Cagebird (oz15520)

About this Plan

Cagebird. Peanut duration model. Rubber power.

Quote: "Not another indoor class - might well be the initial reaction to this topic. Nevertheless, Peanut Duration (PND) has been the success story of last winter's Northern Low-Ceiling Indoor Contests. Entries have exceeded those in the other categories - and there have been new names in the results list.

The concept was promoted (and pushed) by Bernard Hunt and was intended to bridge the gap between duration and scale and hence appeal to a wide audience. There have been similar attempts in the past with Manhatten and Bostonian, well publicised on the other side of the Atlantic. The former has been tried and found wanting in Cardington, and gives models too large and fragile for more restricted sites. Bostonian is smaller but heavier and the models would appear unlikely to bounce off the walls and other obstructions.

Hence it was decided to write a new specification. Whilst choosing Peanut size might well be construed as a gimmick, it rendered some of the implications a little more predictable. The rest of the numbers were chosen to suit the idea of a box fuselage model, light enough to fly for a couple of minutes, strong enough to survive both collisions and handling - and maybe even of 'realistic' appearance (whatever that is)!

My attempts to design a model intended to win under these rules all seemed to lead to diamond pylon layouts. This approach shortens wing mounts and undercarriages, whilst utilising all of the limited wing area as efficiently as possible. Realising what my sketches were starting to resemble, I bowed to the inevitable and used my normal outdoor style of fin shape!

Not knowing just what was needed, my model had most components plug-in and/or adjustable. This makes for easy trimming and encourages trying out new components.

In fact the prototype flew off the board and displayed a very nice power pattern right from the start. On the other hand, its performance was a little disappointing. The first two or three contests showed that 2:15 was about my limit - and I needed more duration if I was going to win anything.

The first step was to abandon the double-surfaced wing (intended to improve rigidity) and build a replacement in the normal indoor style. This was followed by a new propeller assembly with a higher pitch (fig.1). Both changes improved the model - to the tune of an extra 40 seconds or so. Certainly the design as presented has a potential of three minutes under a 25 feet ceiling. Contest scores have not quite reached this figure but have been sufficient to win the February and March events by a comfortble margin.

Flying technique has been similar to that used for EZB - comparatively thick rubber, wound to capacity and then backed-off (unwound) typically up to 10%. This throws away the power burst and enables the model to be flown on the flat part of the torque curve, giving a slow ROG and climb, followed by a long cruise and slow descent. Could I emphasise that this is essentially a low-ceiling technique and inappropriate elsewhere!

Future programmes for Cardington include PND events - so a few pointers might well be worthwhile. For flying in this site, with plenty of available height, I would recommend a finer pitch prop, a long thin motor and flying without back-off. I would not expect problems on power burst with these changes, indeed they should make the model easier and safer to fly. Prophecy is always dangerous but I would expect to see flights in the four to five minute region.

Materials: As with all indoor models it is necessary to select the wood pretty carefully in order to produce a strong light airframe. Nevertheless there would seein no need to resort to using special 'indoor' grade supplies for most items, unless of course, you have them already. The fuselage and tail unit call for 0.060 in balsa - which translates as thin 1/16 - and the required material should be stripped from sheet. Most commercial 1/16in square strip is too large, hard and heavy.

For the basic airframe, balsa cement is a more-than-adequate adhesive and lighter than many of the more modern alternatives. Chose a thin, runny cement and don't use too much..."

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