RAY’S RANT #6 August 30, 2015
The next subject concern’s all metal airplanes, which brought about stressed skin airplanes. They differ a lot from the welded steel frame of the previous aircraft.
We have a few models that are built to replicate that particular airplanes construction. Some of the models I have built are a Topflight DC-3; P-47 Thunderbolt; as well as a Curtiss C-46 Commando. I will be using pictures of the C-46 fuselage being built so you can see how we duplicate the use of formers, stringers, and balsa planking to make the model.
We started the model by doing the top half of the model, laying out stringers to place the top formers on. Then we put in more stringers around the formers to give us a framework to plank with balsa strips. One mistake we made, is to use planks that were too wide at ¾’, so in the final sanding we were stuck with flat spots that would have sanded too much material away to get the roundness we needed. It is best to keep the width of the planking down to ½” on large models, and probably 3/8” on smaller models. The P-47 was covered differently once the formers and stringers were put in place. Patterns were given on the plans to cut out balsa sections, which we soaked in water and pinned the frame to dry. This allowed us to use bigger sections to get the fuselage covered. The DC-3 was done the same way as the P-47, only more stringers than were called for were included to keep the roundness of the airplane.
When planking, the planking is beveled on the side being glued to the first stringer, so there is a good fit. Each plank must be sanded where the glue joint will be, to get the best fit possible. This is time consuming, but better now than later, trying to fill in the bad spots. Planking has to be done on both sides as we go along, to prevent twisting of the fuselage. Once the top is completely covered, we turn the fuse over, and put in the bottom half of the formers, and add stringers, and the fuselage seat for the wing centre section. Then we cover with planking the same as the top, taking care to get a good fit for each plank. Where the planks join each other down the length, we have to stagger these joints for strength. Once fully planked, the next step is to carefully sand the fuse smooth and round so its lines are smooth. The pictures attached should help in understanding this method.
Any wood plane takes time to assemble, and we must be patient in our construction to get a nice model. Too often, we tend to rush the job to get it flying, and the results are not always satisfying. I was once challenged about using sandpaper by an older model. My method was to try and cover up the defects with paint, and that never worked. When you quit the sanding, that will determine the outcome of the finish on the model, so don’t stop until it is the way you want it. Rushing the process will only spoil the expected results. We sort of kept a log book to keep track of the number of hours we three spent on the construction. We show 300 hours, but our book work was not always done. Seeing the actual model in flight is worth all the time constructing the aircraft.
Hopefully the following pictures will help in understanding this method of construction.
Picture #1 Formers and stringers being laid out
Picture #2 planking the top section
Picture #4 Bottom planking being applied
Picture #5 Fuse planked with stab, fin and centre section fitted (note flat spots on fuse after sanding)
Picture #6 Coming together-shows size of the model
Picture #7 Finish being applied
Picture # 8 Ready for flight