Hydrofoils

Discussion in 'Bush / Float flying' started by everyman_flight, Nov 11, 2005.

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  1. Nov 11, 2005 #1

    everyman_flight

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    Dear All,

    Is anyone aware of any seaplanes or amphibiamns that use hydeofoils to get them off the surface of the water? Reasons for using them or not using them would be most interesting. I am surprised that none of the designs I've seen so far use hydrofoils, whilst in the meantime Longshot, the comparatively small world speed record holder for a sail powered boat is a trifoiler.

    Regards, Max.
     
  2. Nov 11, 2005 #2

    RCMusall

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    My Dream Flying Boat

    For sometime now I have been looking for a flying boat that fits my wants with little or virtually no success. Consequently, I have been dabbling in designing my own. As a part of the development process I also have been considering hydrofoils as a means of easing the transfer from water to air, and even more importantly, the reverse. My design evolved into a low wing pusher canard aircraft.

    Surfing the web to see what has already been tried, I found the Merganser, such a craft, designed, built and flown by a naval architect, who primarily designs and builds custom yachts. During my discussion with him, he related that the craft flew great, but landing was a rather exciting event. I did not pursue the comment, but my impression was that when landing with a high angle of attack to reduce speed there was a rather abrupt and exciting change of attitude. This was a problem I had envisioned and was considering, and still am, the use of retractable hydrofoils to alleviate.

    I am now at the decision point of whether to proceed with my dream flying boat, or refine/redesign a partially built Adverturer kit flying boat I recently bought. That and resolving some personal problems will allow a start on my project and the possible use of hydrofoils.

    I would be interested in any pertinent info on hydrofoils that anybody might have.

    I have already searched the NASA and NACA archives, and have tried to find info on naval research, but I still lack any specific design information.

    I have some interesting photos of some of the navy ships on hydrofoils, but it appears the idea was abandon. See attached photo.
     
  3. Nov 11, 2005 #3

    RCMusall

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    Hydrofoil Naval Boat

    For the photo see my member gallery photos
     
  4. Nov 11, 2005 #4

    Topaz

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    It's been done - successfully - but I'm at work and don't have access to any of my references.

    You might check up on some of Thurston's work. I seem to recall him doing some work with a small hydrofoil, but I could be wrong about the guy.

    There was even an Italian plane for the Schnieder Cup that had no floats, only foils. There was a water-prop at the back and a conventional air-prop at the front. Both were clutched to the single engine.

    When you wanted to take off, you clutched the engine to the water prop and accellerated until you got up on the foils. Then you clutched to the air-prop (which was out of the water at that point), and continued accellerating to takeoff speed on that.

    I know they never competed in the final race (this was just prior to WWII), but I seem to recall that it did have some successful test flights. Might be wrong on that last score, though.

    Wild looking thing. I'll post a link if I can find one.

    Edit:

    Turns out it was a Piaggio product, the 'Pegna PC7'.

    Here's a link to some good pictures of the thing.

    And some anecdotal information about midway down this page.

    Apparently it never actually flew, due to driveline problems.
     
    Last edited: Nov 11, 2005
  5. Nov 11, 2005 #5

    StRaNgEdAyS

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    I'd also wonder how hydrofoils would cope with the stresses of landng on water.
    Most of the hydrofoils I've seen are fairly slender items, I seriously doubt they'd handle the impact of the water on landing for very long. You could of course make them retractable, but then that's extra complexity and weight.
    The aircraft's wing itself would do a good job of gradually lifting the hull, as hydrofoils require the boat to be moving at a fair clip before they become effective too, and until that speed comes about they create quite a lot of drag.
     
  6. Nov 12, 2005 #6

    everyman_flight

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    Abrupt change in attitude - I kind of expected something like that! I am under the impression that one of the biggest problems with a float plane is that necessarily there is quite a lot of drag low down in the form of hull, floats or similar, and the engine has to be kept high and well clear of the water. Both give a tendency to nose-down. A hydrofoil is (seemingly) necessarily always below the hull, giving even more leverage to said tendency.

    I thought Hydrofoils would suit the Centaur very nicely. Her hull is of a type that copes with a rough sea very well - she's my current darling and the only real alternative to coming down by parachute writes he kidding only slightly - the tradeoff being that she takes a bit longer to take off. Yet her centre of drag when in the water wouldn't be changed much by hydrofoils. I think - I haven't done any calculations or trials yet.

    Regards, Max
     
  7. Nov 12, 2005 #7

    Topaz

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    IIRC, Thurston was using a rather small hydrofoil under a conventional planing hull to increase the swell height that rather small airplane could handle. That is, the airplane would still be partially supported by the 'foil, yet the nose of the planing hull would be higher off the water and thus be able to handle higher swells, as in the open ocean.

    I think the big problem with hydrofoils is probably weight, although you'd want someone like Orion to make sure of that. From my point of view, having hydrofoils does not reduce the need for a strong (and therefore heavy) hull bottom, since the water/waves are still pounding at the thing until you're foilborne. I suppose that condition would occur at a lower speed than a pure planing hull, but it's only a matter of degree. Since you have to have the reenforced hull anyway, the weight of the foils becomes extra weight that you could do without if you just went to a conventional planing hull.

