The Celera 500L aircraft may fly soon
thedrive.com
thedrive.com
"The patent goes on to describe a notional aircraft that would cruise between 460 and 510 miles per hour at an altitude of up to 65,000 feet, yielding a fuel efficiency rate of between 30 and 42 miles per gallon. To put this in perspective, the Pilatus PC-12, a popular light, single-engine turboprop aircraft has a service ceiling of 30,000 feet, a cruising speed just under 330 miles per hour, and still burns, on average, 66 gallons of jet fuel per hour, for a fuel economy of roughly five miles to the gallon. Even going to a Learjet 70, which has similar speed performance to what's stated in the Celera patent documents, but still nowhere near as high a ceiling, we are talking about roughly three miles per gallon of gas at cruise."
> Exposure to pressure below this limit results in a rapid loss of consciousness, followed by a series of changes to cardiovascular and neurological functions, and eventually death, unless pressure is restored within 60–90 seconds.
I'd say that altitude is the reason for the focus on long distance.
So I suspect only long flights will be operated that high, and there will be some calculation for the optimal altitude for shorter flights.
Another issue is the survivability of incidents. If something goes wrong, for example with your pressure cabin or your oxygen supply, you have only seconds to start your mitigation measures.
https://theconversation.com/air-travel-exposes-you-to-radiat...
Celera: 30-42 MPG Pilatus: 5 MPG Learjet: 3 MPG
Those figures are all in there, it's just maybe written kind of confusingly.
- Who is going to want to take the time to climb to 65,000 feet in this? People going transatlantic? They'll probably still take a Gulfstream.
- Does it still get reasonable range economy at lower altitudes and true airspeeds?
- Nobody will be able to see the runway over the nose on landing.
- That door doesn't look like it'll hold up to pressurization.
- The landing gear looks very light.
- The engine is going to have very tight thermal and mechanical constraints based on its position in the rear of the fuselage.
- I'm assuming it's a turbine engine in here? Trying to turbocharge something enough to get to 65,000 feet is going to be awful and very maintenance intensive.
- Update: Nope, at least one V-12 with multiple turbochargers. If there is more than one engine the complex gearbox to drive the propeller will be difficult to get approved. See the Learfan aircraft [0].
- The propeller is out on a long shaft, may cause issues.
- The propeller is a pusher configuration, which isn't inherently bad, but causes efficiency losses from turbulent air coming off the fuselage.
- Pusher configurations - especially pusher turboprops like the Piaggio Avanti are noisy.
- Update: It's a piston engine. May not be as noisy because it appears that the exhaust is farther upstream than usual. However, cooling everything will be difficult.
- High altitude flight introduces the possibility of coffin corners in the envelope and very little room between overspeed and stall.
- That big engine (for high altitude flight) will reduce room in the cabin considerably.
- Everybody and their mother will probably have a tail strike.
Source: pilot and an aerospace engineering degree.
I think they aim for some kind of long-range air taxi. Small groups which want to travel a long distance from A to B but a very short distance to and from A and B's respective airports. Business trips, most likely.
And probably the plane is no slouch at medium or even short range if it is operated by a non-airline company. Just not "ridiculously efficient".
If it can carry 500 kilos at 65,000 ft for 24 hours without landing, and not cost a ridiculous amount in dollars per flight hour, that's something pretty unique.
In my totally non expert opinion the undercarriage and very low ground clearance also tell me it's intended to fly from paved strips in pristine condition, which is very different than the rough field capabilities of many single and twin airplanes powered by the PT6 turboprop or one of its derivatives.
Here's an example of a retrofit of a COTS platform for bespoke sensor platform use.
https://www.thedrive.com/the-war-zone/19921/these-secretive-...
Teardrop shape greatly reduces turbulent flow behind the fuselage compared to the mainstream tube shape.
I think the shape looks right rather than odd, in particular the bulbous rather than elongated body. Plus with the straight wings this looks well optimised for low skin friction.
