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Monday, October 3, 2022

Doug's Domain

Doug Vetter, ATP/CFI

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X-Cell Custom Flight Test Program

1996 Flight Season

Second Flight Session (Sunday, October 20th, 1996)

I took the heli out Sunday afternoon for several test hops, the first of which was used to tweak the ship's mixture. I simply fired up the engine and slowly leaned the throttle by 2-3 clicks per trial and attempted to bring throttle and head speed to the point that a low hover was possible. This process required four separate modifications of the high needle to obtain the desired result, which simply confirmed that the engine was originally far too rich to run properly (though I do hear the SX likes to be rich near idle). Half-way through this procedure I noticed I had accidentally hit the hovering pitch adjustment lever on the radio at some time during this session, but I'm not sure when. Once I found this and adjusted the mixture one last time, the ship lifted off into a nice 1' hover that I was able to maintain for extended periods. This is when I realized the contribution of the NHP Simulator to my flying skills. I felt like was flying the same X-Cell 60 Custom I flew on the sim--no kidding.

Just as I was bringing the ship back down to earth to refuel, I noticed engine RPM and head speed increase substantially as the engine transitioned from a rich 4-stroke to lean operation. This so happened to coincide with the near depletion of the main tank's fuel supply (header tank still full), so I then decided to make it a personal policy to bring the ship home with at least a 1/4" of fuel remaining in the main tank. This experience also convinced me of the wisdom involved in plumbing a header tank into one's fuel system. It's cheap insurance against a flameout.

What impressed me about the heli by this stage was my observation that everything seemed to be configured correctly. I wasn't sure at this point whether this was due to my thorough study of the setup requirements or the nature of the Schoonard design, or both, but I was still surprised the ship required so little mechanical tweaking this early in its flight test period.. A check of controls revealed near perfect alignment in all axes; only the tail needed five or six clicks of its digital trim to make the bird fly "hands off"...so to speak. Head speed in a condition immediately before hover was verified at 1340-1360 RPM via the 9Z's built-in tach and I estimated hover speed was on target @ 1400RPM. A 1' hover was maintained at EXACTLY 1/2 stick. Blade pitch settings at this point were measured at -1 low, +4 hover +8 degrees high and were deemed appropriate for hover practice.

Later sessions that day allowed me to tweak the gyro gain (was a tad high) and experience my first engine flameout(!) Fortunately, while I had been hovering at 10-15 feet up imediately prior to the flameout, I had returned the ship to a low hover as I watched the main tank fuel supply reach my new "threshold". The flameout was uninteresting: the engine simply and quickly died but the blades had enough momentum in that mode to allow me to increase blade pitch and cushion the touchdown. Afterword, I removed the OS#8 glow plug and found it coated with oil. While I thought this may have been the result of the immediate shutdown with an open throttle (which pulled an unburned charge into the chamber before the engine stopped) I figured this oil was the likely culprit. I cleaned and reinserted the plug, refueled, leaned the high-needle by one click, and continued flight testing without futher difficulty. By the end of the day the ship had finished four tanks of gas and nearly finished its first gallon of fuel.

Third Flight Session (Saturday, October 26th, 1996)

I began the day by, naturally, by attempting to start the 61. For the first time, I noticed the starter could not develop enough torque to overcome the engine's compression. Although I sensed a bit of this the previous weekend, I wrongly attributed this to a dying battery (should've known better, as I have a large deep-cycle marine battery at my disposal). Before I knew the cause of the problem, the only solution I could implement at the time was to loosen the plug just enough to allow the starter to turn the engine at the required speed yet leave it tight enough to support combustion. Fortunately, I was able to strike a happy medium and the engine fired soon thereafter. Once I removed the glow plug heater and tightened the plug, I brought the heli to the "pad" (actually, just a smooth section of grass in my backyard!) and increased throttle for liftoff.

