Landing Gear


Landing Gear

Originally created May 21, 1998, Tailwheel Update August, 2010 (12 short years later).

Main Gear (taildragger configuration)


Here's how the Cleveland wheels mount to the Diehl gear. I really hate the way those bolts almost hit the brake disc. In fact, I had to take a grinder to my bolt heads to keep the disks from being scored. The compromise is locating the bolts so that there is enough edge distance around the bolts at the bottom of the fiberglass legs to prevent tearing them out, or the bolts hittings the discs.


This is the Diehl gear casting and leg installed to the front of the main spar. One question you might ask yourself at this point (now that you've glued and bolted the leg to the casting) is "how can I sand the correct contour into the leading edge of the airfoil with that gear leg in the way?". Were I to do it again, I'd flox nutplates to the back side of the casting and leave the leg removable so that the contour could be sanded and then the leg reinstalled. The black thing to the right is the landing light.


Here you can see that I had to clearance the lower gear brackets so that the caliper could be mounted almost horizontally, otherwise, it would be pointed down toward the ground and almost dragging. The brake line will running around in a 270 degree circle to relieve binding and allow a little flexing.

I've been worrying about prop clearance, since I want to swing a 54" prop and my Corvair engine's thrust line sits 2" below the longeron. That sounds like a lot, but I've seen drawings in the Newsletter that indicate that the thrust line was set to 2.375" below the longeron on at least SOME drawings that came out of the "factory". Troy swings a 60" prop with his C-85, but only has about 4" of ground clearance, but then he normally flies off of asphalt, and he's a great pilot. I'm planning on landing on some grass (although it's kept like a golf course), but would like to have the extra clearance. And I'd like a little taller stance to come a little closer to a full stall landing.


Anyway, the easiest way I've come up with to do that is just add 3" to the length of the lower gear leg bracket (in the vertical direction), which also improves the angle that the gear intersects the wheel fairing and should reduce drag a tad, despite the extra height. There will be an offset so that the bracket will align with the gear leg, rather than being skewed like the Diehl brackets end up. And this will also solve the problem mentioned up in the first paragraph, where the bolts are in such close proximity to the discs. The bolts will be nowhere near the brake disk now.

Now that NavAero is making longer gear legs, I'd go with that.

Standard KR main gear is the "Lamb" tire (now made by Cheng Shin) 11x4.0-5, which is a little shy of 11" diameter undeflected. I bought a set of 5.00x5 tires for my Clevelands in the beginning, but they looked like Tundra tires on the KR, so I gave them to my brother to use on his C-172.

Tailwheel Update -March 22, 2003 - With the engine mounted, and three concrete blocks sitting on each stub wing to simulate the weight of wings and fuel, it was time to check the wheel alignment. Tony Bengelis says shoot for straight ahead in normal attitude (tail high, for a taildragger), and no camber. I thought I'd check to see how close I was going to be, given the "hail Mary" methodology of mounting lower gear attach brackets to gear legs.


I used a $12 Harbor Freight laser level to project a line that I could measure from. This particular level has a removable collimator that splits the pinpoint laser dot into a fine line that is projected at about a 90 angle for a distance that easily visible 50 feet away in darkness. After raising the tail to level the plane, and rolling the plane a little to let the tires get realigned, I clamped the level to the brake disc on one side, leveled it, and turned out the lights.


I measured a distance 20" away from the tire and put duct tape on the floor to mark where the line intersected the floor. I then measured 277 inches further away, and marked another piece of duct tape with the beam's path. I then moved the level to the other brake disk, and repeated the procedure. With the lights turned on, I measured the distance between the beam at the start point (20" from the tire) and 277 inches further away. I came up with a convergence (they got closer together) of 11 inches. I divided 11 by 277 and hit "inverse tangent" on the calculator, which yielded a toe-in of 2.27 degrees. Actually, I didn't have to bother with that. It's just a ratio thing to determine what thickness a shim would need to be. 11/277=x/2.5, where 2.5 is the width of the lower gear bracket. That tells me that I need a shim that is .0993" wider on one side than the other. But since I can split the difference between the two sides, I need a .05" shim on each side. I could probably put a light washer under the front two axle bolts on each side to do that job, but I'll probably get a machinist to mill a shim for each side. That way I can also cure the camber difference that I have between each each side. These are also supposed to be vertical when landing, and mine are 2.9 degrees on the pilot's side, and 1 degree on the passenger side. I'll have to figure out what I need exactly, but I'm confident that I'll get it pretty close.

