Future of Air-travel

[Roadam]

I came across a few interesting things:
Blended Wing Body - New Concept in Passenger Aircraft Check Klingon version
Next thing are propfan engines. As any type of aircraft you build you need an engine that would provide thrust most effectively at certain speeds. Propfan is supposed to be able to increase efficiency by 10-30%.
Green sky thinking - carbon credits and the propfan comeback?-12/06/2007-Los Angeles-Flight International
Airworthy Electric plane!
Green sky thinking - carbon credits and the propfan comeback?-12/06/2007-Los Angeles-Flight International
As I am writing this very late at night I wont comment much. But I think that Any heavier than air aircraft that would be useful cannot rely solely on solar cells.

[CraigD]

Originally Posted by Roadam

I think the future of air travel is in flying wings. No matter what kind of engine you use to propel yourself, its the aerodynamics that limits you to certain speeds and power requirements. Making a plane with less drag compared to what it carries it the way to go.

There’s an aerodynamic conundrum around flying wing vs. “tube and wing” and mixed “blended wing-body” designs. The total surface area (wetted area) is reduced in and minimized in blended wing-bodies and flying wings, reducing parasitic drag (drag not related to producing lift) but in most cases, the wingspan (and resulting aspect ratio) must be reduced, increasing induced drag (drag related to producing lift). The result of this tradeoff is often that blended wing-bodies and FWs often have about the same efficiency as equivalent conventional TAWs.

Another issue with FWs – one of which model airplane hobbyists like myself, and early full-scale designers like the legendary Jack Northropare/were acutely aware – is stability, in particular pitch (nose up/down) stability.

With a TAW aircraft, either of the conventional horizontal stabilizer wing in the rear or in the front (canard) configuration, static (no control input required) pitch stability is due to differences in the lift of front and rear wing at different pitches. With a single FW, however, this difference must occur in different sections of the wing, and, unless the wind is extraordinarily long, such as with a delta wing, the effective arm of the correcting force much shorter than the TAW. It’s hard to build an efficient flying wing that’s statically stable, so most of even the oldest flying wings have used some sort of active system, either mechanical or computerized.

Practically, however, the stability issues is, I think, a non-issue, as most large modern aircraft are currently critically dependent on computer control systems. The old-fashioned design goal of making a plane that can be flown in the event of a complete power outage is, except for the small niche of lower-quality control “sport/experimental” planes, and “brush planes” and others designed for lower-tech support environments, of little relevance.

Originally Posted by Roadam

And another thing. Flying wings have more or less flat top. So it would be easier to fir PVs onto it.

A very good point, IMHO.

Originally Posted by Roadam

But I think that Any heavier than air aircraft that would be useful cannot rely solely on solar cells.

I agree. This is almost a certainty, as for a typical solar power output, the solar power flux at Earth is at theoretical max about 680 W/m^2. A large aircraft like a 747 has a total top cross section area of about 1000 m^2, so a 100% efficient direct solar system on a clear summer day would have about 700000 W, but needs about 200 times that much to have the same performance.

Pure solar airplane are possible, but capable only of low speeds - though very high altitudes. MacCready’s Gossamer Penguin, Solar Challenger (4500 W prop shaft output with the highest speed, about 50 km/h) and the unmanned Helios (21000 W, highest sustained altitude of any winged aircraft of 29523.8 m) are examples.

In cloudy weather and at night, pure solar planes get hardly any power, so can’t sustain altitude.

Practically, then, electric planes must have energy storage, such as batteries of fuel cells. The electric-powered Sonex Waiex sport plane is an example.

I’ve been doing a bit of figuring since I stated

Originally Posted by CraigD

There don’t appear to me to be any major show-stopper barriers to, in the next few years, building a “plug-in solar” electric airliner in the 30-seat, 500 km/h, 1500 km range “regional” class (eg: the BAe Jetstream 41)

The numbers are daunting.

Converting the Jetstream 41 to run on conventional LiPo batteries would give it about 9 minutes flight time, vs. its usual 2.5 hours – about enough take off, run a single pattern, and land. Assuming the best batteries available by about 2012, the flight time increases to about 27 minutes. Hydrogen fuel cells give about the same result.

Clearly, a 30-seat battery electric airliner would need to be designed from scratch, minimizing airframe mass and maximizing battery mass. By rough scaling estimate, the total mass would need to be about 15 times that of an equivalent kerosene turboprop, or about half the mass of a 400 passenger 747.

These number cause me to seriously rethink the feasibility of battery or fuel cell electric airliners, and lead me to wonder what options remain. Nuclear?

[Flying Binghi]

These number cause me to seriously rethink the feasibility of battery or fuel cell electric airliners, and lead me to wonder what options remain. Nuclear?

One option perhaps, is to look at some past designs.

I would suggest Bio-diesel could be a replacement for Jet-A

Some extracts from Dieselair -

The forgotten secret of the superb German diesel flying boats.

-Germany built many flying boats (1930s) for various uses, most of them using the Junkers Jumo 205 diesel 2-stroke opposite pistons, with powers from 600 to 880 HP.

