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Comment by scarier | Hacker News Reader

For some perspective, the Scaled Composites Catbird (powered by a 210-hp V6) achieved just over 20 mpg at 200 mph with close to 1000 lbs of payload (it could carry a pilot and four passengers) in the late '80s and early '90s.

Amateur-built experimentals have achieved upwards of 50 mpg in realistic flying conditions, but they generally tended to be tandem-seat designs with minimal frontal area and low-powered engines.

More recently, the Pipistrel Taurus G4 (a highly modified sailplane with an electric motor between twin fuselages, designed to carry a pilot and three passengers) achieved just over 100 mpg at ~107 mph.

I eagerly await proof that the Celera--a significantly larger, heavier, and faster aircraft than Rutan's Catbird--actually achieves similar fuel economy. If true, it would be a pretty incredible leap for an industry that's been largely stagnant for decades, but these sorts of claims have a long history of being either sadly mistaken or outright fraudulent.

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Definitely some extraodinary claims that will require extraordinary evidence to prove. Especially getting 20+ mpg for 4500 miles, while flying at 450mph, which is near the top end of what piston/propeller aircraft are capable of. For reference, the P51 (one of the fastest fighters of WWII) had a comparable top speed. The Piaggio Avanti [0] has a somewhat similar design and top speed (460 high speed cruise), but has twin turboprops and a far shorter range and far lower claimed mpg.

[0] https://en.wikipedia.org/wiki/Piaggio_P.180_Avanti

The Piaggio II (https://www.aircraftcompare.com/aircraft/piaggio-p180-avanti...) is missing several modern aerodynamic and efficiency features like winglets and gets 15MPG and has a 1600 Mile range. Significantly beating it’s fuel efficiency at similar speeds seems reasonable just eyeballing the two designs. Getting the full 20MPG at 450MPH might be a stretch, but it’s not all that unreasonable.

Also, higher aerodynamic efficiency means lower HP requirements. Moving that weight savings to fuel can boost range even further.

PS: Winglets are actually really old technology. It’s making the trade offs worth it including significantly increased weight at the wing tip that’s new.

I’m not sure those mpg numbers are correct: the more fuel efficient Piaggio EVO update, with winglets etc, in the extended range version can hold about 450 gallons of Jet A and has a 1770nm range, so even with plenty of reserves that doesn’t get it anywhere above half of 15mpg (from what I can find IFR reserve comes out to 75 gallons, thus 4.72mpg nautical or 5.4 statute).

Which is why the jump in efficiency would be so extraordinary.

Turboprops are less fuel efficient, they just have a higher power to weight ratio than piston engines.

I recall from the last time this plane hit the news cycle that it is designed to cruise at 60,000 feet where air density is lower and better fuel efficiency can be had.

To put that claim into context the manned single engine piston height record is held by a specially modified Rutan Long Ez and was around 35,000ft.

Prop planes don’t work well at higher elevation. There’s nothing for the prop to work against. It’s why jet engines, with their compression, work better.

Props work better than jets at low elevation where the span of a propeller can work against a lot of high density air.

Much of the improved efficiency comes from the engine[1], which claims "50% lower fuel burn compared to turbine engines in the same power category".

The engine company is German and so we can make lots of jokes about German companies' fuel efficiency claims I guess.

Nevertheless, it has been around since 2012 and is used in a few planes already, so presumably there is some measurable improvement there or they'd have taken the claim down by now?

For comparison, this engine has a Specific fuel consumption of 210 g/kW/h, while a P&W PT6A-6 (older, slightly more powerful: 431 kW vs 368kW) has 0.408 kg/kW/hr[2]

[1] https://red-aircraft.com/?lang=en

[2] http://www.all-aero.com/index.php/contactus/64-engines-power...

Still, a plane with half the aerodynamic drag and twice the BSFC is only getting 4x the fuel efficiency, not the ~10x they're claiming. Even if they're making a bit of "free" thrust from their cooling system (which has been a thing since WWII), I don't see what accounts for the rest, even ignoring that the Celera likely has a significant increase in frontal area due to the standing-height cabin.

Re “free thrust/WWII”: Real Engineering recently did a great summary of the P47 Thunderbolt intercooler and general craziness of the engine at https://youtu.be/IwqTN5fhMR8

They are claiming slightly under 10x fuel efficiency compared to a jet (2-3 mpg vs 18-25 mpg).

That doesn't seem completely unreasonable.

A Pilatus PC-12 (which is the turoprop competition here) NXG gets around 4.3 mpg.

