by Bill Reynolds
Modern design with a hint of nostalgia
When I first saw this plan, I thought, 'now this is a nice little aeroplane', and the more you look at it the greater number of variations you can come up with. For instance, as it is, a 30's style sportster, - fit a pair of spats and lower the windscreen line for a Thompson Trophy racer, - remove the headrest, lower the windscreen to almost horizontal, fit floats, and we have a Schneider Trophy seaplane, - lift the rear turtle deck high enough to fit a blown canopy and we have a modern sports aerobatic machine, - the combinations are almost endless and I predict we will be seeing quite a number of these neat little machines in all the above guises, and some I haven't even thought of yet!. Doubtless you want to know how it flies before you pass judgment or decide to start cutting up your valuable stock of balsa and ply. So here it is.
YES, IT FLIES!!!! After a very long wait (over four months) all three things came together, these being, a perfect weather day, a day clear of work responsibilities and me running out of excuses.
So off to the club field on an absolutely perfect morning. First up, a couple of quick flights with the old Hustler to loosen up the thumbs, and then, assemble the Roaring 40, double check everything I could think of including a range check of the radio. So far, all OK. Finally I fired up the HP 40 Gold Cup, adjusted the needle for slightly rich, readjusted the mid range, and about this time, the voice of a club member from close by summed it all up with 'are you going to fly the @#&* thing or just play with it!'
Onto the strip, try one ground handling run, face into the wind, and away. The tail lifts after a fairly short run and she tracks as straight as you could wish. Acceleration is good and lift off takes about 30 meters unless you yank it off. Minimal trim adjustment made this maiden flight almost an anticlimax, the stall is fairly gentle and straight ahead, the dead stick glide is smooth and landings nice and easy. I haven't tried any aerobatics yet but a word of warning - if you are looking for nice scale-like manoeuvres, keep your control surface movements reasonably small as this aircraft can be very sensitive to over-controlling. I am very happy with the result of my labours. I have a semi scale aircraft which looks good, is easy to handle, flies without nail biting and should give me many enjoyable and fun filled flights.
BUILDING THE MODEL
Now down to the serious business of making a room full of sanding dust and shavings. Like most scratch builders these days I cut as comprehensive a kit of parts as I can glean from the plan before I start any assembly work. This seems to make the job flow more smoothly when I don't have to stop and cut parts for every operation and it also allows a more complete check of parts fit before you open the glue pot.
A conventional aircraft consists of three main components:- fuselage, wings, and tail section. If you start by constructing the tailplane, construction is nice and simple, just assemble all the outline parts you have already cut, add a few spacers and braces as per the plan, sand the edges up and that's it. Follow this with the fin, sand up the rudder and elevators and the whole tail is ready for covering. If you now look back to the start of this paragraph you will suddenly realise that the job must be one third complete. At least I try to con myself this way.
Start by fabricating two sides (left and right) with doublers, 3mm x 6.5mm spruce top longerons, and 9.5mm tri-stock lower edge corner stiffeners. Lay one side on your perfectly flat building surface, inside up, and glue in formers F2, F3 and F4 all nice and neat and precisely square with the side. Then add the other side and clamp firmly till completely dry. If you fit the cockpit floor at this stage it will help to maintain this 'squareness'. Now the basic structure goes into my fuselage jig. I usually glue stiffeners, about 3mm x 6.5mm, across each of the balsa formers to prevent them splitting when clamping pressure is applied whilst pulling the sides in to the tail end. This is only necessary of course if the formers are cut with grain running vertically. At this stage, ascertain the position of the engine mount on the firewall, drill and fit blind nuts, and temporarily position the motor so as to determine the run of the throttle cable. During this operation decide whether to use a wedge behind the motor mount for the required side thrust or to offset the firewall. Either way you will have fixed the mount off centre on the firewall so that the propeller shaft and spinner back plate will emerge from the cowl front on the centre line. You can now drill F2 & F3 with a normal length drill bit to pass the cable outer or pushrod. Now pull in the nose and fix the firewall in with triangle gussets and a good serve of epoxy. Pull in the tail end adding F5, F6 and F7 and the tail post with the slot for the ply tailskid pre-cut. When all this has set, add the rear deck stringers.
This is a good time to finalise fuel tank position and height and install supports for the tank floor. Also this is the time to determine fuel line runs, and to install the tank and lines with appropriate foam packing as the area is not accessible later. The forward deck can now be planked and finished. On to the spinner back plate, tack glue a piece of 1.5mm sheet as a spacer, then a 1.5mm or 2mm nose ring followed by the cowl front block. Assemble this onto your motor with one of those old broken propellers (you always wondered why you kept them, now you know). Mount the assembly in the aircraft, having carefully closed off all the openings in the motor to avoid ingestion of dust and other nasties. Fill in between the firewall and the front block with 9.5mm sheet all glued together but not to the firewall. Before moving anything run a pencil line round the rear face of the cowl sheets on the outline of the fuselage at the firewall, then remove the spinner and you have a great monstrosity which looks exactly like what it is - a rectangular box with a spinner attached. Pull off the spinner and glue 9.5 tri-stock in the internal corners of the box and then take to it with a knife, razor plane and sanding block. In almost no time you will have a room full of chips and dust. Oh yes, you should also have a nicely contoured engine cowling, that is if you remembered when to stop.
