The curse of royalty free music strikes again
If your video is about the subject of many people's phobias you would do well to check that the work experience kid hasn't slapped on some inappropriately ominous background music.
The first hydrocarbon/electric aircraft has taken to the skies over Southern England as part of trials to find out if such combo systems have a place in aviation's future. Youtube Video The aircraft, a heavily modified microlight, uses a conventional four-stroke petrol engine as its main power source and an electric motor …
Isn't that a bit inefficient? I mean converting the energy from petrol to electricity instead of just using it to propel the plane.
It's hard to see where the gains are coming from in general unless the battery is fully charged from the mains before take off. In which case the 30% figure might be the petrol saved due to the electric energy doing the work during take off. I wonder how quickly the 30% drops if the flight is over 100 miles, for example.
Perhaps the next step will be having retractable "wind mills" to recover energy when the plane descends... a kind of regenerative braking for the air!
"Isn't that a bit inefficient? "
Undoubtedly. But in a prototype that doesn't matter one hoot, because you're focusing on getting other more important bits to either work (at all) or to deliver some previously unachieved efficiency.
Regenerative braking is possible in theory, in practice it will never happen, because the aircraft's drag is normally the only braking it ever needs other than on approach and landing, and the weight penalty of any additional energy recovery gear would more than counteract the tiny recovered amount of energy.
I think where this hybrid tech eventually find a home is in keeping larger unmanned craft airborne for longer, rather than manned aircraft.
This rates as one of the clearest explanations from 'an expert' on a technical subject that I have heard in years.
I can see Tesla putting money into such a thing.
Also I would like one, a friend has a mini airstrip about ten minutes from my house where he flies a Paratrike, I think I prefer the powered glider better control on a gusty landing.
- Is it a plug-in hybrid? I assume it is since it has to have some charge in the batteries to assist during take-off
- Does it have 'regenerative braking'?
The reason a hybrid car 'works' is because there is a lot of stop-start traffic so the regenerative braking can actually charge the batteries, and any 'idle' or excess power from the petrol engine is used to charge the batteries.
How exactly does a 'hybrid' system benefit an aircraft which usually has a fairly short acceleration phase, then a very long cruise and than a fairly short deceleration phase?
You beat me to it, have a pint on me.
Maybe they need to add something to convert the flow of air over the wings / body back into electrical energy...hang on, how about another propeller that's not powered but instead spins in the airflow and is attached to a generator...looks like I've invented perpetual motion, first & second law of thermodynamics pah.
The video explains it pretty well, the example aircraft would normally need a 17kw engine to provide enough power for take off, but cruise would only use about half that (which means the engine has to be tuned for a wide operating range, rather than optimum efficiency in a small range).
The hybrid runs a much small engine (7kw), this means it can be kept in a small operating range making it more efficient. The batteries drain during take off, once established in the cruise you run the engine at a little over the power you need to recharge the batteries in case you need maximum power or have an engine failure.
So it's not like a road hybrid were the batteries are frequently being charged/drained as road conditions dictate, but rather by the phase of the flight.
Wouldn't a simpler solution to this issue seems to have two small petrol engines instead of one big one?
Much like the ekranoplans of the past have dedicated take-off engines than shut them down when not in use. That way you don't have to lug two different power-storage devices petrol and li-po.
And your not so tiny mind is quite correct. When you are landing, you raise the nose to bleed off energy and kill the lift. If the land is sloping upwards at a significant angle, the amount that you need to raise the nose will most likely be above the angle at which the wing will cease to fly, resulting in, at best, a very heavy landing.
Wright-Patterson AFB in Ohio has a runway like that. They've used it for soapbox derbys also. I don't what gains in efficiency were possible or much about what testing they did (pretty secret stuff goes on there) but one of the public statements was "testing different takeoff and landing modes". At one point it was SAC base and either the bombers or the intercepters used that runway.
You need the power for climbing. At some point you leave the runway and start heading upwards. The sloaped runway doesn't help with that part, and depends on the wind being in the right direction. It also makes takeoff and landing more tricky (and yes, I've flown in and out of airfields like this).
A small internal combustion engine, sized for the cruise regime, can be quite efficient, with a little on top to charge the battery. And the power boost from the electric motor for take-off and climb will be much quieter . With the relatively long cruise, it doesn't need a huge excess to recharge the battery. I doubt this plane has much spare weight, but adding solar panels would be possible.
