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Dear All,

Pursuing the theme of "landing is a tougher nut to crack than taking off" on the basis that you can choose whether to take off but once you're up you've got to come down sooner or later: Does anyone know of any research into using parachutes to slow down seaplanes coming in to land?

The idea is to minimise the speed of the first contact between water and plane. If you could come down to say 40 knots 3 feet above the wave crests of some pretty rough water, then deploy the parachute, how much could you slow down before hitting the surface? I imagine the parachute being fitted somewhere in the tail as high up as structurally convenient to help maintain the high angle of attack.

The other option is to deploy the parachute from the top of the plane and come down vertically, an ideal solution from the rough water perspective, but as you are all aware that gives precious little control over where you land!

Regards, Max
 

StRaNgEdAyS

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very odd idea, but then I've come out with some odd ones myself...:gig:
I've only ever seen 'chutes used to slow high performance aircraft down after landing. I usd to watch the miracles land at Townsville all the time.
The miracles I refer to were the Mirage III fighters we had before they got the F/A18's.
They were refered to as "miracles" because it was a miracle that some of them were still flying.
 

Topaz

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I think I'd be more worried about what happens after you touch down on the surface: The parachute becomes an instant sea-anchor and rips out of the airframe, carrying away anything to which it's attached.

I know Rutan used small parachutes as lightweight in-flight airbrakes on the recent 'Virgin World Flyer', but that of course was a landplane.
 

Falco Rob

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The parachute becomes an instant sea-anchor
I agree . . even if you manage to land without stalling in or having your bum ripped off when the parachute stops you in your tracks, how do you retrieve a soggy mass of fabric and cord before it sinks and drags you down with it, or gets snagged on some underwater obstacle as you're taxiing to shore? (Assuming you have enough power to overcome the sea-anchor it has now become)

A novel idea, but I think I'd rather take my chances with a higher landing speed.
 
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Retrieving the soggy mess is easy - trip line attatched to the middle of the chute. Same as with parachute sea anchors - you mentioned the things first! I was more concerned with reloading the chute at the end of the tail without going for a swim.

Keeping the thing out of the water is just like keeping the prop out of the water - limit the diameter and mount it high up. What I haven't bothered to do is to figure out how much drag such a chute would give.

Flaps - good idea! Brings me straight onto the next question: Very few ultralight flying boats seem to have the things. Why? It's not as if their landing speed is all that low when regarded as the speed of a water craft rather than an airplane. Twenty knots is fast for just about any sailing enthusiast - hydrofoil and board sailers excepted - and for aircraft we're talking 40. I don't get the kittens about water landing for no reason!

Best Wishes,

Max aka explain it to me again please because I'm only a beginner.
 
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The catchy thing about a chute ... is that (a) slowing down using air is surely a much more controlled way of doing it than slapping into a wave and (b) the bit about if you mount a chute high up and a long way back you have a pretty insuperable force pointing the aircraft in the right direction - nose up and into the wind - at a time when the water is doing its best to buffet you all over the place.

Regards, Max
 

Rhino

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I still don't understand the original question. Is this for some type of emergency purpose? If not, I still can't fathom the need for a chute. Does your aircraft not slow down when you chop the throttle? If not, please share your secrets. Assuming you slow to just over stall speed when landing, what is the need to slow further? I know of no aircraft that will not continue to slow in level flight with no power applied. If you anticipate contacting the water below stall speed instead of above or at it, then you don't need a chute at all. A gun or bottle of pills would be a much cheaper way of commiting suicide, and they don't require you to build anything.
 

Falco Rob

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Hello, anybody heard of FLAPS?
Brilliant ! (Said in an Irish accent while holding a bottle of Guinness)

Now, where do ya think they should go . . . maybe under the fuselage and hinged at the trailing edge.
That should slow ya down on contact with the water.

