Celera 500L -- A much more efficient private aircraft

[berkeman]

TL;DR Summary

Interesting design point -- Because of its shape and engine, it is about 10x more fuel efficient than a private jet, possibly offering charter costs comparable to commercial air travel.

I saw this on CNN's website today:

https://www.cnn.com/travel/article/celera-500l-plane/index.html

The main claim is that the shape and overall design is more efficient than traditional aircraft design, and they are listing impressive fuel economy and operating costs. They say that the range and speed make non-stop private flights within the US a reality. It will be interesting to see how this progresses.

And they make a good point: At a time when air travel is down because of the pandemic, having the ability to travel just with your family members or your close associates could be a big advantage.

 

[berkeman]

BTW, here is the company's website: https://www.ottoaviation.com/

 

[Vanadium 50]

The wings look itty-bitty. Is the fuselage a lifting body?

 

[berkeman]

The wings look itty-bitty. Is the fuselage a lifting body?

Interesting question. We probably need somebody like @boneh3ad to chime in on that question. It does brag about its glide ratio, though, under the Performance tab at Otto's website (link above):

Gliding Capability
The Celera 500L has a glide ratio of 22:1 (typical GA aircraft of similar size have a glide ratio of < 9:1). At an altitude of 30,000ft The Celera 500L can glide up to 125 miles with no engine power. This is roughly 3x better than the typical aircraft.

 

[anorlunda]

I like it. Usually, only NASA and huge corporations do R&D on new airplanes. It is refreshing to see the private sector doing it on their own.

Their website says that it has completed 31 test flights. That is very very early in a development cycle. There are many issues like stability and behavior in extreme states that influence safety. For example, the early Lear Jets were reputed to require the utmost in pilot skills. It offers an opportunity for the kind of public/private partnership that we are bad at in the USA. Could NASA offer assistance without impinging on the intellectual property rights of the inventors?

The website also shows more pictures. The wings are small but not tiny. But to get radically different performance, we must expect radically different shape and size.

 

[DaveC426913]

The wings look itty-bitty. Is the fuselage a lifting body?

 

[berkeman]

For example, the early Lear Jets were reputed to require the utmost in pilot skills.

Yeah, when I saw the quote below on the Otto website, I was a bit surprised that they don't use fly-by-wire or other technology to aid in stability. Maybe the design is inherently more stable than other aircraft like the Leer Jets?

Safety
The Celera 500L is designed with safety in mind. No fuel in wings. Mechanically linked flight controls. Plus, reliable and redundant aircraft systems including the RED A03 engine. The engine effectively operates as two 6-cylinder engines, allowing for continued power and operation of all critical systems under numerous failure scenarios. All of this and more ensures the highest level of safety and compliance within FAA regulations.

 

[DaveC426913]

No fuel in wings.

That can't be why wings on standard aircraft are so bulky by comparison, can it?

If - just for fun - we took a regular commercial lear jet, and stripped out the wing tanks, putting the fuel in the fuselage - would the wings still need the same camber and depth? Or would they be radically thinner, like the Celera?

(high-speed, swept-wing design notwithstanding)

 

[boneh3ad]

The need for fuel tanks in the wings is absolutely a key driver in how thick they are on a typical aircraft. Still, this is a surprisingly small wingspan for wings with such a small chord, so one would have to think they are deriving some lift from that body (and, in fact, its OML does resemble a natural laminar flow airfoil to a degree).

 

[etudiant]

The idea is high speed cruise at relatively high altitude, so smaller wings are adequate. Piston engines allow much lower costs than any turbine and laminar flow helps efficiency.
Obvious issues are low speed handling, (the small wing may require relatively high landing speeds, even if big flaps help mitigate that) as well as high speed handling, as the 460 mph max cruise speed is getting close to mach effects. The airplane looks to be a hot rod and likely will be a handful to manage, especially as the controls are stated to be mechanical rather than fly by wire/computer assisted.
Afaik, the absolute speed record for a piston engined aircraft is only about 530 mph, using a more than 2000 hp engine, so cruising at 460 mph with just 550 hp would be very impressive.

 

[phinds]

Summary:: Interesting design point -- Because of its shape and engine, it is about 10x more fuel efficient than a private jet, possibly offering charter costs comparable to commercial air travel.

Really amazing. Very cool. Thanks for posting.

 

[256bits]

Safety feature
No fuel in wings.
How is that a safety feature, and under what circumstances?

Glide ratio.
The Celera 500L has a glide ratio of 22:1 (typical GA aircraft of similar size have a glide ratio of < 9:1)
That is verging upon the lower end ratio for a glider aircraft, which typically have a thin body and long thin wings. I think their comparison to similar aircraft ( which aircraft is similar to this one as its in its own category with the design ) must be a referral to a clunky Cessna, or Beechcraft. ( 50 year or so old design )

This particular Learjet has a 16 L/D ratio.
https://en.wikipedia.org/wiki/Learjet_25#:~:text=This is a glide ratio,and more modern light jets.

