Hydrogen Fuel Cells?

I’m not sure how a fuel cell apparatus compares on weight against a 2-stroke engine.

The energy in 2.2 pounds (1 kilogram) of hydrogen gas is about the same as the energy in 1 gallon (6.2 pounds, 2.8 kilograms) of gasoline.

PEM Hydrogen Fuel Cell is 40-45% efficient.
Repeated google searches fail to give any % efficiency of a 2-stroke engine.

You can have a hybrid power supply that consists of some combination of Fuel Cells, Batteries, and Supercapacitors:

The issue is that Hydrogen has a poor volumetric energy density, and must be kept compressed to keep size down. This requires a strong reinforced tank, like a COPV, which is what adds weight.

Furthermore, compressed Hydrogen isn’t that widely available, as compared to gasoline or electricity. Sure, you can make your own hydrogen through electrolysis, but how are you going to compress it into a tank?

The typical gasoline 2 stroke paramotor engine is right around 15% efficient at a cruise. so from each pound of fuel you will get around 0.8 kwh after engine efficiency losses.

With a fuel cell even if you can only manage 30% efficiency and a motor with 90% efficiency, you could still get 4.83kwh per pound of hydrogen.

The main problems with hydrogen is that it either needs to be kept at roughly -250 degrees fahrenheit or compressed to 3000psi. So any method of storage will be very heavy. You also have the problem that hydrogen will leak through much smaller cracks than any other gas or liquid which can lead to fires.

Potentially the biggest issues is the fuel cell itself. I haven’t checked for about a year now, but if I remember right a 4kw worth of commercially available fuel cells was something like 80 pounds and $10,000. If these numbers are correct, fuel cells would need to have about 12 times the energy density and be about 48 times cheaper per kw of power before they would be a viable solution for paramotors. I do believe this may happen someday but I don’t think it is here yet.

Another interesting technology that I think may someday work on paramotors is a gasoline fuel cell. They get many efficiency advantages like a hydrogen fuel cell, but you get to eliminate all the problems that come with hydrogen. The disadvantage of gasoline fuel cells is that they have very little development and they need to run at something like 600 degrees fahrenheit which has caused a lot of problems for development in the past.

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The UK-based company Intelligent Energy already makes hydrogen fuel cells which can be integrated into UAV drones:

Intelligent Energy makes a 2.4 kW fuel cell module, which equates to about 3.2 hp:

If you used that 2.4 kW in connection with batteries or a supercapacitor, then the batteries/supercap could give you “takeoff power” while the fuel cell itself could be enough for regular cruising.

Here’s a demonstration involving the Tarot-X4, which is a known consumer-level drone:

Ballard Power Systems, one of the most well known fuel cell makers, has been touting their own fuel cell-powered drone::

Or what about Direct Methanol Fuel Cells?

Methanol isn’t as widely available as gasoline, but it’s still available.

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Bob27, I don’t think the 5-gallon limit applies to anything but gasoline. For instance, if you could fly with a propane tank, I don’t think the 5-gallon rule would automatically apply to that propane tank.

EFOY makes DMFC - right now they’re selling to boat owners:

Kraftwerk says they have a new fuel cell that will work with natural gas (methane):

Natural gas is much more compressible and containable than hydrogen.

Their technology is SOFC (Solid Oxide Fuel Cell), which means the reformer is built into the process.
I remember reading over a decade ago, about Siemens doing cutting-edge research on the technology.

Meanwhile, Compressed Natural Gas (CNG) cylinder conversion kits for scooters are available in other countries at an affordable cost:

This is straight out of part 103-7:

19 MAXIMUM FUEL CAPACITY OF A POWERED ULTRALIGHT VEHICLE.
The maximum fuel capacity for a powered ultralight vehicle is 5 U.S. gallons. Any powered
ultralight with fuel tank(s) exceeding this capacity is ineligible for operation
as an ultralight vehicle.
a. Determination of Fuel Capacity. The total volume, including all
available space for usable and unusable fuel in the fuel tank or tanks on the
vehicle is the total fuel capacity. The fuel in the lines, pump, strainer, and
carburetor is not considered in a calculation of total volume.

