Otto Aviation Group LLC Celera 500L
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What makes me worry about this project is the Russian background of the Redair engine. Despite the company is in Germany (next to the Nürburgring), its owner is Russian and he still seams to be very conected to Russia. I Gues using this engine in the US will be next to unpossible due to the political situation.
Drag will increase substantially with high lift devices like Fowler flaps added and their associated tracks.
Typical aircraft cabins leak down pretty fast in my experience. You'd have a substantial loss in less than 10 seconds as most aircraft use inflatable door seals. Would have to get down below 25,000 feet really quickly so let's call that a 12,000+ fpm descent roughly. That would be quite a feat without exceeding Vne. The human environment is untenable at 40,000 to 50,000 feet cabin altitude in less than 30 seconds. With extra attention to detail and a different way of door sealing, leakage could be reduced but this all takes time to implement and prove to the FAA.
My point with the Rotax example was to look at the size of the turbo and HX parts on an only 80hp engine (yes granted for operation at 85K feet). Now extrapolate that to an engine producing more than 6X the power- requiring at least 6X the mass flow at any given altitude. Both would be 3 stage systems.
Having produced HX ducting for turbocharged, liquid cooled aircraft, I disagree that this would be simple in Celera with an eye on minimal drag impact. Packaging would be most challenging indeed with multiple HXs in this case. Cars don't try to minimize cooling drag via the Meredith Effect which will be very important here where engine and charge cooling loads will be far higher and more challenging than on cars operating in dense air at far lower pressure ratios. Stacking HXs results in massive momentum loss and high cooling drag in aircraft, the extra frontal area introduced by unstacking them results in more drag. It's a fine balancing act.
The turbine has almost no cooling drag and doesn't need charge cooling either, resulting in a cleaner airframe and less drag overall so requires less hp. It also has useful exhaust thrust. This helps offset the power loss at altitude.
As Elon Musk famously said- "Prototypes are easy, production is hard". This will certainly apply to this very complex aircraft breaking a lot of new ground and especially so with the certification process it will have to go through. Not to be taken lightly if you understand what will be involved there.
The Celera prototype speeds haven't be published yet, even at 25,000 feet, which is suspicious after all this time has passed. If it really does what's been projected, why not show the world and generate more interest in the project? This would help raising investment money as well which this project will surely need to clear the certification hurdle...
I guess we sit back and see what happens here over the next 12-24 months.
Typical aircraft cabins leak down pretty fast in my experience. You'd have a substantial loss in less than 10 seconds as most aircraft use inflatable door seals. Would have to get down below 25,000 feet really quickly so let's call that a 12,000+ fpm descent roughly. That would be quite a feat without exceeding Vne. The human environment is untenable at 40,000 to 50,000 feet cabin altitude in less than 30 seconds. With extra attention to detail and a different way of door sealing, leakage could be reduced but this all takes time to implement and prove to the FAA.
My point with the Rotax example was to look at the size of the turbo and HX parts on an only 80hp engine (yes granted for operation at 85K feet). Now extrapolate that to an engine producing more than 6X the power- requiring at least 6X the mass flow at any given altitude. Both would be 3 stage systems.
Having produced HX ducting for turbocharged, liquid cooled aircraft, I disagree that this would be simple in Celera with an eye on minimal drag impact. Packaging would be most challenging indeed with multiple HXs in this case. Cars don't try to minimize cooling drag via the Meredith Effect which will be very important here where engine and charge cooling loads will be far higher and more challenging than on cars operating in dense air at far lower pressure ratios. Stacking HXs results in massive momentum loss and high cooling drag in aircraft, the extra frontal area introduced by unstacking them results in more drag. It's a fine balancing act.
The turbine has almost no cooling drag and doesn't need charge cooling either, resulting in a cleaner airframe and less drag overall so requires less hp. It also has useful exhaust thrust. This helps offset the power loss at altitude.
As Elon Musk famously said- "Prototypes are easy, production is hard". This will certainly apply to this very complex aircraft breaking a lot of new ground and especially so with the certification process it will have to go through. Not to be taken lightly if you understand what will be involved there.
