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Elytron 2S: The out-of-the-box tiltrotor concept

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July 23, 2014

A Elytron 2S (shown here in a proposed seven-seater version) is a tiltrotor aircraft that ...

A Elytron 2S (shown here in a proposed seven-seater version) is a tiltrotor aircraft that uses a Prandtl's box wing design

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Some people are never satisfied. You give them a plane, and they say it can’t hover. You give them a helicopter, and they say it can’t fly very high or fast. Looking to combine the advantages of both fixed-wing aircraft and helicopters, Elytron Aircraft LLC of Mountain View, California is developing the Elytron 2S, a small tiltrotor aircraft that uses a box wing configuration and is aimed at the civilian market.

Airplanes and helicopters do well in their respective aeronautical niches. Airplanes can fly high, fast, far, and carry heavy loads, while helicopters can hover, fly backwards, land and take off vertically, and maneuver in very tight spaces. The tricky thing is when jobs arise where requirements overlap; like an airplane that can land vertically, or a helicopter than can fly at high altitude.

Though there have been some aggressive development projects in recent years, such as the Bell V-280, the AugustaWestland Project Zero and AW609, the only operational manned, prop-driven aircraft that manages this sort of hybrid flight is the V-22 Osprey tiltrotor aircraft.

In service with the US Marine Corps and the air forces of the US, Japan and Israel, the military tiltrotor spent many years in controversial development and, to this day, no civilian version has taken off. This is unfortunate because early visions of tiltrotor aircraft saw them employed as air taxis, short haul transports, and in other civilian applications.

The Elytron 2S is a new take on tiltrotor configuration that incorporates an unconventional wing design to create a hybrid aircraft with greater performance – especially in the difficult transition between vertical and horizontal flight. One of a family of aircraft developed by the Elytron company over the past decade, the 2S is intended to combine the features of a helicopter and a fixed-wing aircraft, with the company seeing applications for emergency medical services, search and rescue, air taxis, and oil exploration.

The designs for the Elytron 2S technology demonstrator (left) and a seven-seater version f...

Comparing the 2S to the Osprey, the most obvious difference is its wing configuration, known as Prandtl's box wing design. It looks exotic and futuristic, but it’s actually a variation on a wing concept that dates back to the earliest days of aviation when it was used by the pioneer flyer Louis Bleriot in 1906. It has also been used more recently by Lockheed Martin for one of its concept jets.

2S’s design uses two pairs of wings. One pair is set forward on the fuselage and is swept back. A second pair is set on top of the tail and swept forward. The tips of the fore and aft wings are linked by winglets, forming a skewed box. With this layout the forces are distributed through the box structure, making it stronger and lighter. It also provides a high aspect ratio for greater lift of about 15 percent over conventional wings.

This results in greater fuel efficiency and less weight. In addition, the box wing is more stable, has better glide ratios and is less prone to stalling. In all, this makes Prandtl's box wing very suitable for short take-off and landing craft. The stall factor is particularly important because it helps keep the 2S in the air during the vertical to horizontal flight transition.

So far, this is unusual, but not unprecedented. According to Elytron, the novel bit about the 2S is the extra pair of rotating wings mounted amidships, which contain the motors and props. The rotary wings, called "proprotors," are powered by two 90-degree gearboxes and are mounted on a single, centrally-mounted tilt wing that travels through 100 degrees and has four control surfaces.

The Elytron 2S is the extra pair of rotating wings mounted amidships, which contain the mo...

Elytron says that this arrangement inside the box wing obviates interference with the proprotors’ thrust, while the winglets protect against rotor strikes. Because the proprotors can drop to the horizontal for forward flight, the blades don’t have the disadvantage of helicopter rotors where the retreating side of the rotors slows the craft and introduces unwanted torque. The design of the proprotors is much less complicated than a helicopter rotor with no need to angle or feather the rotors, so the linkages are simpler and their fewer parts are spread out through the wing.

According to Elytron, the result of all this is low drag at high speed in a craft that can fly two to three times the speed of an equivalent helicopter and, if the V-22 is an example, it will have a higher operating ceiling. It’s also safer because its glide ratio means that the rotors don’t need to autorotate during an emergency landing. If that doesn't work. Elytron says it will install a ballistic parachute.

The Elytron 2S is a two-seater technology demonstrator built using fast prototyping with carbon composite materials. The company says that it plans to install a 450 bhp turbocharged race engine in the 2S with the goal of conducting flight tests next year. If successful, the next phase will include building a seven-seater version for commercial use. In the meantime, the 2S is on display at the Oshkosh Airshow through August 3.

Source: Elytron

About the Author
David Szondy David Szondy is a freelance writer based in Monroe, Washington. An award-winning playwright, he has contributed to Charged and iQ magazine and is the author of the website Tales of Future Past.   All articles by David Szondy
13 Comments

Nice concept.

I can't establish if it has hover capabilities (doesn't appear to) or if it a STOL (Short Take OFF / Landing) aircraft with a low stall speed.

