Low Friction Bearings, Aluminum Impeller Maximize Wind Speed Indicator

July 1999

From sailors to scientists, kite flyers to foresters, and pilots to golfers, the Kestrel 1000 and 2000 anemometers are being appreciated for their convenience and accuracy. Nielsen-Kellerman Company, Chester, PA recently released both products to an eager marketplace, thanks to the design help of Bird Precision. Wind speed indicators have been around for many years, but a lightweight and highly accurate digital version had remained elusive to manufacturers until Nielsen-Kellerman went to the drawing board. Previous designs often have been cumbersome analog devices weighing more than one pound and providing only moderate accuracy.

Design Details

Nielsen-Kellerman’s goal was to create a highly accurate hand-held anemometer less than 5 inches long and weighing only 1.5 ounces. Other anemometers on the market did not allow the accuracy Nielsen-Kellerman sought, mainly due to their material make-up. Steel rollerbearings often are used, and plastic is often used for the impeller’s shaft. Plastic wears easily, and since most anemometers’ Impellers cannot be replaced, a worn shaft usually means a new unit is necessary.

Nielsen-Kellerman approached Bird Precision, Waltham, MA to help in the design of an ultra sensitive, low friction jewel bearing and alloy impeller shaft. Bird Precision accepted the challenge, delivering super polished sapphire conical vee bearings, chosen for their ultra low coefficient of friction of better than 0.15 against steel. Sapphire is next to diamond in wear resistance, and also was chosen for its long life. For the shaft, Bird Precision recommended their hardened proprietary alloy, which is known for its non-magnetic, non-corrosive and wear resistant qualities. The sapphire vee bearings and shafts were critically matched for minimum friction and high performance. A precision-engineered anodized aluminum impeller with a large diameter-to-weight ratio concluded the improved design.

Bird’s bearings allow the Kestrel’s impeller to register almost imperceptible breezes (down to 0.7 mph), yet also measure gale force winds (up to 89 mph) with an accuracy of 3% or better. The 25mm patented impeller is protected from damage by a fiberglass housing but if necessary, can be replaced simply and inexpensively without tools. This anemometer is currently the only one on the market with a user-replaceable impeller.

Many Industries Served

Unlike many others on the market, the digital display offers settings for knots, meters per second, kilometers per hour, miles per hour, feet per minute and Beaufort. Thanks to all of these improvements, the Kestrel 1000 pocket Wind Meter and the Kestrel 2000 Wind Speed / Temperature/ Wind chill indicator are being marketed to a variety of industries beyond the obvious aviation pilots, balloonists, hang-gliders and other "flyers".

The Kestrel’s biggest market is actually the marine industry. Sailors and even windsurfers can use the indicator both on land and water to test wind speed and direction, an improvement over common masthead indicators that are difficult to read and impossible to use on land. Another industry interested in the improved anemometer includes HVAC technicians, who can use the indicator to balance central heating and air systems. The maximum volume flow of a system is known at installation. By holding an anemometer in front of a heating or air duct, technicians can check the current volume flow, determine any leaks and then balance the system. In these situations, an anemometer with low start speed requirements is necessary. Many of the hand-held anemometers currently on the market create significant friction (due to roller bearings or plastic impellers) and require a considerable wind speed to start the blade moving. Because Kestrel’s jewel bearings are almost frictionless, and the impeller is extremely lightweight, a very low start speed is required.

Similar to HVAC technicians, spray booth operators must constantly check the ventilation of their booths to ensure that the harmful chemicals being sprayed are properly removed from the circulating air. Because an operator’s life could be on the
line, the accuracy of the anemometer is extremely important. Fire fighters and forestry engineers use anemometers to track the direction and speed of the wind in case of fire.
Controlling a blaze is often dependent upon knowing which direction and how fast it will move. Though many fire and forestry stations have large wind speed indicators posted on the station’s roof, having a hand-held indicator allows fire fighters to make split-second decisions at the scene.

Along with fire prevention and containment, forestry engineers and environmental engineers use anemometers for erosion control. Recording average wind speeds over time at a given location provides these engineers with data to calculate the rate of erosion in that area. Again, lightweight and accurate anemometers are imperative for accurate calculations. The Kestrel gives not only an instantaneous reading of wind speed, but also can recall the maximum and average wind speed recorded since the unit was turned on. The new accuracy in hand-held anemometers has created interest among farmers as well as crews that apply lawn chemicals. Farmers check wind speed and direction when spraying crops. Lawn technicians do the same when spraying lawns, particularly to calculate the distance the spray will be carried on the wind to ensure the neighbor’s lawn does not end up being sprayed instead. A little accuracy goes a long way in this marketplace.