Tuesday, May 14, 2019

Installing Nose Gear Wheel Pants On The DOG Aviation RV-12

Work on the nose gear fairings for the RV-12 begins by preparing the U-00005A&B nose gear front and aft fairing halves. The process is much the same as the main gear fairings, in that, trimming is required to get close to scribe lines, then fine tuning the fit by careful sanding. Unlike the main gear fairings where a joggle is used to mate the fairing halves, the nose gear fairings are mated via two U-00006B splice strips. The splice strips need to be hand formed to conform to the shape of the U-00005-A front fairing. Although the splice strips will be placed inside the front fairing, I found it easier to first hand bend the splice strips to conform to the outside shape of the front fairing. After the proper shape was obtained, each splice strip was moved to inside the front fairing and tweaked accordingly.
Hand bending the U-00006-B splice strips to conform to the outside shape of the U-00005-A front fairing.
Hand bent splice strip ready for instillation on the U-00005-A front fairing … one down one to go.

After both splice strips are bent, each splice strip is installed on the inside of the front fairing using three Clecos. With both splice strips in place, the remaining rivet holes are match drilled into the U-00005A front fairing.
Both U-00006B splice strips in place on the U-00005A front fairing.  Next step is to match drill all the remaining rivet holes in the splice strips into the front fairing.

After all the holes in the splice strips are match drilled to #40 and with the splice strips still  secured to the front fairing with Clecos, the U-00005B aft fairing is mated to check the overall fit. It will be necessary to bend the splice strips at various locations with fluting pliers/and or flat nose pliers until there is no interference between the splice strips and the aft fairing preventing a proper fit.
My fingers are pointing to the areas of the U-00006B splice strips that required the most tweaking to allow the aft fairing to seat properly onto the splice strips.
As can be seen here, after tweaking the splice strips the aft fairing mates nicely to the front fairing. More adjustments will be made later after the stiffeners and mounting brackets are installed. Of note, blue tape was placed adjacent to areas that required more sanding and the tape was marked …. when the parts were removed, a little sanding was performed on the areas adjacent to the tape.

Next on the agenda is machine countersinking all the #40 rivet holes in the front fairing that will be used to secure the splice strip to the front fairing. The rivet holes in the U-00006B splice strips that will be used for installing the nutplates require dimpling. While the splice strips are still secured to the front fairing with Clecos, masking tape is placed on the splice strips and on the inside of the front fairing adjacent to the splice strip. The reason for the masking tape is a mixture of epoxy resin and flox will be applied under the splice strips prior to riveting. The masking tape will allow for an easy cleanup and prevent the flox from getting onto the portion of the splice strips that will later mate with the aft fairing.
Machine countersinking the freshly drilled rivet holes in the U-00005A front fairing for AN426AD3-3.5 rivets.
The splice strips and inside of the front fairing covered with masking tape ready for the bonding/riveting phase.

The next step involves removing all the Clecos and mixing up a batch of epoxy resin and flox. The splice strips and fiberglass area underneath the splice strips need to be sanded well to scuff up the mating surfaces for the flox mixture. A mixture of epoxy resin and flox is mixed to the consistency of peanut butter and then slathered onto the front fairing in the area under the splice strips. Before the epoxy mixture cures, the splice strips are Clecoed onto the U-00005A front fairing then riveted using AN426AD3-3.5 rivets.

Now that the U-00006B splice strips have been riveted/bonded in place, the U-00006A-1 wheel fairing brackets are riveted onto the splice strips. I deviated from the plans at this point and used AN426AD3-4 solid rivets to rivet the U-00006A-1 wheel fairing brackets to the splice strips. Van’s would have the builder use CCR-264SS-3-2 pop rivets here because the recommended 3” yoke for the rivet squeezer will not clear the bracket. However, there is a longeron yoke in the DOG Aviation tool cart and it clears the bracket enough to allow access so solid rivets can be used.
Setup for the longeron yoke – tall rivet set on the yoke and a thin rivet set on the plunger of the pneumatic squeezer. This combination allowed for enough clearance to rivet the wheel fairing bracket onto the splice strip using solid rivets as opposed to using pop rivets.
Riveting the U-00006A-1 wheel fairing brackets onto the U-00006B splice strips using solid AN425AD3-4 rivets. The longeron yoke allows for just enough clearance to get the job done using solid rivets in lieu of pop rivets.

(Of note: If installing the fairings on the older WD-01230 nose wheel fork the U-00006C drill template would be used along with the brackets WITHOUT the -1 after the part number.. Because the DOG Aviation RV-12 has the new, thicker WD-01230-1 nose wheel fork, it requires the template and mounting brackets be the versions with the -1 on the end of the part number).

