Transterrestrial Musings

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Vaporware. It has round thrust tubes, and you need square ones for supersonic flight.

Posted by Ed Minchau at November 24, 2007 11:52 AM

Right, Ed. Just like the F-16.

Posted by Jane Bernstein at November 24, 2007 01:12 PM

Pretty heavy management team for vaporware.

Probably too heavy for a startup.

The model they are showing doesn't look as if any of the necessary detailed engineering has been factored in.

Time will tell

Posted by Rich at November 24, 2007 01:40 PM

I suppose it depends what you mean by vaporware. Aerion's been around for a while (as has a competitor, QSST), but only recently began accepting letters of intent for their SSBJ. At the Dubai Air Show, they received their first LOI from some rich guy.

It looks like they've made a fair amount of progress, but still need development money or a risk-sharing partner before they start cutting metal.

Posted by Crispytoast at November 24, 2007 03:13 PM

It's a lot of money to build this jet.

I'd guess 5-7 billion dollars.

It's very clever to use the JT-8D-219, i didn't
think it had a high enough exhaust velocity to drive you supersonic, but, the wing and fuselage design look clever.

That double wasp-waist fuselage will be hard to build, i'm not looking forward to the
industrial effort on that.

It's a real big bird, as long as a 737
for 12 people, for that fineness ratio,
they may have trouble sizing the tails,
although the management does appear experienced
and given the experience in fighters, i don't
think the bird is wildly out of the box.

the big one is the cost, at 6 Billion
in, and say you sell, 2000,
that's 30M in Amortized Engineering per,

Figure the parts cost is close to a 737, so
that's about $30M in parts,

add in labor, that's easy 30 million more,

Add Overhead, SGA, profit, and you are
at $150 Million for a 10 passenger aircraft.

a Gulfstream 5 is a 10-20 Pax mach 0.8 bird
for $20M.

It's a real tough story to say you can sell
2 X in speed for 10X in dollars

Posted by anonymous at November 24, 2007 03:39 PM

*yawn*

Call me when they have bent tin to show.

Regards,
Ric

Posted by Ric Locke at November 24, 2007 04:49 PM

Wow, nice-looking.

Anonymous said:
"It's a real tough story to say you can sell
2 X in speed for 10X in dollars"

I'm not so sure about that, put it another way: would you choose half the speed for a tenth of the price? Only on short trips right? Except for those I think most would pay for speed if they could.

The low number of seats might be a selling point if anyone chooses to make a commercial service out of it. It's probably better to have multiple departures according to demand rather than a high number of empty seats on every flight.

How about a New York - London - Dubai - India - Australia - Japan - Alaska - New York service?

Posted by Habitat Hermit at November 25, 2007 01:56 AM

Yeah, Jane, even the F-16. Its inlet looks like a sideways D, and that flat side is there for a good reason. It's the same reason that the thrust tubes on the F/A-18, F-22, F-117, and Concorde have flat sides - to discourage spiral airflow through the thrust tube and encourage linear airflow. Above Mach-1, a spiral airflow through the thrust tube acts as a gyroscope. If they try to make a turn with these two round thrust tubes, they end up with the gyroscope on the inside of the turn moving slower than the one on the outside, thus yanking the plane in the opposite direction of the desired turn, making control impossible. With at least one flat side like the F-16, or with multiple flat sides like on the rest, the spiral airflow is forced to go linear.

So again I say, if they got this fundamental of supersonic flight wrong, then it is vaporware.

Posted by Ed Minchau at November 25, 2007 12:11 PM

I can't speak to the economics or inlet dynamics, but this might help the sonic boom issues:

http://www.nasa.gov/vision/earth/improvingflight/supersonic_jousting.html

http://www.aiaa.org/aerospace/images/articleimages/pdf/OCT2007_Wilson.pdf

http://www.aiaa.org/events/aners/Presentations/ANERS-Henne.pdf

Posted by Frank Glover at November 25, 2007 12:32 PM

The illustrated aircraft looks to me like a kitbash. Supersonic nose and fuselage, subsonic tail structure, and a stubby version of a high subsonic wing. Also, above wing engine inlets is a poor placement for transonic / supersonic. Under the wing would expose the inlets to slower more compressed air.

