Plane selection guide
One of the best concepts for such an aeroplane is the Flying Wing constructed out of EPP (Expanded Polypropyle). This material was initially developed for the automobile industries, for use in bumpers. Soon after, it got adapted by model aeroplane manufacturers for it's unique properties. This foam is elastique and enables us to build a very durable and light flying wing. The Transport requierment limits the wing span to around 140cm. The smaller the wing gets, the more difficult it is to achieve the desired properties (low area-load, universal applicability). Since we want to have some additional gear and big batteries in it, we prefer a thick middle part.
The main requirements for the carrier platform are:
- Aerodynamically stable, but still agile enough to profit from the fast steering inputs a computer controlled system can provide.
- Nothing that causes major injuries or damage (⇒ foam as main building material)
- Long cruising time (preferably over 35 minutes)
- Transportable by plane without having to pay special baggage fees
- Payload: min. 100g (Now possible up to 500g)
- Easy, fast to build and robust construction
The engine setup must match quite a few properties:
- It must be able to give a sufficient performance during flight
- The cruise time should be around 30min
- Nothing too heavy or expensive
- By the setup of the plane (engine at the back, delta wing) we are limited to propeller diameter of ca. 10 to 11 inch.
Some motor selection help can be found at http://flybrushless.com/
A general rule of thumb for power (input) per weight is to have 80+ W/Kg to be able to fly and 300+ W/Kg for vertical climbing. Therefore 200 W/Kg should give us a reasonable amount of power to also carry heavier payloads while maintaining a long cruise time with light payloads. Since we go for a lift-off weight of ca. 1kg, we need a maximum power of around 200W. The weight of the powertrain should not exceed 500g. The engine should be as light as possible, in order to achieve the correct center of gravity without trim weights. With these information we can start looking for a suitable setup. Since the information provided by manufacturers and shops are mostly insufficient and sometimes a tad optimistic, I am going to use a tool called drivecalc. It is available for Linux, Mac and Windows at http://drivecalc.de/. Most of the information that is provided in that tool is measured by independent people.
In the simulation I used two different engines from Hyperion. However, with the found parameter (weight, rpm/V, max current) we can also look for other manufacturers, and choose a good tradeoff between price and quality.