    If you have some specific need for a small plane to land and take off from large swells, then perhaps the extra weight of the foils is justifiable.

    If the option is foils vs. floats, then obviously there are huge drag and weight savings to be had (a la the PC7 above), if only you can figure out how to keep the prop out of the water.
     
  8. Nov 12, 2005 #8

    orion

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    We investigated hydrofoils in depth for use in the take-off and landing modes for application to wing-in-ground effect craft. While some of the characteristics are quite beneficial, there are several drawbacks.

    The first has to do with speed - the configuration that would probably be required for most airplanes suffers some efficiency at lower speeds, just when you need the foils to push the hull out of the water. This would require the wings to be bigger, creating more drag and possibly making them a bit ungainly to retract, and so on.

    The second issue is damage. The hanging foils coud be easily damaged. Furthermore, even a small impact could siginifantly damage the integrity of the airplane's hull, unless of coures you built it like a tank. But then there's the weight.

    And third, the major performance issue is the point where the foil starts nearing the surface and the top of the foil starts getting ventilated. At that instance the foil suddenly looses fifty to sixty percent of its lift force, and thus the suspended weight drops back into the water (this ususally causes a very humorous porpoising action, which can lead to significant damage if not arrested quickly). This makes the design of this type of system very critical sice you have to balance the foil design with the power, the take-off parameters, the issues of trim, etc.

    In other words, not a simple exercise.
     
  9. Nov 15, 2005 #9

    Othman

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    During my graduate studies I authored a thesis on a new waterborne aircraft type/technique called the floatwing.

    The floatwing concept was conceived and patented (being patented) by Ray Richards of Aquavion Systems Corp in Ajax, Ontario, Canada.

    The floatwing is a novel concept that utilizes the wing for buoyancy and for planing, and does away with draggy hulls or floats.

    A few RC models have been successfully tested to prove the concept, and development is underway for a full scale prototype as we speak.

    I've asked Ray to sign up to this forum and give you more information soon.
     
  10. Nov 24, 2005 #10

    aquavion

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    Hello everyone..this is my first post so please bear with me. As Othman has related to you, my company has been developing a new type of seaplane, officially since 1996. Mr. Othman was instrumental in getting the proof-of-concept aircraft operational and in performing wind tunnel testing and stability analysis for this aircraft and is an exceptional aeronautical engineer, both theoretical and practical.

    There were many, many iterations of configurations for this design and at one time I seriously considered the use of hydrofoils as utilized in the Piaggio racer that was mentioned in this forum. I don't think that the very serious matter of loss of lift due to cavitation was mentioned here but this was the reason we opted for another solution, that being the use of a hydroplaning wing. Cavitation occurs when the upper surface pressure of a highly loaded hydrofoil falls to the pressure at which water boils at local water temperature. Under these conditions, separation with loss of lift and much increased drag occurs...the hydrofoil "stumbles" and the craft slows under the increase in drag. During the 60's there was a tremendous rush to produce hydrofoiling watercraft but the cavitation limit (occuring around 50-60 mph at best for most of these craft utilizing "super-cavitating" foils) was most likely one of the reasons that hydrofoils were not utilized for aircraft water takeoffs and landings although Thurston was apparently sucessful with a "skimmer" aircraft he used for some demonstrations but these never saw production in this form.
     
  11. Nov 25, 2005 #11

    orion

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    .. actually I mentioned it in my last post. The phenomenom is refered to as cavitation, ventilation, as well as one or two other titles.
     
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  12. Nov 25, 2005 #12

    Othman

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    Welcome to the forum aquavion. I’m sure we can benefit from your knowledge and experience. I think you’ll also find this place to be a great resource, as it’s always nice to get advice from those who have “been there, done that”.

    By the way, thanks very much for your kind words :)
     
  13. Nov 25, 2005 #13

    Jman

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    Welcome to the group Aquavion.

    Any chance you could post some details of your endeavor in the Manufactures Announcements area? I'm sure I'm not the only one interested in new seaplane designs. I wish you the best of luck!
     
  14. Nov 26, 2005 #14

    aquavion

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    Thanks everyone for your welcomes. This is a great forum to learn from and possibly contribute some kernels of knowledge and experience gained as well.

    Yes, Orion you are correct in saying that the use of the term cavitation is often used interchangebly with the term ventilation however it is generally accepted that these two terms are in fact separate and distinct phenomenon.

    http://www.propline.com/Propeller-General-Information/Propeller_Terminology.htm
     
  15. Nov 26, 2005 #15

    aquavion

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    Opps...I ended the previous post too soon (just waking up here this morning folks!!)

    The cavitation problem that I was referring to can occur when a highly loaded hydrofoil travelling at relatively high speed and at a depth of several foilspans to ensure the generation of upper surface suction lift, is suddenly rotated for example, to a higher angle of attack (less than the stall AOA) to provide rate-of-climb lift to the craft it is supporting. Under these conditions, the upper surface pressure can fall to the vapour pressure of water causing local "boiling" and hence loss of lift. The term ventilation is usually used in the context of the upper surface of the hydrofoil being close to the water surface where it can entrain air (as Orion has mentioned in his post) or where air is purposely introduced for example into the "steps" of hydroplaning hulls of both aircraft and boats to reduce the dynamic coefficient of friction.

