X-Plane!

Discussion in 'Hangar Flying' started by ebonheart_2, Jan 30, 2006.

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  1. Feb 19, 2006 #21

    StRaNgEdAyS

    StRaNgEdAyS

    StRaNgEdAyS

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    Hehehe I figured the pitch out pretty quickly, it's what helped me to actually get off the ground.:gig:
    I'm obviously doing something wrong there, I'll figure it out eventually.
     
  2. Mar 24, 2006 #22

    pylon500

    pylon500

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    Finally got to try and put my project into X-Plane.
    As most other sites say, it's not a totally intuitive or user friendly program and I've still got a lot of bugs to fix, but at least I can now have a look at my plane from various angles.
    Arthur.
     

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  3. Mar 24, 2006 #23

    StRaNgEdAyS

    StRaNgEdAyS

    StRaNgEdAyS

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    Very nice..:)
    I'm almost completed an X-Plane version of the Q-200 as well, I'm working on the cockpit on and off, I cannot seem to get the hang of these cocpkit object bitmaps, but what I've got so far is not half bad...:D
     

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  4. Mar 24, 2006 #24

    Chairboy

    Chairboy

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    I beat X-Plane the other day. The end guy is hard.
     
  5. Mar 3, 2013 #25

    SkyBox

    SkyBox

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    Inspired by Barnaby Wainfain's Facetmobile (facetmobile.com) and using X-Plane 9's Plane Maker module I have designed a light plane emphasizing structural effiiciency, cabin volume, loading envelope and visibilty. (The wing body is all glazing.)

    The basic parameters are a length of 22.75 ft, height of 7.75 feet and a span of 15 ft. The gross weight is 1320 lbs and the engine would be a Rotax 914 (115 hp, turbocharged). The canard airfoil is NACA 0030 tapiring to 0006. The wing body is NACA 0036 and the horizontal stabilizer is NACA 0006. The canard has an incidece of 3.0 degrees relative to the wing body and stabilizer. In cruising flight the AOA of the wing body is 2.5 degrees and makes little lift. During takeoff and landing the wing body conributes >50% of the total lift. During cruise, the wing body provides less than 10% of the total lift. Thus, the functional wing area varies as with AOA.

    There are no curved surfaces. For example, the wing body is made from 5 Warren trusses assembled into right/left & top/bottom mirror images. I am interested in a structure of pultruded fiberglass or carbon tubes, dacron fabric and lexan glazing. Basically, it would be a giant tinkertoy. Pictures are in my album.
     
  6. Mar 3, 2013 #26

    Synergy

    Synergy

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    Skybox,

    I'm not sure why you'd resurrect this ancient thread to make your point, but having done so, I'd like to thank you for the opportunity it presents to make and clarify two important points about X-Plane, which has been a contentious subject matter on this forum.

    1. This thread opens with important commentary from our late and much respected orion, the professional aircraft configurator and designer Mr. Bill Husa.
    Throughout his posts on the subject of X-Plane, which he did not personally use and did not personally investigate on a first-hand basis, Bill tried his best to keep newbies and first timers (in particular) from thinking they'd discovered something just as good as the kinds of advice and experience that comes from professionals such as himself, and he advocated the kind of education that one gets from really learning what is involved in calculating for yourself the answers to the questions of flight.

    Perhaps more importantly as it relates to the forum debate, his preferred process would also shine much light on the practical and structural aspects of the question, among many, many other things. This is an area that X-Plane utterly ignores (through version 10 so far), allowing "designers" to make, analyse for flight, and refine aircraft that would be patently unsafe if built in the real world.

    However, in many other prior posts on this subject I took a different stance than Bill. I began using X-Plane in version 6 as a low fidelity 3-D design tool and as a handy realtime calculator. I found it instantly gratifying and addictive, and learning how to feed it useful facts and buildable, safe aircraft designs was almost as instructive as learning how poorly many real-world aircraft fly: X-Plane can be brutally accurate, and while it's not always appropriate to say that it can duplicate the flight behaviors of a known aircraft to within a few percent or less of flight test data (as is usually the case), it is OK to say that two different aircraft modeled to the same fidelity and with the same care, in its virtual environment, will reveal two different airplanes that truly can be compared with one another.

