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Designers rethink jet aircraft in the quest for shorter take-offs

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November 8, 2010

This computer-generated graphic shows a model of the cruise-efficient, short take-off and ...

This computer-generated graphic shows a model of the cruise-efficient, short take-off and landing (CESTOL) aircraft design that GTRI researchers are investigating (Image: California Polytechnic State University)

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What's wrong with this picture? If you said the engines are upside down, you'd be wrong. The odd engine placement is part of a cruise-efficient, short take-off and landing (CESTOL) aircraft concept from the Georgia Tech Research Institute which also sees mechanical wing-flaps replaced by high-speed blasts of air to generate extra lift. It's hoped that the development of such craft will make more airports available to fixed-wing jet aircraft by enabling take off and landing at steep angles on short runways, as well as reducing engine noise.

The research at the Georgia Tech Research Institute (GTRI) as part of NASA's Hybrid Wing-Body Low-Noise ESTOL Program focuses on developing a CESTOL aircraft similar in size to a Boeing 737 which can carry 100 passengers and travel at 600mph.

"To take off or land on a short runway, an aircraft needs to be able to fly very slowly near the runway," said GTRI principal research engineer Robert J. Englar. "The problem is that flying slowly decreases the lift available for taking off and landing. What's needed is a powered-lift approach that combines low air speed with the increased lift capability required for successful CESTOL operation."

Flipped design

The GTRI team placed turbo-fan engines above the wing of the conceptual CESTOL aircraft, rather than below it. Over-the-wing placement enables very high lift while still providing the necessary engine thrust for take-off and high-speed level flight. As an added bonus it also reduces engine noise.

The powered-lift design relies on a circulation control wing or "blown-wing" which sends high-speed blasts of air over the upper surface of the wings during take-off and landing to generate extra lift.

In most fixed-wing aircraft, Englar explains, mechanical flaps are used at take off and landing to increase the size of the curved wing and augment lift. But the lift generated by conventional wings isn't sufficient for the low flight speeds and steep ascents and descents required by CESTOL aircraft.

The blown wing in the GTRI design uses only one small flap. The key is a narrow slot running along the entire trailing edge of each wing through which compressed air is blown.

The wing flap rotates downward on take-off and landing to form a highly curved aft surface; then air from the slot can be blown over that curved surface to generate high lift – two to four times higher than a conventional mechanical flap.

The GTRI design also uses the interaction between the air coming from the wing slot and the exhaust of the plane's over-the-wing jet engines to achieve even greater lift.

"This strategy allows an aircraft to be flying at a very low speed, while the wing is seeing much higher relative wind speeds on its curved upper surface," Englar said. "We have measured lift coefficients between 8.0 and 10.0 on these pneumatic powered-lift wings at a level flight condition during testing. The normal lift coefficient on a conventional wing at a similar flight condition is less than 1.0." "Our design has to incorporate several trade-offs, yet the entire wing-engine powered-lift system has to perform all of its functions well," said Englar, who leads the aerodynamics portion of GTRI's work.

NASA's Hybrid Wing-Body Low-Noise ESTOL Program is a four-year program led by California Polytechnic State University which includes GTRI.

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8 Comments

Big deal, just waist of money. Ukraine has same configuration aircraft in service for 20 years. Google for AN-72 or Antonov-72, better to watch YouTube.

chimpilot
8th November, 2010 @ 11:54 pm PST

Even bigger deal, the Blackburn - later Hawker Siddeley - Buccaneer had boundary layer control blowing through high pressure slots in the wing - in the 1950's!

Overwing engines have featured in many designs through the years, including the VFW614 feeder liner, although its configuration was chosen more to reduce FOD and lower noise than for high-lift through upper surface blowing. However the unsuccessful competitor to the McDonnell Douglas C17 in the AMST competition - Boeings YC-14 did feature the USB and first flew in 1976.