Looking at the other end, the fin to tailplane fillets are easily made by tacking scrap pieces of 9.5mm sheet in the position the tail assembly will take, filling in the corners with balsa blocks and sanding them to match the rear fuselage contour. Break the whole mess apart, and bingo, instant fairings which fit like they were grown there.
Now let's flip the fuselage over and look at the bottom. I remount it in the jig, which not only holds it straight and square (although it shouldn't move now) but it also leaves both hands free.
Firmly epoxy the undercarriage mounting plate and supporting gussets and F2A wing dowel stiffener in position (F2A could be fixed to front face of F2 before fuselage assembly). Put the fuselage aside at this stage, as we need the wing to line everything up before finishing.
After the usual taping of the wing plan onto your building board and protecting it with old solarfilm backing sheet, you will see that this item is to built in 3 sections: left and right panels and centre section.
Place the lower main spar in its correct position over the plan and trial fit a few ribs. Now cut a strip of 6.5mm balsa and pin it onto the board parallel to the spar and spaced to allow the ribs to sit straight and level with each other. Accurately measure the space between ribs and strip a sheet of 1.5mm balsa to this width, then cut off to a length equal to the depth of each rib as many shear webs as there are rib bays. Starting from the tip end, glue in the first full depth rib which will be at the outboard end of the aileron bay. Follow this with another rib and repeat the process to complete the wing panel but leaving the last inboard bay free for later installation of the dihedral brace. At this stage you have not cut the fronts off any ribs for dihedral braces, this will come later. Now, carefully lay in and fix the top spar. Glue in the shear webbing onto the spars. This is a major contributor to the overall strength of the whole wing structure. Fit the leading edge and the aileron spar and then glue up and fit the tip assembly. You can now add the top leading edge sheeting.
I would suggest you do not try to carry the leading edge sheet through to the tip. I found it impossible to get a smooth curve in this area without splitting the sheet. It is probably better to stop at the last rib and use a separate piece to form the whole tip sheet. Remove this panel from the board and bring the other two to the same stage of being complete on top.
Later has arrived!! Now is the time to run the three panels over and carefully cut slots for the dihedral braces. Here is where you can use another 'good serve' of epoxy as these two items sort of hold the wing together through those impossible manoeuvres which I know are bound to happen sometimes. Use slow setting epoxy for this part as it gives you plenty of time to make absolutely sure of the correct dihedral and that both outer panels are accurately aligned both with the centre section and with each other.
I fabricate the ailerons simply by laying each wing panel on the board and shaping the aileron out of 12.5mm balsa in the bay provided by the wing frame. The wing can now be completed by installing your chosen aileron control system and then adding the bottom sheeting. Now trial fit the ailerons with their hinging, sand the whole shebang and we are ready for covering.
Fit the complete wing to the fuselage and adjust the wing saddle if necessary to give the correct rigging angles. The wing bolts can now be drilled and tapped in their final position. Install the elevator and rudder pushrods of your choice and finish sheeting the fuselage bottom. The wing root fillets are not nearly as difficult as they first appear, just trace the plan and side views onto soft balsa block, cut these outlines, check the fit against the fuselage side and the wing top surface, and when you're happy, gouge, file and sand. Glue the fillets to the fuselage sides while the wing is still in position to ensure best fit. A good clean up and sand and this is ready for covering too.
This was experimental time for me. I had already decided on a 30's semi scale look so a fabric finish was essential. Instead of good old silk, dope and paint I took the plunge and tried Solartex. The colour chosen is 'Linen', as it looks about right and goes well with the green spinner giving enough contrast for trim lines and lettering. The Solartex went on much easier than I had anticipated and I am very happy with the overall appearance. Should you decide to use this material, buy two rolls together and check the batch numbers as there can be slight colour variations. The cowl should not have a fabric look so I called my usual paint supplier who was able to computer match the Solartex and for trim also matched the spinner colour. When all was complete a seal coat of automotive clear was sprayed on just for security. The undercarriage was bent up from sheet aluminium as detailed on the drawing and a stiffener/axle unit added as can be seen from the photos. A pair of 3" Kraft-Hayes classic style wheels completes the whole pretty picture.
Install the radio gear in your usual neat and accurate fashion, with the battery pack at the front of the access area, followed then by the receiver and servos. The cockpit floor, just behind the windscreen is a good spot for the switch, make sure you can get to it, and, Oh yes, there will be a pilot added to my aircraft later, but he wasn't game to risk the test flights, especially with me in charge! Balance point doesn't seem to be too critical but I found a nice smooth handling aircraft resulted with it just on or very slightly ahead of the wing spar.
Good luck. This is a fine little model. Take your time, build straight and you will have a good one. Maybe I will see some of those variations I mentioned at the beginning of this article.
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