In a previous post, I described my 175% super sparrow. I'm totally in love with this airframe design. A couple of weeks back I was flying my super sparrow with a friend. Of course I decided to show off. I floored it downwind and immediately went into a full power loop. A little voice inside my head said this was a bad idea, I should have listened. The wing failed right at the join where the spar ends. As it spiralled to the ground, I was already planning another! So should I just downsize? Nah. Bigger and stronger. Thats the way to go. So just how much bigger. Well after a bit of poking around with illustrator, I figured I could go to 230% and still get each wing on one sheet of A1 only if I made it with ailerons and cut those from a separate piece of foamboard.
So the design goals are;
I have a full ardupilot kit sitting waiting for the right plane and this may well be it.
Power option is still a bit in the air. My kit box gives me three choices.
1. NTM prop drive 35 36 1800kw. Nice motor and would work with a smaller prop
2. Turnigy aerodrive xp 35/48 900kv. This would seem like a better choice and could turn a bigger prop (heavier than the ntm prop drive)
3. The third option/idea is to make it into a twin with 2 x 35 30 1100kv ntm prop drives mounted on wing nacelles. I could pull the battery back a lot this way and make the COG infinitely adjustable.
So what do you guys think? 1,2,3? Maybe another idea?
So I'll move on with some pics so you can see how the build is going.
Just for scale here's me with the wing
The wing is reinforced in a number of ways. Firstly (but not visible here) are three carbon fibre tubes two go the length of each wing and one more braces the two wing halves. Additionally the normal spar has embedded 2mm carbon fibre rod for extra strength. In the photo above you can see that a douple of pieces of foamboard are glued across the center. As well as providing extra strength, this fits snugly inside the wing preventing it from rotating laterally.
Heres the carbon rod extending out past the spar (where my 175% sparrow failed). You can also see here where I've Laminated (but not yet sanded) the outer edges of the wing. I used 24gm carbon fibre cloth and WBPU. I will almost certainly glass the entire wing and more than likely the whole plane.
Remember I mentioned the removable nose section, by pulling out the carbon rod and the screws at the bottom the nose comes off. The inside to the nose is reinforced with 2mm lite ply formers. They also provide nice solid mounting points to zip tie the undercarraige.
The tail section integrates a steerable tail wheel. The mechanism is primarily made from stiff clothes hangar wire bent and formed. I cut an aluminium disc for a wheel hub on the lathe anda rubber tyre on my cnc machine, though I need to redo that.
Next steps will obviously depend on the power choice. If I go with the twin idea, I'll need to mount nacelles before finishing glassing. Stay tuned for more pics as this progresses and I'll also have dxf plans for all the parts used in this build when its done.
So the design goals are;
- 230% and include any strengthening required to ensure no more failures. This makes the wingspan 1660mm (65.3")
- Carbon fibre tube in the wings passing the normal spar ends to ensure my monster sparrow doesn't meet the same fate as my 175% sparrow.
- Fixed landing gear. Throwing a plane that big isn't really an long term option.
- Landing flaps. I'm going to put these on although, I have absolutely no idea how the plane will behave. If I don't like them, I'll disconnect and fix them rigid.
- Removable nose section. In my experience, this is the bit that gets bashed most and I wanted a way to be able to replace the nose without having to rebuild the entire fuse.
- I'll put some lighting in there too just for the cool factor!
I have a full ardupilot kit sitting waiting for the right plane and this may well be it.
Power option is still a bit in the air. My kit box gives me three choices.
1. NTM prop drive 35 36 1800kw. Nice motor and would work with a smaller prop
2. Turnigy aerodrive xp 35/48 900kv. This would seem like a better choice and could turn a bigger prop (heavier than the ntm prop drive)
3. The third option/idea is to make it into a twin with 2 x 35 30 1100kv ntm prop drives mounted on wing nacelles. I could pull the battery back a lot this way and make the COG infinitely adjustable.
So what do you guys think? 1,2,3? Maybe another idea?
So I'll move on with some pics so you can see how the build is going.
Just for scale here's me with the wing
The wing is reinforced in a number of ways. Firstly (but not visible here) are three carbon fibre tubes two go the length of each wing and one more braces the two wing halves. Additionally the normal spar has embedded 2mm carbon fibre rod for extra strength. In the photo above you can see that a douple of pieces of foamboard are glued across the center. As well as providing extra strength, this fits snugly inside the wing preventing it from rotating laterally.
Heres the carbon rod extending out past the spar (where my 175% sparrow failed). You can also see here where I've Laminated (but not yet sanded) the outer edges of the wing. I used 24gm carbon fibre cloth and WBPU. I will almost certainly glass the entire wing and more than likely the whole plane.
Remember I mentioned the removable nose section, by pulling out the carbon rod and the screws at the bottom the nose comes off. The inside to the nose is reinforced with 2mm lite ply formers. They also provide nice solid mounting points to zip tie the undercarraige.
The tail section integrates a steerable tail wheel. The mechanism is primarily made from stiff clothes hangar wire bent and formed. I cut an aluminium disc for a wheel hub on the lathe anda rubber tyre on my cnc machine, though I need to redo that.
Next steps will obviously depend on the power choice. If I go with the twin idea, I'll need to mount nacelles before finishing glassing. Stay tuned for more pics as this progresses and I'll also have dxf plans for all the parts used in this build when its done.