Experience of VW rear engined vehicles tells me there are advantages in having the engine at the back when it comes to noise. I thought the reasons we had the propeller at the front was to have it cool the engine and have the centre of gravity 'right'. This just looks right compared to what has gone on before.
Looking right is not necessarily what you want, we have been stuck too long on what a fast plane should look like. But there is something in aesthetics when it comes to these matters.
Seeing the runway is not necessarily that important, I would prefer a plane that does all the landing itself with no assistance needed. It is not as if a regular jet pilot can see the wheels of the plane when landing.
It's not even clear that this plane is close to the final size.
And to speculate about this strategy, those tradeoffs are valid input.
Engine cooling: diesel engines need substantially less cooling than petrol engines, hp-for-hp.
Gearbox certification: you are generalizing from one example. Every turboprop has a gearbox. Most helicopters have a "complex" gearbox, coupling two (and sometimes three) engines.
Long propeller shaft: Not really a hard problem. Helicopter tail shafts seem more difficult.
Pusher efficiency: The propeller efficiency will be a bit lower for the reasons you mention, however the overall aerodynamic efficiency is likely to be higher. There are plenty of citations for this.
Pusher noise: Again, you are generalizing from one example (Avanti, in which the source of the noise is largely the turbine exhaust interacting with the propeller blades).
Forward visibility: I suspect they intend to use a camera. Other solutions are possible also. WW2 fighters had no forward visibility on landing.
Landing gear and door, tail strikes: yes, probably "prototype" stage engineering
Coffin corner: The potential problems are a consequence of specific airplane design. They are easy to avoid, though admittedly by sacrificing a smidgin of performance.
High altitude flight: I can't see that thing getting to 65,000 feet with that propeller and those wings... the number was taken from the patent, it seems, and may not have real world significance with the current design.
Overall, I think it is great to see a bit of innovation and experimentation happening in aviation again.
From a passenger perspective?
Why is this, Aerodynamics?
I would have thought that a pusher configuration would have been a net benefit from a passenger noise POV, and aerodynamics wouldn't make much difference on the ground, would they???
I’m not sure about what you mean with “who flies in class A airspace?” Most airlines and bizjets cruise in class A because their fuel burn is ridiculous at lower altitudes.
The reason that class A becomes to class E above 60,000 ft is because hardly any planes can fly that high. This plane almost certainly won’t go that high, regardless of what the patent application says.
Edit for clarity on why helix’s comment doesn’t make a ton of sense- airspaces go like this:
FL600 (approx 60k ft) and up: Class E
18k ft to FL600: Class A, only IFR flight is allowed, no VFR (even if the weather is good).
below 18k ft to 700 or 1,200 ft above ground: Class E, except around airports, where it can be Class B (big airport), Class C (medium airport), Class D (small airport with control tower), or still Class E (small airport without control tower).
below 700 or 1,200 ft above the ground: Class G, except around airports. Class G is uncontrolled, but you still have to follow the law- no buzzing residential areas and such. You cannot file an IFR flight plan in Class G space, mainly because ATC can’t reliably see you and prevent collisions with other planes.
Class E is controlled airspace but you can fly VFR without filling a flight plan; you are required to fly at altitudes that are xxx,500 ft so you don’t hit planes flying IFR at the xxx,000 altitudes.
You would have to file an IFR flight plan to get to 65k ft because you would transit Class A airspace during your climb and descent.
I really hope they manage to finish the prototype and get it flying!
The power required to fly at a given speed is the product of that speed and the drag at that speed. If this is truly an apples-to-apples comparison, it implies Synergy is producing half the drag of the reference airplane at twice the speed. Drag of an airplane goes approximately (a good approximation, when we are talking about maximum achievable speeds) with the square of the airspeed, and therefore this is implicitly a claim that the these innovations reduce the drag coefficient of Synergy by (by, not to) 7/8.
Given the effort it takes to reduce sailplane drag by a few percent, and the enthusiasm within that community to adopt whatever it will take to do so, I will be skeptical until I see a quantitative explanation based on actual measurements.
