Friday, September 29, 2017

Removing The U-1220 Main Gear Legs For Priming

Savvy RV-12 builders following the Blog may have noticed the gear legs on the DOG Aviation RV-12 were not primed … even though the gear legs are just about the only component on the RV-12 that Van’s assembly instructions make a special note in bold print informing the builder to MAKE SURE the gear legs are primed with a high quality primer, preferably epoxy primer. During the late fall massive primer session for the finishing kit parts, the gear legs were overlooked because they were at the bottom of a crate with cardboard over them …. out of sight, out of mind. This oversight was not noticed until it was time to install the gear legs so the decision was made to continue moving forward and deal with it later …. and later would be now. Because the gear legs are showing signs of the beginnings of corrosion, as can be seen in the photo below, felt it would be best to make it right during the condition inspection.
The beginnings of surface corrosion can be seen because of the lack primer on the gear leg. Priming the U-1220 gear legs is called for in the plans … Van’s recommends an epoxy primer as a first choice. The corrosion developing on both gear legs looked pretty much the same as this right main gear leg.

Removing the main gear legs involves removing the wheel and axle/brake assembly. Decided to take a short cut and not remove the brake lines from the calipers. This was accomplished by removing the wheel nut after removing the two bolts that secure the outboard brake pad … this allows the wheel/rotor assembly to be removed from the axle leaving the caliper and inboard brake shoe attached to the axle assembly. After the wheel was removed from the axle, a thick paint stir stick (the thick type used to mix 5 gallon pails of paint) was quickly used as a substitute rotor and the outboard brake pad was bolted back on finger tight. The reason for placing the thick paint stick between the brake pads is to prevent the brake piston in the caliper from popping out of the caliper and creating a huge mess of brake fluid everywhere. Felt this would be a good idea because the brake assembly will be off the gear legs for a few days, so didn’t want any unexpected surprises similar to what a friend experienced with his airplane’s caliper piston popping out overnight and draining all the brake fluid onto the floor of his hangar.
My finger is pointing to the paint stick placed between the two brake pads to prevent the piston from popping out of the caliper during the extended time the brake assembly will be off the aircraft.

After removing the axle assemblies from the gear legs, each gear leg was easily unbolted from the center channel and removed. The gear leg removal was a piece of cake … (but the same could not be said when it came time for reassembly). The corrosion on the gear legs was cleaned up by soaking the gear legs in Alumiprep 33 which is basically phosphoric acid with cleaners formulated to clean aluminum. Long time readers of the DOG Aviation Blog may recall Alumiprep 33 was also used when preparing all the wing ribs for primer. Because the surface of the gear legs are not perfectly smooth, a brass wire brush was used to help clean down into the pores of the metal.
In addition to being a product to clean and prepare aluminum for priming, Alumiprep 33 is also a great product for helping to remove surface corrosion on aluminum.

After using Alumiprep 33, it is necessary to give the parts a good rinse with water. Although not called for, I used distilled water for the rinse water. Unfortunately, after using Alumiprep 33 and rinsing the parts off really well ... as soon as the parts are dry, they need to be primed immediately. This made for a long work session by the time all the spray gun cleanup was completed.
Both U-1220 main gear legs freshly primed with Akzo epoxy primer and ready to reinstall.

Reinstalling the gear legs was a total fight … not fun … in fact, it was a pain in the neck both literally and figuratively. The difficulty stems from lack of access. When the gear legs are first installed on the RV-12 access is good because, in addition to the access hole in the belly skin, the F-1275G cover plate is not installed yet. Without the cover plate in position, the gear hardware is easily accessed with both hands. However, after the main gear legs are installed, the left and right F-1275G cover plates are riveted onto the fuselage leaving only a tiny slot for the gear legs to pass through.
Photo of the F-1275G cover plate … this plate is not riveted in place until after the gear legs are installed. As one can see from the photo, when the F-1275G cover plate is riveted in place, it eliminates all access for a second hand to reach the gear leg mounting hardware. This is one area where I feel using nutplates to secure the F-1275G cover plate would have been a great idea …. but in reality, once the main gear legs are installed, there is no need to remove them on a regular basis. That said, having the F-1275G cover plate secured with screws would sure make checking the bolt torque much simpler.

