Archive for category Empennage
1.0 Hours -
Today, I was able to fit the left HS tip, construct the wood rib for it, and bond both the ribs to both tips. This time, I decided to bond the ribs in place while the tips were clecoed on the HS. Since the tips deform quite a bit when not clecoed in place, I was worried that the fit may not be quite right if I removed the tips and bonded the ribs outside the HS. Once the flox set, I removed the tips and laid a fillet of flox around the inside joint of each tip/rib combo. Tomorrow, I’ll reinforce them with some glass.
On a more positive note, about one more month until my wings arrive. Hopefully, when it comes time to order the fuselage, I’ll be able to save the money earlier and not have a construction gap after the wings are completed.
1.0 Hours -
The HS tips require the most work of all the empennage tips. Since some metal is cut from the end of the stabilizer to accommodate the elevators, an equal amount of the HS tip also has to be removed. In addition, the horizontal stabilizer is not pre-punched for the tip attachment locations. This is the only part of the empennage where an entire row of rivet holes is missing. Like the VS tip, the HS tips are also open ended and I will need to make some wood ribs to close them off.
I started by trimming the tip. Using my Dremel, I cut about 0.2” from the flange, and removed over an inch from the aft end to allow the elevator to swing. Being cautious, I made sure to remove less than required from the aft end. It’s much easier to sand it down the rest of the way than to rebuild it with fiberglass.
Next, I needed to measure and mark the horizontal stabilizer for the tip attachment holes. Since the flange on the tip is 0.5” wide, I decided that my rivet holes should be 0.25” from the edge of the HS. Drawing this line was the easy part. Now, how do I decide on the number of rivets to use to attach the tip and how far apart do they need to be spaced?
After looking at the other empennage tips (all of which have different rivet spacing), I decided to place the first rivet 1” from the leading edge and then place three more rivets at 1.25” intervals for a total of four rivets per side. Once I marked this pattern, I used a center punch and then drilled the holes to #40.
Another difficulty with the HS tips is that they are not quite wide enough. If I clamp one side to the HS, the other side is almost a half inch from the flange. However, they do easily stretch to fit the HS. With this in mind, I clamped both sides of the tip in place and started match drilling the tip to the holes I had just made in the HS. As with the other tips, I drilled my first hole, then carefully re-checked the fit before moving on to the next hole.
Once all the holes were drilled and the tip was clecoed on, I attached the elevator to check how much more of the tip would need to be removed. Fortunately, not much! The aft end of the tip will require a bit more sanding in order to make a nice, even gap the entire length. The elevator tip also sticks out a bit more than the HS tip. To fix this, I’ll probably put a layer of micro on and then sand it to shape so that it is even with the elevator’s tip. On one builder’s site, I saw that they actually closed the entire HS/elevator tip gap with micro, sand the final shape, then re-cut the gap with a saw. I may try this as well.
0.5 Hours -
The vertical stabilizer tip is now complete. Well, it is attached to the vertical stabilizer, but it still needs some work before I’ll be happy with it.
Once the micro/fiberglass was set on my new forward flange, I removed the peel-ply and gave the entire tip another light sanding with fine grit paper. I wanted to seal the micro layer on the aft surface and decided to try a technique I read about on another builders site. I simply mixed a batch of epoxy, used a brush to paint the epoxy onto the micro, then used a squeegee to scrape off as much of the epoxy as possible leaving a very thin layer than, hopefully, will fill any pinholes. Once this layer became tacky (about 45 minutes) I repeated the process and then left the tip to dry overnight.
The next day, I had a smooth, hard surface on the micro. I final sanded it to smooth the epoxy and then riveted the tip to the vertical stabilizer. There is still a significant gap on the leading edge between the metal and fiberglass, but I’ve sat the vertical stabilizer aside for now as I decide how to handle the gap. I can either fill it with some micro and sand it smooth, or I can fill it and then tape the entire seam and rivets with glass. If I go the glass route, I’ll do it on all the empennage tips for consistency. However, since the vertical stabilizer tip is the only one I’m really not happy with so far, I’m leaning towards just filling the gap and calling it good. On to the horizontal stabilizer tips.
0.7 Hours -
After my first layer of micro set, it had a few large bubbles in it and many small ones too. In an attempt to get rid of them, I started to sand down the micro. However, I sanded as far as I could and the bubbles were still barely visible. While I could have left it as is, I decided to mix another batch of micro and place another layer on the tip.
