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RUBBER POWERED HELI DESIGN 101 (Read 7250 times)
Jun 7th, 2017 at 2:52pm

Mario I. Arguello   Offline

Vintage MIA Scale R/B
Powered Helis

Posts: 13
 
Introduction

Hi I'm Mario I. Arguello owner of MIA Micro-FLIGHT http://www.micro-flight.com/mia-micro-flight.htm, designer-manufacturer of unique RC model products since the early 80's.

When I started my company, it was originally called MIA Designs and if you have Google searched for MIA Rubber Powered Helis, you will see the MIA Designs associated with them, but basically it is an extension of MIA Micro-FLIGHT.

Rubber powered helis was one area of interest to me to study better their characteristics, inexpensively, quickly and in the comfort of home.  I could design whatever came to my mind, built it fast, test it, and refine each model thereafter for a given result. This lead to interest by some people who were interested in my work and this lead to making kits for sale. From there I went on to making other products which can be seen also on my Facebook page https://www.facebook.com/mario.arguello.395 or my You Tube channel https://www.youtube.com/channel/UCefEQgOboCP5AHVyphzjq-Q.

Let me start by sharing what I  learned  about making rubber powered helis.

First of all the obvious:

Unlike a stick and tissue rubber powered "scale" airplanes, where the airplane has the advantage of lift assist by a large wing surface, with direct propulsion via a propeller, thrust line in line more less with the lifting surfaces, the key challenge in designing an scale rubber powered "helicopter" is the direct propulsion to the rotor blades to provide enough rpm and thrust to lift the scale model to obtain a somewhat satisfying flight time.  Where the airplane can actually pick up lift on its own once the prop gets is to enough altitude and momentum and the plane can glide and rely less on the motor thrust, a traditional helicopter relies constantly on the rotor for sustained lift.

If you could simply use the rubber motor to power a small propeller and let the rotor blades somehow spin on their own, it would be a much better proposition, but then, this would not be a helicopter, but a gyrocopter instead.  Since this is about helicopters and not gyrocopters, I will try to keep focus on subject.

A truly in scale stick and tissue helicopter, requires a lot more wood, pieces and thus can become very heavy for a typical rubber motor system to lift, by virtue of what I just described above. The more in scale, the heavier and less flight time.

The solution is keeping the scale of the model as simple as possible.  How I achieved max flight times while keeping a rather scale-ish look on some of my early designs was to minimize structure and mechanics complexity where it was not required. An example of this is the early MIA MD500R/B heli  which was featured in an early 90's Flying Models magazine  Earl Van Gorder Column. I will have to dig out the videos I did at the Chicago Hobby and Model show, convert them to present viewable media to show some of the early flights of the MIA MD500R/B powered helicopter I did back then and sold in those early years.

You cannot get any simpler than the MIA Rubber powered designs with a scale look, they are not simply profiles stick and rubber, in fact this is why I started designing mine the way I did, after wanting a scale rubber powered helicopter with satisfying flight times. The compromise was simply, simplify and simplify a full scale structure, without simplifying too much and loose the scale-ish look. 

The MIA MD500R/B heli plans call for 2 profile stick and tissue walls, from which they sandwich the motor and rotor box around the model's CG, and from which careful amount of cross bracing is applied to maintain a 3D scale look.  I had built full body in scale stick and tissue versions but it was impossible to keep the weight low, and flight times high, so I settle for the design spec as described. Once I found this sweet spot in the design I made all sorts of other heli designs in similar fashion with satisfying flights.

While I was designing rubber powered helis I was also doing 3D CAD modeling and this early form of art helped me visualize and conceptualize many other rubber powered designs in scale using "triangulation", AKA Polygon framework for the heli structures. By reducing the number of N-gon points to build up the bodies, I was able to obtain some interesting scale-ish and very appealing looks, but on many designs I kept them uncovered and simply used a rubber motor to maintain acceptable flight times.

In my quest to extract the most energy from a given number of loops/thickness of rubber, I invented several mechanical contraptions, which I used on simpler to very complex  rubber powered heli designs.  Time permitting I will have to dig out some old photos scan and upload for online viewing. But one of the more simpler and effective means to extract as much flight time from a rubber motor was via a lightweight flex cable with a rubber motor placed horizontally, as used on the [b]MIA Shark
« Last Edit: Jun 11th, 2017 at 2:59pm by Mario I. Arguello »  
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