A simple jig made up of aluminum angle attached to the flap worktable allows us to get the spars perfectly straight as the flap is drilled and assembled. A twisted flap will require disassembly and replacement of many parts. It is worth taking the time to get it right the first time.
Just to recap, I bought a partly completed GlaStar project [See “Taking Over Someone Else’s Project,” December 2017] and got it shipped to me from Florida. The previous builder had installed fuel cells (bladders) to increase fuel capacity and had already closed up the wings. Considering their age, I felt that the fuel cells needed to be checked out, so they had to be extracted from the wings and sent back to the manufacturer. I also wanted to install Sportsman flaps in lieu of the original flaps in order to gain the performance advantages of the newer design. This also required that the wings be partly opened up to gain access for the new flap tracks.
The fuel cells had to come out to either be replaced or rebuilt. That meant removing the main ribs from each end of each wing. The center ribs at the root of each wing are particularly difficult to install because there are no straight shots with either a drill or a rivet set into any of the rivets that hold it in place. Memories of struggling with and cussing at these rivets on previous projects came back to us as we started on this task. With some patience and concerted effort, the ribs yielded, giving us access to the fuel cells at either end of the wings—mains near the root and auxiliaries at the tips.
Removing the root rib to gain access to the fuel cell is a major pain. Here the author is bending a long drill bit to align it with the rib to be removed. There are no straight shots into any of these rivets. It was similarly difficult to install new rivets later after the fuel cells had been overhauled.
The fuel cells looked good, but it was way too hard to extract and reinstall them to leave anything to chance, so off they went to be overhauled. We could have elected to replace the bladders with aluminum tanks from Glasair, but the cost of doing so would exceed the cost of overhauling the fuel cells by a factor of four. That was $1500 we could spend on something else.
The author (left) uses a hemostat to fish a rivet into place while Zaleski reaches into the empty fuel cell cavity to position the bucking bar. Note the extended rivet set in the rivet gun that was made especially for this task.
When the fuel cells came back, we still had some work to do before they went back in. The fuel lines and vent lines needed some work, as did the transfer pumps that moved fuel from the auxiliary tanks to the mains. One of the pumps was badly corroded, so it had to go, and the fuel lines from the pumps to the main tanks were improperly sized. A few new fittings and some aluminum fuel line material solved that problem.
The auxiliary fuel cell goes back into the wing after being overhauled. It is a little tricky to get all the wrinkles out of the bottom side and secure the top to the Velcro strips on the top skin that keep it from collapsing when fuel is removed.
Another issue was an accumulation of junk inside the wings, no doubt put there by some enterprising rodents somewhere along the line. After their nesting material was fished out and vacuumed up, and a few corroded spots cleaned and primed, we were in good shape to proceed with the rest of the wing work. Some chewed-up electrical conduit also got replaced. These are the kinds of things you find in a project that has been sitting for a while.
Co-builder Ed Zaleski works to remove varmint debris from the wings with a shop vacuum. It is amazing what tight spaces these little guys can get into and how hard it is to extract what they have left behind.
One of our early decisions was to replace the standard GlaStar flaps with the later and much improved Sportsman flaps. Dimensionally the wings are the same, so there is no reason why the Sportsman flaps won’t work, but to use them, the GlaStar flap tracks had to be replaced. If the wings were still open, this would be a very easy task, but in this case, the wings were complete and closed up, casting doubt on whether or not we could change the flap tracks without removing the top wing skins, a job we were in no hurry to tackle. With some patience and ingenuity, we were able to extract the old flap tracks without dismantling the wings, but there were times that we weren’t so sure it would work out. It helped to have the fuel cells out of the way, especially when it came time to buck the rivets for the new flap tracks.
Zaleski marks the centerline of the main spar with a scribe tool and Sharpie. The pre-punched rivet holes in the flap skin must line up with this mark to be properly positioned for drilling and riveting. Cleaveland Aircraft Tool calls this an edge marker block (Item #6352) on their website. It is well worth the $19 cost if you need to do this kind of layout work.
Glasair Aviation sent us some new flap track parts, which went together quite quickly. It is so much easier to work with new parts out in the open. After giving them a coat of self-etching primer, we got down to the task of riveting them into place. The rivets that held the tracks to the aft spars were deep inside the cove skins, which forced us to create an extra-long rivet set. Our airport buddy and Harmon Rocket builder, Jerry Scott, came to the rescue with just the right pieces for this task. It is very nice to have other airplane builders nearby. I can’t even count how many times we have either borrowed or lent parts or tools to fellow builders, speeding the day’s progress along, instead of stopping to track down a special wrench or the one last screw needed to complete a task. This helps offset the travel time disadvantage of building at the airport versus at home.
