M-24 (oz16380)

About this Plan

M-24 (AKA T-412). Free flight competition model, for rubber power. Wingspan 1300 mm.

Published in L'Aquilone as the T-412, later kitted by MOVO as the M-24.

Direct submission to Outerzone.

Quote (google-translated): "A model of refined elegance, for connoisseurs only.

'Here is an excellent rubber-band model with elegant lines and excellent performance. We recommend its construction to experienced model airplane enthusiasts who wish to successfully compete in competitions. As for the design, we would like all those who submit diagrams for publication to adhere to the Raggi system: precise, clean work, and a pleasure to examine.'

This is how L'Aquilone (The Kite) in 1942 accompanied the publication of the triptych and description of the T-412, designed by Enea Torielli and drawn by Pierluigi Raggi.

'To my eye, this is the most beautiful machine on my list.'

This is how Ben Buckle described the model in the early 1980s, announcing the availability of the full-size drawing for £2.80. It was actually the MOVO M24, but it was the same model, designed this time by Torielli himself and marketed in 142 by Movo, which apparently also provided - if not the box - the materials package and probably some construction notes.

In fact, on the MOVO drawing, various numbers appear next to various parts, which only make sense if they refer to or recall corresponding numbers on the materials or instruction sheets. I purchased the drawing from Ben Buckle in the 1980s: I was impressed by the model's elegant lines and equally elegant construction solutions. In any case, it was a fairly complicated machine ('quite involved,' according to Ben); the initial idea of ??immediately starting to build it quickly lost its substance, and the drawing was lost along with so many others that never came to be.

A year ago, while trying to sort out my crazy mess, I came across the heliographic drawing again and noticed that the lines of the drawing had faded over time and that everything was disappearing in an unstoppable general yellowing. To salvage what could be salvaged, I had a photocopy made, which turned out awful, but at least captured what remained of the beautiful drawing.

In March 2005, at the Amato Prati Memorial in Modena, I met the excellent Marcello Zunica, whom I knew was already involved in the salvage and reproduction of certain Kanneworff Wakefields. I showed him the wreckage of the MOVO M24 board and suggested salvaging it.

In March 2005, at the Amato Prati Memorial in Modena, I met the excellent Marcello Zunica, whom I knew was already involved in the salvage and reproduction of certain Kanneworff Wakefields. I showed him the wreckage of the MOVO M24 drawing and offered to salvage it. Marcello immediately agreed and threw himself into the task, which soon proved more arduous than expected: the biggest problem was combining or mediating the MOVO drawing with the well-made but small triptych of the Aquilone, which contained measurement tables for drawing wings, planes, fuselage, and especially the hexagonal frames and wingtips at 1:1 scale. It seemed he was getting nowhere.

Added to this was the question: should I faithfully remake the drawing, merely correcting and tweaking dimensional inconsistencies, or should I update and rationalize some constructional solutions, without violating its historical originality? For months, a rich correspondence took place, with proposals and sketches being sent from Ferrara to Padua, and the corresponding solutions, "fine-tuned" by the CAD wizard, being sent from Padua to Ferrara.

After nearly a year of exchanging model airplane bullshit, here is the result of Marcello's labors in the attached table. The final decision was to adhere as closely as possible to Torielli's table, reserving any suggestions for construction rationalization for later notes.

More than sixty years after its conception, I'd like to offer some personal considerations on the aerodynamic design and structural concepts. Torielli adopted the Italian SL1 for the wing, a good profile with a shape and characteristics equivalent to those of the more famous RAF 32 and Eiffel 400; He added a convex tailplane, the St Cyr 52 (a profile that, poor thing, has always been used - even in subsequent decades - only on tailplanes).

The limited longitudinal dihedral (wing +2°, tailplanes at 0°) is a bit surprising, and even more surprising is what can be glimpsed on the evanescent MOVO table: the CG appears to be indicated at 35% of the leading chord, when, with the lifting planes, around 45% would seem justified, but with a wing incidence of 3 or 4°. I'd like to have the SL1 polar chart handy, to avoid any possible stupidity. Such an advanced CG certainly suggests a diabolical ability to stay light in the tail... The inverse stability coefficient is an exceptional 1, already a low and 'advanced' value for the time.

From the propeller block measurements, I was tempted to draw a graph: with a diameter of 45 cm, the geometric pitch is fairly regular, around 70 cm. Assuming a blade angle of between 5° and 6°, the actual pitch would be around 60 cm, still an acceptable value but quite 'fast' with the described coil (90 mm2).

The overall impression is of a model with a good rate of climb, unloaded at around 35 seconds, and a still fairly fast glide, considering the angle of attack and its aerodynamic refinement. With the current tires (at least 1,000 rpm instead of the 600 described), the model should easily exceed the average flight time of 2 minutes, which Torielli indicates is achievable.

Construction

Without necessarily updating the construction criteria adopted, there are nevertheless some things that need to be rationalized if one wishes to remake and fly the model today. Nothing to complain about for the wing and floor spars (although I don't know how easy it will be to find 0.5 poplar veneer). Nothing to complain about the frame construction system, with 2x6 balsa sections (a system, if I recall correctly, revived years later by Sadorin in his 'Merlu'). Nothing to complain about the fuselage construction on a ladder and its elegant partial covering in 2-gauge balsa.

I was perplexed by the ribs, described as being made of 0.8 mm lightweight balsa. On a large string, I find 0.8 mm balsa too flexible, and the laborious, yet elegant, lightweighting process would result in a weight saving - depending on the balsa - of between 1 and 2 grams, further reducing the stiffness of the parts. If I were to remake the model, I would use solid 1 mm or better yet, 1.2 mm ribs in a choice lightweight quarter grain, which I think can be found for a good price at Mike Woodhouse, in Great Britain, of course..."

Supplementary file notes

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