Thursday, July 30, 2015

Wheels and Tires Trifecta

The instillation of the tube and tire on the Matco split nosewheel is a very easy task. The inside of tire was given a liberal dusting with baby powder … which will help the tube move around during the initial inflate and deflate sequences thus preventing kinks. After the entire inside of the tire was nicely coated, the excess powder was poured out. The nut and washer are to be removed from the tube and it too received a liberal dusting of baby powder. The valve stem on the tube needs to be positioned adjacent to the red dot on the tire.
Dusting the inside of the tire with baby powder helps the tube move around as it expands, this will help prevent the possibility of kinks.
After the tube is finagled into the tire, the valve stem needs to be placed adjacent to the red dot on the tire. Note how the tube at this point could be easily pinched by the wheel halves.

Looking at the above photo, one can see how the tube would be very easy to pinch if the wheel halves were installed now. Before installing the wheel halves, I turned down the regulator on the air compressor and also turned down the air valve on the end of the air hose so the air flowed very slowly. A small amount of air was pumped into the tube allowing it to draw itself into the tire and away from the center where the wheel halves will come together.
Placing a small amount of air into the tube will draw the tube into the tire and away from the center … now the wheel halves can be installed without much fear of pinching the tube.

There are three Allen hex head bolts that need to be removed to split the nosewheel halves. The hole in the wheel where the tube valve stem goes through is comprised of a half moon cut out on each wheel half. One of the wheel halves had a little edge around the cutout so it was sanded a little to make it smooth.
Nosewheel halves separated and ready to install onto the tire and tube.

I forgot to take a photo of installing the two nosewheel halves, nothing difficult here. Just slip the wheel halves in from either side of the tire and bolt them together, then torque. I looked on the Matco site and could not find a reference to use the washer and nut that comes with the tube. Actually, the way the wheel is built, there is really no way to get a wrench inside the small holes to tighten the nut. So I’m guessing that unlike the main gear which has brakes, they feel the washer and nut is not needed to lock the tube onto the nosewheel.

Moving onto the main gear wheels, the same procedure was used to dust the tires and tubes with baby powder then insert the tube into the tire and slightly inflate the tube to pull it into the tire and away from the center where the wheel halves mate. Note the center hub needs to be removed to allow enough clearance for the valve stem to be inserted into the wheel and to allow access for a wrench to tighten the washer and nut onto the valve stem. Unlike the nose wheel, Matco’s instructions call for installing the centering washer and nut onto the valve stem and tightening the tube to the wheel.
One can see the hub needs to be removed to allow enough clearance for the valve stem to be installed through the hole and slot in the wheel.

One issue I ran into was with the dimpled centering washer that is used to center the valve stem in the valve stem hole in the wheel. There was not enough threads showing for the nut to screw onto the valve stem. Matco address this issue in the instructions and mentions some tubes will have this issue and to just use an AN960-516 washer in place of the centering washer that comes with the tube.
Matco instructions saying to use an AN960-516 washer in place of the dimpled centering washer if there is not enough threads on the tube to use the centering washer supplied with the tube.

I tried using an AN960-516 washer and it does work … but as the nut is tightened the valve stem moves around in the hole which I did not like. So I played around a while and came up with a seemingly good solution. As can be seen in the following photo, the stock washer on the left is quite thick and has a recess in the center which centers the stem in the hole on the wheel.
The thick stock centering washer is on the left, AN960-516 washer in the center and a ground down centering washer on the right.

The nut is a larger diameter than the recess in the washer as can be seen in the following photos … so it can’t get down onto the threads. It appeared to me that by removing material to the level of the recess it would provide enough threads showing to get the nut started on the valve stem threads. This proved to be true.
One can see the nut is larger than the recess in the centering washer and can’t quite get onto the valve stem threads.
The recess of the stock washer on the left can easily be seen in this photo. The washer on the right was ground down on the Scotch-Brite wheel and hand filed to even it out. This was later filed more to entirely remove the small remaining ridge altogether leading to success.
Final result, the washer is now flat on the nut side so the nut can now catch the threads on the valve stem and the dimple in the washer is left untouched so it can still center the valve stem in the hole on the Matco wheel.