Arthur, yer a bloody genius.
 

cgwendling

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I don't know if you are from the US, but the stall speed of US ultralights is 24 calibrated knots or less. That being said your approach speed should be no more than about 32 knots. You will flare and wait for the plane to settle, all the while it will be slowing. When you actually touch the water you should be right around 24 knots or less. I see no reason for additional slowing devices.
If you are from another place ignore all of the above.
:D
 

jgnunn

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if your plane is already getting close to stall speed during a landing, isnt releasing a parachute gonna abruptly reduce your speed past stall? - resulting in you falling like a brick, since the plane is no longer flying anymore...
 
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Exactly - but falling like a brick from three feet up and attaining a landing speed of 20 knots might be preferable to landing horizontally into the side of a wave at 40 knots. Maybe. Just an idea. I'd even be interested if it took me from 20 knots to 10. I know about water and it's that that I'm scared of, not falling out of the sky!

Best Wishes, Max
 
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ultralight stall speed 24 knots or below - thanks - useful number.

I've also started to find a few small float planes with fixed second foils below the trailing edge of the main foil. That is certainly an easy - to implement way of going about the problem.

Regards, Max
 

Topaz

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Well, flying-boat hull design is a fairly mature science. You'll forgive me (us) for scratching (our) heads, but building a hull that can withstand water landings at 20, 40, or even 60mph or better has been done successfully quite a goodly number of times.

Is there a particular reason you don't trust that well-established technology? Or perhaps you have a landing-in-big-waves requirement of which we're unaware?
 
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Landing in big waves is just about the only thing I'm interested in. Any statistics you have for aircraft and maximum wave height that they can come down in would be most appreciated.

The best that I've seen so far for a small(ish) plane is the Centaur that can supposedly come down reliably in 0.9m (1 yard) high waves and has an ultimate wave height of about 1.1m. Most 2-6 man planes where I've been able to get numbers have a wave height limit of something like 18 inches (0.45 m) which is much too small to be any use for me. Fine for a small landlocked lake but not for a loch open to the Atlantic at one end and carrying the swell of the last storm. The Centaur incidentally uses a modern hull design, not one of the 1950s breed flat planing hulls. Sailing hull design has moved on a long way since then. It's not like fencing where the art reached a peak but rather an active area of development where there are real breakthroughs every few years.

I am an experienced boater but fairly new to aircraft, so there are probably lots of things I ought to know about planes but don't yet. I'm trying to find out about all the tricks that can be used to improve rough water handling characteristics and then decide whether to plonk for a Centaur or try to make something better. There is probably enough researcher in my family to make the latter the preferred choice anyway! (Always a source of trouble, sometimes with terrific results!)

Yep, any wave height statistics, stall speeds, wing & float configurations etc received gratefully.

Regards, Max
 

Topaz

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Ahh, now I understand.

I don't have any explicit data for you - hopefully one of the members with direct experience in seaplane hull design will drop in on this thread - but in the meantime I might be able to point you in some useful directions.

I took a look at the Centaur website. Interesting design. Looks like a development of the Sea Knife hullform the USN was testing back in the '80's. IIRC, they had a similar need for high speed in relatively high sea states, but that there was some problems with stability. Hopefully the Centaur folks have resolved that.

One thing I would caution you about the Centaur is that they don't seem to have flown a full-size version of the design yet. It's encouraging that they've done some large-scale model work, but that's not the same as testing a full-size airplane. It's a sad truth in the small-plane industry that much is often promised before all the facts are in, with the result that many seemingly 'breakthrough' designs turn out to have flaws that take more time and resources to resolve than the company has available. Be careful with your money until the thing is proven and reviewed independantly.

As far as high-sea-state seaplane hulls, most of the work of which I'm aware has related to the use of small hydrofoils to lift the hull clear below the speed at which the wing can actually support the aircraft. The only reference I was able to find on the web was:

Levy, Howard, "HRV-1 Hydrofoil Amphibian," Air Progress - The News Magazine of Aviation, Condé Nast Publications, New York, Feb 1968, vol 22 no. 2, pp. cover, 38-39, 73-74.

