Define the Mission

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Where do we start?

You might think that a sketch is a good place to begin. But it turns out that airplanes are shaped more by physics than the imagination of the designer, and the realities of aerodynamics and structures and the materials you’re working with will quickly shape that awesome first sketch into something a lot more conventional-looking. Ask me how I know!

That said, I do believe the designer can do a lot to make an airplane more pleasing to the eye. We’ve all seen quirky, crude, even clunky-looking planes that still fly quite well, but one of our goals here is to merge the functional needs with an eye toward proportion and scale–in a word, elegance. We’ll see how it works out.

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Your mission, should you choose to accept it…

The place any serious designer has to start is defining the mission requirements, which in the simplest terms are:

• How much stuff do we need to carry? (weight)
• How far do we need to fly? (range)
• How fast do we want to get there? (cruise speed)
• How slow do we want to land? (stall speed)

Obviously, each airplane’s shape has a lot to do with the answers to these three questions and the compromises made by the designer if one of those items is really important.

There can be other important priorities the designer has to consider, too:

• How much will it cost to build?
• How much will it cost to operate?
• Will it be easy to build?
• Will it be easy to maintain?
• Will it keep the occupants safe in an accident?

So we see that the designer has his work cut out for himself.

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The ellipsair mission

Although there are lots of fantastic experimental (homebuilt) aircraft that accomplish their mission very well, my building partner and I found that the ones on the more affordable end of the spectrum tend to sacrifice size and useful load more that we’d like. We wanted a plane that:

• Could carry a payload of 560 lb
  • 460 lb of crew
  • 25 lb of equipment (fire extinguisher, chocks, spare tire tubes, tools, etc.)
  • 75 lb of baggage
• Could cruise between 180 and 200 mph,
• Stalls at about 58 mph, and
• Has a minimum range of 650 miles.

Now, if that sounds a lot like a Van’s RV-14 to you, congratulations–you figured that out quicker than we did! But, we want to build using composites, and we wondered if it might be possible to achieve similar performance with a little less power (read: lower cost) by keeping the plane light and focusing on drag reduction.

In the next post, we’ll explore how our desired stall speed affects wing loading (W/S).