Saturday, March 10th, 2012 09:58 am GMT -7 Saturday, March 10th, 2012 09:58 am GMT -7Saturday, March 10th, 2012 09:58 am GMT -7
 
Kilo 3D airplane design logo

I’m designing an inexpensive aerobatic/3D airplane weighing about two pounds (1 kg). Follow along as the design takes shape.

 

 

 

Project Goals

I love designing airplanes. There’s no better way to learn how airplanes really fly than to experiment by making changes to a design. By turning this construction project into a design tutorial, I hope you will end up with a great flying airplane that you are comfortable evolving into your very own unique design.

I know there’s no shortage of free airplane designs on the web. But finding a well-tested and fully debugged design is rare. Finding a design that also talks about the trade-offs that the designer made is extremely rare. I hope to help fill-in that gap.

This is going to be a design done in real time. As I write this, I have not built any prototypes yet. I expect to make mistakes along the way. But hopefully every mistake will be a learning experience for us both. Warning! If all you want to do is build a well-tested design, you are better off waiting until the design is all done. But if your eventual goal is to go off and create your own original design, there is no better way to learn than to make mistakes right along with me.

Having designed, built, and flown several other original model airplane designs in the past, I have a lot of knowledge that I will be applying to this process. I expect the end result to be something anybody would be proud of. Since my primary goal is to use this project as a learning experience, I will explain as best as possible my reasoning behind all the design decisions.

Ready to get started? Good!

Airplane Design Goals

I have been wanting to use the creation of a new original design as a tutorial since the website relaunch two months ago. I spent a long time thinking about which project I should do. I appreciate the help of those that completed my online polls and sent me emails. I specially want to thank Tony from Australia, who has provided me much feedback and greatly helped shape my ideas. Michael P., an old friend, shared some really interesting building techniques that I plan to use.

In the end, I decided to build the airplane that I felt would have the greatest appeal to the website visitors. In the United States, a park flyer is a model airplane weighing less than two pounds (900 g) and flying at less than 60 mph (100 kph). Being park pilot legal made a lot of sense, so two pounds became my weight ceiling.

Those familiar with my previous designs know that “cheap and easy” are major driving goals with all of them. I like to use readily available materials and easy to master building techniques. I don’t feel that they compromise the flying performance or crash-worthiness if the design is carefully thought out.

I love building with foam. It is inexpensive and goes together very quickly. Wood is a fantastic reinforcing material for foam airplanes. I avoid composites because of the costs and negatives to using epoxy resins.

Sport aerobatic models are very popular. Designing an inexpensive and easy to build 3D capable model would be a challenge. The more I thought about the idea, the more I liked it.

So that was it. A two pound sport aerobatic model airplane with 3D capabilities built primarily out of foam. Hence the name, Kilo3D.

The Competition

With a goal in mind, I set out to learn what others had come up with before me. There’s no shortage of two pound 3D airplanes around, so it was more a matter of finding well-respected designs. After talking to friends, reading reviews, watching videos of them flying, and testing them out with my RC flight simulator, I came up with a list.

Multiplex Parkmaster
Multiplex Acromaster
ElectriFly Reactor 3D
E-Flite Extra 260
E-Flite Twist 3D
ElectriFly Edge 540
3DHS Edge 540

I collected basic specifications on these airplanes and computed a few useful results. Of all the videos I watched, I was most impressed with the performance of the Multiplex Acromaster. I noticed that it has a low wing loading and a low aspect ratio.

 

Multiplex Multiplex ElectriFly E-Flite E-Flite ElectriFly 3DHS Avg
Parkmst Acromst Reactor3D Extra260 Twist3D Edge540 Edge540
wing span in 39 43 41.5 43 35 41 41
wing area in^2 450 583 384 375 404 353 375
fuselage len in 40 45 42 40 34.5 39.5 38
flying weight oz 21 35 27 29 29.6 32 35
scale factor 12.0 14.0 16.9 18.0 20.9 22.1 22.8 18.1
wing loading oz/ft^2 6.7 8.6 10.1 11.1 10.6 13.1 13.4 10.5
aspect ratio 3.4 3.2 4.5 4.9 3.0 4.8 4.5 4.0
fuse/wing span 1.03 1.05 1.01 0.93 0.99 0.96 0.93 1.0

 

Power System

There are a lot of electric outrunner motor choices for the two-pound airplane weight range. I wanted to pick something that was popular, had good performance, and was reasonably priced.

I liked what E-flite had done with their Park 480 motor (1020Kv). There’s a very similar Park 480 from Turnigy that also looked like a solid purchase. Deciding to use these motors ended up being an easy decision.

 

E-flite Park 480 Brushless Outrunner Motor, 1020Kv http://j.mp/Ax4mf0 $50
E-flite 2100mAh 3S 11.1V 20C LiPo, 13AWG EC3 http://j.mp/xguBqM $35
E-flite 40-Amp Brushless ESC (V2) http://j.mp/zsuw8G $55
E-flite 11 x 4.7 Slow Flyer Propeller (2) http://j.mp/yTH4zl $5
TOTAL $145
Turnigy Park480 Brushless Outrunner 1020kv http://j.mp/zfx6r6 $20
Turnigy nano-tech 2200mah 3S 25~50C Lipo Pack http://j.mp/xUc00V $17
Hobbyking SS Series 35-40A ESC http://j.mp/xJWvrW $11
GWS EP Propeller (RD-1147 279x119mm) (6pcs/set) http://j.mp/xoQdNL $5
TOTAL $53

 

After I had picked the motor, deciding on the battery, speed control and propeller was relatively easy. Again, I looked at the model airplanes that were most similar to my goal and followed their lead. I may end up experimenting with different batteries and propellers, but these were enough to start.

Materials

As a preliminary step, I drove around town to see what materials I had readily available that I could use in this design. I looked at what the local craft stores (Hobby Lobby and Michael’s) and hardware stores (Lowe’s and Home Depot) had in stock.

I found some large pieces of foam and long dowels that looked like they would be perfect for this design.

 

Cellfoam 88 (XPS) 11.5 47 1/8 3 mm
Cellfoam 88 (XPS) 11.5 47 3/16 5 mm
Cellfoam 88 (XPS) 11.5 47 3/8 10 mm
Round dowel, poplar 48 1/8 3 mm
Round dowel, poplar 48 3/16 5 mm
Round dowel, poplar 48 1/4 6 mm
Round dowel, poplar 48 5/16 8 mm
Square dowel, poplar 36 1/4 6 mm
Square dowel, poplar 36 3/8 10 mm

 

Next Time

In the next installment of this design series, I will talk about the preliminary design that I came up with for this airplane. Comments? Suggestions? Let me know.

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