The plan build article by Peter Miller - 31/1/11
The Tipsy Junior was designed by one of Belgium’s leading aviation pioneers, Ernest Tips, who was both the managing director of Avions Fairey - the Belgian subsidiary of the British marque - and the man behind the famous Tipsy Nipper.
The first Junior, which carried the registration OO-TIT, was powered by a Mikron engine and made its maiden flight at Gosselies in 1946. Two years later, ‘TIT was flown to England and was demonstrated at White Waltham, along with her JAP-powered sibling, OO-ULA. ‘ULA was sold to Fairey and remained in England, where the company subsequently fitted her with a Mikron engine and re-registered her as G-AMVP.
Fairey’s original intention had been to both manufacture the Junior and sell plans to home builders, much as France’s Turbulent was later produced by factories as well as individuals. Unlike Druine, however, Fairey later decided that any commercial benefits from the sale of plans were far outweighed by the risk to its reputation if a home-built Junior were to be involved in an accident.
During her life, ‘VP enjoyed a brief moment of glory when she logged a landing on the Ark Royal in ‘57, but damage sustained during a forced landing in ‘93 put an end to her flying career. ‘TIT, the original aircraft, was also written-off in a landing accident, but fortunately for posterity, construction of Tips’ third Junior was never actually completed, and the airframe has survived to the present day.
A SIMPLE SCALE BUILD
Although the Nipper is the better known aircraft, the Tipsy Junior is actually the more popular subject for modellers, possibly because its shape is simple to build but also a little unusual. When I drew up my plans, I opted for 1/6 scale, reasoning that the resulting model would be ideally suited to .19 or .25 two-stroke and .26 to .30 four-stroke engines, and its 44” wingspan should fit into most modellers’ cars.
You’ll find that the majority of the model’s construction is quite simple and conventional, making it a good subject for someone attempting their first scale build, or looking for their first low-wing aircraft.
There are a couple of design points worth mentioning, however, one of which is the engine mounting - a set-up that goes back to my control-line days. I’ve used engine bearers to support not only the engine but also the front part of that long cowling. In this way, you need only detach the silencer in order to be able to remove the whole cowl, which then gives you full access to the tank and engine. The only other area of construction that may strike you as different is the lower rear fuselage, but you’ll find that this is actually quite straightforward. Hopefully the photos and drawings should make everything clear.
You’ll find it helpful to cut yourself a complete kit of fuselage parts before starting assembly, as you’ll actually be working on two separate units to begin with, and will need to have quite a number of parts to hand.
Start off by gluing the 1/32” ply doublers to the sides and then, working over the plan, assemble the sides and formers F6 - F10. While they’re drying, make a start on the front of the fuselage by assembling the engine bearers and F1 - F3. It’s vital that you to get this assembly true, mind, or you’ll throw the thrust line out and the rest of the fuselage will end up a distorted mess.
Once the front assembly’s dry, you can fit the tank box. I used a 4oz SLEC tank, having found that nothing else would fit unless I was willing to cut out the rear of the tank bay in F2. That, however, would have displaced the servos which I’d planned to position there. Of course, if you’re going to use a four-stroke engine in your Junior, opening up the rear of the tank box may prove unavoidable as you might have to move the tank backwards so as to clear the carburettor.
Returning to the rear fuselage, add formers F4 and F5, then, while still working over the plan, join the front bearer assembly to the rear fuselage, making certain that the bearers line up with the top of the fuselage sides. Once that’s done, you can build some strength into the framework by shaping and fitting pieces of triangular stock into the corners.
Now’s the time to fit the scrap block in front of F10 ready to receive the hinge and the ply tail wheel mount, and to add the cockpit floor. You can also fit the rolled sheet turtle deck in front of the cockpit at this point.
The next steps are straightforward, so we’ll run through them quickly:
1. Fit and secure the control snakes - it’ll be harder to do once the stringers are in place.
2. Fit the top stringers (remembering to cut the rebates for the sheet first) and add the sheeting between F4 and F5.
3. Fit F6a, F6b and F6c (which may need some trimming) and add the bottom stringers followed by the sheeting between F6a and F6c. Don’t worry about the wing fairings just now - we’ll tackle them later.
4. Fit the 1/4” ply wing locating plate together with its T-nut, and then fit the 1/2” sheet under F1 and F2.
5. Fit the 1/4” sheet tailplane mounts, noting that these aren’t parallel but are carefully designed to give the tailplane a whole 2° of positive incidence.
