Fuel Cells

[bruce.markle]

Gang -
Just saw this about fuel cells, looks like they have it working on a small UAV.
They have stacks rated at 1 KW weighing 4.4 lbs, not counting H2 tank. So about a dozen of these would fly a gull around quite nicely, with a enough leftover for charging a climb battery...
http://www.horizonfuelcell.com/#!copy-o ... tions/ccm4 http://www.horizonfuelcell.com/#!copy-o ... tions/ccm4

[rahulchoudhary73]

works out to nearly half the specific power or power/weight density compared to the wankel-genie (last one i saw was an engiro re2 20kw/69lb dry weight); and then a highly flammable h2 tank this close to a human in the air, refuelling cost and airfield infra..

btw, why are generators measured in kVA and not simply kW? there's even some conversion factor like 0.75 or something

also, there seems to be this average rule of thumb for large power plants at least, ~2,000$s per kW, +- 20% depending on the type of cycle; wonder how all these myriads of portable energy sources measure up..

[blaswichk]

Around here generators are rated in KW, ( which also is KVA since W= V x A), and electric motors mostly rated in HP which happens to be 746 watts, usually rounded to 750 watts. I also wonder about how much the H2 tank might weigh.

[rahulchoudhary73]

37lb for a capacity of 34L; they're called type IV composite tanks at 5000psi; even saw a photo of one that passed a bullet test; are these common there now? did read about H2 production getting a major boost there recently
http://www.qtww.com/assets/u/TankBrochure34L40L.pdf

[bruce.markle]

Have been keeping my eye on the Aixro “range extender”, used to be the RE15-2 is now the RE 20-2. Weighs 32 KG (64 lbs) and puts out 15 to 20 KW. A wankel go-cart engine hooked to a generator. The old 15-2 specs said it burned 5 Liters/Hr at full load, which is pretty fuel efficient as well. Haven’t seen anything else with its power to weight ratio, except for ones with a couple of low single digit HP model airplane engines…



http://translate.google.com/translate?hl=en <http://translate.google.com/translate?h ... _qdr%3Dall> &sl=de&u=http://www.aixro.de/produkte/wankel-xf4 ... _qdr%3Dall

[rahulchoudhary73]

Yes, just that 32A doesn't quite make the grade for gull yet (or maybe it may because of the high voltage due to the high rpm; but then another transformer would be needed..)

eGull at 65mph cruise needed 40A with the 20KW Joby in Mark's Arlington dazzle couple of years ago; wonder what today's stats look like, across the entire speed range

[bruce.markle]

The 32A discussed would work out to a supply voltage of 625 Volts if it operated at the 20KW power rating.



They talk about output voltage ranges from 60 to 570 vdc are possible. This would be done by using a different number of winding turns on the generator, lower turns and bigger wire to give lower voltage and allow more current. So if you ordered it with the lowest output voltage version, 60 volts, you would get 333 Amps at the rated power. So I think you simply have to ask for a lower voltage higher current output based on your needs.



With respect to asking, there is a big note on the PDF data sheet saying “NO SALE TO PRIVATE PERSONS”. So I guess it’s not worth our time to ask, or to ask for pricing info either. Too bad…

[rahulchoudhary73]

Thanks, Bruce; with an ampacity rating of 2.5A per sq. mm, that'll be one humongous wire, wonder how many turns does it really take..... like Blowin' in the wind by Bob Dylan ;)

[mkoxxy]

20kW is plenty to keep eGulls in the air, even after completely draining
the battery. But 32kg = 70.5lbs, plus it's water-cooled, so add the weight
of a (very small) radiator. 10l = 2hrs = 2.5gal = 15lbs + tank. We are
quickly approaching 100lbs. But if an eGull could carry that, and if the
required volume could be found, it would extend range enough to make
x-country feasible. Mark could *fly* an eGull to Oshkosh! Forget tent and
sleeping bag, though.

[bruce.markle]

Yep, I like the hybrid idea, and you just strap it in the back cargo area as
payload. With the Hybrid range extender (with some batteries, say 10
minutes of climb = 20 minutes of cruise), you could climb really well with
both power sources, fly for quite a while if you run out of gas or it
breaks, and recharge while cruising (size generator for cruise power plus
10%).



You can then easily get rid of it when we get gee whiz carbon nanotube or
zero point energy batteries.



So a soaring gull (can better handle higher gross weights) with a Zero
motor and controller would be a great core aircraft. Locate the batteries
and/or generator on the CG so you don't have issues in the future as the
energy system gets lighter.