Why would hybrid not work for “constant high power”? As long as the engine can deliver the “constant high power” needed for cruise – if it can be done with a 1950es engine, surely it can be done with a ca2010 single-rpm engine. If the installed weight of the system is then less than a similar legacy powertrain, why not.
Because in “constant power” regime (however low or high) there is no use for the hybrid additions, making them dead weight that still must be carried along?
I am willing to believe contemporary technology could derive the same power from a somewhat lighter engine, especially if running at constant rpm – but I still have to see the difference big enough to make up for the extra weight. Not to mention the added complexity which will increase downtime and maintenance cost.
The metal weight and structure of the Lycosaurus engine that allows it to hold 100% of rated power for takeoff is just as dead during the 95% of the flight yet no one seems to be complaining much about that.
PS – before we get the usual “modern car engines can’t maintain constant high power by design”: http://drive2.subaru.com/Spr09/Spr09_20years.htm
I think for a cross country plane the maximum weight budget for hybrid drive generator, takeoff battery, power electronics, motor and cables is the weight saved by reducing IC engine power by around 25%, and increasing engine rpm. If you could stay within that weight budget, you might get slightly better fuel efficiency (SFC) in cruise as a result of the IC engine running at 100% power versus 65% power, depending on how power dense and therefore relatively inefficient you made the smaller engine, and the sum of the driveline power conversion inefficiencies. That might free up a little more weight budget as a result of smaller fuel tanks.
The protection is against IC engine failure is balanced by having additional stuff in the driveline between the engine and prop. Lightweight electric motor drive electronics are not particularly reliable.
Ship propulsion is broadly comparable to aircraft, moreso than for cars. Some ships, destroyers for instance, have a load situation that is intrinsically inefficient. They hold power under 20% for long periods while waiting for the infrequent call to be somewhere else fast. They are more like a motor glider in that respect and some of them have implemented various hybrid solutions for that reason. Cargo ship requirements and solutions are more like a going places plane: one prop, one low rpm engine, one cruise speed, relatively good driveline efficiency at constant high percentage power.
Are you sure the engine and prop are coupled at all. I’ve read the words but it’s not clear. Effectively the primary and only driving motor is electric. It’s power comes from two sources, batteries or a generator (or both). The generator happens to be petrol driven presumably because the engine is lighter than a diesel and very efficient if set up to run at two or three rpm settings only.
This is exactly the set up in a Vauxhall Opel Ampera or the Mitsubishi Outlander PHEV car.
I can quite see that hanging a prop only on an electric motor might be technically difficult but I’d be surprised if the generator power plant is connected in the traditional manner to the prop.
The ICE driveshaft is connected only to the generator, not to the prop. You can see it pretty clearly in the video – the ICE is running but the prop isn’t.
That’s what I’d have expected. In that case the generator engine needs two or three fixed settings only and should be very efficient. its should be a fantastic solution and I’ll be watching it closely.
STOLman wrote:
That’s what I’d have expected. In that case the generator engine needs two or three fixed settings only and should be very efficient. its should be a fantastic solution and I’ll be watching it closely.
Umm, are there such very efficient generators around? Where are they and what is their efficiency and power-to-weight?
Conceivably, it should be possible to design (high-revving? turbocharged?) ICE engine optimized for single RPM with very good power-to-weight and solid reliability, but somehow nobody has done so yet.
Ideally, you would want to have something like this https://en.wikipedia.org/wiki/Free-piston_linear_generator
working, saving weight on crankshaft (and also the extra generator in the Hypstair), but they are always in the future…
There is a chance that a generator engine from automotive hybrids might be employed, although those will probably be too weak.
As it is, there is no place for hybrid in conventional GA airplane, the numbers just don’t add up.
A hybrid makes sense in a motoglider cruising on 25-30% power – those currently have no good engine options – either the engine is undersized and takeoff/climb performance suffers, or they are wasting powerful engine and either running it at too low power (and possibly damaging it), or just wasting fuel. Still, to make it work, advances in batteries and generators are needed.
There are some second-order potential benefits to hybrid, but also second-order drawbacks (especially because it is still a new technology with associated problems and gotchas).
A hybrid makes sense in a motoglider cruising on 25-30% power – those currently have no good engine options – either the engine is undersized and takeoff/climb performance suffers, or they are wasting powerful engine and either running it at too low power (and possibly damaging it), or just wasting fuel. Still, to make it work, advances in batteries and generators are needed.
Exactly, and this is what any analysis always comes back to… despite many people wishing physics could be reinvented.
There is no way to make the numbers add up if you need reasonably high cruise power, because then you may as well screw the prop straight onto the ICE and you get this
or this
and you save the generator, the batteries, the 3 phase inverter for the motor, the control electronics for the whole thing, etc 
Maybe there is a future in GA in the form of motorgliders cruising at Vbg at say 30% power but nobody has managed to build a workable machine other than for, ahem, motor gliding, with a tight cockpit and enough payload to carry a toothbrush.
The only real “mission-capable” flight which is done near Vbg is big jets and they get decent speeds by crusing just short of coffin corner, with a huge TAS gain at FL300+. A 747 flying at Vbg (or any other speed for that matter) at 2000ft would probably not even cross the Atlantic… Vbg of a 747 at low level is about 170kt at MTOW (1.3Vs assumed) and the distance is 2500nm or so…
That 1943 patent is great I wonder why nobody has had a go at it properly? Maybe there is something that has been overlooked? There is obviously a massive market for power generation by burning fossil fuels, at all sizes.
Hmm. A bit off topic, but I don’t know anyone who’d cruise in a motorglider at V_bg. Not in powered mode and very seldom in gliding mode, too. (Unless you redefine V_bg as changing with meteorological and flight tactical influences, of course.)