As a side note, it is best to leave the center hub off until after the nut on the valve stem is tightened down … this will give the builder much more room for a wrench to tighten the nut onto the valve stem.
Finished instillation of the modified centering washer on the Matco wheel. Looking closely, one can see there are threads showing beyond the nut, so filing the washer down worked out great.

The same procedure as above was utilized when installing the tire and tube on the remaining matco main gear wheel.
Finished trifecta of wheels ready for instillation on the axles.

Tuesday, July 28, 2015

Matco Answers Questions At Oshkosh

Much like a moth is attracted to flame, once again I found myself being drawn to the Mecca of experimental aviation … Oshkosh. As the moth, I did get a tad burned from catching a little too much sun while walking around AirVenture for a handful of days. As always, had a great time at the show and the weather was about as good as it gets.

One of the last tasks performed on the DOG Aviation RV-12 prior to leaving for Oshkosh was installing the landing gear and the Matco axles. As mentioned in the posting two posts prior, reading Matcos’ instillation manual for the wheels and brakes raised a few questions. While at AirVenture, I was able to track down Matco and received answers to a few of the questions I had regarding the instructions for the Matco wheel and brakes supplied in the RV-12 finishing kit from Van’s Aircraft.

I asked about the lubrication page at the back of the instruction manual calling for the use of an anti-seize lubricant on the wheel bolt threads … yet that was not mentioned in the assembly instructions. The answer: At one time different components were used that benefited from use of anti-seize lubricant. The anti-seize lubricant is no longer required … the lubricant list at the end of the manual has not been updated to reflect this change.

Other question regarded the Matco manual mentioning to check the clearance between the disc and brake pad, but offers no guidance on how to make the adjustment. The answer: Matco adjusts the brake caliper to the brake disc clearance at the factory using the Matco axle. Because the RV-12 uses both a Matco wheel/brake assembly and the Matco axle, no adjustment is necessary.  The adjustment only comes into play when using a third party axle with the Matco wheel/brake assembly.

The third and final question posed to Matco regarded the torque value specified for the two AN4 bolts that go through the caliper and secure the inboard brake pad. The torque is listed at 100 inch pounds which is double the 50 inch pound (low end value) for an AN4 bolt. The Answer: Because the caliper bolts at this location utilize Nord-Lock washers, a much higher torque value is necessary to overcome the drag imposed by the Nord-Lock washers as the bolts are tightened. The resulting torque on these bolts is within the specifications for an AN4 bolt.

Sunday, July 19, 2015

Left Landing Gear Axle Installed

This will be the last post on the DOG Aviation Blog for at least a week. Yes, it is that time of the year again for the annual pilgrimage to Oshkosh Wisconsin to attend the week long AirVenture aviation extravaganza put on by the Experimental Aircraft Association. Today’s work session was short because of last minute chores that needed to be completed prior to leaving town.

Below is a photo of what the back side of the wheel assembly looks  like as received from Matco. The brake plate is wire tied onto the axle and the axle bolt is installed ... keeping the inner and outer bearings in place on the axle, along with the wheel/hub assembly.
The Matco wheel assembly viewed from behind as shipped from Matco.

After gaining experience yesterday with the Matco wheel and brake assembly for the right landing gear and becoming familiar with the Matco wheel parts, installing the axle today on the left landing gear leg was a snap. From playing around with the wheel and brake components for the right side, a couple of things have been discovered. Basically, there are two options for installing or removing the wheels … but only one of which allows for testing of the landing gear axle alignment. Option one - remove the tire/wheel/hub but leave the brake disc on the axle and between the brake pads. This is accomplished by removing the three Allen screws seen in the photo below and removing the large nut at the end of the axle and pulling the tire/wheel/hub off the axle. The previous post has a photo that shows the brake disc on the axle of the right gear leg illustrating the result of this method.
Here is a photo taken from the backside of the wheel. One can see the three Allen screws that attach the brake disc to the wheel/hub assembly. Removing these three screws and the large nut on the end of the axle will allow the tire/wheel/hub to be removed leaving the brake disc behind on the axle.