Cool design, but whether it wins the hearts and minds with its rear push engine is to be seen.
Range and operating fuel costs seem to be a big plus though.

I was a bit surprised that they don't use fly-by-wire

If they do loose engine power, then mechanical linkages still work, and the L/D stays stays the same.
They do not have to stick out a RAT ( one of those auxilary turbines that extend out in flight with engine loss for instrument power and whatnot ), or rely on the battery for the same. Glide time - they don't say - maybe 30 minutes or more from 30,000 feet.

 

[Lnewqban]

The short distance between wings and horizontal stabilizer calls my attention regarding pitch stability at low speeds.

Previous designs with piston engines located at the tail had problems with cooling at low speeds.
That, and the need to cool the turbos, may the the reason for the not so aerodynamic big scoop.

This picture shows a five bladed, variable pitch propeller and what seems to be all-moving vertical and horizontal stabilizers.

The shape of the fuselage, as well as the blended cockpit windscreen, look similar to the teardrop type fuselages of Bell X-1 and SpaceShipOne.

 

[Lnewqban]

Copied from:
https://patents.google.com/patent/US9446835B2/en

“The propeller airfoil sections and section incidence angles are configured to provide maximum efficiency at cruise at 50,000 ft. altitude and above. Propeller diameter is also optimized for the high altitude cruise environment and as a result essentially eliminates supersonic blade velocities during low altitude operation. The optimum propeller diameter is slightly smaller than maximum fuselage diameter which coincidentally reduces the probability of bird strike and other foreign object damage.

The propeller is connected to two engines by a drive shaft extending from the output shaft of a gear box. The engines are liquid-cooled diesel engines driving torque converters connected to the gear box. Multi-stage turbo charging is provided to compensate for altitude and to provide cabin pressurization. Engine heat exchangers, turbo chargers and intercooler heat exchangers are all mounted in ducts configured to provide thermal recovery of waste heat for supplemental propulsion. Engine exhaust is likewise used in the rear of the same duct to provide an injection pump function both for cooling air circulation during low speed operation and to provide additional thrust during flight.”

 

[russ_watters]

The wings look itty-bitty. Is the fuselage a lifting body?

Perhaps it's an illusion: the bullet shape creates a large volume, but does't necessarily imply a high weight.

10x the fuel economy at similar performance is quite a claim.

 

[Lnewqban]

https://www.thedrive.com/the-war-zo...lutionary-celera-500l-officially-breaks-cover

 

[Lnewqban]

In the video of the previous link, the air scoops can be seen working.
They remind me of the Meredith effect achieved by the air scoop of the P-51.

Please, see:
https://en.m.wikipedia.org/wiki/Meredith_effect

https://www.neillwatson.com/historic-motorsport/p51-mustang-meredith-effect-lee-atwood/

 

[DaveE]

Curious about the weight and balance calculations for this design. At first, I thought the fuel has to go in the back, but I don't think that works because of the balance change as the fuel is consumed. Honestly, to my untrained eye, it looks like this plane needs ballast!

BTW, one reason that most aircraft store fuel in the wings is that you want the center of gravity near the center of lift whether the tanks are full or empty. Also, if you put the weight of the fuel in the wings, where the lift is, then you don't need as much strength in the wing to fuselage joints.

 

[phinds]

Also, if you put the weight of the fuel in the wings, where the lift is, then you don't need as much strength in the wing to fuselage joints.

But I would think you would need MORE of that strength when you land than if the fuel were not in the wings. I mean, you really don't want the wings to snap off every time you land. Gets to be a maintenance problem.

 

[DaveE]

you really don't want the wings to snap off every time you land

Yea, that would be bad!

It depends on lots of stuff.
- where are the landing gear?
- how do those forces compare to other phases of flight (like turbulence or extreme maneuvers)?
- where are the other loads (weight) in the design.

 

[etudiant]

This is really pretty ambitious, a 50,000+ ft cruising altitude for max efficiency.
That is getting close to Concorde altitudes and is well above the existing jet traffic.
Frankly, if the tests hold up, they will have immediate demand from the military, the cost/performance is compelling.
I'd be a lot less comfortable in it as a guest passenger, it does not look to be a very forgiving design and there is the experience of the earlier high performance twins, the Ted Smith Aerostar and the Mitsubishi MU-2, both of which had much more than their share of accidents because their pilots were overtaxed.

 

[boneh3ad]

as well as high speed handling, as the 460 mph max cruise speed is getting close to mach effects.

What do you mean by "Mach effects?" That's not a technical term. If you intend that to mean "compressibility effects," then we've long since passed that threshold. That's roughly Mach 0.7 at cruise. Be that as it may, that doesn't necessarily introduce any control issues. Long gone are the days of believing there is a sound barrier.

 

[anorlunda]

- where are the landing gear?

You see them in the photo in #13. They are not under the wings. That raises yet another stability question; tipping during taxi or crosswinds while parked.

Question: Do some aircraft pump fuel fore/aft during flight to change the C.G.?