The lack of access created a huge problem dealing with the U-1202 outer attach bracket and associated bolts … this is because only one hand barely fits into the inspection hole on the belly of the airplane making it seemingly impossible to hold the bracket (which is about 6" or so further in from the access hole) and install a bolt at the same time all with one hand. After fighting and fighting with the hardware inside the center channel for a very very long time and exhausting my entire dictionary of choice cuss words, Bernie came up with a brilliant idea that was simple and truly worked quite well … once we learned the “how to”, quick progress was made. Bernie suggested sliding a wooden dowel rod or brass rod into the gap between the gear leg and fuselage skin to hold the bracket in place so the mounting bolt could be inserted. This worked out great! As an example, I could roughly position the U-1202 attach bracket and Bernie inserted the rod to hold the bracket in position so I could let go of the bracket and free my hand  for inserting a bolt into the bracket and subsequently up into the center channel. This method also came in handy when torqueing the bolts on the attach bracket … I could not see the bolt when my hand was in the access hole, so I would hold the socket end of the torque wrench so I could feel it slip onto the bolt then Bernie reached in with the rod and pushed up on the torque wrench to keep it in position on the head of the bolt while I repositioned my hands to the handle to begin torqueing the bolt.
Bernie’s idea of inserting either a brass rod or dowel rod through the gap adjacent to the gear leg and pressing up on the U-1202 bracket or the torque wrench to free my hand for a few moments worked great.

With both main gear legs now reinstalled, bolted and torqued down ... the axle, caliper and brake assemblies were reinstalled on the gear legs. Decided to switch the wheel bearing grease to a full synthetic grease so the wheel bearings were washed in mineral spirits (akin to Stoddard fluid) and blown out with compressed air. This was repeated three or four times until the bearings were spotless. I would caution fellow builders not to let the bearings spin when blowing them off with compressed air …. it is always a temptation, but it is truly not good for the bearings. After hand packing the bearings with fresh full synthetic grease, the wheels were placed back on the axles.

The following was mentioned previously in the Blog the first time the wheels were installed ... but bears repeating. The wheel assemblies used on the RV-12 are manufactured by Matco. The wheel bearings supplied by Matco for the wheel assemblies used on the RV-12 ARE NOT the typical automotive wheel bearing so the procedure for tightening the axle nut is different. On a car, the axle nut is tightened until there is a slight drag placed on the wheel bearings then the axle nut is backed off a little and locked in place with a cotter pin. This method will not work for the Matco wheels used on the RV-12 because the bearings used by Matco have a built in grease seal. The procedure for tightening the axle nut on the Matco wheel is to tighten the axle nut while slowly rotating the wheel … all the while looking at the grease seals. The grease seals will spin with the wheel until such time as there is sufficient pressure applied to the bearings by the axle nut that the pressure prevents the grease seals from spinning when the wheel is rotated. This is UNLIKE a car wheel because the axle nut IS NOT backed off from this point. In fact, if the cotter pin won’t drop into one of the holes in the axle, the axle nut is TIGHTENED a little further until it does. The result is not a free spinning wheel, but one that has a little bit of drag … this is fine, because the bearings are designed this way.

Sunday, September 24, 2017

RV-12 Nose Gear Fork Upgrade/Modification

Now that the DOG Aviation RV-12 is out of service for the annual condition inspection felt it would be a good time to change the nose wheel fork to the new WD-1230-1 RV-12 gear fork Van’s Aircraft has changed over to. The reason behind this change stems from a few RV-12 builders experiencing cracking of the nose forks adjacent to the welds and in a couple of cases, a complete collapse of the nose fork. It is felt that extensive flying from sod fields was a major contributing factor to the stress cracks forming.