The Celera prototype speeds haven't be published yet, even at 25,000 feet, which is suspicious after all this time has passed. If it really does what's been projected, why not show the world and generate more interest in the project? This would help raising investment money as well which this project will surely need to clear the certification hurdle...
I guess we sit back and see what happens here over the next 12-24 months.
Bleed air for climatization/pressurization cost a lot of energy, so that airlines try to minimize the amount of fresh air in the cabin. The European regulations demand 0.25 kg/min (=0.004166 kg/s) for every passenger during normal operation (https://www.easa.europa.eu/downloads/47113/en). Let’s say, the amount of air exchange is similar in the Otto Celera.
The Otto Celera has an internal cabin volume of 448 ft³ (https://www.thedrive.com/the-war-zo...lutionary-celera-500l-officially-breaks-cover) this is equivalent to about 12.5 m³. The density of the cabin air (I choose 8000 ft equivalent) is about 0.86 kg/m³. There are max. 6 persons on board, so the required air flow will be 6*0.004166 kg/s = 0.025 kg/s or 0.029 m³/s. This means, it takes 430 s or 7 min for the climatization, to replace the whole volume of the cabin. Lets assume, the use about 50 % more air flow for comfort reasons, then it would still take around 5 min to replace the internal volume.
Now we think about your thesis, that aircrafts cabins are leaking so much, the there is a significant pressure drop within 10 s if the pressurization system fails. Lets say, the internal pressure would fell down to 75 % of the regular pressure within 10 sec, even with a constant outflow, this would mean the air is leaking out with 0.269 kg/s this is 10 times more than the pressurization system is capable!
We see, you are pretending things which are completely unrealistic.
Going back to the Rotax:
For every reader with basic knowledge about turbo chargers, it should be clear, that the number of stages is largely depending on the required density ratio. Youre mentioned Rotax is operating in an atmosphere (85000 ft) where the density is less than 20% of the maximum flight height of the Otto Celera (50000 ft. I gave you this link, so you could have easily verified it (https://www.digitaldutch.com/atmoscalc/). It is very obvious, that you need at least one more charging stage, to keep the required density increase is 5 times higher!
Its not the main point, but you are also wrong about the influence of the size, so bigger the engine, so bigger the turbos, so higher the pressure ratio par stage. The fact, that the Rotax works fine with three stages in 85000 shows, that the Redair Diesel would work happily with two stages in 50000 ft.
What do you think, why the Rotax was choosen over a turbine, just because the engineers have been crazy and didn’t know about turbines? The answer is, because the triple charged Rotax produces more power at 85000 ft than even a PT6 would do. A PT6 with 1000 kw on the ground would merely have 28 kw (38 HP) at 85000 ft (and having problems with flame outs). Turbines run at an air fuel ratio between 40-50, gasoline engines at 14.5 and Diesel at about 17-18 at full load. You need about 2.5 times as much air for the same power output in a turbine than in a piston engine, that’s why a turbine for 85000 ft would be heavier and bigger than the Rotax. The low-pressure Turbo of the Rotax may be huge, but the low pressure part of a competing turbine would be 2.5 times bigger!
Turbomatching for the Redair:
I did some simple math to match the LP turbos for the Redair engine and as we could see (see my postings above) they aren’t especially big in regard to the engine and even more so in regard to the huge engine compartment (thanks to the rear position in the wide body circular fuselage). If you are so experienced in matching turbos, why don’t you show me that I’m wrong? I mean, not by silly comparisons, but by some simple calculations.
Cooling for cars is critical when driving slowly uphill behind a truck while pulling a trailer, this is totally different than cooling an aircraft engine at 740 km/h in -50 °C. Cars don’t use the Meredith effect, because in normal operation it has no measurable effect. Even race cars don’t focus either on that (because even Formula 1 cars drive relative slow, compared to past props) but their cooling system is built quite similar to Junkers Düsenkühler, which is the style of cooler producing the Meredith Effect (Race cars are not allowed to use variable cooling exhaust geometry, which would be required for the Meredith Effect).