A big part of making the Sportsman flaps work on the GlaStar is changing the flap tracks. The new Sportsman flap track is above in gray, and the old GlaStar flap track that we removed is below in green. The Sportsman flap track makes a major change in how the flap extends.
On each wing we did finally get stuck on one row of rivets where we just couldn’t buck them or use CherryMAX rivets without a great deal of extra trouble. With reluctance we substituted stainless steel screws for three rivets in each wing. They are loaded in tension in this application and their strength easily exceeds the aluminum rivets they replace, so there shouldn’t be any problems with their use. We also used some CherryMAX rivets in some other places where access was not available. I do not endorse the wholesale substitution of solid aircraft rivets with CherryMAX rivets, but they can be a lifesaver in places where access for bucking is not available. If you use these rivets, be sure to also use the Cherry G-27 riveter for best results. Note that these rivets are very strong in shear but not nearly as strong in tension. Any rivet substitution needs to take this into consideration.
With generous amounts of improvising, adapting, and overcoming, we managed to get four Sportsman flap tracks installed on our GlaStar wings. And we didn’t have to take the wings apart to do it. With all of this done, we could install the fuel cells in the wings and reinstall the center ribs that had to come out to give us access.
A conventional gear arrangement (taildragger) was a given in this project. The idea is to create a plane with some decent short field and off-airport capabilities that also performs well in cruise. This utility performance is the forte of the GlaStar, and we wanted to capitalize on that or even improve upon it.
We used a piece of aluminum angle to get the gear legs level and straight. Here Zaleski checks the gap between the stub axle and the angle to be sure it is the same as the other side. Once the gear is positioned properly, the retaining bolts can be installed.
While working on a friend’s Sportsman, I found out about some extended gear legs available from Langair Machining. They make gear legs for most RVs and standard gear legs for the GlaStar and Glasair Sportsman. These special gear legs have a larger diameter for rough fields and are three inches longer than standard. They also utilize the bolt-on Grove stub axles. This will give better prop clearance on rough fields and allow a higher angle of attack on takeoff and landing. They add cost (ugh!) and weight (double ugh!), but the benefits seem worth the cost.
Gear leg installation is just the same as it is with the standard gear legs. They must be aligned and set to let the plane sit level and not have any toe-in or toe-out. The tough part of the gear leg installation is drilling the holes for the retainer bolts. The trick to making this process easier is to start the bolt holes in the plane, but then remove the gear legs and drill the holes in a drill press or milling machine. This makes it much easier to keep the holes straight and to control the speed and pressure on the drill bit.
At the other end, the project came with a leaf spring and Scott 3200 tailwheel already in place. The tailwheel will work well after we replace the steering arms with ones that have bent-up tabs, but we are thinking about the Airframes Alaska T3 suspension. No final decision has been made on that yet.
Aileron Servo Tab
Originally the GlaStar suffered from heavy aileron forces. After a number of complaints, Stoddard-Hamilton came out with an aileron servo tab retrofit kit that solved that problem and created very nice harmony between aileron and elevator stick forces. The servo tab worked so well that it was carried forward into the Glasair Sportsman when it came out years later. Since this was a very old kit, it had not been retrofitted with the servo tab, so this was definitely on the to-do list for this plane.
A 3×23-inch section is cut out of the left aileron and turned into a servo tab. The tab lightens roll forces by acting in the opposite direction of the movement of the aileron to which it is attached. Thus, when the aileron deflects up, the tab deflects down. This downward deflection of the tab pushes the aileron up.
To install the tab, we cut a piece out of the trailing edge of the left aileron that was about 2 inches wide and 23 inches long. An abrasive cutoff wheel works best for this, since it would have been very difficult to make the required cuts with shears. A quarter-inch pilot hole drilled into the corner before the cut helped to reduce stress cracking from that point. Once the notch was cut into the aileron, a piano hinge was riveted into place for the servo tab. Assembling the tab was very straightforward, with standard AD rivets used where there was access, and pull rivets used where it was not possible to buck standard rivets. The actuating rod and pivot placement will be completed when the aileron gets installed on the plane later.
A good way to tell if your drill is straight when drilling into new sheet metal is to look at the reflection of the drill bit. If the drill bit and its mirror image form a straight line, your drill is going in straight. If it bends where the bit meets its reflection, you need to reposition the drill.