    In any case, this is maybe a moot point since the overall result is the same....sudden loss of lift and and increase in drag.

    Thanks Jman for your suggestion and encouragement....I will have a look at the Manfacturer's section for posting.

    Ray Richards.
     
  16. Nov 26, 2005 #16

    Jman

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    Is the likelihood of cavitation happening directly linked to the amount of lift the airfoil is producing?

    Believe me when I say that I know absolutely nothing about hydrofoils but I was curious if you could design a hydrofoil system that actually reduces AOA of the hydrofoil as the aircraft speeds up and the wing of the aircraft begins to take the load?
     
  17. Nov 26, 2005 #17

    orion

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    Aquavion, thanks for the clear-up of the terminology - I've worked on several hydrofoil application progams now and have generally used the ventilation term in connection with the foils and cavitation only with props. But in our applications the ventilation term was more applicable to some of our operating parameters. Cavitation was of a little bit less concern. Oh well, live and learn.
     
  18. Nov 26, 2005 #18

    aquavion

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    Yes Jman, I think it might be possible to develope a variable AOA system to reduce hydrodynamic lift as speed increases with the hydrofoils becoming unloaded by the wing above. The aerodynamic lift-off or stall speed of the aircraft would probably need to be less than 40 mph (just a guess here) since the hydrodynamic drag of the hydrofoil(s) and in particular their support struts could represent a huge amount of drag due to the 800 times more dense medium through which you are trying to move them, cavitation problems aside. Barracudas can only sustain 40-50 mph bursts of speed for very short periods of time with high energy burns during the feat. I guess with a big enough engine and gas reserves this would be possible although I have not done the calculation. I rejected the use of hydrofoils ultimately on the more practical basis of their susceptibility to damage or picking up weeds (which BTW can really increase their drag coefficient) and the potentially disasterous results of a "stumble" or maybe even a "tuck".

    Thurston although seems to have achieved something along these lines with his "Skimmer Amphibian" which utilized a single strut ( Oleo or some such shock absorber included) attached to a fully submersed hydrofoil located (I think) at the cg of the aircraft. I don't have all the details but one objective of the study if memory serves was to determine whether the shock mounting was effective in reducing impact loads when alighting on the surface of the water, which apparently it was.

    I hope I have contributed to the answer to your question.
     
  19. Nov 27, 2005 #19

    everyman_flight

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    Is that speed for barracuda the fish or Barracuda the torpedo? The number I read for the torpedo was of the order of 800 km/h (roughly 530 mph), although the Diehl website itself only admits to "over 360 km/h", more in the ball park of the old Soviet Shkval. I haven't heard of a US version but that might just be because it's strictly under wraps.

    morgenwelt - in German I'm afraid

    Diehl - German again

    wiki - less informative but at least it's in English - and refers to a US research lab

    The B. has a cavitating nosecone and the cavitation bubble is expanded to surround the rest of the torpedo using some of the rocket exhaust. When the torpedo was first announced I did look hard for a range but could find none quoted. I looked again a couple of days ago (prompted by this discussion) but still nothing. Supposed uses include anti-torpedo and anti-submarine (presumably having travelled the majority of the distance by air) neither of which has much of a range requirement but I don't actually know. If I did I probably wouldn't be allowed to tell anyway!


    Best Wishes, Max

    ----------

    Famous last words: Shkval reportedly has a range of 7 km and China has bought 40 of them.
    here

    I am painfully aware of how much this posting relies on unreliable sources, but what can one do?
     
    Last edited: Nov 27, 2005
  20. Nov 27, 2005 #20

    everyman_flight

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    By a tuck, do you mean pitching forward and burying the nose in the water? That which multihull sailors call undercutting?

    Orion mentioned the existence of "serious disadvantages" in using long slender hulls at high speed. Can you expand on that?

    In the sailing world I understand that the most significant changes of the last 10 or so years have been:
    1) The design of catamaran hulls (long & slender) that rise partially out of the water and plane without the aid of external foils.
    2) Catamarans equipped with hydrofoils. (current speed sailing record, also the commercial hobie trifoiler)
    3) Surfboards that are both short (small wetted area hence fast) and stable (the two apparently didn't use to go together).
    4) More variable geometry below the waterline on monohulls, with canting keels for better ballast positioning and different arrangements of lateral resistance foils. The ability to control complex arrangements is better thanks to smaller cheaper and more powerful electronics. (Not relevant here but significant in terms of how long it takes to sail around the world.)

    It seemed sensible to look at sailing hydrofoils rather than powered ones because fast sailing boat territory is 20-40 knots and the upper end of that is about the stall speed of a small conventional plane. I'm not hoping to build a supersonic plane with a 160 knot take off speed, exciting though that would be!

    The impression I get is that people have tried hydrofoils on planes and haven't had much luck. Thanks for the details! It's a pleasure to communicate with people who know their subject matter as well as you do.

    Regards, Max
     
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