Otto Celera has announced, that they are waiting for the next engine variant with multi stage turbocharging and only tried out the single stage variant, so there is nothing suspicious about it. The real problem is certainly the Russian background of the Redair company, now it will be completely impossible to build an American Aircraft with an engines from a Russian owned Company,
I prove all my arguments with calculations, you should do the same. It takes much more effort, to prove that your allegations (all without any basic facts backing them up) are wrong than just pretending new allegations. Do you have any evidence, that fowler flaps increase the wind drag significantly? Would be a good start to give some sources for that.
Edit:
according to the final report of this incident (https://aviation-safety.net/database/record.php?id=20010824-1 click on final report, go to page 96) the maximum cabin leakage rate (A332) according to the specification is 700 ft/min, so no sudden pressure drop occures within 10 s.
The Otto Celera has an internal cabin volume of 448 ft³ (https://www.thedrive.com/the-war-zo...lutionary-celera-500l-officially-breaks-cover) this is equivalent to about 12.5 m³. The density of the cabin air (I choose 8000 ft equivalent) is about 0.86 kg/m³. There are max. 6 persons on board, so the required air flow will be 6*0.004166 kg/s = 0.025 kg/s or 0.029 m³/s. This means, it takes 430 s or 7 min for the climatization, to replace the whole volume of the cabin. Lets assume, the use about 50 % more air flow for comfort reasons, then it would still take around 5 min to replace the internal volume.
Now we think about your thesis, that aircrafts cabins are leaking so much, the there is a significant pressure drop within 10 s if the pressurization system fails. Lets say, the internal pressure would fell down to 75 % of the regular pressure within 10 sec, even with a constant outflow, this would mean the air is leaking out with 0.269 kg/s this is 10 times more than the pressurization system is capable!
We see, you are pretending things which are completely unrealistic.
Going back to the Rotax:
For every reader with basic knowledge about turbo chargers, it should be clear, that the number of stages is largely depending on the required density ratio. Youre mentioned Rotax is operating in an atmosphere (85000 ft) where the density is less than 20% of the maximum flight height of the Otto Celera (50000 ft. I gave you this link, so you could have easily verified it (https://www.digitaldutch.com/atmoscalc/). It is very obvious, that you need at least one more charging stage, to keep the required density increase is 5 times higher!
Its not the main point, but you are also wrong about the influence of the size, so bigger the engine, so bigger the turbos, so higher the pressure ratio par stage. The fact, that the Rotax works fine with three stages in 85000 shows, that the Redair Diesel would work happily with two stages in 50000 ft.
What do you think, why the Rotax was choosen over a turbine, just because the engineers have been crazy and didn’t know about turbines? The answer is, because the triple charged Rotax produces more power at 85000 ft than even a PT6 would do. A PT6 with 1000 kw on the ground would merely have 28 kw (38 HP) at 85000 ft (and having problems with flame outs). Turbines run at an air fuel ratio between 40-50, gasoline engines at 14.5 and Diesel at about 17-18 at full load. You need about 2.5 times as much air for the same power output in a turbine than in a piston engine, that’s why a turbine for 85000 ft would be heavier and bigger than the Rotax. The low-pressure Turbo of the Rotax may be huge, but the low pressure part of a competing turbine would be 2.5 times bigger!
Turbomatching for the Redair:
I did some simple math to match the LP turbos for the Redair engine and as we could see (see my postings above) they aren’t especially big in regard to the engine and even more so in regard to the huge engine compartment (thanks to the rear position in the wide body circular fuselage). If you are so experienced in matching turbos, why don’t you show me that I’m wrong? I mean, not by silly comparisons, but by some simple calculations.
Cooling for cars is critical when driving slowly uphill behind a truck while pulling a trailer, this is totally different than cooling an aircraft engine at 740 km/h in -50 °C. Cars don’t use the Meredith effect, because in normal operation it has no measurable effect. Even race cars don’t focus either on that (because even Formula 1 cars drive relative slow, compared to past props) but their cooling system is built quite similar to Junkers Düsenkühler, which is the style of cooler producing the Meredith Effect (Race cars are not allowed to use variable cooling exhaust geometry, which would be required for the Meredith Effect).
