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Old 28th Nov 2021, 11:36
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Originally Posted by Heston View Post
https://orsted.co.uk/energy-solution...wable-hydrogen
First website I found when Googling.
Originally Posted by Uplinker View Post
"Great. Where are you going to get the hydrogen from?......PDR"

You 'split' sea water into its constituent oxygen and hydrogen gases using electrolysis. We did it in chemistry at school. You just need sea water and electricity connected to two electrodes submerged in the water. A chemical reaction takes place and the hydrogen gas accumulates above the negative electrode, the oxygen above the positive.

Use wind turbines, solar panels or tidal flow turbines to provide the electricity to split the seawater, and you produce hydrogen.

Note: Sea water rather than pure water because the salts in the seawater make it electrically conductive.
That's my point - hydrogen is not an energy source, merely an energy transfer mechanism. You need energy made by some other means and then you "transform" it into hydrogen in a process that's inefficient and produces waste products (salts). Schoolboys say that burning hydrogen in internal and gas-turbine engines is "clean" because the exhaust is just water. This is (of course) not actually true. when you burn hydrogen in air at the pressures and temperatures you need for effective propulsion you also end up burning the nitrogen in the air and producing significant quantities of the nitrates which are ALSO one of the concerning pollutants. You could use the hydrogen in fuel cells for an electric final drive, but that's completely dependant on rare metal catalysts (a scarce and non-renewable material), making the problem worse rather than better - these materials make the platinum used in catalytic converters (which is already running into supply problems) look positively abundant. So if you're using the same generating plants as the grate unwashed are using for heat, light, cooking and social media then you can expect to join a queue. If they are being told they must have a cold house and can only watch strictly for 2 hours a day to conserve electricity I don't think aviation will be high on their list in that queue, and recreational aviation will be right up there with politicians on their list of hate objects.

Hydrogen can't be liquified at normal temperatures, so it has to be stored in pressurised bottles. The usual parametric is that to store hydrogen at a pressure that gives a third of the energy per litre of petrol needs "tanks" that will weigh twice the weight of the hydrogen being contained. The equivalent number for petrol is about 5% (for three times the amount of "effective fuel"). With all of this factored in the use of hydrogen fuel comes out pretty close to batteries in terms of MTOW limits with considerably fewer safety issues. Yes, the weight reduces with use, but not by anywhere near as much as it does for petrol because the basic fuel is lighter and the tanks themselves are [massively] heavier. Hydrogen does have the advantage of quicker refuelling, but has much more complicated fuelling equipment requirements.

I'm not saying it's not the answer - merely that it's a much more complex and nuanced question than most of these simplistic "we can use hydrogen and everything will be the same - everyone else is just to thick to see it blah blah" rants suggest.

PDR
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Old 28th Nov 2021, 11:38
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Originally Posted by ShyTorque View Post
A problem for larger ‘lectric aircraft is that unlike liquid fuelled ones they don’t “burn off” weight as fuel is used. This will cause design challenges because as we know, larger aircraft can take off at a higher all up weight than at which they can land. Undercarriages will have to be stronger and heavier, reducing payload.

Also, it won’t be possible to trade off fuel uplift for extra performance demands, such as at high density altitudes or short runways.

As always, design is a compromise.
For hydrogen fuelled aircraft, of course, the opposite is true; as fuel burns off, they become heavier.

Probably.
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Old 28th Nov 2021, 11:59
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For hydrogen fuelled aircraft, of course, the opposite is true; as fuel burns off, they become heavier.
Probably.
Probably only after the pressure in the tank falls below about 10 bar. Starting at 700 bar, say, it will become lighter as the fuel is used.
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Old 28th Nov 2021, 12:31
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You will note from my earlier post where I introduced the hydrogen topic that I said for ground based transport. This is because the extra weight compared to petrol etc. doesn't matter too much.
Hydrocarbon fuels have a very good specific energy density - ie energy available for weight. Much better than current battery technology and hydrogen (glad to see that PDR1 has done a bit of research now). That's one reason why they are going to be so hard to replace in aircraft.
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Old 28th Nov 2021, 13:13
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Whether all-electric engines or hydrogen powered units wins the day is going to be determined by development. The developments of potential will not be done by aviation manufacturers because the costs are too large. The adoration of the squeeze and bang engines supplied by clung click magnetos and using fuel that may destroy the earth is misplaced. We have got to look forward to engines that are earth kind and don't fall to bits over a short time as the current engines in use do. My mentors hammered into me the realism of engine failure and the need for a high level of skill in forced landing; this had been very real for them with the current engines.

