Earlier I wrote about using carbon fiber tubes as building blocks in model construction. I built the basic box frame pictured below:
I had some time to kill so I decided to flesh it out to fly it. Now bear in mind that I started this as a build concept, so I really did not have a specific design in mind. I used some basic parameters from HERE and decided to use the wing from my HobbyZone Super Cub. Framed out it looked like this:
I loaded it up with Spektrum s75 servos for the tail and rudder and used the Scorpion Motor and ESC for powering it with a 2100 Lipo with a GWS EP 11 x 8 prop. All up it weighed in at 25 ounces – about the same weight as the stock Super Cub, so not unreasonable.
Usually I like to first run a new model on the ground to get a feel for it, but as there was snow on the ground, I couldn't this time, so I decided to hand launch it. I pre-flighted making sure the controls were OK, launched and it took off like a shot heading towards the ground. I gave it up a little up elevator and it flew straight ahead at a good clip. I applied some rudder to turn it away from the rapidly looming trees, and NOTHING.
Right, left – nothing. I quickly throttled down and it made a rough landing but clear of the trees.
Figuring maybe the vertical stab was too large, I cut it and the elevator back (that's the picture above). Out again and same thing – great flying straight ahead, but does not turn.
Then I figure maybe not enough control movement so I move the control rods to get more deflection and try again.
Same deal! This is now the third dirt crunch and I figure "enough of this!" I think the problem was that the Super Cub wing's stability overwhelmed the small rudder, further rendered ineffective by the small moment arm of the frame's length. I proved my point that this construction method in fact is pretty tough – the only damage to the plane was a small chip off the balsa frame by the firewall:
The front was unscathed:
I'm satisfied that this frame can take a beating, but how much? I'm not going to fly it into a brick wall to find out, so I decided to place it between two stacks of books and stand on it. I very tenderly lower myself into place and it creaks a little but holds my 175 pounds – not bad!
I have to get a picture of this, so I set it up and tell my wife to get the camera. While she's getting it, I step on it again, only this time was the killer – I crunched it:
Damn! That would have been a great picture!
However, I must point out that I stood on the frame's mid point – this is typically not where models fail in hard landing or crashes, unless somehow you manage to fly into a wall sideways at a real good clip. I have no doubt that if I stood on this frame lengthwise, it would hold my weight no problem; I thought about doing this but balancing on the firewall or tail end was not in the cards for me.
CONCLUSIONS
Carbon fiber tube construction in a frame will result in considerable strength, greatly exceeding the failure point of typical balsa or foam frames by a wide margin. Coupling this construction method with a sound plane design should yield a very durable, long lived model.
Carbon Fiber Frame Test
Tough stuff – how I tested it
Earlier I wrote about using carbon fiber tubes as building blocks in model construction. I built the basic box frame pictured below:
I had some time to kill so I decided to flesh it out to fly it. Now bear in mind that I started this as a build concept, so I really did not have a specific design in mind. I used some basic parameters from HERE and decided to use the wing from my HobbyZone Super Cub. Framed out it looked like this:
I loaded it up with Spektrum s75 servos for the tail and rudder and used the Scorpion Motor and ESC for powering it with a 2100 Lipo with a GWS EP 11 x 8 prop. All up it weighed in at 25 ounces – about the same weight as the stock Super Cub, so not unreasonable.
Usually I like to first run a new model on the ground to get a feel for it, but as there was snow on the ground, I couldn't this time, so I decided to hand launch it. I pre-flighted making sure the controls were OK, launched and it took off like a shot heading towards the ground. I gave it up a little up elevator and it flew straight ahead at a good clip. I applied some rudder to turn it away from the rapidly looming trees, and NOTHING.
Right, left – nothing. I quickly throttled down and it made a rough landing but clear of the trees.
Figuring maybe the vertical stab was too large, I cut it and the elevator back (that's the picture above). Out again and same thing – great flying straight ahead, but does not turn.
Then I figure maybe not enough control movement so I move the control rods to get more deflection and try again.
Same deal! This is now the third dirt crunch and I figure "enough of this!" I think the problem was that the Super Cub wing's stability overwhelmed the small rudder, further rendered ineffective by the small moment arm of the frame's length. I proved my point that this construction method in fact is pretty tough – the only damage to the plane was a small chip off the balsa frame by the firewall:
The front was unscathed:
I'm satisfied that this frame can take a beating, but how much? I'm not going to fly it into a brick wall to find out, so I decided to place it between two stacks of books and stand on it. I very tenderly lower myself into place and it creaks a little but holds my 175 pounds – not bad!
I have to get a picture of this, so I set it up and tell my wife to get the camera. While she's getting it, I step on it again, only this time was the killer – I crunched it:
Damn! That would have been a great picture!
However, I must point out that I stood on the frame's mid point – this is typically not where models fail in hard landing or crashes, unless somehow you manage to fly into a wall sideways at a real good clip. I have no doubt that if I stood on this frame lengthwise, it would hold my weight no problem; I thought about doing this but balancing on the firewall or tail end was not in the cards for me.
Carbon fiber tube construction in a frame will result in considerable strength, greatly exceeding the failure point of typical balsa or foam frames by a wide margin. Coupling this construction method with a sound plane design should yield a very durable, long lived model.