>Especially getting 20+ mpg for 4500 miles, while flying at 450mph

That's not what they're claiming though. They're claiming that:

1. 20+ mpg

2. maximum speed of 450 mph

3. range of 4500 miles

are possible individually, not that 1+2+3 are possible all at the same time.

TFA did not say maximum speed 450mph, it said "maximum cruising speed of at least 450mph" Still doesn't mean it gets 18-25mpg at 450.

If it can realistically do half of 4500 miles at 450mph, there are a lot of interesting routes (Gets you as far as Tel-Aviv from London, Boston to Phoenix, or Los Angeles to Miami).

Using that completely-pulled-out-of-my-ass number of half the range at 450, and assuming quadratic drag, the full range would be at about 300mph, so a roughly 12 hour flight from New York to London at a cost of $5k.

$5k plus pilots (I’d want two for a transatlantic flight). And you’d still be stuck inside a very small space for 12 hours, with what’s likely to be a porta-potty level lavatory and minimalist galley. Oh, and a single piston engine, which is less reliable than turbines, over a lot of very cold water. Not sure that would be the best use case for this plane.

Well, the size of aircraft certainly allows for fully enclosed, proper lavatory. CJ3 used for size comparison, has one.

Everything deserves to have a Version 1.0

I have high hopes for the future efforts

Plus airports, airspace, immigration, depreciation, insurance. So more like 20k.

12 hours transatlantic is probably worse than coach (or premium coach at least) transatlantic in 7 hours for most cases.

With these specs (which are completely fictional at this point), it's the size and cost of a light-jet with the speed and range of a mid-sized jet, which is a under-served niche with the increasing numbers of people in the "very wealthy, but not quite embarassingly wealthy"

The single engine is a concern.

Something like Garmin Autonomí might eventually allow for single pilot flights while maintaining a reasonable level of safety.

https://www.garmin.com/en-US/autonomi/

Sure, there are all kinds of trade offs between speed, range, useful load, altitude, burn rate, etc. But it’s really the combination of 450, 4500, and 20+ that would make this plane revolutionary. Otherwise it wouldn’t be all that interesting. And if we are to take seriously their claim of competing with commercial aviation, then it would really have to perform pretty close to all three of those numbers at the same time to even have a chance.

Edit: just to add a few numbers from the back of my napkin. To go 4500 miles, it would probably need to do 20mpg anyway. That’s 225 gallons of fuel. JetA is 6.7lb/gl, so ~1500lb. Not sure a small plane could carry a whole lot more than that without giving up all the useful load. And if it can only cruise at ~300mph in order to go 4500 miles, then we’re looking at a 15-hour flight in a pretty confined space with likely fairly basic amenities. It’s not exactly bringing back the glamour of aviation.

Well, from London to New York is apparently about 3500 miles, and a 15 hour journey for that sounds reasonable.

A single engine plane is most likely not going to be used for ocean crossings regularly, for safety reasons, even if it is technically capable of it. Additionally, I'm not sure it has enough spare fuel reserves to make the trip with enough margin for error or unforeseen circumstances.

Single engine aircraft with a range of around 800 miles are regularly ferried across the Atlantic. Now, I'm not for a minute suggesting that this is an everyday pleasure flight, it's something which takes planning, preparation and additional equipment. However, all I'm pointing out is that range would be the least of your problems if any of the claims prove true.

If you are interested this site gives a good overview of the routes and the legs involved http://220kts.com/ferry-flights/atlantic-ferry-routes.html

Ferrying is not a paying passenger flight, correct?

How would single-engine craft comply with ETOPS - the relevant standard for passenger flights, or equivalent?

https://en.wikipedia.org/wiki/ETOPS

https://aerosavvy.com/etops/

The short answer is they don't and it's pointless to ask about it since these flights are conducted under part 91 for private aviation. There is almost no charter or scheduled flights allowed on single engine aircraft in Europe and the few that do exist are using single engine turbines on an exemption (the exemption is based on the fact turbines have a demonstrated order of magnitude better reliability).

> There is almost no charter or scheduled flights allowed on single engine aircraft in Europe

So, without new regulation, this aircraft will not carry out "charter or scheduled flights in Europe" ?

This has changed relatively recently (2017) in the EASA rules and single-engine IFR charter flying is possible without special exemptions as long as the engine has demonstrated good reliability (basically it means turbine engines).

This airplane has a "2 in 1" engine. Two separate engines running on one physical engine block. So there is some engine redundancy.

yes but that really only matters if the second "engine" produces enough power for maneuvering if the first one fails. Plus, there is still mechanical interconnectedness so it isn't truly redundant. That said it is likely far safer than a traditional twin, the axiom with those is if you lose one engine the second will fly you all the way to the scene of the crash.

