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  • Years in Sport

Ratings and Rigging

  • Rigging Back
    Senior Rigger
  1. To throw some numbers in, I claculated a Reynolds number for each arm wing on the Rigor Mortis to be 2666666 (no jokes about all the 6s...). The Reynolds number for a laminar flow has to be less than 2100 so we are about 1270 times over it! This should clear any doubt. *********************************** EG Suits ***********************************
  2. I agree 100% with Robi that talking about laminar flow in the wing suit contest is borderline meaningless. Having seen Robi kind of opened a “Pandora’s box” let us talk about other common misconceptions about wing suit design. First let me say it is normal but erroneous to look at many airplane wing designs and try or think about implementing them in a wing suit. As much as we think we can fly like an airplane we are not airplanes: We do not have an engine and a rigid frame. However there are hints that we can draw from basic understanding of airplane fluid dynamics. For instance if we analyze the sweep angle of a wing it is my opinion that only one right conclusion can be drown: A high sweep angle is not efficient in a wing suit. Of course Robi and Jari will disagree on this one because on many of their suits the arm wings have quite a bit of swept-back. Swept-back wings were designed to address the issues related to supersonic flights. For the record few test pilots have died because engineers overlooked this problem even though the phenomenon was known before technology allowed for supersonic flights. When approaching the speed of sound (770 mph), something peculiar happens: A sharp drop in pressure is generated aft of the nose of the aircraft. If this drop in pressure happenes in high humidity, a cloud is formed around the aircraft leading the very cool images of airplanes passing the speed of sound. This is known as the Mach cone. Why this happens is actually pretty simple. Any moving object generates sound waves that in general travel aft of the object at subsonic speeds. As the speed approaches the one of sound, those waves “collapse” into one, usually at the nose of the aircraft, and this sudden raise in pressure is also responsible for the “sonic boom”. Actually there is a second boom when the tail passes the shock wave but human hearing is not sensitive enough to detect the two and only one is heard. As the nose is “loaded” with high pressure, aft parts of the aircraft including he wings have much lower pressure. This higher pressure intuitively increases the temperature. Both the increase in pressure and temperature on the nose of the aircraft have detrimental effects on the wings namely an increase in drag that if compromises the whole leading edge it could result in total loss of lift. Implementing a sweep angle on the wings allows for a reduction of this type of drag. I said a sweep angle and not just swept-back because a swept-forward will also work as in the case of the X-29 for instance. However a swept-forward design introduces some disadvantages like wing-tip twist, wing-tip-first stalls (which rob aileron efficiency more than any other stalls), not to talk about higher cost of manufacturing. The reason behind the sweep angle is to reduce the effect of compressibility responsible for the cone to approach the leading edge. So in theory the higher the sweep angle the higher the speed the code reaches the leading edge inducing a drastic reduction of drag, up to a point. So why don’t all aircrafts have swept-back wings? In short because at lower speeds, the disadvantages are greater than the advantages namely less lift produced, more drag, “Sabre dance” (the pitch up close to the stall point), among others. There is also IMO another disadvantage in having swept-back wings on a wing suit and this is the lower aspect ratio. Same goes for narrow leg stance, the aspect ratio is lower and all things being equal a wing with higher aspect ratio will produce more lift and less drag. I also disagree with Robi with his analogy to the Space Shuttle. This “aircraft” is not an airplane per se and introducing such a design as a “normal” aircraft will get the person fired! The Space Shuttle is a compromise aircraft: it has to take off vertically strapped to some giant rockets, it has to orbit the earth, it has to re-enter the earth atmosphere reaching temperature that melt most metals, then it has to overcome Mach numbers over 20, and finally manage to land…and those things do not land pretty, they come in hot, having little flare power and nowadays NASA pilots do not even land them anymore leaving computers the job. If we really want to “rob” ideas from aircraft wing aerodynamics in order to implement or evaluate them in a wing suit contest, then we should look at aircrafts such as gliders where in general high-aspect ratio straight wings are preferred. I do agree with Robi when he says gravity is our only engine, there is very little doubt about that! *********************************** EG Suits ***********************************
  3. I'll be there with demos (Volturius and Rigor Mortis). It should be a good time. *********************************** EG Suits ***********************************