We always knew there would be ups and downs during this project and a couple of weekends ago we certainly experienced some downs.
It all started out well, having been in touch with the University of Oxford we were able to use our plane to do some testing in Wytham Woods. Wytham is a small village north west of Oxford and the woods there are a site of specific scientific interest (SSSI) and as such are in use for a large number of research projects by the University.
Our plan was to fly a circuit on the inside of a number of tree lines and see if we can record anything.
The motor shaft of the Mk2 plane unfortunately broke during it's last flight (see the landing in the video) so we decided to use the Mk1 plane (the Bix3) and attach a composite tube on the underside at the back of the plane to increase the distance from the propeller to the microphone.
The first flight using the stabilisation and auto-leveling on the flight controller (FBWA mode) went well and we were happy to go ahead and load up the waypoints and set off on an autonomous mission.
Below is what we actually flew although the auto section (in blue) doesn't show accurate altitude. During the auto section of the flight the plane was actually increasing in speed and losing altitude. You might be able to make out the little plane models that are on the flight lines - these show the attitude of the plane.
Unfortunately, the plane impacted the ground at the end of the auto line. It was a pretty hard crash and I'm sorry to say we don't have any photos as we were quite disappointed at the time and didn't think of this.
As a brief description, the battery was found approximately 30 feet away (it was placed externally on the plane for CG control); the motor had unattached from its housing and the propeller had chewed through the flap and a part of the left wing before impacting the ground and breaking in several places (the only part of the prop left on the motor was the hub); the wings had also unattached from each other and broken their connectors to the fuselage; the fuselage itself was cracked in several places.
So, this wasn't exactly ideal and to compound this, we had no idea why the plane crashed which was probably the major concern. After discussion with the programmers of the flight control firmware we discovered that the plane didn't have enough elevator authority to correct its descent and needed the PID settings to be updated.
After a fair bit of time spent gluing small bits of EPO together we think the plane should fly again!
This all happened on our first night of a weekend of testing. We still had a couple of days to try and get something flying so we moved onto using the Mk2 plane and testing this with a new motor.
Using a set up of a 4S battery on the Mk2 we were able to fly a test fight of the plane, fully loaded with the bat detector and landing gear (to help protect the motor and prop).
However, our costly weekend wasn't about to stop there and we discovered that when we used the 3S battery the prop just wasn't able to generate enough thrust for level flight and we floated down for fairly gentle landings. Given that we're already stressing the motor more than we should by using a 4S battery it's just not the right set up to fly the weight that we want to.
The Bix3 wing that we're using isn't designed to fly with the wing loading we're putting on it. As our power system also isn't able to generate enough thrust we've decided that the current design of the Mk2 is not suitable for our needs.
What we're therefore decided is we need a new plane that can support the larger flying weights we require (circa 3 kg). So, we're in the process of designing and building a Mk3 plane which should fit our needs really well!
Keep your eyes on the blog for some specs and 3D models of what we're looking to build!