There's a link to the motor manufacturer in the article (but it's down right now). As I recall the two motors are identical with no common parts other than the engine block.

Especially if you're saving time at either end by skipping all the Heathrow delays (long security checks, baggage check, etc)

People who fly privately don't need to go through any checks ?

Not the ones protecting expensive commerical planes.

And here I was thinking it was to protect the passengers.

No need to protect the passengers if there aren't any other people on your flight!

Only if it has cryosleep chambers on-board.

I'd take any sleeping pod any time, even if I had to bring my own sandwiches, piss into a bottle and have 0 entertainment than sit for more than 8 hours in economy flight of any current airline.

I'd similarly prefer a low-headroom bunk bed. I think the problem is bracing for take-off and landing and evacuations.

I'm calling bullshit. Compare it to the TBM900 which has a 900hp turbine engine and vastly similar layout. There is no way they can go 60 knots faster on 300 less horse power.

And even if they somehow pull off that trick, that short skinny wing will make the MU-2 feel like a safe family minivan.

The layout/payload may be similar to a TBM, but I'm guessing the wing loading and cruise altitude will be higher. So it's definitely feasible to go faster on less power.

Aerodynamic drag is a square relation so the difference in drag there is about 40%. With 65% of the power.

I think occam's razor applies here. Either the aerodynamics of reasonably modern aircraft designs leave a huge amount on the table or this startup is telling fibs.

There are other reasons to be suspicious, modern diesel engines rely on a large amount of turbo charging to achieve sea level rated power, it's difficult to believe they are able to maintain this rated power to 50,000ft or 60,000ft. (In the case of the TBM the engine is actually capable of about 1300hp at sea level but is "flat rated" to what it can maintain at altitude).

Finally, almost all high altitude aircraft have long wings (think the U2 as that is not far from what we are talking about here). Adding longer wings typically increases high altitude performance (there are aircraft with model variants where the wings got longer, like the twin commander). This aircraft appears to have borrowed a couple of surfboards.

> I think occam's razor applies here. Either the aerodynamics of reasonably modern aircraft designs leave a huge amount on the table or this startup is telling fibs.

Aerodynamics of reasonably modern aircraft designs do leave a huge amount on the table. Generally for good reasons, though. The 500L is clearly almost entirely a laminar-flow design, unlike conventional aircraft (including the one you linked). Experience from gliders have shown that a small laminar flow design like this can have less than a third of the drag of what a conventionally shaped design of roughly similar size.

There are two major downsides to designing like this:

Firstly, the shape is entirely determined by physics, leaving very little wiggle room for manufacturing or practical concerns. Without modern composites, cost-effectively manufacturing the frame is impractical.

Secondly, the great drag properties are very dependent on the properties of the skin of the aircraft. Laminar-flow gliders can have their glide ratios halved after accumulating a few too many insects on the leading edge. If you want to fly very high, (as this plane seems to want to), better hope you have an amazing de-icing system, or even a very small amount of ice will trash your aerodynamics.

Don't forget low speed handling and stall characteristics.

There are so many places where the practically of this aircraft would fall down. Good luck fitting deicing boots to a wing which needs to be kept so clean polishing it makes a difference.

Also, good luck trying to get an clearence to climb to 60,000ft around any busy international airspace. Regardless of any aerodynamics miracles this aircraft pulls off I'm sure we agree that it's climb performance will be distinctly average. That means it's going to take well over an hour to get up there. 20 mins or more could be spent in the RVSM band (FL280+) where most of the airliners are, expect to be vectored all over the sky while this happens. This is already a problem in something like the CJ2 which like to cruise higher than the airliners but aren't quite as fast. It's climb performance is considerably better than you would expect from this aircraft.

If they reduce drag, which is exactly what they are claiming to have achieved, that would reduce the amount of horse power needed to overcome that drag. Less HP translates into better fuel economy.

Basically this plane has the engine mounted on the back, which means center of gravity and wing position are quite a bit different. The nose cone looks very streamlined and crucially the wings are in front of the vortex produced by the prop. I'm guessing that that adds up to a bit of reduction in drag. The reason many planes have the engines mounted on the other side probably have to do with things like cooling, engine size, and other practical concerns.

They are claiming improvements across almost all areas. If it flew as fast and as far as the competition on 50% less fuel, that would be amazing. If it flew 60 knots faster in the same fuel and payload, awesome!