Unfortunately, I’m still trying to figure out the right consistency for the micro mixture and I made this batch too thin. I spread it on the tip and carefully watched for bubbles to rise to the top so that I could pop them. When I thought it was good to go, I went back inside and left the epoxy/micro mixture to set overnight. When I checked it the next morning, the surface with the micro looked good, with no bubbles, but the micro mixture had also run down the side of the tip in several long, thick drips. Looks like I’m in for some sanding! (I should have taken a photo of this for a before and after, but didn’t think about it at the time.)
The micro sands fairly easy. I started with some fairly coarse grit sandpaper and ended with finer grit. In the end, I was very happy with the tip.
When I initially fit the tip, the forward part of the flange was too wide and would not easily fit inside the VS. To fix this, I did like on the rudder top tip and cut off some of the forward flange. However, when I re-fit the tip, there was a small gap between the VS and the tip. To fix this, I decided to place one, small piece of fiberglass inside the forward end of the VS tip and then fill the outside with some micro. Once this dries, I should be able to sand it down so that the original gap is eliminated.
Maybe this fiberglass stuff isn’t so bad after all. At least you can fix your mistakes!
0.8 Hours -
My order from Aircraft Spruce arrived on Saturday. It contained epoxy, fiberglass, flocked cotton, and glass bubbles, everything I needed to complete the fiberglass work on the vertical stabilizer tip.
The first thing I did was to mix a batch of flox, consisting of epoxy and flocked cotton, and use it to bond my balsa rib to the VS tip. I used a bit of flox along the edge of the rib to glue it into place and then I laid a fillet of flox around the rib/tip junction on the inside of the tip. This mixture took a considerable amount of time to dry, so I had to let it sit until Sunday morning (keep in mind that this is my first time using this stuff…I know my fillet is a bit ugly and I probably used way more flox than I needed to begin with).
Once the flox was dry, I sanded it a bit in preparation for laying a ply of fiberglass cloth to reinforce the rib. I bought 3 yards of Rutan bi-directional fiberglass cloth. I’ve opted for bi-directional because it can be used more universally. The bi-directional weave is good for flat lay-ups and it also allows the fabric to drape over curved surfaces better than a uni-directional fabric. Plus, it was invented by Burt Rutan, so it has got to be good!
To wet the cloth, I’m using the plastic sandwich method. I have a sheet on 1 mil plastic which I place on a cutting mat. Next, I place my fiberglass cloth on the plastic. Then, I mix my epoxy, pour it onto the cloth, and place another sheet of plastic on top of it. With a plastic squeegee, I then move the epoxy around until the entire piece of cloth is wet (it is easy to tell when it is ready because the cloth practically becomes invisible). Once wet, I make a few final passes with the squeegee to squeeze out as much of the excess epoxy as possible. Finally, I used a rotary cutter to cut my cloth, inside the plastic, to the appropriate shape. Once cut, I can easily peel off the plastic and place my wetted fiberglass where it is needed.
The only problem I ran into was that it was difficult to get my big hands inside the tip to move the cloth to the exact correct spot and smooth out any air bubbles. Fortunately, this cloth will not be visible on the finished product. Hopefully, I’ll have my fiberglass skills refined by the time I get to the forward canopy skirt!
Another few hours and the fiberglass was dry enough for me to move onto the next step. The forward surface of the tip, where my balsa rib is visible, is a little rough from the flox and the rib is not perfectly lined up with the edge of the tip. To fill in the gaps and smooth it out, I mixed up a batch of epoxy with glass bubbles and placed a layer of this on the forward surface of the rib. I have to admit, the glass bubbles are easy to work with and kind of neat too! Once they dry, it should be easy to sand the tip to the final shape.
1.7 Hours -
The vertical stabilizer tip is a little more complicated than the other tips I’ve worked on so far. This is mainly because it is the first tip I’ve worked on that has to be fitted using another tip (the rudder top tip) as your guide for trimming, and the aft end of the VS tip is left open by Van’s which means it requires closing before it is mounted. Van’s gives you two methods for closing the rib: 1) temporary foam and fiberglass, or 2) permanent wood and fiberglass. I’ve opted to make a wood rib out of balsa which will be bonded to the tip and reinforced with a single ply of fiberglass.
