Engineering wise, George said the math had pretty much been done
by Riley Aircraft, but the paperwork involved in getting it through the
FAA was very difficult and time consuming. Surprisingly, writing and
getting approval of the alterations to the AFM, Aircraft Flight Manual, involved a great deal of effort. These changes included a gross
weight increase from 4630 to 5100 pounds, an empty weight
increase from 2840 to 3594 pounds. The operating parameters,
landing and takeoff distances, pretty much stayed the same, only
now they can be exceeded.
Coinciding with the engine changes were the modifications to the
camera mount. There was a shake in the original mount which
prohibited its use at speeds above 120 KIAS. With the new mount
a lot of attention was devoted to this shaking problem and it’s
reportedly solved. So far there hasn’t been any appreciable
movement above 140 KIAS.
The flight tests went very well with no cooling problems noted even
at the maximum climb rates of well over 2000 FPM. There’s no
telling how fast the plane will actually cruise with all that parasitic
drag hanging out there, but the test pilot, Dave Stevenson, said it
will probably cruise comfortably at over 150 KIAS.
Stevenson said the major concern is protecting the camera. When
the camera is run down to the bottom of the mount, giving it a clear
360-degree view under the plane, it’s below the wheels. He figures
that if there’s a malfunction and the camera won’t retract, he’ll have
to land inverted since the camera system costs more than the plane.
The Flight
Once you manage to get into the left seat, the scene is very familiar.
There’s the standard twin-engine quadrant with a pair of prop,
throttle, and mixture controls in the center console. The rudder trim,
a horizontal wheel, is below the throttles, and below this is the
hydraulic dip stick which has an admonition plaque to check every
25 hours.
With the camera hanging outside, you’ll want to screw in a little
rudder trim to maintain straight flight without taxing your leg. The
normal dirty stall speed for the aircraft, a 1976 G model, is 61 knots,
and with the STOL kit installed it was actually even lower, but
Stevenson normally takes off at 80 MPH with 15 degrees of flaps.
In the push-pull configuration you do any engine procedures and
power increases with the rear engine first. This is so you can hear
the engine and be able to identify any problems. The front engine
will drown out any sounds you may want to hear from the rear.
Stevenson and I flew the pre-mod plane and I recall watching the
end of the 3000 foot runway coming nervously close before we
lifted off. The climb rate, close to sea level and at about 100 MPH,
was an anemic 500 FPM, and not for very long. Once at altitude
Stevenson found the only way to get to a decent speed was to dive
to the cruise altitude to put it on the step. There’s a lot of argument
about this, but with all that drag it worked for this 337.
With the new IO-550 engines, all these considerations are moot.
There’s a 3000 fpm climb without the camera and over 2000 fpm
with it attached, and these numbers are at 110 KIAS. Cruise speeds,
without the camera but with the mount attached, are between 175 to
180 KIAS, and, with the camera mounted they’re in the neighborhood
of 145 KIAS at about 55%. Stevenson checked the single engine
climb at 3500 foot MSL and was able to get 500 FPM with the
camera installed. The old engines simply gave you some time to
look for a place to put it down—there was no up or level with one
engine and the camera.
The goal of the mod is to be able to fly at 150 KIAS with the camera
down and operating. This speed will allow Wolfe Air's production
team to fly along with just about any plane flying. And it seems as if
that’s easily attainable.
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