Various aspects of airframe design for UAV

It explains the airframe design guidelines of Unmanned aircraft

1. AIRFRAME DESIGN & STEALTH 20AE2048 U n m a nned A i r cra f t S y s t e m s

2. OUTLINE 🞭 A s p e cts o f A i r f r a me d e s ign 🞤 Scale effects 🞤 Packaging Density 🞤 Aerodynamics 🞤 Structures and Mechanisms 🞤 Selection of Power plants 🞤 Ancillary equipment

3. A S PEC T S O F A I RFRAM E D E S IGN 🞭 The design of an unmanned air vehicle system, of th e a i rborne el e men t ) has t o tha t o f a m a nned a i r cra f t (particularly simi l ar aims system 🞭 To achieve the required performance with the necessary integrity and reliability with minimum life-cycle costs

4. A S PEC T S O F A I RFRAM E D E S IGN 🞭 Procedures adopted to achieve these aims are similar and use similar technology 🞭 However, there are differences in the following aspects : 🞤 Electronic flight control system is lighter and requires less volume than an aircrew and their habitation 🞤 Majority of UAV are required to carry only sensor payloads rather than heavy payloads of armament, passengers or freight 🞤 Strong natural scale effects which operate to the advantage of smaller structures and mechanisms

5. A S PEC T S O F A I RFRAM E D E S IGN 1 . S c a l e E f f e ct s : Manned Aircraft - All Up Mass (AUM) Unmanned Aircraft - All Up Mass (AUM) Titan Tornado - 340 kg Airbus A380 - 5,90,000 kg Antonov An 225- 6,40,000 kg Raphael Skylight - 6 kg Northrop-Grumman Global Hawk – 12,000 kg The smallest fixed-wing UAV are two orders of magnitude smaller, in terms of mass, than their smallest manned counterparts

6. A S PEC T S O F A I RFRAM E D E S IGN 1 . S c a l e E f f e ct s : Manned Rotorcraft - All Up Mass (AUM) Unmanned Rotorcraft - All Up Mass (AUM) Robinson R22 - 623 kg Mil 12 helicopter – 97,000 kg EADS Scorpio 6 - 20 kg Schiebel Camcopter– 200 kg

7. A S PEC T S O F A I RFRAM E D E S IGN 1 . S c a l e E f f e ct s : Care must be taken when extending the scaling laws to such low masses Lightest helicopter UAV design is, as the fixed-wing UAV, two orders of magnitude lighter than its manned counterpart Possible to determine the effect that the differences of scale can have in the design of UAV aircraft Done through the use of the principles of “Froude Scaling”

8. A S PEC T S O F A I RFRAM E D E S IGN 🞭 Linear dimension ratio is L a /L m , = n (scale factor) 🞤 where subscript a indicates ‘actual’, m indicates ‘model’ 🞭 For a model system where n = 10 , an aircraft model represents a full-scale aircraft having linear dimensions 10 times that of the model and areas 1 t i m e s those of the model 1 . S c a l e E f f e c t s :

9. A S PEC T S O F A I RFRAM E D E S IGN 1 . S c a l e E f f e c t s : 🞭 But the actual size system operates in the same dens i ty o f ai r ρ , an d gr a vi t ati o n f iel d s tren g th g as the model 🞭 Thus a small aircraft, built observing these criteria, of the same configuration as one of ten times the size will exhibit similar characteristics when flying at, say, 31.6 m/s to its larger brother flying at 100 m/s

10. A S PEC T S O F A I RFRAM E D E S IGN 2 . Pa c k a g i n g D e n s i t y : 🞭 The size and weight of the UAV can be significantly reduced compared with a manned aircraft designed for the same role by taking advantage of the ability to achieve a high density of packaging (aircraft mass/aircraft volume) and the structural and aerodynamic benefits which result

