Cirrus Design is homing in on the desired attributes for its production Vision SJ50 single-engine personal jet after more than 120h of successful initial test flights with its "V1" verification prototype aircraft.
Included in the significant, yet "subtle" changes for the five-passenger Williams International FJ33-4A-19-powered single is a new engine tailpipe that greatly decreases nose-down pitch coupling with power application, which is particularly crucial for go-arounds. Piper Aircraft this summer came to a similar conclusion for its single-engined PiperJet, trading a complex automatic elevator trim system for a 6° up tailpipe cant at the cost of cruise speed.
By increasing the Vision's tailpipe cant angle from 6.5° for V1 to 12° upward for the production aircraft, Cirrus has reduced the pilot's side-stick controller forces by 67% to hold the nose level during worst case go-around thrust applications, says Mike Van Staagen, Cirrus vice president for advanced development.
Combined with the engine's 8.5° downward tilt with respect to the horizontal, the thrust vector for the production aircraft will be 3.5° up compared with 2° down for the V1, requiring the wing to provide a portion of the lift that had previously been provided by the engine thrust.
The price for enhanced controllability will be the loss of 3-4kt (5.5-7.4km/h) airspeed compared with the V1, which Cirrus says has a maximum cruise speed of 319kt (590km/h). The company maintains that the production version will have at least a 300kt top speed and 1,850km (1,000nm) range with reserves. Priced at perhaps $1.25 million equipped, Cirrus estimates its first jet could be ready for deliveries in 2011.
In an effort to lighten the aircraft, increasing useful load and/or range, Cirrus will tilt the V-tail forward, rotating the leading edge of the tail fins down roughly 8 deg measured on their respective chord plane, leaving the dihedral unchanged, says Van Staagen.
The changes allowed for a weight reduction of 18kg (40lb) by eliminating a complex mechanical device needed to linearize rudder-vator inputs, reducing twisting loads and allowing for lighter weight attach points and fuselage attach points."
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WEIGHTS FOR CIRRUS SJ50 VISION
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Weight savings will also come from removing the right door and shortening the fuselage by 11.4cm (4.5in) although passenger room should not suffer due to slimmer seats. Cirrus is also evaluating pneumatic de-icing boots as opposed to the traditional TKS fluid system on its piston-powered aircraft, a change that will save 18kg (40lb), says Van Staagen.
The company is also studying a variety of ventral fin designs for stability and for use as a yaw damper rather than performing the function with the rudder-vator.
"We have yet to be surprised," says Van Staagen of the V1 test programme to date. Test pilots so far have mapped out the entire centre-of-gravity envelope, maximum and minimum speeds and in-flight engine restarts, and as of early December were currently completing stall performance tests. Cirrus planned to formally file paperwork to begin the US Federal Aviation Administration certification process on 17 December.
Source: Flight International
