Raisbeck Engineering is here with a new product-but, as yet,
no firm commitment to full-scale production. In fact, the company's
focus here is to talk to owner-operators of the Learjet 35/36
and find out how much it's worth to fix a design snag with the
original airplane. Dr. Raisbeck has recommended major plastic
surgery. The first five to ten patients to volunteer will undergo
surgery at Galvin Flying Service in Seattle under Dr. Raisbeck's
personal supervision at an introductory price of $200,000.
The Raisbeck ZR drag-reduction kit is one of the most extensive
aerodynamic retrofits ever designed for any aircraft, let alone
by an aftermarket supplier. Its principal goal is to reduce the
increase in drag that afflicts 30-series Learjets above Mach 0.76.
Raisbeck's engineers have identified the culprit-a narrow air
gap, a "nozzle" formed between wing and the TFE731's
inlet lip, which is fatter, farther forward and closer to the
wing than the nose cowl of the CJ610 turbojet that Bill Lear originally
put on the airplane.
How bad was it? Raisbeck cranked up the computational fluid dynamics-a
tool that used to be the province of Lockheed, Boeing and anyone
else who could spring for a Cray, if you remember Crays-and found
airflow in the gap that was moving Mach 1.6 when the rest of the
airplane merely wanted to go Mach 0.81. One air molecule, asked
for comment, said "Ouch." That's drag on the Dame Edna
level.
The trick has been to fix the problem without a new wing, while
improving the Learjet's low-speed handling and avoiding other
potentially dire effects. Raisbeck's answer is a kit of parts
that includes a delta-shaped composite wing glove, with a large-radius,
"rooftop" pressure distribution, super-critical airfoil;
a reflexed flap with a degree of twist from root to tip; and a
"horizontal winglet" or "batwing" in the corner
between the tip-tank and the trailing edge. The glove and the
flap, between them, re-shape the airflow over the wing, reducing
peak velocity and drag. This can reduce overall drag by as much
as 10 percent as the aircraft approaches its 0.81 Mmo. At normal
cruise speeds, drag is reduced by 6 percent.
Founder and CEO Jim Raisbeck, at the age of 67, "just thought
it was time to address the issue," says spokesman Dave Gustafson.
Compared with earlier Raisbeck projects, "the development
costs have been staggering," including 105 test flights before
the NBAA debut of the modified airplane-and that's why the company
is talking to the customers before cranking up full-scale kit
manufacturing.
