Floating more than an idea

Floating More Than an Idea A primer on aircraft floats By Greg Napert July / August 1998 In several distinct areas of the country, and in locations around the world, float equipped planes, otherwise known as seaplanes, are a normal...


Says Mathisen, "To give you an idea of float prices, the cheapest float that we build as a straight float is around $20,000 which is our Model 2100, which fits a SuperCub, PA12, Husky, Skyhawk. These floats as an amphibious float is $33,000. Our most expensive float, which fits on a Twin Otter, runs $482,000 a pair. With a water drop system for fire fighting, they are $650,000."

Mathisen explains the cost is justified through the rather extensive number of man-hours that go into building a float and the exceptional utility you get from them as an operator. "The material costs in these floats is fairly significant, but by far and away, the labor cost is the biggest contributing factor to the cost of the float. Everything is hand riveted and hand fitted and this can take some time. Much is misunderstood about the amount of material, number of bulkheads and number of rivets that go into building floats and the provisions that need to be made for attaching them to the aircraft.

Mathisen continues, "Many modifications may need to be made to the aircraft if it doesn't have a seaplane kit on it.

For instance, from the day a Cessna Caravan comes in the door, to the day it leaves, it takes us three weeks to configure the airframe for floats. Some of the modifications are structural, some are flight control related — like elevator down springs — or on the smaller ones, rudder centering systems to help prevent rudder lockup and to add stability in flight, finlets for yaw stability, etc. Typically the installation costs are set aside, but as an example, the Super Cub installation costs are around $4,000. The aircraft's hydraulics and electrical systems may need modification as well, but that varies from aircraft to aircraft. And, this is assuming that the aircraft has a sea plane kit already installed."

"If you start with a Ôgeneric' land airplane, you typically need to add a seaplane kit to include a propeller that can provide better static thrust (critical for taking off with floats), and hoisting rings, and corrosion proofing — so you've got to factor in these costs as well.

Mathisen adds, "There are extreme variations in the complexity of the installation from aircraft to aircraft. A Super Cub, for example, is fairly simple, requiring attach fittings to the lower longerons of the fuselage, whereas a Cessna 172 typically requires a beefing up of the fuselage by adding stringers or doublers."

Up goes the weight
Despite rumors to the contrary, Mathisen says that floats do add weight to the airplane. For example, he says, "On the Caravan, the float adds roughly 1,000 pounds to the aircraft. If you take away the weight of the original landing gear, you come up with the exchange weight. On this aircraft, the exchange weight works out to roughly 700 pounds."

This extra weight will take the Caravan from a useful load of around 3,600 pounds to around 3,000 pounds. So, you do have to take that into account. On a Super Cub, a straight float will reduce the useful load by around 170 pounds, depending on the float. The useful load ends up being around 350 to 400 pounds, and the gross weight goes from around 1,750 to around 2,000 lbs with the float installation."

Keeping it simple
Mathisen says that one of Wipaire's great successes with its floats has been the simplicity of the landing gear or hydraulic system. "Instead of the old single hydraulic actuator running a series of cables and pulleys to retract everything, we use simple dedicated actuators on their own, so it's all hydraulic, there's no mechanical linkage involved other than downlocks which are very simple. With our floats, if you lose hydraulics, the landing gear stays where it's at — it has a mechanical downlock and uplock so you don't have to worry about having a gear in transit."

Corrosion — the biggest challenge
Mathisen says that because of the nature of the float, corrosion is by far the most challenging aspect of float maintenance. This is compounded by the fact that most of its larger floats, such as on the Twin Otters and Caravans, 75 percent to 80 percent operate in warm/humid salt water.

He explains that Wipaire takes many corrosion prevention measures in-house, when it builds floats, that its customers have brought to light over the years.

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