How Efficient Can An Airplane Be? The Celera 500L Sets To Find Out

One of the current hype trends is the supposedly imminent revolution in air transport. So many companies showing digital renderings and mockups to illustrate their own utopic vision for the future, reaching fevered pitch at events like CES 2020. But aviation has a long history of machinery that turned out to be impractical. Wouldn’t it be great if a company focused their resources on building real aircraft and get real data before cranking up their hype machine? The people at Otto Aviation thought so, and their Celera 500L has reportedly taken to the skies.

If you said “Otto who?” you are not alone. The company has zero PR activity to speak of. Limited internet attention started from aviation fans spotting the Celera 500L under construction at its Southern California airfield. Its unusual exterior appearance and proximity to Hollywood made some dismiss it at first as a movie prop. Anyone with a passing interest in aerospace engineering could immediately see aerodynamics was a priority in this design, its long thin unswept glider-like wings implies the goal is fuel efficiency rather than speed. This was confirmed by internet sleuths uncovering patents filed by people associated with the company.

The patents include very lofty fuel efficiency goals, and industry veterans are skeptical. Fuel is a huge factor in aircraft operating costs where small increases in efficiency translate to big dollars over a plane’s lifetime. It’s hard to believe every other plane maker would deliberately leave so much on the table. There must be far more to the 500L inside that teardrop shaped body, with innovations and potentially making some trade-offs no other company has made. We can see two of them from the outside: the 500L traded off some pilot visibility for aerodynamics, and it has very little ground clearance to absorb the impact of less-than-ideal landings.

It’s certainly possible the ideas leading to this plane will fail to pan out in reality like so many ideas before them. Aerospace engineering is a field littered with debris of concepts that looked great on paper but crashed against a hard and unforgiving reality. But at least Otto Aviation is trying something new by building real hardware to get real data, something well worth recognizing in a sea of hyped up fantasy renderings.

[Photo via SoCal Airshow Review]

83 thoughts on “How Efficient Can An Airplane Be? The Celera 500L Sets To Find Out

  1. No revolution until a general solution is found for the Navier-Stokes equation, or until a cheap/reliable/safe/high-energy-density alternative fuel and powerplant are developed. Anything else is just a contest to see who can draw the coolest airplane.

      1. If you want to take off from rest, you are going to start motion and become airborne in the speed region where compressibility effects are negligible, generally under 0.3 M. Further, at transitional Mach speeds and beyond, the majority of your aircraft behind the leading shock and localized shock waves will experience incrompressible flow… Plenty of N-S applicable airflow in our most modern CFD analysis, but it’s still based around the results of generalized geometries with known solutions, with a lot of assumptions and interpolations thrown in…

        Don’t get me wrong, CFD is intense, impressive, and becomes increasingly better. But we are not yet at the point where we can fully understand and predict airflow in full. When we do, research, computation, and experimentation will lead to advancements in aviation (and other areas) that are not presently possible.

      2. Grab some air in your hand. Try to compress it. Did you feel the squeeze or did it easily escape? That’s the reason that subsonic aerodynamics is considered incompressible – not because air cannot be compressed but that air that is free to get out of the way is very difficult to compress. As long as one is sneaking up on the air at speeds lower than the speed of sound (which is the speed of pressure waves in air) the air has a chance to escape. Obviously the closer to the speed of sound, the less chance the air has to dodge an oncoming plane, but up to 1/3 the speed of sound the effect is small enough it doesn’t matter.

        It becomes really noticeable near 80% of the speed of sound because, as the air is deflected around the object, the local speed of the air can reach the speed of sound. In addition, because the speed of sound is temperature dependent, as the air goes from being slightly compressed to the place that compression is being released, the temp drops and so does the speed of sound, so this is another mechanism where the air can reach sonic speeds. I’ve seen this in the form of shock waves on the top of subsonic airplane wings just at the maximum depth of the airfoil via the shadows from the sunshine through the change in refractive index as the air changes density.

    1. DNS and increased computing power mean we don’t need a general solution. Just brute force the answer.

      But efficiency is secondary. It is cost that is the issue. Making carbon neutral or even negative fuel is possible today. It is just way too expensive relative to fossil fuels.

      1. Yes, we can brute force a good answer, but not a perfect one. If we could, wind tunnel testing would be obsolete. And the constant quest in science is not to say “well, we got pretty close.”

        1. Actually, that is *exactly* the constant quest in engineering, which is what we’re talking about here. Let’s leave perfection to the pure scientists who never have to touch the real world.

          1. Negative. The quest in engineering is to produce a system that is capable of completely operating within the contraints for which it was designed, while still containing a factor of safety, hopefully witin budget.

            For those with more capital, engineering can and does take on the role of advancement in capabilities to push limits or even set new limits. In the real world, this often is driven by economics and politics, as well as a stategy for keeping an entity relevant well-placed to secure future unknown endeavors. But is certainly well within the realm of engineering.

