Boeing team successfully tests SMART Materials rotor

[Heliport]

Boeing Integrated Defense Systems Press Release Boeing-Led Team Successfully Tests SMART Materials Helicopter Rotor
ST. LOUIS - A team led by The Boeing Company has successfully used advanced materials in the design, development and testing of a revolutionary new helicopter rotor that could benefit all rotorcraft.

The Smart Material Actuated Rotor Technology (SMART) system offers an 80 percent vibration reduction, a jet-smooth ride and other benefits. It employs existing materials to drive on-blade trailing edge flaps to reduce vibration and noise and improve aerodynamic performance.

Whirl tower testing was conducted by Boeing at its Mesa, Ariz., rotorcraft facility. The $10 million joint program teaming Boeing with the Defense Advanced Research Projects Agency (DARPA), NASA, the U.S. Army and three universities achieves unprecedented aerodynamic flow control.

http://www.boeing.com/news/releases/2004/photorelease/q2/smart_rotor_pic_1-t.jpg http://www.boeing.com/news/releases/2004/photorelease/q2/smart_rotor_pic_2-t.jpg

The goal of DARPA’s Smart Materials and Structures Demonstration program is to create a shift in the design of undersea vehicles and torpedoes, aircraft wings, engine inlets, and helicopter rotor blades.

The rotor system is now ready for forward flight testing to quantify significant improvements in vibration, noise, and aerodynamic performance expected. With completion of wind tunnel and/or flight testing, commercial, military, and unmanned helicopters could incorporate this technology within five years.

The SMART active flap rotor system used for the whirl tower tests is a modified five-bladed, bearingless MD 900 Explorer helicopter rotor. Each 17-foot long blade incorporates actuator assemblies that move a single flap on its trailing edge. During 13 hours of whirl tower testing, the flap actuators operated for seven hours under a full range of conditions.

“These successful whirl tower tests demonstrated that the active flap system works in full scale, confirming it meets the requirement,” said Friedrich Straub, Boeing principal investigator in Mesa. “This can provide up to 80 percent vibration reduction and reduce noise for a helicopter passing overhead.”

The vibration reduction and performance improvement should provide a jet-smooth ride, significantly reducing helicopter life cycle costs, increase productivity and fleet readiness. Proving the integration, robust operation, and authority of the flap system was the key objective met by the whirl tower tests.
“This technology development program evaluates the potential of dynamically morphing blade structures to achieve revolutionary improvements in rotorcraft performance and mission capability,” said William Warmbrodt, chief of the Aeromechanics Branch at NASA Ames.

[RDRickster]

What do they mean by "bearingless... helicopter rotor?"

[helimatt]

Someone correct me if I'm wrong, but bearingless means all the hinges are elastomeric

[IHL]

I don't understand, what do the flaps do? Do the move to increase or decrease the angle of attack instead of the blade flapping up or down ?

[Shawn Coyle]

The flaps will work like the servo tabs on the Kaman rotors- changing the blade camber to change the lift. But instead of being behind the blade, it looks like it's incorporated into the blade and will appear more as an aileron on a wing - albeit a very rapidly moving one.

[moosp]

I guess this is way above my understanding of aerodynamics, but is the idea to reduce the Coefficient of Lift on the advancing blade from that on the retreating one? Flaps up advancing, flaps down retreating? I suppose this would mean that the "flapping" (as the word applies to rotor systems) would be reduced, which would reduce vibration.

As for noise, again out of my depth here, but for a fixed wing, flaps down makes more noise than one that is clean for a given speed. So using a trailing edge flap system to reduce noise seems counter-intuitive.

The more I learn of aerodynamics, I find the less I know...

[Dave_Jackson]

IHL

As a continuation of Shawn's comments; If the trailing flap is located back behind the blade (Kaman) and/or the blade is tortionally flexible, a downward motion of the tab will pitch the blade down. Alternatively, if the trailing flap is located within the blade and the blade is tortionally stiff, a downward motion of the tab will result in additional blade lift. These are, of course, opposite results.
_________________

It appears that the Boeing SMART rotor utilizes a swashplate and pitch links for the primary blade pitch setting. This swashplate might be simple a conventional 1/P one, or it might include actuators to provide a Higher Harmonic Control. The SMART flap is a supplement to the swashplate and it is used to reduce vibration. Its contribution to increased lift will probably be in the range of 2 - 6%.

Here is an overview of a leading and trailing edge concept. (http://www.isd.uni-stuttgart.de/sfb409/projectA5.html) In this concept there are two profile changes taking place. The forward one is changing the camber of the blade and the second one is changing the angle of the trailing tab. This totally sealed 'morphing' of the blade profile should be very aerodynamically clean. As with the Boeing SMART rotor, the primary blade pitch changes must be provided by another mechanism.

Subject to correction by a higher authority, I believe that the following is a valid summation of trailing flap rotor controls;
~ The Kaman style flap provides primary flight control but it cannot provide high frequency vibration control.
~ The Boeing embedded flap provides high frequency vibration control but it cannot provide primary flight control.
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An overview of smart materials, (http://www.spa.com/smtdsmart.htm), for the interested.

[NickLappos]

Dave hasit right. The servo-flaps on the blades are electrically activated and have small authority. This makes them fast enough to provide accurate small inputs above 1 per revolution frequency, so they can excite the blade to damp vibrations and perhaps quell noise. The flaps are not able to create enough lift change to fully control the helo (yet).
A version that I have seen uses piezo-electric servos to bend the blade trailing edge a bit, these may be similar.

[Lu Zuckerman]

From a reliability point of view what happens if one of the servo tabs or its’ electrical signal fail? If the tabs are to minimize if not eliminate vibration then what type of condition is manifested in this case? Is it similar to a blade being out of track or is it worse?

Does the tab return to its' neutral position or does it remain in its' last commanded position in event of a signal or tab failure? What is the effect in this case?

:E :E

[Dave_Jackson]

Lu,

Tabs intended for vibration reduction have high frequency and low amplitude. Because of the low amplitude, a failure will probably result in nothing more than increased vibration.