Plane & Pilot
Tuesday, August 24, 2010

King Kong "Little" Cub


CubCrafters’ top LSA offers a big surprise when the throttle goes forward



The result of the horsepower upgrade and weight reduction is a climb rate you might more typically associate with a corporate turboprop. The Carbon Cub SS leaps off the ground in less than 200 feet and scores an initial 2,100 fpm uphill from sea level. The 180 hp rating is good for five minutes.

This suggests near-helicopter capability. It’s very likely the Carbon Cub SS could duplicate the near impossible, semi-vertical climb performance of a Helio Stallion. Years ago at the Alaska Airman’s Association Convention in Anchorage, I witnessed the Helio’s simulated box-canyon climb demonstration.

Imagine the airplane is at the bottom of a box canyon that’s no more than, say, 500 yards on a side. (Never mind how it got there.) The pilot lines up along the longest axis, goes to full power, releases the brakes, runs less than 100 feet, rotates hard and almost immediately rolls into a 45-degree bank in either direction at an airspeed of 40-50 knots. He then maintains that tight rate of turn and gradually corkscrews up and out of his box canyon. The Helio pilot didn’t suggest anyone had actually used this technique in a REAL box canyon (again, how would you get there?), but it certainly makes an impressive demonstration.

As you might imagine, identifying cruise performance on the Carbon Cub SS is simply a matter of acknowledging the top speed limit set by the FAA. Max cruise has been set at 120 knots by simply limiting cruise power to 80 hp, about 45% of total rated power.

One benefit of the low power setting is that it results in a proportionately low fuel burn. At an estimated sfc of .42 lbs/hp/hr, consumption works out to 5.5-6.0 gph. With 12 gallons in each wing tank, and head pressure sight gauges in each wing root to identify the level, you can linger aloft for three hours plus reserve, probably enough for most people.

Cruising at the speed limit of 120 knots means you can plan on 300-350 sm range, if that’s your mission, and of course, there’s no reason to use economy cruise as you’re already there. Visibility is excellent from either seat.

The Cub does its best work in short-field mode. One reason is the big flaps, deployed logically enough by a lever at top-left cabin. The flaps extend to 50 degrees, and you can imagine what that does to stall speed. Another is the Boundary Layer Research Vortex Generators. These re-energize the boundary layer on the top trailing edge, reduce stall slightly and actually enhance aileron control at the lower edge of the envelope. There’s nothing negative about them (except that they probably do make the airplane a little harder to wash).

Even with 29-inch tundra tires mounted, you can fly final at whatever speed you feel comfortable, down to probably 40 mph. Dirty stall is about 31 mph, so 50 will work well as a conservative number. I had a buddy in Alaska years ago who used to fly his Super Cub at such a slow speed on final, the airspeed needle was bouncing around the bottom of the dial. He was actually flying in the stall, not a trick for the faint of heart.



Labels: LSAsPiston Singles

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