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Thursday, April 18, 2024

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Doug's Domain

Doug Vetter, ATP/CFI

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X-Cell Custom Building Insights

Contents

Canopy

When it came time to paint the X-Cell canopy, I researched the best methods and came up with the startling realization that the automotive lacquers used by most heli builders to paint their canopies would have put a $150+ dent in my wallet...to say nothing of the cost of acquiring a top-quality airbrush to do the job in the first place. Given that this put the price of a canopy at well over $200, I was glad to hear from some friends on the heli list and the net, in general, that Tim Schoonard of Miniature Aircraft would do a nice job on my canopy AND do it for a reasonable price. I called Tim the next day, discussed my options, and found he would do a simple color-fade job for merely $95 as long as I traded in my canopy and fins. "No problem..." I said.

When the canopy arrived I was very pleasantly surprised to see that not only did he paint the canopy exactly to my specifications, but he did a great job sealing and reinforcing the canopy halves. My particular design was one I had seen in the color Miniature Aircraft catalog and faded from a bright purple at the top through candy-apple red, orange, yellow, and finally to white at its base. While I did see another cool blue-greenish fade in the catalog that I heard looked rather nice close-up, Tim and others on the net all suggested I go with the bright "neon" colors to enhance contrast/visibility against a blue sky and as long as I didn't allow the heli to sit in bright sun for prolonged periods, the neon colors would hold up indefinitely.

The bottom line is that Tim does a great job for a fair price (in fact, it would be a good deal if $150, IMHO, but don't tell him I said so...given my skill level this canopy may not live forever!). If you don't mind blowing $200+ and breathing vapors all day, I recommend you paint your canopy yourself. If you're like me, though, you'll give Tim a call. (And NO, he didn't pay me to say that!)

Rotor Head

The X-Cell Custom's main rotor head is clearly top-notch, from the quality of parts used to the symmetrical, balanced design. The only part I had trouble assembling was the flybar and paddles. Given that I had already dumped several thousand dollars into the kit, I found it almost laughable that MA's answer to properly aligning the flybar paddles was "buy the MA flybar alignment kit #xxxx", which would have set me back an additional $35. Instead of interrupt the building process, I decided to create some cardboard templates to fit over the paddles to aid in alignment.

Fortunately, I had recently celebrated my birthday and had a ready supply of cards to sacrifice for the task at hand. To create the templates I simply took an average size card that was taller than it was wide and cut it at the fold. I then took both pieces in hand, placed one over the other to verify they were equally cut, and then placed them flat on the table. A paddle was retreived from the kit and centered vertically over the top 1/3 of the cards with the leading and trailing edges to the left, and right, respectively, so that I could trace an exact profile of the airfoil on them. Before I completed the entire outline, however, I checked to verify that the paddles were symmetrical so I could, in turn, correctly assume the chord line of the airfoil would be perfectly horizontal or parallel to the top and bottom sides of the cards. Once this was confirmed, I used a ruler calibrated in mm to exactly mark an equal distance down from the top of the cards, drew a line between them, and used this line to properly align the paddles and scribe their profile on the cards. Lastly, I placed the cards on a cutting surface and used my VERY sharp X-Acto knife to cut out the slightly undersized outline through both cards at the same time. The result was a set of perfectly aligned, symmetrical paddle alignment tools that cost a lot less than $35!

The next problem involved securing the flybar tightly enough to keep it immobile as I threaded the paddles onto it, but in such a way as to prevent damage to any parts. The fix for this turned out to be quick and easy; I liberally wrapped the jaws of a large (10") Channel-Lock tool with vinyl electrical tape and adjusted it to allow the perfect amount of leverage to safely grip the flybar. The key to this tool was the large "teeth" on both jaws. Even taped, the teeth formed small hills and valleys which kept the flybar perpendicular to the jaws and prevented the tape from moving as well.

Once I had all of these tools fabricated, I spread a thin line of Slo-ZAP CA glue on the threads of the flybar and proceeded to quickly but carefully thread the paddles onto the flybar to the depth specified in the manual. This distance was marked on the flybar and verified to within 1 mm with my calipers (oh, what would I do without my calipers?!?) Before the CA had a chance to set up, I slid the paddle alignment tools on the paddles with the long side facing up, turned the entire head assembly over, and held it just above my tabletop to verify the cards met it with no angle. Done!