However, they are claiming improvements across the board. 3x the range, significantly faster, flies higher, uses less fuel. It doesn't pass a sniff test.

Compare it to the Grob Strato 2c. Notice how long the wings are by comparison? This is a feature of nearly all subsonic high altitude aircraft. Also notice the how long the props are on the Grob, another feature of high altitude aircraft conspicuously missing on this aircraft.

Pusher aircraft are not new. In fact they are as old as powered aviation itself. They generally aren't significantly more efficient.

https://en.m.wikipedia.org/wiki/Grob_Strato_2C

I think that the evidence can be really simple (not extraordinary) - just gas it up, fly it for 4500miles in about 11hrs.

Just a nitpick, extraordinary claims normally do not require extraordinary evidence. For example, to gather evidence that, for example, there is a man who could run for 50mph in short bursts, it would require nothing but ordinary evidence. Have a nice day!

I think this airplane is pressurized, flies very high and has a big turbocharger. And it has a diesel engine, so the MPG means a different thing - diesel is denser.

It's optimized differently to the experimentals, and it's more useful commercially. Flying high avoids a lot of weather issues. You don't have to cancel flights because of weather.

The drag from the streamlined shape is very low. It's just a textbook minimum drag shape.

The cruise speed advertised does seem high still.

While the shape might work well for drag, looks matter, especially with private aviation. This thing just doesn't look very sleek or impressive.

Cost to repair and insurance is also a very significant part of the cost, so if this is difficult to land or costly to repair, it won't be very popular.

If it comes even close to the claimed efficiency it could look like a 1961 Skoda and nobody would care

All of that helps, but a pilot flying an unpressurized experimental can still get up to 17.5k' VFR on oxygen. Assuming the Celera cruises around FL250, you're talking the difference between ~300KTAS and ~350 KTAS at 200 KIAS. I'd be shocked if they cruise much above FL300, regardless of how high their service ceiling proves to be--for anything other than a really long-distance flight, they'll spend too much time climbing to altitude for it to be worth the effort.

This is optimized for really long distance flight, thousands of miles. That’s the whole point. Cruise height of 30,000ft, I think.

Why would you be shocked by flying at heights comparable to typical jet aircraft flying similar distances?

I wouldn't be surprised by a long-range cruise altitude around FL300, but if it was FL450 I'd be extremely surprised. If the plane achieves the advertised 20mpg on a hypothetical 4500-mile flight at FL500, but only makes a small fraction of that on a more realistic 400-mile regional hop at FL210, it's not really a practical success.

(Aside: the advertised range seems like drastic overkill for something designed to offer a cheap alternative to private jets--it's difficult to overstate how much it sucks being cooped up in a tiny plane for over 11 hours, even if you have the luxury of rich leather seats, can stand up in the cabin, and don't have to pee into plastic bags. Even if a family wants to charter a private jet from LA to the Bahamas for a long weekend, it'd be miserable trying to one-leg it.)

The whole business case for this vehicle is that it enables extremely low cost granular travel between distant city pairs. The short regional hop is not its target market. It’s designed to be competitive with commercial air travel.

That's fair--400 miles is on the shorter end of the spectrum.

Still, "low cost" is relative to a chartered private jet--which, emphatically, is not a service that people purchase because it's the most economical option--rather than a commercial airliner (although, if true, the SFC per passenger of the Celera would be in the same ballpark as modern commercial airliners, which is very impressive). The average domestic flight is under 1000 statute miles (https://www.bts.gov/content/average-length-haul-domestic-fre...), so this plane needs to offer compelling efficiency gains at ~500-1500 mile ranges in order to compete with existing services, unless they're strictly planning to fill the niche of one-leg, long-range flights that existing private jets don't have the legs for.

No, they intend to compete with like commercial travel, maybe business class at first, in price per seat per trip to charter an aircraft like this.

$300/hour charter price with 6 seats for a 5 hour trip (2000 miles) is about $250 per seat each way. This is pretty competitive.

$328/hr is the advertised operating cost of the aircraft (fuel and maintenance), not anything close to what a charter would actually charge. Commercial airline operating costs, including crew salary and overhead, are roughly an order of magnitude more (~$3000/hour is a rough, somewhat conservative, number for something like a B737, including fuel, crew, maintenance, and aircraft depreciation/rental costs). The airline is paying under $20 per passenger-hour for all expenses, while a charter service operating with volunteer pilots, free airplanes, and no other costs would break even at ~$55 per passenger-hour (assuming the $328/hr estimate is accurate, which is still very much an open question for an aircraft that's still undergoing initial flight testing and may never be produced in significant volume). Even the best-case scenario doesn't strike me as particularly competitive.

