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  1. S

    Thickening airfoils (specifically E214)?

    Airfoiltools.com uses Xfoil to estimate airfoil characteristics. So your xflr5 simulations are just as good as their results.
  2. S

    Computational Fluid Dynamics

    XFoil is perfectly capable of analyzing high Re flows. Since the algorithms assume a clean separation between viscous and inviscid layers, I am guesstimating that working Re numbers should be at least 10,000. Anything less than that would require a direct numerical solution.
  3. S

    Computational Fluid Dynamics

    For "normal" Re regimes, OpenFOAM employs various numerical schemes that average out the turbulence effects. For very low speeds (Re<1000), there is DNS (direct numerical solver) that will solve the N-S equations directly. But for 99% of real life cases, one must employ some kind of RANS...
  4. S

    Computational Fluid Dynamics

    I have found OpenFOAM to be quite useful when evaluating design changes. Any iterative modifications to the aerodynamics can be evaluated on a comparative basis. And no, one does not need to be able to derive the Navier-Stokes equations in order to be able to use the software.
  5. S

    Inspecting OLD fiberglass?

    I know that this is not a scientific test, but one can take a really stiff brush (not a wirebrush, but one with stiff bristles nonetheless) and try to brush a suspected area. If the resin flakes off, you are in trouble.
  6. S

    Initial Calculations, .6 AR WIG Flying Boat, Airfoil Performance - Check My Numbers!

    Re: Initial Calculations, .6 AR WIG Flying Boat, Airfoil Performance - Check My Numbe The upper CL limit for ground effect is the 2D CL. I remember back in school that we analyzed ground effect by considering two wings flying mirror image of each other, with the ground plane being the...
  7. S

    Initial Calculations, .6 AR WIG Flying Boat, Airfoil Performance - Check My Numbers!

    Re: Initial Calculations, .6 AR WIG Flying Boat, Airfoil Performance - Check My Numbe You can install XFLR5. It has a handy graphic interface and it uses xfoil for calculations.
  8. S

    Initial Calculations, .6 AR WIG Flying Boat, Airfoil Performance - Check My Numbers!

    Re: Initial Calculations, .6 AR WIG Flying Boat, Airfoil Performance - Check My Numbe Do you have a picture of the 2d airfoil? Unless this is a highly cambered, flapped airfoil, I doubt you can achieve a CL of 3.0. It would help to run the same simulations in xfoil and javafoil to confirm the...
  9. S

    Design parameters for STOL landing gear

    Thank you for the responses. That's what I was looking for.
  10. S

    Simulating airfoil roughness in XFoil runs?

    For fair weather recreational flying, you are likely to encounter high turbulence closer to the ground. Consequently I would run airfoil simulations at high CL and low Ncrit to account for takeoff and landing conditions. Here the numbers of interest are max CL. For cruising, I would run the...
  11. S

    Simulating airfoil roughness in XFoil runs?

    If you want to get technical, neither the Xfoil mechanisms nor the wind tunnel sand paper strips simulate bug splatter. The only way to test bug splatter in a wind tunnel is to do just that: test a wing with dead bugs on it.
  12. S

    Simulating airfoil roughness in XFoil runs?

    Xfoil has no way of simulating airfoil roughness, but has a way of simulating air turbulence. This is accomplished via a parameter called Ncrit, which controls the growth of Tollmien-Schlichting waves. (see https://en.wikipedia.org/wiki/Tollmien–Schlichting_wave ) Without going into technical...
  13. S

    Additional Static Load Testing Discussion: Semantics of Duration

    Short answer: there is no difference between fully static and steady state static load tests. By "steady state" I mean that the rate of change in the load magnitude is small enough to to avoid resonance and material fatigue issues. The only reason I would load a structure incrementally is when I...
  14. S

    Extended section airfoil question please

    The main lift mechanism for subsonic airfoils is uneven pressure distribution between upper and lower surfaces. This means that the airflow close to the surface of the airfoil must be faster than ambient airflow (because of Bernoulli). The only way to speed up the flow is through acceleration...
  15. S

    Reliability of gas vs electric motors

    For homebuilts I would argue that from a $$$$ perspective, electric (motors) are more reliable. One can purchase an industrially rated electric motor for a lot less than one would spend for an aviation gas engine. The weak link, as people have mentioned are the batteries. I would be more worried...
  16. S

    Matrix Calculator FREE!

    For the most part, stand alone matrix calculators are quite useless. One needs to automatically feed in the data either from a data file or through some other means in order to streamline the calculations. But every computer programming language does have function/module libraries that handle...
  17. S

    Design parameters for STOL landing gear

    I suspect that there ought to be some kind of suspension... But let me rephrase the question: what kind of vertical deceleration (in G's) does the landing gear experience during a rough STOL landing?
  18. S

    Design parameters for STOL landing gear

    I have noticed that STOL airframes take quite a beating during landing. Assuming a worst case scenario, what is a reasonable design load for such a landing gear? The airframe itself is designed for 6G.
  19. S

    Making a Box Beam

    My first intention is composites. But I am open to any other suggestions.
  20. S

    Making a Box Beam

    This is a highly cambered airfoil, which puts the center of pressure far behind the 1/4 chord. There will be a leading edge rigid skin, but that's for aerodynamic (laminar flow) purposes only.
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