It is claimed that the innovations mainly reduce the induced drag, but this makes the claim even more surprising, as induced drag decreases with speed, and so, therefore, do the benefits of reducing it.
The PC12 has speed to destination as a design criteria, and enough thrust to take off from runway length at small airports. If you remove those two constraints and say you don't care about raw speed so much, and it'll always fly from fields with 6500+ ft runways, that opens up new possibilities in design for long endurance.
Studying the design of the rutan Voyager, take a look at the wing length/shape and the 11,000 ft takeoff roll. That's one end of the extreme deep end of design possibilities. This is sort of a compromise somewhere in between.
The use of a diesel engine tells me that somebody cares about squeezing the very best kilojoule per kilogram ratio from a liquid fuel.
Is diesel more efficient on a per-kilo basis than kerosene? I always thought kerosene packs a bigger punch so you can carry less of it for the same distance.
Also if the plane is intended to fly both that high/slow and that low/slow that probably informs the wing choice. Less air resistance and lift up there.
Jet fuel is 43MJ/kg
https://en.m.wikipedia.org/wiki/Energy_density
A big part of it has to be how much is lost to heat, an internal combustion engine is far from efficient... But then again neither is a turbine.
This relationship breaks down for very short HC (methane, basic alcohols).
Differences in effective energy density result from the combustion cycle used: Otto is better than Diesel for the same compression ratio, but you can’t easily get high compression ratio w/ Otto. Therefore Diesels are, typically, more efficient.
However, if you use methane (high compression) in an Otto cycle with turbo compounding, you’ll probably beat diesel. But then you have NOx emissions
This relationship breaks down for very short HC (methane, basic alcohols).
Differences in effective energy density result from the combustion cycle used: Otto is better than Diesel for the same compression ratio, but you can’t easily get high compression ratio
I wonder how they get that much more perfomance, assuming they do.
I mean, I know they ordinarily touch down nose up, but still it looks like low clearance.
Edit: Oh, i forgot: PRICE?
If it's not extremely stiff, I don't know how a hard landing would not result in fuselage contact.
Also, the pusher prop concept was tested extensively many years ago, but seems to have disappeared off the radar of most aero engine manufacturers. I don't know the exact reasons, but I am presuming that they had problems with efficiency, or more likely issues with the blade tips reaching sonic velocity (which will be higher risk with this aircraft if it cruises at FL065).
It's a workable solution, but most 'seat of the pants' pilots would eschew such things.
We'll see what, if anything, becomes of the Terrafugia too.
But at higher altitudes, the speed of sound is considerably lower, and the radial velocity of the prop blade tips start to reach sonic velocity, with the corresponding significant increase in drag, thus requiring more torque to spin at constant RPM, resulting in decreased fuel efficiency.
The test bed pushers on commercial jets were a far shorter set of (more numerous) blades for that exact reason. This particular aircraft seems to have a standard sized propeller, with a greater blade length, and corresponding greater radial tip velocity.
I'm assuming you meant FL200. (20000' MSL, not 2000' MSL.)
Rutan has a lot of great looking planes. Unfortunately they had limited success. People still try now and again to introduce flying-wings, but I guess the above is one factor why it doesn't seem to take.
This is the only thing that makes sense about this design. It's the result of optimizing some parameter at the expense of all others. Maybe the maths makes sense but it looks ugly and I've never seen an ugly machine that worked well.
So why do all modern fighters look similar and nothing like this?
I'm not sure if there is a stated "breakthrough" in fuel efficiency. Slow, straight wing, glider-like airplanes with turbos and electronic engine controls were already better than some SUVs.
What am I missing? Aircraft are such illustrative examples of the whole concept of tradeoffs.
If center of gravity is far back with a really short tail moment arm and most of the big body is in the front, there could be control, stability and center of gravity issues. Is it possible to ealk around the cabin during flight?
Piaggio Avanti is somewhat similar on being an advanced concept with high efficiency. I think they just stopped the manufacture.