First, I did my initial fitting of the tip to the VS. Unlike the other tips, the flange of the VS tip did not need to be trimmed. However, the aft end of the tip extended into the area of the VS where the rudder fits and would require trimming in order to let the rudder swing. I temporarily mounted the tip and then marked the area that I wanted to trim off. Using my Dremel, I purposely trimmed off less than was required since I can always trim more off, while adding some back is more difficult.
Once the initial trimming was complete, I attached the rudder to the VS for the first time. This was an awkward assembly. First, I tried to assemble them laying flat on my workbench. However, I could not get the upper most hinge assembled this way. So, I had to stand them on the corner of the workbench and insert the temporary assembly pins while balancing both pieces (they are big). Once I managed to assemble all three hinges, I could balance the VS/rudder assembly on the bench by simple swinging the rudder one direction or the other.
To my surprise, the VS required no trimming in order to allow the rudder to swing. In addition, the amount I trimmed off the VS tip was almost perfect. It just needed to be sanded a bit to even both sides out and remove any jagged edges.
The fiberglass portion of the VS tip was ready, so I moved on to the wood portion. With the tip clecoed to the VS, I measured the width and length of the tip and used these dimensions to cut a rectangular piece of 1/4” balsa. I then traced the outside of the tip on the balsa and trimmed the wood to the shape of the tip. Finally, I sanded the rib until it fit snuggly inside the tip.
I have a fiberglass supply order in with Aircraft Spruce which should arrive tomorrow. Once that arrives, I’ll have everything I need to bond the balsa rib to the tip and reinforce it. My plan is to bond the rib to the tip and reinforce it with one layer of fiberglass cloth. I then make a slurry of epoxy and glass bubbles and use that to fill the end of the tip. Once dried, I should be able to sand the slurry, leaving a nice, flat aft end of the tip. At least that is the plan!
1.5 Hours -
For my third tip, I decided to install the top rudder tip. I’m avoiding the horizontal and vertical stabilizer tips for as long as I can because those have to be closed before they can be installed.
The rudder tip required a bit more work than the elevator tips, but it is the best looking of the three so far. As with the two elevator tips, the flange of the rudder tip had to be trimmed slightly in order to allow it nestle up against the flange of the rudder’s tip rib. In addition, a short section of the flange at the aft end of the tip had to be completely removed to accommodate the AEX wedge in the rudder’s trailing edge. I ended up removing about one inch of the aft flange.
After trimming the flanges, the tip still would not fit well on the forward end. I really had to squeeze the tip to get the forward end to slide into the rudder. The problem here is that the forward surface of the tip does not have a flange built into it like the rest of the tip…it is simply flat. Therefore, I decided to make my own flange by sanding away the gel-coat with my Dremel’s sanding drum. Once my homemade flange was complete, the tip slid into place easily and fit perfectly.
With the fit acceptable, I proceeded to drill the tip to the rib. Initially, I drilled the holes to #40. They were then enlarged to #30. However, the aft three holes on each side were already drilled to #30 and dimpled during rudder assembly per the plans. If I had not done this earlier, it would have been almost impossible to dimple them now. For these holes, I very carefully match-drilled the tip using only a #30 drill.
Once drilled, I deburred and dimpled the holes in the rudder. The holes in the tip were countersunk, once again, using my Dremel with a conical grinding bit. I also glued aluminum rivet washers to the inside of each hole on the tip as I did on the elevators. After the glue on the rivet washers had some time to set, I went ahead and attached the tip using CS4-4 blind rivets.
The final result looks very good. There is less waviness in the seam than is on the elevator tips, and there is only a very slight gap on one corner of the forward face of the tip. I put a picture of this gap below, but the camera makes it look much bigger than it actually is. As with the other tips I’ve done so far, I’m planning to leave it as it is now. If I decide to paint the plane later down the road, I may glass over the seam and fill the gaps at that point.
1.8 Hours -
The left elevator tip was installed in the same manner as the right tip. I thought this tip would go on in about half the time of the right one. However, it ended up only taking about 10 minutes less, but it was easier and looks slightly better. At least I got smart this time and used a shop vac to suck away dust as I cut away the fiberglass flange with my Dremel. Granted, I still wore a respirator and safety goggles while cutting.
