altitudinous flying

[DavidIAm]

i am impressed by the video of quads and how fast they move in any direction.

the concept here is how high can i build a quadcopter to go?

contest: who can get their quadcopter the highest on a fixed size of battery?

i imagine that the ideal prop for higher altitudes is different than down at sea level.

but fortunately the speed of sound is higher up there leading to higher potential prop tip speeds... so would be able to run larger props at higher rpm to get lift even at altitude.

if could maintain 10m/s vertical for 600 seconds the unit could be 6 km or 20K feet up. take a photo up there!

but i want to log altimeter over time curve with quad going straight up. what do you think? can optimise for climbing?

 

[fixnfly]

Either special waivers would be needed for that altitude, or it would have to be done in some other country then the US. 20,000ft is also really high for a quad.

 

[DavidIAm]

lets skip the legalities.

I am interested in the technical aspects the aeronautical and power concerns, feasibility of hardware. how you would design one go higher.

any thoughts on that?

 

[fixnfly]

Flite at high altitudes is possible. Full size helicopters do it to some degree, and Nasa is developing a helicopter to fly from a mars rover.

http://forum.flitetest.com/showthread.php?30353-R-C-Copter-on-Mars!

Legal issues may be able to be solved, they do let amature balloons fly that high with permits.

As for the technical and aeronautical aspects, I would have to break out the textbooks, engineering paper, and octave (poor man's matlab) to do some simulations. Power limitations on flight time would be an issue. It also may help to design your own props to be more efficient in thinner air and higher rpm.

 

[Hai-Lee]

Does your envisaged design have a special recovery system, (Parachute or similar)?

If not and you wish to reuse the vehicle you will require to build a reserve of power far beyond the power required to attain the target altitude. The thrust to just maintain altitude must equal the weight of the vehicle and at high altitude the air is thinner and so far more must be moved to obtain the required thrust.

I have not researched the exact air pressure at 20,000 ft but I expect that it is in the order of half or so of the air pressure at sea level.
A vehicle which weighs in at 5 kilograms would require a thrust of 10 kilograms just to maintain altitude and if the vehicle was to accelerate at a near uniform rate from ground to peak altitude then a far greater thrust to weight ratio would be required.

As a sensible direction to explore would be to build a Quad/helicopter hybrid where the fixed pitch Quad props were replaced with large disk multi-bladed rotor disks with variable pitch mechanisms. Such an approach would allow for near constant thrust levels to be obtainable without overloading the lift motors and wasting energy through motor heating by allowing for low pitch on take off and higher pitch at higher altitudes.

With a little extra engineering input from those who know the formula/s it might be possible to reduce the weight of the power reserve for recovery by factoring in an auto-rotation function for the descent and recovery.

 

[Fluburtur]

This might help you