Recent content by Dusan

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  1. Dusan

    What do you think about "e-soaring"?

    Not sure for the exact results for the Phoenix, but the theory is simple: There is always more induced drag with shorter wingspan. The theory also states that the minimum drag is at the speed where induced and parasite drag are equal, and here the answer is not so simple: A shorter wingspan...
  2. Dusan

    What do you think about "e-soaring"?

    I totally agree with this and what I can say is that although every component is important, the most important factor designing an aircraft - and especially one with electric propulsion that has, lets say - specific energy challenges, the most important factor is the aerodynamic performance...
  3. Dusan

    What do you think about "e-soaring"?

    Really skewed report. The author is clearly biased towards the hydrogen economy (since he is "President of H2Gen Innovations"). The report is from 2009, since then Tesla demonstrated plenty the viability of pure electric vehicles. Anyway, the report compares only the battery specific energy vs...
  4. Dusan

    Hybrid or electric theory?

    There is a range of RPM electric motors can deliver constant power, good motor designs can get close to max power. By using different controls algorithm you get 'field weakening' enabling the electric motor to increase speed by reducing torque. The motor can be designed for low RPM, close to max...
  5. Dusan

    Interesting device to change torque and rpm on motors

    This is electric motor field weakening through mechanical means, almost as old as development of the electric motor. It enables the motor to speed up without increasing power, but reducing torque. It enables the motor to behave as having a continuous gearbox attached, able to configure from for...
  6. Dusan

    Electric Hybrid

    Hybrid electric does not make sense for current, existing aircraft. The turbofans are capable of getting up to 60% thermodynamic efficiency while flying at -50 C, 30,000 ft. A hybrid electric cannot even match that, fuel cells systems can do only marginally better, but at the expense of much...
  7. Dusan

    Prop design software/books

    xrotor by Mark Drela: http://web.mit.edu/drela/Public/web/xrotor/
  8. Dusan

    Certification of Vertical Take Off Vehicle

    I discovered this video on you-tube today, it demonstrates that electric helicopters are definitely better performers, the builder claims "21kW in the hover, 17 above ETL" Compare that to Ehang 184 multi-copter: "Power required to hover 47 kW", from https://www.mdpi.com/2226-4310/6/3/26/pdf
  9. Dusan

    Certification of Vertical Take Off Vehicle

    Several props have an aerodynamic penalty in reduced Reynolds number compared to a single larger rotor/prop. Some are arguing that the benefit of multi-rotors is reduced mechanical complexity, redundancy, etc, so it's a good solution. I'm inclined to differ, since the aerodynamics is the most...
  10. Dusan

    Certification of Vertical Take Off Vehicle

    The propeller/wing combination is not really the best. The most efficient flying is exploiting the large L/D of wings. A good airfoil provides L/D of about 100 driving total aircraft L/D of 20 or more. That means for each 20lbs weight you need only 1lbs thrust force to fly straight and level...
  11. Dusan

    Certification of Vertical Take Off Vehicle

    The channel wing is not really good for VTOL flight. Custer invented it as he wanted a wing that is not capable of stalling. The NACA's 1953 test (Langley Full-Scale-Tunnel Tests of the Custer Channel Wing Airplane. National Advisory Committee for Aeronautics, 1953) shows that about 8% lift is...
  12. Dusan

    Certification of Vertical Take Off Vehicle

    Hi Wayne, let her contact me, I'm also doing a lot of work in the VTOL space.
  13. Dusan

    Pusher verses tractor propeller

    No, and side forces are probably more relevant to a back mounted propeller as it is more distanced from the CG so it has more arm, the moment created is larger.
  14. Dusan

    Pusher verses tractor propeller

    Most planes are designed with oversize empennage to cope with propeller de-stabilizing effects, rotating stream flow-fuselage interactions, and so on. If the prop is mounted behind the fuse, the effects are much smaller, the empennage can be sized similarly to what is customary for gliders. The...
  15. Dusan

    Pusher verses tractor propeller

    The pusher prop theoretically ingest and re-energize the boundary layer so overall the plane should be more efficient, but at the same time the prop needs to cope with dirty air coming in, so the prop efficiency and noise suffers. Eventually the design - as all engineering is a compromise. Not...
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