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The Possibility of Nitro-Electric Battery Replacement

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Patrick

Sun Nov 10 2013, 06:53AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Im thinking of trying to replace a 400 gram battery which will fly a 1.4kg tricopter for 6-9 minutes with a 700gram nitro-electric contraption for 30-60minute flights. similar in implementation to diesel-electric trains, as we need to move from expensive toys to real and practical machines. (im also investigating fuel-cells)

My purpose for all the drone work ive been doing is as follows. First, the killing capabilities of drones have clearly been proved beyond any doubt. but... second, the saving of and assisting professionals question has not at all been settled, can these elaborate devices really be used by and assist police and firefighters? or are these devices merely expensive toys?

without longer flight time, i fear we are firmly in the later category...

for a start im thinking of a nitro piston OS 46AX engine, at 0.7 to 1 electrical HP to lift a 1.7kg -ish machine for 30 to 60 minutes at a a time. this engine is capable of 1.4 HP output normally for RC flight purposes, and wheighs 270 to 400 grams.

initial idea:
[liquid fuel] => [Piston] => [3-Phase PM Motor] => [Diodes (maybe SPMS?) ] => (useful electricity to drone)

most of what i fear revolves around piston inefficiency, conversion inefficiency and weight of an all-up system...

not sure if any of this is even possible, much less wise...Any better ideas for a solution to my problem will be enthusiastically appreciated.

Shrad

Sun Nov 10 2013, 10:08AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

hafnium jet ;) I heard somewhere they are somewhat already done

a 75keV excitation of hafnium dimers would induce spontaneous emission of 2,5MeV energy beam, which would be used to heat a small quantity of water in a compression chamber to achieve thrust through an exhaust

but this is just a rumor and I have not read anything about that anywhere...

BigBad

Sun Nov 10 2013, 10:17PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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Posts: 600

How many watts?

edit: I suppose about 500 watts or more.

I was trying to work out whether power beaming might be practical.

I suppose it's mostly a safety and EMC type thing.

If you can get the power density down to ~100w per square metre it wouldn't be immediately unsafe even if you were directly hit by the beam.

Patrick

Mon Nov 11 2013, 04:35AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

with beaming, you wouldnt need any of the battery mass or power storage parts as in a fuel cell. so the "beam'ed" power could be less than what ie already measeured. the battery is at least 25% of the vehicals mass... thats for a useful duration of flight for several minutes...

The "free piston" type is an interesting idea. Here :

wiki:

BigBad

Mon Nov 11 2013, 04:19PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

with beaming it's conceivable to use the propeller as the aerial

the free piston thing ought to work in principle, but would probably give high vibration; and unless I'm missing something I think if you've got an IC engine on board you might as well use it to drive the rotor directly rather than go through the conversions.

Another idea would be to use an off-the-shelf centrally mounted gas turbine/jet engine to give high pressure air, and use that to blow air through the rotor tips, either like a tip rotor, or like a boomerang.

Patrick

Mon Nov 11 2013, 11:33PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Yeah others have built IC engine driven multirotors bur they're hard to keep predictable.

radiotech

Tue Nov 12 2013, 06:13AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

A magnetohydrodynamic generator would provide a higher efficiency plus
provide a hot gas exhaust which may be used in a turbine booster to turn
the prop along with the electric motor. The idea is the motor will need less
torque if the turbine is also pushing it around.

Patrick

Wed Nov 13 2013, 12:18AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

radiotech wrote ...

A magnetohydrodynamic generator would provide a higher efficiency plus
provide a hot gas exhaust which may be used in a turbine booster to turn
the prop along with the electric motor. The idea is the motor will need less
torque if the turbine is also pushing it around.

The problem is its hard to control speed and acceleration of each independent prop. And the PIDs, are only as good as the fidelity of the end controls response.

BigBad

Wed Nov 13 2013, 03:47AM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

Apparently wikipedia says that nitro RC helis get up to 15 minutes of flight time.

30-60 minutes may be pushing it, unless you've got some really clever trick.

Patrick

Wed Nov 13 2013, 04:58AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

BigBad wrote ...

Apparently wikipedia says that nitro RC helis get up to 15 minutes of flight time.

30-60 minutes may be pushing it, unless you've got some really clever trick.

Time of flight is mostly a function of fuel tank volume. 15 minutes is typically enough to do heli fun flying.
A tank 4 times greater is no biggie, if planned for in the design phase...so long as the whole thing doesn't weigh a ton.

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