2.0 Hours -
With the wing kit on order and the wing stands essentially done, I have nothing that I can do on the airplane except work on the fiberglass empennage tips. I was going to leave these parts off until just before the empennage components are attached to the fuselage, however, I really enjoy working on the plane and do not want to sit idle for another month and a half while waiting for the wing kit to arrive. With this in mind, I decided to start working on the tips.
Some people just rivet the tips on and call it good, others rivet them on and then glass over the seam so that there is a perfectly smooth transition from aluminum to fiberglass. For now, I’m just going to rivet them on. After seeing how they look, I’ll decide if I want to fill them. the nice thing is that I could fill them at anytime in the future…even after flying.
Starting with the right elevator, I quickly saw that the flange on the tips was too long and would need to be trimmed. Also, the flange on the forward end of the tip must be removed to compensate for the location of the counterweight.
After carefully measuring and marking the tip flange, I proceeded to remove the excess material using my Dremel with a cutoff wheel. Cutting the fiberglass generates a lot of dust. After making a small cut, I decided to put my respirator on. Unfortunately, the respirator doesn’t prevent the dust from getting all over me and everything else in the garage. Oh, and that dust can make you itch too!
Once the flange was trimmed, I did a test fit. A little more sanding and the fit looked good. I started to drill the tip to the elevator using a #40 drill. The elevator is pre-punched but the tip isn’t. I would drill one hole, cleco the tip to the elevator, adjust the fit, and drill the next hole. Once all the holes were drilled to #40, I enlarged them to #30 in order to accept the CS4-4 blind rivets.
After drilling and deburring, I dimpled the holes in the elevator using my pneumatic squeezer. The tip, however, must be countersunk. Since fiberglass is abrasive, and I’ve been told it will ruin a countersink bit, I decided to try making the countersinks with a conical grinding tool attached to my Dremel. Surprisingly, this seemed to work well…at least well enough to justify not buying another countersink bit specifically for fiberglass work.
The tips are attached to the empennage using CS4-4 blind rivets. Van’s instructs you to attach the tip directly to the elevator. However, many builders elect to bond a strip of aluminum to the inside of the tip along the rivet line. The aluminum adds strength and gives the rivet something a bit firmer to grip. I elected to use another method…aluminum rivet washers. These washers have a perfect 1/8” inner diameter and serve the same purpose as an aluminum backing strip. However, rather than placing a strip along the entire length of the tip, the rivets are simply bonded to each hole with some E6000 adhesive. This is simple and it should save some weight in the overall aircraft (at least a few ounces).
Once the glue had some time to set, I went ahead and riveted the tip in place on the elevator. Overall, the fit is good, but there is some waviness/gaps in the joint. I think this is probably unavoidable, and, for now, I’m going to plan on leaving it this way since it is very minor. If, further down the road, I decide to paint the plane, I’ll probably glass the joint over at that point.
The control surfaces of the RV are balanced, meaning they have a counterweight attached to them. I believe this is done to reduce flutter and also ease the amount of force needed to move the stick in flight. To my surprise, the right elevator is almost perfectly balanced as it is now. The counterweight is only slightly heavy which is perfect in the event that I decide to paint it (the paint adds significant weight to the control surfaces and the overall airplane).
1.0 Hours -
With so little left to do on the empennage, I haven’t been spending much time in the garage lately. However, today I decided to finish fitting the elevators to the horizontal stabilizer.
This was another step that turned out to be simpler than I expected. Basically, all I had to do was attach an elevator, clamp the elevator to the horizontal stabilizer so that it is “in trail”, insert my drill bushing into the center bearing, and drill a #40 hole in the elevator horn. I started with the left elevator and then did the right.
Once both elevator horns were drilled, I had to enlarge the initial hole from a #40 to 1/4”. To do this, I just stepped up drill bit sizes until I was at 1/4”. I could have used my unibit for this, but I’ve found that it chatters too much and it is easy to make the hole uneven or too large. Since this is a crucial attachment point, I didn’t want to risk it.
After both holes were enlarged, I reattached both elevators to the horizontal stabilizer and checked that the elevators moved freely, at all hinge points, through the entire range of motion. Everything looked great!
With the elevators done, the empennage is complete minus the fiberglass tips. My wings are scheduled to be shipped the week of May 17th, so we’ll see if I last that long or get bored and go buy myself some West System epoxy for attaching the tips.