I also taped the laser to the top of the vertical stabilizer and projected a beam across the centerline of the firewall, across the same 277 inch line. I marked where it intersected the floor too. This allowed me to determine that my centerline is only off by about an inch over a distance of 80 inches, which is a deviation from straight ahead of only .7 degrees. Close enough for KR work! Later, after the engine was completely installed, I used a plumbob from the center of the prop hub to find the CL up front, and from the tailwheel spring to define the rear line, and reverified the aircraft centerline. The two were within an eighth inch, so I'm pretty confident about that.

There's no telling how many ground handling problems are caused by something as simple as imperfect alignment, and it's too eazy to check and fix to just leave it to chance.

November 2004 , Now that the wings are attached, the engine is completely installed, and almost everything is exactly as it will be for flying, I've revisted the alignment so I can do the final adjustment. A funny thing happened with the fuel tanks 3/4 full and 150 pounds of pilot in the left seat...the excessive camber in the pilot's side almost went away! So now all I have to worry about is the toe-in, which also improved with weight. It's now only 2.09 degrees, so a simple 1/32" shim on one side would correct it by 1.33 degrees, reducing it to .76 degrees, and still very close to being aligned with the fuselage. That's definitely close enough for KR work!

Updated August, 2007
I have to say that I can't imagine an airplane tracking any better, or being any easier to takeoff and land with, than this KR has been! I land on grass quite often, and even with 12" grass, I've yet to have any kind of problem with the 11x4-5.00 tires. But I've landed with a flat tire three times so far in 460 hours of flying and over 1000 landings (triple that if you count bounces).

As I was getting ready to fly to the Corvair Wings and Wheels thing in Alliance Ohio, I noticed my tire was low. I had a can of "AirUp" from Walmart on hand for just such an emergency, and put about 3 ounces of the can into the tire. It filled it up and sealed the inside from future leaks. I'd been told that this would lead to a big imbalance in the tire, and the gear would shake a lot on takeoff. Sure enough, it did...but only the first time. On subsequent takeoffs and landings (and I've done at least 25 since then) it's been as smooth as ever, and the tire is still holding air just fine. The beauty of this solution is that the stuff is still in the tire, and any more tube pinches will probably be sealed before I land. To me, this is 3 ounces of insurance, and I'm quite happy to carry it around with me inside that inner tube. In fact, I'd been carrying a full can for a year in anticipation, so it will actually save me some weight by just carrying three ounces in each tire!

This has worked on my mountain bike for about 10 years now. Before that, I got 2 or 3 flats a year due to thorns, and I got tired of pushing a bike around. Yes, the KR tubes/tires are thoroughly talcum powdered and I keep them inflated to about 45 psi.


My chocks are a sort of go-no-go gauge that makes it easy to tell if my tires are a little low. I put them under the brake disk, so if the tire deflates between flights, it's difficult to get the chock out, and even I can tell they're low. These chocks are my home hangar chocks. "On the road", I use two thin aluminum angles I keep in my flight bag...or a nickel will do too...


Here's how I jack up my airplane when I'm working on it in the hangar. "On the road", I just find somebody to crawl under the spar and lift with their back while I change a tire or something (I've only had to do that once, however). That torn wing/leg fairing was done on my first flight, where I tested the gear with a 5.5 g landing.