Unfortunately, extended flight was not to be mine this day. For some reason, the engine produced suitable smoke and appeared to be running as it did the previous weekend, yet as soon as I would attempt hover, the ship would fly for no longer than about 2 minutes before it flamed-out. I spent nearly the entire day playing with the mixture needles, which were previously set at 2.0 in-idle, mid-closed, high 1.5. Throughout the day I worked primarily with the high needle, because that produced the most significant results last weekend. However, after approximately 15 *very* short hops, I figured something else was wrong.

By the end of the day, I had managed to determine that the hover mixture was too lean, as the engine was superheating and dying as a result. I was finally able to get the engine to run for extended periods by enrichening both the high and idle needles. Naturally, this caused the engine to "load-up" at prolonged idle and run very rough at hover with a low (1150RPM) head speed. While I knew this was not a complete solution, it pointed me in the right direction. Throughout the day I communicated with Severin Beauvais [address outdated], a fellow pilot I met over the heli list who had experienced the same trouble with his SX. In addition, that evening I looked through many of the heli-list posts I had saved regarding the SX (one of which was written by Severin) and this learning experience finally gave me the knowledge necessary to fix the problem the following day.

The starting problem was later suggested by a heli-list member to be caused by engine flooding. I was told that even if one uses a kill-switch to close the throttle, one must place a clothespin or other clamp on the fuel line leading to the carb immediately following shutdown, otherwise the latent pressure in the system at shutdown will force fuel into the top of the cylinder, decreasing the available volume, and thus substantially increase compression at TDC(top dead center).

Fourth Flight Session (Sunday, October 27, 1996)

This day produced the most enjoyment since I began flight testing, as the SX exhibited none of its poor traits. With the mid needle now set at 0.5 turns + 2 clicks rich, and hover pitch & throttle adjusted to approximately 4 degrees and 47% throttle, respectively, head speed picked up and the ship started to perform.

Most of the day was spent proving out the engine in a low hover (1 foot), so while it was uneventful from the perspective of the single onlooker (my brother), my hovering abilities steadily increased. By the end of the day I had put another few tanks through the engine and convinced myself that with the help of Severin and others, I had successfully troubleshooted and solved the difficulty that plagued the engine. Shortly before I had completed the last tank of the day I brought the ship up to a 10 foot hover and down again without difficulty.

Fifth Flight Session (Saturday, November 2, 1996)

The weekend of November 2nd and 3rd served to remind me that mother nature had indeed declared the arrival of Fall. Winds precluded flight until late in the day on Saturday, and by then I was only able to fly a single tank through the ship before dark. Aside from this being my first opportunity to fly in a consistant wind, the flight was uneventful and without any significant developments. Sunday as well provided less-than-hospitable weather, so rather than risk the ship at this early stage of learning, I decided to work around the house instead. At the close of the weekend I had put a total of about 1.5 gallons of Cool Power 15% fuel through the ship.

Sixth & Seventh Flight Sessions (Weekend of November 9th/10th, 1996)

This weekend went well, with only one surprise. I had become very comfortable with hovering and by the end of the weekend had transitioned into circling the ship around me and had as a result briefly transitioned into slow forward flight on the upwind and downwind legs of the pattern. All was going well until the second to last flight of the day on Sunday when, after a sustained session of circling, I advanced the throttle and cyclic slightly to pick up speed on the upwind leg and was suddenly greeted with a loss of power and erratic tail behavior (and my first thought was "why do things like this always happen when I'm pushing the limit?). :-) I immediately set the ship down and ran up to it to hear the engine "sputtering" with a very hollow sound, rather than the distinctive deep, methodical rumble associated with the MAS Nitro Pipe. Upon closer inspection I found the silicone coupler that joins the pipe and header had cleanly fractured at the boundary between the two pieces, disconnecting the pipe from the header. This not only removed the backpressure essential to the proper operation of the engine, but also removed the source of fuel system pressure and immediately caused the engine to lean out.

The fix was simple. Given that I had purchased a 1-foot piece of AeroTrend blue silicone coupler material, I simply waited for the whole system to cool down (no, actually, I'm lying...in a rush to fix the problem I burnt my fingers, then I decided to wait 10 minutes for it to cool down!) and then installed a new coupler. With the repair complete, I cautiously flew another tank through the ship to verify no damage had been done, and then called it a weekend.

