The Future of Flight

Roland Piquepaille writes "With "High Times," the Economist delivers a very long and extremely well-documented article about the future of aviation during the next fifty years. It tells us about pilotless planes, with 32 countries currently developing more than 250 models of unmanned aerial vehicles (UAV), primarily for combat purposes. The article also looks at future civilian pilotless planes and at the future of personal aviation. But what captivated my attention in this article was the last part about future commercial supersonic and hypersonic (at least five times the speed of sound) planes. In particular, the Economist describes the HyperSoar. "The HyperSoar is a concept for a craft flying at ten times the speed of sound and able to reach any point on the globe within two hours." This overview contains more details and references about the HyperSoar which would fly from Los Angeles to New York in 35 minutes."

HyperSoar and Hyper-X

[John Hansen]

The only fly in HyperSoar's ointment is that its success is highly dependent upon Hyper-X [nasa.gov]. Note how similar the designs are.

Additionally, Hyper-X is designed to use the engine block as a heatsink. It will run for a few minutes (which is all it needs to do to get up to speed) and then the engine will melt and the aircraft will splash into the Pacific. I don't think that would be a good thing for a passenger aircraft.

Re:It's nearly 2004....

[turgid]

Nyeah, here [moller.com], of course!

Re:Flight sick?

[Jesrad]

Actually, it would mean:
- strong acceleration during take-off and climb
- low gravity during most of the flight, oscillating between 0.2 to 0.8 g, or maybe an alternation of weightlessness and 1g gravity. I'm sure most tourists would appreciate a free fall experience as a bonus ;)
- strong deceleration during the whole approach

Re:Mach 5?

[Chairboy]

Remarkably bad math. Escape velocity is closer to Mach 25.

Oh, and flying upside down doesn't have a magical affect on whether or not you escape or not.

Re:flying cars

[atherton2]

Eclipse Aviation of Albuquerque, New Mexico have produced a Air taxi capable of carring 5 people upto 1500 Km, but for this to be widely adopted 'free flight' must first exist. This allows piolts to plot there own jouneys, cutting distances and utlising more airspace. 'free flight' relies on each aircraft having it's own computer that allows aircraft to avoid each other. For more information see this weeks (13/12/03) New Scientist p28-33.

Re:2hrs...impressive!!

[hedgehogbrains]

The impression of weightlessness has got nothing to do with altitude. Gravitional force remains strong in low Earth orbit. The reason orbiting astronauts feel feel weightless is because they are effectively 'falling' in the same trajectory as their craft. There are no attractive forces between the craft and the passenger. The same would apply for a craft at 200,000 ft if air friction were negligble.

Saving time also means saving fuel

[Jesrad]

Before someone posts about how rockets are fuel-inefficient compared to other engines, I'd like to point out that it mostly depends on the cruise speed of the aircraft.

If the plane completes the flight in ten times less time than a conventional subsonic plane, then its engines are burning fuel for ten times less time as well.

Modern high-bypass turbofan engines have a specific fuel consumption (SFC) rate around 0.5 lb of fuel per lb of thrust per hour. Current liquid fuel rockets' SFC is around 10, and solid / hybrid rockets' SFC is around 5. But the concept of "pound of thrust" evolves with speed: for example, a reciprocating engine with a propeller will give you much more (approximately four times as much) pounds of thrust than the number of HP the engine develops, _at low speeds_. At 375 mph, you get one pound of thrust per HP. And beyond, you get much less. That's why high subsonic planes use turbofans and the slower planes still use propellers.

At supersonic speeds the fuel consumption per distance covered of a turbofan engine can grow as high as 3+, but that of a rocket engine does not grow with speed, so there's a given speed beyond which rockets are more efficient than turbofans.

Science Friday - NPR

[TimeOut42]

This article sounds just like a show that was on NPR the other day http://www.sciencefriday.com/pages/2003/Dec/hour2_ 121203.html

They had 'experts' talking about why supersonic commercial flight isn't hot, explains where our personal aircraft are at, sub orbital flights, etc.

It was an interesting listen!

Sean

Re:According to my own virtual tests

[Al-Hala]

Airplanes are stable or unstable due to their roles.

Fighters are inherently unstable, to allow the radical combat sequences dictated by dogfighting. It's true some of the current fighters are unflyable without constant computer assisted tuning.

Large passenger jets ARE inherently stable. The use of computers to control the flight surfaces are dictated by demands for maximum fuel economy, which means constant re-adjustment of CG's, trim, and other parameters.

Nothing in their design prevents them from being flown on purely hydraulic controls in an emergency.

RTFA

[InfiniteWisdom]

RTFA:The g forces would vary between 1.5g and weightlessness

Re:Environmental Issues?

[Senor_Pedo]

Actually, the energy cost for travel by flight is really no higher than for other transport methods. Consider a quick calculation:

A 747-400 has a range of about 8400 miles, and a fuel capacity of about 57,000 gallons. Multiply that by 410 seats, you get around 60 mpg per passenger. And Boeing's new 7E7 "Dreaminer" is touting much higher efficiency than any of their previous jets. Airbus is doing well too, with the new A380 and Rolls Royce Trent 900 engines. Fuel capacity of 82,000 gallons, range of 8000 miles, 555 seats. Thats around 55 mpg per passenger.

So those numbers are way better than the CAFE (Corporate Average Fuel Economy) standards in the US, currently 20.6 mpg I believe, not including the SUV's buzzing around the suburbs that aren't subject to those rules.

