Aerodynamics - thundercat racing inflatable

Discussion in 'Hydrodynamics and Aerodynamics' started by Roflhat, Oct 13, 2015.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    If blow-overs were an easy fix, it would have been adopted in racing circles. It sounds very dangerous in one of these things, without safety capsules and the like, to be tossed out at 60 mph.
     
  2. jimburden
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    jimburden Junior Member

    Imagine the smallest of the jet skis or like one of your boats pontoons. The engine could be placed low in the bottom of the bow, followed by the prop in a slot, followed by the fuel tank, followed by the operator fully enclosed and squatting or recumbantly laied back. The goal is to keep the weight low in the hull for self righting. The same ultra deep vees on the sponsons of your boat would slice through the higher waves instead of going air born, You would lean into turns like a racing motor cycle. 3 G turns might be a little much accept on very flat water but possible like ice racing motor cycles. the bow should have small hydrofoils to limit plunge depths through waves since now most of the weight would be forward of the hulls side and top area.
     
  3. whitepointer23

    whitepointer23 Previous Member

    They are race boats. Most powered by 50 hp tohatsu motors. Built for racing in surf. Not at 60 mph though.
     
  4. Roflhat
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    Roflhat Thundercat - 70.10mph

    OK, I think I can picture it now. It might be possible to add some poles behind the transom, placing the tail about a meter behind the transom and a meter over above the top of the engine, so as to give it clean air. The difficult part might be trying to keep it as light as possible. Would a spoiler similar to this but flat work? But wider and bigger, more similar to the hydroplace tail. Are the vertical parts neccessary for my application? I can see more difficulty getting them in place.
    [​IMG]
    If I extend the mounting arms to attach onto the transom. Then where the two bolts are on the side of the one pictured I could drill more holes above and beneath the rear hole so as to adjust the angle of attack.
    Here is a video of the world record holder, although this was a failed attempt.


    I see what you are getting at, but it's a completely different boat design. I don't see the design you're talking about being too good in waves. I have a fair bit of experience driving jet skis but once the sea starts to get rough the ride is very uncomfortable. The thundercat can go almost as fast in rough water as it can on flat, it rides on a cushion of air between the hijackers, so the ride is much more comfortable.
     
  5. powerabout
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    powerabout Senior Member

    some guys are racing them with old F3 OMC's powerheads that are over 100hp, crazy!
     
  6. jimburden
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    jimburden Junior Member

    The tail is a good idea as a retrofit as you see the traction wings on race cars.

    Moving the engine to the bow of your existing boat has the same effect in it makes the whole exisitng boat hull into a tail by placing the mass forward. A small set of forward slanting hydro foils mounted on the cavitation plate would lift the motor if it got too deep. The motor then becomes a turning centerboard or more appropriately a bow rudder like a front wheel drive automobile the the boat follows into turns. The whole skeg and upper works of the outboard would need to be streamlined since it is no longer in the shadow of the bow. Examples are the 1938 Van sized Fuller Dymaxion car, able to carry up to eleven passengers being front axle drive and tear drop streamlined with a ford V-8 of the day was able to beat a dirt track stock car speed record and do 120 MPH on the highway in 1938. It might be best to solidly mount the outboard behind a center hull looking similar to the outboard hulls.

    The difference between all jet skis and the single hull boat I am describing is greater width, frontal area, flatter hull Vee, lower efficency propulsion in a jet drive and higher center of gravity. No jet ski ever built was well designed. Only a few prototypes have fully enclosed the operator and tens of thousands of people world wide have died driving jet skis because of lack of protection from the elements. Sharper image had a submarine hydrofoil jet ski for sale that with not ultra deep vee approximated the small boat I was describing. There is not a prototype for this, not even close. On your semi rigid inflatable sea sled if you enclosed and tapered down to the bottom center plate the whole rear end of the boat you would gain about 10% to 20% in speed and more lift yet but the front drive engine would hold the bow down. I used a full 20 gallon gas tank about 150 pounds, as far forward as possible in the bow of our faster Vee hull to hold its bow down and give us more time on the water at 7 gallons and hour. Now I think about it at 65 MPH we could have traveled about 350 miles with the two rear tanks as well. Just remembring my high school years. Jim Burden Lincoln Nebraska
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    Huh ?
     
