Hole Shot construction gets underway, starting with the fuselage
Bob Hunt [[email protected]]
It's time to build! I trust that those of you who are going to follow along with this project have obtained plans for the Hole Shot or for one of the other flapless models I mentioned last time.
I like to start with the fuselage. The Hole Shot has a 3/8-inch-thick profile fuselage. It should be cut from 3/8-inch medium to medium-firm balsa.
Transferring the plan to balsa
I use the pin-punch method to transfer shapes from plans to balsa. I lay the plans over the balsa stock and hold it in place securely. Then I use a straight pin to punch holes through the plans and into the balsa at roughly 1/4-inch intervals around the perimeter of the piece I want to duplicate. When I have punched the entire outline, I remove the plans and connect the pinholes with a fine ball-point pen. It's important not to forget to pin-punch around the wing and tail openings and the motor-mount slots.
Cutting the fuselage blank
I use a scroll saw to cut the fuselage blank. If you are going to be a serious builder you should purchase a good scroll saw right away if you don't have one. It's an investment in building quality.
The scroll saw should have a quick-release mechanism to allow the blade to be fed through starter holes in places where you have to cut out a portion of the interior of a part. Such a place on the Hole Shot fuselage would be the wing hole.
I'll add to this list of necessary tools and describe how to use them as we proceed. Hey, that's the whole purpose of this series after all!
Motor mounts and weight consciousness
The hard 3/8-inch square maple motor mounts are next to be measured and cut. I drill lightening holes in my mounts well aft of the area where the engine will be positioned.
This is a good place to discuss weight consciousness. The way to achieve light models is to look at each part you intend to glue into or onto the model and ask yourself if it is too heavy and too strong for the job it has to do.
The path to lightweight building is simple. Be conscious of grain—not gram or ounce! There are 15.43 grains in a gram. If you leave an extra gram here or there 28.35 times, you've added an ounce. I know; that sounds ridiculous, but those who think and build with this thought in mind always seem to produce outstandingly light models. Lightweight building is a frame of mind!
Use your scroll saw to cut shallow notches the width of the blade in the maple mounts on the edge where they will contact the fuselage blank. These notches should only be approximately 1/32 inch deep. They will allow for more gluing surface and yield a much stronger bond.
Install the maple mounts using a mix of slow-cure epoxy and microballoons. Slow-cure epoxy will work its way deeper into the wood fibers on either side of the bond before it hardens. I've seen components on airplanes built with fast-cure epoxies come apart after a season or two. The microballoons are also important. Epoxy is just a mix of resin and hardener. There's not much in there to actually form a solid mechanical bond. By adding a small amount of fiberglass microballoons to the mix, you get a much stronger grip between epoxied pieces and it will not break down easily in time. This is especially important in regions where there is high stress or vibration, such as in the motor-mount area.
Be sure to wipe any excess epoxy/microballoon mixture from the fuselage side surface. We want a flat and clean surface on which to glue the doublers.
Installing fuselage doublers
Once the epoxy on the motor mounts has cured, cut and install the 1/16-inch birch-plywood fuselage doublers in the nose area. You can use the fuselage blank as a template to lay out the doublers. Cut them out slightly oversize using your new scroll saw and attach them to the fuselage using the slow-cure epoxy/microballoon mix. Weight this sandwich of parts down flat against a clean, hard, flat surface. Make sure nothing has shifted before you go off to let the epoxy cure.
Once the epoxy has cured, carve and sand the edges of the doublers flush with the fuselage blank. Plywood can be tough to carve and sand, and this is where the proper tool and technique must be applied.
Also included in this column:
- The pin-punch part-transfer method
- The treasured scroll saw
- Building light is a state of mind
- Use long-cure epoxy because...
- Carving and sanding skills
I'll stop here and discuss more tools. I'll be doing a lot of that in this series.
Carving and sanding
Carving and sanding are two of the most used and useful skills in building. You must learn as much as you can about how to control a knife and a sanding block. These two tools will make or break your model in regards to how perfect it looks when it's finished.
The ability to safely and skillfully control a knife is imperative if you want to learn to build well. There are many different types of knife handles and knife blades, and they all have specific applications.
Knives and blades
The most common modeling knife blade is the ubiquitous #11. It is fairly narrow and tapers sharply to a fine point. This blade is sharp and can cut easily through most densities of balsa, and it can even be used to whittle thin plywood. It is usually mounted in an aluminum handle that is approximately 1/4–5/16 inch in diameter.
You can usually find handles in hobby shops to accept #11 blades that have rubber or polyurethane coatings, and these are much easier to grip. Many of these handles also feature hexagon-shaped end pieces that are designed to keep the knife from rolling off the table and finding your big toe. (Ouch!)
You usually hold the #11 blade handle like a pen might be held for cutting and grip it firmly in the palm of your hand for whittling. I've found that hobby-grade #11 blades vary greatly in quality and the ability to hold an edge. You want to purchase high-grade blades.
I buy these blades in boxes of 100 at a time and change them often. I've tried sharpening them with some of the specialty sharpening devices but have found that once the stock edge is dulled, the blade will not hold a resharpened edge very well. Nothing will ruin a part quicker than a dull knife blade!