The forward and aft fairings are mated together so the U-00006C-1 drill template can be used to create mounting holes in the U-00006A-1 wheel fairing brackets. The wheel fairing brackets will end up sitting directly on top of the nose wheel fork and screw into the U-00006E-1 fairing bracket mounts which have already been riveted onto the nose wheel fork for at least a year. The drill template insures the mounting holes drilled into the U-00006A-1 wheel fairing brackets will align with the holes pre-drilled in the U-00006E-1 fairing bracket mounts attached to the nose gear fork. The drill template is temporarily installed with two screws … one screw into the aft hole of each wheel fairing bracket. Once in place, a line is drawn along the edge of both wheel fairing brackets onto the drill template. The line in the following photo is very hard to see because I only had a black sharpie available at the time the photo was taken.  The reason for the lines is because the holes in the drill template can’t be drilled with the aft fairing installed … however, the shape WILL change when the aft fairing is removed. So the lines drawn onto the drill template will allow the builder to clamp the drill template onto the wheel fairing bracket in the exact position as marked when the aft fairing was installed.
With the U-00006C-1 drill template (bare aluminum) attached, a line is drawn onto the template down along the edge of the U-00006A-1 brackets. Hard to see in this photo because black ink was used, but the line can be seen as a dark shadow. This line will be used as an alignment aid when the aft fairing is removed to allow access for drilling.

After the lines were drawn onto the drill template, the aft fairing was removed and the drill template was clamped so the lines drawn were in the same position as when the aft fairing was mated with the front fairing. Using the holes in the drill template, the remaining four holes were match drilled into the wheel fairing brackets. The newly drilled holes are then used to temporarily attach the U-00006D-1 doubler plates onto the U-00006A-1 wheel fairing brackets. Existing rivet holes in the U-00006D-1 doubler plates are used to match drill into the wheel fairing brackets.

Here is where I ran into a BIG problem … The next step calls for dimpling the newly drilled #40 holes in the U-00006A-1 wheel fairing brackets.  I ran into a bit of a problem here that will likely affect all builders that have the new thicker nose wheel fork. The thicker nose wheel fork required Van’s to change the mounting brackets and doublers to accommodate the MUCH thicker material used on the nose wheel fork. The new brackets and doublers have a -1 after the part number and give the builder just barely enough room to create the required dimples. Clearances are so tight, the yoke on the rivet squeezer touches the fiberglass preventing the dimple die from being square with the rivet holes along the outboard edges of the U-00006A-1 brackets. To complicate matters even more, assuming the yoke would have enough clearance, the standard dimple die would not clear the already installed nutplates and, if used, a standard dimple die would cut into the radius or fillet of the bracket and likely create a lopsided dimple that is too shallow not to mention probably creating  a gouge in the fillet. Not good.
As one can see, even if the squeezer yoke would clear the fiberglass, the rivet holes are too close to the flange on the U-00006A-1 wheel fairing bracket which will cause the male dimple die to cut into the radius or fillet.
Even assuming the dimple die would clear the fillet, the rivet holes adjacent to the already installed nutplates are so close  a standard dimple die won’t clear the nutplate  … as can be seen here.

To more or less solve the issue, the DOG Aviation Procurement Department ordered a 3/32” close quarters die set from Cleaveland Aircraft Tool … the part number for the dies is DIE4263CQ.  For those not familiar with close quarters dimple dies, the dies are typically used in areas where the yoke on a squeezer is too thick to allow access. Close quarters dimple dies are made with a hole through the center of the dies which allows a nail to be inserted through the dies. The nail is placed in a hand rivet puller and as the rivet puller is squeezed, it pulls up on the nail compressing the two dies together …. thus creating the dimple in the aluminum skin.

There is a small problem using the close quarters dimple dies for dimpling the wheel fairing bracket ….  the bracket is much thicker metal than the dies are designed to dimple. Close quarters die sets were primarily developed for use on control surfaces that are typically made from .016” aluminum. The wheel fairing bracket is much thicker than that … which poses a slight problem because it requires more force to create a deep dimple. The main issue is the copper nails supplied with the dies are WAY too soft for the tension required to form dimples in the thicker aluminum used on the brackets … and the steel finishing nails, although slightly stronger, are also not up to the task because of the tiny head on the nail. My solution was to obtain some 6D 2” box nails which have the same diameter as the holes in the 3/23” close quarter dies.
The Cleaveland Aircraft Tool 3/32” close quarters die set comes with the copper nails and steel finishing nails shown on the top row. I purchased the 6D x 2” box nails separately because they can take more force and will dimple the thicker metal on the wheel fairing brackets. The 6D nails will still fail if an excessive amount of force is used … but you WILL have a dimple to work with.
As can be seen here, the male close quarter dimple die is too large of a diameter and will cut into the radius or fillet of the bracket … so it will be necessary to grind down one side of the die so it will clear the radius of the bracket.
After grinding to create a little taper on one side of the male close quarter dimple die, the die will now clear the radius or fillet on the wheel fairing bracket.

