Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency

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• Hacker News
• anything that gets rid of leaded fuel on prop aircraft is a win even if 0% efficiency improvement
  by ck2
• If you care about leaded fuel, the culprit now is general aviation - small airports, Cessnas, not commercial flights. If you go work on it, let me know, I'll help you!
  by Schiendelman
• This is about replacing a turboprop with a slightly smaller turboprop and electric motor/generator+battery. The turboprop burns Jet-A, not leaded aviation gasoline.
  by jabl
• Love a gearbox those guys over at P&W. Can't get enough gearboxes.
  by aunty_helen
• This is why it makes sense to carbon price the private jets. On a smaller plane you can innovate much faster.
  by whazor
• I wonder if during descent instead of cutting power alot to control speed it can instead use the energy to charge the batteries.
  by krunck
• I'm not sure how that would help. If you're descending it's probably to land, and then you can recharge the batteries with electricity from the ground. That would be more efficient (and cheaper) than burning fuel to charge them.
  by ggreer
• Says that it's boost-only in all the literature I could see, so it can only add power to the prop not generate with it. Regardless, you don't really get into a position where you're harvesting energy in a plane - you just use less power while you're descending. Unlike in a car, most of a passenger jet's flight time is at speeds where drag (which squares with speed) basically means you'd have to nose down at a very aggressive angle to actually pick up speed without the engines providing thrust. The plane's engines are almost always under some kind of load until it is on the tarmac and slowing down so there isn't any opportunity to "regen" during a normal flight.
  by tgtweak
• Since they can put a huge battery onboard why don't they also electrify runway taxiing?

  I cringe every time a jet plane has to spool up, burning god knows how many gallons of fuel, just to go 15mph on the runway.

  by whatever1
• 1300 HP electric engine power, now that's an achievement.

  I do wonder if prop engines can act as "windmills" (similar to turbine engines, which often in accidents still have been found to provide a bit of hydraulic power), which means regenerative braking could be used instead of speedbrakes.

  by mschuster91
• After they land, they usually sit around for a while. Not really super important to charge the battery on decent I wouldn't think. Would be interesting to get rid of the battery entirely (or reduce the size) and have a beefed up magsafe plug that was attached during lift off, and came unplugged once it was at cruising altitude.
  by soperj
• There would never be a reason to use windmilling props in flight for electrical generation. Even when descending, airliners like the Dash 8 need at least some forward thrust in order to maintain control and stay on the glide slope. They only use reverse thrust for a few seconds during the landing roll.
  by nradov
• I've seen references to this capability in reporting elsewhere. It's less useful in an aircraft than a car because you can gradually descend, reducing power proportionally as you're preparing to land. But I'm guessing this is part of where the claimed 30% improvement in efficiency comes from.
  by paunchy
• There are times where the intent is to rapidly shed energy and systems/procedures designed for that (spoilers, speed breaks, slipping the aircraft). I suspect though that implementing any kind of efficient regenerative capability during these times will be something that is developed later/as an afterthought initially. That being said dismissing the idea out of hand is probably wrong. If this system is used during takeoff and climb and would be needed for landing/go around then I imagine they would want minimum energy levels in the batteries so there is probably going to be some system to tap the generator to give them an ability to have minimum energy for landing. Why tap the generator if you can scavenge along the way or just build in robbing power from the prop as the connection to get that power. This system probably naturally beefs up the generator substantially on these aircraft to give them essentially this exact capability. Hmmm.. as I type, the more I think it may happen very quickly honestly. But I'm not an aerospace engineer so this is all a guess!
  by jmward01
• Only AI stories show up now, so they had to call it an Ai craft I guess.
  by soperj
• Rtx has an interesting patent [1] on this that highlights some of the novelties of this setup vs a traditional hybrid (planetary motor/generator like in a Prius):

  It's a boost-only motor, it doesn't/can't harvest energy on descent.

  The patented solution (transient smoothing under auto-throttle control) puts electric motors on both the low spool and high spool, then uses a power-splitting algorithm to route high-frequency thrust changes to the electric motors while keeping fuel flow nearly constant on the thermal engine (turbine). The turbine cruises at a steady operating point with tight compressor/turbine clearances and the electric motor smooths out the spikes that are normally there with turbulence and load changes. Benefits: lower fuel burn, longer turbine life (fewer blade-rub risks from speed variation), and smoother ride quality since the auto-throttle bandwidth improves. This setup (based on the various cutaways and photos so far) seems to be only a single 1MW motor so it only runs on the low spool but can still help modulate the turbine decently in the same way it does in the Koenigsegg Regera's hybrid electric setup, that removes the need for a flywheel because the electric motor can smooth out the gas motor's inherent lumpiness.

  Also disclosed in a previous press release [2], it's only a 200kWh battery so at 1MW peak boost (cited load during takeoff/ascent) it would only run for ~10-15 minutes at the beginning of the flight.

