Gojett - Making Supersonic Testing Affordable
11:36 PM on Feb 29, 2012
Starkey Aerospace - Starcor - is a start-up company formed by University of Colorado Boulder assistant professor Ryan Starkey to develop a small, low-cost, supersonic unmanned aircraft. My colleague Guy Norris wrote about them first, in AW&ST's Leading Edge column. Now UC-Boulder has followed suit.
All photos: Ryan Starkey
Inspired by the X-15, Starkey hopes the 50kg UAV will reinvigorate high-speed flight testing by providing a reusable flying testbed that, at $50,000-100,000, is affordable enough that losing the vehicle would not jeopardize the program. Other potential uses include penetrating storms and military reconnaissance.
The Gojett project to develop both the airframe and its small, fuel-efficient turbojet engine have been under way at CU-Boulder for three years and is now transitioning to Starcor, which has funding in place to take its prototype through to taxi tests while it raises funds for flight testing and construction of a high-speed vehicle for transonic and supersonic flights in 2013.
The engineering test unit aircraft is scheduled to be complete in April. Its modified US Microjet AT-450 turbojet is to be integrated by July, with ground and taxi testing planned for August-September. The AT-450 may be used for low-speed flight testing, but Starcor plans to install a modified, more-powerful AMT Netherlands Titan turbojet for higher-speed testing from December to February 2013.
"The biggest problem we have with UAVs is that small engines are inefficient," says Starkey, mostly because turbojets in this class emerged from the hobby-shop world. The Gojett project was initiated to develop a competitive small turbojet by modifying the off-the-shelf AT-450 to increase its thrust-to-weight ratio. This engine can be used for low-speed tests, but lacks the thrust to power the vehicle through the transonic drag rise - hence plans to use the Titan.
Starkey (left), with CU-Boulder students
All this is a precursor to flights with Starcor's own engine, the L-FX00. This is a 200lb-thrust lubrication-free turbojet with variable-area nozzle, afterburner and fluidic thrust-vectoring. The goal of L-XF00 development is to double the fuel-efficiency and thrust of current engines within the same frontal area and with a time between overhaul (TBO) exceeding 1,000 hours - 10-40 times that of existing model-aircraft/small-UAV turbojets.
Starkey says the fuel-efficiency and thrust-to-weight goals have been demonstrated with a modified AT-450. Work to demonstrate the extended TBO is under way with the US Naval Research Laboratory; lubrication-free capability with NASA Gleen; and thrust vectoring with NASA Langley - the thrust-vectoring test stand is to be complete in a month, he says.
The UAV itself will be 5.8ft long, with a 4.2ft-span cranked delta wing. Flight control will be provided by elevons and the fluidic-injection thrust-vectoring system. A pitot inlet will feed the afterburning turbojet. The initial vehicle is targeted at Mach 1.4, but the eventual aim is a UAV capable of Mach 1.6-1.7.
Schlieren images of the UAV at Mach 1.32 in
the US Air Force Academy Trisonic Tunnel
Like all start-ups Starcor is looking for money. "We require about $50,000 to finish both our prototype and final vehicle work, with significantly more needed to pay for the high-speed flight testing," says Starkey. Budget constraints explain why the UAV will fly first with the modified AT-450, then the Titan, before the L-FX00 ever takes to the air.
"Money may accelerate our schedule somewhat, but we will not put the final engine into the vehicle until we are certain we have any issues worked out," he says. "Breaking a modified COTS engine is cheap, but breaking a prototype is not, especially coupled with an expense vehicle."
awt, unmanned, propulsion, supersonics