To use the 6D nail a small amount of filing is necessary. The tip of the nail requires a little dressing so the nail will slide through the holes in the dimple dies. Also, the area near the head of the nail and the portion of the nail that has the groves will also need some minor filing so the head of the nail will sit flat on the male dimple die. The modified close quarter’s dies were used with a hand rivet puller to create dimples on the row of holes closest to the radius of the angle.

The down side: Because of the thickness of the wheel fairing brackets, the formed dimples were not quite deep as I would have preferred. The simple solution … now that dimples are formed, they can be made a little deeper by using a C clamp. A short nail was used to keep the dies aligned and a C clamp was used to squeeze the dies a little more to tweak the dimples making them a little deeper.
The C clamp, close quarter dimple die set and a short nail will be used to make the dimples slightly deeper.
The shortened nail will go into the male die as shown here.
Using a C clamp and the tiny piece of nail to keep the close quarter dies aligned, the depth of the already formed dimple was improved. The curious may be asking themselves “John, why didn’t you use the C clamp in the first place”? Answer … because the male die is tapered, there is no guarantee the dimple won’t start sinking into the aluminum at an angle when using a C clamp …. Pulling a nail that sits flat to the dimple die assures the male die stays relatively centered in the rivet hole as the dimple forms. Once there is a dimple to work with, the male die will be nicely seated and there won't be a chance for the die to wander.

After all the dimples have been formed in the U-00006A-1 wheel fairing brackets, the underside of the U-00006D-1 doublers need to be machine countersunk at every #40 hole so the doubler will nest on top of the wheel fairing bracket. The countersink cage was set to a couple of clicks deeper than flush to insure the dimples in the U-00006A-1 brackets nested nicely in the U-00006D-1 doublers. Finally, the doublers were riveted onto the brackets with AN426AD3-4 rivets.
Top view of the completed U-00005A front wheel fairing.
Bottom view of the completed U-00005A front wheel fairing ready for instillation on the RV-12’s nose gear. Note how well the flush rivets on the outboard row turned out … had to unexpectedly jump through a few hoops to get to this point … but now all is well.
Assembled forward and aft fairing sections. I'm pleased with the overall fit.

Time to take all the parts to the hangar and begin the final fitting process on the DOG Aviation RV-12.

Normally, work would  continue by installing the U-00006E-1 fairing bracket mounts onto the new thicker WD-01230-1 nose wheel fork. I performed this step when the nose wheel fork was upgraded to the new stronger WD-01230-1 nose wheel fork … so it is time to move on to the trial fitting of the U-00005A front fairing on the RV-12's nose wheel fork.

As with the fairings for the main gear, the nose wheel fairings require the same ½” of clearance all around between the tire and the fairing. In addition, the nose wheel fork needs to be rotated from stop to stop and the fiberglass material needs to be removed from the U-00005A fairing until there is at least  1/8”of clearance between the front fairing and the WD-1201 nose gear leg throughout the nose wheel fork's full range of motion. After that was accomplished, the U-00005B aft fairing was attached and checked for at least 1/8” of clearance between it and the WD-1201 nose gear leg. The aft fairing also requires trimming along the edges to obtain the required ½” clearance between the fairing and the tire.
Initial trial fit of attaching the U-00005A front wheel fairing to the U-00006E-1 fairing bracket mounts on nose wheel fork. Fortunately, all the mounting holes aligned nicely.  Here again the ½” wide piece of aluminum will be used as a gauge for obtaining the required ½” clearance between the fairing and the tire.
Both the U-00005A front and U-00005B aft fairings mounted in position on the nose wheel fork. The fit is excellent but a little fiberglass still needs to be removed from the forward edge of the aft fairing under the gear leg to obtain the required 1/8” clearance. In addition, both fairings require fiberglass removal to obtain the required ½” clearance between the tire and the forward and aft fairings.

After the desired fairing clearances are obtained, the next item in the plans calls for working on the U-00007 nose leg fairing trim. HOWEVER, I have decided NOT to install the nose leg fairing trim on the DOG Aviation RV-12. The reason being, I’m not really thrilled about the thought of drilling two holes into the nose gear leg and tapping them for 8-32 threads just so the U-00007 trim piece can be mounted onto the WD-1201 nose gear leg. So I’m taking a pass on this one.

There was one place along the bottom bend of the fairings where the curve was off slightly between the two fairing halves … this was easily fixed by tightening all the screws up and using a heat gun to gently soften the fiberglass while pressing on it with a block of wood to gently reshape the curve. As can be seen in the above photo, the curve is now perfect.

At this point, other than paint, the nose gear fairing is complete!!!.