Engine running

At Aero last month, electrical flight was one of the big topics. They even had an airshow with an electric aerobatics plane! I’m curious to see how things will develop from here and if we’ll ever see electrical systems replacing the good old gasoline engines and turbines on a big scale. In the automotive sector, we’re not that far away, it seems.

Anyway, in this case, Hans is paying for the gas, so I guess it’s no big deal. But if he ever got wind of Chuck’s approach to fuel efficiency, he’d probably ask Julio to install an automatic start-stop-mechanism in the Cessna engine, haha!

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12 comments on “Engine running
  1. Fred W. says:

    Would not want to try that in real life – Cylinder head temp would likely rise high enough to destroy the aluminum.

  2. Bernd says:

    Yes, aerobatics is sort of the ideal application for electric flight until battery technology improves vastly; competition flights are just short enough for it to work out. And the missing noise isn’t such a big deal, the prop still makes enough of it.

  3. Johsua says:

    Batteries will never be a feasible replacement for one reason: energy density. A battery requires you to take your oxidizing agent with you while you can use the oxygen in the air for gas. It basically doubles your weight a given fuel. Worse, batteries are not compact so they take up a huge amount of room relative to the gas it is supposed to replace.

    Long story short, batteries are too big and heavy due to the laws of physics to make a practical replacement. Even for a car the range is too limited for everything but the shortest range driving. You can’t make a long haul anything with batteries.

    Then this kicks the can down the road. You stored the energy but you have to generate it. That means building more fossil fuel plants or nuclear plants. Alternatives can’t even get close to powering the current grid. They are hopeless for meeting the added demand of transportation even without the loss inherent in storage.

  4. mike says:

    @Fred W. – There are a lot of things Chuck does I wouldn’t want to try in real life, HAHA!

  5. Bernd says:

    Joshua, that’s a bit short-sighted.

    Battery chemistry is not fuel, it may be possible to get close to half the energy density of chemical fuel, although nobody has as of yet the slightest idea how, but the laws of physics do not, in principle, prevent it. And if we get there, we’re done, because electric motors are almost three times as efficient in converting the energy into mechanical work. They are not heat engines, and thus not limited by carnot efficiency.

  6. Bernd says:

    Joshua, addendum:

    You are currently right about generation and storage of power, we are nowhere near where we need to be, but, again, there’s no principle physical reasons why we couldn’t get there with nuclear fusion, photovoltaics, wind power and superior storage. It’s going to take a long time, I will probably not live to see it.

  7. Quill says:

    Putting too much gas in can be quite a conundrum – there is no easy way of getting it back out. Maybe the fuel drains, but that certainly wouldn’t be practical, would take longer than running the engine probably and would be a huge hassle. As for electric aircraft, I see two initial roles. One is low-power high efficiency trainers, sort of motor-glider like aircraft that could do a 1.5 hour training flight on a charge (all while flying relatively slowly), with very low operating costs (extremely simple maintenance, no fuel, just some electricity) I guess the Airbus E-fan is of this type, tough somewhat outlandish – I’ve seen far more conventional aircraft of this sort in development, though none are on the market just yet. A few electric motorgliders are, not yet up to where their gasoline-powered counterparts are in terms of performance, but they’ve come far enough to be useful. The other role is short duration high-power, such as the aerobatic aircraft others have mentioned. They’re limited in range, fine when they only need to fly a few minutes at a time, and have loads of power. I could see this working well for glider towing as well, short flights where they go up at full power (would be a very quick glider tow, far faster than a Pawnee or something), descend with the windmilling propeller as a generator partially re-charging the batteries (airplane regenerative braking), then sit on the charger for 20 minutes between tows. Long-range, anything used for transportation (the majority of aviation) will take a bit longer, but I think we’ll get there eventually, gradually moving up in size and range, initially GA, then regional aircraft, then short-haul airliners, eventually long-haul widebodies.

