parachute recovery: eg. Nishant Tactical UAV from DRDO, India; Skylite from Bluebird Systems, Isreal.
3. Air bag recovery. Eg. Skylark I, Skylark-I-LE etc from M/s Elbit Israel.
4. Combination of Parachute and Air Bag: eg. Nishant Tactical UAV from DRDO, India.

5. Sling / Net recovery: Suitable for Naval carriers and Army with accurate landing / recovery zone. eg. Aerosonde (AAI Textron USA)
6. Belly landing: Suitable for air vehicle with all up weight is less than 5 kg. In this case the parts susceptible to damage are replaced, if required. Most of the Commercially Off the Shelf airframe and low weight micro UAV fall in this category. Eg: WASP and Raven (Aerovironment, USA);
7. Vertical Take Off and Landing (VTOL): Fixed wing UAV having tilt rotor and Rotary Wing UAVs fall in this category. Eg: Panther, Mjpi Panther from IAI, Isreal,

5. Draw backs of prior art
1) For Mini/ Micro UAVs, which are used by Infantry / hobbyists, runway may not be available. So recovery/ landing of UAV is done by one of the other methods like parachute, sling/ net, or belly landing.
2) In each of the above resorted methods (except belly landing), the system is either too complicated, expensive or bulky.
3) In case of landing by parachute only, the UAV and the expensive payloads is susceptible to minor damages which necessitate replacement of certain airframe parts. This involves possession of repair kit/ inventory of airframe parts by operators.

4) In case of recovery of UAV by belly landing only, the UAV and the expensive payloads is susceptible to damages which necessitate replacement of certain airframe parts. This involves possession of repair kit/ inventory of airframe parts.
5) Air borne endurance of UAV is decreased due to weight penalty of landing aids like Air bag including electrically operated blower.
6) Certification of recovery method using complicated system like airbag recovery system, GPS based sling/ net recovery is expensive due to a number of trials involved.
6. Comparison between prior art and present invention
1. This invention will eliminate the costs associated with testing and certification of expensive and complicated recovery methods (air bag recovery, Sling/ net recovery).
2. This landing aid System will be light unlike recovery methods like parachute or air bag, and improve mission endurance.
2. This will be very useful for micro/ mini UAV due to restriction on the air vehicle's All Up Weight (AUW). This will also eliminate/reduce the airframe components to be maintained as repair kit thereby making ready availability of UAV for next flight/ mission.
7. Aim of the invention
Aim of the invention is to provide innovative method of landing/ recovery of mini / micro UAVs which is simple to design, manufacture, test and implement and protect the payloads and airframe structure from damage due to belly landing which is a common recovery method for micro/ mini UAVs. This landing aid is applicable only to fixed wing UAV and not to VTOL or Rotary UAVs.

8. Summary of the present invention
a) Landing aids is an important element in recovery of an UAV to prevent damage to airframe and expensive payloads.
b) This landing aid is applicable only to fixed wing aircraft and not to VTOL or Rotary UAVs. This system may be used in conjunction with compact parachute recovery system.
c) For mini / micro UAV which has a restriction on all up weight as well as costs, this innovative light weight, simple and inexpensive landing aid is designed to meet mission requirements like minimal drag, light weight.
d) Designed to meet recovery requirements like reliable deployment.
e) Type testing and certification cycle time will be shorter than other recovery methods available presently.
f) This system does not have any EMI/ EMC emissions.
g) Designed for long life.
h) Designed for zero maintenance.
i) Suitable for all speeds of mini and micro UAVs.
9. Brief description of drawings
Fig-l: Front view of the Mini/Micro UAV showing extended & retracted position of landing aid. Fig-2: Operation of Landing aid with microswitch.
10. Statement of invention
Retractable Landing Aid will provide protection to expensive payloads and other airframe parts and
maintain high availability of the UAV for next mission.
This invention meets all the mission (minimal drag, light weight) and recovery (reliable deployment)
requirements.
11. Detailed description of invention
The retractable landing aid consists of a torsion spring (1) held by an actuator lever (2) which is a part of microswitch actuator (3). The torsion spring is a thin steel wire / composite which is held by lever of the actuator. The UAV is brought in visual range near designated landing area and the actuator is activated to release the landing aid (spring). Upon receiving actuation signal, the actuator lever

rotates thereby releasing the torsion spring. The extended torsion spring will act as a landing aid to absorb the kinetic energy of impact of the UAV and prevent damage to payloads and airframe. The landing aid is designed to dissipate the kinetic energy of impact to structure. Based on the strength of structure and the maximum energy to be absorbed (depends on weight of UAV and its descent velocity), the landing aid will be designed to be crushed in case of impact energy is more than that tolerable by the structure. This will keep the weight of the landing aid to minimal.

Claims
1. This Retractable Landing aid is unique and has been designed keeping in view the simplicity and reliability of deployment.
2. Unlike Conventional Landing gear of a modern aircraft which comprises of 3.5 to 5% of the gross aircraft weight and 15 to 20 % of the structural weight U1 this retractable landing aid will comprise of less than 2.5% of the All Up Weight of UAV.
3. This system stands apart from other recovery systems found on mini/ micro UAVs for the following reasons - a. Light weight b. Maintenance free. C. Long life. D. Reliable deployment.
4. The cost of trials involved in certification of the system is negligible due to its simplicity and reliability of design.
5. The design is such that the landing aid can be easily replaced on UAV externally without dismantling any major parts. The repair kit is minimal; the availability of UAV for next mission is high.
6. The applicability of this unique landing aid can be extended to other UAVs with non conventional landing (without runway facility) by suitably designing the torsion spring. Further safety to payloads can be improved by incorporating compression springs / Leaf spring in the mechanism by keeping the same principle of dissipation of energy of landing (impact) through spring.