11. A S PEC T S O F A I RFRAM E D E S IGN 2 . Pa c k a g i n g D e n s i t y : 🞭 The specific gravity (SG) 🞤 of people is little less than unity (0.98) 🞤 effective SG of the occupied cockpit for most light manned aircraft to an overall value of order 0.1 (i.e. about 100 kg/m3) or less - effect of providing them with room for access and to operate 🞤 Electronics and optics for a UAV (>1)

12. A S PEC T S O F A I RFRAM E D E S IGN 2 . Pa c k a g i n g D e n s i t y : 🞭 The specific gravity (SG) of 🞤 Electro-optic sensor (eyes), AFCS (brain), radio and power supplies, (communication, etc.) and support structure of a UAV will typically be about 0.7 (700 kg/m 3 ) 🞤 Engines, transmissions, actuators and electrical generators have SG of about 5–6 (5000–6000 kg/m 3 )

13. A S PEC T S O F A I RFRAM E D E S IGN 3 . A e r o d y n a mic s : 🞭 An indicative measure of the response to air turbulence of an aircraft, and to some degree its relative aerodynamic efficiency, may be given by the ratio  of its surface area to its mass 🞭 The larger the surface area, the more it may be disturbed by aerodynamic forces 🞭 The greater its mass, so greater will be its inertia (resistance) to the imposed forces

14. A S PEC T S O F A I RFRAM E D E S IGN 3 . A e r o d y n a mic s : 🞭 UAV, being generally smaller than manned aircraft, will tend to suffer more aerodynamic disturbance in turbulent air 🞭 The smaller aircraft suffers a higher friction and profile drag of both wings and body for the same shape as a larger aircraft as it operates at a lower Reynolds number

15. A S PEC T S O F A I RFRAM E D E S IGN 4 . S t r u ctur e s a n d M e c h a n i s m s : 🞭 Loads in larger aircraft are much higher than their smaller counterparts and so require materials of greater specific strength and stiffness to carry those loads over greater distances without failure through direct loading, bending or buckling

16. A S PEC T S O F A I RFRAM E D E S IGN 4 . S t r u ctur e s a n d M e c h a n i s m s : 🞭 Most UAV benefit through smaller scale in that loads are lighter and are required to be carried over shorter distances 🞭 This reduces the probability of buckling though attention must still be paid to ensuring that the structure is robust enough for man- handling

17. A S PEC T S O F A I RFRAM E D E S IGN 🞭 The great majority of UAV in p o w e r ed b y i n t e r nal c o m b ustion most of those have piston engines 🞤 a) T w o - st r o k e (t w o - c y c l e) e n gi n es 🞤 b ) F ou r - st r o k e e ngi n es 🞤 c) S t epped pis t on e n gi n es 🞤 d) R o ta r y engi n es operat i on are engi n es and 5 . S e l e c t io n o f P o w e r p l a n t s :

18. A S PEC T S O F A I RFRAM E D E S IGN 5 . S e l e c t io n o f P o w e r p l a n t s :

19. A S PEC T S O F A I RFRAM E D E S IGN 5 . S e l e c t io n o f P o w e r p l a n t s : 🞭 Gas-turbine engines are quieter than piston engines and produce smooth power at low mass/power ratios 🞤 (i) turbo-jet units which are designed to produce thrust (kN) from a high-velocity jet for direct propulsion 🞤 (ii) Turbo-shaft units which produce power (kW) in an output shaft which may drive a propeller or helicopter rotor to provide thrust

20. A S PEC T S O F A I RFRAM E D E S IGN 6 . A n c i l l a r y E q u i p m e n t : 🞭 Existing aircraft-approved and certified equipments, available for the lightest manned aircraft, are too large and heavy to appropriately meet the requirements of the smaller UAV

21. A S PEC T S O F A I RFRAM E D E S IGN 6 . A n c i l l a r y E q u i p m e n t : 🞭 F o r th e sma l ler U A V , p r o bl e ms m a y ari s e in sourcing alternators, appropriately actuators, sized ai r - d a ta sensors, electrical sys t ems, ba t t erie s , attitude and altitude fasteners, external lighting, antennae, etc.