Option two – (and the one RV-12 builders will want to use during initial assembly), is to remove the two AN4 bolts attaching the brake shoe to the caliper then remove the large nut on the axle. By doing this the brake disc AND tire/wheel/hub assembly will come off the axle as one assembly. This is preferable during initial instillation because a test needs to be performed involving the placement of wooden blocks on the axles and running a string between the left and right gear legs to determine if there is a need to correct for toe in or toe out by using shims. As I discovered, the alignment test using the blocks can not be performed if the brake disc is on the axle ... so I had to remove the brake disc from the right gear leg.
Removing the two AN4 caliper bolts my finger is pointing to along with the nut on the end of the axle my other finger is point to will result in the brake disc being removed with the tire/wheel/hub as can be seen on the right in the photo. Builders will want to do this for the initial instillation.

I hope other builders, like myself, that find Matco’s documentation lacking and appreciate a couple of photos of a process will find the above helpful.

As previously mentioned, installing the axle on the left gear leg is a snap once one becomes familiar with how the parts interact with one another. It seemingly only took a few minutes once the parts were rounded up. Here again the U-00003 bracket from the wheel fairing kit was installed on the inside of the left gear leg and the washers called for in the plans omitted because the U-00003 is being installed now. For more information on the topic, refer to the previous post.
With the U-00003 bracket for the fairing kit in position on the inboard side of the gear leg, the Matco brake plate/caliper assembly is slid over the axle and bolted onto the left gear leg.
Tightening down the four axle bolts to prepare them for final torquing.

The wheel alignment test consists of using two F-1211 wooden blocks placed on each axle so a string can be drawn tightly between the blocks to determine if there is a toe in or toe out condition.  A toe in condition will lift the string from the blocks. A toe out condition will press the string hard against the blocks, so to get an accurate read of toe out, the blocks need to be moved to the aft side of the axles.
This is looking good … the alignment string is barely touching the wooden block.
Will be holding off on installing the rest of the wheel and brake components until after AirVenture where I hopefully can catch up with Matco representatives and ask some questions addressed in the previous post.

Instillation of Matco Wheels & Brake Assembly Begins

Yesterday, in addition to drilling and lightly sanding the edges of the aft window, work shifted to installing the Matco wheel and brake assemblies. The Matco wheels and brake components had been left in the plastic wrap which turned out to be somewhat problematic because inside the bundle was an instruction book which left little to be desired. The printed instructions, what little there is, were easy enough to read, but the illustrated parts breakdown is, in my case, hard to read. However, after going online to Matco’s WEB site this morning, I discovered part of the issue … the illustrated parts breakdown is actually in color, which often prints out as light shades of grey making it hard to read. There is a chart that basically shows all the hardware with the exception of the brake line fittings gets torqued to 100 inch pounds. Return from the future: I questioned Matco about torquing the two AN4 caliper bolts to 100 inch pounds (which is twice the 50 inch pound low end value for an AN4 bolt). The answer: Matco said because the two caliper bolts use Nord-Lock washers, the increased torque value is to overcome the friction created by the Nord-Loc washers.

