American Dynamics Flight Systems: AD-1 UAV

AD-150 UAV

Startup company American Dynamics Flight Systems has been developing a UAV to address the needs of the various services for high speed cargo UAVS most notably the Marine Corps VTOL Group IV Program and Medium Programs, the USAF Unmanned Cargo VTOL UAV Program, and the US Coast Guard's VTOL UAV Program.

All of these programs are requiring fairly high speeds, a cruise at least 250 kts, which pretty much rules out a conventional helicopters which tend to cruise at less than 175 kts.

The solution that was adopted on the V-22 is a tilt rotor, where the propellers are pivoted from horizontal to vertical in the transition from horizontal flight to vertical takeoffs and landings.

Typical swashplate (source: Wikipedia

The issue with a tilt rotor system is that, even more than in a conventional helicopter, managing the transition from horizontal to vertical flight can become difficult and complex.

In the V-22, this is handled with a cyclic type control system that mirrors the swash plate type setups that exist on helicopters.

While this is obviously a known quantity in vertical lift mode, issues in transition to wing-borne flight had to be resolved before the tilt-rotor could become viable, there is a cost in complexity, cost, and reliability in using a complex prop assembly for such a system.

ADF Concept

Moves in pitch and yaw

The solution for the AD-1 is different. A ducted fan which is controllable in pitch and yaw, but where the pitch of the fan is fixed is used, the High Torque Aerial Lift (HTAL).

Pitch is obviously a given in any tilt rotor, which theoretically makes the addition of yaw actuators for the propulsors less complex, and hence lighter, cheaper, and more reliable than going with a full up cyclic control system.

Fixed Aluminum Prop

This sort of control system has been used in the past, at the dawn of the development of helicopters, where the use of tilting rotor hub, rather than a swash plate style cyclic was, for example, used by Raúl Pateras Pescara used this on his early helicopters in the 1920s, where he pitched the hub forward to allow for forward flight without the need for a separate propeller to provide lateral thrust.

The application to a tilt-rotor aircraft, and the use of rotor hub in yaw, appear to be unique, and a patent is pending.

Propulsor shroud panel

Additionally, the use of a shrouded propulsor provides for greater thrust/lift for a given disk area, by acting as a nozzle to accelerate flow.

The shrouds themselves have composite skins. The panel shown is well under 10 pounds.

The use of a shrouded prop should also simplify deck handling, since it mitigates against the possibility of someone walking into a moving prop, and there are added efficiencies because the down wash in vertical lift mode does not impinge on the wing.

All moving ruddervators

It should be noted that the aircraft has been designed from the outset to be low cost, and so notwithstanding its appearance, it is not designed to be a low-observable ("stealth") airframe.

The top mounted inlet is intended to minimize the possibility of FOD damage to the engine, the all moving ruddervators were developed after it was determined that a rear moving flap on a conventional rudder fin would not provide sufficient control authority, and the wing configuration is designed to minimize pitch changes during transition from vertical to horizontal flight.

Wind tunnel model

AD1 Development

ADF is relying heavily on computational fluid dynamics (CFD) to determine the characteristics of the, and according to Paul Vasilescu, VP of Engineering, their experiences at the Paul Vasilescu Glen L. Martin wind tunnel at the University of Maryland have been closer to the calculated predictions than any prior systems tested at the facility.

The simulations are run on 64 bit Linux rack mount systems, with some of the more complex simulations, which are being modeled in 6 degrees of freedom.

Instrumented Test Rig

The propulsors have been modeled, both in full size, and at the reduced size in which they will be tested in the wind tunnel, which should serve to further validate the mathematical modeling.

It is anticipated that the propulsors will be tested in full scale on an "iron bird" instrumented test rig at Aberdeen Proving Ground, where ADFS hopes to, "Confirm CFD performance data for hover in ground effect (HIGE) and hover out of ground effect (HOGE)," later this year, using a T53 turboshaft, used on the original UH-1 models, but flight models will use the T700, which is currently in use on the AH-64 and UH-60.

The mechanical design is done in SolidWorks^®, which I've used extensively, and should be more than capable of generated the required geometries, though it's associated FEA package, Cosmos^®, is intended for less intensive analysis.

AD-1 Manufacturing Capabilities

Applied Dynamics Flight Systems has a 14,700 square foot manufacturing facility at the Jessup headquarters with 3 & 4 axis CNC mills, and anticipates being able to assemble 12 units a year upon receipt of a contract.

Manufacturing workshare

Paths not taken

At this point, the company does not believe that there is a reasonable market for civilian applications for UAVS, the FAA has not yet come up with a coherent regulatory environment, and the technology to allow UAVs to operate in civilian airspace, so called "sense and avoid" technology, is immature.

They believe the situation to be rather similar in terms of ambulance applications on the battle field, an area where the Israeli firm Urban Aeronautics' similarly sized Air Mule is attempting to carve out a niche, there are serious issues with landing aircraft into unprepared areas, as many of the cues that a pilot has in a cockpit are lost on a remote display, and so additional technology needs to be developed in terms of automated imaging and auto-landing systems before one can expect a UAV


Full presentation in PDF after the break.

Full size photos can be viewed by clicking on the images.

Applied Dynamics Flight Systems Presentation Feb 17, 2010