          2. “Let’s leave perfection to the pure scientists who never have to touch the real world.”

            And then there was that mathematician who only pursued Theoretical Math because
            he didn’t want his work used in warfare (artillery solutions and such).
            Only to have his work used in the development of the atom bomb.

          3. “The quest in engineering is to produce a system that is capable of completely operating within the contraints for which it was designed” – the hardest part of any engineering discipline has been handily left out of this statement: the actual design!

    2. The US Navy can pull CO2 and H2 (via electrolysis) out of seawater then reform it into synthetic aviation fuel, the plan is to use electricity from the nuclear power plants on carriers to do this, then the fleet has a continuous source of fuel as the same stuff will work fine in ships. Now interpolate that to a future where there are commercial fusion or fission reactors in large numbers and it is obvious where medium sized, medium to long range aircraft, are going to get their fuel from.

          1. Holy crap, the two above posts combine to give the best definition of interpolate that I have ever encountered. Extrapolation but to values within the dataset.

    1. I’ve been watching that project for years. Get over there and give Pete some love. He’s in the last 10% stage of a suuuuuuuper complex and ambitious project. Would def benefit from some support.

  2. Yeah I’d call that evolutionary, a number of things that have been known for decades finally all collected up in one airframe. The kind of thing we were seeing from Rutan before they got distracted with space.

    1. Probably not. Lilienthal is known in aviation as a great inspiration, but engineering wise he made really bad guesses about how aerodynamics worked. The Wright brothers used his information and found that it was wrong by a large margin. Otto also never appreciated the need for moveable control surfaces. These were certainly factors in the flight that led to Otto’s death.

    2. I wouldn’t name an aircraft company after him. He had his calculations wrong, which the Wright Bros proved were wrong by building their own wind tunnel and via their experiments with gliders. Then Otto ended up dead by crashing one of his gliders. Pretty much the only person it’d be worse to name an aircraft company after would be Samuel P. Langley. All he managed to do was throw a few not-flying machines into the Potomac then throw shade at the Wrights for quite a while.

  3. Biplane with high aspect ratio wings – with enough space between them – offers very high lift with very light structure … Almost nobody works on that concept, somewhat surprisingly.

        1. They did that in the 60s, in concept form at least. While they were figuring out the final shape of the F-111. One concept was to have a delta wing and a pair of extra wings extended for take off and low speed cruise.

      1. Yes, by the time you’ve separated them enough vertically to reduce interplane drag to virtually nil you’ve made a fuselage that’s twice as tall as you need, or other structure above it dragging it’s fingers in the airstream. Also you have doubled the tip losses you have to deal with.

        However, there’s still areas where a set of weirdly lashed together compromises turn out to be the best thing, bush planes for example, you don’t want too much wingspan. Possibly you could wangle a set of parameters that gives you STOL and economical cruise and long range, with lifting capacity of 4 people plus luggage and you’d be on to a winner.

        1. Thank you. I was looking for data about how biplane wing spacing influences drag vs lift, but was unable to find much useful information. Sufficient separation should allow for almost zero interference effect btw the wings, from what I could find.

          And structure would be far lighter compared with monoplane of similar wing area.

          1. You can probably dig some good stuff out of older books on … There’s also a trove of aero technical information booting around in a multi GB archive called “for your eyes only” found where large files are commonly shared.

        2. X-Wing, or at least angle the upper wings upwards. Could also make them a reverse gull wing but with the main span level. With modern composite construction a biplane needs no wing to wing struts or other connections. Rutan’s Quickie and Quickie 2 are essentially biplanes with an extreme reverse stagger and no elevator.

    1. I guess looks CAN be deceiving, huh?

      I expect the fuselage with that shape is giving a reasonable amount of lift, decreasing wings (wings are drag) is really better for efficiency.

    2. arthurptj: That was my first impression, but note that while stubby, the wings DO have a high aspect ratio. This just means it’s designed for high speed. Clearly, while efficiency was a design factor, it was NOT the highest priority.

      1. Well yes and no, there’s a bit of a sweet spot in the lower transonic area, where drag switches to Mach divergent drag, and if you designed your wings right, total drag actually drops from what it was 50-100 mph slower. (Before mach drag curve gets steeper) If you designed your wings wrong, it’s a vertical brick wall that no power will push you through. So you can get your efficiency at typical buzzbox doctor killer speeds under 200mph, or you can get it the other side of about 450… to 650ish…. highly design dependant. Anyway, to get to there, you’ve got to go through the hump in the middle, which either means having too much power or not enough wing. The trick is finding a powerplant that can supply lots, but have a low BSFC regime when the load drops off. (Typical powered transport problem of having a motor that’s 4x too big to be most economical for the steady state/speed condition.)