They included an excerpt:

"... the hydrofoil seaplane can operate in sea states three times the size safely handled by a basic seaplane... For almost five years, David B. Thurston, President of... Thurston Aircraft Corporation of Sanford Maine has been conducting relatively unpublicized hydro-ski and hydrofoil development and flight evaluation programs for the US Naval Air Systems Command (NAVAIRSYSCOM)... It was during Spring 1964 that the Naval Air Test Center at Patuxent conducted an evaluation of an Edo-developed Grunberg hydrofoil on a Grumman JRF-5G... A second generation seaplane hydrofoil configuration called for a single, small foil positioned below the hull. The resulting design was a single supercavitating, penetrating hydrofoil considered suitable for use on the Grumman Hy-16 Albatross... a modified 1960 Lake LA-4A Skimmer amphibian was chosen as a scale flight test bed."

If you're serious about doing your own design, it might be worthwhile contacting David Thurston about the hydrofoil technique.

Other ways of accomplishing the same goal included hydroskis, test flown on the Convair Sea Dart supersonic(!) jet seaplane fighter. Photos here They never did resolve all of the ski problems, but they might be more tractable with a smaller, lighter, slower aircraft.

Depending on your range and speed requirements, however, it might be more profitable to look into a helicopter or STOL landplane, since they avoid the wave-height problem altogether.

Good luck, and I for one would love to hear more of your project as it develops
 
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orion

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Small craft operations are rather difficult to accomodate with some of the technologies mentioned, simply from the standpoint of servicability and damage tolerance. For instance, I do remember reading some of Mr. Thurston's work, as well as research done by several Naval laboratories and other technical research centers, including work done at several high end tow tank facilities. In all cases the work was specifically pointed at larger amphibious or hull-borne craft and in virtually every case it was evidenced and admitted that the technologies would have limited application to smaller, general aviation craft.

Imagine the hydrofoil hanging down below the hull on a small airplane. All it would take was either a hiddeen sand bar or mud bank, or a semi-submerged deadhead (log), or even an area of dense underwater growth near the surface, to ruin your whole day. When applied to larger vehicles, this is not so much an issue since they would be landing well out away from the shore, then taxiing in. As such, hidden shallow spots or debris would not be an issue. As for submerged logs, the structures would most likely be substantial enough to take a certain amount of impact (up to a specified diamter), beyond which they would have to brake loose in a very predictable manner.

In a small aircraft this is not as workable since even a small impact could cause damage to the primary flotation. And then you have the issue of load balance between that imposed by an impact and tht imposed by a typical landing. Here the two loads are much closer together than what you would see in a larger, commercial size aircraft.

And so the most common configuration is the more conventional hull since it does have an inherent capability of skimming over shallow areas or even submerged logs, with little or no damage.

The Centaur uses an interesting hybrid hull but the configuration is certainly nothing new or revolutionary. The basic shape is based on work that dates back to the eary fifties. Generally the shape is refered to as a wave-piercing design and is characterized by a long, sleek, narrow beam loft that can achieve some pretty impressive speeds without transitioning to the more classical planing configuration. However there are a few drawbacks, especially at higher speed and so the Centaur combines this idea with a more convetnional concept, that of the hydro-ski. The ski surfaces are evidenced by the longitudinal steps in the hull. This provides the hull with a level of planing capability, something which the wave-piercing hull by itself does not have. The unique feature therefore is not so much the technology but more so the combination of the two. The system does have patents but I'm not sure how well they'll stand up here in the US since the technology and the combination has been researched and published here in the US thirty to forty years ago. I don't remember the exact documents but I do recall on a nmber of occassions seeing the configuration in several reports as I was gathering data for one of our contracts about ten years ago.

As far as the Sea Dart is concerned, that was a failure from day one. Yes it did work, sort of, but the ski design was of the wrong type so at the start of the run, rather than trying to achieve a planing attitude, the skis actually sucked the airplane downward, deeper into the water (they were convex rather than concave and additionally, they created a low pressure field on the aft end of the airplane while in the water - notice the extremely high aoa on take-off). Their angle was also very far off from optimal (optimal is about 4.5 to 7 degrees or so).

However, given your sea state requirements, it is possible that some form of optimized hydro ski, or ski/planing hull combination, just might be your ideal solution.
 
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