 

[phinds]

You see them in the photo in #13. They are not under the wings. That raises yet another stability question; tipping during taxi or crosswinds while parked.

Looks pretty stable to me: landing gear appears to be wider than the body by just a bit and almost all of the weight is in the body

 

[jrmichler]

High speed on low power means small wings to reduce drag. Small wings require higher speeds for takeoff and landing. High takeoff and landing speeds require long smooth runways similar to what business jets need. The narrow chord would also indicate a small range of allowable CG.

Jon Sharp's NXT is a race plane with similar power and performance to the Celera. It has takeoff and pattern speeds comparable to jet airliners. This article has a nice discussion of flying the NXT: https://www.avweb.com/recent-updates/experimentals/special-delivery/.

 

[Vanadium 50]

I mean, you really don't want the wings to snap off every time you land. Gets to be a maintenance problem.

Wings, schmings. In 1983 an F-15 lost a wing in flight. The pilot landed safely. The plane got a brand new wing and was returned to service.

 

[Vanadium 50]

I was a bit surprised that they don't use fly-by-wire or other technology to aid in stability.

It's not clear that mechanically linked controls is safer than FBW. As a non-aviator, I would expect that there are situations where one is better and situations where the other is. It's also not clear that safest of all would be a 777-like system which is normally FBW but with backup mechanical controls.

 

[phinds]

Wings, schmings. In 1983 an F-15 lost a wing in flight. The pilot landed safely. The plane got a brand new wing and was returned to service.

Wowzers !

 

[DaveE]

Do some aircraft pump fuel fore/aft during flight to change the C.G.?

Yes. The A330 has tanks in the tail (called "trim tanks"). The computers automatically pump it forward to adjust balance as fuel is consumed.

edit: I don't think this is really for trim though. I think it's just a way to carry more fuel when you've used up the space under the center of lift.

 

[jrmichler]

Their claims of cruising at high altitudes are contraindicated by the engine type certificate, which states that the engine is certified for a maximum altitude of 25,000 feet: https://rgl.faa.gov/Regulatory_and_...ce1c8625806100527957/$FILE/E00092EN_Rev_0.pdf

There is also some interesting commentary after the Avweb article about this airplane: https://www.avweb.com/aviation-news...iation-officially-introduces-the-celera-500l/. Especially the comments about turbocharging diesel engines and high altitudes.

 

[Vanadium 50]

Their claims of cruising at high altitudes are contraindicated by the engine type certificate, which states that the engine is certified for a maximum altitude of 25,000 feet

Yeah, but they have two of them and 25,000+25,000 = 50,000.

 

[cmb]

A cruising speed of 450mph (odd units) 'and' 25mpg seems quite a claim.

Be better to know the full operating profile first.

I tend to think we've been making and optimising aircraft for a long time, unclear where such a massive improvement comes from.

I recall when I was learning to fly in the UK, there was a guy based there who owned a 'motorised glider' and commuted back to his home in Netherlands every weekend in it (weather permitting, presumably) and he said it delivered 120mpg. I see no reason that could not be done similarly on a larger scale, but 450mph with that sort of efficiency seems slightly on the wild side.

I mean, sure, if you want to 'potter along' at 80 kt and you get "25mpg" (ground distance?), or maybe there is an efficient climb out and then engine-off for a glide decent, etc., sure. I'd like to see the claim for 25mpg + 450mph made together.

Rarely do you get something for nothing, especially on the delta between existing aircraft and a new one.

 

[gleem]

That is also what I have been thinking. One usually would expect an improvement in design would result in an increase in fuel economy of maybe 5 to 15% considering aircraft have been evolving for over a hundred years. A new design resulting in an 800% increase in fuel economy can only be considered as astonishing. One would have thought that the concepts used for this aircraft would have already been discovered and implemented long ago considering everybody has available the same development tools, knowledge, and education. Was something fundamental in aircraft design overlooked all this time?

 

[gleem]

I did some quick calcs to check the HP and thrust needed for level flight.

450 kts

22 nm/gal ---> 20.5 gal/hr
Fuel --=> density = 6.7 lbs/gal
Energy content of fuel used = 5220 Kcal/lb
wgt of fuel used per hour = 137.4 lbs./hr
Energy used per hours 717,230 kcal/hr
If 1 kcal/sec = 3600 kcal/hr = 5.613 HP
Then the rate of energy use is 1118 HP. If the efficiency is 40% then the useful HP delivered is 447 HP

How much thrust is needed?

F⋅v = power = F ⋅ 450 ⋅(6076/3600) lbs ft/sec = f ⋅760 ft/sec = 447 Hp = 245,850 ft lbs/sec
F = 323 lbs of thrust.

Does this seem reasonable?

 

[boneh3ad]

You see them in the photo in #13. They are not under the wings. That raises yet another stability question; tipping during taxi or crosswinds while parked.

The fact that fuel isn't stored in the wings would tend to make it more stable in this instance since so little mass is located outside the width of the gear.