Hydrogen fuel cells would be great, but they're nowhere near production status for commercial transport flight.

hypersoar

[cybercuzco]

Im currently doing my masters project on the feasibility of the hypersoar concept. In a nutshell, its possible, but with some caveats. One of the main reasons you want to do a periodic trajectory is to reduce drag and heating of the aircraft. If you stay at a constant altitude, all that heat builds up and eventually melts your plane. If you skip out of the atmosphere the heat should radiate to space, reducing your total heat load. The problem comes when you come back in. You go deeper into the atmosphere at a higher temperature than you would at a constant altitute. Ultimately your total heat load is lower, but your maximum temperature is higher by about 20% (in degrees K) which is enough to require some more exotic materials. The other thing is that you require alot of lift for pulling out of the dive at the bottom of your trajectory. So you need a high L/D ratio, which for a hypersonic vehicle is about 4. So you need wings and structure to hold the wings etc. Thirdly, you need an engine with enough thrust to overcome the drag at the bottom of the dive. If your engine isnt pushing harder than the air is pushing back, you just slow down and fall to earth. If its not pushing hard enough to bring you back to your initial velocity, you cant go very far. For my preliminary vehicle design I found that a vechile of ~500 tons with a L/D of 4 needs a thrust of about 2g's or about a million newtons If your vehicle is too light, it cant push far enough into the atmosphere to generate thrust (im using an airbreathing engine) and you crash. If its too heavy you go in to far and burn up. There is a specific range of weights and engine on-off conditions that are required for a successful trajectory. I think Ive got it worked out, but I need to do some more analysis over winter break

35 minutes plus 150 minutes of overhead...

[Anonymous Coward]

Sure, the plane can get from LA to NY in 35 minutes, but you can't. First, you have to the airport 2+ hours before boarding beings just to be searched for finger nail clippers and eyeglass screwdrivers. Then there is the 10 to 15 minutes of boarding and disembarking. So it still is 3 hours to get from LA to NY, not much better than in 1999.

So, given today's commercial aviation environment and the way the Bush administration has made the US hated by even its friends, why would anyone even care at this point in time?

Too bad we let the terrorists terrorize us into this sad state of affairs.

Re:According to my own virtual tests

[Zixia]

Fighters are inherently unstable, to allow the radical combat sequences dictated by dogfighting.

While it is true that modern fighters are inherently unstable, it is untrue that this is to add manoeuvrability. I have copied below an article, from someone who knows this better than me, in an attempt to stop this myth from continuing forever:

With reference to the recent column under the heading "Flying Off Balance", I'm afraid this caused much gnashing of teeth and bashing of the head against the proverbial brick wall! The concept that instability leads to high agility is a fallacy that dates back over 40 years to the days when autostabilisers were being developed to address the handling deficiencies of various early American jets and persists to this day.

OK, let's start with the basics:

1. Many modern supersonic jets have a negative Static Margin (ie they have the C of G behind the Neutral Point) which makes them aerodynamically unstable, and they are made controllable by use of a full-authority autostabilisation system. This is true.

2. These modern supersonic jets are designed with inherent instability to give enhanced agility. This is NOT true. Not only is it not the reason why the aircraft are designed in this way, it is also not true that an unstable aeroplane is more agile.

I know this is contrary to the received wisdom, but let's just examine what's going on. Most of the following is grossly oversimplified to avoid the use of mathematics, and is also rather over-generalised, but it is valid and accurate for the purposes of this discussion. Professional aerodynamicists are requested to stop reading this now and flip forward a few pages where there are some excellent kit reviews to read.

"Agility" of an aircraft in the pitching plane is determined by how quickly it can apply the lift forces to pull the 'G'. This in turn is dependant on how quickly the angle of attack can be increased - the pitch-plane angular acceleration, or more to the point the INSTANTANEOUS pitch-plane angular acceleration. Now a clever chap called Newton once showed that in any constant mass situation the acceleration of an object was dependant solely on the mass of the object and the sizes of the forces applied to it. The same is just as true for angular accelerations, except that we substitute "moments of inertia" for mass and use the "moments" of the forces as any attentive GCSE science pupil will be able to tell you. You will note that nothing has made reference to the "angular stability" of the object, because it's irrelevant and so we have just demonstrated that instability does NOT increase agility (QED).

Fine, so why DO we bother with all this negative-stability-and-fly-by-wire cockamamie? After all, it would be so much simpler, cheaper and more reliable to simply connect a conventional aircraft hydraulic system (or even a pushrod) between the stick and the control surfaces! The answer is simple - it reduces the supersonic fuel consumption.

[What? Where did that come from? What's this guy been smoking!? I mean one minute I was dozing through a bit about stability and the next thing I know you're blathering on about fuel consumption. How can these be related?? - Ed].

To understand this we need to briefly look at another bit of aerodynamics, the concept of "Trim Drag". We all know that with a stable aeroplane you place the CG in front of the "centre of pressure" (I'd prefer to use "Neutral Point" but let's keep it simple) which makes the aeroplane pitch downwards. We oppose this by having a tailplane to push the tail down or a foreplane to lift the nose up and voila! We have a stable aeroplane. The actual amount of effort the tailplane/foreplane has to exert to do this depends on how far the CG is from the centre of pressure, and we call this the "Static Margin". Those who have paid a bit of attention, rather than chatting up the totty at the back, will also know that the act of generating lift inherently generates drag.