It mentions nothing about fuel type, type of fuel tank or any exemptions. It just says that any tank that holds fuel can not be bigger than 5 U.S. gallons. Hydrogen is a fuel and the pressurized tank is also a fuel tank, so it would be illegal to go bigger than 5 gallons even with hydrogen.

You must realize that these rules where written in 1984 and they never expected ultralights to use a fuel such as hydrogen for power. The FAA has made amendments to part 103-7 many times in the past to adjust for changes in the sport, so there is a chance they may change the fuel volume limit to a weight limit if hydrogen becomes popular.

I am interested to see what they do with their solid oxide fuel cell. They make things a lot simpler and improve fuel cell efficiency, but they can´t use the oxygen from the surrounding air which means the fuel cell only lasts a few tanks or you need to constantly replace the oxidizer.

The thing is that rule has never been enforced - certainly not in regard to alternative fuels. I’ve never even heard of batteries being subjected to any regulation under Part 103. Can batteries be considered a fuel? We know that they’re potentially combustible, and some Tesla vehicles have even gone up in flames.

Bob27, even if Intelligent Energy’s fuel cells aren’t currently ready to power paramotors, they can still do plenty for drones. That’s enough of a market for the time being, to allow the technology to continue to evolve until it’s suitable for paramotor use.

I don’t know about these SOFCs in particular, but I’d never heard that SOFCs in general can’t use surrounding oxygen. I think they have some kind of zirconia or zeolite type structures that allow oxygen to penetrate.

Ah but the regulations don’t say anything about standard temperature and pressure. We just need to compress the hydrogen at higher PSI for more flight time! Good luck doing that with gasoline.

You could get nearly twice the hydrogen by going with 10,000 psi tanks instead of the 3000psi tanks used by Intelligent energy. Your tanks may weigh over 35 pounds, but who is counting anyway? Lol.

You would be fine as a single person doing this, but if a large scale company did this and caught the FAAs attention, they could have a big problem on their hands. If I were to make more than one paramotor with more than a 5 gallon hydrogen tank, I would contact the FAA before hand just to be on the safe side.

The battery pack is an interesting topic. Reading through the laws it appears like only the tank size of the paramotor is limited and technically a battery doesn’t count as a fuel tank. I don’t think the original creators ever imagined batteries and fuel cells being used to power ultralights. But, even if a battery did count as a fuel tank, I haven’t seen a paramotor that uses 5 gallons in volume worth of batteries. For example the OpenPPG SP140 uses 264, 21700 cells. Each cell is 24.245 ccm in volume for a total volume of 6.4 liters or 1.69 U.S. gallons. Even if you add in the entire volume of the completed battery pack, it’s still about 2.5 gallons. For the X4, each battery pack is 1.471 liters for a total of 3.11 gallons with eight of them. So I don’t think battery volume is a big problem if the law applies to them or not.

Very true. The current world record flight with a multi-rotor drone is about 8 hours and it was powered off a hydrogen fuel cell. The current record for electric multi-rotor drone is only 3 hours. Like I said before, I do agree with you that fuel cells likely will have a bright future with paramotors.

Your right, I must have been thinking of a different type of fuel cell.

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https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/data/interps/2012/carpenter-rainbowaviationservices%20-%20(2012)%20legal%20interpretation.pdf says that batteries and electric power are legal for ultralight (but not for light sport, without special exemption), but their weight is considered structural rather than fuel – so electric aircraft are not given the extra 30+ pounds of weight allowance.
I think I’ve seen a ruling expressing this even more directly, and saying that the concern is that batteries don’t lose weight and become lighter (and therefore safer in a crash) as the flight continues, but I can’t find it just now.

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