Ed, the wing / fuselage intersection typically involves some very complicated aerodynamics and the drag resulting from this intersection is creatively named 'intersection drag'. The main issue is that the aft portion of the wing section is tapering away and expanding the air and if the fuselage isn't anything but a flat wall, it's also going to be typically trying to expand the air as well as the fuselage begins to taper. When you have the wing and fuselage both tapering and expanding the air, you have a high chance of airflow separation which causes tremendous amounts of drag.

In a low wing configuration, you generally see large wing / fuselage fillets to try to minimize intersection drag and counter the affects of both wing and fuselage expanding the air. The shape of many wing / fuselage fillets end up creating more a 'flat wall' intersection against the wing root in order to minimize airflow separation in this region. Take a look at the Raytheon Premier 1 as an exaggerated example of how the aerodynamicist is trying to create a nice 'wall' against the wing root (see pic below). The engineer is creating a lot more surface area (wetted area) by creating such a large fillet but wetted area is 'cheap' compared to the drag created by separation in this region.

In a mid mounted wing (think Aerostar or the Celera), the fuselage shape at the wing root is nearly a flat wall aready and not typically tapered at the wing root. In short, it's the ideal placement of a wing to minimize intersection drag, which is why Ted Smith made the Aerostar a mid wing. Of course the downside of this config is that the wing is occupying a great deal of valuable space in the middle of the fuselage or cabin. The Celera is countering this by placing the wing far back on the fuselage, outside the cabin. Of course the downside of this is that now the airplane becomes short coupled, requiring a larger horizontal stabilizer or displaying unfavorable pitch characteristics or having a small CG envelope.

As in all things, everything is a trade off...

I might suggest that given the certification issues + fact that it’s a diesel (is the engine actually certified yet?), this might in fact be a play for an efficient and relatively fast drone to sell to DoD. Would make lots of sense as a drone - all the issues with aerodynamic stability would effectively be mitigated by its being remotely piloted. Good efficiency, think of the potential loiter time at high altitudes. No windows needed.

That’s what I would be considering if I had to monetize this thing.

Don,

Thank you for the explanation. It was understandable and helpful.

Ed

Indeed it is, in Europe and the United States. (Link to FAA TCDS)




500hp for takeoff and 460hp continuous. There are a couple of regulatory gotchas- the TCDS says up to 25,000 feet and for installation in Part 23 aircraft. I wouldn't say those are show stoppers but they are certainly obstacles to get past.


Back to my question about how much does the thing weigh, if all 460hp is available at 50,000 feet and 400KTAS, and I do some really basic performance calculations using the claimed 22:1 glide ratio, then it'll have to weigh no more than 8,000lbs to get that high. If it can maintain level flight at a lower airspeed (and if that L:D ratio is optimized for a lower airspeed) then about 10-12,000lbs is theoretically possible. I wouldn't expect the airplane to get all the way up there at max gross weight though, but at reduced fuel and by leaving some of the passenger seats empty.

Maybe they're overboosting the engine. Maybe they're also getting some jet thrust from the exhaust, augmenting the exhaust, or doing something clever to get more thrust.*

Everything is a tradeoff...

Like I said, as a technical achievement this one is going to be pretty interesting. I'm pretty excited to see how much they achieve.



* The famous radiator/intercooler nacelles on the P-38 didn't so much produce thrust to make the airplane go faster as they made approximately as much thrust as the barn door radiators created drag. In a sense they were sort of "invisible" to the airflow and the airplane had near-zero cooling drag... that's a really big deal and an impressive technical achievement. The belly scoop arrangement on the P-51 did something very similar.

Anybody read Peter Garrison’s write-up in December’s Flying magazine? According to him, 65,000 feet at 400 knots is pretty far fetched. Interesting read.

I read it last night, coincidentally. I was a little surprised to find that his math shows that they're so far off of their predictions.

This isn't a new phenomenon, of course, but the Celera team has the air of not being run by crackpots. I thought maybe this one would be different.

Would you mind posting a link to the article. Could'nt find it

Thanks!

Would you mind posting a link to the article. Couldn't find it.

A google search found the article on a different site. Whoever Magzter is, they don't seem to be doing Flying any favors.

https://www.magzter.com/article/Flying- ... elera-500L

The last line of Peter Garrison’s article is a good one.

If the Celera delivers Piper Meridian levels of performance (260 to 300 kts at FL300) on 47% less fuel and with a bigger cabin, that’s a good result that could find a market.

I am at least as exited about the certified RED diesel as any of the rest of the program. A 500hp Diesel (assuming reliable and within reason on cost) could spawn a whole collection of interesting pressurized singles that would have a big efficiency advantage over the single engine turboprops and legacy pressurized twins.

FAA TCDS for the engine- https://rgl.faa.gov/Regulatory_and_Guid ... _Rev_0.pdf

Engine alone is 800 lbs. Would still need prop, oil tank (dry sump oil systems), oil cooler and coolant radiator. So a complete power plant package is well over 1000 lbs.

Same engine (RED a03) is used on a Russian military drone Altius-M, which was late and over budget; the program was effectively cancelled and re-started in 2017, with the materials transferred to a new prime contractor. The top altitude for that thing was 50,000 ft. Not quite the U-2 with props that Russian generals wanted.

https://en.wikipedia.org/wiki/Junkers_Jumo_205

https://www.youtube.com/watch?v=8WDkj0ZYuiA

The Germans were able to get up reasonably close to altitude and decent engine performance in WWII with a Diesel. The speed was not there but it was not a very streamlined airframe. Engines were heavy but they made it work.

Why is there so much reliance on electronic controls in modern Aero Diesels?
No matter the performance at least the Celera is flying with its engine and the engine is type certified compared to the vaporware Zoche Aero Diesel which makes the press from time to time.

Though Thielert was certified also...

I've read through the Garrison article at a local Barnes & Noble cafe. I think he's making some good points, although I cannot check his calculations.

One thing he failed to notice, but which may support his focus on cooling drag, is the evolutuon of Celera 500. The spy photos from the time it was rolled out in 2017 show a very different intake and exhaust arrangement: it had surface intakes and a hot plate for exhaust. The left side had a variable geometry scoop. The 2020 version is entirely different: it features twin P-51 style housings, which presumably cover expansion plenum for radiators.

Other thing is something that he explained off-hand: that the laminar flow of a rotation body ends just after the maximum diameter. It interested me since 2017 just why Celera has its egg backwards. The subsonic minimum resistance body has its maximum diameter about a third off the tip. But Celera's maximum diameter is about where the wing is, way back. Garrison's remark explains why it is so: they want to maintain the laminar flow along 2/3 of the fuselage. I'm sure he realized it, but forgot to make it explicit in the article.

Interesting fairly long video on this plane..
https://www.youtube.com/watch?v=E38cc-4TvX8