Posted by Peter at November 25, 2007 02:10 PM

Aerion's been around for a few years and have stated in the trade pubs they don't intend to cut metal. They intend to take the design as far as they can, and then partner with a manufacturer to build the airplane. I think their major focus has been the wing, though I realize that everything has to be integrated w/ the nacelles to close the design.

Economically, it's going to be a bizjet, not an airliner. The expected high price per item will make a lot more sense if it's sold in fractional shares. That's a big reason Cessna and Gulfstream have been selling so many airplanes for the last decade.

A lot of people have bought into Cessna's Citation X, which cruises pretty reliably at M.90-.92 over a four or five hour trip. People will pay for speed, even if it's perceived (The GV cruises at M.86 and sips Jet A compared to the Cit X).

Besides the political problem of noise footprints, ATC capacity will be the bigger driver. New York is a major bizjet destination, and as it is now everyone gets slowed down three to four hundred miles out when inbound to the terminal area. That just about kills the advantage of crusing in the magic 90% Mach range.

Posted by Pat C at November 25, 2007 03:00 PM

Ed, I'm a surgeon but I did major in Mech E as an undergrad. I had to take a supersonic fluids class, and I remember a fair bit of it.

I'm sure those readers who are daily engaged with problems of supersonic flow can amplify, but it's isn't the case that "a supersonic inlet has to have a flat side to avoid spiral flow." At supersonic speeds, there's a normal shock at the inlet, and the subsonic air beyond it is decelerated to a speed slow enough to prevent the blade tips of the engine from being supersonic.

Looking at the F-16, the inlet is curved upwards on both its top and bottom. The fuselage is likewise curved, not flat, on the bottom.

I can only think that you might have been confused about the boundary layer diverter, to prevent turbulent air from being ingested into the engine. To suggest that the angular momentum of the air flowing through the engine could overwhelm the angular momentum of the engine itself strikes me as implausible.

Would you prefer the SR-71 as a better counterexample to your assertion? I mean, I agree with you that the inlet in the pretty pictures of the supersonic business jet "doesn't look right".. and I'm not an aerodynamicist and can't say what the problem is. But the "It isn't square" criticism doesn't seem to explain the facts of existing aircraft.

Posted by Jane Bernstein at November 25, 2007 06:50 PM

The wing is a dead ringer for the notched ogive of the Miles M52 supersonic project from 1942-46.

That particular cellular design has each cell with different fundamental frequencies of vibration, making it particularly good in the transsonic regime. We know enough now to know that it's overdesigned and far stronger than it need be, but it's simple to make with cheap and low cost tools. Using modern composites, it could be quite thin and flexible yet carry a potload of fuel.

The wing design at least is exactly appropriate for a near-sonic cruise over land, and speeds of about Mach 1.4-1.6 over water.

The engine inlets don't match, unless they have a splitter plate inside, as per the BAe Lightning, Mig21, Tu-22 etc etc, all of which have annular intakes with at least one splitter plate to give laminar flow.

If I had a guess, I'd say they were looking at very low-tech solutions from the 40's, 50's and 60's married with modern materials. It needs to go fast in straight lines, that's all.

Posted by Zoe Brain at November 25, 2007 08:00 PM

if i were going to comment on the nacelles,
what seems odd is the outsides are curved.

the leading edges and cowlings have an apparent radius,
usually when you see a a supersonic inlet, it's got
sharp edges, to minimize drag

Posted by at November 25, 2007 09:43 PM

Jane & Ed - I'm not an aircraft engineer specifically, but I always assumed the engines would be spinning in opposite directions to cancel the momentum. That would solve any problems with gyroscopic torques in any case, as long as they weren't large enough to rip the individual wings off. I do not see how one could contradict Jane's comment that "To suggest that the angular momentum of the air flowing through the engine could overwhelm the angular momentum of the engine itself strikes me as implausible". The engines would have to be turning just as fast and, there's gotta' be a lot more mass there.

Posted by Bart at November 26, 2007 12:10 AM

Jane's a pretty smart woman, best not to argue with her.
As for other technical bliffs, i think the aerion team has
enough basic smarts they can solve them over time.
At leas tthey have an area rule fuselage which RipK doesn't
have in it's NEW XP.

