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Otto Aviation Celera 500L


dnl42

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That looks a weird one – very Rubenesque, but an amazing project. Strange to think that the future of air travel may mean going back to props.

 

I think Frank Whittle has just turned in his grave.

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43 minutes ago, Gorby said:

Strange to think that the future of air travel may mean going back to props

There has literally never been a year in which turbojet and turbofan aircraft used for passenger transport have outnumbered piston and turboprop aircraft. Especially when you look at small types like this.

 

We'll see.

 

The PR for this aircraft is impressive but it's a lot less innovative than it is suggesting itself to be. In essence it's incredibly similar to the 1980 Learavia LearFan,  but the main diffference being a V-12 turbodiesel instead of turboprop power.  Historically this pusher design layout has frequently led to cooling and engine-life problems when coupled with piston engines, and diesels have hada very patchy record in getting accepted into general aviation despite their theoretical advantages, including of course the ability to burn cheap jet jet fuel rather than expensive AVGAS (and also the long term supply concerns for AVGAS). 

 

Here are a pair of Learfans. That was an really interesting design with a lot of talent and resource round it, but it didn;t make it commercially. 

 

Two_Learfans_at_Reno_1982_(6579626527).j

Edited by Work In Progress
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1 hour ago, Gorby said:

That looks a weird one – very Rubenesque, but an amazing project. Strange to think that the future of air travel may mean going back to props.

 

I think Frank Whittle has just turned in his grave.

I was trying to think where I’d seen that shape before and then it came to me. Just like one of those monster sized blue fin tuna.

 

Then my second thought. A blast from the past. Glamorous Glennis the Bell X-1.

 

https://airandspace.si.edu/collection-objects/bell-x-1-glamorous-glennis-photograph-0

 

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As a general-aviation six-passenger type it can only ever be 'the future of travel' to the extent that any other medium cabin twin already is, in fact less so on the basis that it's an SEP type (single-engine piston)  rather than an MEP (multi-engine piston), SET or MET (where T=turbine).  

 

Of course one cannot expect the lay general public by and large to give a lot of thought to the full implications of this in advance, but the intention here is clearly to use a Performance Group C type for missions where most of the similar GA fleet is currently Group B, and the inherent expectation of the paying public is that "airliners" are "safe", which really means Performance Group A,  or B at a push.  And not just the paying public, of course, but also everyone living underneath where they fly. 

 

Even taking my own risks I don't fly SEP outside gliding range of a lit airfield at night and I really don't recommend anyone else to. I also don't fly SEP over water without life-jacket actually being worn and dinghy in the aircraft, and I don't fly SEP over mountainous or large woodland areas I can't glide clear of without a parachute. 

 

Unless you're bush-flying in largely uninhabited territory, with passengers who are genuinely aware of the risks, any single-engine piston type is unacceptable for fare-paying passenger ops over water, at night, over conurbations, and in IMC.  SET is inherently a lot safer than SEP, due to the inherent reliability of modern turbine engines, and the millions of hours of flight ops providing the statistical basis for that. Which is why you can make a reasonable safety case for conducting many types of operation using a single turboprop (e.g. the PC-12 or the excellent Cessna Caravan I) that you cannot safely or legally do in, say, an AN-2 or an Otter still fitted with the original R-1340. 

 

The turbopro P&W PT6 has an in-flight shutdown rate of one per 651,000 operating hours, as of 2016. That is good enough for most purposes. The long-run average for certified piston aero engines is in the region of one per 10,000 hours. That is good enough for many purposes. but nowhere near good enough for a single one of them to carry fare-paying passengers over cities, at night, over water, etc etc.  Perhaps whoever's cooked up this new diesel V-12 can make it 65 times as reliable as the rest of the aerospace industry has been able to, but... really? And even if they could it would take a couple of decades of less safety-critical ops to prove.

 

Incidentally one of the main barriers to the Learfan becoming a commercial proposition was that the two engines had a single point of failure in the transmission, the two engines being geared onto a common prop shaft. The FAA quite reasonably determined that it did not qualify as having two independent powerplants each capable of enabling a flight to continue in the event of a failure. Although it had two actual engines it did not provide all the power-system redundancy that an MET should provide. 

 

Since that time attitudes towards SET have become more flexible due to the excellent service record that has been built up.  So if they ditch the piston engine and go with a turboprop there is no reason why it should not operate where a PC-12 or Caravan can.

Edited by Work In Progress
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