Electric Typhoon (oz10805)
About this Plan
Electric Typhoon. Radio control scale model WWII fighter, for electric power, with geared Astro Cobalt 05 motor.
Quote: "Master of the electric scale model, here's Dave Chinery's Typhoon.
You must be mad! - was the reaction to my proposal to build an electric Typhoon. I have long been impressed by the chunky, pugnacious look of the full-size aircraft, and the choice of colour schemes, so when I wanted to select a 'handy size' scale job for my next project I decided to look at the possibilities a little more closely.
At first sight, the 'Tiffy' is a strange choice for an electric scale model, with its small, thick wing and cavernous radiator cowling making for one of the bluntest shapes in the fighter business. However, look at it the right way, and these handicaps can be turned into virtues.
One of the first things I look for in a prospective electric scale prototype is where to put the main nicad pack. Since it is the heaviest single part of the model, two essential factors must be located to get the model's CG in the right place. This is not always easy in a scale model due to limitations on fuselage shape and the ability to build in access hatches, etc. If the motor leaves enough room, the logical place to put the pack is in the engine cowling, but this often results in the model tending to nose-heaviness. This was the case with both my Spitfire and the much shorter-nosed Typhoon.
In the case of the Tiffy, the deep chin radiator gives plenty of room to put the nicad pack below the motor, and the low location has other advantages! Having found somewhere to put the power pack, you must consider the landing loads, which may be severe in a small, heavily loaded model like the Tiffy. The logical thing to do is to land on the pack, dissipating all its kinetic energy direct to the ground! With this in mind, the radiator cowl on the Typhoon model is reinforced and acts as a skid for landing, the nicad pack being cushioned inside it with foam.
The thick wing that is characteristic of the Typhoon (and the cause of compressibility problems with the real aircraft) is ideal for my favourite form of construction - blue foam. The section also permits a fairly blunt LE which makes the stall a little more docile - a useful feature for a heavily loaded model.
Taking all the above features into account, the model was designed to fit a 540 size motor and a 7-cell nicad pack. Due to the continuous high power output necessary to fly the model sufficiently fast, an Astro Cobalt 05 motor was selected. In addition to its good power output, its superior efficiency (over ferrite motors) would maximise flight time from the finite energy available from the batteries.
The blunt nose entry made a geared propeller drive essential, and the model was designed round an MFA Olympus belt drive turning a 12 x 7 prop. It was felt that, at the expected flying speed, the model might still be undergeared with this combination, so the motor pulley was changed for a 20 tooth type, giving a 2:1 ratio instead of the usual 2.4:1. The new pulley, a Davall 20MP-025, can be obtained from a number of engineers ball and roller bearing factors, and just fits the standard MFA unit without changing the belt.
Another general point regarding the use of the Astro motor in combination with the Olympus unit; the protruding brush holders of the motor can foul the rear nylon bearing bush of the Olympus unit. This can be avoided by removing some of the plastic bush moulding and a short length of shaft, or rotating the motor a few degrees about its axis, taking advantage of the play in the slots for the motor securing screws.
Construction: Construction of the model is not difficult, although some stages may be novel to the average modeller. It is suggested that the wing is made first, as it will be easier to make the wing seat/fillet area of the fuselage if the wing is available to fit it.
The wing is made from 2in blue foam, the straight tapered blank being wire cut in the usual way using the templates shown on the plan. I find it best to cut two blocks to the correct plan view shape (leave tips square) before attaching the templates to the tips and roots. Be sure to set the correct washout using the datum lines shown on the template drawings.
The templates are slightly oversize on thickness, so if inexperienced cutting results in ridges in the cut surfaces, there is a little excess for sanding off. The pair of wing blanks (you did make two opposite halves, didn't you?) can now be rounded off at the tip, and the balsa LE, TE, and laminated tips added, PVA glue being best for this..."
Electric Typhoon, Radio Modeller, May 1988.
Direct submission to Outerzone.
Supplementary file notes
Article pages, thanks to RFJ.
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