Sam Buchanan Project Sam Buchanan Project Legal Eagle XL-58 w/Black Max Brakes You know you've achieved perfection in design, not when you have nothing more to add, but when you have nothing more to take away. --Antoine de Saint-Exupery 172571732 6x6 rim end view Legal Eagle XL-58 has Black Max 1000 wheels and brakes from Free Bird Innovations. These are 6 x 6 polished and welded aluminum wheels that are set up for tubeless tires. The wheels are nicely made and highly polished. 172571733 6x6 rim side view The Black Max set is a little pricey at first blush but when the ease of setting up the disk brakes is considered, the price becomes a bit more reasonable. The very light weight of the set is also attractive. 172571734 Light weight tire The tires appear to be sourced from the wheelbarrow aisle of a hardware store. They have a "2 ply rating", are very light and flexible with a 500 lb rating. It remains to be seen how long they will last on an asphalt runway. At least replacements should be readily available at minimum cost (hate to think about having to mount replacements, however.......). 172571838 Mounted Tire The only problem encountered in getting the wheels assembled was seating the tire beads. This was accomplished only after getting down in the floor with the wheels and doing some 'splainin' to the wheels with rather stern language. The trick is to get one bead seated on the rim, then the tire can be inflated. Instructions are included but it takes some serious grunt work to get the first bead seated. There is a video on this website that show a simple trick to mount these tires in less then 1 miunute The narrow tires take on a new personality when mounted on the wide wheels. I intend to run a minimal amount of pressure--the tires will be the only means of shock absorption in my version of the XL gear. 172571839 Caliper Assembly Here is a caliper and disk. The disk floats which simplifies installation. All the bits and pieces are nicely machined and black anodized. 172571835 Master Cylinder The master cylinder which mounts on the control stick. Both brakes are applied simultaneously. 172571836 Axle 5/8" steel axles are supplied in the kit and are machined for a woodruff key which anchors the caliper. It will be necessary to drill a hole in the inboard end of the axle to anchor it to the gear. The XL plans call for the axles to slip into 3/4" x .062 tubing. This tubing is about .002" undersized to accept the axles. A better choice would be 3/4" x .059 tubing. I didn't want to order more tubing so the axles spent some quality time on the belt sander as I carefully reduced the diameter about .002". They now slip into the .062 tubing. 172571837 Gear Leg The standard Legal Eagle landing gear incorporates two shock struts with compression springs. I intend to try using the low-pressure Black Max tires for the sole means of suspension on XL-58. Since the spring struts aren't going to be used, an attempt will be made to lower the parts count in the gear set. Instead of the standard steel tube vee braces and struts, this version of the gear will use a tube axle carry through and cable x-bracing. The axle carry through tube is 3/4" x .062 at the ends to accept the 5/8" Black Max axles, and transitions to 5/8" x .035 across the middle of the span. The tube was supported in a fixture that locates it in proper alignment with the fuse. All the standard XL geometry will be retained, only the means of bracing will be modified. 172571840 Ground Clearance Here we see the ground clearance available with the fat Black Max tires. Unloaded, the axle provides ~6" of ground clearance. Even with the tires compressed by landing loads several inches of clearance will be available, plenty for operations in any condition other than an emergency arrival on inhospitable terrain. In that case, other factors will most likely have higher priority....... The plumb bob is suspended from a point equal to the leading edge of the wing per the plans and centers on midspan of the tube. We are now ready to begin building the gear legs. Note: The 17.5" dimension on dwg 22 needs to be ignored if using the Black Max wheels. This makes the 2x6 blocks under the jig unnecessary. See photos below. 172571841 Air Frame All the structural parts of the gear are now assembled. Addition of the cable x-bracing will complete the gear set. 172571842 Simple Gear This is certainly a simple gear. There is no doubt it is lighter and less involved to build than the standard XL gear assembly, the unknown is how robust it will be in the field. Landing loads with the plane aligned with the runway centerline should be accommodated as well as with the standard gear. Sideloads are the question mark--this gear may be best suited for the experienced pilot who is less likely to fly the XL to an...ah...arrival. I'm debating replacing the axle crosstube with a single length of 3/4" x .059 instead of the 5/8" x .035. The 5/8" tubing has some flex and heavy side loading will load the tube in compression which in an extreme case could lead to buckling and loss of integrity of the entire system. The weight tradeoff would be slight, yield a stiffer assembly and lower the parts count even more. On the other hand, this is the classic conundrum of figuring out how much strength to build into a design. We can't design a very lightweight aircraft to survive unreasonable punishment, we just want it to be strong and light enough to absorb routine operating loads. XL-58 will be flown by a pilot with over twelve-hundred tailwheel hours; consequently, design considerations are different than would be the case for a primary trainer. The standard XL gear is certainly satisfactory and proven, this is merely an exercise in trying to make a simple design even simpler without compromising the strength of the plane. 172571843 Gear Assembled For the first time, XL-58 was capable of being rolled out of the shop on its new gear. 172571845 Cables A button cut and drilled from a 1" delrin stick prevents the cables from chaffing where they cross. The upper cable attachments are to the forward gear leg bolts. This was deemed lighter and simpler than using additional hardware in the standard strut bolt holes. 172571844 Modification I wasn't satisfied with the very limited amount of adjustability of the original cables, so a new set was built up that includes two turnbuckles. The cables can now be easily tensioned tightly and this really firms up the gear. More better. 172571846 Additional Rigidity Shown here is the 1/4" rod added to the mitered joint at the fitting so there would be more meat. I also added the horizontal member for additional rigidity of the gear leg. 172571847 Modified Gear The gear described above performed well on paved runways. I was, however, concerned about how the axle crossbar would effect landings in tall grass. The gear was modified to resemble the gear described in the plans. Because the low-pressure tires have provided sufficient suspension, no spring arrangement was included in the modification. This simplified construction and reduces maintenance. 172571848 Upgraded Tire The standard Black Max tires are Lawn Pro wheelbarrow tires that are very light. The light weight is admirable but the minimal amount of tread doesn't last very long on paved runways. I wore out the first set of tires in less than twenty hours. The round tire profile means the tire patch is primarily confined to the center portion of the tread which doesn't help tread life. 172571849 Tire Options The Black Max wheels are based on 6" x 6" go-kart wheels so there are quite a few tire options if we are willing to use a slightly heavier tire. A very common garden tractor tire is the Carlisle 15x6x6 which costs less than the Black Max tires but has a lot more beef. It is tubeless, and the wider cross section makes for a pretty simple install on the wide Black Max wheels. These photos illustrate the increased diameter and tread width of the Carlisle tires. They are also designed to run at low pressure and I've found 10 psi is all that is needed for the XL. The greater volume of the tires also provide more shock absorption and have more than enough load capcity to accommodate the XL at gross weight. Time will tell if the tread lasts longer than the Black Max tires. They certainly give the XL gear a more substantial appearance and should handle rough strips better than the smaller tires. Update 9/24/12; The Carlisle tires are the ticket for the Black Max wheels. Very little tread wear has occurred over the course of an entire summer of flying off a grooved paved runway. The tires are much better at cushioning rough field landings than the lighter tires. Recommended. 172571850