    My first point, therefore, is that X-Plane is awesome; perhaps the single best thing the readers of this forum can obtain, learn, and use to advance their understanding (and comfort level with) the mysterious, wonderful process of creating the 'dynamic and aerodynamic' subsystems of a novel or modified aircraft design. The software is a brilliant packaging of a brilliant concept, and I have found few criticisms, orion's included, that are able to find its tender spots accurately.

    In other words, if you know what I know, you can be devastating critic: you can warn the world all about how risky it is to trust people's lives to the output of a cheap software running basic calculations from a questionable and/or unqualified input. I rarely find that necessary.

    2. But this is one of those times. A Facetmobile-inspired, low aspect ratio, canard, presumed lifting body, novel, flat-faceted aircraft may or may not fly just exactly as X-Plane predicts it to, which is always the case.

    However, normally that spread between 'exactly' and 'not exactly' is less than the subjective differences between pilots and existing examples of the same aircraft. That is why, for most configurations and conditions of design, the program is so awesome.

    In your case the spread could be the difference between 'low-cost homebuilt nirvana' and 'cheap coffin with wings.'

    X-Plane cannot tell you that answer, although it can provide guidance to help qualified investigators make peace with the challenges involved. Although it is perfectly OK with me for someone to go fly something they designed using their best guesses- with minimal certainty, just like they did back in the day- it is NOT alright with me to suggest that 'having a powerful tool like X-Plane' has removed one ounce of the risk involved in doing so.

    X-Plane ascertains how much lift to ascribe to vortex development on the basis of simplified assumptions about planform: sweep angle of the quarter chord line is the first determinant; I'm not sure whether taper ratio is allowed to (thereby) infer the leading edge sweep or not; it's quite possible (and let's just say that it does, because if I recall correctly the textbook method it uses has the necessary term in it.) However, the foil geometry in such a case is sensitive and critical. You'd need sweep-specific, 3-D derived, yet accurate 2-D airfoil polars to make X-Plane work in even a limited alpha range with faceted airfoils. Such a thing is simply an oxymoron, especially for a BWB: one has so much influence over the other, neither can reasonably be predicted in isolation, and therefore cannot predictably coexist.

    And that's not the problem either. The problem is that high alpha and departure conditions get weird for either sharp and/or flat foils, OR with lifting bodies, especially when vortex lift is developed. It makes a canard a particularly bad idea. This multiple-combined sensitivity is bad enough, but it doesn't end there. Each influence creates another for the rest of the plane that has to fly in it.

    Yes, I would model it in X-Plane and analyze the flight model dump (a text file) in a variety of flight conditions once the thing was flyable at level that seemed reasonably good. Then I'd build a properly-scaled VERY LARGE model with 1:1 power loading (the same model power loading as fullscale power loading). Think 50% size or better. There is absolutely NO WAY I'd fly something like that with a person aboard unless the X-Plane predictions for the 50% model matched exactly to the demonstrated flight behaviors of the scale model.

    We live 90 years past the time when it was necessary to design as blindly as one would be doing by relying on X-Plane in this case. What does that imply?

    On the one hand,
    most of us consistently prove to be pansies compared to the mostly-ordinary people who designed the airplanes of the first eight decades or so. Come on, folks, airplanes ARE NOT hard technology! Your house (and your pocket, for that matter) is FULL of hard technology... a thousand times more innovative than the most innovative aircraft ever flown.

    On the other hand, we have a lot to lose by being so blissfully unaware -of both the challenge and the simplicity, it seems- of applying our collective intelligence to the solutions of flight sans insight and/or common sense. orion kept all of us thinking twice... then three, then four times... about what we were doing. I'd rather this forum were the brakes than the throttle for homebuilding. The proper attitude is that we have a lot to learn.