And yet, no EPA emissions regulations exist for aircraft at all.
I am glad to see aircraft efficiency improve regardless.
When all aircraft were grounded the day of the WTC attacks of 9/11/2001 and the following few days, meteorologists noticed that the average US temperatures decreased a few degrees.
Since then there have been investigations into contrails reflecting and retaining heat in much the same way as the CO2 greenhouse effect.
search for "contrails global warming"
random article: https://phys.org/news/2011-03-airplane-contrails-worse-co2-e...
Long story short: no clouds equals cold nights. Contrails are a form of cloud and contribute a little to the aforementioned dampening effects.
I wonder if we could tune them and use it to control the weather (minimize the effect during hot spells, maximize it during cold spells).
- https://www.nesdis.noaa.gov/content/do-contrails-affect-cond...
- https://news.psu.edu/story/361041/2015/06/18/research/jet-co...
- https://en.wikipedia.org/wiki/Contrail#Contrails_and_climate
And it takes a while to climb to 65000 feet. Especially if the engine isn't as powerful as jet engines usually are (yes, it's more complicated...).
Another point is safety. Bigger airplanes usually have fewer accidents, not just because the pilots are more experienced, but also because of higher robustness against weather, time to correct mistakes, and fewer dangerous actions (landings) per passenger. Basically fewer chances to screw up with pilots that have a very long track record of not screwing up.
The fact is that none of the features given in the article are novel, so why have they not been combined before? Some of them were, in fact, in the Republic XF-12 [1], and the idea of using a diesel with much more turbo-charging than is usual, as an aero engine, was seen in the Napier Nomad [2] (it was actually a two-stroke turbo compound, with, in one version, a sort of afterburner between the diesel and turbine stages!)
The usual experience of putting together several different incremental changes is that there are unanticipated problems, and the whole is less than the sum of the parts.
While I am skeptical that this airplane will deliver on its promises, I do not want to be entirely negative. It is possible that changing circumstances have produced an opportunity that was neither recognized or exploitable before.
Once gas turbines were developed, progress on piston aero-engines essentially came to a halt, but piston engines continued to be developed for cars, at least following the oil crises of the 70s, so that piston engines are now much more efficient, lighter and, importantly, reliable than they were (even diesels.) These developments have been making their way into aviation, but so far almost exclusively in the niches where piston engines were still being used.
Another development has been the use of composites, which permit the development of effective laminar-flow airfoils (several WWII-era aircraft nominally had such wings, but there is considerable doubt as to their effectiveness, as it is difficult to make metal wings to the stringent tolerances needed.) This capability has been used in sailplanes for decades, but is only slowly extending beyond that niche (more so now that electric airplanes are feasible.)
AFAIK, the Boeing Condor drone is the only piston-engined airplane to reach 65,000 feet, and the closest piloted flights have been some 15,000 feet short, but if this project can get a piston-engined, payload-carrying airplane cruising at that altitude without too many compromises, I think it has a chance of making a difference. The retro-futuristic appearance of this prototype is probably mostly incidental.
(That's because it's still a big and heavy car. Even with a conventional internal combustion engine, you can get a better mileage, if you are willing for a more European style smaller, lighter car.
Relative to its weight and size, a Prius is pretty efficient.)
Europeans would also drive bigger cars, if their petrol was as cheap as in America.
And you can see the Americans reacting to at-times more expensive petrol by buying smaller cars for a while.
The data usually cited for this is studies showing that it is safer in given collision conditions. On the other hand, collisions are more likely, rollovers are more likely, and rollovers are disproportionately fatal for vehicle occupants compared to collisions.
In any case, my argument is basically that some people prefer bigger cars; but Europeans don't get to act on that preference as much because their fuel is more expensive. So you'd see different cars, even if they preferences were exactly the same. (They are not exactly the same.)
Why are larger vehicles inherently more fun? A go-cart is fun. A double decker not so much (I would guess anyway).