Otto Celera has announced, that they are waiting for the next engine variant with multi stage turbocharging and only tried out the single stage variant, so there is nothing suspicious about it. The real problem is certainly the Russian background of the Redair company, now it will be completely impossible to build an American Aircraft with an engines from a Russian owned Company,
I prove all my arguments with calculations, you should do the same. It takes much more effort, to prove that your allegations (all without any basic facts backing them up) are wrong than just pretending new allegations. Do you have any evidence, that fowler flaps increase the wind drag significantly? Would be a good start to give some sources for that.
Edit:
according to the final report of this incident (https://aviation-safety.net/database/record.php?id=20010824-1 click on final report, go to page 96) the maximum cabin leakage rate (A332) according to the specification is 700 ft/min, so no sudden pressure drop occures within 10 s.
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Redair is giving some information about their high altitude variant of the RED03 engine on their homepage, there is no direct connection to the Otto Celera, but it is very likely designed with that in mind. They are using a two stage system (as predicted) and you can also see the frontal area of this arangement on their side (https://red-aircraft.com/a03-engine/). The width of the two stage variant is about the same as the width of standart turbocharged Continentals.
To get an impression of the size of the cooling system, a look on the water cooled heigh (16.000 m) flying BV 155 can give a good impression. This is a heavier and surly less aerodynamic plane than the Otto Celera (take a look on the outer plumping...) and so it needed three times more horsepower for flying slightly slower than the Celera. The cooling system of the Celera can be about a third of the size, which can easily fit inside the large engine bay of the Celera. Designing efficient intake/exhaust ducts and the interference with the prop will make it an intresting job, but nothing which seams unsolvable.
Here a link to another thread which is about an high altitude piston engine propulsion system:
Thanks for the very interesting discussion, gentlemen.
Could you give us a hint about the engine design you mentioned in this post?
Forest Green
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T. A. Gardner
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Something a bit newer you probably never heard of...
That is the Otto Aviation Celera 500L diesel powered 'executive' aircraft. They've been working on it for more than a decade with fuel efficiency in mind.
There seems to be a lot of patents flying around (pun intended) it and all sorts of other odd goings on...
www.thedrive.com
It seems the company is kind of secretive about this plane and it has the 'smell' of crazy people about it...
That is the Otto Aviation Celera 500L diesel powered 'executive' aircraft. They've been working on it for more than a decade with fuel efficiency in mind.
There seems to be a lot of patents flying around (pun intended) it and all sorts of other odd goings on...
The Mysterious And Potentially Revolutionary Celera 500L Aircraft May Fly Soon
New details about its engine, together with other design features, point to extremely efficient performance that could change commercial air travel.
www.thedrive.com
It seems the company is kind of secretive about this plane and it has the 'smell' of crazy people about it...
martinbayer
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In my bicontinental aerospace career, I've come across way too many breathless claims of revolutionary system performance published even in supposedly respectable industry media to hold my breath until Jane's (which I continue to consider the gold standard of accurate engineering reporting) has a quantified flight demonstrated entry on the design. As a youngster who was subject to so-called humanistic education back in the day in Good Old Western Germany, the sentence "Hic Rhodus, hic salta" comes readliy to mind. But the resident thread for this Otto Celera 500L (I just can't help wonder what happened to design numbers 1 through 499 and associated letters A though Z - an enquiring mind wants to know???) distorted winged egg can be found here: https://www.secretprojects.co.uk/threads/otto-aviation-group-llc-celera-500l.28904/. So far they seem to be long on claims and short on verifiable proofs. Ah, the exciting life of an aerospace upstart...Something a bit newer you probably never heard of...
That is the Otto Aviation Celera 500L diesel powered 'executive' aircraft. They've been working on it for more than a decade with fuel efficiency in mind.
There seems to be a lot of patents flying around (pun intended) it and all sorts of other odd goings on...
The Mysterious And Potentially Revolutionary Celera 500L Aircraft May Fly Soon
New details about its engine, together with other design features, point to extremely efficient performance that could change commercial air travel.
It seems the company is kind of secretive about this plane and it has the 'smell' of crazy people about it...
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