Ken King
23rd July, 2014 @ 10:13 pm PDT

@ Ken King

I had the same questions (and the same opinion; "Nice concept").

I think the fact that the rotating wing goes through 100 degrees means that it does actually hover, though how it moves sideways or rotates in the horizontal plane is not obvious. I assume that it is possible to adjust the attack angle of the prop blades on one side relative to that of those on the other side in order to achieve these manouvres. I take "so the linkages are simpler" as a clue - what else would the linkages be for if not to adjust the angle of the prop blades?

Mel Tisdale
24th July, 2014 @ 02:50 am PDT

Their site claims vertical takeoff and landing.

This is pretty much a continuation of the V-22 Osprey. And twin rotor helicopter controls were solved as far back as the CH-47 Chinook.

digi_owl
24th July, 2014 @ 04:33 am PDT

Adding the box wing adds unnecessary weight to lift in vertical flight mode.

Slowburn
24th July, 2014 @ 07:50 am PDT

Doesn't matter, as long as it can easily hover. Hover time is like 1% of the flight time.

Tim Jonson
24th July, 2014 @ 08:57 am PDT

SlowKlue: LANDING GEAR is also just dead weight most of the time but still pretty handy to have when LANDING & TAKING OFF.

Overall I think this is a great idea, but check back with me when they build in one of those aircraft parachutes. This also is dead weight until you need it. Given the frequency with which the bright ideas of small aircraft innovators wind up plowing a field I would not get in one of these unless it had a built in aircraft parachute. Screw whining about the extra weight.

StWils
24th July, 2014 @ 10:42 am PDT

This vehicle needs to have its wings redesigned. so for the company is trying to fly something ugly and aesthetics are just as important as functionality.

Gargamoth
24th July, 2014 @ 11:08 am PDT

@tilsdale There is no feathering (angle adjustment) on the prop blades according to the article. My guess is that fore/aft leveling is accomplished with rotation of the proprotor and side to side leveling is accomplished by differing the prop speeds. Rotating the plane (pivoting in place) could be done with asymmetrical rotation of the proprotor - one prop pointed forward, the other backward. How well that works compared to a tail rotor remains to be seen...

Shishkabugs
24th July, 2014 @ 11:22 am PDT

G-moth: aesthetics is subjective. If this design accomplishes their goal, and I believe it will, the improved functionality will quickly turn this ugly duckling into a beauty. See: Rudolph The Red Nosed Reindeer.

I am a big fan of the tilt-wing, i.e., control wing, i.e., pivot wing, i.e., Spratt wing built but not tested before the Wrights flew. If the Wrights had not been so convinced of their assumption that the pilot should control stability, and tested the inherently stable control-wing given to them for that purpose, they would have flown earlier, and the history of aircraft design would have changed.

From the control-wing came the freewing, which does everything the 2S hopes to do and more. Unfortunately, the inventor, Hugh Schmittle will only build military drones because it is lucrative and risk free.

Don Duncan
24th July, 2014 @ 12:46 pm PDT

Having seen how the Osprey has been fielded finally and the expense of it I'm not a big fan of a multi-task aircraft.

The Osprey has a life only because the USMC was so convinced it was what they needed that they spent a large proportion of their meagre budget to keep funding it.

Once fielded, the powers that be, with no practical experience tried to ram it down our throats insisting it would do our particular mission even after demonstrations showed it woefully inadequate. It has an extremely high blade loading for very rugged terrain. Forget small rocks and branches, that sucker could blow really large and heavy objects around at unimproved landing sites!

Being a long time rotary wing pilot perhaps biases my opinion but on the other hand perhaps it adds some insight to the issue?

All my best wishes to those who continue to want and try to achieve an aircraft that can do the jobs of both fixed wing and rotary wing. I will continue to prefer one or the other depending on the tasks required.

Dr. Veritas
24th July, 2014 @ 08:41 pm PDT

@ StWils

The wing holding the rotors provides lift at high speed so you don't need the box wing there and at low speed the vertical flight mode the box wings aren't producing enough lift to matter and makes the plane heavier which reduces the load. The only "useful" thing it appears to do is cordon off the rotors.

Slowburn
25th July, 2014 @ 03:14 am PDT

Why not use the quad copter arrangement, scaled up, and wings added for forward flight? A thrust propeller driven from the lift rotors would provide forward speed.

windykites1
25th July, 2014 @ 06:54 am PDT

@shiskabugs

You could be right. It does state: " ... mounted on a single, centrally-mounted tilt wing that travels through 100 degrees ...", which lead to my confusion. If it is split and they can be angled to each other then a lot more manoeuvrability is possible. I missed the plural on the motors and thought it was only one central motor driving the two rotors through the 90 degree gearboxes, sorry for that. Clearly, varying the motor speed gives even more manoeuvrability. Problem solved.

Mel Tisdale
25th July, 2014 @ 07:34 am PDT
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