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Mike Studerís Corvair-Powered Cassutt

By Mike Studer, for Experimenter

Cassutt

When considering his options for an aircraft to build, Mike Studer’s goals were simple. He simply wanted a fun, fast aircraft that was reasonably inexpensive to build, own, and operate. That’s why he opted to build the sport version of the Cassutt. The Cassutt is a small, single-seat, mid-wing experimental aircraft, made mainly for air racing. It was designed by Tom Cassutt in 1951 and can still be built today from plans as an experimental, amateur-built airplane. No kits have ever been available; this is a plans-only build. The aircraft is still active in the race scene today and used in the Formula One class competitions every year at the Reno National Championship Air Races.

The Cassutt is a very basic aircraft in terms of design. Ailerons, elevator, and rudder handle the three axes without the use of flaps. The undercarriage consists of fixed main gear, made from aluminum bar stock, and a spring steel tail wheel. The fuselage is made from tube steel, with wings from wood, all of which is covered in fabric; the wings are a Hershey bar design with a constant chord. Plans detail two versions of the airplane, a racing version and a sport version, with the main difference being the length of the wing. A 15-foot wingspan is specified for the racing version, with a 17-foot option for the sport version. Keep in mind that a Piper Cub has a 36-foot wingspan, making the Cassutt nearly half its size.

The Cassutt Special (as referred to by Wikipedia)
Specifications for the Cassutt III racer  

General characteristics

Crew

One pilot

Length

16 feet (4.88 meters)

Height

4 feet (1.22 meters)

Wingspan

15 feet (4.57 meters)

Wing area

68 feet2 (6.30 meters2)

Empty weight

500 pounds (227 kilograms)

Gross weight

850 pounds (386 kilograms)

Powerplant

1 × Continental O-200, 100 hp (65 kilowatts)

Performance

Maximum speed

248 mph (400 kilometers/hour)

Rate of climb

1,500 fpm (7.6 meters/second)

Range

450 miles (725 kilometers/hour)

The Cassutt has been tested to 400 mph (corrected airspeed). It’s rated to +/- 6g, although Tom Cassutt had pulled over 12g in testing.

In general the above specifications are correct. However, when you talk race planes there are some wild variations, limited by the rules, of course. One of the big differences between racing versions is the wing. Many racers use the Grove tapered chord wing. I’ve seen the collection of Cassutts at Reno, and no two are alike. There are similarities, but everyone tries different things to go fast—that’s racing.

There’s some good information in the Formula One racing rules. I downloaded them for reference. Some of those rules were learned the hard way.

Tailwheel
New tailwheel steering

As far as the provisions of FAR 21.191(g), where an experimental amateur-built aircraft is defined as an aircraft of which the major portion has been fabricated and assembled by a person(s) who undertook the construction project solely for their own education or recreation is concerned, building a Cassutt taught me every type of construction imaginable. Welded steel, wood, fiberglass, aluminum, as well as cloth covering were all used in the construction of the plane. My fuselage had flown once before prior to my ownership; someone had tried to convert it for some sort of aerobatic mission—with recumbent seating. I took out the plans and my reciprocating saw and welder, then made the airframe match the plans.

Cassutt
Mike Studer trucked in his Cassutt and test-ran it outside to everybody’s delight during the 2010 CorvairCollege at Livermore, California. Even with a mild Corvair, this aircraft is easily capable of exceeding 200 mph.

In retrospect it probably would have been easier if I had started the build from scratch. Fixing things really adds hours to the project, which I found out again with the wing.

I inherited the wing in an unfinished state. Many ribs had come loose from the main spar, and it’s only covering was years and years of spider webs. I’m guessing that the wing had been hanging around in various people’s hangars for over 20 years. So I had to inspect and repair it, and since it was a race wing, I had to lengthen it. The main spar had a big crack in it; I had to make a new one. That’s another lesson I learned: Don’t leave unvarnished wood hanging around in the rafters for years on end. The wood dries out and cracks as it gets really hot out here in the summer (115°F in the shade). The only thing I kept from the original wing were the ribs, rear spar, and trailing edge. Splices were made per the procedures found in Advisory Circular 43.13 (Acceptable Methods, Techniques, and Practices). But I deviated a little by using structural epoxy and some carbon fiber here and there. It came out very nice.

Onto My Engine
Thanks to William Wynne, I’ve converted from scratch a Chevrolet Corvair engine for my project. The Corvair is an air-cooled, six-cylinder, horizontally opposed, 2700-cc (164-cubic-inch) automobile engine that’s rated at 110 hp—derated to 100 hp when converted for aviation. Chevrolet produced the Corvair and all its variants from 1960 through 1969. It’s since been proven to be well suited for aircraft use if converted properly. I’ve flown in aircraft using the Corvairs and can attest that the engines are very smooth running and intuitive to operate. I’ve built the basic stock version of this engine for now. I may build a second one in the future but with more horsepower, although I doubt I’ll need it.

Engine
The long block installed before any accessories

Engine
The accessories and systems in place before baffling

Engine
Temporary cooling air plenum in place for initial test runs

Engine
The underside showing the oil cooler and updraft carburetor

Click each photo for a larger image

I designed and constructed several of the conversion parts myself for this engine, including my own rear starter system, and to date, everything works well. The system offered by William is mounted at the front of the engine and is beyond question in its reliability.

I use a Marvel-Schebler MA3SPA updraft carburetor. After pumping the throttle three times, the engine starts right up. I can taxi outside around the hangar to warm up the oil and everything performs as expected. I’ve noticed that it’s much easier to navigate around obstacles without any wings installed on my fuselage—but the wing will be installed very soon.

Current Status as of October 1, 2011
We conducted a preliminary weight and balance check on the plane the other day. It came out to 511 pounds with the unsheathed wing on the fuselage. That seemed a bit high. Then I remembered the fuel tank was three-quarters full! That accounts for at least 60 to 70 pounds. I feel better about it now.
 

Cockpit
Larger view

The wing is currently under construction, and I’m in the process of sheeting it with 3/32-inch mahogany plywood. Next I have to build and attach the ailerons which are made from welded steel tubing covered with fabric. I also have to design, construct, and install some fiberglass wingtips. After those steps, I’ll make a fiberglass cowl to cover the engine and the area in front of the pilot. Then I’ll cover the fuselage, paint the whole thing, and get it signed off. For this project, I’ve been working on and off since January of 2001, but I hope to have it in the air very soon.

So look for a follow-up report in a future issue of EAA’s Experimenter e-newsletter!

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