Nothing new here...

snave
9th November, 2010 @ 04:29 am PST

Nice try. Few years late:

http://hondajet.honda.com/default.aspx?bhcp=1

Mark Petereit
9th November, 2010 @ 05:25 am PST

Blown flaps are a 50 year old technology, it's about time it found its way on to an airliner. http://en.wikipedia.org/wiki/Blown_flap

This just copies the YC-14 engine configuration, and as aforementioned the russians have down it before too.

I note no mention of variable camber / variable geometry wings - that's another area lacking in modern aircraft design.

I'd love to see something on a civilian airliner catapult application like the Navy carrier ships - they've been making short take offs look easy for years.

PeetEngineer
9th November, 2010 @ 06:22 am PST

As Mark writes, blown flaps are a very old technology, but one that is complex, and will certainly not work if one engine fails - how do you plan to land then? Engines above the wing is used by Honda, and was used by a German VFW614 commuter aircraft of the 70's, that never got into large-scale production. Interstingly it also used reversed sweep, which theoretically might decrease cruise drag.

Blowing systems, like that of the Buccaneer, are very noisy, thus not ideal for a quiet plane - as these are supposed to be.

So these STOL aircraft will ascend rapidly to minimize ground noise, thus relying on very steep ascends, on widely spaced engines - how the hell will it fly on one engine?! Or, in the bright future of tomorrow, no engines ever fail?!

So I think this design is a dead-end!

Tord
17th December, 2010 @ 11:16 am PST

Old Roberto di Bartini idea. This was applyed on Bartini Beriev VVA-14 Vertikal`no-Vzletayuschaya Amphibia (vertical take-off amphibious aircraft) This genius calculated that more optiml engine places is over wings. This can able to make over 10-30% of fuel or have very good landing characteristics.



Владислав Лебедев
27th January, 2012 @ 07:22 am PST

Bartini effect used.

Владислав Лебедев
27th January, 2012 @ 08:00 am PST

These engines don't appear to be any more widely spaced than in any other win Passenger jet.... (I don't think any twin (turbofan) is controllable on the ground to the extent that you are advised to take off with only one engine.... while all twins in use are rated to fly on one engine.... ) Imagine trying to fly a B747 with 2 engines on one wing, out... talk about off axis thrust....

The An72, doesn't have a pressurised plenum for directly blowing the flaps....

Merely engine blast washing over the upper surface of the flaps..

Amazingly, there are conventional planes which use blown flaps, the C17 has blown flaps, the difference is that it is blown from under the wing, however the double slotted flaps effectively apply the coanda effect to direct air over their upper surface (as the flaps are almost full width the lift is increased by the engine thrust.... Note most Airliners and other turbo fan planes have a gap in the control surfaces at the engine, to avoid heating problems.)...

Another historical thing is that most aircraft designers think that only the upper wing surface is useful, and the lower surface is just there to hang stuff off...

Have a look at any 3-4th gen fighter jet.. the wing os so cluttered that the turbulence under the wing would almost cancel out the high pressure zone.... Of course the planes still work, because the wing area is multiplied to account or the lift lost by sticking things on the pylons... (5th gen fighters tend to not have as much garbage under their wings, for stealth reasons.... However they aren't really used that much... Due to ongoing Design flaws and manufacturers recalls...

The underside of a wing is very important and the plane flies better if it is clean. (hey may enable a more efficient aerofoil for cruise...)

Anyhow, this is only a teaser... wait untill the plane is built, and becomes operational, the market will decide if it is any good.... May be a waste of time.. But have any of the naysayers actually got any data on the matter??? (I may be mistaken but probably none of them are aerodynamicists (PhD)....(Not that I think the average aerodynamicist thinks much outside their little box..))

Wasn't so long ago that the mention of any form of "Coanda effect" was sneered at by all those "knew better". (only mentioned by silly flying saucer people).. must be desperate times for the mainstream to even consider such an abomination... we all know that the "Coanda effect" doesn't exist.(jk).. and only Daniel Bernoulli is able to account for aerodynamic effects....

MD
21st July, 2012 @ 02:13 am PDT
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