  8. whitepointer23

    whitepointer23 Previous Member

    Yes i know what you mean :confused:. I hope there are no legal complications if the op tries these ideas and gets injured or worse. Is that a concern with web forums ?.
     
  9. Grey Ghost
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    Grey Ghost Senior Member

    Jet skis are involved in many more accidents per hour than other boats - think of how they're used -- no surprise. Tens of thousands of fatalities is an exaggeration though.

    Example US stats:
     

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  10. jimburden
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    jimburden Junior Member

    I apologize for the over statement.

    The avaialble figures are not complete anywhere I looked after I made the foolish statement. In Nebraska alone this was the main cause of boating accidents and there were fatalities. My wife worked for the Nebraska Game and Parks commission for 23 years and we heard about the problem frequently. Exposure to the elements from taking off without cold weather wet or survival suits use to be a big problem according to a national magazine article I read a decade or more ago. For reasons not known to me the statistics under state deaths. I am still interested in fully enclosed all weather boats of all kinds and am curious how safety in boats would be improved with unsinkable self righting floatation. Cabin enclosures that can be opened for activities but closed for foul weather and going distances at high speed. Imagine motor cycles without helmets, cars without seat belts, open cockpit aircraft, no roll cages on race cars. Should not fast boats have some precasions? I know this is for another forum or thread.
     
  11. markdrela
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    markdrela Senior Member

    That should work. But you don't want any camber, and forget the endplates. I would also make a sheet-aluminum airfoil wrapper around each vertical strut. That should reduce the strut drag by 10x or so. At 65 mph, the max lift or downforce the tail can possibly see is about 15 lbs per square foot of horizontal tail area. Size the structure accordingly.
     
  12. markdrela
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    markdrela Senior Member

    Yikes!
    At max speed that thing looks like it's basically flying. It it was aerodynamically pitch-stable it wouldn't have flipped over.

    The yaw stability also looks sketchy, so I wouldn't skip adding vertical tail area as well. See my previous post on wrapping the mounting struts with sheet metal fairings, which will make fine vertical tails.
     
  13. jimburden
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    jimburden Junior Member

    The trailing wing would need similar lift.

    I think a trailing wing will need similar lift ahead of the center of gravity as the forward spanning hull section provides before in surface effect it starts to lift up. This is part of the reason even heavy multihulls have open nets instead of solid decks to keep the air under the hulls from overturning the boats. The lifiting advantage of a Russian Ekranoplan are many times the efficency of water planing and hydrofoils. You still bennifit from a surface effect wedge lift at the stern where most of the weight is. What about a spring loaded flap closing off the transom air gap? A previous suggestion that you cut out the deck back to the sitting area might be a good idea. All you need up front is an airfoil mast section to couple the hulls together at the bow. This foil might be variable in angle for trim to hold the bow down as on rail dragsters. The trailing wing is still a good idea and if it provides lift at a lower drag penalty than the hull's Vee steps then that might be a gain in speed as well as stability.
     
  14. markdrela
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    markdrela Senior Member

    No. The rear tail's incidence angle would be set so that it carries little or no lift. If it did carry a large fraction of the lift, then it wouldn't act as a stabilizer.

    The first primitive rule of an aerodynamically pitch-stable lifting configuration is:
    "The stuff in front must have a greater lift per square foot than the stuff in back"

    So to increase the pitch stability we must...
    * Shift CG towards the front
    * Add relatively unloaded surface area in the back
    * Both
     

  15. Petros
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    Petros Senior Member

    you want to kill the lift up front, not add lift in the rear (that may help keep it horizonatl longer, but if it is pitch unstable it will not help). the whole deck/hull/wing assembly should be looked at for dynamic pitch stability, a non-lifting rear foil may help there, but you need to know how the whole vessel will act in the ground effects of near surface aerodynamics before you can hope to fix it. IOW, how the pitching moment changes with changes in angle of attack. generally you want a negative change in pitching moment (nose down moment) for an increase in angle of attack, but damping may be important as well. The location of the center of gravity is critical too. A complex problem.
     
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