The biggest one, is i think aerion underestimates how hard this
job is and how much money it is, and how hard it is to raise.

Elipse has burned through 3 Billion so far, and will burn
abother 3 billion to make a 6 passenger subsonic jet.

Aerion has to be looking at twice that, they could be
looking at 10X that, and that's a whole lot of money to raise.

Posted by at November 26, 2007 10:38 AM

If one doesn't argue with smart women then just who is one supposed to argue with? The not-so-smart ones? ^_^

I'd like both Ed and Jane (and everyone else) to continue for the benefit of those of us who know far less about supersonic inlets.

Posted by Habitat Hermit at November 26, 2007 06:02 PM

Off the top of my head-

Kuchemann talks about this in his Aerodyanics of Aircraft. There are two basic supersonic cruise designs, the delta and the trapezoidal. Both are tradeoffs. The SR-71 and the Concorde demonstrate the first, the F-104 the second (though it was not really a _cruise_ vehicle). Essentially you trade off skin friction versus high wing loading.

A big drawback to the trapezoid is the lack of wing volume for fuel, so this fuel needs to be stored in the fuselage, using up payload volume - and being centrally located not allowing for bending relief in the wing structural members at max weight, causing weight growth there (and this growth cacading throughh the rest of the structural design).

The pics show a leading edge extension, so they may be trying to use a vortex to increase lift. But there is the chance of vortex ingestion and engine unstart with the engines mounted where they are shown. Vortex generation and LEX design would be a very wind tunnel inten$$ive investigation.

The position of the horizontal tail is interesing - T-tails have their own deep stall issues, but this HT is located where high speed flow and acoustic radiation from the engines/exhaust might be a signifigant issue.

The smallish wings means a very complicated "self disassembly" with leading and trailing edge flaps. Even so high angles of attack on landing and takeoff might be expected, relative to a standard bizjet.

Another possible issue: I seem to recall that FAR's for engine fratricide concerns made the HSCT designers move away from the centralized B-1A engine mounting design (semi-wave-rider) to pods outboard on the wings, but it's been a while.

Kind of a kluge of stuff here, but it'd be fun to work on. I'd expect multiples of the standard bizjet development costs though.

It is nice to see NASA Dryden and NASA-836 get a nod. 836 was also the testbed for the aero-spike stuff from Grumman in the last year.

Posted by Ed at November 26, 2007 09:38 PM

At the risk of arguing with a smart woman...

Jane, the air moving through the SR-71 engines moved at Mach 0.5 even when the plane itself was doing Mach 3.2, due to the spike in front of the engines. The Aerion has no such spike. Apples and oranges.

Posted by Ed Minchau at November 27, 2007 02:45 PM

Ed, the air moving through ANY jet engine with a turbine in it is moving at around Mach 0.5 by the time it gets to the compressor, regardless of the speed. That's sort of what the inlet is for, you know? To recover the total pressure of the flight condition at a speed the engine can tolerate. It was on the test!

In the case of the SR-71, there's a very complex inlet that has supersonic flow for much of its length, until it positions the final normal shock right before the compressor. The complexity arises in driving the normal shock position back and forth with controls so it's always in the right spot.

The air moving through the F-16s engine (or the F-15s, same engine IIRC) is also at Mach 0.5 even when the plane itself is going triple that speed. The difference between them (one with a round inlet, one with a square one with movable bits) is that the F-15 goes faster and hence needs to adapt the shocks inside its inlet to the flight speed - not to as extreme a degree as the SR-71 but a fair bit. The F-16 is slower; all it needs is a simple inlet that doesn't let it go as fast but weighs less and can't break or anything.

None of this has anything to do with the "need a flat side to prevent spiral flow" comment you made earlier but that'd just be piling on.

So in the case of Aerion, I would guess that they have picked a fixed inlet, but not a normal shock inlet. Basically, since their airplane only needs to move at one speed, they chose a configuration of angles and such that looks like an F-15s inlet inside at one specific speed, but without the movable feature since there's no requirement for that. But that's just speculation.

Thanks for this conversation, Ed. You actually made me look up my old notes from UCLA. Fun!

Posted by Jane Bernstein at November 28, 2007 09:36 AM

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