Air Over Hydraulic

Kenmore Air Beaver: just add water

Before my visit to Kenmore Air, my seaplane experience was limited to two flights, both on assignment for Flight International .

The first was in a de Havilland Twin Otter in the US Virgin Islands, hosted by Seaborne Airlines . That turbine-powered aircraft sported conventional floats and seemed at home in the shallow waters surrounding St Croix.

The second flight was in a Bombardier 415 amphibian, operated by the province of Ontario, in which I was able to practise scoop and drop operations, essential to fight forest fires. The aircraft was a joy to handle on Lake Hamilton, a body of water between the USA and Canada.

Kenmore Air operates eight piston DHC-2 Beavers, two turbine Beavers and six DHC-3T Otters. For my familiarisation flight we would fly one of the piston Beavers. The Beaver, perhaps the world's most recognisable "bush plane", was designed after the Second World War to tackle the needs of the Canadian back-country.

A huge commercial success, more than 1,600 Beavers had been delivered when production ceased in 1967. The Beaver was designed to be equipped with both floats and skis, but my first experience with the type was in a wheeled Beaver as a student at the US Air Force test pilot school.

Having learned to fly in tricycle-gear aircraft, I initially found its tail dragger stance and radial engine intimidating. While my recollections of that flight have faded over the intervening 30 years, I remembered that once airborne it was a docile and honest aircraft that required a bit of footwork to keep in co-ordinated flight. On the ground I found the Beaver easier to handle than a Pitts S2, a type I had flown several times with an air force colleague.

While a stock Beaver is a capable aircraft, a Beaver on floats is a different animal. Adding floats to an aircraft limits its ultimate performance capabilities while at the same time liberating it from runways and terra firma.

Kenmore's Beavers are mounted on Edo floats. The all-aluminium equipment, each with nine compartments, are sized to provide flotation of 180% of the aircraft's maximum allowed gross weight. Kenmore liked the Edo float so much, it bought the company in 1998 and now manufactures floats for its own and retail customer use. The Edo 4930 float installation accounts for 151kg (333lb) of the Beaver's empty weight, which ranges from 1,573kg to 1,673kg for Kenmore's seaplanes.

air over hydraulic system

We are designing a machine that uses a saw that is controlled by a cylinder. My boss is worried about chatter as the saw cuts due to the air compressing in the cylinder. he would like me to design an air-over-oil system to make the cut smoother. I've never done this but I envision a tank with pressured air in the top, oil in the bottom; pushing oil through a flow control valve and actuating the cylinder. the cylinder we are using has a 2" bore and 18" stroke. Any one ever designed a system like this? How would I size the holding tank? If you must push the saw hard into the material (not a good thing) rather than allowing it's own weight to cut, then you would be better off with a full hydraulic system or better yet a lead screw drive and stepper motor. There is little sense in pushing a blade hard into the material being cut. It will do more damage to the blade than it will aid the speed of cutting. Metal can only be removed at the rate the teeth can scrape up a mouthful. I don't think I have seen anything like that with air and oil in the same space, certainly not for saw-feed. I have seen air/oil systems where a larger diameter air cylinder was used to power a smaller diameter hydraulic to increase output pressure when the max air pressure was not high enough. But, even then, any vibrating or reciprocating load is transferred back to the air cylinder which acts like a spring at max air pressure. It is not pressure that makes a good saw cut. It is the load per tooth. If a smooth steady cut is important then a mechanical system (lead screw) is the only way. However, if they are cutting various types of material and various cross sections, then they are unlikely to need more than about 20-lbs contact pressure at the teeth and then adjust the down-speed for a constant tooth load. I think the "Boss" is looking at this from the wrong end. Let Engineers do the Engineering. Folks have been making cylinders that are piggy backed like this for years. There's a hydraulic cylinder on the back of an air. They have flow controls for adjusting your speed of exit oil. We've been using a pair of them on a dual head abbrasive cut-off saw for years. The particular model we run if you want to do a search and see what they look like etc. is an Allenair CHFLH... Others make these as well. You will just need to start off choked back and slowly tweek it up until you're getting a good feed rate for your material and cutting tool. If you want steadier yet...

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