Flights of fancy

Discussion in 'Boat Design' started by CanQua, Sep 24, 2009.

  1. CanQua
    Joined: Jul 2008
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    CanQua Junior Member

    I was recently discussing airships and a point was brought up as to why there were no wooden versions as imagined in books and movies. Of course it was brought up that wooden boats are extremely heavy. Then, being in composites myself, I started to really wonder what modern materials could be used to create the inhabitable part of an airship.

    So imagine if you will for a moment, the possibilities of building a ship, which by design was made to travel, not in water, but in the air. You want the lightest possible weight that can stand the stresses of being blown about a bit, and stable enough points for landing. You also want the styling of a turn of the century(last one, not this one) wooden. Brass and elegance if you will. Streamlining is an added bonus, but not the largest concern as air is just a tad less dense than water.


    This is a p-791 being developed by lockheed martin. First photos are from 2007. If you want to google the images there are many more now.

    [​IMG]

    Of course aesthetics were not the concern, as with almost any military vehicle. There are so many balsa cored composites boats, that it only seems natural to use similar materials focusing on the beauty of a classic ship. Skinning one with natural wood would indeed add to the weight, but it's more than acceptable for the look. Not a veneer, but not necessarily a structural part of the overall composite. And not being concerned with righting the boat so to speak, as the cabin area is now the technically the keel.

    I'm curious as to the lightest weight some of our designers here think would be a possibility. I'd ask the LTA(lighter than air) groups, but I don't think their collective knowledge is as dense as the population we have here. Hoping the sheer number of knowledgeable poeple we have accessing the forums here would lend me a bit of their thoughts. No offense to the airplane communities, but I beleive there are boats that are far above and beyond anything that was ever put into the air for pure beauty. The worst forces acting on the design would be those that you force upon it with whatever power source you decide to impliment.

    So if you have a boat design you've modeled, what is the lightest you could make it. Change the density of the water in your programs to that of air and see how forces act on your hull. If you're crazy enough to attempt the ballon itself, use hydrogen as it's still the best material (and yes I'm aware that painting your balloon with rocket fuel for it's reflective properties are far outweighed by the fact that rocket fuel is a bit inflammable). I don't believe that's up for debate.

    I'm neither asking for a design to be created, nor saying I'll ever have the funding to build one myself. Simply another mental exercise as a slight distraction from the daily grind.

    It was either this or read through the 32,528 posts that have been written since I was last reading these forums. Feel free to post models, concepts, discussions, materials you've used in the past, anything you might feel relevant.

    So, any ideas?
     
    Last edited: Sep 24, 2009
  2. apex1

    apex1 Guest

    If wooden boats would be so "extremely heavy" why did people build even airplanes of wood?
    Remember the largest airplane for about 5 decades was a wooden one!
     
  3. Yellowjacket
    Joined: May 2009
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    Yellowjacket Senior Member

    Remember that the airplane that you are speaking of was designed to use wood specifically because during the war aluminum was scarce.

    You can debate all you want about how wonderful wood is, but if it was better than aluminum every airplane you climb into would be made of it. They aren't, so maybe there is something here you don't know.

    Aside from issues with life due to rot and the elements, there are structual fatigue issues that make it far less suitable for a pressurized airplane. Think about desiging a pressurized airframe in wood and trying to make it anywhere near as light as aluminum or composite. It simply isn't close. Wood wing aircraft, such as the Bellanca and older wood wing Mooney's are notorious for rot and life issues.

    Wood is good material for boats where section modulus is just as important as strength. Where you have higher surface loads and you need that section modulus, then wood makes sense. Aluminum and composites are both far better airframe materials than wood.

    Some balsa in the floor if skinned by composites or aluminum on the upper surface is about all you could or should hope for in terms of using wood in this kind of application.
     
  4. wardd
    Joined: Apr 2009
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    wardd Senior Member

    the only advantage wood has as a construction material for airplanes is if it crashes at sea you can hold on to a chunk till help arrives
     
  5. apex1

    apex1 Guest

    Ja, and.................?:?:
    Is that worth nothing?:rolleyes:




    And who said wood is a good material to build airplanes? Just the statement that wooden boats are "extremely heavy" is idiotic!

    Regards
    Richard
     
  6. CanQua
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    CanQua Junior Member

    Perhaps the message has gone astray a bit. Wooden boats designed for water, are extremely heavy...as an airship. Please take any solid wood boat from 100 years ago, and check it's displacement with the amount of hydrogen needed for lift.

    Lets say 60 foot that weighs in at 36,000 pounds to make it easy.

    480,000 cubic feet of hydrogen needed at 70 pounds of lift per 1000 cubic feet at sea level.

    Rounding, you'd need a sphere that's 98 feet in diameter to lift it. Doesn't sound that bad until you look at it compared to the ship it's carrying to scale.
    [​IMG]

    And this is with a perfect spere which would have to have it's own structure, a free standing balloon would be around 3 times that height.

    [​IMG]

    Lightweight composite construction makes this thought a bit more obtainable of the romanticized versions popular in art.


    Now a wooden structure designed to be as light as possible can have some amazing results in the air.

    We're not talking about a wooden aircraft, but just having the outer appearance of a beautiful old ship, with all modern materials underneath. Nor are we talking about designing something that has to stay aloft with wings and the stresses that they endure.

    Not even talking about pressurization. The higher you go the more air you'd have to displace by considerable amounts to obtain the same lift. Even the added weight of the air would add more to this again.

    Think personal pleasure craft. I've not seen but a few passenger air balloons that are pressurized. Something more along those lines.
     

  7. Petros
    Joined: Oct 2007
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    Petros Senior Member

    The lightest wing (per unit area) ever designed is the wood truss/fabric covered wing. Wood is a perfectly suitable aircraft building material, and when optimized for it's properties, can be better than most modern construction methods. Wood also has much better fatigue properties than aluminum. Wood fighter aircraft were made up through WWII and the first German jet aircraft had plywood wings! Wood also cost less than most other construction material.

    The problem with wood is it is not well suited to assembly line construction methods, too much hand selecting and fitting of each part, very high labor costs. It also tends to rot when left out in the weather, except for sea planes. Wood sea planes actually hold up better than aluminum ones, AL corrodes in sea water (hence the wood Huges Hercules, aka the spruce goose, actually made of mahogany plywood).

    If there is no dimensional limitation on the member size, most structures, when optimized, can be made cheaper and lighter in wood. There are even a few custom builders of wood bicycle frames! Most smaller buildings are made in wood. Wood just does not lend itself to mass production methods, and you can end up with some pretty bulky structures. And of course very large structures are not practical in wood (sky scrapers or battle ships).

    wood is a wonderful building material, it is mass produced by nature, it is none toxic, easy to work with simple tools, renewable and very attractive. The "factories" (i.e. forests) where it is made are also very pleasant places to be compared to foundys and chemical plants. To make it last unfortunately it has to be kept dry.

    As a professional engineer I have designed structures in composite, steel, aluminum, concrete and wood. I have the most amount of processional experience designing wood structures. So I know what I am talking about. And I have built 9 boats, one fiberglass (never again), and 8 wood ones. I like working with wood, it is pleasant, it look nice, and it cost less to build wood boats. That is good enough for me.
     
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