# Celera 500l Progress

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#### PMD

##### Well-Known Member
CNN article. Probably not a good source of factual information.

#### TFF

##### Well-Known Member
If the airplane is aerodynamically brilliant, they will end up putting a jet in it. As much of a piston engine lover, that I am, it’s not cool anymore.

While I think the electric revolution is being pushed instead of evolving like it should, no one is going to stick money into a new piston engine. A multimillion super car, sure. They only have to make a couple of dozen.

Mass produced for aviation, not without someone like Musk that will subsidize it. F Lee Bailey when he owned Enstrom Helicopters pushed to get 300 helicopters manufactured, because that was the number, in the wild,made it hard to shut the doors. He subsidized the company with his pocket.

Musk isn’t investing in sealing wax is he?

#### tspear

##### Well-Known Member
If the airplane is aerodynamically brilliant, they will end up putting a jet in it. As much of a piston engine lover, that I am, it’s not cool anymore.

While I think the electric revolution is being pushed instead of evolving like it should, no one is going to stick money into a new piston engine. A multimillion super car, sure. They only have to make a couple of dozen.

Mass produced for aviation, not without someone like Musk that will subsidize it. F Lee Bailey when he owned Enstrom Helicopters pushed to get 300 helicopters manufactured, because that was the number, in the wild,made it hard to shut the doors. He subsidized the company with his pocket.

Musk isn’t investing in sealing wax is he?

The RED engine already burns Jet-A

Tim

#### trimtab

##### Well-Known Member
I'm still trying to validate the "Several flights reached airspeeds of over 250 mph at altitudes up to 15,000 feet which projects to an airspeed of 460 mph at 50,000 feet" statement.

I cannot seem to make that claim make sense unless they were using a great deal less than full rated power at 15,000 feet to achieve 250 mph. Any takers to show how to make that leap?

Even with granting a magical wish to maintain propeller efficiency and the pressurized aspiration?

#### rv6ejguy

##### Well-Known Member
I can only guess that both RED and Otto have some pretty smart engineers working for them but I see some pretty big hurdles to overcome.

The wing loading would seem pretty high to fly at these speeds efficiently at FL500.

You probably need 3 stage turbocharging to maintain power on the diesel up there. It's been done on SI engines experimentally but is very challenging technically to make sure none of the compressors go into choke or surge over the typical power settings used. That's likely 6 turbos required on this V12 engine, 3 per bank. Lots of packaging concerns there.

The very high pressure ratios required here demand immense charge cooling and with that comes drag and finding the volume to fit the required heat exchangers. Ditto on the water cooling in such low density air.

Pretty sure the prop used here won't work very well at 50,000 feet. The pusher design and short landing gear on the prototype limits using anything much larger.

This design is much more likely to succeed technically and in the market with a turbine replacing the CI engine.

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#### TFF

##### Well-Known Member
Still a piston engine. Who is going to put the money into something that has a public stigma on the world stage? CO2 less combustion engine is the only way a new one would be considered.

#### Kyle Boatright

##### Well-Known Member
Still a piston engine. Who is going to put the money into something that has a public stigma on the world stage? CO2 less combustion engine is the only way a new one would be considered.

Help me understand this CO2 less engine?

I think the point (or a point) is that this is supposed to be several times as efficient as current offerings. No, it isn't zero emissions, but their claims indicate it will have a fraction of the C02 emissions as conventional types. If that's true, and if the engine has near-turbine reliability, it'll sell like hotcakes. If it has the performance, but the engine is problematic, they can revert to a turboprop with relative ease (other than the fuel fraction issue).

#### trimtab

##### Well-Known Member
Theranos had some good molecular biologists and engineers working for them also. And....

The prop development efforts oriented at high altitude, low Re ops look pretty different than familiar props (think Mars copter), and the efficiency compromises are large...you can have a well-matched higher Re prop operate with close to 80% throughout a low altitude window at cruise, but it is likely to exhibit propulsive efficiencies in the 60-65% range at 50k'. Or you can have the reverse. Or you can have a prop that performs poorly in both regimes. It isn't clear to me what a prop that can perform well at both altitude ranges would even look like.

Turboprops that fly at high altitude struggle mightily with this struggle, turning nearly a third of their SHP into heat.

Then there is the boosting. Multistaged boosting has real problems at altitude with regards to maintaining functionality without a lot of effort. And failure to maintain control in testing has indicated an unrecoverable loss of boost until the altitude can be reduced to be able to restart the engines...in other words, if anything gets wonky, you are screwed until you descend low enough to be able to start the engine again.

Turbines do not have that problem to the same extent, although they can. Piston engines have that problem right out of the gate. It's a problem that is distinct from whether one can get the boost in the first place....which is a large looming issue of course. This issue is whether, if boost is lost for even a tiny interval, if the engine can be recovered without a massive descent. A dual engine design might be able to port enough boost to allow an engine restart to the inoperative engine, but not likely while producing prop torque.