Other than the hard to read illustrated parts breakdown, there is NOTHING about how to disassemble or reassemble the wheels … NOTHING!!! Reading the Matco instructions left me with many more questions than answers. For instance, toward the end of the instructions is a section called lubricants. Here a specific type of anti seize lubricant is mentioned (which turns out to be graphite based) and is listed for wheel bolts and nuts …. Yet, there is no mention in the actual assembly instructions (or lack there of) to use anti seize lube on the wheel hardware during assembly. Return from the future: Matco said at one time different components were used which benifited from the anti-seize lubricant ... it is no longer required. Another inconsistency is the requirement to check for the required spacing between the brake pads and disc based on a reference to a drawing … but nothing is mentioned about how or what adjustments to make if the clearance is not correct. Return from the future: Matco said the caliper/brake position is adjusted to the disc at the factory using a Matco axle, because the wheel/brake assembly is installed using a Matco axle, no adjustment is necessary since it was already done at the factory. Only builders using third party axles will need to get involved with this adjustment. The bearings are to be hand packed with grease and all the ones mentioned are aviation greases. I went online to check the properties of one of them and it turned out to be a full synthetic with a NLGI rating of #2 …  after checking the synthetic grease already purchased for the bearings, it seems to have the same NLGI #2 rating and also a slightly higher temperature rating as well. So the grease already purchased is probability OK, but want to talk to Matco first … so will have to wait until Monday. Since this is Oshkosh week, will likely need to talk to them at the show. Return from the future: I could not get an answer from Matco about using a high quality synthetic automotive wheel bearing grease. They said they know the bearings will peform well with the recommended aviation greases.
Matco wheel and brake assembly disassembled for bearing packing and tire instillation … unit on right is as shipped.

As can be seen above, the Matco wheels and brakes need to be disassembled for instillation. The wheels are made in two halves which need to be split so the tube and tire can be easily fitted without needing tire tools to do the job. However, some care must be taken when taking the wheels apart … as the parts are marked with reference to the holes for the tube’s valve stem.

The half of the wheel that goes adjacent to the valve stem hole is marked as seen in this photo.

The hub is also marked so it can be placed adjacent to the valve stem hole … also note the hole this creates down below where the hub meets the wheel … this creates the exit point for the 90 degree valve stem.

The axle mounting hardware will change depending on if the builder is installing the wheel fairing kit or not. If builders installing wheel fairings follow the instructions at this point, you find yourself taking everything apart again to install the hardware for the wheel fairings. Builder tip: If installing the wheel fairing kit, do not install the two bolt washers highlighted in yellow in the following photo. Jump ahead to look at section 36 you will see the washers are to be removed when the U-00003 bracket mount is installed on the inboard side of the gear leg … which means all the bolts have to be removed so may as well install the U-00003 bracket and also omit the washers now so the work does not have to be done twice.
In section 36 for the wheel fairing instillation, the builder is instructed to remove the washers that are highlighted in yellow. Builders NOT installing wheel fairings will want to install these washers.
Photo of section 36 shows the instillation of the U-00003 bracket on the inboard side of the gear legs.

Decided I could go ahead and install the axle and U-00003 bracket mount onto the right gear leg. The four AN4-16A bolts were located and a feeble attempt was made to install the axle assembly. Of note, the two threaded holes in the outboard face of the axle need to be positioned so they are horizontal ... the threaded holes will be used later to install a bracket for the wheel fairing kit.
Installing the U-00003 bracket mount onto the inboard side of the right gear leg.

During the attempt to install the axle assembly along with the brake plate and disc assembly, it was quickly discovered that there was no room between the axle assembly and the locknuts to get a socket to slip over the nut … even tried the thinner 1/4" drive sockets and there was still not enough room.
Quickly discovered that what I attempted to try here did not work because of clearance issues with the nuts and no access for wrenches.

The two bolts going through the caliper do needed to be removed so the brake disc can be separated from the assembly … this will allow an open end wrench to be placed on the mounting nuts with just the brake plate installed.
With the brake disc removed, there is easy access to the axle nuts for an open end wrench ... also note the two threaded holes in the end of the axle need to be horizontal.
Tightening the four axle bolts with the brake disc removed.
Disc and caliper reassembled and ready for the hub with bearings and the wheel/tire assembly.

Not being sure about the grease, anti seize lube or rotor clearance adjustments, will not assemble any further until a conversation with Matco has taken place to clear up my questions.