To Van’s credit, the nose fork was redesigned and made from much thicker materials and the nose wheel mounting hardware was also changed in such a fashion to allow for full torqueing of the wheel axle without pressing on the bearings. (With the old assembly, the wheel nut was tightened until the wheel bearing was compressed creating a drag on the wheel then the nut was backed off 1/4 turn… the new hardware allows the axle nut to be tightened to full torque specs for the hardware without compressing the bearing to the point of placing a drag on the wheel).

Because the DOG Aviation RV-12 will be flown almost exclusively from paved runways, I was not going to change the nose wheel fork to the new model. What tipped the scale in favor of making the switch now was discovering wheel pants (still sitting on the shelves) installed on the old nose wheel fork can be reinstalled on the new nose wheel fork assembly … but it requires drilling six new  mounting holes. So, should I switch to the new nose fork at a later date after installing the wheel pants on the old style fork, it means there will be six vacated holes that will need to be filled, sanded and of course the wheel pants will need repainting. After hearing that, decided to just switch over to the new wheel fork now and that way there won’t be any issues when attaching the wheel pants when I get around to it. So the new nose fork was ordered along with the hardware changes necessary to install the wheel fork and wheel pants.
Photo of all the parts that come with the new wheel fork assembly and the additional hardware for the wheel pant attachment. The bag contains wave washers, new wheel spacers, longer bolts for the tow bar mounting point and a longer axle bolt with lock nut.

The above parts were separated where necessary, edges smoothed then the parts were prepared for primer then sprayed. One major difference that is quickly apparent is how much thicker the material is on the new nose fork which is very evident when looking at how the wheel pants will mount. As can be seen in the photo below, the old nose wheel fork was bent forming a flange that the wheel pants attach onto with nutplates … because the new wheel fork material is so much thicker, aluminum brackets need to be riveted onto the new nose wheel fork using long AN470AD4-9 rivets so there is a mounting surface for the wheel pants. One tip here, if priming, try not to get any primer inside the bushing the axle passes through or the two bushings that are on either side of the wheel because it will need to be removed to allow the axle bolt to pass through the tight fitting bushings … ask me how I know?

Frequent readers of the DOG Aviation Blog know I embrace modifications that make sense to me … so prior to installing the new nose fork, decided to add a grease fitting so the two bushings inside the nose fork can be kept well lubricated. The modification was quite easy ... just drilled a hole in the front of the new nose fork and tapped it for a standard grease fitting thread.
As one can see in this photo, the new WD-1230-1 nose wheel fork for the RV-12 on the left is much beefier than the old nose wheel fork on the right which was thin enough to bend creating a mounting flange for the wheel pants. The new wheel fork is too thick to bend like that, so there are rivet holes along the upper edge what will allow for mounting a bracket onto the side of the wheel fork for later use to mount the wheel pants. Also of note, one can see the grease fitting modification that was added to the nose fork.

Decided to begin the condition inspection by placing the RV-12 on a sawhorse so the new nose wheel fork could be installed. The new nose wheel fork comes with longer AN5 bolts for the toe bar attachment points (all the old washers are reused). Because I plan on installing the wheel pants in the near future, also riveted the mounting brackets in place. With the nose fork now ready to install, the swap was easy … but I did run into a small confusing hiccup by not looking at the new drawings. At first, I incorrectly “assumed” that the two Belleville washers and flat washer that were under the castle nut of the old nose wheel fork would be reused … but the hole in the gear leg for the cotter pin was not visible. I quickly figured out if the flat washer was removed, the hole for the cotter pin would be visible … when all else fails read the instructions. After referring to the new drawing, sure enough, it was discovered the large flat washer is not used with the new nose wheel fork … the castle nut now rides directly on the Belleville washers.