The failures of modern electrical systems such as Pilot DAR's vehicle ECU that could fill with water with no means to escape. Once drained the unit was good and reliable enough to be used for a further decade and more. The DA42 with a back up battery that could not be recharged nor replicate the performance of the main battery, even for a short period. Not even a pilot alert warning was included in the design. Both of these is blinkered poor and sloppy design. To blame the pilot for not knowing the manual back to front is unfair and not human. The DA 42 aircraft had an external power socket to permit a start of both engines. Although the manual instructs that the external power should be disconnected after the first is started it does not warn that the second engine should not also be started the same way. It does not warn that you must wait for the flat battery to recharge sufficiently to a minimum level before takeoff in order to be relied upon later.

James Reason developed the 'Swiss Cheese' theory for a very good reason. Modern engineering should not be dissed: cracked engine shells, cylinder heads detaching and failing magnetos are things of the past and sadly of the present. Design isn't just about getting things to work economically, it is also about the operation. The worlds manufacturing Industry is well aware of this while the aviation industry still demands its customers to gain the equivalent of a master degree in the use of its products and also foresee events that they can't be bothered to warn you of.
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Old 28th Nov 2021, 13:17
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Originally Posted by Heston View Post
Hydrocarbon fuels have a very good specific energy density - ie energy available for weight. Much better than current battery technology and hydrogen (glad to see that PDR1 has done a bit of research now).
On a point of information - PDR1 does not need to be patronised* on this topic, and nor does he need to do any research because PDR1 is actually involved in studies around future aircraft propulsion systems and is thoroughly familiar with the pros and cons of the different options. All that PDR1 is trying to do is get across the point that it's not a matter of "simply switch to hydrogen and the job is done, as any idiot can see" because only idiots see it that way. In shear weight/size/performance terms there is as good a case for revisiting the nuclear propulsion concepts first played with in the 1950s (especially since the intervening 60 years of experience with micro-reactors in naval applications has massively matured the enabling technologies). It's unlikely to happen because of public perceptions about safety (as much as anything else), but then the hydrogen fuel lobby haven't yet given an answer on how the BLEVE risk which would make every hydrogen-fuelled vehicle (car or aeroplane) a potential FAE of almost atomic-bomb proportions.

PDR

* For Heston's benefit - "patronised" means "talked down to"

Last edited by PDR1; 28th Nov 2021 at 13:41.
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Old 28th Nov 2021, 13:25
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Calm please... There is a lot to learn, as we pursue less polluting flying, I'm sure that we can all learn something....

If the non aviation portion of society continues to notice that aircraft are the only means of transport not going green, we will have less and less sympathy (and extension of the availability of gasoline and jet fuel). Uunifying, and doing our best is the most wise path to sustaining our industry.
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Old 28th Nov 2021, 15:08
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Originally Posted by PDR1 View Post
Great. Where are you going to get the hydrogen from? It may be different in your part of the world, but around here hydrogen mines are a little thin on the ground...

PDR
For PDR's benefit, can I point out that this was the first patronising post?

Batteries and hydrogen are both "only" energy storage and transfer mechanisms. The assumption all along is the original source of the energy will be green, from wind or whatever.
But PDR makes a good point - I agree that it is likely that hydrogen tech won't work in aviation because of the weight issue, whereas we may get sufficient specific energy density from batteries eventually.
The Catch 22 though is that that will only happen if development continues for automotive use. If ground transport goes hydrogen, as I believe it will, then development of battery technology will grind to a halt, leaving aviation without a solution.
The recent demonstration of artificial "green" fuel for aviation use may turn out to be the answer.

I was doing research into alternative battery materials in the 1970s, so I think I know that progress has been slow. Hydrogen is pretty recent by comparison.

Last edited by Heston; 28th Nov 2021 at 15:57.
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Old 28th Nov 2021, 16:39
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I accept that that there was good patronage on both sides (to quote Agent Orange).

I'm not particularly promoting batteries either, just (as I said) making the point that it is not a clear binary debate. Tracing the value-chain from energy source to power developed in both cases shows that the battery line in more efficient and has lower overall emissions, but that doesn't inherently make it ideal because of its fundamental limitations in terms of range, turn-around time etc.

I think a rational solution would look to tap into the resource which is both carbon neutral and depressingly renewable - so we should consider whether a propulsion system fuelled with rendered climate-change protester oil might not be the best solution. I fear there would be no lack of volunteers to work in the climate-protester rendering plants.

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Old 28th Nov 2021, 17:52
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Step changes in aircraft were always engine driven

1) A piston engine with a high enough power to weight ratio to allow flight: The Wright bothers engine
2) A piston engine with enough power to give meaningful performance: The Gnome rotory
3) A piston engine that can produce enough horsepower to make air transport practical. The P&W and Curtis 9 and 18 cylinder radial engines
4) The first jet engines
5)???
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Old 28th Nov 2021, 18:00
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This is true - if steam engines had been lighter the first powered heavier than air flight could have happened long before 1903. We could have had steam punk style aircraft; that would have been cool.
Is an anti-gravity drive needed next?
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Old 28th Nov 2021, 18:08
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Originally Posted by Big Pistons Forever View Post
3) A piston engine that can produce enough horsepower to make air transport practical. The P&W and Curtis 9 and 18 cylinder radial engines
I think Rolls Royce, Napier, Bristol and DeHavilland, Hispana, BMW, Junkers and quite a few others might be coughing & spluttering a bit at that.

