Five Years With Melmoth 2
(continued) If you think about something long enough, however, a light usually goes on. I still have not unraveled the mystery of existence—why is there something, when there could be nothing?—but I did at last notice that what those two cylinders had in common was that the unfinned surfaces of their exhaust ports were not adjacent to another cylinder. On all the other cylinders, the neighbor formed a converging channel that accelerated a stream of air over the hot exhaust-port surface. I added baffles to duplicate that effect on the two corner cylinders, and their temperatures dropped by 40° F.
But still there were cooling issues. I could not maintain a long climb on a 100° day without temperatures getting near the top of the green, and, conversely, on below-standard days I could barely keep temperatures from dropping out of the bottom of the green at economy cruise or when descending. An additional problem turned up during long periods of taxiing or idling: Fuel would begin to boil in the injector distributor, which sat on the top of the engine, making for an extremely rough idle.
I fixed the fuel problem by moving the distributor to a position below and in front of the engine, in the single cooling air inlet under the spinner. Now almost all of the fuel plumbing is on the cold side of the engine.
I experimented a good deal with cowl flaps. The air outlets are in an unusual location, in the cowling top just behind the spinner. I tried chutes with a simple flush exit ramp, and then with a guide vane in the middle of the chute. The guide vane approach looked promising, and I tried it first with the trailing edge of the vane flush with the top of the cowl and then with a raised trailing edge, so that the vane formed a sort of hood over the outgoing air. Each modification brought maximum temperatures down further while of course making the overcooling problem more severe. Interestingly—since cooling drag is a matter of great concern to experimenters—none of these changes affected speed in a measurable way.
Eventually, I mounted the vanes on pivots with an electric motor to operate them. Cooling on hot days is no longer a concern, but this is not yet a perfect solution. Temperatures are still too low at economy cruise, even with the air outlets choked down to a total of 18 square inches (the inlet area is 55), and while the engine runs too cool, the oil temperature still hovers some 30° F above the recommended 170°.
I usually cruise at around 11,000 or 12,000 feet, 165 ktas, eight gallons an hour. As an adherent of the Church of Alcor and GAMI, I lean 50 to 75 degrees to the lean side of peak EGT. The tuned GAMI injectors keep the EGT peaks of the different cylinders sufficiently close to one another that such a lean mixture does not cause roughness (which is usually due to different cylinders running at different mixtures, and therefore developing different amounts of power). I have not been able to make use of very high altitudes, however, because I start to get misses above around 16,000 feet. This was a problem on the first Melmoth as well, until I installed pressurized Slick mags; I am currently using my original unpressurized Bendixes again. I’ll get around to putting the Slicks back on one day, but for the most part I prefer to cruise below oxygen altitudes anyway.
I still have a long list of future projects. One is to move the aileron hinge lines aft in order to reduce the stick forces in roll. But the principal and current one is to get the flaps into working order. The airplane has big Fowler flaps that travel all the way to the trailing edge of the wing before deflecting 30 degrees; but it has no actuation system for them. Actually, I’ve never missed them; I usually operate on the light side, the airbrake—two square feet of board that pops out of the belly—slows the airplane down and keeps it from floating, and the wheel brakes are powerful. But it’s not about practical necessity; it’s about making a certain style of airplane—a rather complicated one, full of confusing gadgets.
What has held the flaps up for a long time has been the design and fabrication of a system for synchronizing them. In retrospect I think it would probably have been simpler to do this with screw jacks and torque tubes, as Boeing does, but, for whatever now-forgotten reason, I decided to actuate them hydraulically. Since hydraulic fluid neither apportions itself equally to the two sides of an airplane, nor cooperatively moves the inboard end of a tapered flap faster and farther than the outboard end, I had to come up with a system to make it do those things in spite of itself. By the time you read this, the results of my efforts will probably have found their way onto the website where I sporadically narrate the airplane’s progress, melmoth2.com.
By the end of its second year, the first Melmoth had flown to Europe, and to Japan by the end of the third. Melmoth 2 is a more backward child; despite its 3,000-mile range, it has not been more than 2,000 miles from home. Ah, for the days of 50-cent avgas again!
Also read these related stories:
Melmoth Flies… Again!
Melmoth 2: A Personal Airplane
Cleaning Up Melmoth
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