Rapier (oz8496)

About this Plan

Rapier. Radio control sport model. Aerobatic model for .61 power. Wingspan 62in, wing area 618 sq in.

Quote: "Pete Malone's 'Slim-line' multi is quick to build and so economical.

WHEN I obtained my first proportional outfit, I was in something of a quandary as to what model to put it in to 'convert to propo flying, as no kits on the market at that time (something over two years ago), seemed to have the features I was looking for. Eventually, as I had by me a design of my own - originally intended for my old 10 channel reed outfit and a Merco .35 motor - I decided to build this. However, I no longer had the .35 so a MkII Merco .61 was bolted onto the front end instead! The model had a 56 x 11 in wing, with no dihedral, mounted on top of a box fuselage of 1/8 sheet - and the finished article (for want of a better word) weighed in at around 5 lb. Everyone said that I must be mad to attempt to learn to fly proportional on an unproven model, which looked positively lethal. As it turned out, on the first flight, after a ropey hand-launch, the good power-weight ratio paid off - and the thing just climbed out!

Ever since building that aircraft I have maintained that lightness is a prime factor, where performance and ease of flying is concerned.

One of my fairly recent designs has used a small 54 x 10 in wing but, after building and flying three of these models (and my friend one) we have gone off the idea of using small aircraft. It seems that tiny defects can have a magnified effect with smaller machines - for instance, the effect of a cylinder-head protruding from one side, with a sidewinder design (of which more anon). Motor torque also becomes less controllable, and a heavy glass fibre propeller can produce some strange gyroscopic precession. Actually, of course, small aircraft can be great fun for general sport and pleasure flying - let it not be thought that I am knocking them - but if you are concerned with contest pattern flying, they do have their limitations and one must arrive at a compromise when deciding upon the size of a projected model.

Design points: The Rapier was designed with the foregoing experience in mind, and the weight was kept to an absolute minimum. The original came out at 5-3/4 lb, but no doubt some builders could shave several ounces off this. The fuselage was designed with the minimum practical cross-sectional dimensions; this suits my taste and, anyway, the less wood that's used, the cheaper and lighter the model will be. As a matter of interest, I actually attempted to bring the weight of the third model in the series up to over 6 lb to try out a pet theory, but I failed to do so and it came out at 5-3/4 lb again.

Weighty problem: The theory was that a reasonably heavy model - say 6-1/2 or 7 lb, flies faster through the manoeuvres. It seems to me that momentum plays a larger part in most aerobatics than does the engine. That is, for the short time a model is in a climb during manoeuvres. This is borne out by the fact that when one applies rudder, despite the large amount of sidethrust, the motor has not enough effect to skid the model round in a turn unless it is flying very slowly and the motor is suddenly opened up. This is, of course, considering a model with no dihedral.

This brings me to an important point regarding trim, which I have only considered after reading Keith Jones's words concerning loops and outside loops. Although Keith's method cured the trouble, it did not, I feel, go right to the cause..."

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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