Tailwheel


My four inch tailwheel was sold by Wicks Aircraft as the "Homebuilder's Special", which comes in three variations, depending on the angle of the tailwheel spring. I have the one with the shallowest angle, the "20 degree" version. Wicks Aircraft and Aircraft Spruce and Specialty sell them as well. Contact info for the manufacturer is:

Aviation Products, Inc
114 Bryant St.
Ojai, CA 93023
ph/fax (805) 646-6042

Tailwheel update, March 2010 - My first tailwheel lasted me for about 1600 landings, including my "learning phase". At that point the tread was wearing a little thin, so I bought a new one from Aircraft Spruce. After installing the new one, it seemed noisier than the previous one during landing and taxiing. On a KR, the aft fuselage acts as a megaphone, and any tailwheel noise is amplified and aimed at the pilot. After about 200 more landings, it was noisy enough that I worried about failure, so I removed the wheel to see if the bearing was "toast".



Upon removal, I was amazed to see the balls were rusty, with no sign of grease. It actually rattled! since I still had my original tailwheel with the 1600 landings, I put it back on and things quieted back down again. I put another 400 landings on it, and now it was really getting thin, so I ordered a new one from Aircraft Spruce.


This time I had the good sense to check the bearings, and was shocked to see no sign of grease again! The thing literally rattled when shaken. This was about a year after I'd bought the previous one, so this is more than one that "slipped through the grease crack". Upon checking the Aircraft Spruce catalog, they sell the "4 inch Homebuilder's Special Tailwheel" for $23.85, and also mention a "Longlife Sealed Bearing" for $2.95 each, which makes you wonder what they ship in the "Homebuilder's Special" tailwheel. I called and asked if the special bearing was an option with the tailwheel, or if they were a separate item that was supposed to be user-installed. I was told the bearings are a separate item, and could not be bought installed. Hmmmm. I wonder why you'd want Longlife Bearings for your tailwheel, when the ones in my original tailwheel were still fine even though the tread is almost gone? I thought the Aircraft Spruce catalog might be a clue..."These high quality bearings are superior bearings furnished with homebuilders tailwheels" , but that doesn't even make sense, unless they left out the "to" in front of "bearings furnished".

I checked the original wheel that came on the tailwheel assembly and clearly it was grease packed, and appeared to be a much better "sealed" bearing, so somebody thought it was a good idea 10 years ago when I bought the original one from Wicks. Gee, has Aviation Products started shipping "short life" bearings with their swiveling tailwheel assemblies now? That deserved a phone call! I couldn't imagine that AS&S or Aviation Products would think that a shopping cart caster with a cheap bearing with no grease could stand the rigors of a 70 mph experimental aircraft landing, or would intentionally sell wheels with no grease packed in them for any reason. I'd think (and now I KNOW) the life expectancy of a dry bearing called upon for 65 mph touchdowns is going to be "somewhat" limited!

So I called Aviation Products and asked what kind of bearing they put in their tailwheels and was told "heavy duty sealed bearings, greased for life is the only way we sell them...why wouldn't you use the best?" I also learned that Aircraft Spruce orders the assembly from Aviation Products MINUS the wheel for some reason! Although I didn't hear it from Aviation Products, one must assume that AS&S substitutes the less expensive R&K caster with the ungreased and unprotected bearings and saves a few bucks. And after your ungreased bearings rapidly wear out, you'll either buy a new tailwheel (with no grease), or if you're really enterprising, you'll put new bearings in it.

But maybe they figure us airplane builders are astute enough to notice (although I didn't) that there's no grease down in those bearings. So maybe I just need to get smart and grease the things...but how? I guess I could rig up a syringe with a tube fastened to it and sort of dab some on the outside of the bearing, but that's not how I learned to pack bearings. In the automotive world you use a "bearing packer", but the 5/8" hole for the shaft won't work with that. I've seen pointy attachments for grease guns, but it wouldn't fit down the hole. Or you just work the grease in by hand...if you have them in your hand. So I called R&K bearings to ask how you're supposed to lube these dry bearings down inside that tiny hole and was told that those are sold for use with "hollow shafts with grease fittings". Hmmmm...the Aviation Products wheel shafts don't have grease fittings in them, and have no accomodation for a grease fitting, so how's that supposed to work? I guess that's another reason Aviation Products only provides sealed, greased bearings.

