Fact or fiction? Is it possible to load an amphibian till the floats are both submerged and still fly the aircraft? It sounds unlikely to me, however I have friends that swear its true.

172heavy wrote:Fact or fiction? Is it possible to load an amphibian till the floats are both submerged and still fly the aircraft? It sounds unlikely to me, however I have friends that swear its true.

Assuming you're talking about a twin float amphibious float plane? If so, and if both floats are actually submerged, you are now sinking. Last I checked, submarines don't fly for shit.....

Now, I have seen some floatplanes where the floats are riding pretty low in the water, and were still able to get airborne, but the floats were definitely not submerged.

MTV

172heavy wrote:Fact or fiction? Is it possible to load an amphibian till the floats are both submerged and still fly the aircraft? It sounds unlikely to me, however I have friends that swear its true.

That represents an incredible amount of drag to overcome in order to get airborne... This is a pretty good illustration of what I'm talking about:

Wow. No thanks.

I have a friend whose family runs a float operation on Vancouver Island in British Columbia called CoVal Air. He told me that they have actually started the takeoff run in Beavers where the floats are almost completely submerged, as in the top of the float was just at the water level.

I wasn't there to see it, and I have zero float experience, but that is the story I was told. Float experience or not, it sounds like pretty poor judgment to me.

Since water pressure increases the further below the surface you go, the buoyancy created from a fixed volume of air should increase as that volume sinks deeper below the surface. So, it stands to reason that (assuming they are water and air tight) the floats would not sink like a submarine once they are weighed down underwater, but merely rise or fall until reaching their new neutral buoyancy level.

Since we have some very experienced float pilots on this forum, and I believe we even have a former submariner, they can feel free to correct me if my physics have eluded me.

With my little bit of SES experience obtaining my add-on this past July, there was so much emphasis on keeping the bows of the floats up that I can't imagine loading so much that they would be at or below the surface:

*I was taught to taxi slowly, with full aft elevator.
*The take-off run was likewise begun with full aft elevator.
*If the take-off was rejected, full aft elevator upon chopping the throttle.
*As soon as the floats touched on landing, the elevator was smoothly brought to full aft, again.
*My DE got on me for too slow an approach speed during the engine out exercise, because that would mean less elevator to make sure that the bows were raised.

All that FWIW.

Cary

The way I looked at it is once the float is under water it can’t displace any more water, thus they have reached there limit of buoyancy, it then stands to reason that if the center of gravity is higher than the submerged float, the aircraft would role over , the video of the Fire Boss attempting to maneuver with the floats riding low in the water is further evidence that this is a myth.

Now for the second half of this tall story: the gentlemen claims that while he was in a full arm and shoulder cast he rented/piloted and flew a Beaver, loaded in this configuration, Is there any one that would conceder renting a Beaver to a pilot in a shoulder cast? Is there any one in Alaska that rents amphibious Beavers? Total BS I think.

I'm not a float plane pilot but I am an engineer dealing with subsurface soil and water conditions. Buoyancy is all about displacement volume; once a closed vessel is submerged it cannot gain buoyancy unless it encounters a fluid with greater density. Water is essentially not compressible for the example of an aircraft float in fresh or salt water, so fluid density is constant. Water pressure pushing down on the top of the submerged float would counteract any increased pressure on the bottom of the float, so no benefit from increased water pressure. In fact, the increased pressure on the float would cause it to be gradually compressed so it would lose volume and buoyancy as it sinks further beneath the surface. I call BS on amphib ops with submerged floats.

With some airframe/float combination, loaded heavy, water will actually come over the top of the float if the pilot doesn't hold full aft elevator. The Maule on Aqua floats comes to mind.

They LOOK like they're going to submerge, but they don't....the aft portion of the float is still well above water.

BUT there are other issues with this: Floats are designed to be water tight on the bottoms and sides. But the tops of the floats contain pump out fittings, and while these are plugged, they will leak some water if submerged.

Bottom line, though is if the floats were actually submerged, the water would flow over the tops, creating as much "negative lift" as the bottoms create lift.

And, the airplane would have to be loaded so far over gross that the likelihood of flying is near zero.

And, yeah, sure, in Alaska, there are all sorts of places that'll rent a Beaver to a guy in a cast......

Tell the guy to talk to his doctor about getting some Valium.

MTV

Zero float experience but plenty of underwriter experience. If the floats are totally submerged then it stands to reason the plane will be totally submerged a short time later.

Oh and some subs can fly http://www.youtube.com/watch?v=JrU0bYq7KPQ

WTF cammo an a sub. Must be so yo can hide from the Chief of the Boat.

Tim

If you believe him..I've got some ocean front property in AZ for sale!

qmdv wrote:Zero float experience but plenty of underwriter experience. If the floats are totally submerged then it stands to reason the plane will be totally submerged a short time later.

Oh and some subs can fly http://www.youtube.com/watch?v=JrU0bYq7KPQ

WTF cammo an a sub. Must be so yo can hide from the Chief of the Boat.

Tim

Man, I never liked those emergency blow tests......always a big list on the surface till they'd get some low pressure air to equalize the tanks......

MTV

General rule from memory... was MAYBE the aft 20% of the floats might be getting wet when fully loaded. And then on a non-windy day.
Taxi out with a float actually submerged... well, the first three letters tell you what you are driving.
The letters BS tell you what your "friend" was full of. And, as mentioned... one of the non glamorous duties each day was pumping out each float compartment.... with a hand pump. The tops have holes and rubber balls in them. Not the way submarines are built. On a boring day, you could count the rivets though. That would keep you busy for a while...

Anybody notice in the you tube video that was about the Virginia Class boat it showed a fast attack doing an emergency surface. It is done at flank speed from about 400 feet, blow ballast tanks, full rise on the stern planes and full rise on the fairwater planes and up you go. but the Virginia has no fairwater planes. Must be a Permit, Sturgeon, or LA Class boat.

tim

We did it from test depth...594 class. I didn't like angles and dangles... Scammed the reactor and blew the main seal of the starboard SSMG. Spent about 12 hours in the surface fixing that. Engine room was sure quiet!