The Lawnmower has a slight Flutter

Throughout the process of building the UAV I had been experimenting with SPAD (Simple Plastic Aircraft Design) planes.  Since they are simple and quick to build and cheap material wise, one can build a plane to try out a concept and discard it if it does not work.

First SPAD in it's original form

First SPAD in it’s original form

I started off with a fairly traditional layout sans the V-tail which worked quite well and flew quite well.  The biggest flaws were the too short tail moment which could bite you if you got the GC only a little bit wrong and the too small size to carry any usable size stills camera.

The second design was better.  It had a pusher prop, leaving the nose free for camera equipment.  Also a V-Tail design, that paid off at least once when I had a servo come loose, while still maintaining enough control for a safe landing.  Since the two panels of a V-Tail doubles as both elevator and rudder, losing one, means you only lose 50% of your elevator and rudder control.  It’s thus naturally redundant.  Due to the pusher design, it had to have a fairly deep section body so that the prop can clear the tail boom.  Much the same as the current plane I use for camera work.  It had tricycle undercarriage, which made it a breeze to take off on a good surface.

From left to right, Lawnmower, SF2 and SF1.

From left to right, Lawnmower, SF2 and SF1.

The disadvantages of this plane is that it’s still too small for a stills camera, the wheels are too small for rough field take off and landing.  Also, like the current UAV plane, the deep section body doesn’t like crosswinds, and give funny pendulum effects while flying, making it overall not a very nice plane to fly.

My third scratch designed and built SPAD.

My third scratch designed and built SPAD.

My latest SPAD is again a much more traditional plane.  Even though I don’t carry the camera in it, it will carry the camera easily.  Of all the planes I have, this is the sweetest one to fly.  It handles well and is always a pleasure to fly.  It has one small flaw that led to the name I gave it : The Lawnmower.  It’s a fairly long plane which means that it stands on it’s wheels in a near to level attitude.  The plane is a tail dragger which means I cannot increase the angle of attack on the main wing on take off by rotating when I have sufficient speed.  This all means that I need quite a high take off speed to get into the air, even though it can fly quite slow once in the air.  So, when doing take-offs on grass, it tends to look like a rogue lawnmower as it tries to gain enough speed whilst chopping and throwing up grass with the fairly low to the ground propellor.

I also found that the large tail fin is not nearly stiff enough for high speed flying as I got a scary amount of flutter on the one flyby I did.  As luck would have it, I had the keychain camera pointing right at the tail when it happened!  (See the video below).

All in all, it’s still an enjoyable plane.  It glides surprisingly well and seems to have fairly low drag compared to the UAV I use for camera work.  This is quite surprising if you take into account how badly it’s finished aerodynamics wise!

I am already formulating a layout based on an American spy drone as the next plane I will build.  I will keep this blog updated once I start with that.


About delabu

I am a software developer, coding mainly in Java and specializing in the GIS field.

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