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Float Plane Sea State limiting factors, lack of outriggers?

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Float Plane Sea State limiting factors, lack of outriggers?

Unread postby flyinggibbon » Wed Jan 16, 2013 8:54 pm

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.

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Re: Float Plane Sea State limiting factors, lack of outrigge

Unread postby KlausNW » Thu Jan 17, 2013 10:19 pm

Which flying hull aircraft are you referring to?

The size of the aircraft has a lot more to do with how big of waves it can handle then whether it is float pantoon or hull type design.

For example, a Twin Otter can handle the same size waves as does the Grumman Goose. They're about the same size and weight category. The Lake amphib and the Cessna 180 are about the same size and weight but the 180 with the right floats can handle a lot bigger waves.

Maybe I'm just not understanding the question...
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Re: Float Plane Sea State limiting factors, lack of outrigge

Unread postby flyinggibbon » Fri Jan 18, 2013 12:47 am

Klaus,

The question is not really about flying boats vs floats, it's really about what defines the maximum sea state you can land in, is it float design, float volume, outriggers for stability, float length, aircraft weight or some other variable?

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Re: Float Plane Sea State limiting factors, lack of outrigge

Unread postby KlausNW » Fri Jan 18, 2013 9:08 am

The two biggest factors is how deep the "V" of the haul is and the over all size and weight. Obviously a PBY will land in bigger seas then a J-3 cub.
The common "V" is about 24 degrees. PeeKay floats have a deeper "V" and are known for being better rough water floats but, you have a longer takeoff run.
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Re: Float Plane Sea State limiting factors, lack of outrigge

Unread postby Rajay » Sat Jan 19, 2013 4:24 pm

KlausNW wrote:For example, a Twin Otter can handle the same size waves as does the Grumman Goose. They're about the same size and weight category.

They might be the same "category" (i.e. "small aircraft" 12,500 lbs or less) but that doesn't make them actually the same in terms of size or weight.

The Twotter is 13.5 feet longer and 16 feet wider (51' 9" vs. 38' 4" and 65' 0" vs. 49' 0" respectively) than a Goose and a basic G-21A grosses out at only 8,000 lbs (up to as much as 9,200 lbs with certain mods) whereas the earliest -1 series (1 prototype and 4 pre-production) Twotter started at 11,000 lbs and later versions went up to 12,500 lbs. The Goose had two 450 hp R-985 radials; the Twotter two 550 or 620 shp turbines - totals = 900 vs. up to 1,240. Also, the Goose was certified with only 8 seats total but some variants of the Twotter had as many as 24 seats (including crew.)

In general, those numbers add up to the Twotter being something like 35-40% bigger than a Goose - and yet doesn't handle waves as big as it does. From everything that I have ever seen or heard on the subject, the almost universal consensus on the reason why is because it is not a "boat" and instead has floats.

Not saying you're "wrong" - just that you could pick a better comparison for an example.
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Re: Float Plane Sea State limiting factors, lack of outrigge

Unread postby KlausNW » Sat Jan 19, 2013 6:16 pm

You're right those are not the best two under 12,500 aircraft to use for comparison.
What would you suggest as the best rough water under 12,500 lbs. gross seaplanes?
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Re: Float Plane Sea State limiting factors, lack of outrigge

Unread postby Rajay » Wed Mar 13, 2013 11:05 am

KlausNW wrote:You're right those are not the best two under 12,500 aircraft to use for comparison. What would you suggest as the best rough water under 12,500 lbs. gross seaplanes?


Sorry Klaus (in particular) but I really didn't have a good answer to your last question there. Maybe we have all been just taking this issue for granted and assuming the so-called “truth” of this issue was whatever we had picked up from rumor, second or third-hand stories, and “conventional wisdom” as the case may be.

I say that because after shooting arrows at your Grumman G-21A Goose “flying boat” versus DeHavilland (Viking) DHC-6 Twin Otter on floats comparison, it occurred to me that one answer to your question above might be the McKinnon G-21G Turbo Goose because it is rated up to 12,500 lbs just like the Twotter, but it is essentially no bigger than the original Goose (in other words, it is still significantly smaller than the Twotter) but maybe those facts only cloud this issue/question further!

As far as I know, from what I have heard from the many Goose pilots with whom I have talked and/or corresponded over the last 7 years, the wave/sea state capabilities of the 8,000 lb. Grumman G-21A and the 12,500 lb. McKinnon G-21G are essentially the same – up to 3 feet (which just so happens to tie in with and correspond to the aforementioned general “rule of thumb” of being equal to half the height of the “float” or in the case of a flying boat, the fuselage/hull itself.) At least that is how they are most frequently quoted – although several old-timers have chuckled and added commentary to the effect that the Goose can handle bigger waves than can the crew or passengers!

KlausNW wrote:Which flying hull aircraft are you referring to?