#### Marc Zeitlin

##### Exalted Grand Poobah
I'm still trying to validate the "Several flights reached airspeeds of over 250 mph at altitudes up to 15,000 feet which projects to an airspeed of 460 mph at 50,000 feet" statement.

I cannot seem to make that claim make sense unless they were using a great deal less than full rated power at 15,000 feet to achieve 250 mph. Any takers to show how to make that leap?
I can't address the prop issues at higher altitudes, nor the turbocharging issues, nor the cooling issues.

However, purely from an IAS/TAS standpoint, 250 mph TAS at 15K ft at the temps generally seen around here is about 190 mph IAS. So _IF_ it can maintain 190 mph IAS all the way up to 50K ft., then TAS will be about 500 mph. Apparently they're derating things a bit.

#### rv6ejguy

##### Well-Known Member
If you flame out a CI engine at 50,000 feet, you have zero chances of relight until you drop back down below 10,000 feet or so. This is a big drawback to a single engined CI powered airplane. Most CI aero engines have to maintain at least 40 inches up high or they can go wonky. Ignition is accomplished by heat of compression, not spark.

#### rv6ejguy

##### Well-Known Member
250mph at 15,000 feet is matched by some existing turbocharged piston GA aircraft like Lancairs, Glasairs, Ventures etc. Nothing earth shattering there. The question is what is the fuel flow loaded with pax on the Celera.

#### tspear

##### Well-Known Member
If you flame out a CI engine at 50,000 feet, you have zero chances of relight until you drop back down below 10,000 feet or so. This is a big drawback to a single engined CI powered airplane. Most CI aero engines have to maintain at least 40 inches up high or they can go wonky. Ignition is accomplished by heat of compression, not spark.

Not sure if it was the RED CI engine or another one attempting certification. A while back I read of a CI engine which had a few technical tricks to handle restart at higher altitudes.
1. Igniters, also used for cold starting.
2. Compressed air tank; enough air for just for a few rotations. Once engine running, small inefficient pump will build a new compressed air charge.
3. Small electric root blower, can run for about 30 seconds before the engine over heats. Used after the compressed air tank has fired off.

Tim

#### rv6ejguy

##### Well-Known Member
Not sure if it was the RED CI engine or another one attempting certification. A while back I read of a CI engine which had a few technical tricks to handle restart at higher altitudes.
1. Igniters, also used for cold starting.
2. Compressed air tank; enough air for just for a few rotations. Once engine running, small inefficient pump will build a new compressed air charge.
3. Small electric root blower, can run for about 30 seconds before the engine over heats. Used after the compressed air tank has fired off.

Tim

Yes, it's possible to add more things like this, more weight and complexity though.

#### trimtab

##### Well-Known Member
I can't address the prop issues at higher altitudes, nor the turbocharging issues, nor the cooling issues.

However, purely from an IAS/TAS standpoint, 250 mph TAS at 15K ft at the temps generally seen around here is about 190 mph IAS. So _IF_ it can maintain 190 mph IAS all the way up to 50K ft., then TAS will be about 500 mph. Apparently they're derating things a bit.
The constant IAS calculation would be where the story becomes murky. Yes, constant IAS means 490-500 mph, but that is exactly why my view oscillates between confusion and skepticism. The thrust available decreases with TAS. The power required for a given IAS rises with altitude (proportional to 1/sqrt of density differences). This is why the IAS drops for a turbocharged prop driven airplane at constant BHP...resulting in a large deviation from the "constant IAS" calculation. To maintain constant IAS, BHP has to increase markedly.

For a practical example, look at a POH for the P210 or PA-31, and track the real TAS capability. Calculating the excess HP available at 2000 msl vs 20000 msl at constant BHP tracks the basic relationships very well and is actually less than the calculated capabilities probably due to prop efficiency loss or perhaps even pressurization demands.

The major prop manufacturers each acknowledge the deleterious effects of density altitude on propeller propulsive efficiency. And more than one turbo manufacturer acknowledges the issues associated with pressure losses in a compression ignition engine at high altitude. It is a fundamental risk.

All of these are large, big ticket problems to solve.

I don't get anything out of scribbling away to prove bumblebees can't fly, and it's a waste of time to do so. I am instead genuinely curious how these calculations could work out to be so different from what a team of engineers that are working on this every day seem to think. It would be nice to know what is behind that gap, that's all.

In the past, the answer has come in the form of bad faith and investment scheming. In this case, I'd like to keep an open mind and learn something newish instead.

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#### tspear

##### Well-Known Member
@trimtab

Can you explain this section "The power required for a given IAS rises with altitude (proportional to 1/sqrt of density differences) "
I think it is related to something I have read multiple times years ago over on BT. That for piston planes, for a constant L/D ratio (e.g. constant IAS), the MPG stays the same regardless of altitude. Are these related, and does it make sense (and do I recall it correctly).

Tim