Pure speculation, await confirmation from others.

Amphibious aircraft are ungainly, and fly slower. Thus the drag from rivet heads is not worth worrying about.

and better pressure-sealing [water-tightness].

Regards, Wil Taylor

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what sort of skin thickness ? I suspect very thin, 0.04" ? (so no thickness for CSK)

I like the tightness suggested by Will, but I'd've thought we could seal a CSK ... but then I thought about the normal job a CSK rivet does (retain internal pressure (naturally closing the skin around the CSK), easily sealed on the high pressure side) as opposed to a rivet on a seaplane, sitting in the water (difficult to seal on the high pressure, outside, side, pressure is trying to open up the CSK).

another day in paradise, or is paradise one day closer ?

I'm willing to bet that somebody at NACA actually tested this... roughly 1935...

STF

Tension loads on the rivet heads may also be higher in the wet areas due to the water loads.

verymadmac,please explain,I don't exactly understand what water load you're talking about,hydrostatic,I'm assuming ?

I can't say I have been involved with floats or hulls but my thinking was that given the 800 fold increase in density from air to water the standard design assumptions relating to rivets may not completely apply. While NAS807 doesn't appear to include any suction cases (I didn't put an numbers in it to make sure), failure to get on to the step in glassy conditions, water loops & the like may allow suction to occur on the hull. Throw in a concave frame, and the resultant rivet loading is likely to be far more aggressive than normal aerodynamic loads.

A bit of googling shows this report which notes suction of 2 & 5 psi aft of the step on Sunderlands.
http://naca.central.cranfield.ac.uk/reports/arc/rm...


Another thought is that in inter-rivet buckling the fixivity of dome heads is 4 verse 1 for CSK's, under water loads this may reduce flexing of the skin relative to the rivet head/ frame, improving the durability of water tightness.

Interesting question. The first thing that came to mind was it is a legacy design issue, since many of the production amphibious aircraft with aluminum airframes were designed long ago. But looking at more recent amphibious airframe structures like the CL-415 or the US-2, it appears they do use protruding head rivets.

VMM, I see your concern,can say I never considered such,thanks for explanation.

Hey guys, thanks for all the replies. I was very curious to know this reason and I saw it on the CL-415 as tbuelna pointed above. It was not just at the bottom, but both at the top of the fuselage and the bottom of the fuselage.

It would appear that countersunk rivets are used in some applications, here is a repair manual for Wipeline floats check pages 52 to 62 with repair details.
B.E.

You are judged not by what you know, but by what you can do.

• http://www.wipaire.com/pdf/service_manuals/1002554.pdf