-The most economical plane would be the glider if it could glide for ever, which is why the most economical planes, and therefore the ones with the longest range, are the ones with a high aspect ratio (ratio of wing length to width) giving them a lower induced drag and a most efficient gliding ratio.

Therefore, to obtain a long range, basically you need a high aspect ratio, and an optimal cruise speed of some 1.3 to 1.5 times stalling speed clean. And here comes the problem with gasoline engines: at 1/3rd to 1/4th their nominal power, the specific fuel consumption (fuel consumed per HP-hour) becomes lousy because combustion is no more in optimal conditions.

At same fractional power, the diesel is as efficient as at full power. So maintaining cruise speed may require down to 50% of the fuel flow needed with gasoline engines operating at same fractional power, meaning so much more range.

A cargo diesel motor glider with a very high aspect ratio cruising around 100 kts could very well again be the most effective way to ship goods by air.

W W W . D I E S E L A I R . C O M -- The Diesel Air Newsletter -- Home

[Roadam]

Lets dream high electrical permittivity! EEStor - Wikipedia, the free encyclopedia

Btw, that sonex Wainex plane could have about 100kg worth of batteries with 52kw motor. So with current LiPoly tech it could store 12kWh. From estimates that it has 42mpg mileage !! and from that to about 17kwh/100km you could probably fly this thing for about 60-70 km. With Eesto estimates that could be extended from 150 to 400 km. That is a all great, so lets dream electric. :P

Maybe for Australian bushes where you can be stranded in the wild without electricity, that kind of a plane fitted with solar cells would be great even if you could only do jumps of around 100km.

[CraigD]

Originally Posted by Flying Binghi

Some extracts from Dieselair –
…
At same fractional power, the diesel is as efficient as at full power. So maintaining cruise speed may require down to 50% of the fuel flow needed with gasoline engines operating at same fractional power, meaning so much more range.
…
W W W . D I E S E L A I R . C O M -- The Diesel Air Newsletter -- Home

Very interesting references to what appears to be a recent resurgence in popularity of diesel aircraft! The 4-seat Diamond DA42 Twin Star in particular in a pretty amazing (with the addition of only a 26 gallon (118 L) added fuel tank, and throttled back to 42% power, in 2004 one made the first nonstop Atlantic crossing by a diesel airplane!), as is the Centurion 2.0 L engine system, which can be retrofitted into such popular light singles as the Cessna 172. I hope Thielert’s current financial woes present only a brief obstacle to the use of this remarkable engine system.

That said, I’m uncertain that, outside of a niche like light aircraft, diesel pistonprop are anywhere near as good as turboprop in any area other than purchase and maintenance cost, factors that are significant in the light aircraft market, but not very in the air carrier market.

Originally Posted by Flying Binghi

I would suggest Bio-diesel could be a replacement for Jet-A

An excellent suggestion, and one highly likely, I think, to be realized when a large, long-term increase in the cost of petrodiesel is clearly imminent or upon us.

The major challenge with replacing petrodiesel with biodiesel in aviation and other cold environment applications is its higher solidification (congealing) temperature. Unless a reliable technique of blending or cracking current biodiesel to overcome this issue is developed, a 90%+ biodiesel jet, turboprop, or diesel pistonprop all-season and commercial carrier altitude aircraft will need to have a fairly elaborate fuel heating and pre-shutdown flushing system. As these issues have been successfully addressed in other biodiesel, I don’t think this challenge presents a difficult barrier to biodiesel aviation.

[goku]

what about ram jet engines?
resistance is energy
the ram engine has no moving propellars to compress the air for combustion, insted it uses resistance to compress the air.

Ramjet - Wikipedia, the free encyclopedia

i imagine every forward facing surface of resistance being used for the ram engine

[Moontanman]

Originally Posted by goku

what about ram jet engines?
resistance is energy
the ram engine has no moving propellars to compress the air for combustion, insted it uses resistance to compress the air.

Ramjet - Wikipedia, the free encyclopedia

i imagine every forward facing surface of resistance being used for the ram engine

The main problem with Ram Jets is they have to be moving to work, you cannot take off with a ram jet only. Ram Jets are also difficult to throttle and can flame out easily, they also use more fuel than a good turbofan jet.

[CraigD]

Originally Posted by goku

what about ram jet engines?
resistance is energy

Originally Posted by Moontanman

The main problem with Ram Jets is they have to be moving to work, you cannot take off with a ram jet only. Ram Jets are also difficult to throttle and can flame out easily, they also use more fuel than a good turbofan jet.

Another problem with ramjets (or scramjets) is not only must they be moving to work, they must be moving fast. Although it’s possible to run one at airspeeds as low as 100 MPH or so, they are very inefficient below about mach 0.5, and only approach or even exceed turbojet efficiency around mach 3.

Resistance does requires energy, and resistance varies about with the square of airspeed, so usually, higher speed aircraft takes more energy to carry the same load the same distance. So, as a general rule, improving energy the energy efficiency of an aircraft (or any vehicle where most of its drag is parasitic drag) requires lowering its speed. So, rather than motors that work better at higher speeds, motors that work better at lower speeds, such as turboprops, are needed.