A complete report on the aerodynamic and strength design of an ul aircraft

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by christos, Nov 9, 2018.

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  1. Nov 17, 2018 #21

    dino

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    Just using the grade A eyeball method, your L/D with wing aspect ratio of 8.2 will I think be closer to 12 than to 25. Also empty weight of 250kg will be very hard to achieve. The software and renderings are very impressive and a great tool to achieve your results. Keep at it.
     
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  2. Nov 17, 2018 #22

    pictsidhe

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    The best math processing bang for the buck are graphics cards. Linux machines are limited to 8 graphics cores per machine. About 4 years ago, I had a lot running, I can't remember how many TeraFLOPs I had, but I appeared to have the most powerful computer in Wales...
    For infrequent use such as designing a plane every few years, I'd leave a PC grind for days or a week. Not all computations are suitable for the massively parallel processing that is used in clusters.
     
  3. Nov 18, 2018 #23

    christos

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    Owo! You are a veteran! You are a realy hero! I am glad to speak with you!!
    It would be too hard to solve it without a commercial computer... i feel you :)
     
  4. Nov 18, 2018 #24

    christos

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    Yes it is hard to make it so light weigth but i will it. It is a reason i go with subaru. I need it so light because i want to be able to operate as ul in united kingdom Only subaru and rotax (and jabiru, but i don't know about new models) are so light weigth.
    Yes glide ratio is good because of natural laminar flow design :)
     
  5. Nov 18, 2018 #25

    dino

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    Even assuming 100% laminar flow 25/1 is very optimistic. Look at your induced drag at best L/D speed.
     
  6. Nov 18, 2018 #26

    christos

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    Let me make it clear that landing's gear drag does not include. As i said above it is a "retractable" version's glide ratio.
    Make a search for sea avio. It is retractable (it is slotted, better but more complex. And too complex to put cruise flap).
    A natural laminar aircraft has a lot of advantages :)
     
  7. Nov 20, 2018 #27

    christos

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    Stress forces resulting from a dynamic response analysis (for loads in flutter condition) in the LISA finite element program.

     
    Last edited by a moderator: Mar 20, 2019
  8. Dec 3, 2018 #28

    flyboy2160

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  9. Dec 6, 2018 #29

    christos

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    No, it is a flutter analysis. I calculated in openfoam time depend load and i runed dynamic response analysis in lisa software. Flutter is an aeroelastic problem.
    Thanks for your interest, let me know if you need something else :)

    I am working on a more detailed report for you aeronautical friends :) (it will contain laminate analysis -matrix model in lisa etc- because i notice that it is a good techinal report but it isn't detailed enough for a homebuilder)

    Best regards!
     
    Last edited: Dec 6, 2018
  10. Dec 7, 2018 #30

    flyboy2160

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    I know what flutter is. You still haven't explained what you did. Flutter depends on a coupling of different modes. I don't see where you did anything like that. Have you ever studied classical flutter analysis or did you just make up your own definition?
     
  11. Dec 7, 2018 #31

    proppastie

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    I do not think it is reasonable for OP to show all his inputs to all the software he has used......but as I understand it ....as he said " Flutter is an aeroelastic problem" so I do not think he made up that definition. Perhaps you can show us your flutter calculations for the aircraft you are designing.
     
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  12. Dec 7, 2018 #32

    christos

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    Hmmm you still don't understand.
    First i made modal analysis and after it i run dynamic response analysis (under time depend load which i calculated in OpenFoam).
    Let me know if you need something else
     
  13. Jan 3, 2019 #33

    christos

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    Happy new year! Best wishes for 2019!
    As I promised I start a more detailed technical report. Not only because I want to advertise my design but additionally because (I think) some people want to design and built their own planes. So this technical report (maybe) will be useful.
    I like planes since I was a child and I want to build my own plane. My studies at university (i am a civil engineer) was useful throughout the design. It required to study structural analysis and it is highly recommended study finite element analysis for someone who wants to design a plane. You can design a plane with classic structural analysis and hand calculations but you need a finite element analysis software if you want to solve a sandwich structure and/or to run a flutter analysis. Theoretically, you can solve anything by hand calculations but you will spend a lot of time. It is not possible in the real world.
    Also before you choose the software you have to choose structure materials. Because some software isn't solving laminate materials (if you want to build a composite aircraft).
    There are a lot of software out there which you can use. From free open source to very expensive commercial like ansys.
    I go with open source and low-cost commercial software because I don’t have enough money to buy expensive commercial software and I believe that open source is the best choice (personal opinion)
    So I choose Lisa fea software for structural analysis, code aster for non-linear structural analysis, xfoil for airfoil analysis, VLM software for 3d simple analysis (avl or xflr5 aero vsp, or a cheap commercial like Hanley innovations) and OpenFOAM for computational fluid dynamics.
    After that, I start to study regulations to make sure that I will design a good plane for me.
    At the start, I dream to build a four-seater plane but I think that it is really uncommon to fly with 3 other people, also a four-seater is experimental and it is more expensive to own it, for these reasons I go with the ultralight. But because maybe in future I will need a four-seater, I design it as a four-seater. 2 seats for adults in the front area and 2 seats for children or light adults. Additionally, I plan to build a kit and USA is a very interesting country because it has a lot of excellent homebuilders. For this reason, I designed it as lsa, but strong enough to carry 2 extra children and light enough to fly in Europe as an ultralight. Also, I have to make a low time and easy to build kit, so a well and simple designed composite laminate structure, will be a good choice (maybe the best one).
     
