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Thread: Frontal Area and Drag

  1. #11

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    Your ballast dilemma is not new. If you want to see how other engineers have solved the issue of moveable ballast take a look at the Lake seaplanes and the the homebuilt helicopters. A friend who owned Lake 250 I think had movable ballast for flying solo or with passengers. I recall that a couple of friends who built Rotorway helicopters had some sort of moveable ballast.

    Of course, ballast that has no other function steals performance so if you can find a way to say make the main battery mount on a sliding tray so that it can be moveable ballast, rather than just using chunks of lead, you can minimize the penalty.

    By the way, if you make the ballast removable, you will have problems hopping a friend over to another airport and then dropping them off to return solo. That's why ballast almost always is permanently attached somehow.

    Best of luck,

    Wes
    N78PS

  2. #12
    Mike Switzer's Avatar
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    Quote Originally Posted by WLIU View Post
    By the way, if you make the ballast removable, you will have problems hopping a friend over to another airport and then dropping them off to return solo. That's why ballast almost always is permanently attached somehow
    I was actually considering some sort of arrangement to hold water, which could be drained or added as needed. If I make it permanent, the minimum weight & location required for solo flight with a 150lb pilot would cause cg problems when fully loaded - if i make it permanent in a location that is good for all loading scenarios more weight will be required. Of course at this point it is all just a swag anyway as I don't know the actual fuselage weight until I do the structural analysis.

  3. #13

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    I was suggesting something like a sliding tray with quick release pins to allow it to be moved fore and aft. One of the new RG 35Ah batteries weighs something like 25lbs. The Odyssey dry cells weight 15 lbs. The FAA requires certified airplanes to secure something like a battery against a 9G forward accelleration, so a couple of tubular 4130 rails will easily handle those loads.

    Water freezes in the winter so your flying year may be limited using H2O as ballast. And antifreeze is more $$ and upsets the environmentalists if you casually dump it down the airport storm drains. You will notice that the sailplanes that use water ballast go south for the winter or hide in trailers 4 months or so of the year.

    Best of luck,

    Wes
    N78PS

  4. #14
    Mike Switzer's Avatar
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    I had already thought about the water freezing. If I put the batteries all the way in the tip of the nose it still isn't enough. I'm gonna mess with the numbers some more today.

  5. #15
    Flyfalcons's Avatar
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    Quote Originally Posted by Bill View Post
    Why can't we have this kind of article in Sport Aviation? As a builder, I am really interested in frontal area and drag, and their effects on my airplane.
    They need to keep room in the mag for Mac to drone on about flying IFR in his Baron.
    Ryan Winslow
    EAA 525529
    Stinson 108-1 "Big Red", RV-7 under construction

  6. #16

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    " it still isn't enough."

    Sounds like Mother Nature is trying to tell you that you need a longer nose....

    Best of luck,

    Wes
    N78PS

  7. #17
    Mike Switzer's Avatar
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    50lb of ballast that I can move from the nose to the CG will fix the problem. I hate the thought of carrying around 50 lb of dead weight.

  8. #18
    rwanttaja's Avatar
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    Quote Originally Posted by Mike Switzer View Post
    50lb of ballast that I can move from the nose to the CG will fix the problem. I hate the thought of carrying around 50 lb of dead weight.
    And if you're expecting other folks to build and fly the aircraft, there's always someone who will forget to move the weight or decide it's not necessary.

    Also, there can be effects that even the professional designers don't anticipate. Recall the crash of the BD-12 on its first flight:

    "During the flight the pilot said the '...longitudinal handling qualities were found to be undesirable and a proper 'flare' aircraft attitude was not achieved prior to touchdown.' When the airplane touchdown occurred, the landing gear failed.

    "The pilot said the center of gravity (C.G.) calculations placed the C.G. at the mid-range point on the C.G. envelope before flight. He said that he and engineering personnel from the company decided that the airplane had an aft C.G. during their analysis of the accident. The pilot also said that the airplane's fuselage had a forward aerodynamic center due to its elliptical shape. According to the pilot both factors created a longitudinal control problem with the amount of up stabilator deflection available."


    The BD-12 had required ballast in the nose to get the CG forward to the point where the engineers thought it was mid-range. And, it apparently wasn't.

    You're right to be considering the mechanical issues more than the aerodynamic ones, right now... the more you depart from the Long-EZ planform, the more risk you're taking.

    If you decide to go with a side-by-side setup, you might look into the Cozy and see how they handle it the CG issues.

    Ron Wanttaja

  9. #19
    Mike Switzer's Avatar
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    Quote Originally Posted by rwanttaja View Post
    And if you're expecting other folks to build and fly the aircraft, there's always someone who will forget to move the weight or decide it's not necessary.
    That is exactly what I don't like about it.

    Quote Originally Posted by rwanttaja View Post
    If you decide to go with a side-by-side setup, you might look into the Cozy and see how they handle it the CG issues.
    It has been a while but I have looked at it - they didn't allow for much useful load increase over the Long-EZ, and if I remember correctly the Cozy & Velocity both add ballast to the nose. I suppose I should take another look at those plans, but I don't remember any significant change.

    If I turn it into a twin I can make all the W&B issues go away, but I don't really want to go that route - we are back to adding drag, plus complexity. The whole point of this exercise was to make something easy to build. (if you know how to weld)
    Last edited by Mike Switzer; 09-04-2012 at 06:29 AM. Reason: spell check malfunction..

  10. #20

    Serious magazine content

    I take Ron Wanttaja's point regarding writing for Sport Aviation. He knows what he is talking about.

    But I think our magazine, Sport Aviation, no longer has much room for serious technical content. A couple years ago at Oshkosh, after his seminar, I spoke with Neal Willford, the Cessna engineer. I thanked him for some of the great technical/design articles he had written. And also mentioned my point about the seeming lack of technical content in the magazine. He agreed. He said he had submitted another article to Sport Aviation but it did not get published. He said they offered to publish it online, but did not have room for it in the magazine. Neal said he just did not want to write articles if they would not make it into print.

    I joined EAA in 1964, in what I now think of as the Paul Poberezny/Jack Cox era. Actual technical content was the main staple of Sport Aviation. Now they seem to think their main audience is more interested in human interest stuff. They may be right. I still prefer the old Sport Aviation.

    Ron Borovec

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