Estimated reading time 13 minutes, 24 seconds.
The teaming effort between Advanced Tactics Inc, of Torrance, California, and Rotor X Aircraft Manufacturing Company, of Chandler, Arizona, known as the AT/RX team promises to provide one of the best solutions for the U.S. Air Force AFWERX HSVTOL Challenge final selection.
Don Shaw, CEO of Advanced Tactics Inc., states that, “The AT/RX Barracuda design has been developed and refined for over a decade with the objective of creating a VTOL aircraft with superior performance, affordability and reliability, while avoiding the shortcomings of other High Speed VTOL aircraft designs that may have been submitted to the USAF AFWERX HSVTOL Challenge.” Several United States and international patents have been granted for the Barracuda design. The AT/RX Barracuda will also benefit from analysis by the Georgia Institute of Technology (GaTech), School of Aerospace Engineering, Vertical Lift Research Center of Excellence (VLRCOE). The GaTech VLRCOE will be conducting aerodynamic analysis using Vortex Lattice and Computational Fluid Dynamics (CFD) methods to help refine the Barracuda design.
The USAF AFWERX HSVTOL Challenge team recently met in their Las Vegas facility with 35 companies/teams that were initially selected from the 218 proposals that were submitted. This meeting was to get to know the participants even further before making a final selection of just a few of the companies/teams to rapidly prototype their aircraft and demonstrate it within 18 to 24 months. AT/RX plans to have a scaled manned version flying in the first 6 months with the finished aircraft within 18 to 24 months from program kick-off. It’s an ambitious program and seeks the most innovative of the initial participants to move to the final funded phase to make an aircraft that will have the performance of fixed wing aircraft with jet-like speeds while not requiring runways. One of the key objectives of the AFWERX HSVTOL Challenge is to replace the HH-60 Pave Hawk helicopter and other slower helicopters with a long-range VTOL aircraft with jet-like speed.
The AT/RX Barracuda uses four engines instead of just two engines. This doubles the survivability of the aircraft because if one engine is damaged the diagonally opposite engine is automatically throttled-back, and the other 2 engines are throttled up. This allows the Barracuda to continue flying in the cruise configuration, and it also allows the Barracuda to execute a fully controlled and safe landing when in the VTOL configuration.
Another feature of the Barracuda design is that the engines are completely independent. There is no heavy, complicated and expensive cross-shafting and linkages connecting the 2 engines. And no complex and costly gear-box systems to drive those shafts. Each engine is independently controlled on the Barracuda by the onboard flight control and engine management system. Cross-shafting is essential on any type of VTOL aircraft that only has 2 engines (one on each wing) providing thrust in the VTOL mode. This is because in the 2-engine aircraft – if one engine dies the other engine must drive both propellers, otherwise the aircraft is totally uncontrollable and will crash. Therefore these 2-engine VTOL aircraft require constant inspection and maintenance of the entire cross-shaft system while adding thousands of pounds of additional weight to the airframe.
Another reason that the Barracuda uses 4 engines, mounted on struts or pylons, is so that there is never any downwash from the proprotors onto the wings. The Barracuda avoids downwash on the wings throughout the entire flight regime – whether in VTOL, cruise, or transition between VTOL and cruise. The downwash experienced by all the 2-engine VTOL aircraft causes significant loss of thrust in the VTOL configuration, and enormous turbulence around the wing during both VTOL and transition between VTOL and cruise – with corresponding instability and control problems (which have often caused fatal crashes). In addition, that turbulence under this type of 2-engine VTOL aircraft has earned the under-belly hoisting hatch the nick name of “hell hole” by the troops that have to ingress or egress via that hatch.
Another issue with the 2-engine VTOL aircraft is the instability caused when the engines transition between VTOL and cruise. Stability and maneuverability must be performed by aerodynamic surfaces because engines cannot respond fast enough for roll control, and there is no thrust-vectoring or vanes to control pitch or yaw. And because of the dramatically shifting turbulence, the flight surfaces must quickly compensate for the turbulence while managing the attitude of the aircraft. The Barracuda simply does not have any of those problems.
A tilt-wing design was briefly considered early in the design analysis that led to the Barracuda. The tilt-wing design was quickly rejected for several reasons. A 2-engine tilt-wing design still requires cross-shafting just like the other 2-engine VTOL designs. This is for the same reason – maintaining control if one engine dies. Another reason is that, even though the aerodynamic surfaces on a tilt-wing are always in the prop-wash and can provide roll and yaw control, the ability to control the pitch of the aircraft either requires a complex control system (like those used by the 2-engine tilt-rotor designs) or a vertically oriented thruster (usually a fan or ducted fan) in the tail of the aircraft. It is well known that tilt-wing aircraft can experience controllability problems (including a fatal crash of an X plane) caused by tail-thruster failure. The Barracuda does not use, nor need, such a tail thruster – thereby eliminating that single-point-of-failure.
Some tilt-wing and tilt-rotor designs use two wings with engines mounted on them. During cruise, the rear wing and propulsors, must deal with the turbulence caused by the forward wing and propulsors. Again, the barracuda does not experience those problems. Also, the multi-wing multi-engine designs result in an aircraft that is more complex and expensive that the clean, uncomplicated, and more cost-effective Barracuda design. Finally, it should be noted that many of the multi-engine (tilt-wing or tilt-rotor) designs use small-diameter propellers. This is essential for keeping the aircraft from becoming enormous just to accommodate multiple large-diameter propellers on the same wing. The physics of propulsion clearly shows that small-diameter propellers are much less efficient than large-diameter propellers or proprotors. You don’t see any operational helicopter that use many small propellers for lift because “bigger is better.”
Along those lines, there are some designs that have tried to use a multitude of “small” propellers for vertical thrust, resulting in less payload and endurance capability, because all of them have had to face the unyielding physics of propulsive efficiency. Some have stubbornly continued with the many-little-engine design, while others have faced reality and changed their design to larger propellers or proprotors combined with a wing (or wings). The Barracuda designers let the physics do the talking, and never went down that path to begin with.