But how do you put new bearings in this thing? As a former mechanic, I thought this would be a piece of cake to upgrade my old rusty balls to a sealed setup...after all, I have a 30 ton press in my basement. The 30 ton press woudn't touch it when trying to press the shaft spacer through because I was basically trying to press the bearing apart. Then I realized you'd need a special tool that could reach down inside and past one bearing and expand to drive the opposite side out. R&K casters agreed...it was a special tool.


After a beer or two, it occured to me to try a smaller diameter brass drift inserted at an angle from one side, and whack on the other side. It took about 10 whacks, with a 180 degree rotation each time, for the bearing to fall out. Of course if these were new bearings this process would damage them by overloading one or two balls rather than all of them sharing the load, but it can be done. You wouldn't want to do this unless the bearings were bad, so driving out the ungreased bearings for a proper grease packing is probably a non-starter...you'd just have to trash them and install the lubed ones. And when you're done you could have just bought the sealed version from Aviation Products and saved yourself the trouble (and the premature bearing failure).


Here's a good view of the rusty balls. Not what you want on an airplane that lands at 65 mph, or even 40 mph, or even your shopping cart, unless you have hollow axles and grease them (as intended by the manufacturer).


The original, the rusty one from AS&S (Aircraft Spruce and Specialty), and the soon-to-be-rusty "new" one. As you can see, the original provided a lot more service than the un-lubricated version from AS&S, even though the casters are both the same model from R&K, which can be ordered with your choice of several bearing configurations. AS&S chooses to send you the only unsealed version (and presumably), whereas Aviation Products chose the sealed version that outlasts the tread. we're only talking a few dollars difference between sealed and unsealed, so I don't get it. I called Aircraft Spruce to notify them that they were selling tailwheels for aircraft that had no grease in their bearings, and the customer service person I talked to seemed concerned, and would speak to her buyers about it. The next day she called back and said something like "the buyer says these are the proper bearings, they are what we specify, they are what they are, and we have the optional Longlife Sealed Ball Bearings, p/n 06-00060 if you want to upgrade". I wondered how long this had been going on, and my 2005 catalog shows the same "longlife" replacement bearings. That's a long history of replacing un-lubed bearings.


Well the last thing I wanted was to buy bearings from Aircraft Spruce to fix a problem that they apparently created, so I bought a set from McMaster Carr and quickly installed them using a large socket (the press would have taken another minute or two, but would have been the "proper way" to do it). I flew it a few hours later and it was so quiet I forgot to listen for it.


The sealed bearing in my second tailwheel looks like proper aircraft equipment, unlike the dry bearing version on the left from AS&S. And just so you'll know, Aviation Products sells their full swiveling steerable tailwheel assembly to the public for $238, with sealed and lubricated bearings installed in the wheel. Or you can buy what appears to be the same unit from Aircraft Spruce as the Homebuilder's Special 4" Diameter Full Swivel/Steerable, P/N L-692, $288.95 (a mere $50 more), and get bearings that rattle and are not lubricated in any way. Wicks appears to sell similar dry bearings on their tailwheel, judging by the photos on their web site, but I could be wrong about that. They show a 3/8" bore tailwheel in the picture. Their 4" tailwheel info is confusing, as is most of their website. For example, I'd think they'd still sell the 4" swiveling/locking tailwheel assembly, but you'd never know it from their website.

Contact info for Aviation Products:
Aviation Products, Inc:
114 Bryant St.
Ojai, CA 93023
ph/fax (805) 646-6042

Aviation Products also sells all replacement parts for the assembly, such as the aluminum housing itself. I believe their wheel is $39, with "good" bearings...


Gear Leg Extension Experiment - August 2007


I finally got around to extending my gear legs. What I expect from this is a lower landing speed due to the higher angle of attack (getting closer to full stall and 4 more inches of prop clearance so I can spin a longer, more efficient prop. Now I can move from a 54" diameter prop to a 58" diameter prop, and still have an extra 2" of ground clearance.

