Krumpler Corsair (oz15500)

About this Plan

Krumpler Corsair. Radio control sport model. Wingspan 36 in, for Cox .020 power.

Direct submission to Outerzone.

Quote: "A 36 inch span free-flight or single channel RC sports model, the Krumpler Corsair. Guessing by the design and the radio system shown on the plan, I would assume that it dates from somewhere in the early to mid nineteen-seventies.

Although it looks vaguely like a Dornier Wal flying boat, I don't imagine that it was ever flown from water, given the lack of sponsons or tip floats.
More to follow! Dilwyn"

Update 27/8/2024: Added article, thanks to Pit.

Quote: "This 36 in span sport model, designed for the Cox 020 engine can be flown free flight or with rudder only R/C. Krumpler Corsair, by WD Binns.

The Corsair was inspired, if that is the right word, by a non-scale flying boat I had many years ago, powered by the much missed Jetex 200. This looked most appealing in the air, and its happy trick of sliding along the ground on landing instead of cartwheeling fin over nose was worth watching on its own. Also I hadn't got a flying boat. The Corsair was rule-of-thumb built off the board without any drawings, and with the addition of 1/16 incidence and 1/64 downthrust flew to perfection. She is to me, simplicity itself, so any competent modeller should need no explanation in detail.

Fuselage: The two sides are made from 3/32 square hard balsa. Steam the bottom longerons to shape; build one side over the plan using a layer of polythene sheet to stop the glue sticking to the plan. Then construct the other side on top of the first to ensure they are both exactly the same. Now cut out all of the fuselage formers. Note F2 and F3 are a sandwich of ply and balsa. Steam the sides at the front so that they take up the curve of the plan view of the fuselage.

With the sides upside down over the plan view, glue the rear ends together and hold with pegs while setting. Now add formers F4, F3 and F2. When set, remove from the plan and add F1, F4A, FX, F3A and F2A and all the cross braces.

The rudder-only control mechanism is based on the old fashioned escapement principal. This allows the whole tail unit which is held on with rubber bands to be knocked off in a rough landing. Drill a hole in the rear of the fuselage for an 18swg brass tube for the rudder control lever. Cyano the brass tube in place.

Cover the top rear end as shown with a slot to locate the tail unit. Bend the wire cabane struts and bind to side and bottom cross pieces. Solder the top 18 swg wire wing support in place. Now glue the sheet area of the sides and bottom keel in place.

I find the best way to do this is using instant cyano glue. First damp the joint to be glued using a cloth, hold together and place a few drops of glue at the joint. This method allows quick tacking in place of curved areas; in fact I would build the whole aircraft using cyano if it were not so expensive in my opinion.

The front cockpit area is removable to give access to the radio gear. Cut the top deck F5 from 1/32 sheet balsa and shape to fit the fuselage. Add the ply reinforcements and half round formers F6, F7 and F8. Cut out the 1/32 sheet covering and the holes for the cockpit. Glue in place and add card tubes for the cockpit sides. These are finished off with electrical insulation tube split down its length and glued around the tube edges.

Before finishing the fuselage, build the tail assembly and fit in place.

Now place the servo and radiogear in the fuselage at a position that gives roughly the correct centre of balance. Fit the servo and rudder control lever in place, using servo tape, or make bearers for the servo. Cover the top of the fuselage under the cabane struts with 1/32 sheet balsa (cross grain) making a hatch to gain access to the servo.

Wings: Build in the two halves leaving out the centre ribs. Glue the two wing halves together at the correct dihedral angle (2-1/2 in under one tip) and add the dihedral keepers, engine mount and the two centre ribs. Now cover the leading edge and the centre section top and bottom with 1/32 sheet balsa.

Covering: The whole model is covered in heavyweight tissue and given three coats of 50/50 dope thinners. The total weight of the model should not exceed 12oz., so be careful not to put too much coloured paint and fuel proofer on! The original was powered by a Cox 020 motor and a home-made tank was made and fitted to the side of the engine mount.

Flying: If the CG is at the mainspar and you've got everything else right, you may now launch it. It will then worry you sick as with the ordinary Cox 020 it will only just climb away. So let it get some height before you upset it with the rudder. It flies very well indeed, but resents too much interference. The old-age pensioners like myself who know about single channel will remember this vividly. With practice because it has only just enough power, it will stooge along at 50 ft with an occasional nudge to bring it round, and you can relax and admire it. Bring it into wind to land, and it will slide along the grass in a highly rewarding manner.

It will not take off water as it lacks power. If you intend to land it on water, you will need wing tip floats as otherwise it will tip over (but it does float!)

Now if you like it can be flown as a free flight model; simply switch off the radio or take it out, and add ballast to the nose to give the correct CG. Be careful, she climbs away very well and goes a very long way on a very little fuel as a free flighter.

I have had a lot of pleasure with the model which looks well in the air, and so far has taken some bad landings with only damage to the tissue. Tail and wings knock off without trouble, and if you tie the rubber bands to the cabane with a loose loop of carpet thread, you won't even lose them.

Calm weather I am afraid, as otherwise she tends to blow away, but a lot of fun. "

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