Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.
Issue link: http://experimenter.epubxp.com/i/378679
30 Vol.3 No.9 / September 2014 INTRODUCING THE THATCHER CX5 A postfl ight debriefi ng with Mr. Thatcher determined that the fuel pressure was not an actual concern after all. As it turned out, running the electric pump along with the mechan- ical pump caused a confl ict between the two, resulting in low but seemingly adequate fuel pressure. So the fi x was simple; don't run the electric pump unless the mechanical unit fails. The pumps are plumbed in parallel since the mechanical pump won't allow fuel to pass if it fails. This was tested this early on. The second fl ight used the same routine at fi rst: a climb to 1,000 feet, leveling of in the pattern, and if all instruments were in the green, continue to 2,500 feet. On the fi rst fl ight, climb speed was set at 80 mph. On the second fl ight, from 1,000 feet on up, Glen increased the speed to 90 mph at about 24 inches of manifold pressure (MP) and still indicated 500 fpm. At altitude, Glen reduced the throttle to 22 inches MP and was indicating 115 mph. He said he tried to relax and just enjoy the moment—checking the instruments constantly, of course. The oil temp crept up to 190°F or so, and Glen made a mental note that it was a bit high for a winter day. Glen fl ew for about 20 minutes, feeling the controls. Ailerons were very responsive, almost as good as the smaller, lighter, shorter-wingspan CX4. No adverse yaw was detected; elevator was very responsive. The landing was less eventful than the fi rst. The things that struck Glen the most on the fi rst two fi rst fl ights were the climb rate and the view out the canopy. With the low cowl and instrument panel and the wing back out of the way, Glen felt he could see everything—the best of any plane he has ever fl own and that is saying a lot. Glen has fl own about 60 dif erent designs in all, and he equates the CX5 to a bit "better than a Beech T-34 Mentor." While the CX4 also has superb vis- ibility, the CX5 beats it. T HE REF INEMEN T OF A GOOD DE SIGN Since those fi rst fl ights, Glen has completed the required 40 hours of Phase I fl ight testing, and in the process, Mr. Thatcher tuned the airplane exactly the way he wanted it to be and has begun of ering plan sets. "Good is not good enough; it must be better than good—it must feel natural to taxi and fl y," Glen told us. "It should never fi ght the pilot in any way." The three main areas that were tweaked as a result of Glen's testing and feedback are the tail feathers, engine cool- ing, dive brake, and wheel brakes. The initial taxi runs showed that it needed more elevator authority and that the engine wasn't cooling well enough for fl ight. So vents were added to the bottom of the cowl, the oil cooler inlet was enlarged a little, and a new horizontal stabilizer and elevator was built, painted, and installed. The cowl changes made a huge dif erence and now every- thing is in the green for cruise—the oil temperature is down to 185°F and cylinder head temps (CHT) to 350°F while at cruise. The brake system was changed several times to get it the way they wanted. Changes included dif erent master cylinders as well as linkage geometry modifi cations. T HE RE V M A S T ER R-2300 Mr. Thatcher is exceedingly pleased with his choice of the 2331-cc Revmaster R-2300 engine featured in the Novem- ber 2011 issue of Experimenter. Chosen for its power and the company's reputation, the engine has a self-reliant ignition system and a built-in mechanical fuel pump, qualities that Mr. Thatcher likes. The intent was to have an engine that's com- pletely self-sustaining during a total electrical failure. With the redundant ignition systems, dual internal charging systems, and mechanical fuel pump, it is; one can lose the entire electrical system and the engine will still run just fi ne. The engine came with an aftermarket oil cooler attached to the bottom of the engine. It also has a spin-on oil fi lter. Typi- cally, VW engines simply have a mesh screen that only cap- tures pieces that are too large to cause any real problems. It's the small particles that get past the screen and into the bear- ings and rings that cause problems. These particles can now be caught by the FRAM oil fi lter. Joe Horvath of Revmaster Aviation recommends 20-50 multiviscosity oil. Glen and Mr. Thatcher prefer to use Valvoline 20-50 racing oil because of its zinc content. The CX5's fuel system is set up so that one can run of either the left or the right fuel tank, or both. One can also shut of the fuel completely. Each tank has 10 gallons usable fuel, and Revmaster recommends 91 octane fuel or better. Glen started out fl ying on 100LL but gradually added non-ethanol premium auto fuel. Fuel burn on the 1600-cc VW in the prototype CX4 is amaz- ingly meager. Glen reports that he can fl y conservatively and burn less than 3 gallons per hour (gph), and he can include 40 minutes of touch-and-goes. Of course, the fuel burn on the 2331-cc VW-powered CX5 is higher, but it is still possible to match the CX4's 3 gph at very low speed with 4 gph being burned at 65 percent power. As previously stated, Mr. Thatcher and Glen are happy with the Revmaster engine. It's reported to pull very well. Glen is not a small person (250 pounds plus) and is usually fl ying with full fuel most of the time, putting his operating weight right up there with the all-up weight of two "normal"-sized people. And yet he still sees a 1,000-fpm climb rate. CON T ROL A ND S TA BIL I T Y The controls in the CX5 are standard three-axis. The throttle quadrant is mounted on the left with the elevator trim on the right, in both the front and rear cockpits. The front cockpit has the instrument panel, nav/comm radios, electric speed brake switch, and aileron trim. The fuel selector is in front as well. Both cockpits have tons of room and good canopy clearance. Glen is 5 feet 10 inches tall and has a good 5 inches of head clearance even while sitting on a 3-inch cushion. The plane is reported to be stable, staying put where the pilot leaves it. It has neutral spiral stability, so after entering a bank and with the stick returned, the plane continues to turn exactly as it was left; it doesn't tend to steepen or come out of the bank. Photography courtesy of Dr. Glen Bradley