Yeee-Haa!
That was the unbridled reaction to my first solo takeoff in a Carbon Cub SS, the new LSA from CubCrafters. When I pushed the little black knob forward to unleash the 180 hp CC340 engine, the tail lightened swiftly and the airplane quickly started dancing softly on its 29-inch Alaska Bushwheel Airstreak tires before I realized I was the only one not quite ready to fly. In spite of my slow response, takeoff roll was just a few hundred feet, and the climb rate was invigorating, inviting comparison to a helicopter instead of an airplane. CubCrafters likes to call this aircraft a "high performance LSA," and it is.
Did I mention that I was departing from a grass strip just south of Denver called Rocky Mountain Airpark at an elevation of 6,295 feet and a temperature of 70 degrees? That makes for a rather formidable density altitude of 8,400 feet. Impressive performance for a high-altitude takeoff! There's nothing quite like a light aircraft with a big engine to put a smile on your face.
The airplane's remarkable performance is due not only to a big power plant (more about that later) but also to a very aggressive weight awareness program during its design and manufacture. The aircraft's basic structure is "tried and true" chromoly 4130 steel, still one of the very best strength-to-weight (and crashworthy) structures in aviation, but instead of just duplicating the architecture that Piper employed for the original Cub, the engineers at CubCrafters began with a nearly clean sheet to design the original "Carbon Cub," now called Sport Cub S2, with its 100 hp Continental, and subsequently this macho sibling, the Carbon Cub SS. Both models are still offered by the company, and aside from the obvious power plant differences, the two are essentially identical.
Even though there's a $35,000 difference between the Sport Cub S2 and the 180 hp Carbon Cub, since Carbon Cub SS deliveries began in June 2009, CubCrafters has sold only one Continental-powered aircraft. Everybody, it seems, loves a hot rod.
Grams, Not Pounds
Weight is the big issue with all LSA because of the 1,320-pound maximum gross weight limitation. This makes for some very difficult strength-versus-weight decisions by light-sport manufacturers when designing an aircraft. It isn't easy to design and build an aircraft that light that will carry two people and at least some fuel without careful compromises and thoughtful design choices. Company founder Jim Richmond's mantra is: "Weight is the enemy."
The empty weight of the Carbon Cub is about 350 pounds less than that of CubCrafters' FAR Part 23-certified Top Cub, a much-improved Super Cub clone, and about 250 pounds less than an average 150 hp Piper Super Cub. How did CubCrafters pull this off? Engineering. When designing the original Carbon Cub, CubCrafters' engineers used modern computer-aided design and load analysis to create a structure that is simpler, has fewer parts and is much lighter than what C.G. Taylor could even dream about in the '30s when he designed the original Piper, nee Taylor Cub; Piper's engineers still didn't have the technology to design such a sophisticated structure in the '50s, when they designed the Super Cub. Amazingly, the total parts count for this aircraft is about half that of a standard Super Cub. None of the parts are interchangeable. CubCrafters has further reduced the number of parts by making the left and right ailerons identical - same with the flaps. The Sport and Carbon Cub wings attach quite differently than the original Cub's do, and though the aluminum spar is the same as in a Piper wing, each Carbon Cub wing weighs 22 pounds less than a Super Cub's. Smaller parts and fittings are made in-house on CNC machines, resulting not only in simpler, updated designs, but also, most importantly, lighter ones. Truly, some of the parts are great examples of modern industrial artwork.
CubCrafters has six full-time engineers at the firm, and four of them are kept busy just maintaining the drawings on their Top Cub and the Sport/Carbon Cubs. The cost of maintaining these drawings is "staggering," Richmond says, but it's the cost of doing business for a manufacturer who builds aircraft both FAA-certified and to ASTM standards.
E-LSA Versus S-LSA
The empty weight on this aircraft, with the optional Alaska Bushwheels, was 932 pounds (it's 38 pounds lighter with standard 6.00 x 6 wheels). This throws it into the E-LSA, or Experimental-Light Sport Aircraft, category rather than the S-LSA, or Special-Light Sport Aircraft, category that the aircraft was delivered with. This is because there is a formula-derived maximum empty weight unique to every LSA, and the Carbon Cub's limit is 900 pounds. So to add the big tires and other options, you must change the category. There are other upsides to this change: You no longer have to stay in conformance with ASTM standards (you can modify your aircraft at will); a private pilot or higher can fly it night VFR; and perhaps most appealingly, after completing a 16-hour FAA-approved course, you can get your repairman's certificate and maintain your own aircraft. This category swap is quite common; about 50 percent of the Carbon Cubs that leave the factory are delivered that way.
To take photos of the engine, we removed a serious handful of screws to pull the upper cowl. Yes, screws. Though mechanics probably won't be happy about it when they have to pull the carbon-fiber cowl, screws were chosen over Dzus fasteners to save weight. When I lifted the upper cowl free of the aircraft, I was amazed at how light it was. Though I guessed it at about a pound, Richmond said that a complete cowling is about 6 pounds, and the upper half is probably closer to 2 pounds. That's still amazingly light. But it didn't feel flimsy at all.
The engine compartment has a large (again carbon) plenum to better direct cooling air across and down through the cylinders. The proprietary CC340 engine is a Lycoming O-320 clone, with many ECI components. CubCrafters uses ECI O-320 cylinders instead of O-360 jugs to save weight, increases the stroke slightly and adds dual electronic ignition to bump up the horsepower to 180. It has a lightweight starter, alternator, wiring harness and oil lines. The oil sump is sheet metal instead of cast aluminum, saving 11 pounds. And the unique four-into-one exhaust system, designed especially for CubCrafters by Sky Dynamics, has no welds and weighs just 6.2 pounds.