The moral of the story? It does pay to buy a little extra of "consumables" like coupler material, fuel, glow plugs, fuel line, etc...just so you don't waste valuable flying time due to a lack of parts. I have also declared that I plan to replace the couplers once per gallon of fuel, regardless of their cosmetic appearance. This coupler looked like the day it was installed, nearly 2 gallons of fuel ago; even its inner wall was in good condition. Murphy's law in action.

Eighth Flight Session (Saturday, November 16th, 1996)

Although this past week had once again demonstrated to inhabitants of the Northeast US that fall (if not winter) had arrived, with average high temperatures in the 30's, mother nature knew I wanted to fly my heli so she found her way to bring the high temperatures into the 40's and 50's for this weekend.

The morning was still in the 30's so I decided to wait until mid afternoon to go flying. After I pondered how well my hover and slow-forward flight progress had been the previous weekend, I figured it was time to shrink the size of the training gear by moving the wiffle balls inward to a point about 1" from the skids and sawing off the remaining ends of the 1/2" dowel rods. Once I secured the tapered rubber washers that secure the balls on the dowel to the wood with CA, I preflighted the machine and brought it outside to the "pad".

Aside from being quite rich at idle, the ship ran well until I nearly finished the tank of gas. Immediately following liftoff I noticed that the ship was a lot more "skittish" and agile with the reduction in training gear size & weight. As well, I noticed the tail started to twitch a little more, so I set the ship down and turned the gyro sensitivity down from about the 1:00 position to 12:30. This improved the situation, but I felt something was still not right.

During the next refueling procedure, I went over my usual post-flight inspection procedure and 'lo and behold, I found my aluminum header cracked nearly half-way through. I brought the ship back to the workbench to examine the damage. The crack didn't exactly follow the length of the casting seam, but the seam did appear to contribute to the crack's overall length.

Sunday was spent chatting with fellow pilots via the h-list regarding this problem and I was been told by two MAS reps to expect a free replacement. When I asked about a stainless steel replacement they mentioned that MAS had just released one and would likely swap the two with a payment for the difference in cost. Can't wait to see how this is handled.

Ninth Flight Session (Saturday, December 7th, 1996)

Shortly after the last flight test session I called Miniature and asked them to send me a replacement header. They agreed, and promised to ship it out to arrive this Saturday. When the package arrived I opened it to find a nicely made stainless steel header, though shortly into the installation process it became clear that they had sent me the type designed for the X-Cell Gas (rearward, not vertical exit as required with my choice of pipe).

They later informed me that they had been experiencing trouble getting the German manufacturer to deliver the product and were thus out of inventory on the vertical exit models, so they pulled this unit from a demo model rather than a shelf of prepackaged units. Sadly, the weather had recently turned unseasonably warm for that weekend, so I missed out on some of the last good flying weather of the year. Debbie @ Minature graciously apologized and sent me one of their rather nice full-color catalogs (a $10 value).

Due to the lack of available SS headers, the following week I sent both the incorrect SS header and the faulty AL header back to Miniature and awaited delivery of another AL header so I could get my ship back in the air as soon as possible.

By the way...if you're new to helicopters and X-Cell ships in particular and feel a little nervous ordering their products via mail order "sight-unseen", Minature's color catalog is a rather inexpensive insurance policy against the shipment of incorrect or undesired parts. All parts are clearly photographed and described. This is no "Tower Hobbies" circular, mind you.

Tenth Flight Session (Saturday, December 21st, 1996)

The new replacement AL header arrived this past week. Once I installed it and performed some basic checks (checking for loose nuts and bolts and the like) I successfully consumed a couple of tanks.

The ship had performed well over the last few test sessions but I noticed a slightly increased tendency of the collective mechanism to "stick" while I experimented with flight along the ship's vertical axis. Once I fixed that problem and found the ship performed better than ever, I decided that initial flight testing had been accomplished. Given the nature of the fix, I included the full description of the problem