Tuesday, 25 February 2014

Atos VR mosquito/power keel

So there hasn't been too much flying since Lanzarote, the weather has been awful- however Chris and I have managed to get a few days out on our power units on the good days that have been either too light for ridge soaring or blowing west/wsw where we don't have hills to launch from. It's great flying with other people and power flying is the same, it makes rigging/de rigging much better and also makes the flight more memorable having others to share it with. 

Since selling my Axxess rigid wing which handled the Mosquito really nicely, I have been using a Willswing U2 160 which has been great  BUT rigid wings are SOOOO much better when it comes to strapping a power unit to, they handle exactly the same with power as they do without, the climb rate is much better which means much less fuel used and much less noise at level flight, the glide with the engine off is almost the same as without the mosquito- they are just awesome! 

 On the last flight on the U2 I was over 5000ft at Brighton, looking at the great cumulus clouds 3000ft below and remembered once again how much I LOVE this type of flying. I always like to be free flying, getting as far as I can using only Thermals, wind and your body and brain to try and stay in the air- but flying over and around the clouds enjoying the views that normal free-flying will never give you is incredible. I realised in my last flight that I really want to get back on a rigid wing with the mosquito ready for those thermic days that aren't suited to our hills in the downs, to use it like an aerotow launch- climb to 2000ft, engine off and go as far as you can using themals. 

The problem was I have sold my Axxess and had bought a VR which has a tail plane, the tail would get in the way of the propellor so has been unusable (without the tail the glider would be too unstable).

A.I.R have come up with two solutions to this- 

Option 1 - A shortened Stinger with the tail moved forward but fixed to a higher angle so it's doing more work to make up for having less leverage. These are a lot of money though, a.i.r USA are charging $695.00!!!! Not for me!

Option 2 - this is a clever device, it's a shortened keel when the engine is on, but the when you switch the engine off to start your thermic xc, it electrically extends back to the full length. Impressive but even more expensive than the shorter one!!!!

So they are the two options I have found. I cant fly the VR without the tail, but can't afford either of those options. So I attempted making my own keel and try and copy option 1.

The first problem was sourcing the tubing, the stinger is 44mm but I only had the imperial version of the same tube which was very close to fitting but just a little too tight. After sanding the end down for about an hour and drilling two holes for the spring clip that holds the keel in place-  I had a starting point. The mosquito requires the keel no further back than 1300mm from the hang point so that was where I had to cut the stinger.
As you can see in the above photo, I also drilled 4 holes to slide two old fibreglass battens in I got from a friend with this job in mind, these help the glider rest on the mosquito harness when not in use and not slide off to one side. To stop them vibrating or lifting in flight I put jubilee clips around them inside the stinger to hold them tightly in place as you can see in the next photo.

So the easy bit was now done, but how am I going to mount the tail onto the stinger? A carbon one from A.i.r would be very expensive so I decided to try and make one out of fibreglass instead.

 Firstly I knew the tail needed to be fixed at the same angle of the highest point the adjustable tail goes up to, which is 35mm from the keel. I then copied the shape of the current tail holder out of foam, sanded it down, and joined it to a bit of tubing the next size up from the stinger tubing (so that once finished I could slide it onto my stinger) and then wrapped the whole lot in fibreglass (twice!) before wrapping it I pushed two bolts into the foam which will act as the locater bumps for the tail and a nut to take the bolt that attaches the tail (I also put a washer above this nut to make a larger surface area to pull against underneath the fibreglass). I also drilled 8 holes it the tube so the fibre glass would have something to grab hold of and so the tube would never spin inside the fibreglass mould. Confused? I am! But hopefully the pictures will clear it up.

After the fibre glass had set, i sanded it all down and slid the tube over the stinger I'd made. I got it exactly level and pop rivitered it in place.

Here it is all together...

As you can see from the picture below, the front of the mould is not attached to a tube. This is so it will slide over the keel and be a little further forward to allow the back of the tail to be within the 1300mm mosquito limit (hang strap to keel end).

Hopefully I will get out for a test fly on it this weekend and report back with the flight. I am hoping to wrap it in some carbon fibre to make it prettier and clean a couple of other bits up, but as this is currently untested, I need to make sure the angles don't need adjusting first.

If anyone else is thinking of making there own shortened stinger and need any help, feel free to mail me chipmunkluke(at)yahoo.co.uk 

many thanks to Nicos for the tubing, Ian for the battens and Steve Elkins at Avian for answering all my phone calls with question after question.

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