  4. Looks like yet another in a long series of interesting experimental research aircraft that will be unlikely to see commercial use of any kind.
    Personally, I fail to see anything revolutionary about the aircraft. In fact, I fail to see anything there that wasn’t already well-known aerospace tech by the 1980’s (which is when I started paying attention to aviation tech), though I would love to be proven wrong with some details about its construction and powerplant.

    1. The powerplant developments look most interesting and novel (in the details), but from link digging, it’s all a bit “will they, won’t they” with doubt over which one it will finally use. The airframe should be efficient with any powerplant, the V12 kerosene motor should be efficient without the airframe, but the two married should make excellent numbers. However, could be years before the motor is approved, or the airframe is approved, because sticking a new motor in a new airframe is always approval hell, they often go apparently separate ways for a few years before finally getting together a couple of years into production.

  5. This keeps getting touted as being outrageous and revolutionary – the similar Piaggio Avanti (which is already very efficient) has been in production for some time. There has been some speculation as to whether the product will carry people rather than cameras and sensors though – likely it will be adapted for whomever writes a check.

    1. Other than both being straight wing pushers, they’re nothing alike. The subject of this article is single engine and has a conventional wing and tail placement instead of a canard wing out front with the main wing far aft.

      1. With high speed boundary layer compression, surface feature sizes above the order of yada yada blah blah (Left as exercise for the reader.) (Arcane Reynolds numbery crap)

        Rule of thumb version, you want something smaller than the rivets they had to grind flat on photo reconnaissance Spitfires.

    1. That’s definitely a two edged sword, get your nose in teh gubbmint trough, but it may limit your export options of the civvie version in the future. Then you can be cut off at a political whim, and end up spending all your profits paying off politicos to try and get your snout back in.

      1. Missed a thought. I don’t think it’s really designed for time in the air, but distance per gallon, which at 500 mph or so might only be 4 hours. That’s gonna be something like 16 gallons an hour, something “inefficient” doing 15mpg buzzing along at 150mph stays in the air at 10 gallons an hour.

        1. Well yes if you’re a multi-product company, if you only have one string to your fiddle they’re not going to be quite as confident that you’ll be around to “take care of them” should they suddenly be retired.

  6. Prediction: Fully autonomous personal passenger plane.
    1. The full size hatch. Tall enough to admit anyone.
    2. Low clearance to the tarmac.
    A. Easy enough for some handicapped to use.
    B. Does not require “airstairs.”
    3. The body appears tall enough to allow people to -easily- stand inside of it.
    4. The (apparent) turbo-prop engine are more fuel efficient for shorter hops.

  7. From what I can gather it’s supposed to be competing against small small business jets as it supposed to cruise at over 400mph and 65,000 feet
    The odd thing it’s supposedly running a V12 piston engine burning jet fuel but I find these performance numbers a bit optimistic for a diesel engine as it would be tough to achieve even with a high performance gasoline engine running high octane fuel.
    Probably actually a turbo prop or the performance numbers are actually much lower.
    The landing gear seems to ride too low to handle less than idea landing that will inevitably happen but it could be articulated and be in a higher position during landing and lower for boarding.
    On visibility a set of cameras and maybe a periscope for back up could handle that.

    1. The Soviets managed a 2000HP V12 aero-diesel in the early 40s, so I don’t get why anyone would think it unpossible, even if some Jalopy Journal type said he was making it in his home shop.

      1. IIRC, the Germans (don’t want to use the “N” word) during WWII also had an experimental diesel aviation engine (ran on coal oil?).
        But they lost the war, so it doesn’t matter!

        1. They had the Jumos in service in many twin engine types, they were of lower output though, and their 2000HP + effort was a 24 cylinder so I didn’t want to get into the “but 24!!” arguments. After the war, Napier did a lot of development on the Nomad line, but it wasn’t taken up due to the new hawtness being turboprops.

          Nowadays, if someone held a gun to my head and said “Make a 400mph plus diesel aircraft or else” I’d want to look at the Rolls Royce Perkins Challenger 2 tank motor, which I think is basically a diesel Merlin. Now in tank form it only gets half the HP we’d be after, but practically every aero motor that went into a tank got derated by as much as two thirds for durability, heat elimination, combat survivability etc reasons, so hopefully the converse is true and you’d get a lot more out of it as an aero engine.

  8. Seems to be a stretch variation of the egg-fuselage-pushes-through-air fuel-efficient design that we see in several European light aircraft. Improved with cleaner fuselage, integrated tail and cleaned-up gear, although with engine intakes where the air is supposed to be scooting towards the back to help push it along. Hmmm
    Very interesting!

  9. Visibility issues? Have you ever been inside a Cheyenne III? It looks like it has useful front windows for the pilots but the top of the instrument panel is right about eye level unless the pilots are extra long in the torso.

  10. Wow. This aircraft will have the narrowest CofG range imaginable, given the straight wing and its narrow chord. Unless they have weight-shift with fuel like the Concorde, I cannot imagine where the pax and bags would go, or to be able to vary the load by more than a slim woman and an equally light companion.

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