FREE FLIGHT SPORT and SCALE
Fernando Ramos, 19361 Mesa Dr., Villa Park CA 92861; E-mail: [email protected]
I am a died-in-the-wool plan-builder; about 95% of my building is from plans only. Once in a while, I will succumb to buying a kit that promises wonderful things.
Some time ago, Guillow came out with a large Grumman Hellcat. For some reason, this airplane has always caught my fancy, plus any model of this airplane is a wonderful flier.
I recently got the urge to build this kit; the fly in the ointment, so to speak, is that all of the Guillow kits use the half-shell method for the fuselage (building the left side of the fuselage on the plan, gluing the bulkheads onto an upper and lower plane profile. A side keel is then added. When this structure is dry, it is removed from the plan, and the right-side bulkheads are glued to the left, followed by all of the stringers).
The problem I have always had, is that trying to keep the bulkheads perfectly straight or aligned has been a pain. So about 25 years ago, I introduced a fixture that makes this type of construction quite easy. I thought that a review of this simple device is in order.
The idea is to hold all of the bulkheads with the proper spacing, while also being perfectly vertical. This allows the entire upper half of the fuselage to be complexly framed. When this structure has dried, it is removed from the fixture, and the lower half can be completed. The end result is that you have an accurately built fuselage with minimum effort.
The fixture can be made from almost any kind of wood. If plywood is used, I would choose 1/4. Balsa is also a good choice. (When I was teaching, I would get the shop teacher to plane pine down to 1/4 inch thickness.) I had a large stock of 1/4 balsa, so I opted to use it for this project.
The base of the fixture has to be slightly longer than the fuselage, and the width just a bit wider than the widest bulkhead of the model. The height is determined by using the side view of the model. The side keel, which can be found on the side view of the plan about midway of the model, is straight from the front bulkhead to the rear bulkhead. Measure from this side keel, using the deepest bulkhead, and add just a bit to this dimension; this will be the height of the fixture. (From here on, I will call these parts that hold the bulkheads "risers.")
I start by ripping the balsa to the proper width. I then draw a
FF Sport & Scale
side notch of the bulkheads. Each piece is identical.
I use the plan side view to determine the bulkhead locations. Using a pencil and a square, I draw across the base where each bulkhead riser will go. I prefer a pencil for this job, in case I make an error; I can erase the pencil mark quite easily.
Glue each riser to the base using the pencil line for reference, making certain that the centerline of each riser is aligned with the centerline of the base. Also make certain that the risers are vertical. (Some designs might have bulkheads that are not vertical; the risers will have to be angled accordingly). The Hellihead at the front bulkhead angled slightly downward.
When all of the risers have been attached to the base and have dried, it is time to mount the bulkheads. You are ready to punch out the bulkheads from the balsa sheet from the kit. I have yet to be able to punch out these parts without great difficulty, but here is a hint that will alleviate the problem:
Block-sand the back side of the entire sheet of balsa with fairly coarse (220-grit) sandpaper. Note that you cannot see any of the bulkheads from the back side of the balsa sheet. Before long, you will see the parts coming through. At this point, you will be able to punch out the parts with little effort.
Glue the left and right halves of the bulkheads together. Pin mine down while the glue dries, so that they will remain flat. A photo shows how each bulkhead is mounted onto the risers. Note that each bulkhead has four elongated notches: top, bottom, and left and right sides. You will use the two side notches and the bottom notch to align the bulkhead onto the riser. The two side notches should line up with the top of the riser and the bottom notch should be aligned with the centerline of the riser. This gives three points of alignment, which is more than adequate.
I prefer to start at the back of the fixture, so that I do not have to look over bulkheads. I feel that this makes the task quite a bit easier to do.
What is the best way to temporarily mount the bulkheads to the risers? Years ago, I used rubber cement, which made removal easy. However, I have found that rubber cement doesn't work like it used to. (Have you noticed how almost any kind of glue sticks to waxed paper?)
I now use medium cyanoacrylate (CyA) glue, using just a small dot under each piece. This is more than adequate to hold them in place while completing the upper half of the model. When it is time to remove the structure from the fixture, all you have to do is use a razor blade to pop each side loose.
Here's something you might want to consider:
Those of you who are familiar with the half-shell method know that when it comes time to put the stringers into the notches, the alignment is anything but straight. The stringers go up and down, requiring opening of the notches so that the stringers will flow straight as they should.
One technique that I have used quite often is to sand 1/16 from each bulkhead, except those at the front and rear. That way, when it is time to glue the stringers in place, they just lay on top of the bulkheads, instead of into notches. It's easier to align each stringer from front to back, and you will not have to scallop the bulkheads between stringers so that only the bulkheads will show after covering.
After all of the bulkheads have been temporarily attached to the bulkheads, the two side keels are positioned into the side notches and flush with the top of the risers. I used medium CyA, and very sparingly, to glue the two keels into the bulkheads. If you are not careful here, you will play havoc trying to remove the structure from the fixture.
Next comes the upper keel (often called the "crutch"), to be glued into the upper notches. By now, the fuselage is taking on the appearance of an airplane.
The stringers are now glued into place, alternating from side to side to avoid any tendency of the fuselage to pull to one side or the other. This is mostly true if you are not using a fixture.
When this structure is dry, it can be removed from the fixture, but first you may want to consider that this type of construction requires sheeting, gluing between bulkheads and stringers. It is a lot easier to do it while the fuselage is still in the fixture.
After the fuselage has been removed from the fixture, you can glue the lower keel in place and glue the remainder of the stringers onto the fuselage.
The small effort needed to build the fixture is certainly worth the time, as you will produce an accurately built fuselage.
For those of you who like to use the half-shell type of construction, are scratch-builders, and want a superlight fuselage, read on.
Instead of using the typical balsa bulkhead, you can undercut each bulkhead template by 1/16. (Hint: After making a photocopy of the templates, I draw the 1/16 undersize on only one half of the bulkhead. I crease the template down the middle, and cut on the undercut line. When the template is unfolded, you will have a template with both halves the same.) Glue the paper template onto some heavy cardboard, then laminate 1/32 x 1/16 or 3/32 basswood around this template. Don't forget to wax the template so that the lamination will not be glued to it.
Before removing the lamination from the template, sand the "bulge" where the lamination ends, and mark where the side and bottom keels are located. Naturally, these will be used to place them correctly on the fixture. The rest of the construction is done as previously mentioned. Again, you will have an accurately and very lightly built fuselage.
Dave Diels of Diels Engineering, Inc. (Box 263, Amherst OH 44001), who for years has been kitting some really fine Rubber Flying Scale models, has two new items: the Brewster Buffalo and the Japanese Ki-43. Both kits provide enough information to make the variants, and the plans are very informative and complete. For those who enjoy information sheets that help about construction along with the model, these kits are a real treat.
Ever since Dave started this business, I have always felt that the kits provided were worth the price of the kit, and the quality of the wood is always first-rate. This is true even of the parts which are vacuum-formed canopies. The cost of the kits is less than $30. Send him a buck to get his latest listing of kits and plans. His kits will typically use the half-shell method, so you can order one of his kits and make up a fixture to build the model!
Thanks to all of you who have been sending me your club newsletters; I really enjoy reading them. This keeps me in touch with the various kinds of modeling activities. Thanks also to those of you who have taken the time to send E-mail. I do appreciate these messages. If you have some topic that you would like for me to cover, please advise and I will try my best to accommodate. MA
Transcribed from original scans by AI. Minor OCR errors may remain.
