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Monday, October 3, 2022

Doug's Domain

Doug Vetter, ATP/CFI

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X-Cell Custom First Flight!

10-19-96, 5:05PM

A friend of mine who flight tested full-size aircraft for a military aircraft contractor once told me the best way to approach testing the unknown is to set a few clear, approachable goals for each mission, reach them with the very best effort you can muster, and then "get the damn thing on the ground in one piece". This attitude was my own as I watched for a break in the rain that had promised to spoil my first-flight weekend. About 2PM, I looked outside and the rain had stopped, but the ground was still soaking wet. By 4PM, however, I saw the tiniest peak of sun and decided this was a sign for me to take my painstakingly crafted X-Cell Custom out of the "lair" for its first flight. I had only wanted to test basic operation of the rotor systems, but as some test pilots do, I found myself led a bit beyond my original mission parameters. :-)

After sitting idle for nearly three months since the break-in period, I was impressed that my good 'ol 61SX fired up immediately and settled into a nice idle. I then disconnected the glow heater, moved the ship to the runup area, and gave it a bit of throttle. While the engine tried to spool up the blades as throttle increased, the initial friction in the rotor/tail-rotor system, coupled with what I later determined to be an overly rich idle-mixture setting, caused the engine to bog down. I deemed a shutdown necessary so I placed the throttle stick below the threshold necessary to operate the momentary switch I configured to reduce throttle position to zero, (9Z does it again!), hit the switch, and watched the blades spool down.

While I refueled, I recalled most of my problems during the break-in resulted from an overly rich mixture, so I decided to kill two birds with one stone and lean both the idle screw (1/4 turn in) and high-needle (about 2-3 clicks in) before I restarted. This time I gave the blades a helping hand and brought throttle up past clutch engagement and eventually to 3/8 stick. It was a beautiful sight. The blades started to spin--wobbly at first--but faster and faster, while as power rose, the blades fell into the correct lead-lag setting. Before I attempted additional throttle, I used the radio's built-in tachometer to find RPM @ 1040. Satisfied that this was normal for that stick setting, I stepped back and further advanced the throttle. As I approached 1/2 stick, the entire rotor system came into balance and started to generate a beautiful, authoritative, throaty rumble, synchronous with the pass of every blade (thank you Mr. Koll!).

Unfortunately, as I passed 1/2 stick and what I'd guess to be about 1300RPM, the engine began to bog down again. I took this to mean one of two things: 1) the high needle was still too rich, or 2) the throttle curve was behind the pitch curve. Given that I was running so little pitch (4 degrees @ 1/2 stick) and the drop in rotor RPM was coincident with a change in engine tone, I figured mixture was the root cause of the problem. Then, as I backed off a bit on the throttle, the engine and rotor system came back to life...so well, in fact, that rotor RPM picked up to the point that I was able to lift the heli, ever so briefly, from the ground. For a few moments it reached an altitude of about 3" before it gently settled back to earth. Not wanting to push my luck on this day of milestones, I decided to play a bit more and then shut down for the day. Mission accomplished!

As I walked the heli back to the starting area, I figured a bit of mixture tweaking would be required to get the heli into the air next time but I felt confident about how the ship ran and how all of my building and learning came together to produce this successful first flight. My thanks go out to all of the folks on the heli list [link unavailable] and rec.models.rc.helicopter for helping me fill the holes in my experience with their incredible knowledge, to the Schoonard's for building such a fine example of mechanical engineering, and to Mr. Koll for building the best blade balancer in the industry.