Our experience with the Sportsman flaps made the decision to install them on the GlaStar a fairly easy one. They work much better aerodynamically and are much easier to deploy. The original GlaStar flaps take some real muscle power to extend them, especially if you are a little fast. The Sportsman flaps also have a 10-knot higher extension speed. The only problem was, it had only been done once before that we know of, and that case involved wings that were not yet closed up. This would be the first attempt to install the Sportsman flap tracks and flaps on essentially finished wings. We were pretty sure it would work, but we would have been very disappointed if our substantial investment in parts and time did not pay off. As it turned out, the installation went fairly well.
Once the wings were completed, we were anxious to get to the task of building new flaps. It was nice to work with new material after reworking previously assembled parts. It just goes faster with fewer problems. The assembly process is simple enough. First, we attached the nose ribs to the flap hinge points and actuating points. All of these ribs got doublers that had to be trimmed to fit and drilled for rivet holes. These were then deburred, primed, and riveted together. Next, these and the other ribs were Clecoed to the main spar, with the main ribs also attached to the aft spar. All of the holes then got drilled to size. After that, everything came apart for deburring before getting riveted together. We decided not to prime the internal parts that would not be exposed to any weather to save weight and time.
With all of that done, it was time to mark the rib center lines and begin attaching the skins. The spars and ribs are not predrilled in either the GlaStar or the Sportsman. So, the prepunched holes in the skin determine the rivet locations after the holes are aligned with lines that must be marked on the underlying parts. This isn’t quite as easy as working with the match-hole drilled parts of an RV-12, but it isn’t too difficult. It is just important to get started correctly. A piece of aluminum angle attached to the worktable served as a jig. Once the spar was checked for straightness, the skin was placed into position, and the first hole was drilled at one end and then the other. Next, a hole was drilled near the middle, and then at the quarter points along the spar line. This prevents the skin from warping or sliding out of position. Once it is well-secured, the rest of the holes can be drilled. The same process is used with the ribs and the aft spar.
With all of the holes drilled, it is time to take everything apart and deburr everything in preparation for final riveting. This is not the most fun part, but it is very important. Any burs left in place can keep the parts from coming together completely as they are riveted. Once the bottom of the skin is riveted into place, it will be time to flip everything over and work on the top part.
With both wings completed they get hung out of the way to make room for other work. The new flaps are next, so we needed room for the 10-foot-long worktable that was required for that task.
Lessons Learned So Far
We are relearning the need to go slowly, read the book, and be patient. It has been too easy to just jump in and start working. No major mistakes have come from this, but at least a handful of poorly done rivets have been replaced. This is a lesson that we should have remembered from before.
We installed one of the fuel cells without the vent tube in place. Too many distractions on “social” Saturdays led to missing this important part. Unfortunately, the fuel cell will probably have to come out to fix this, which means taking out some rivets again. It is wonderful to have friends come by and help or just socialize, but extra care must be taken to prevent distractions from turning into mistakes. When we built the first GlaStar, we worked at home until the very end. This meant that few people came by to chat. With each new project, now all built at the airport, more and more friends seem to come by. It is common for several of us to go to lunch together on Saturday, sometimes driving if we are in a hurry or are short of planes, at other times flying somewhere nearby. I wouldn’t give this up, but it does present some challenges that seem to be greater than what we had experienced in the past.
Perhaps the biggest lesson learned is to really take your time evaluating the parts you are getting if you are buying a partly completed kit. I did my own pre-purchase inspection, being quite familiar with the GlaStar and the seller. I gave things a pretty good once-over, but not good enough. I missed that the brake calipers were not there. This didn’t really matter too much because I planned to change the wheels and brakes anyway, but it was annoying to have missed something so obvious. The mistake that really cost money was missing three of the four required seat tracks. These items cost $120 each. I also missed the door latches, but those will be easy to make. Lastly, we ended up with a lot of miscellaneous hardware that we can’t use and are missing a lot of miscellaneous hardware that should have been there. This doesn’t cost much in terms of money, but it makes for a lot of extra trips to Aircraft Spruce to get little things that I thought we had. Luckily, Spruce is only a 20-minute drive from the hangar, but each trip costs at least an hour of build time every time it happens. We are getting better at planning for this, but we still get surprised now and then.
One more surprise was how much effort it took to get the debris left inside the wings by various varmint guests over the years. Their junk is very difficult to get out of the nose section where there are a lot of ribs and very limited access. There were also a few minor corrosion spots in the main part of the wing, but these were easily corrected with some elbow grease and a shot of self-etching primer. There seems to be no corrosion in the nose area, which is really good news.
The best surprise has been seeing how much fun it is to build again when there is no pressure to get things done on a schedule. That doesn’t mean we don’t want to finish in a reasonable amount of time, but we are not committing to any fixed end date. We build when we can for whatever time we have available. It will get finished when it gets finished. Things are not going as quickly as I thought they would, but they are moving forward at a pace that is satisfying.