11 hours in a private plane with lots of room and being able to lay down flat or be in a zero gravity chair would be sheer luxury compared to many flights I've taken. My last long distance flight took 24 hours of travel to get from San Jose to Israel with 3 legs in Coach and going through multiple security gates. One time I flew 16 hours Coach from LA to Guanzhou China and that was a second leg. My tail bone was in pain for a day from sitting that long.

If an airplane like this meant being able to fly private, it's completely worth it. One other factor you have to consider is that this plane can probably use tiny airports which shaves a 4 hours of additional driving and security gates. I'd rather be in a slower flying plane for 7 hours than fly for 4 hours but spend 4 additional hours at security gates and car traffic.

Their patent application implies that it is optimized for cruising at 50,000 feet.

[1]https://patentimages.storage.googleapis.com/3b/f3/9a/928c862...

I mean, their patent application also claims an SFC of ~30-42 MPG at 460-510 mph...

A design cruising altitude of FL500 implies that they're seeing nearly all of their efficiency improvements due to the thin air at altitude (flying around 200 mph indicated, which isn't totally unreasonable for 20 mpg in a small-ish piston-prop), but I doubt they have the climb rate to actually reach that altitude in anything short of a transcontinental flight.

I like to think they crunched the performance numbers once or twice, but if they're off by the same amount they were with their initial SFC calculations, there's no way they'll reach an acceptable cruising altitude during an average flight.

The design of the body reduces drag and acts as a mechanism for lift.

https://en.wikipedia.org/wiki/Lifting_body

A lifting body sounds like you are getting something for free, but it does not really work out that way. In terms of efficiency, what matters is the overall lift/drag ratio, and so the first issue is whether shaping the fuselage for lift can be done without creating so much extra drag as to reduce the overall lift/drag ratio. In this regard, note that fuselages are long and narrow, while efficient wings are wide in span and short in chord.

A second factor is the effect of a lifting body on stability, and the cost of compensating for it. Even in the case of nominally non-lifting fuselages, they tend to produce lift at high angles of attack, and that tends to be destabilizing, producing an increasing pitch-up moment as the angle of attack increases (ordinary straight wings do too, but the effect is proportionately less, as the wing chord is considerably less than the fuselage length.) This has to be corrected with measures (typically a larger stablizer) that also create drag. Having a fuselage designed to produce lift exacerbates this problem, commensurably with the amount of lift being generated.

Modern sailplane design is a case study in the persuit of aerodynamic efficiency, at least at low speeds, and lifting bodies have not proved to be useful. The fact is that, once you are flying, you do not need more lift; what you want is less drag.

You don't have to cancel flights because of weather.

I don't think many flights today are cancelled because of weather on the route there, it's the weather over each airport, which would still impact this aircraft.

Small unpressurized planes do cancel a lot of flights since they fly lower and are affected by weather.

Many other six seat planes are like that.

Ahhh.. of course. Good point.

Feel the same, rooting for them but website is still a bit light on actual data and a lot of startup speak, wondering how they would get that big of an improvement vs similarly shaped (Avanti EVO) or powered (DA62) aircraft.

Other question is how safe the simplicity of the shape is, no front wing / canard with presumably very variable CG, or if they’ll have to sacrifice a lot of initial specs to make it work. Also if one should feel comfortable about the only semi-redundant engine over long stretches of water.

The CG question is really good, but considering the very conventional tail on the prototype, I imagine it has about the same acceptable CG range as a similar passenger aircraft. The wing just looks like it's way too far back since the engine's in the back instead of the front.

Hopefully it's not intended to do regular transoceanic flights, but it should be fine for shorter crossings (e.g. Great Lakes, Mediterranean north/south, etc.).

Well, at least it's clear that they have no competition in piston powered niche because all pressurised piston aircrafts died out. Any remote equivalents are dual engine planes.

Piper would like to please remind you that it is still selling the PA-46 Malibu / Mirage / M350 pressurized piston single.

Has anyone asked Rutan what he thinks about the Celera?

My RV-7 gets ~25 mpg depending on winds, power settings, etc. It’s been done before in private aviation. But, this is a very interesting design. Like you said, aviation does have a long history of new designs making big claims that don’t pan out in reality. I wonder what tradeoffs they made to achieve those results. It’s encouraging they’re into test flying phase, though.

Stands to reason that a modified glider will achieve the best efficiency characteristics. That is after all, practically speaking, the raison d'ètre for sailplanes.

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