  14. Jan 4, 2019 #34

    Captain Bravo

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    Very interesting project Christos. I wish I could go back 25 years ago and be an aerospace engineer instead of an I.T. guy.

    I am interested in a similar concept in order to replace my current ride, a DA20-C1 which weights 528 kg empty. I am looking for more range and also an ifr capable airplane. The DA20-C1 does not have the metallic mesh in the composite of the wings, therefore impossible to certify for IFR. The wing would be destroyed by a lightning strike.

    One thing to consider is that with a target empty weight of only 250 kg, your airplane will be difficult to land in strong gusty crosswinds.

    Cheers,

    Pascal
     
  15. Jan 4, 2019 #35

    christos

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    Dear Mr Pascal,
    Thank you for your kindly words! Diamond is a really excellent aircraft. It has a Wortmann fx63 airfoil. It is very good for the climb.
    I think that you need a good rudder in case of gusty crosswinds. Also, a thin fuselage is useful.
    Diamond's fuselage is thin and is very good for crosswinds.

    I design a good and big rudder because of small displacement. I believe that it will be fine. I am flying ultralights and I didn't have any problem.
    ## crosswind=<15 knots

    Last but not least, I design it for economy trips. It will be good for someone who needs an "economy traveller" but not good for someone who needs an aerobatic for example. In this case, an RV will be a much better choice.

    ##i didn't fly yet a diamond, I told that it has good climb characteristic because of airfoil's technical data.
     
  16. Jan 4, 2019 #36

    BJC

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    A comment for those not familiar with the DA-20: The original version, the -A1, used an 80 HP Rotax. Since climb rate is a function of power available in excess of what is required for level flight, Pascal’s -C1’s has good performance, but the -A1 is rather lethargic, especially in summertime temperatures here in Florida.

    I think that I would enjoy flying a -C1 much more than the -A1.


    BJC
     
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  17. Jan 5, 2019 #37

    christos

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    Fx airfoil seems very good for climb and glide. A 100hp version should be much better.
     
  18. Jan 6, 2019 #38

    christos

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    Good evening my friends!
    The second part of the design:
    Now you know what do you want and you are ready to start the computational part of the design.
    1) Select a good airfoil for your operation goals. It is very important. Because if you want a stol aircraft you have to go with a thick airfoil with good lift characteristics, if you want an aerobatic, you have to go with a stall stable airfoil etc. I want a fast long-range traveller, so I need an efficiency airfoil.
    For this reason, I select a natural laminar flow airfoil and I developed a simple low operation energy boundary layer controller. It isn’t something new but isn’t common in small planes. But thanks to OpenFoam I develop one for my application. It is a vacuum boundary layer controller and my airfoil will be 85% laminar flow in the upper surface. It will be a simple but very important for aircraft’s efficiency mechanism. It needs only 7 amp and 12 volts. It is small enough to operate in a Rotax version (I am planning to buy one to test the plane). I design it around Rotax engines (rather than I prefer Subaru for a lot of reasons) because it has to operate well with an aeronautical engine if I want to make a kit from it.
    Also, I design a cruise flap, but it wasn’t possible to use it with a slotted flap. The slotted flap will reduce the wing’s area, but it becomes too complex to a kit plane. Finally, I choose flaperons. It will operate as ailerons, cruise flap and flap at the same time. It isn’t something new, a lot of LSA and ultralight has flaperons. Some of them for the same reason.

    Now you have the first 3d model of your plane.

    2) Run a simple vortex lattice method analysis of your aircraft. Make sure that it is good enough for your goals and make a stability analysis. You don’t know exactly centre of gravity, but you will check stability again after you finish finite element analysis of the aircraft.
    3) Make your 3d mesh model, choose loads and run your analysis. It seems easy but it is one of the most important parts of your design. Make a good grid to make sure that your results are accurate. Study about your construction materials carefully etc.
    4) Run a stability analysis. Now you know the centre of gravity of your plane.
    5) Choose computational fluid dynamic software to solve your plane. Vortex lattice method software is good but you have to run it in a really CFD software if you want to take accurate results about stall behaviour etc. There is a lot of software, I go with OpenFoam because it is open source and it is maybe the most powerful CFD software. Keep in your mind that you will need a really good pc. I run complex models and wasn’t possible to run them on a pc and I bought computing hours. It is a good choice.
    6) Run a flatter analysis.
    7) Run an elasto-plastic analysis (collision)
    8) You are ready

    **I will post screenshots from software

    Thank you!
     
  19. Jan 6, 2019 #39

    BJC

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    Will your boundary layer control system be operational for all phases of flight, or for cruise climb and cruise only?


    BJC
     
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  20. Jan 6, 2019 #40

    christos

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    I design it for a better economy, glide ratio and for better top speed. According climb boundary layer getting thicker and speed is high. It should not be so useful for this phase of flight... You will have to use a more powerful suction to take the best.
     

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