RCRCM Sunbird – Build Report – Concepts

Last Update: 29.12.2018

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Building Standards

On the flying field, a small plane like the Sunbird will not attract much attention. However, Flying Tom’s critical key figure „Franken PNP pro Zentimeter Spannweite“ (Swiss currency units for Plug-N-Play standard according to Horizon Hobby by centimetre of wing span) is 4.6. This value concerning a glider plainly shows that the Sunbird is an investment rather than a purchase of consumables.

We want to operate the Sunbird for several years without frequent cobbling. With regard to a future sale, conservation of value will be a guiding principle for our solution designs. The Sunbird has to comply with Flying Tom’s high quality standards:

  1. Normal operation is possible without tools and without fumbling and dodging.
  2. Everything we build into the plane – or attach to it – stays there firmly until it is removed on purpose.
  3. Electric and electronic components can be replaced with regular tools and without destroying surfaces, structure elements or neighbouring components.
  4. The durability and quality of detailed solutions has higher priority than saving take-off weight.
  5. The model is documented.


There is not much to be done in terms of aerodynamics. The wings‘ angle of incidence is set by the factory  and the tail is all-flying. We have all flexibility we need to configure the difference in angle of incidence between wing and tail.

All control surfaces are sawed out and fastened neatly. Moving them (cautiously!) to their respective stops reveals enough travel to meet our requirements.

Our Sunbird is to get a crow configuration – or a butterfly, as we prefer to say in German – right from the text book. With our previous gliders we put up with best-effort attempts. This meant that the full downward deflection of the flaps of at least 80 angular degrees was never reached. This was not an issue of the control surfaces or their attachment to the wing, but of the geometry of the linkage (servos, rods, horns). In order to actually make the flaps work as air brakes with „drop-the-anchor!“-deceleration, they have to throw at least 80 degrees. If it is less, they are regular flaps increasing lift rather than reducing speed. This time we will get it right.

Power Supply

There were no plans for doing any experiments with the equipment nor were we hunting for innovation. The Sunbird was to reach flying status as fast and with as little effort as possible. We intended to use the components recommended by RCRCM and our dealer.

Thus, following servos were on the shopping list: KST DS245H NV Digital and KST DS115MG Digital. Both types would not have been able to cope with the voltage of a fully charged 2s lipo battery. So, initially, we went for a classic low volt set-up with a 4 cell / 4.8 volts or 5-cell / 6 volts NiMH-battery.

But the DS245 servo is no longer produced. Only a few remainders are left on the markets and future availability of spares is uncertain.We decided earlier – as explained in our German blog entry Jäger und Sammler (hunter-gatherer) – to discontinue running an expensive spare parts store for the components we use in our planes. So we opt for KST’s  successor servo familiy X08. These operate between 6 bis 8.4 volts, which is exactly the voltage range of a 2s lipo battery. The Sunbird will be first a high volt setup.


Propulsion isn’t, of course. We are not building an E-Sunbird (not this time …).

But we need some means to cope with unexpected calms at the slope or to enable test flights in the plain. So we will add a hook for high start or a bungee.

Health Hazards

The Sunbird is made of carbon fibre composites. Similar to asbestos, carbon fibres are suspected to cause cancer when inhaled.

We are not going to abrade a lot of carbon material from our Sunbird. The fibres are no threat at all as long as they are cast in resin. However, we do not know whether lose fibres come with the kit or not, in the cavities of the fuselage for example. It may be a good idea to wash all the parts thoroughly prior to use.

For all drilling, grinding  and sanding of carbon material wo go outside and use breathing protection. You don’t want to see that black dust on your workbench and above all, you don’t want it in your breathing air. Do not rely on regular vacuum cleaners. This will help nothing but distribute the mess evenly in your apartment.

Maybe we are kind of paranoid. Actually, we have no idea how nasty these carbon fibres really are compared to all the hellish stuff we usually handle when building our models …

[⇐ Intro] | [⇑ Overview] | [Bill Of Materials ⇒]