Micro Air Vehicles A love story. That endures. Maybe…. Michael V. OL US Air Force Research Lab Aerospace Systems Directorate AIAA Applied Aerodynamics TC Workshop on MAVs 11 January 2014, SciTech

The MAV catechism (apocryphal version?) 1. small things are cool. Info, nano, bio. Miniaturization is relentless. Why not in air platforms? 2. flying things are cool. Small flying things are even cooler! 3. not everything in aeronautics is hypersonics, combustion, heat transfer or turbulence modeling! 4. we want better connection between fundamental research and applications. 5. big systems are expensive and require too much long-term planning. 6. so MAVs are great...small, flying, not hypersonic, comparatively inexpensive, "easy" to test. 7. but they don't speak to a traditional Air Force mission, there is no (yet) “must have” payload, and hardware will be developed by non-defense industry anyway 8. and maybe aeronautical things don't scale (nuclear doesn't scale, right)? 9. meanwhile, times are tough in the Public Sector (look around the room; who is here?) 10. so here we are. We have some questions to answer.

What is a(n) MAV? Late 1990s (DARPA, McMichael and Francis): size and mass 2005 (DARPA, Darryll Pines): NAV, again size and mass June 2006 MAV Workshop (AFOSR, Jefferies, Denver CO) 2008: AFRL MAV Team (Parker et al.): “bird-sized 2015 goal and “insect- sized 2030” goal” “Physics-based”: operating Re is so low that fully attached flow over lifting surfaces is generally impossible, and flight consists of managing separation Outcome? Pacing issue is componentry? AeroVironment Hummingbird “completed” the task [anecdotal] gust-tolerance NOT yet solved MAV MURIs (Brown/MIT and Michigan) What do we know in 2014, that we didn’t in 2006? Goals downscoped, no “demonstrator” emerged AIAA FDTC low-Re DG, AVT-101, -149, -202,…

History Repeats Itself Every 5-10 years: a textbook T. J. Mueller, et al., ~2000Wei Shyy et al., 2013 Rhett Jefferies, Denver 2006 Every 5-10 years: a workshop

Flight modalities Woods, Henderson and Lock Aeronautical Journal, Vol 105, N. 1045, March 2001 Fixed-wing (+ prop) Rotary-wing (or quad) Flapping-wing (empennage?) Efficiency Maneuverability/gust tolerance

Research Areas Autonomy and collaborative control Sensors Actuation, mechanization, transmissions, FSI Energy (batteries, micro-engines) Materials Aerodynamics AFRL Aerospace Systems Directorate Investment Areas

Some observations in MAV aerodynamics AIAA FDTC low-Re Discussion Group ( ) NATO Scientific and Technology Organization… AVT-101 ( ) AVT-149 ( ) AVT-202 ( ) CFD vs. experiments and analysis… validation and complementary strengths Role of transition and facility flow quality Wind tunnels vs. water tunnels (and tanks) Relate kinematics to flowfield evolution to aero force/moment coefficient history

The four prime test conditions: -rectilinear translation at various fixed (or varying) incidences -pitch in a fixed (or varying) free-stream -wing rotational acceleration at fixed incidence -wing pitch during a steady rotation. Parameters: Reynolds number, peak incidence angle, reduced frequency and plate aspect ratio

Some observations in unsteady aerodynamics Phenomenological buildup of aerodynamic models for maneuvering, gust response and flow control applications Case-study: flowfield evolution for pitching plates K = 0.2; left: leading edge pivot point, max lift occurs at θ = 34.2º; right: trailing edge pivot point, taken at ∆t′ = 1 later at θ = 57.1º. Case-study: surging inextensible membrane wing Membrane nominally at 45-deg, surging Data: Kenneth Granlund, Peter Mancini, and a cast of… several

C L,D Some observations in unsteady aerodynamics Case-study: surging rotating vs. translating plates, 45-deg incidence C L,D Rotation and translation produce similar force histories, but flowfield evolution is very different (e.g., Garmann and Visbal) Data: Kenneth Granlund “high” Re: translation produces slightly higher forces… despite LEV detachment “low” Re: net aero force no longer wall-normal

Aerodynamics vs. Other disciplines in MAVs 1.Attendees are mostly fluid dynamicists (or airplane aerodynamicists) because (1) this is sponsored by Applied Aero TC, and (2) MAVs have been so pivotal in motivating incompressible aerodynamics 2. But other disciplines might pace MAV development! 3. Think in terms of airplane design (the system), not just constituent disciplines 4. Think in terms of capabilities (many MAVs are part of sensor suite?) – “system of systems”

What We Hope to Hear Today 1. From academia: what's been done that's genuinely intellectually compelling? What forthrightly prompts more questions than it answers? (as opposed to just convincing gullible program managers to fund work that's less inferior than competing work?) 2. From government: is there any real science that we have transitioned to engineering? Is the bottleneck in the supply of science, or in our imagination in transitioning it? 3. From industry: can a profit be turned from MAVs? What science (and engineering) should be done, to make MAVs useful? And if they are not (or not yet) useful, what useful products or knowledge could be spun off? 4. From everyone: if we hold another such workshop in 2022, and you find yourself again in attendance, what do you hope to be able to say, that you're unable to say presently?