TESTING FLY-BY-WIRE INNOVATIONS FOR FUTURE BIZJETS
The Tacit Clear Test Management Project (TMP) is a Test Pilot School student-led test of a brand new fly-by-wire flight control system. The student team is comprised of two pilots and three flight test engineers, from the USAF and the Italian Air Force. The Test Management Project is the largest single project completed by the students during the 48-week syllabus, and brings together all elements of the course. The U.S. Army Aviation Development Directorate is the customer, and Cessna/Textron has developed the flight control system. As part of the development process, flight test data detailing the actual aerodynamic responses of Calspan’s Lear 3 was gathered. This data was used to create a new mathematical model of our Learjet’s inflight characteristics. This more accurate model was then used by Cessna to develop their flight control system, and will be used extensively at the USAF Test Pilot School for their Handling Qualities simulator and for future Learjet-based test programs.
Calspan’s role in the Tacit Clear project was to integrate the new control system with our VSS system, and provide engineering and Instructor/Safety Pilot support for the flight testing. Edwards Site Manager Jason Kirkpatrick led the planning and coordination efforts, working with Flight’s engineers and contracting expertise. Ryan McMahon handled the engineering to integrate Cessna’s system with our Learjet’s VSS computers, and the functional checkout at Niagara Falls using our in-house hot bench. Jay Kemper integrated the new model and control system into the TPS Handling Qualities simulator, which the students used as an integral tool for their test program. Evan Thomas and Paul Deppe flew as Safety Pilot with the students, Noel Welsh provided primary maintenance support, and George Camann was on-site at Edwards to provide immediate engineering support.
The first phase of the Tacit Clear test focused on two areas: verifying the accuracy of the new aerodynamic model of our Learjet, and the basic flight characteristics of the Cessna fly-by-wire control system. The second phase of testing will aim to stress the handling qualities and performance of the Cessna control system, by flying close formation tasks with a T-38 jet trainer and performing landings. The flights and landings mark the first-ever use of this new Cessna fly-by-wire control system. The students will fly up to 10 flights in Lear 3.
The first flight of the Cessna control system was flown by a Cessna crew on February 23rd, with Calspan test pilot Evan Thomas acting as Safety Pilot. The first flight checked calibration, basic operation and expected responses of the control system. The flight control system is designed for a future business jet, and incorporates a modern design philosophy. The pilot commands ‘g’ blended with airspeed in the pitch axis, roll rate in roll and sideslip angle in the yaw axis. Next, the system was handed to the Test Pilot School student team for their evaluation. The students began with conventional flight test techniques on the ‘basic’ Learjet itself to verify the aerodynamic modeling. Then the flight test will incorporate more difficult handling qualities tasks. A highlight of the testing will be close formation flight with a USAF T-38, intended to expose any problems with high workload flying or potential for hazardous pilot-induced oscillations. Finally, the students will take the new flight control system to offset precision landings and ensure it is capable of safe operation in the most critical phase of any flight.
Beyond providing unique “real world” flight test experience to the Test Pilot School students, this project will also provide an accurate aerodynamic Learjet model to Calspan and provide the Cessna/Textron engineering team with essential experience for future fly-by-wire control systems in their business jet products.