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?