  Seems most of the savings are due in part to not using as much fuel during takeoff (~20% of a 1-hour flight's fuel) but also in large part to the under-sizing and optimization of the thermal turbine to keep it running in it's peak efficiency zone for more of the flight (~10% of a 1-hour flight's fuel).

  Curious how the safety margins work here - if the battery is depleted on takeoff (aborted takeoff) or there's an issue that requires descent-then-reascent, if the batteries can't be replenished in-flight there could be a power deficit in that window where you'd normally have 2+2MW of gas turbine power for the plane and now you only have 1+1mw of gas turbine power.

  [1] https://patents.google.com/patent/US20250296689A1/en

  [2] https://www.aerospacetestinginternational.com/news/h55-deliv...

  by tgtweak
• I’d imagine the apu could recharge it during flight at least somewhat.
  by bilsbie
• Why not just use the larger turbine with the efficiency benefits ? Or does downsizing the turbine save on so much weight that it makes a big enough difference?
  by Melatonic
• This is very clever: instead of focusing on electric only flight, just make the existing engine fly in the most efficient window while the electric engine buffers the flight profile.

  Like a big-boy prius.

  by _diyar
• More like an Edison Motors hybrid system.
  by tgtweak
• I kind of wonder how the orders of magnitude work out for solar and wing area.

  Solar cells are actually quite thin and could be almost like paint on the wings of aircraft. I wonder if the energy generated vs required is even ballpark. There is plenty of sun at 30,000 feet during the day.

  by m463
• Cars have a wide operating band, which is why hybrids make sense. Fundamentally, hybrid cars want to run the engine at a narrow set of operating points that are most efficient, and use a reservoir to do time arbitrage on the energy generated during driving. It's more than just regen to recover energy already spent -- the motor also lets you navigate the engine map to pick your point of operation. Ideally, the engine and the wheels are fully decoupled, at which point the engine rpm would just be constant. The battery and motor just move energy around.

  Planes aren't really like this, they're actually a lot closer to boats. They move from fixed operating point to fixed operating point, and the engine is optimized around this. There's a lot less fat to trim, because the engines already have a narrow operating band.

  That's not to say that this won't work; Pratt obviously knows what they're doing. But it's probably not an accident they've gone for smaller turboprops. I actually think the biggest opportunity for hybrid propulsion is in smaller drones where you want high performance piston engines, because tip clearance becomes an issue for gas turbines. A turboprop might suffer similar performance challenges that would make a hybrid configuration make sense.

  Edit: just saw a post below on the relevant patents. Looks like they're using hybridization to decouple the two shafts. Without the motors, they're coupled via the gas path. With the motors, you can navigate the maps of the two shafts independently. I'm guessing this lets them pick a combination of shaft states that saves fuel. Most of that is pretty uncontroversial, but I'm surprised the claimed fuel savings are that high. As I mentioned above, it's probably because it's a turboprop on a small aircraft.

  by coderenegade
• I think there are startups making a similar sort of engine for general aviation. It's good to see that there is development of the same idea for commercial aviation.

  This isn't like a hybrid car. It's a parallel hybrid, where the gas engine is just big enough for efficient cruise at altitude, and the electric motor/generator provides extra power for takeoff and ascent (or go-around power), and then charges slowly during cruise if needed.

  This means that the battery is quite small and light, having only enough charge to take off and get to altitude.

  I suspect that this system probably improves safety as well, if architected properly. If one or both of the gas engines fail, so long as they are not seized, that electric motor can still provide some power for diversion.

  by avidiax
• The fuel burn of take-off and climb substantially lightens the aircraft for cruise. Electric batteries have no such effect, you're carrying all that dead weight for the rest of the flight. This reduces the passenger or cargo capacity of the aircraft, which reduces potential revenue.

  And what if you need two go-arounds?

  by SoftTalker
• Hybrid cars are mostly parallel hybrids. Only the Chevy Volt comes to mind as a serial hybrid.
  by idontwantthis
• >This isn't like a hybrid car. It's a parallel hybrid, where the gas engine is just big enough for efficient cruise at altitude, and the electric motor/generator provides extra power for takeoff and ascent (or go-around power), and then charges slowly during cruise if needed.

  Isn't that exactly what hybrid cars (e.g. Prius) are? Extremely efficient gas engine for highway cruising, but insufficient for acceleration, which is aided by electric motors?

  by kspacewalk2
• Not “30% fuel efficiency”, but an improvement of 30%.

  FTA: “The project aims to demonstrate up to 30% improved fuel efficiency for a typical 250-nautical-mile regional turboprop mission”

  by Someone
• HN title mangling strikes again.
  by stymaar
• I was so confused by the title - I thought jets were fairly efficient at ~40%-50% of theoretical maximum and turbofans can't be that far behind. It would maybe make sense for a single prop aircraft.

  30% improvement makes much more sense.

  by c0n5pir4cy