Seaplane retracting gear.

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WonderousMountain

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We've thought about it. So what would it take to retract skis, floats, or vary the hull so that the gear doesn't create "a lot" of cruise drag. Weight would likely be more, given the engineering challenge. Still I'm curios what the more innovative and experienced designers know/think about it.

Wonderous Mountain
 

jhausch

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There was a booth at OSH last year where some guys were showing a concept where the floats folded into the hull. Not sure if it went anywhere.
 

skeeter_ca

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Some have fully retractable gear that go up into the fuselage. Look at the grummens for that. Look at the icon amphib. Look at the osprey II. Look at the Lakes. All these have retracts that fully get out of the wind. Glass Goose fold back into the wing partially. Volmers, Seabees, Sea-reys just flip them up out of the way and hang in the breese. Everything is a compromise when designing a plane, especially an amphibious one. Not only does it weight more, which can be critical in a small two place, but the complexity goes way up. More points for failure, higher maintence time and cost. Just how much speed would be gained versus the cost depends on the aircraft.
 

WonderousMountain

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Just to be clear I am talking about dedicated seaplanes mostly and skis and floats that retract to give smooth profiles, instead of the more common "boat-like" appearance.
 

skeeter_ca

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Ahh......... Now thats an engineering challenge. Probably been tried and millions spent developing something to never come. Good luck!
 

Robby

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FWIW and a bit of food for thought -

I always liked the old Catalina PBY design that had the wing tip floats retract horizontally so that they became the wingtips in flight !!
Interesting mechanism.
 

Jay Kempf

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Dornier Seastar has an interesting system too.
The biggest drag on a seaplane is the step in the hull. Everything else can be designed around. I designed a step long ago that had an inflatable bag so that it hinged out for takeoff and then the air was pumped out of the bag to retract it to flush for cruise. That way no mechanism to seal. That combined with standard retracts would get all but the ski mode done. I suppose for ski operation you could just put skis on for the winter. Or more complicated rig skis to the retracts (gear doors) to come down an extra few inches with an auxiliary system.
 

Dan Thomas

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FWIW and a bit of food for thought -

I always liked the old Catalina PBY design that had the wing tip floats retract horizontally so that they became the wingtips in flight !!
Interesting mechanism.
It works, but it also works against the flight capabilites. When do we need the most lift? Taking off and landing on the water, to minimize the rough ride and to break free of the water's drag. When are the PBY's wings the shortest and generating less lift? Taking off and landing on the water.

Dan
 

Dan Thomas

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I don't understand why retracting the step isn't long since solved and incorporated in all seaplanes.
Because the step's drag is minimal and retracting it adds weight, complexity, cost, and the chance of forgetting to extend it, which would result in serious handling problems immediately at touchdown and quite likely an accident.

Dan
 

Jay Kempf

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Because the step's drag is minimal and retracting it adds weight, complexity, cost, and the chance of forgetting to extend it, which would result in serious handling problems immediately at touchdown and quite likely an accident.

Dan
It is not my understanding that the step adds minimal drag. Of course that is an it depends statement. The subject that I reacted to was the seaplane turbojet airliner. Those speeds do bring the step drag into play.
 

Dan Thomas

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How about retractable hydrofoils...?

For the weight of an airplane they could be truly tiny to make enough lift to get the airplane out of the water...

If you look at the size of the huge Boeing 929 hydrofoil which carries up to 400 pax and look at those little wings that provide the lift to get that 200 ton boat out of the water it is truly amazing...

Even human powered hydrofoils are twice as fast as any conventional rowing craft...I think the flyak (hydrofoil kayak) goes something like 25 mph which is really moving on water...and on muscle power no less...
Dave Thurston, the designer of the Teal amphib, which was a certified airplane and eventually evolved into the Lake series of amphibs, experimented with retractable hydrofoils.

Here it is, in February of 1968:

519-T67HuCL._SS500_.jpg

Obviously, since 44 years have passed, the idea didn't pan out like he hoped. History is full of such ideas. Most of the ideas in forums like this have been tried and discarded. Once in a while we might see something new but it almost always arises out of technology that did not exist previously: the LS-1, computers, new alloys and plastics, and so on.

Dan (the guy with a mind full of disorganized trivia)
 

Dan Thomas

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It is not my understanding that the step adds minimal drag. Of course that is an it depends statement. The subject that I reacted to was the seaplane turbojet airliner. Those speeds do bring the step drag into play.
Yeah, they would, with drag increasing by the square of the increase in speed. Airliners benefit from the economies of scale: a big airplane can lift much more than you think, and can benefit from expensive systems. A small airplane gets really limited by the weight (you lose payload) and complexity (you lose space inside, increase failure points, and add cost). A good example is the six-seat Cessna 210; you can get a pressurized version (P210) to fly high (but now you need backup oxygen tanks, lines and masks) and put deice boots on it to go through heavy weather, and a radar pod under the wing and radar in the panel to show you the storms and hail and heavy rain, and Stormscope to show you the lightning strikes. And a three-axis autopilot. Now you have most of the equipment of an airliner in a six-seat airplane, but it has become an airplane for two people and some baggage. Not much better than many homebuilts, though it will get there faster and safer.

Double the size of the airplane. Twice the span and twice the chord make four times the wing area. Double the speed and increase the lift on that larger area, and see the lifting capacity go up. Big airplanes can afford to fool with fancy, heavy systems. We, the guys stuck with little airplanes, are limited in our choices.

Dan
 

orion

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Regarding why the step is not retracted, it is mainly because the step does not cause all that much drag and the retraction system, with all the associated systems and seals, would probably penalize the craft more than the drag reduction would benefit. While the hull's wetted area and shape certainly creates an addition drag count and penalizes the plane's cruise, in this case it really does not matter since long distance cruising is not what this airplane was designed for. But the penalizing drag on this airplane comes from a number of sources, of which the hull is only one.
 
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