BEARERS AND COWL
Using brass or tinplate, cut two strips and drill them to match the engine mounting holes. After positioning the engine on the bearers, place the nuts over the two strips of tin and bolt the engine down tightly. Now solder the nuts to the plates, taking care not to solder the bolts to the nuts! Finally, screw the plates to the bearers with small screws. Of course, Those with the skill and equipment might prefer to drill and tap 1/8” dural plates instead of soldering nuts to brass or tin plates.
The top of the cowl is fabricated from laminations of 1/2” and 1/4” sheet as shown, and glued into place permanently, leaving the foremost 1/16” of the bearers proud of the sheeting so that you’ve got something onto which you can glue the front of the cowl. If you’re going to use a two-stroke engine, you’ll probably need to spend some time trimming and hollowing out the front of the cowl so as to clear the carb’. It’s also worth mentioning here that I found the scale air intake too small to cool the engine in hot weather. In the interests of engine longevity, then, you may want to sacrifice scale accuracy and make the intake bigger.
The detachable part of the cowl, meanwhile, is built from the two formers, the sides, and the 1/2” sheet underside, with triangular stock added in the corners at the bottom. I also fitted large section triangular stock behind the cylinder to deflect cooling air round the back. Lastly, after you’ve cut out all the necessary holes and installed the throttle runs, fit some pieces of scrap balsa to C1 and F1 to provide locating blocks for the cowl.
The cowl itself is held in place using 1/16” ply plates, located on the inner face, and screws that run through thin metal strips and into 1/8” Liteply discs on the outer face (see plan section X-X for clarity).
Since the wing fairings have to be built with the wing in situ, we’d better take a look at cutting some ribs. Incidentally, as we’ve already installed the wing retaining plate I can recommend a brilliant method of transferring the bolt location to the wing assembly, when it’s finally done! How? Well, using a short length of spare bolt, sharpen the end with a pencil sharpener and then screw the bolt into the nut until the point just protrudes outside the fuselage. Then, offer up the wing and, by pressing it down into place, use the point of the bolt to mark it just where the hole should be.
The rear parts of the fairings are formed by F6a, while the bottom parts are cut from 1/32” ply, and then glued-up and held in place on the fuselage by the wing. Remember, covering the wing with a thin polythene sheet while you do this will help prevent it being inadvertently glued to the fuselage.
Once the glue has dried, remove the wing and fit the tops of the fairings, which are made from 1/64” ply. Map pins are handy for holding the ply pieces to F6a while clothes pegs will clamp them to the bottom parts of the fairings.
The wings themselves are very easy to build because they’re flat on the bottom with no taper. Start by cutting out all the ribs and laminating them as shown on the plan, noting that the slots in R1 form a hole for the wing dowel when the two wings are joined. The trailing edges, meanwhile, are a non-standard shape and have to be formed from 3/8” sheet with a razor plane. Cut the rib slots carefully as shown. The leading edge strips are then made from 1/8” sheet, and the undercarriage mounts from 1/4” ply.
Begin assembling the wings by pinning down the main spar and raising it with a scrap of 1/16” sheet; the rear spar isn’t raised and so is pinned flat to the board.
Next, pin down all the ribs. R1s must be angled to allow for the 1” dihedral under each tip, and you’ll find that it helps to support the R1 and R2 ribs using 1/16” scrap while you do this. Fit the 1/4” sheet infill above the rear spar at the aileron bay, and then add the aileron leading edge which is also made from 1/4” sheet.
Again, the following steps are straightforward if labour intensive, so I’ll save you a little time by talking you through them quickly:
1. Add the aileron ribs taking care not to separate the trailing edge at this stage.
2. Fit the various 1/2” sheet pieces to take the aileron hinges, and add the ply plate for the control horn.
3. Fit the 1/8” sheet leading edge and the various gussets in the corners, as shown.
4. Fit the 1/16” sheet webs to the front of the main spar.
5. Fit the aileron bellcranks and pushrods so that the ‘rods just overlap in the middle. It’s easier to do this job now rather than trying to thread one long pushrod down the whole wing later on. It also makes adjustment easier.
JOINING AND SHEETING
Lift the wing from the board and sand the roots flat. The fit between the two needs to be perfect - this is actually more important than getting the dihedral angle exact - and then shape the leading edges to match the ribs.
To join the wing panels, pin one of them to the board and, without using any glue at this stage, check that the dihedral brace brings the other into perfect alignment with it; use scrap material to prop up the far wing tip and ensure perfect contact. Once you’re happy that everything fits, glue the assembly together using aliphatic resin and leave it to set overnight.
