Diamond Hybird Electric Quad Tilt-Rotor Aircraft

[hesham]

Hi,

the Diamond Aircraft company of Austrian design a hybird electric quad tilt-rotor civil
and business aircraft.

http://flightclub.jalopnik.com/diamonds-hybrid-electric-quad-tiltrotor-for-civilians-l-1734642759

 

[LowObservable]

Sounds like an excellent idea.

 

[sferrin]

Actually it does. With today's electronics the X-19 might have been viable, but this takes it one further. Going electric you remove a lot of things like drive shafts, gear boxes, transmissions, etc. (for the most part anyway). Then again you need better batteries. Maybe in another 20 years.

 

[hesham]

Sounds like an excellent idea.

That's right LowObservable.

 

[AeroFranz]

The pilot's field of view looks poor.
I'm assuming the internal combustion engine and generators are in the tailcone, fed by some invisible intake.

 

[flanker]

Actually it does. With today's electronics the X-19 might have been viable, but this takes it one further. Going electric you remove a lot of things like drive shafts, gear boxes, transmissions, etc. (for the most part anyway). Then again you need better batteries. Maybe in another 20 years.

I think Elon Musk has said that for a fully electric aircraft one preferably needs 400Wh/kg energy density or more. Right now it is around 280Wh-300Wh/kg. However, energy density is improving at a rate of ~7% per year so 400Wh/kg can be achieved in 5 years or so. And that is for a fully electric aircraft, for a hybrid one arguably doesn't need 400Wh/kg. Energy efficiency of an electric engine is ridiculous (90-95%) so one simply needs a lot less energy to carry around than fuel.

 

[AeroFranz]

'Conventional' mechanical transmission from turboshaft to propeller includes losses in the gearbox and whatever intermediary t-boxes. For the layout shown i would be surprised if you lost 6-5%.

For a hybrid-electric aircraft, the turboshaft spins a gearbox (95-98% efficient), which spins generators (95%), which use cables with non-negligible heating losses (99%), to power motors (95%) of a certain efficiency. As you can see there are more links in the power chain and more losses.

I believe where hybrid-electric shines is it enables things like distributed propulsion, redundancy, flight controls that rely on thrust and not control surface deflection, and other nifty tricks that are second-order effects, so you need to take advantage of a bunch of those to claim superiority over a mechanical transmission.

For a purely electric solution, you are right that battery specific energy is the key enabler. However i'm a bit more pessimistic on the timeline. For man-rated commercial flight, you will need mature batteries (not laboratory experiments) that can be manufactured in large volumes and are affordable. Right now i would peg the limit at 250 kW.h/kg (things you can buy in reasonable quantities at reasonable cost). Who knows, if Elon really can deliver on his mega-factory he just might make the goal closer...

 

[yasotay]

'Conventional' mechanical transmission from turboshaft to propeller includes losses in the gearbox and whatever intermediary t-boxes. For the layout shown i would be surprised if you lost 6-5%.

For a hybrid-electric aircraft, the turboshaft spins a gearbox (95-98% efficient), which spins generators (95%), which use cables with non-negligible heating losses (99%), to power motors (95%) of a certain efficiency. As you can see there are more links in the power chain and more losses.

I believe where hybrid-electric shines is it enables things like distributed propulsion, redundancy, flight controls that rely on thrust and not control surface deflection, and other nifty tricks that are second-order effects, so you need to take advantage of a bunch of those to claim superiority over a mechanical transmission.

For a purely electric solution, you are right that battery specific energy is the key enabler. However i'm a bit more pessimistic on the timeline. For man-rated commercial flight, you will need mature batteries (not laboratory experiments) that can be manufactured in large volumes and are affordable. Right now i would peg the limit at 250 kW.h/kg (things you can buy in reasonable quantities at reasonable cost). Who knows, if Elon really can deliver on his mega-factory he just might make the goal closer...

As usual Aero has dumped some reality into the discussion... party pooper!

That said, you don't get to the "man-rated commercial flight...mature (affordable) batteries" if someone does not take on the project of getting their.

 

[mz]

The generator's gearbox could have lot less ratio and potential to be a lot simpler than a helicopter / tiltrotor gearbox. Don't know if the propellers are driven by direct drive permanent magnet motors, I'd imagine so.

So as a whole you end up with an aircraft that has a lot less mechanical gears. (They probably drive the cost per flight hour up a lot.) There's more power electronics then.

 

[AeroFranz]

As usual Aero has dumped some reality into the discussion... party pooper!

That said, you don't get to the "man-rated commercial flight...mature (affordable) batteries" if someone does not take on the project of getting their.

I don't know when it happened, i became a surly curmudgeon ;D and yes, somebody has to invest and tackle the problem. One more bitter comment and i'll shut up: the car market is indeed pushing batteries, but because they typically care less about weight, they are not necessarily the type of batteries that the airplane makers want.
That being said, i really like what Pipistrel has been doing with their Virus trainer, and i think electrics is the first big change to happen in the GA industry that could halt its downward spiral.

 

[LowObservable]

Where I do think electrics might become interesting would be in using small, possibly recuperative turbine engines. (I'm thinking out loud here, so I may have this all wrong.)

One problem with small turbines is that they want to spin insanely fast, which results in a relatively big and heavy transmission. That could make an alternator+motor more attractive.

Then if you wanted a pusher, you avoid the perennial problem of either a long driveshaft or a heavy engine in the tail. Or it would make distributed propulsion easier to do.

Another possibility would be a hybrid drive and dual propulsors (fans maybe, either side of the tail, perhaps with fixed pitch and variable stators?) which would give you twin-engine capability (and all you'd need the battery for is get-you-home, electrical power in descent, 45min at high efficiency speeds, and the ability to fly a landing pattern).

Quad Tilt Rotors, however, are the spawn of Satan.

 

[VTOLicious]

Gentlemen, speaking of hybrid electric aircraft, distributed propulsion, energy density,...and the spawn of satan ;D

What's your opinion on Aurora's Lightning Strike VTOL?

http://www.secretprojects.co.uk/forum/index.php/topic,18534.45.html

BR Michael

 

[flanker]

'Conventional' mechanical transmission from turboshaft to propeller includes losses in the gearbox and whatever intermediary t-boxes. For the layout shown i would be surprised if you lost 6-5%.

For a hybrid-electric aircraft, the turboshaft spins a gearbox (95-98% efficient), which spins generators (95%), which use cables with non-negligible heating losses (99%), to power motors (95%) of a certain efficiency. As you can see there are more links in the power chain and more losses.

Any particular reason you decided to drop the efficiency of anything that is gasoline powered? (gas turbine or ICE, efficiency is crap vs electric engine)

 

[AeroFranz]

I was looking at the hybrid-electric case specifically, comparing a mechanical vs electric power transmission, and assuming that the shaft power was produced in the same way in both cases by either a gas turbine or ICE engine.

In the case of the pure electric vs ICE engine, yes the ICE has a mechanical efficiency that is dismal...but it can count on a fuel that has what? 128,000 BTUs/gal? Compare to whatever the equivalent figure is for the best battery around.
For a given desired amount of output power, it's hard to come up with a complete electric system that is competitive in terms of weight. It's only when you can claim some synergies, like distributed actuators/control effectors, redundancy, that you can get some of that weight back and even the trade.