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Old 28th Nov 2021, 18:52
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Instead of discussing which is the best or most likely alternative for fossil fuels, we had better realise that energy, of whatever kind or origin, is rapidly becoming more and more rare and thus more and more expensive. It seems obvious to me that activities that rely on large quantities of energy will become - as they once were - the exclusive playground of the well-to-do. Which includes private flying, motorboating, karting, and several more.
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Old 28th Nov 2021, 20:14
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Originally Posted by PDR1 View Post
I think Rolls Royce, Napier, Bristol and DeHavilland, Hispana, BMW, Junkers and quite a few others might be coughing & spluttering a bit at that.

PDR
Nice try but the vast majority of piston engined airliners had American radial engines. European protectionism allowed more expensive and less reliable engines to see service but the production numbers tell the tale. Particularly post WW2 the vast majority of airliners in service were powered by American engines including those used by every major European.

In any case it doesn’t matter, the point remains that the reliability and efficiency of the big radials allowed practical passenger air travel for the first time.
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Old 28th Nov 2021, 20:29
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Actually, Heston, see: https://en.wikipedia.org/wiki/John_Stringfellow

In 1848 Stringfellow achieved the first powered flight using an unmanned 10 ft wingspan steam-powered monoplane built in a disused lace factory in Chard, Somerset.
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Old 28th Nov 2021, 20:45
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When fossil fuel was first used, the idea that enough CO2 would be produced to affect the Earth's climate would have been unbelievable.
Plants use CO2 to make their food. They excrete O2.
is there any possibility that hydrogen from water could increase the atmospheric O2, before it is converted back to H2O?
This could have an impact on fires and on respiration.

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Old 28th Nov 2021, 22:05
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Although the manual instructs that the external power should be disconnected after the first is started it does not warn that the second engine should not also be started the same way. It does not warn that you must wait for the flat battery to recharge sufficiently to a minimum level before takeoff in order to be relied upon later.
I believe you are incorrect.
I’d have to dig into my pile of old manuals but the DA-42 1.7 did come with a warning not to start both engines with external power.
I believe also the Battery Master switch was never turned on so the electrical system was running off the generators without the benefit of the buffering function of a battery and the ECU’s “blinked” as a result of the brief fluctuation as the electric hydraulic pump kicked in.
The backup batteries installed as a result of that pilot induced incident did not have to be rechargeable as per EASA certification.
The original Thielert 1.7L was and is still my favorite engine for that airplane.
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Old 29th Nov 2021, 00:43
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What a subject, pages could be written, yes engines are not as reliable as they could be certainly Lycomings have many uncorrected design flaws, so that many never make TBO, without some work.

To make Hydrogen with electricity needs clean water not sea water and platinum for the electrodes ( have to mine an asteroid for the amount needed)
at the moment it is made from natural gas which produces 9kg of CO2 for every Kilo of it. So not so clean.
Also as it costs about a million pounds to build a Hydrogen filling station, I don't see airfields rushing to install them.

Electric motor/battery combination has to be consider as a package and compared to the weight of ICE and fuel together to be compared.
So the extra weight of the battery can be offset against a lighter electric motor. So when batteries reach about 2.5 Klw/hour/Kilo then liquid fuel is dead.
Note there is a 300hp 15kg electric motor on the market but it does rev at 20,000rpm so the gear box would add extra weight.

A bit off subject Lycoming have a certified electronic Mag on the market and are fitting one on new engines along with a normal mag as backup
this means ships power is required to run but it does produces a higher spark voltage and cheaper automotive spark plugs can be used.
Improves starting and more reliable. The next item to improve things would be dumping the 14 volt lead acid battery for a LiFePo4 Lithium (they don't burn)
but would would require a small redesign of the alternator regulator for the correct charge voltages and must have overvoltage protection.
These changes are relatively low cost but I believe would improve reliability.
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Old 29th Nov 2021, 05:55
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In my estimation the test of an engine is its fuel efficiency, the fuel burned for each horsepower produced, crunched some numbers and a Lycoming O-720 at 75% best economy comes out at 34.44%, R-3350 at the same setting 35.71%. Pretty good I'd say, without hanging electricity dependent bits off of it. Haven't been able to find car figures to compare, I've read that all the do dad electronics on todays average car has more to do with meeting pollution requirements than improving economy
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Old 29th Nov 2021, 06:57
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There is no conflict between fuel economy and pollution, at least not as regards CO2: if you burn 20% more fuel then you'll produce 20% more CO2. Electronics do help to optimise the process though, reducing CO and other things even worse than CO2.
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