"A small internal combustion engine, sized for the cruise regime, can be quite efficient,"
Indeed in most petrol/hybrid cars a modified Atkinson cycle engine is used that has a higher fuel efficiency than normal (Otto) engines at the expense of lower output for a given engine size. The battery then provides the extra power required for acceleration/hill climb. Regenerative braking is a bonus for urban use or descents.
I think the clue is in the bit about replace all engines & fuel with electric stuff and it's good for 10 mins flight. Instead of 10 hours or so in an airliner. Even a microlight is required to have 1 hour duration at full throttle (although maybe SSDR lets you off this). Petrol (or AVGAS) is not the expensive bit in flying anyway - but it is a very concentrated energy source, much better than electricity. So any percentage of electric in the hybrid is sub-optimal.
But said boffin gets to play with a microlight, Paul Dewhurst gets to fly it for free and Boeing gets to pay, so taxpayers money isn't wasted and everyone is happy.
When you buy petrol at a garage it is of course taxed, whether you put it in a car or an aircraft. AVGAS too is taxed (and is more expensive than petrol), as I believe is AVTUR (kerosene) used for private flying.
Aircraft capital & maintenance costs and hangarage are generally more expensive than fuel costs - certainly at the lighter end of the aircraft scale.
Passenger duty is a different tax (but still basically the Government taking money off people under threat of imprisonment).
"When you buy petrol at a garage it is of course taxed, whether you put it in a car or an aircraft. AVGAS too is taxed (and is more expensive than petrol), as I believe is AVTUR (kerosene) used for private flying."
A quick scan over https://www.gov.uk/fuel-duty and following the links on duty relief seem to indicate that AVGAS is 20p/l less than petrol and AVTUR is the same duty as petrol but for commercial use, both AVGAS and AVTUR are duty free.
"With current AVGAS prices being about £1.80/litre"
Thanks for that. I didn't realise AVGAS was more expensive than petrol even with it's 20p lower duty rates. Is the £1.80/litre the private recreational rate with duty and VAT applied or is that the duty free, VAT reclaimable commercial price?
Well, electric motors have lot more torque so it makes sense to some degree for take off, but you would need to work out the power to weight ratio to see if its any benifit, but the next question is, why not put solar cells on the wings as well and during decent you could have turbines generating power as gravity pulls you out of the sky.
didn't someone design or make a plane that could fly indefinitely using a similar approach?
anywho, much like cars that argument petrol engines with electric (rather then the horrific electric only jobs) if any improvments can be made with hybrid approaches then go for it, as long as it benefits it and isn't a publicity stunt it sounds like a win win idea cars do have an advantage with breaking directly feedling the batteries off the motors but im sure the boffins could work out something for planes too :)
The story is about how to spend grant money when you can get it for free...
For the same reason that EVs are impractical for 99% of the world, battery powered or assisted airplanes are also impractical. Even when the aircraft is sitting on the ground and the batteries are being charged, electricity isn't free. The batteries aren't free. The maintenance isn't free. The disposal of toxic dead batteries isn't free. The problems with high tech batteries in EVs as well as commercial aircraft for auxiliary power have been documented.
The sad reality is that even with newer battery designs, they make no sense at all for aircraft as far as powering the aircraft in flight. Naturally of course if you can get some grant to research what we already know, you'll find a means to spend it and make it look like a techno breakthrough.
You can spend $5000 more for a Prius, save $600 per year on gas, and every eight years buy another $5000 battery. Well, that was the metric prior to the saudi oil dump and $2/gallon US gas. Until the monopolists bust their 'fracking' competition and embargo again, there is NO excuse for hybrid autos, and there will never be an excuse for hybrid aircraft, excepting government slush fund fiction.
Motors and engines are different beasts. Engines can be used to power a motor but not the other way around. Look at it like this. (Fuel->Engine->Generator->Motor->Load) makes sense, but this (Battery/FuelCell/Mains/(Fuel+Engine+Generator)->Motor->Engine->Load) does not.
Therefore a pargraph such as this;
"The aircraft uses its petrol and electric engines simultaneously during takeoff, which is the most power-demanding part of any flight. Once the pilot reaches cruising altitude the electric engine can be switched over to power generation and recharge the batteries, or used to augment the petrol engine to save fuel."
Should be rewritten to something more like this;
"The aircraft uses its petrol engine and electric motor simultaneously during takeoff, which is the most power-demanding part of any flight. Once the pilot reaches cruising altitude the electric motor can be driven by the engine as a generator to recharge the batteries, or used to augment the petrol engine to save fuel."
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