9/96 Addendum (READ THIS!):

Little did I realize the extraordinary precision required to configure the flybar paddle angles, so what I thought was spectacular during my "eyeball" of the situation above produced an assembly wildly out of specification during the pre-flight configuration. Since I CA'd the paddles on the flybar I had no hope of moving (or removing) them so I had to break out my Dremel and sacrifice the flybar and paddles ($25). Of course, to add insult to injury, I broke down and bought that $@#!% flybar alignment kit for $35, bringing the total cost of this goof to $60. Bottom line? Consider the purchase of the flybar alignment kit mandatory if you don't have an equivalent method of setting the relative angle between the paddles to EXACTLY zero (0) degrees. If you don't, you won't be able to complete the preflight configuration properly and your ship will shake like crazy (if fly at all!).i

While I had the flybar assembly apart I decided to add the GS Precision flybar stiffener kit, which consisted of a couple short lengths of graphite tubing with an I.D. designed for the X-Cell / 60 size flybar and four purple-anodized alumninum caps with miniature set-screws. After three tanks of fuel I've concluded that this $15 mod has produced a significant positive impact on control response and hover performance.

I would also tend to think that control response during acro would also increase substantially with this mod as a result of lower flybar flexing, but I haven't reached the point in my flying skill to verify this claim. This is most certainly an optional mod, as the X-Cell performs beautifully without it, but if you're getting ready to build, or have the money to burn on a flybar/paddle combo + the cost of this kit, I recommend it.

Elevator Bellcrank

In sharp contrast to all other parts of the kit built thusfar, the elevator swing arm seemed to be a bit oddly engineered, in that it fit tightly around the mainshaft; so tight, in fact, that during assembly I envisioned my heli jerking fore and aft as the static friction of this unit took its toll. While several BPs on the net told me that this tight fit was entirely normal and would work itself out after a few hours of flight, this was the first time I questioned the rationale of the kit designer. Frankly, I couldn't see the need for this fit at this stage of the building process, but hoped the rotation of the mainshaft would remove a few thousandths of plastic from the bellcrank assembly during my planned runup tests and produce smooth control action.

Collective Pitch Mechanism

During the ship's initial assembly process and the first few gallons of flight, I noticed a heightened degree of static friction on the collective mechanism due, I believed, to the swashplate bearing-to-mainshaft tolerance (covered with an advisory memo shipped with the kit). The problem only seemed to cause a slight binding when physically cycling the collective up or down. However, after I became more comfortable with the ship and began to exercise it about the vertical axis the binding revealed its ugly head. Not content to lose my ship over this "stickiness" in routine flight, I removed the head assembly and discovered the plastic washout hub (Part # 0219) inner diameter insufficiently large to allow free movement over the mainshaft. To solve the problem I wrapped a 2" piece of 320 grit emery cloth around the shank of a large screwdriver and proceeded to remove enough material from the I.D. of the washout hub to prevent any binding on the mainshaft. After reassembly I flew the machine and was pleased to find the binding gone and my flying remarkably smooth as a result.

Washout Unit

All went well in the assembly of this unit, but this was the first time I had to deal with Minature Aircraft's answer to the cotter pin--the circlip (#106-08). This tiny semicircular clip is designed to fit into a machined groove at the end of an axle so to retain items installed on the axle. Thankfully, MA was kind enough to include two additional circlips, as my experience showed they tended to spontaneously sprout scramjet engines and blast off from my pliers at near the speed of light, never to be seen again. If you're at the hobby store picking up supplies for your X-Cell, pick up a few extra of item #106-08. Thankfully, I was able to recover a sufficient number of circlips to finish the job, but I spent more than a minute or two on my hands and knees looking for them. Ugh!

Engine / Fan & Shroud Assemblies

This section was one of the more gratifying parts of the building process, as I was finally able to blend "real world" parts with the kit's. It also served as the turning point in the assembly of the frames, which were a loose, shaky mess until the engine and mount were installed and aligned within the frames. Before installing the cooling fan and shroud, I was faced with a contridiction between the "heli-Bible" (Ray's manual), which said "most fans will need some [balancing] work", and the opinion of local pilots and hobby store owner, who said (paraphrased) "even today's injection molded plastic fans are on the money and don't need balancing". After rigging the fan up on a high point balancer and getting conflicting results, I decided to leave the unit alone. I suppose my first start will tell me if I made the correct decision.