  8. Johsua says:

    Bernd, it is correct that Battery chemistry is not fuel but the principles are actually very closely related. It all comes back to the good old conservation of energy. Thus the reason for a theoretical 1/2 energy density. In a world where we are struggling to make practical aircraft on a “fully efficient” storage system that 50% really counts. Also, upping the efficiency of a battery also makes it very dangerous even if unknown processes could do it. See the exploding laptops for details. I think some cartoonists where poking fun at a certain Boeing aircraft for that 🙂

    I didn’t want to really go into it, but in terms of generation fusion and fission is really the only long term solutions. Problem is that people are scared of fission mostly without reason and fusion has been 10-20 years off for 50 years. Photovoltaics are really inefficient and require lots of rare materials and extensive processes to make. Not to mention the problems with where to put the solar panels. Solar is actually really dirty. Wind is simply unreliable and not omnipresent and storage is, well, problematic.

    Actually, that brings up the real alternative. Synthetic petroleum fuels are perfectly possible and carbon neutral. The only draw backs is that it is expensive and not economically feasible at the current time.

  9. Bernd says:

    Joshua, I think we actually agree on most issues. My point is that if the theoretical limit for batteries is around 1/2 the energy density of fossil (or other combustible) fuel, and if we can get close to that in practice (which is a *huge IF*) then we’re golden, because electric motors are inherently more than twice as efficient as any form of heat engine.

  10. markm says:

    It’s much worse than 50%. The highest energy/mass fuel-oxidizer combination for both air-breathing engines and onboard oxidizer engines such as rockets is hydrogen + oxygen: 2H2 + O2 = 2H2O. That takes 8 kg of oxygen to 1 kg of fuel, 89% oxygen. It would also be the ideal fuel for fuel cells, except for the difficulty of carrying a tank of hydrogen. For hydrocarbons, the combustion product is H2O and CO2. C+O2 = CO2 takes 32 kg of oxygen to burn 12 kg of carbon, 73% oxygen.

    But you don’t burn hydrocarbons in batteries. Lithium combines with oxygen 2Li + O2 = 2LiO, 16 kg oxygen to 14 of lithium. But batteries don’t use elemental oxygen, either. The lithium reacts with some complex (and therefore much heavier) chemical. I would expect the theoretical limit on energy density for a battery to be under 1/10th that of a tank of avgas. You’d get a shorter range, plus recharging takes longer than refueling.

    Fuel cells (using atmospheric O2) would be a better approach in the long run, but we’d need a much better power to weight ratio than the ones now available, plus a practical way to store hydrogen without either liquefying it or using a tank that is much heavier than the gas it contains. Or we’d need a lightweight fuel cell that oxidizes both hydrogen and carbon so the fuel can be a hydrocarbon, or at worst an alcohol.

  11. Bernd says:

    markm, all true as far as it goes, but we’re not talking about current (or future, enhanced) Li-Ion batteries, but theoretical physcial limits of chemical batteries of *any* kind. And they could conceivably be much better than Li-Ion, although nobody knows how.

    The problem with recharging is also mostly limited by current technology, and for small private planes at least not so much by theoretical limits. Recharging an airliner will probably remain impractical, though.

    The solution seems to be battery-change, but that, too, will only be practical for small-scale applications.

    Methanol fuel cells are an option, but they are also not yet competitive by a long margin.

  12. markm says:

    Bernd: Any future battery chemistry will still use the same elements, with the same atomic weights and the same bonding energy – and any high energy to weight batteries will use the first nine elements (hydrogen to fluorine), because past flourine the weight goes up but neither the bond energy nor the number of bonds increases.

    There are possible improvements in reducing the weight of the inactive parts of the battery relative to the energy-storing active components, in reducing charge time, and in extending the battery life, but I don’t see any way that a box holding both fuel and oxidizer in forms stable enough to travel is going to come within 20% of the energy content of a tank of gasoline for an air-burning engine.

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