There's 3.75" of vertical lift here, which is equivalent to gear legs being 5.3" longer (almost as long as Larry Flesner's and Jeff Scott's gear legs). I also slid the wheels back a tad to see if that'll improve three point landings. The caliper is awaiting hookup in this picture. The extensions are made of 1/4" 4130 steel, TIG welded, and powder coated, hacked out in my basement (and it shows). These come with a 12 ounce weight penalty each, but I could've (and should've) shaved some of that off.


As you can see here, N56ML got a lot more "proud", and looks kinda "bad" to me! Taxi visibility will get worse, but that's OK, because it just means I'll have to sit up on the seat a little higher. It does resemble Larry's and Jeff's airplanes. Now wheel pants and gear leg fairings can commence.

Well, the longer gear didn't last long...the legs were too floppy, given the longer moment arm they were working through, and landings were a little on the squirrely side as the were able to twist around more. Taxiing visibility went from dismal to non-existant, and it was a lot harder to step into the plane. I couldn't detect any real change in landing speed either. So they only lasted about two weeks before I removed the extensions and got back to normal. To be fair, I could have made them work by wrapping a few more layers of glass around the gear to stiffen them up, but the over-the-nose visibility would have been more dangerous.

Wheel Fairings - I added wheel fairings in September 2007, because I didn't want to show up at the KR Gathering again without them. It didn't take nearly as long as I thought it would to attach them...I just needed to sit down a study the situation long enough, and then just DO IT. I bought Klaus Savier's Lightspeed Engineering wheel pants for an RV, which are not cheap, but are reputed to be some of the most efficient. RV wheel pants are similar and less expensive. They came as a matched set with joggles already done, splitting vertically around the axle point.

I'd have used John Backer's, except with the big Cleveland brakes, I'd have had to cut a huge chunk of those beautiful pants off and fair the whole mess in around the lower brackets, and John's fairings are way too nice to butcher like that.


The first step after leveling the fuselage (so the fairings are level with the world) was to set the rear wheel fairing on a block of wood and ascertain where to remove fiberglass to enable it to slide forward for a tight fit. Then I bent up an aluminum bracket to put under the two upper bracket attach bolts, which picked up a screw on both front and back parts of the fairing.


Then I used two pieces of angle screwed together to form a Z-bracket, fastened under the rear two lower bracket bolts, which take care of the lower rear part of the fairing.


The axle was about the only outboard place I could use for support, so I welded a bracket onto the axle nut, and then welded a nut plate to the center of it (centered so it wouldn't matter which cotter pin hole was used).


After the aft fairing was mounted by slotting it to slide onto the gear leg and clear the tire, I did the same with the front. Because the fairings are translucent, I could see where to match drill the axle screw hole and that leveled up the fairing left to right. Then I blocked up the front and rear of the fairing so it looked level, and parallel to the top longeron. Then I just match drilled the fairing and the aluminum brackets, then came back and installed nutplates on the alumium parts, and screws through the fairings and into the brackets. The last step was to match drill the mating halves about every four inches around the periphery of the joggle to connect the two halves together...nutplates on the inside, then screws through both parts into the nutplates.

The extra leg notch in the forward part of the fairing near the top was done when I had the previously mentioned gear leg extensions installed, and was toying with adding fairings at that point. That upper location would be optimal because it would eliminate the sharp angle between the leg and the fairing, improving the drag situation, but it was not to be. The OSB clamped to the gear is to facilitate jacking the plane up with a common floor jack. It's funny to see silicone sheet in contact with the leg itself. I used to be so careful about such things...

The whole process was much quicker than I thought, and took less than a Saturday, as I recall. They proved to be worth a solid 10-12 mph on the top end, so I'm still kicking myself that I didn't install them earlier, given how easy it is...

Next airplane I'll use something like these wheels with brake disks that are recessed. This would allow a smaller and narrower wheel fairing like the very aerodynamic ones John Backer makes. These wheels are also lighter, I suspect, because the disks are lighter.


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Email me at N56ML"at"hiwaay.net