Curtiss Robin (oz11824)
About this Plan
Indoor Curtiss Robin. Indoor rubber scale model.
Direct submission to Outerzone.
Update 21/12/2019: Added article, thanks to RFJ.
Quote: "Indoor Curtiss Robin, by Walter H Taylor.
Now we have scale invading the ranks of indoor flight. Good duration with realistic flight makes an excellent indoor project.
With exactly 1000 turns on the loop of 1/8 Pirelli, the Robin moved down the floor slowly and realistically, raised its tail and eased into the air in a gentle right turn. On the fifth circle of the auditorium, the craft had levelled off just under the forty foot beams and was cruising along like a microfilm duration job. This is really living! Just settle back in a chair and enjoy yourself, in the knowledge that you won't have to go tearing off through the boondocks to retrieve the errant wanderer! At just over four minutes she cruises in, power-on, touches down in a beautiful wheel landing, rolling fifteen feet before the tail skid touches and she stops - prop still ticking over.
The Curtiss Robin was chosen for this project because its simple lines allow the ultra-light construction desired, while still retaining prototype effect. Much scale detail could have been added, but was omitted to improve duration. You may choose to add such additional detail as oleos, exhaust, radiator and markings - but who can tell they're missing while looking up from forty feet below.
If you're looking for a sure fire attention-getter at your indoor flying sessions, or just want to try something a little different, we recommend the Robin. All of our flying thus far has been under a forty foot ceiling, and our duration falls between 3:30 and 4:05. With a higher ceiling available, and the proper power-prop combination, there is no reason why the Robin can't get into the seven to eight minute class.
Construction Details: While overall construction is simple, care should be exercised in selecting materials. The original model was constructed entirely from indoor quality balsa, and we used Jem Condenser paper as covering material on all compo-nents. We suggest a fast drying cement with a minimum shrinkage factor.
Fuselage: Longerons from 1/16 sq med. stock. Uprights are 1/16 sq or 1/16 x 1/32 'B' stock as indicated on plan. Build both sides at once, one over the other, and allow to dry thoroughly before removing from plan. Join the sides with top and bottom members, working from tail to nose. Add Jap tissue diagonal bracing after entire structure has been carefully sanded with 400 A.
The nose is built by cutting nose side pieces from 1/32 'C' stock, spot-gluing them to the front uprights, and after drying, covering this assembly from top to bottom with 1/32 'C' stock. When dry, cut the nose assembly off the front of fuselage, sand to finished shape, and cement a 1/32 sheet facing to the inside of each side piece to act as nose key. The thrust button is built by laminating 1/16 sheet cross-grain. Cut and sand to shape and cement to nose assembly. The nose assembly may now be drilled for shaft, and small brass washers cemented securely to both the back side of assembly and the front of thrust button to allow for thrust adjustment and to minimize 'prop wobble.' The rear hook station is cut from 1/32 med hard sheet and the .025 wire hook installed before mounting in the fuselage. Use cement sparingly and wisely, remembering that any tail heaviness will have to be compensated by ballast to the nose, all which will restrict performance.
Wing: Make a plywood rib template and cut all ribs from 1/32 'C' stock. Both leading and trailing edges are 1/16 round 'B' stock. Make a 34 sheet form the shape of wing tip and form the tips from 1/32 sq 'B' stock by soaking in hot water, pinning on form and drying in oven. (Pre-heat oven to 350 degrees and then turn oven off before placing materials in). Construct wing in one piece and add dihe-dral after removing from plan. The 1/16 x 1/32 'B' stock spar is then added, completing the wing. Tail Surfaces: Constructed entirely from 1/32 'B' stock, with tips made in the same manner as wing tips.
Propeller: The prop block should be selected from 4 to 5-1/2 lb per cubic foot stock, and should be carved in the usual indoor manner, leaving the immediate hub area somewhat thicker than on an indoor prop of equivalent size. The blades should then be thinned sufficiently to allow pitch change as power decreases.
Wheels: The large scale-like wheels enhance the appearance of the Robin, and are worth the little additional effort. Cut two center rims 1-3/4 diameter from soft 1/8 sheet and face these rims on both sides with 1/32 'C' stock. Next, draw four circles 1-1/4 in diameter on soft 1/16 sheet. Cut out and discard the circles, and proceed to sand and bevel the inside of these circles to tire shape before attempting to cut them out of the sheet. When this is done, carefully cut each of the circles out..."
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User commentsI was struck by the part in the article on carving the propellor where it says 'the blades should then be thinned sufficiently to allow pitch change as power decreases...' - it never really ocurred to me that a balsa prop blade would flex in that way, giving lower pitch at higher rpm.
SteveWMD - 22/12/2019
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