Fixed gear amphibian?

Discussion in 'Bush / Float flying' started by Floydr92, Nov 6, 2014.

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  1. Nov 10, 2014 #21

    Kingfisher

    Kingfisher

    Kingfisher

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    The way I have built mine is to simulate a retractable gear, I can take the wheels out for on water ops. However, I had thought about sinking-in the wheels enough so they could stay as a fixed gear. Should my plane actually fly, I plan to experiment with that or a skid plate as Himat suggests, further down the road.
    IMG_1187.jpg
     
  2. Nov 11, 2014 #22

    BBerson

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    I think narrow wheels mounted on the side of float, instead of cutting draggy holes in the float bottom.
     
  3. Nov 11, 2014 #23

    Kingfisher

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    Pooh...just to be clear, if you are building a model with traditional step floats, you will likely be able to take off and land without any wheels. For a full scale, I doubt the thin wheels on the side would be less draggy than recessed narrow wheels. The holes can be tight around the wheels in the bottom.
     
  4. Jan 16, 2015 #24

    Riggerrob

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    Back in the 1930's Seversky flew a few floatplane prototypes that had fixed wheels. The main wheels only protruded a little below the keels of the floats. As soon as the (dual) tail wheels touched down, they pivoted the tails of the floats up so that the plane could rest at the same angle as a regular tail-dragger (about 17 degrees nose-high at rest). Nice idea, but few modern pilots receive their initial training in tail-draggers and insurance companies charge more to insure tail-draggers. Insurance companies also charge more to insure float planes and they also charge extra to insure airplanes with retractable undercarriage, because sooner-or-later many retractables land with wheels up. At a minimum, that requires re-painting the belly.
     
  5. Jan 16, 2015 #25

    Riggerrob

    Riggerrob

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    Narrow wheels work fine on hard-surfaced runways. But what if you want to taxi up onto a sandy beach for the night? Then you need hard-packed sand or wide tires.
     
  6. Jan 16, 2015 #26

    Riggerrob

    Riggerrob

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    Agreed. I have been sketching a small amphibian. The mission involves launching from a sea level airport (asphalt or concrete runway) or harbor near a major city and flying to a mountain lake for the weekend. The primary advantage to launching from a harbor is its proximity to downtown. The disadvantage is the high cost of storing the plane at a marina. Folding wings would reduce the cost of storage. At a minimum, I want to be able to pull the plane far enough up a beach that I don't have to worry about it sinking or floating away during the weekend. Sunday evening we take-off from the mountain lake, then land back in the harbor or airport.
     
  7. Jan 16, 2015 #27

    Riggerrob

    Riggerrob

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    Lots of small amphibians leave retracted wheels exposed to the wind. They cruise so slowly that covering retracted wheels makes little difference. One reason is that all seaplanes have huge draggy wings. The huge wings are needed for the STOL at the lake end of the mission. Slow, short landings dramatically reduce the beating that waves always deliver to hulls and floats. The less the wave loads on floats, the lighter you can build them. Conversely STOL always requires a huge wing that is never going to cruise very fast. While they were designing the Beaver bushplane, deHavilland engineers asked bush pilots how important a fast cruise speed was to their missions. Bush pilots replied that cruise speed was irrelevant as long as they could fly directly from one lake to a lake in the next valley. IOW an 80 knot cruise in a (10 mile straight line is always faster than a canoe or dog-sled that has to flow river valleys 40 or more miles out of the way. Ergo few amphibians cruise much more than 100 mph and only the fanciest military flying boats could cruise at 200 mph. Richard Van Grunsven has proven that fixed gear is simpler, lighter and cheaper at cruise speeds less than 20 mph.
     
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  8. Jan 18, 2015 #28

    Magnus Wallner

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    The Republic Seabee has a very simple solution to the landing gear issue. I think I've seen something similar in the flying RIB's you see sometimes.

    Having the wheels "hang down" beneath the keel creates a lot of drag, I know from experience with faulty "up locks" on amphibious floats. Especially if the wheel starts to rotate. I don't know why but I guess it's the same as when ditching a land plane, it's better to lock the brakes so that the wheels skid on the water initially rather than dig in.
     
  9. Feb 5, 2015 #29

    Riggerrob

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    How much do those RIBs weight? What is the maximum displacement?
     
  10. Feb 6, 2015 #30

    BBerson

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    I figure on soft sand the narrow wheels will sink in until the float rides on the sand. The wheels should only be about 2" lower than the float bottom.
    Talking about a 250 pound ultralight. I think I can drag 250pounds.
    Not practical for heavy aircraft.
     

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