Float Plane Sea State limiting factors, lack of outriggers

[flyinggibbon]

Obviously having too much time on my hands, I was wondering why boat-hulled planes can land in far higher sea states (Beaufort scale) than twin float planes?

Is it due to the design of the floats i.e. their V hull is not deep enough or the length of the floats (both things which in normal vessels affect ride), the lack of volume in the 2 floats as opposed to single hull or indeed the surface area in connection with the water, the fact that aircraft weight is generally lighter for a floatplane or is the fact that generally floatplanes do not have outrigger floats to stabilise in Bad Weather?

Thanks in advance.

Best

FG

[High and Behind]

There's a lot more structure in a flying boat than in a float having said that the hull is just like a big float.
The struts and bracing are the weak point in the float plane.

Not out of the realm of possibilities to snap a gear leg fitting in big water.

The volume isn't really issue it's where and how the load is being exerted on the airframe.

In a boats case the hull is the airframe. Floats are merely an appendage. And like all appendages sometimes they break.

Wing floats are for stability at slow speeds.

[LousyFisherman]

Center of gravity is a lot lower, increasing stability

LF

[182-SS]

High and behind pretty much summed it up. Just to add to that, Your right regarding the deep V, a deep V handles rough water significantly better. Eg. In the case of say, a Cessna 185, the Cap 3000 floats with the deep V make landing in a 2 foot chop do able with minimal abuse to the machine and the pilot/passengers whereas if you had the EDO 2960 in the same rough water it is so jarring and rough that you may scare some passengers and/or eventually break something on your machine.

Weight and displacement is a contributing factor, the fact that a flying boat with its single hull has the entire weight of the aircraft cutting through the water with the single V whereas a float plane is spreading its weight and water displacement and the ability to use the V’s to cut through the waves over 2 floats which may or may not be hitting the same wave at the same time (as waves are not always uniform)

[Cat Driver]

The answer to this question is not all that cut and dried because all flying boats are not the same when it comes to landing on rough water.

As an example the Cessna 185 on floats will take bigger waves than a Lake Amphibian.

And many flying boats are wave / swell limited due to their propensity to porpoise.

[LousyFisherman]

As an example the Cessna 185 on floats will take bigger waves than a Lake Amphibian.

Interesting, what are the specific reasons in this case Cat?. Does a 180 have the same advantage?

And many flying boats are wave / swell limited due to their propensity to porpoise.

Thank you, some of us are still learning from you

LF

[Cat Driver]

Interesting, what are the specific reasons in this case Cat?. Does a 180 have the same advantage?

Any small float plane will have better rough water capabilities than the Lake Amphibian due to the ability of floats to cut through the water compared to the wide flat hull of a lake, also the Lake has a high thrustline and should the pilot get into a power changing scenario trying to control pitch changes on rough water it can and does add to pitch instability and increased porpoising to hull breakup..

[Cat Driver]

I see the mods have cleaned this thread up and it is now only addressing the subject....

....soooo...

I am going to add a bit more to the discussion in the hope some here will get a better grasp of why flying boats and float planes have different handling characteristics.

The biggest differences between the two types is due to having far more hull in the water the flying boat can and does poropise if the attitude on water contact is not correct.

Note:

Each flying boat will have different water handling characteristics due to the hull shape, for instance the Grumman Widgeon is a real bitch for proposing on rough water whereas the Sea Bee is rather docile on rough water as far as its porpoising is concerned.

So in the KISS mode of explaining why flying boats porpoise.

If you contact the water on landing with the nose attitude to high the aft section of the hull back of the step will contact the water first resulting in the nose pitching down, the fulcrum point is the step around which the pitching movement has now started.

As the nose pitches down the bow of the flying boat will be forced into the water with the result being it will be forced back up out of the water and the upward force will instantly be transferred back to the aft section of the hull with far more force than the first water contact and once again the rocking motion will be nose down and the bow will dig even more forcefully into the water .......you now are into the start of porpoise number three....which in most cases will be your final porpoise for that adventure...

in big flying boats such as the Catalina with which I am most familial with the airplane now breaks up and generally is a fatal event.

**********************************************************************************

There Damn it I posted something that may satisfy even my most ardent foes here on Avcanada.

Now I am going back in the garage to work on the Cub.

[bgandrews]

Thx Cat!

[Cat Driver]

Every once in a while I go into the deciding to post helpful info mode..

I have two distinct teaching modes.

Mode one is when I teach for pay I am not interested in working for peanuts as I believe in the fair reward concept.

Mode two is every once in a while I sense that someone here is truly interested in learning how these things really do work...and occasionally I try to explain it in the most understandable of terms.

[CLguy]

Well Cat you are correct in a large flying boat such as the PBY but when you look at the CL-215/415 porpoising is pretty much a nonevent. I remember the days on the PBY having Captains terrified of getting into a porpoise. Today's flying boat Captains don't even think those thoughts!

[Cat Driver]

Good morning CL.....are you still flying the 415?

Eventually you will have to retire like Driving Rain and I did...but I guess you are still a puppy compared to us.

Yes I understand the 415 is far different from a PBY and I hope the people who read this also read what I wrote...not all flying boats handle the same as it is dependent on hull shape for their hydrodynamic / aerodynamic characteristics.

The most exciting for proposing for me was the Widgeon, the PBY was only a problem if you let it get out of control.