    When we know as much as THEY did and use the tools THEY WISH THEY HAD (X-Plane)... well then there will begin a new era; one in which the present antiques of the sky are respected for what they are, not for what they have been assumed to be.
     
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  7. Mar 3, 2013 #27

    SkyBox

    SkyBox

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    Synergy,

    Thank you for your very thoughtful and informative response. This was my first post on this website and I am a complete novice.

    In building a radio control model you recommend a 50% scale. By that, you mean that if the actual wingspan is 15 ft the model's wingspan would be 7.5 ft? Assuming the model weighs 40 lbs, the wing loading would be 12% that of the real airplane. Is this correct? (Pardon my ignorance, but I am a novice to the world of radio contol models.)
    That being said, I think the idea of a 50% scale SkyBox Seater is a great idea.
     
  8. Mar 4, 2013 #28

    wizzardworks

    wizzardworks

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    SkyBox, I am a strong advocate of X-Plane and use it on conventional as well as canard configurations. I looked into the data in the aircraft files that ship with the program and have not found any entries skewed to alter the performance of the flight models and they perform similarly to the real ones I have flown. The planes I enter occasionally require getting airfoil data from worldofkraus and coordinates from the UIUC database to make the required airfoil files in the sim
    airfoil-maker section. Often the data available is for RC models and at the wrong Reynolds number for a full sized aircraft. I do use my created airfoil (.afl) files but also run the sim with airfoils that ship in the sim database on the model to see if it behaves similarly. The sim uses the maximum cross sectional area of the fuselage you enter for flat plate drag and a data entry for how streamlined the shape is. This seems to work well on conventional configurations, however a lifting body needs to generate fuselage data and therefore must be entered as a wing. After you have used up the 4 wings and horizontal stab in the wings section of planemaker you can use the 2 V-stab wings as wings by defining the dihedral to what you need. There is a way of defining a miscelaneous body as a wing or to be calculated in the sim as a wing. The point is that in your lifting body the entire external surface has to be flown as a wing or combinations of wings. This much of your design is likely doable. The real problem is coming up with lift, drag, and moment coeffecients for a faceted surface. I don't know of any published data for this and you would have to use something like X-foil to generate the required graphs and then use those in X-planes airfoil maker to make something the sim can use as an airfoil. As I remember the airfoil maker section you enter points on the curves where they cross axises, make an abrupt change of direction, stall angle, and AOA for 0 lift. Intuition tells me that the curves for a faceted surface would have a lot of discontinuitys along the curve with no way to enter them. It just doesn't seem that for your design that X-plane is a good fit.
    The model idea proposed by Synergy would seem to be the solution. He has a model of the plane he is building that is a wonder to see in flight, just spectacular. For your design the faceted surfaces could be cut on a block of foam with a hotwire and have 2 layers of light fiberglass as a surface. The wing loading needs to be the same pounds per square foot as the full size design. An object twice as big in all dimensions is 8 times the volume. This is a cubed relationship. The lift per unit area will not be cubed. So the area in square feet at the chord line of the surface devided by the weight needs to be the same. As an RC model a faceted design should be terrible to control trying to anticipate it's movemenbts from the ground. Aircraft such as the F-117 werent possible before computerized stability augmentation. You might want to look into the RC helicopters for the RC hardware. They have solid state gyros like in a cell phone or I-Pad for under $7 and integrated servo controllers for whatever movable surfaces you have. Usually we wish someone good luck but in this case we need to bump that up to devine guidance.
    wizzardworks
     
  9. Mar 4, 2013 #29

    topspeed100

    topspeed100

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    I assume the X-plane cannot be totally of the course...but I would like to remind that for instance Bird of Prey ( by Boeing ) flew just unlike the computer analysis let to believe.
     

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