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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Hi all.
Has anyone here actually managed to build any large (ie >1m diameter) model lenticular (ie disc shaped) craft? I had a look at examples on the Internet and it seems that Coanda effect craft do exist and thanks to advanced LiPo cells molded into the aluminium casing can be quite sturdy indeed with large counter rotating fans inside 3D printed over carbon for maximum efficiency.
It occurs to me that a lot of existing models have a habit of being unstable in high winds, whereas a disc or lenticular shaped craft with feedback to hold it in position and ducted fans inside could hold its own so to speak without expending anywhere near as much power.
As far as powering it, retractable segmented Fresnel lenses and solar cells on the top might work here as landing it for a short time say 1 hour would allow it to "hop" to its destination just as some birds land briefly while over small islands to let the motors cool down and fully recharge the onboard batteries. Taking off again would just be a matter of dumping the supercapacitor bank(s) into the motors to overcome gravity and then substitute with battery power once airborne.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Weve done the maths for one of these in another thread. It's always a trade-off between efficiency and manouverability. Efficiency requires low disc loading and manouverability requires high disc loading.
We set out to design for efficiency and ended up with four 30" rotors. We've also realised we want to spin them so the tips almost go supersonic, AND we need the profiles to be 'perfect' in oder to get laminar fow.
Most commercially available drone rotors are designed for very high disc loadings. This results in good manouverability but poor flight times/payload capacity.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Hmm. Wonder if a hybrid ion wind/rotor system would work? ie blow air through an ion plate arrangement past thin wires, like a boosted ionocraft? But negatively charge the motors and props to -10KV as well so the gaps can be larger for more thrust.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Yeah, it was pointed out that there was a mismatch.
How would the poor efficiency be overcome? I thought maybe use a rotating porous surface (ie tiny holes) and blow air through these to exploit boundary layer effects. ie the two surfaces spin in opposite directions with a central nexus containing the controls and gyros.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Conundrum wrote ...
How would the poor efficiency be overcome?
All the losses are from the periphery of the column of accelerated air. If this column is fast moving and of small area, losses are huge. If the column is slow moving with a large area, losses are negligible.
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