I am in the process of starting to build an ultralight that will be a tail dragger with floats, and in my conversations with the fellows I'm building it with, we've realized we've never seen a plane like it before. Does this mean we are doing something dumb? Thanks in advance.

  • $\begingroup$ Maybe for floats to be sufficiently buoyant they have to be so big that they can also be statically stable on their own (like having four main wheels and no tailwheel) so there is no need to tail drag, whereas on land you can save weight and just use two main wheels (or skis, but those are still much smaller than floats) but then you need a tail wheel to balance. $\endgroup$ – DKNguyen Aug 8 '20 at 1:18
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    $\begingroup$ Welcome to aviation.SE! Where the wheels are isn't relevant to an aircraft on floats so I'm not sure what you're asking. There are lots of J-3s and other 'tailwheels' on floats. There's even a DC-3 out there. $\endgroup$ – Pondlife Aug 8 '20 at 1:28
  • $\begingroup$ @Pondlife I think the OP is not referring to tail draggers that have been converted to have floats, but planes that literally drag something at the tail through the water. $\endgroup$ – DKNguyen Aug 8 '20 at 1:29
  • $\begingroup$ @DKNguyen Thanks, that does make sense and John's answer describes exactly that $\endgroup$ – Pondlife Aug 8 '20 at 1:31
  • $\begingroup$ Taildraggers are susceptible to ground loops. That’s bad enough on land, but much worse on water. $\endgroup$ – MD88Fan yesterday

It's been tried before (there isn't all that much in aviation that hadn't already been tried by WWII). The tail float means the aircraft CG is aft of the hydrodynamic center of the main floats, and like a tailwheel airplane, the machine will be dynamically unstable, steering wise, when on the step, same as a wheeled taildragger and you will have to prevent it from switching ends with your feet the entire time it's on the water moving.

It could be a real handful to take off and land, especially when there are waves and gusty winds (and seaplanes do have to cope with crosswinds from time to time). You have to make the rear float steerable, and you have to give it enough lateral bite in the water to have good leverage in steering the thing when below the speed that the air rudder is working. I don't think there is any drag advantage to 3 smaller floats vs 2 larger ones.

Traildragger advantages, like prop clearance, aren't that much of a benefit here, and since the conventional float configuration is so much easier to control, why bother with a taildragger float setup?

Ideas come along for new configurations all the time, but if you dig enough you find that somewhere in the distant past it's already been tried, and while it may have been functional, the "old" conventional way that everybody uses has been around so long because it's simply what works best.

enter image description here

  • $\begingroup$ So it kind of begs the question...why not take the same approach on land? Why is prop clearance not a problem on float planes anyways? $\endgroup$ – DKNguyen Aug 8 '20 at 1:31
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    $\begingroup$ When you start the takeoff run on a normal floatplane, you drive the nose up high with full aft elevator at the start until you start to come up on the step. So there isn't really the need to have the nose pointing up all the time. Also the level attitude when displacement taxiing makes you much less susceptible to winds. Tail low slow taxiing on the water adds a whole new flavour to the hazards. Water impingement on the prop on seaplanes (which does a lot of damage over time) is mostly a problem of taking off in significant chop when you are just getting started. $\endgroup$ – John K Aug 8 '20 at 2:49
  • $\begingroup$ On the airplane pictured, it looks like a wave could rip the rudder right off. Eeeek! $\endgroup$ – Bob Jarvis - Reinstate Monica Aug 8 '20 at 15:30
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    $\begingroup$ @DKNuygen The floats have to be big anyway, and because they're long the CoG nearly always lies within their footprint. You could, if you wanted, have a landplane with four wheels (roughly where the ends of the floats would be) on long legs which would sit almost horizontal at rest. But why bother? It'd be heavier than it needs to be. $\endgroup$ – BlokeDownThePub Aug 8 '20 at 16:19

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