Tuesday, March 31, 2009

Helicopters and Airships

In another lifetime, I became familiar with aspects of helicopter design issues and am a sucker for any improvements that are trotted out. This proposed work is going to take years but appears to be a nice incremental step in the right direction. It has led me to other musings.

Helicopter design is a marvelous tradeoff, technically consisting of ten thousand moving parts flying in formation, as any fixed wing pilot can tell you. Having said that, it hovers, provides lift, and travels from point to point at a decent speed in excess of a hundred miles per hour, but not a lot more.

The better design option is the coaxial system presently used on the Russian KA-25 made by Karmov. It took decades to master control and modern methods have surely advanced that technology. I do not know the current state of the Karmov art but rigid blades must be incorporated by now. I need to see a new one at an air show. What I would dearly love to see is a joint venture between Karmov and Bombardier to completely modernize the technology from the ground up and have the product introduced into the global market.

The Karmov design is the best available for heavy lift tasks needing rapid turn around like logging. It just needs a North American partner, not locked into other protocols and that is Bombardier’s position.

The issue of vertical lift opens another door. Helicopter lift is an order of magnitude too small to deal with container traffic. That has been relegated to surface transport presently optimized to around sixty miles per hour. Because it is locked onto surface based systems, there is a high energy component involved just to sustain movement.

I have already posted on how it is possible to use the existing rail system to remove a large fraction of that energy loss. It is feasible to use existing rail beds and infrastructure to float the cargo on air to eliminate friction and equipment drag and possibly some of the hardware weight.

That still leaves us with the short haul work. This might well be handled by heavy lift shaped air ships capable of maintaining speeds of sixty plus miles per hour. They are free of the roads and can travel directly between the container depot and the customer. The hardware will be tricky to perfect but should be possible. The props main task will be to force the craft down for pick up and discharge and to provide for horizontal travel.

Can such a design compete with trucks? Lock on and lock off should be very quick and actual movement by direct flight. The volume throughput should be much larger than could ever be achieved by the truck.

Most thinking on air ship economics is based on long haul competition in which an airship might carry a container at sixty mile per hour between cities over long distances. The problem is that creates a huge weather problem injecting major uncertainty. Most of that problem disappears in short haul work. You are still dealing with adverse weather from time to time but not as critically in terms of cargo movement. Strong winds and squalls are the major concern, yet they are usually short lived. Flying into a hanger and locking down should become practice at once, or even locking down behind high protective wind shields is a cheaper option as we are looking at excessive roof spans.

Such craft can deliver containers continuously around the clock with occasional shutdowns to allow passing weather to move on, while eliminating thousands of miles of road haulage and time.

Future Helicopters Get SMART



Helicopters today are considered a loud, bumpy and inefficient mode for day-to-day domestic travel—best reserved for medical emergencies, traffic reporting and hovering over celebrity weddings.
But NASA research into rotor blades made with shape-changing materials could change that view.

Twenty years from now, large rotorcraft could be making short hops between cities such as New York and Washington, carrying as many as 100 passengers at a time in comfort and safety.

Routine transportation by rotorcraft could help ease air traffic congestion around the nation's airports. But noise and vibration must be reduced significantly before the public can embrace the idea.

"Today's limitations preclude us from having such an airplane," said William Warmbrodt, chief of the Aeromechanics Branch at NASA's Ames Research Center in California, "so NASA is reaching beyond today's technology for the future."

The piezoelectric actuators can change and adapt the rotor blade while in motion.

The solution could lie in rotor blades made with piezoelectric materials that flex when subjected to electrical fields, not unlike the way human muscles work when stimulated by a current of electricity sent from the brain.

Helicopter rotors rely on passive designs, such as the blade shape, to optimize the efficiency of the system. In contrast, an airplane's wing has evolved to include flaps, slats and even the ability to change its shape in flight.

NASA researchers and others are attempting to incorporate the same characteristics and capabilities in a helicopter blade.

NASA and the Defense Advanced Research Projects Agency, also known as DARPA, the U.S. Army, and The Boeing Company have spent the past decade experimenting with smart material actuated rotor, or SMART, technology, which includes the piezoelectric materials. "SMART rotor technology holds the promise of substantially improving the performance of the rotor and allowing it to fly much farther using the same amount of fuel, while also enabling much quieter operations," Warmbrodt said.

There is more than just promise that SMART Rotor technology can reduce noise significantly. There's proof.

The only full-scale SMART Rotor ever constructed in the United States was run through a series of wind tunnel tests between February and April 2008 in the National Full-Scale Aerodynamics Complex at Ames. The SMART Rotor partners joined with the U.S. Air Force, which operates the tunnel, to complete the demonstration.

A SMART Rotor using piezoelectric actuators to drive the trailing edge flaps was tested in the 40- by 80-foot tunnel in 155-knot wind to simulate conditions the rotor design would experience in high-speed forward flight. The rotor also was tested at cruise speed conditions of 124 knots to determine which of three trailing edge flap patterns produced the least vibration and noise. One descent condition also was tested.

Results showed that the SMART Rotor can reduce by half the amount of noise it puts out within the controlled environment of the wind tunnel. The ultimate test of SMART rotor noise reduction capability would come from flight tests on a real helicopter, where the effects of noise that reproduces through the atmosphere and around terrain could be evaluated as well.

The test data also will help future researchers use computers to simulate how differently-shaped SMART Rotors would behave in flight under various conditions of altitude and speed. For now that remains tough to do.

"Today's supercomputers are unable to accurately model the unsteady physics of helicopter rotors and their interaction with the air," Warmbrodt said. "But we're working on it."

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