Another useful blade is the whittler type (commonly called a #26). It fits into a somewhat larger-diameter handle—usually approximately 1/2 inch—and features a long, flat surface with a cutting edge on one side. This blade is useful for carving blocks and tapering long sheets of balsa.
Sanding blocks and technique
There are many different types of sanding blocks. I strongly recommend the type that requires you to attach the sandpaper to the block's surface with some sort of contact cement.
The sanding blocks that have soft pads between the block and the sandpaper are useless for our purposes. You want the sandpaper to lay firm against the block, and contact-cementing it to the block's surface is the only way I know to achieve this.
I advise against wrapping a loose piece of sandpaper around a block and holding it in place with hand pressure. The paper can slip and bunch up, ruining the sanded surface.
When you use the contact cement to attach the sandpaper to the block, make certain that the block surface and the backside of the sandpaper are clean and smooth. After attaching the sandpaper, press the block, sandpaper face down, against a flat table and press hard. You want the sandpaper to lay flat against the block.
While you are pressing down, roll the block over on its edges a few times. This will make the sandpaper fold around the block a bit and prevent the corners and edges of the sandpaper from digging into the surface you are sanding.
There are many very nice commercially available sanding blocks that fit the criteria I have described. Great Planes has an extensive line of Easy-Touch extruded-aluminum sanding blocks to which sandpaper can be attached with contact cement.
I suggest getting several Easy-Touch blocks in several lengths. The blocks range in size from 11 to 44 inches. I use the 11-inch variety most of the time, but I find the long blocks to be extremely useful in sanding the surface of the sheeting on a foam-core wing.
You should purchase enough sanding blocks that you have several grits of sandpaper available at any given time. I like a full range of grits between 180 and 320 for general building purposes.
After you have worn out the sandpaper, lay the block in a shallow pan filled with a small amount of mineral spirits. (Do this outside!) The sandpaper will delaminate fairly quickly, and then the block can be wiped clean and resurfaced. Keep your sanding blocks fresh and sharp by changing the sandpaper often!
Perma-Grit makes another useful sanding block. This company has a wide range of sanding and cutting tools, and although they are fairly expensive they last virtually forever!
Tiny bits of tungsten are welded onto a metal plate, and that forms the sanding surface. Perma-Grit has a line of sanding blocks that are extruded rectangles with different grits of tungsten on each side.
The advantage of the Perma-Grit sanding block is that it can be set on its side with the sanding surface 90° to your building board. This allows you to square up pieces almost perfectly with little effort.
After you have sanded an area—especially where two parts meet—run your finger over the seam. If you can feel that seam, you will see it after the model is finished.
Sanding an area where two parts of dissimilar densities are joined is even more of a challenge because the softer material will sand more easily and quickly than the harder material will. Ridges, bumps, and uneven curves are often the result.
You will need to learn how to control your sanding blocks to work the harder material against the soft without removing too much of the latter. For this reason you should never sand without using a block of some sort. Uneven hand pressure on the back of a piece of otherwise unsupported sandpaper will yield ripples and low spots.
The subject of sanding blocks and knives and the techniques required to master them completely would take many pages to cover. In a future issue there will be a comprehensive article about cutting and sanding as part of a series about model building.
Finishing the fuselage edges
Back to the fuselage. Carve most of the excess 1/16-inch plywood from the doublers using the #11 blade knife. Try to get within 1/32 inch of the balsa fuselage core piece with the carving process. Finish by sanding the edge flush against a Perma-Grit sanding bar laid on its side or carefully sand the edge with a normal block, checking often to ensure that you are not angling the edge.
Sand the entire edge of the balsa fuselage so it is smooth and properly contoured from a profile view.
Before the top and bottom edges of the fuselage can be rounded, you must scribe a centerline on the edges. I suggest that you do this with a #2 pencil. If you use a ball-point pen for this job, be sure to sand off all the ink. Any ink left on the balsa after sanding could bleed through and ruin an otherwise perfect paint job later.
Sand the edges of the balsa fuselage core to a pleasing round shape. Do not round off the area where the plywood doublers are attached. You can break that edge slightly with a sanding block, but it should not be fully rounded.
At the rear end of the plywood doublers there will be a drop-off to the surface of the balsa fuselage core piece. You can add balsa "ramps" to fair this step in smoothly if you like.
Decide which type of landing gear you are going to use and drill the appropriate holes in the doublers in the correct spots. The Hole Shot can be built with normal two-wheel landing gear or with a single strut for a one-wheel type. The one-wheel gear is lighter and simpler, but the choice is yours.
Wow, we're out of space already and all we've done is make the fuselage! The idea behind this series is to learn to build using proper techniques, tools, and materials. It will take a while to complete this project, but by then you should be armed with impressive building skills and have a shop full of great tools and know how to use them. We are on our way.
I can only submit three photos for use in this column each time. I hope the written descriptions of the building process and the other things I cover will be clear enough.
I am taking many pictures as I proceed with this project and will gladly e-mail a set of low-resolution photo files to anyone who requests them as we go. Simply send a request to me at the e-mail address in the headline of this column.
Til next time, Fly Stunt! MA
Sources
- Great Planes Model Manufacturing
(217) 398-3630 www.greatplanes.com
- Perma-Grit Tools
44 (0) 1529 455 034 www.permagrit.com/hobby.php
Transcribed from original scans by AI. Minor OCR errors may remain.
