BuiltWithNOF

MIKE ROACH’S MODEL AIRCRAFT

SAUNDERS-ROE PRINCESS

About a decade ago Bob Wealthy (of Solent Sky Museum and B-N Islander fame) gave me a set of works drawings of the aeroplane and mentioned the George Dexter PSS model, which had flown successfully but was then hanging in a museum in the Isle of Wight. At that time I was making 36” span biplanes for speed 400 motors, and it took the next ten years for me to gain experience of large light structures, courtesy of Canadian-based designer Ivan Pettigrew, with a 100” span Short “Golden Hind” flying boat proving eventually that three cells and four small motors was more than enough for scale flight off water. The water in question is Longham Reservoir, north of Bournemouth, the Club’s “own” site for electric-powered water flying.

My Princess’s structure is entirely conventional and in the Pettigrew mode; a balsa ladder frame and formers for the fuselage, sheeted all over and the hull glassed. The tailplane and fin are removable for storage and transport, leaving quite a few cubic feet of air enclosed by a pound or so of wood and covering. The wing is E270 at 14% thickness: fat enough to look like the real thing, but with a model’s airfoil section. One big advantage of a thick wing is that it can be built light. Mine has a 2mm hard balsa vertical spar with 3mm square hardwood top and bottom. Most of the ribs are 6mm depron with only the load-bearing ones from balsa or thin ply. The tips outboard of the motors are detachable and contain the aileron and float retract servos. The latter are noisy worm drive units and are the only thing that has failed, not really being man enough for the job.  A rebuild of the wing-tips is pending. In other respects the wing is conventional, with huge flaps on the centre section. These are completely unnecessary as the model will fly slowly enough to alight on a duck-pond, but they do look very good when fully extended, with floats down, on the approach to land.

After assembling the wing and fuselage in the car park, the two components can be carried the quarter of a mile to our favourite flying point, where they are bolted together and two parallel-wired 3-cell 4000nAh batteries inserted. For the first flights I had great difficulty getting the model to track straight on the water and had to abort many attempts before finally getting into the air, when she became a complete pussy-cat and flew perfectly, looking graceful, at ease in the air and very much like the real thing back in the 1950s.  Experiments showed that moving the CG back an inch was enough to lift that long nose out of the water during take-off and hand-brake turns are a thing of the past.

There were two major events early on in the model’s life: first was a series of flights for Bob, who brought some Saunders-Roe friends with him, when I was able to demonstrate the full flight envelope and bring the odd tear to the odd eye. It was a breezy morning and this may have had something to do with it. The second was when I ran out of power on a downwind leg and made the mistake of trying to turn back – a stall and a smack into the water was my lesson that day. Amazingly the only casualty was a wing joiner blade, which snapped in half and prevented any structural damage. A few days later she was flying again.

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Princess-0141

Wingspan: 128”, Height: 29”, Length: 77.5”
Wing area about: 13.3 sq ft, wing at 3 degrees to fuselage datum, thrust-line parallel with datum.
Flying weight: 10 lbs, Wing loading: about 12 oz/sq ft
Balance point: 30% root chord seems to work well. The sweep-back helps.

Controls:
Aileron: servo in each outer wing section, Elevator: servo in each section, Rudder: servo in fin.
Floats: electric retract in each wing tip.

Motors: one Robotbirds basic 40A speed controller per motor installed under the centre section.
Motor type: (all on 9 x 6” APCE props, all motors from the Robotbirds Value Outrunners range). Props rotate opposite hand port and starboard.
Inner four: 2836/1120kV
Outer two: 2826/1000kV

Power: one 5000 or two 4000mAh 3S Li Poly batteries, Power consumption: between 400 and 500 mA per minute.

RX: Orange 7 channel, TX: Spektrum DX7e with mixed rudder and motors on full flap

Materials:
Balsa from SLEC:
1/16th x 4 x 36. At the very least 25 sheets; 3/32” x 3 x 36 five; 1/8th x 3 x 36, one; ” x 3 x 36 one; ” square strip 24. 6mm Depron (most wing ribs) one sheet

Covering: Solartex over glasscloth on lower hull, China-Kote aluminium and Super Oracover white. Variously Deluxe Models Foam Armour, Sand n’Seal, Eze Kote and Model Lite filler. Z Poxy 20 minute epoxy and Perfect Paints sanding sealer.

Markings: vinyl RAF markings and lettering by Tim Calvert (tim@modelmarkings.co.uk) Dry transfer lettering and badges by the builder. Markings were designed for an alternative history where the RAF ferried the three prototypes to Thorney Island and outfitted them for Transport Command.

Glues: one full bottle of Titebond II, some 20 minute epoxy, as little cyano as I could get away with.

Total costs about 400 (OK, more than 400)

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