What NASA’s up to:
“There are three barriers particular to civil supersonic flight; sonic boom, high altitude emissions and airport noise. Of the three, boom is the most significant problem,” said Peter Coen, manager of NASA’s High Speed Project with the agency’s Aeronautics Research Mission Directorate’s Fundamental Aeronautics Program.
There’s a fourth barrier not mentioned: the low L/D, which restricts range and makes for high fuel costs. If that problem doesn’t get solved, it will never become a huge market, and will mostly be restricted to business jets.
I thought most of the fuel consumption on the Concorde came from needing to use the afterburners to go supersonic? Modern military low-bypass turbofans have enough power to weight ratio to go supersonic on dry thrust alone.
Assuming it’s true (I thought they were for takeoff), why would it need to do that? Because it had a cruise L/D of about seven, whereas subsonic airliners are more like eighteen or so.
Concorde needed after-burner for take-off and to get through the sound barrier, once it was supersonic it only needed dry thrust.
Yes, that’s what I thought. Afterburners just for takeoff and transition. But even dry they burned a lot of kerosene to push all the wave drag out of the way, and generate dB on the ground.
To be accurate, it’s the product of speed and L/D ratio that is proportional to range. In theory, if the speed goes from Mach 0.8 to Mach 2.0, the L/D can drop from 17.5 to 7.0, as the product of the two is the same. This assumes a very good inlet, of course, and constant SFC – an oversimplification – but faster can be traded for higher L/D to some extent.
Yes, to some extent (obviously you’ll burn less fuel if you’re not in the air as long), but it’s also a very inefficient aircraft in terms of passenger/weight ratio, due to the narrow fuselage and huge delta wings. If they didn’t have to worry about the supersonic drag (and extra skin drag) they’d do a lot better as well.
The way we normally sit in an airliner is horribly inefficient for high-speed flight. The easiest solution is to have passengers lay down, lined up head to toe along the length of the fuselage, to get a dense packing with a high fineness ratio, perhaps in a stack that’s two or three people wide and two or three tall. Obviously fat people will have to board first, and then thin people can be wedged in around them. Perhaps the passengers could also strap something like snowboards to their feet to create a tray table for the person in back of them. I figure the seating method could be advertised as “fly like Superman does!”
Anyway, getting full suction on the leading edge would help a little bit, and perhaps part of the horizontal component of wave drag could be canceled out with end plates, similar to the idea of a cylinder that cancels the shock wave internally. If the speed can get high enough there’s always the possibility of a skip glider, if the passenger puke doesn’t become too much of a problem.
This Sanger Silverbird/DynaSoar type skip glider keeps coming back to the pages of AvWeek. Besides the passenger puke problem, I thought this has “issues” with the thermal protection, and this is why people gave up on it?
George, that sounds a bit like the seating redesign project I had in economics in college. Instead of going the usual route; small changes and marketing spin, I went for a radical new plan. My professor hated it.
The plan was to replace seats with horizontal padded squared tubes; the aisle at one end, maybe a window at the other (at the time, flat screen monitors didn’t exist, but they’d have worked for this). Passengers could sleep (I find sleeping impossible in airline seats) and be comfortable. It’s also safer in an impact than a regular seat. Accessing the upper ones would be done via drop down steps. This concept actually allows higher seating density than even the cattle-class seats of today. So, more comfort, safer, plus higher density (thus lower ticket prices). I thought those would be good selling points.
I got a D, because the prof rated the concept as utterly unworkable. The reason he gave, though, makes me roll my eyes; he said that even on short-haul flights, the passengers get meals, and they’d be facing the wrong way to receive them. HE also pointed out that on an average flight, the real limiter in density is luggage; the average passenger takes two cases. Since that time, of course, the airlines have massively cut back on such things.
That was a stupid reason to derate the concept. The real reason is the number of claustraphobes in the market (of which I’m one).
@ Rand,
I agree on the claustrophobia issue, I’m one myself. But… have you ever been condemned to a middle seat in cattle class on a 12 hour or longer flight, with the seat each side occupied by large passengers? I have, including one memorable 15 hour nonstop to Hong Kong. I find that claustrophobic too, and though the tube idea gives me the creeps, it’s less than that. I think I could have coped had I entered feet first. I don’t mind seats for short flights (such as transcontinental) but I really do crave to lie down when it’s much over 10 hours. Sometimes I’m lucky and spot an empty row in the back so I can flip the armrests up and lie down, but not often.
We have Xanax for that. ^_^
I guess the basic packing options are luge, skeleton, and bobsled. If all people had ever seen was bobsled, they might dismiss the idea that anyone could go down the track lying down.
It can be hard to predict what the public will and won’t accept, or how they’ll end up using a particular thing. I don’t anyone here would’ve guessed that young people would switch to text (telegraph) instead of voice or video for personal conversation. All those decades that AT&T was working on video phones, and it turns out people would’ve preferred to use a teletype, and I’ll bet not a single engineer or marketing guru would’ve believed it.
Maybe speed time L/D = range for some flight trajectories.
But going back to Newtonian physics, Work = Force times Distance.
Force is your gross weight divided by L/D.
Distance is range.
Work is energy, that is, your fuel.
Are you thinking of speed times specific impulse or speed time specific fuel consumption being a constant? A Mach .8 engine burning .6 lbs fuel/lb-thrust-hr being equivalent to a Mach 2.4 engine burning 1.8 lbs fuel/lb-thrust-hr? Those two engines are equally fuel efficient. But if drag goes up with speed, the supersonic jet will have to trade payload for range.
Another way to further attenuate shockwave impact on the ground is to fly higher.
As with most things, I think engine tech will be the key as to whether or not this is commercially viable.
Fuel usage; In spite of the afterburner need for T/O and transition, Concorde wasn’t actually all that bad compared to its subsonic contemporaries at the time it was designed. It carried about 26000 gallons of fuel, compared to a 707, which carried about 23,000 gallons in its last version. That works out to Concorde having only about half the passenger-miles-per-gallon of a 707, not bad at all.
The biggest problem with Concorde’s engines is they were massively inefficient at low speed. Even taxiing took massive amounts. A Concorde with modern engines (similar to those in the F-22 for supercruise) might actually be far more commercially viable. Fuel usage ranges of double to triple per passenger mile should be no real barrier; the cost of a first class seat compared to economy is far greater.
I hope they make the needed breakthroughs; supersonic air travel is something I think about a lot, especially while on flights over 12 hours.
So what is the L/D for suborbital? Even on the supersonic London/Sydney run, that’s six hours in a tube. That means bathrooms, beverages, diversions, etc.
An hour flight time changes that completely. Bathrooms “might” not be as needed. Neither is meal service.
So what is the L/D for suborbital?
That’s not a meaningful question.
I’ve seen some interesting designs to improve supersonic L/D. “Supersonic biplane” that trapped Mach waves between a pair of wings, ideally avoiding most form drag from the thick wings. An overhead mounted wing that caught Mach waves from the nose for extra lift. Unfortunately these designs tend to be fairly sensitive to Mach number.
That’s the Bosemann bi-plane. Unfortunately, while the wings don’t have much wave drag, they don’t have any lift, either. There’s actually a related approach to this that I partially control the IP for, and I hope we’ll get some funding this year to pursue it.