Cosman special


Evolution of an Airplane

What results when a father-and-son team cross a Star-Lite and an RV-3? The Cosman Speedster!


There is a saying: "By small and simple things, great things are brought to pass." Voyager, for example, started out as a sketch on a paper napkin. This is the story of an airplane that started out as a telephone conversation between a father and his son.

Jim Cosman, who flew B-17s during WW-ll, and his son Mike, a computer designer, were wondering aloud how fast a specially built, Continental A-65-powered airplane could fly. During their phone conversation, they set two design goals that would be the ground rules by which they would build such an airplane. It would be a single-place personal transportation airplane and it would have a top speed that was as close to 200 mph as possible. Their plan was to sacrifice everything but safety for speed.

Mike was the designer/engineer on the project and his father would help build it. They decided to build the airplane using moldless [composite] construction. Hot-wiring and fiberglass work was relatively easy and it didn't require special tools. To create the fuselage, two female molds were built first. The fuselage has a Clark foam core that is laminated in multiple layers of fiberglass cloth.

After studying several airfoils, Mike chose the same airfoil that is used on the Lancairs. The 19-foot 10.5 -inch, one-piece wing was built-up in typical no-mold fashion, using multiple layers of fiberglass cloth and a spar cap for strength. When the airplane was completed, it weighed 570 pounds, about 60 pounds more than they had calculated. Its maximum gross weight is 870 pounds, allowing a useful load of 300 pounds.

The Cosman team invited me to examine their handiwork. The airplane looks like a combination of the StarLite and an RV-3. "It isn't everyday that a son will design and engineer an airplane for his father," beamed the elder Cosman. "Though I've designed many model airplanes, this is my first experience at designing and building a real airplane," added his son Mike.

"After Mom died, Dad wanted a way to commute between his home in Riverside, California, and my home in Salt Lake City, Utah. This airplane does the trick. We built a 17-gallon fuel tank for the plane, hoping that that would be enough fuel to make the trip nonstop, but it wasn't. With a fuel consumption rate of 4.2 gph and a cruise speed of 160 mph, he can make the trip in 4 hours, with a fuel stop in St. George, Utah. After 2 hours in the cockpit, Dad is ready to stretch his legs anyway," explained Mike.

I asked the Cosman team if they had any problems during the construction or flight testing. Jim was concerned about engine cooling, so they put a great deal of thought into designing an effective cooling system. They did such a great job, in fact, that they had to decrease the size of the cooling air inlet by half. On hot days, report the Cosmans, the oil temperature holds steady at about 180°F and the cylinder head temp at 385 [degrees].

Throughout the build, the father-and-son team monitored the Speedster's center of gravity very closely. The payoff was that when the plane was finally completed, they did not have to add an ounce of ballast to keep the plane inside the e.g. envelope. In fact, after the first flight, Mike recounted, “Dad had me change the ratio between the control stick and the flaperons back to one-to-one."

The Continental A-65 engine does not have an electrical system, so to start it, someone has to hand-prop it. A handheld radio is used for all necessary in-flight communication with approach controls and towers. Jim admits that it is very awkward and time-consuming having to fly around all the TCAs, but the inconvenience will have to remain until, he hopes, someone develops a mode C transponder that operates from a battery pack.

It took approximately 1400 hours to build the Speedster. Considering that they did not have any real plans to work from because this was an original design, 1400 hours is quite fast. Equally impressive was the total cost of the project: only $4000! They purchased the used engine for $400 and put another $300 into it for a top overhaul. The canopy cost $350 and the propeller $400. The rest of the money was spent on instruments and building and finishing materials.

The Cosmans offered me a chance to fly their airplane. The Speedster fuselage is 17 feet long and has a cockpit that is 25 inches across, but I just could not reach the rudder pedals. Jim, however, was happy to tell me about the performance and flight characteristics of the plane. "It's delightful to fly," he said, smiling. "I notice very little pitch change as I extend the flaps, and the control pressures remain almost constant. The climb rate is spectacular.  Operating from an airport with a field elevation of 4200 feet, it will climb out at 1000 [feet per minute]. Even at 10,000 feet MSL, it will climb at 750 fpm.

"When I first flew the plane, I could only fly at half throttle because the propeller needed more pitch. We've had the prop re-pitched, but it still needs more. I'm sure we'll have to get another propeller. At the present time, I'm getting 175 mph TAS with the Warnke 60x65 propeller. We expect the speed to increase a little with the new propeller and even more when we add wheel pants. At any rate, we are very close to our projected 200-mph maximum speed.

"With a stall speed of 70 mph, the plane is easy to handle during landing. In fact, landings seem to be smoother if I wheel-land the airplane. Handling on the ground is terrific-I don't have to use S-turns to see over the nose where I'm taxiing. To facilitate ground handling, we also installed hydraulic toe brakes," said Jim.

The Cosmans do not plan to offer plans or kits of their airplane. "We don't have the time or desire to get involved in the homebuilt/kitplane business," Jim explained.

When I walked away from the sleek, single-seat Cosman Speedster, I felt just a little bit jealous. I wondered if my sons would design and engineer an airplane like this for their dear, old dad. Only time will tell.


AKA Betty Boop, aka Adrenaline one


Ron Carroway high speed and low speed passes in the Cosman Special