Hot Wire build of the Blunt Nose Versa Wing

This is kind of a continuation of the article called  Balsa Wood build of the Blunt Nose Versa Wing.

In that article I had taken the versa wing and made a 120% size made out of balsa instead of standard foam board.

If you had looked at that article you will know that it didn't last too long as I had a malfunction during some equipment test. This article will journal the build of its replacement but using solid foam and my hot wire cutter.

After bring the parts home from the crashed balsa wing I used the broken wing to make some templates for each end of the foam for hot wire cutting. I'm not going to go much into how to do hot wire cutting because there are a ton of videos out there showing how to do it. That's how I learned. I will say that my hot wire cutter is quite basic. Just a 12v battery and charger. I made a bow out of 1/2" plywood and adjust the heat by adjusting the power wires closer or farther apart where they attach to the cutting wire. Farther apart means less heat. For me the best is to have the power wires about 30" apart or it gets too hot.

Here is my cutter setup. You can see that I use a battery and a light switch to turn it on and off. A spring to hold the wire tight as it heats up and expands.

I did a quick video and a couple of pictures about how to cut a wing. 

First I screw the templates on the end of the foam block.

Next I cut as shown in the video below. This video is not the actual cutting of the plane wings shown in this article but just an instructional video. It is much harder to cut a wing that is narrow on one end compared to the other as you can see in the video. You must go twice as fast at one end and is easy to get ahead of yourself on the short end. It takes some practice.

The following are some picture progress of this build.

This first picture is the parts cut out. Notice my hot wire cutter clamped to the table for vertical cuts. I clamp another straight edge on the table and use it like a table saw.

I cut out the battery and electronics bay

I glued the sections together and covered with monocoat after installing some spars for stiffness.

I reused the same elevons and vertical fins from the crashed balsa built wing and all the electronics.

I mounted the mobius camera up front for flight video

It has a large battery bay and holds two 5200mah batteries

My electronics

Let's go over the electronics left to right.

900mhz wireless telemetry, Minum OSD, 433 mhz OpenLRS Rx, APM 2.6 flight controller, 45A ESC, 600mw Video Tx.

Everything here is the same as the previous version of the versa wing except some of the programming. I really read a lot about the set up of the flight controller for doing RTH in a failsafe condition. I switched the way I was doing it from programming the OpenLRS with the failsafe to doing a low throttle failsafe in the fight controller. This is a much safer way because it will do a RTH even if the control Rx fails completely. See instruction here for this http://ardupilot.org/copter/docs/radio-failsafe.html

Here is the maiden flight. In this flight I am mainly getting the trims all set up and getting the feel for how this flys. I have the two 5200 mah batteries in there so it is heavy. But it slows down fine so this big wing handles the weight just fine. In the middle of the video a kid being pulled on a sled by his dogs gets me tangled up while I'm flying. Only in Canada EH.

While just like my last article about the balsa version this one isn't without incident. I was doing a duration test with 10400mah of battery in there when decided to lower my altitude. After dropping about 50 ft I pulled her back up but it wouldn't have it. It piled directly into the ground. See the crash video.

So now the forensics start. I had noticed for a bit the roll to be a bit sluggish. During the evaluation of the crash site I noticed that the control horns on both elevens had pulled out of the foam. I think during the flight they started to loosen and the pull up from the dive did them both in. This big wing at 2 kg is just to big for the standard FT control horns.

Here is the result of the crash.

So back to the repair shop.

I cut a new nose with the hot wire cutter. Made it about one inch more out the front then the first for more room in the battery compartment.

.Then to reinforce and put in stronger control horns

Here it is all patched up again and ready for another re-maiden.

I have learned some lessons. When using flight controllers read, read, read. Learn all the best practices from other guys in the manuals and on the forums. When it crashes, and it will, don't give up. Learn from the mistakes and move on.

Edit: I was asked in the comments to add scans of  templates for the hot wire cutting. Here is what I have.

Templates for Hot Wire Cutting

Outline of wing

I also was asked what the flight duration is. I finally got out today after a long winter's nap and flew it until I was tired of watching it go round and round. I started with full batteries 2x 5200mah. and flew for 33 mins. After charging I measured that I put back in 7659 mah. That's 232 ma /min so if it ran until the batteries were dead flight would be about 45 mins. Better limit to 40 mins to be safe.