Prior to installing the cotter pin, one thing that needs to be checked is the preload tension … which should be between 18-20 pounds. A piece of wire was placed through the holes for the axle bolt and attached to a digital fish scale. The fish scale is pulled on until the fork swings and the castle nut is progressively tightened to compress the Belleville washers until the nose wheel fork swings at the desired 18-20 pound pull. The assembly ended up around just slightly over 20 foot pounds because that is where the existing hole for the cotter pin aligned with a slot in the castle nut.
The flat washer in my fingers is not used with the new WD-1230-1 RV-12 nose gear fork assembly.. only the two Belleville washers and the castle nut are reused to mount the nose gear fork onto the nose gear leg. The mounting brackets for the wheel pants can be seen here riveted onto the nose fork with AN470AD4-9 rivets.
Completed instillation of the new WD-1230-1 nose gear fork with grease fitting modification on the DOG Aviation RV-12.

With the nose wheel fork upgrades now complete, decided to direct my attention to the main gear legs which were overlooked during the priming session for the finish kit parts. More about that in the next posting.

Friday, September 22, 2017

Preparations For The First Condition Inspection – Sawhorses & Jacks

It is hard to believe a year has passed since the completion of the DOG Aviation RV-12. Unfortunately, that means it is also time for the FAA’s required annual condition inspection. Non-aviation readers of the DOG Aviation Blog may be interested in knowing the FAA requires an aircraft to undergo a complete condition inspection once a year …. this yearly condition inspection is commonly referred to as “the annual” and is typically performed by a FAA licensed A&P (airframe & powerplant) mechanic that has an IA (inspection authorization) rating. One of the perks of building an E-AB (experimental–amateur built) aircraft such as the DOG Aviation RV-12 is that the builder can petition the FAA for a Repairman’s Certificate which authorizes the builder to perform the required annual condition inspection on the aircraft they built.

Being the first condition inspection, it will be necessary to obtain some specialty tools along with jacks and sawhorses strong enough to support the weight of the airplane. At first, I was going to build strong wooden sawhorses but ran across some folding steel sawhorses rated at 1,000 pounds … but the legs were a little too tall. Both Van’s plans and maintenance manual say to obtain sawhorses 25" tall with padding … unfortunately, the steel sawhorses are taller so the legs will need to be cut shorter. Return from the future: Caution only make one sawhorse 25” tall and the other a little taller say 27 1/2" … more on that later.
Folding steel sawhorses rated to 1,000 pounds …. the legs will need to be shortened to make them the required 25".

Because the sawhorses are a little wider than what would be ideal, I decided to install a 2x4 on the top of the sawhorses but make it an inch shorter on each end of the sawhorse …. This effectively makes the sawhorse narrower where the fuselage sits on it. The reason for doing this is because the sawhorse will be placed on the rivet line directly between the steps. The smaller footprint at the top of the sawhorse will clear the steps which come out of the bottom of the fuselage at about a 45° angle.
A 2x4 was screwed onto the top of the sawhorse but was deliberately left an inch or so short on either end to insure clearance between the RV-12’s steps which come out of the fuselage at an angle.

Next the 2x4 was covered with two layers of carpeting and then measurements were made for cutting the legs to obtain a finished height of 25" for one of them and cut the second sawhorse taller say around 27 1/2".
Cut carpeting ready to be attached onto the 2x4.
The completed shorter sawhorse in the front is covered with 2 layers of carpet and the legs have been cut to obtain a finished height of 25".

After cutting both sawhorses to the suggested 25" (which was a mistake), one of them was immediately used between the steps to hold the nose gear off the ground and worked perfectly. Because of the folding legs on the sawhorses, decided it best to use small C-clamps to insure the legs can’t accidently release.
The sawhorse fit perfectly between the steps. Note the use of C-clamps just to make sure the legs can’t fold by accident.