The plastic fan shroud did require modification as per the instructions to allow for the carburetor air filter opening. The design ensures that the carb is constantly bathed in fresh, high velocity air, so this should ensure a good supply of air to the engine during high throttle settings. The modification required only an X-Acto knife and some patience.

I discovered a few things in the manual that may have inconvenienced me, had I not chosen the OS SX 61. Minature Aircraft specified the use of a "Collet Pack" to align the fan on the engine shaft. The kit included the proper collet pack for my OS 61, but I noticed nearly all other engines required the additional purchase of a special collet pack. If you don't have a OS 61 or a varient of it, plan to use the following information to order the correct collet pack when you place your kit order:

Collet Pack Included in kit Engine Application
0546-4 Yes OS 61SX-H, RX-H
0546-7 Yes OS 61SFN-H, RFN-H
0546-9 NO! ENYA 60XF, XLF
46-11 NO! YS 61FSH, FRH
0546-14 NO! Webra 61H (9.5mm OD solid crankshaft) and 50H
0546-15 NO! Webra 61, Pico, Rossi and O.P.S. with special "Heim" type 8.0 mm OD solid crankshaft.
0546-22 NO! Super Tigle 61-H (with 1/4" crankshaft threads)

Some engines' crankshaft threads must also been shortened prior to installation. They are:

These engines do NOT require modification:

Radio Equipment Installation

Most of the radio items were installed without difficulty and according to the instructions, however, a few improvisations deserve mention...

Servo Wheels

The collective and elevator servos required a trimmed-down version of the Futaba full-size servo wheel to support steel balls placed on a 20mm O.D. (total wheel O.D. of 30mm was required). Although a belt sander would have helped to bring the O.D. of the servo wheel down the 1/4" or so required, I instead grabbed my safety goggles and used a cutting wheel on the Dremel tool to cut and then shape the wheel to proper size. Due to the nature of the cut and the fact that I destroyed a few cutting wheels in the process, had I a pana-vise, I would have used it.

Receiver/Gyro/Gyro Amp

I decided to place the gyro in the optional location as specified in the X-Cell plans (on the receiver tray, which hangs in front of the servo tray, and, of course, ahead of the mainshaft). The gyro was affixed to the plastic tray after I used acetone to "break up" the surface of the mating parts to promote better servo tape adhesion. Three layers of servo tape, totaling roughly 1/8" thickness, were used to provide the gyro with the perfect blend of shock isolation and rigid mounting characteristics.

The receiver, gyro amp, and receiver battery were individually wrapped with two thicknesses of 1/4" Goldberg latex foam rubber, held in place temporarily by small pieces of masking tape. The receiver was firmly (but not rigidly) secured to the top-front of the receiver tray with 7" Ty-Wraps. Other items were installed using a similar method...the battery placed directly below the receiver, on the underside of the receiver tray, and the gyro amp secured to the front side of the metal webs of the upper tray support structure.

Receiver wires

All receiver wires, except for the antenna, were twisted at a rate of roughly 1/2 turn per centimeter to help prevent RFI. I've used this technique to build DS1 (T1) carrier wiring harnesses and it seems to work well, though I've never seen this done on a heli, so your mileage may vary.

Glow Plugs & the OS 61SX-H

Okay...maybe this section should be titled "Enya #3 glow plugs and the OS61SX-H". I broke in the engine with OS#8's and ran nearly two full gallons with that plug, but after I balanced the ship to the best of my skill and still couldn't remove all of its vibration, I decided to go with the Enya plug as per a fellow flyer's recommendation. Not only did the Enya plug lessen the SX's vibration, mostly visible through the muffler system, but response and general "feel" improved as well. Lest some of you think this was a self-fulfilling prophecy, I made a point about flying one tank on the OS#8 to warm up the ship before changing plugs. The difference was simply outstanding.

As of this writing I've consumed a gallon on the Enya#3 and can say that unless I change to a fuel that doesn't agree with it, the Enya#3 will be my glow plug of choice from this point on.