The size of the aircraft has a lot more to do with how big of waves it can handle then whether it is float pontoon or hull type design.

For example, a Twin Otter can handle the same size waves as does the Grumman Goose. They're about the same size and weight category. The Lake amphib and the Cessna 180 are about the same size and weight but the 180 with the right floats can handle a lot bigger waves.

Maybe I'm just not understanding the question...


I guess that a part of this issue that I am still having a problem with is your premise that a Twotter “can handle the same size waves as does the Grumman Goose” – it has always been my understanding, again based solely on what I have heard from dozens of other pilots over the years and not from my own personal experience, that even the 8,000 lb. Grumman G-21A Goose, which as we discussed earlier is 35-40% smaller and lighter than a Twotter, can still handle waves significantly larger than the Twotter can. (I’ve always heard that the DHC-6 on floats can handle waves only up to 18 to 24 inches.)

On the other hand, your comparison of a Cessna 180 on floats and a Lake amphibian may still be valid – but I would bet that it is not because the Cessna is a particularly good or exceptional “float” plane that is “better” than the Lake so much as it is because the Lake is an atypical (uncommon) “flying boat” with a particularly low freeboard that is easily swamped – and as such, it simply does not have the wave or sea-state handling capabilities typically associated with other flying boats. (I always want to make the “joke” that that is exactly why it was called a “Lake” and not an “Ocean” or a “Sea” amphibian!)

On the other other hand (you need a third hand to make this work) I recently had a conversation with a former colleague who until very recently had gone on to be involved with the company that acquired the type certificates for the G-111 (A22SO) and HU-16 variants (A33SO) of the Grumman Albatross (the company is Amphibian Aircraft International, Inc.) and he was telling me about his experiences in acting as a seaplane consultant around the world during the last couple of years and all of his first-hand experiences with Twin Otters, the Dornier Seastar, etc.

His impression of the Seastar in particular was that it was also not nearly as capable in terms of wave-handling and sea states as is commonly quoted by the marketing guys at Dornier. To him, it was another “Lake”-like flying boat. So how does that “data” fit into this discussion? In terms of size and weight, the Seastar falls in between the standard G-21A Goose and the heavier McKinnon G-21G or the much larger Twotter – so maybe those parameters are not the governing factors after all. It is noteworthy however that the Seastar seems to have a much shallower and wider hull than for example a Goose – on top of which its use of sponsons for balance instead of outrigger floats effectively makes the hull even wider and relatively more shallow. Plus, it too seems to have a very shallow freeboard.

It’s starting to sound to me as though the hull and/or float design parameters have more to do with it than anything else. A deep vee hull with a high freeboard seem to be the most important factors from what I am seeing and hearing. The “problem” with the floats on float planes is that they always fail on that second factor – freeboard. In the first place, they are primarily planning hulls, not displacement hulls, and even when they are operating in full displacement mode (during a slow taxi) they are effectively swamped or almost submerged and waves can impact over and down on them whereas a full displacement hull with a relatively high freeboard such as on the Goose effectively cuts through waves instead of riding over or under them.

One final point of speculation on my part – we have yet to discuss the factor of center of gravity in terms of the vertical axis. It seems to me as though any float plane is going to have a much higher center of gravity than will a flying boat of a comparable overall size and weight. It further seems to me as though that fact would have to have an influence if not outright impact on the aircraft’s stability in rough water.

What do you think?
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Re: Float Plane Sea State limiting factors, lack of outrigge

Unread postby 9aplus » Thu Mar 14, 2013 6:14 am

Guess we all can learn from best (modern) performer US-2, claiming to be capable to handle 3 m waves....

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http://www.shinmaywa.co.jp/english/guide/us2_index.htm

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Why such good performance, here:
http://www.shinmaywa.co.jp/english/guid ... bility.htm

Cost approx $80 M :elephant:
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Re: Float Plane Sea State limiting factors, lack of outrigge

Unread postby Rajay » Thu Mar 14, 2013 10:29 am

9aplus wrote:Guess we all can learn from best (modern) performer US-2, claiming to be capable to handle 3 m waves...

Image

Cost approx $80 M :elephant:

Interesting. I don't usually count the height of the vertical stabilizer when applying the "half the height of the float/hull" rule of thumb - just the main fuselage itself, which is comparable in function to the floats on a floatplane.

Just estimating it loosely based on that Shinmaywa diagram (and BTW - he's about to land in the water with his wheels down!) I'd say that just the fuselage of the US-2 appears to be about 4 - 4.5 meters in height (40 - 45% of the overall height of the aircraft) and as such, 3 meter waves would be much more than half the height of that "float" - more like 67 - 75%!!!

Once again, I'd bet that the oldtimer's insight might apply - the plane itself might handle those waves, but any crew or passengers would be throwing up and scared to death!
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