Placing the aft sawhorse in position requires lifting the tail section upward. Mike K. was able to give me a hand removing the wings to lighten the load a little. With the wings off and the front of the fuselage sitting on a sawhorse placed between the steps, we inserted a large screwdriver through the aft tie down ring at the tail … Mike used the screwdriver to bench-press the tail upward (Mike said it was not very heavy and was easy to do). While Mike pushed the tail cone upward, I was able to slide the aft sawhorse into position under the fuselage. This is where I ran into an issue with the second sawhorse … discovered that the second sawhorse was to short and didn’t completely lift the main landing gear off the ground enough for a wheel removal. It required blocking the sawhorse up an additional 2 1/4" to get the main gear nicely off the ground.
As can be seen in this photo, cutting the second sawhorse to 25" was a mistake … it is not quite tall enough to completely lift the main gear off the ground without the aid of additional wooden blocks. I would suggest making the second sawhorse 27 1/2" tall so the main gear can be easily serviced. Fellow builders take note: This is not the correct placement for the aft sawhorse, it should be located 6" forward on the rivet line between the rear wing-spar receptacles … the error was caught shortly after this photo was taken and the sawhorse was moved forward.

It bothered me that assistance is needed to bench-press the tail of the airplane every time a tire needs to be inspected/replaced or removed for changing the brake pads and inspecting the wheel bearings. Decided to cobble together a jack that can be used to lift the tail of the RV-12. I have seen various methods used such as mounting the jack on steel wheel rims … but not having direct access to a welder decided to keep it simple and use a 2'x2' plywood base since the RV-12 is such a light airplane. A hydraulic ram jack was purchased from Harbor Freight that has a 3,000 pound capacity and jacks to a height of over 42”. The jack will be placed on a 3/4" thick 2'x2' square of plywood and secured in place by the use of four pieces of 3/4" EMT conduit cut to 27 inches. The outer 2 1/4" of both ends were flattened in a vice then bent to the proper angles.
The makings of the jack … a Harbor Freight jack placed on a 2'x2' square of 3/4" thick plywood. Four 27" long tubes of 3/4" EMT conduit will secure the jack to the plywood base.

After getting all the legs flattened and bent correctly, they were secured to the jack by a hose clamp so holes could be drilled for bolting the legs to the plywood base. The reason the flat areas along the body of the jack are so long is because eventually there will be two clamps used to secure the legs to the body of the jack.
Ready to drill the holes so the support legs can be bolted to the plywood base.

The tie down rings on the RV-12 have a 3/8"-16 thread so decided the easiest way to “couple” the jack to the RV-12 would be to use a HARDENED 3/8"-16 carriage bolt and a 1" steel black pipe cap. Would suggest builders NOT use soft carriage bolts from big box stores … play it safe and use hardened ones ( also used hardened bolts for the support leg mountings as well). Using the pipe cap and carriage bolt has an advantage over a fixed rod solution, in that, the pipe cap will sit over the top of the ram with the rounded head of the carriage bolt contacting the top of the ram. The pipe cap is not a really tight fit over the ram so it can move a little …. this along with the curved head of the carriage bolt will allow for angular movement as the jack lifts the tail upward without placing any angular strain on the threaded portion of the bolt threaded into the tie down receptacle in the tail.
A 3/8" hole was drilled into the center of a 1" black pipe cap and filed square so a hardened  3/8"-16 thread carriage bolt could be inserted and bolted to the cap.
Completed jack ready to lift the tail of the DOG Aviation RV-12. The edges of the support legs still need to be ground down even with the plywood to remove the sharp edges that extend beyond the plywood. Also, although not in this photo, feel it would be a good idea to place some wood screws around the base of the jack to prevent the base from possibly sliding sideways … so will be adding a few screws around the base of the jack.

To lift the RV-12’s tail section, the tie down ring was removed and the pipe cap/carriage bolt assembly was threaded into the tie down ring’s hole. The jack was positioned under the tail cone and jacked up so the ram could be centered with the pipe cap. Once a good alignment was achieved, the tail of the RV-12 was jacked up to make sure the jack would go high enough to lift the fuselage off the aft sawhorse. The ram extended enough to easily raise the main gear wheels off the ground. It worked perfectly.
The jack in position … it easily went high enough to hold the fuselage off the aft sawhorse even with the aft sawhorse on the wooden blocks to make it taller. The jack assembly works like a champ and gets the DOG Aviation seal of approval.

Now that all three wheels are off the ground, it is time to begin the condition inspection on the DOG Aviation RV-12 and make a nose gear change/modification.