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  1. christos

    Question - static load test on spar only

    Depends on the safety factor. As i mentioned it isn't a good idea to go after 50% of the ultimate strength. Because every time you are going after that, small cracks occurred. Now you like to know if you are safe. If you don't know what kind of safety factor 4.4g has, then (personally before do...
  2. christos

    Question - static load test on spar only

    Just a good fea analysis and you are 100%. Trust me. But if you are not sure for the quality of your work, then the only way is a real scale test. If you use the correct glue under correct conditions, then i believe that it is fine. Remember that you can measure the stiffness of the element. If...
  3. christos

    Question - static load test on spar only

    If you know someone else with the same plane you can ask for example, if you put 40pounds on the wind tip, how many inches the deformation is? And make the same test. The old school designs are excellent and the wood is awesome material. I think that you are curious about the glue etc. but if...
  4. christos

    Question - static load test on spar only

    You have first to know what kind of limit 4.4g load is before load it near to it. Because if 4.4g is greater than 50% of ultimate strength i don't recommend you do it and then use it. A good option to test of the build is measured the stiffness of the structure. If it is in design limits then...
  5. christos

    Why is it so hard to be profitable in aviation?

    Only if you love it 😉 The aircraft itself worth for me. If you build an experimental worth because you will save some money (if you are an engineer and make all the paperwork) and will be a little more expensive than a second hand airplane but in the end of the day you will enjoy the route...
  6. christos

    Why is it so hard to be profitable in aviation?

    I think that depends. Previous years there were more aviation enthusiasts ready to work hard for a plane. But many of them didn't complete their project because an aluminium aircraft needs really a lot of hours to complete. I think that for this reason fabric aircraft and composite have their...
  7. christos

    Load Test Question

    I apologize, i didn't see it yet, i saw only the stress calculations without it. Off course, engineers designed and built aircraft a lot of years before the first PC. Finite element analysis is worthwhile in flutter analysis, off course in a light aircraft case, the static aeroelastic analysis...
  8. christos

    Load Test Question

    Thread is interesting but big also. I read it now and maybe I miss it. But I didn't see (in calculations) the moment of air load. Wing skin helps a lot in this load condition(it is the reason for +-45 wing skin fabric in composite structures). Last but not least, stress in wing spar will be...
  9. christos

    Aerobatic Tandem Two-Seater

    About stability, a VLM program is ok. But it is better to check your aircraft around stall with a real CFD solver like yours, OpenFOAM (i prefer it) because you can see how it will operate after the stall. If you go with the traditional (old day) way, you have to be more careful throughout the...
  10. christos

    Aerobatic Tandem Two-Seater

    Eppler code isn't interactive. Xfoil is a better choice (and interactive) for 2d analysis. Eppler code includes some empirical calculations (to simulate turbulence flow) and it is prone to errors. Drella's Xfoil is a better solution. But wing's analysis is a 3d problem and not a 2d, it is much...
  11. christos

    Aerobatic Tandem Two-Seater

    Piper has naca65415, and combinate it with a good chord (the bigger the chord the higher the Reynolds number). As a result, the airfoil is efficiency in aircraft's speed range. It is not only the airfoil of the piper but the overall design. It needs a more careful design a laminar airfoil...
  12. christos

    Aerobatic Tandem Two-Seater

    I meant the CFD code. Did you run the k-omega SST model or something else, also what about the grid? how many cells and how many boundaries layers and how much thick? If you used the auto option of your software, just make sure that it takes the correct values for your problem. For example, if...
  13. christos

    Aerobatic Tandem Two-Seater

    Interesting design. About airfoil, it is not necessary to choose symmetrically. Symmetrical is NACA 00xx series. Also, what CFD model did you use? How many boundaries layers? Best Regards! Christos, civil engineer
  14. christos

    A Wing Design Method for Aerospace Students and Homebuilders; M A Ferman, PHD, PE

    I haven't his book, i only read some pages. It looks interesting, but it also looks too simplified. I hope that you know the difference between "95% of cases" and "95% accuracy".
  15. christos

    Raptor Composite Aircraft

    I apologise. Peter has a lot of "ground" problems and I supposed that we were talking about sea level specs. I believe that he has a lot of way to fly at 20000feet. First of all, the aeroplane is heavier and maybe the wing's area is not enough. It needs a redesign. I believe that the main...
  16. christos

    Raptor Composite Aircraft

    Gtx2867 is good enough up to 500 hp. A 100 mm comp wheel is really too big for something like that. Exhaust house is another problem. Maybe it is small but we need more details to check it. Garrett suggests this turbo up to 550hp and up to 2500cc. Maybe the turbine wheel is too small as a...
  17. christos

    Raptor Composite Aircraft

    Did you mean gtx2867? Is it peter's turbo? # it is high pressure if you read compressor map. What type of exhaust house does it use?
  18. christos

    Raptor Composite Aircraft

    We need the compressor map, airflow and pressure to check if turbo surge.
  19. christos

    Raptor Composite Aircraft

    Could you share with us your calculations? you told that it is a 200hp engine if i remember right. It is a heavy aeroplane, it will not meet Peter's pre-construction performance goals, but it doesn't mean that it will not fly. In any case it is a new canard design, so it needs at least an...
  20. christos

    Raptor Composite Aircraft

    I do not like raptor and I believe that it will not be as good as Peter promised for many reasons. But, could you share with us your calculations? It sounds very interesting In any case, the main problem is that ( I think )he will make the first flight. If Peter read this, I believe that it is...
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