After fitting the hardwood blocks and triangular reinforcement to the undercarriage mounts, lay the 1/8” sheet at the rear of the servo bay, and the 1/8” Liteply floor. When you come to sheet the leading edge of the wing, take great care not to build a warp into the structure: it’s very easy to do if you’re not careful.
Once the sheeting is dry, trim it flush with the leading edge and add the 1/8” leading edge cap strip, which will need to be planed and sanded to shape.
The centre-section sheet comes next, noting that it sits either side of the rear spar, followed by the tips which I made up from laminations of very soft 1/2” sheet and then hollowed out. Incidentally, the 1/16” ply plate that fits under the wing is intended to spread the load of the wing fixing bolt.
You can now fit aileron horns temporarily and make up the aileron pushrods. Once these are correct, cover the bottom of the bellcrank bay with 1/64” ply which is the neatest way of providing the slots for the pushrod exits. The ailerons are removed again for the time being.
The last job on the wing prior to covering is to trim away the leading edge sheet so that you can put the undercarriage wires in position with their SLEC saddle clamps seated securely against the ply. You’ll find that 21/2” wheels give an acceptably scale-ish appearance.
The tailplane is cut from medium to soft 1/4” sheet, and the elevators linked by a 14swg wire joiner after they’ve been covered. The fin is constructed using 1/2” square balsa with 3/32” sheet ribs, and then sanded to give the correct section and also to blend with the rudder. Built on a 1/8” sheet core, the rudder uses 3/16 x 1/2” section balsa and 3/32” ribs on either side. It too needs to sanded to the cross-section shown. By the way, I used Kavan cyano’ hinges for the rudder and elevator.
I’d suggest you cover the tail surfaces before assembly - a process that begins by locating the tailplane on the seats in the fuselage, followed by the fin, whose leading edge goes down into the fuselage and sits against F9. Small blocks on each side of the fin fair it in to the top of F-9.
Colour schemes are a matter of personal taste, of course, but in terms of materials I used a combination of Solarfilm and Solarfilm Supershrink polyester, while the letters were cut from Solartrim. Normally I ask Sigma Signwriting to make any lettering, but this was so easy I did it myself.
The cockpit is simply painted, and furnished with one of J. Perkins 1/7 scale pilots, which is close enough to 1/6 scale for government work.
I fitted Supertec Mini L servos which are just about the only ones that will fit in the locations shown on the plan between the cockpit floor and top of the wing. If you prefer, however, you can use standard servos housed just in front of the instrument panel. As far as the ailerons go, though, there’s enough room to fit a standard size servo. The receiver was positioned aft of the Mini L servos with the battery located just behind F2.
The control surfaces were set with the following throws:
Ailerons - 5/8” each way
Elevator - 3/8 each way
Rudder - 11/4” each way
After adding about 3oz of lead under the cowl, the Junior’s all-up weight was 591/2oz, giving a wing loading of 18oz / sq. ft. You’ll notice that I haven’t yet mentioned which engine I used to pull all this around the sky, and that’s because... well, you’ll see.
For the initial test flights the Junior was fitted with the Fuji 19. I’d bought this second-hand and muttered furiously when I found that it was low on compression. The power was adequate for take-offs from concrete runways, though, even if the first attempts were made a little hairy by a crosswind stirred into turbulence by some mounds of earth. Once clear of the choppiness, however, the model flew very well - or at least it did until the Fuji overheated prompting an ailing plug seal to blow! Still, at least I’d discovered what was causing that low compression.
Much like Fairey and OO-ULA, I then set about installing a new engine, in this case using a Magnum GP 25, and though long grass at the strip meant hand-launching the model, the Junior proved quite at home in gusty 12 - 20mph winds. Fitted with a 9 x 4” prop, she climbed away perfectly, and flew loops that were smooth and round. My rolls, I must admit, were very barrely: I just couldn’t get them axial at all, and suspect that this may be down to the effect of scale incidences. The model was also reluctant to flick roll, probably owing to the wing’s thick, blunt profile.
Slow speed handling, on the other hand, was very good, with the model showing no tendency to drop a wing, and producing a smooth, stable glide, even in gusty wind conditions.
All in all, the Junior makes a pleasant little model that flies nicely with no vices, and will even manage basic aerobatics given a little care.
Name: Tipsy Junior
Model type: Semi-scale light aircraft
Designer: Peter Miller
Fuselage length: 36.5''
Wing area: 462 sq. in.
All-up weight: 59.5oz
Wing loading: 18oz / sq. ft.
Rec’d engine range: .19 - .25 two-stroke,
.26 - .30 four-stroke
Control functions: Aileron, elevator, throttle and rudder
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