Recent content by Dusan

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

  1. D

    Where does one find an aerospace Engineer to hire

    Oh, amazing! If it can do VTOL I might bite!
  2. D

    The Dobson Convertiplane - VTOL

    I searched for it; It's featured in Aviation Week, August 3, 1953, page 26,27. I could not see the whole article, but a low resolution image of it. Maybe someone has a paper copy. Really interesting project. It tries to simplify the tilt wing/rotor design to extreme. I wonder how the concept...
  3. D

    Where have all the flying cars gone???

    Make the wing small enough that the span length is road-able. Joke aside, a series of small span wing fixed wing aircraft were built to compete for "world's smallest" status. Stits SA-2A Sky Baby, Stits DS-1, and Starr Bumble Bee II are among this category having a wingspan well under 8ft. From...
  4. D

    Flying Car ?

    For sure I'm not describing just an flying taxi. I'm envisioning the aircraft of my dreams something similar to this concept: ADR-1, from : Aliptera When manufactured and commercialized, people will be able to buy one, and hopefully able to take-off and land anywhere(within limits) and not to...
  5. D

    Flying Car ?

    An roadable aircraft, certified for road and air operations is a big compromise. It will never drive or fly effectively as the engineering requirements are opposite. Most likely it will be outperformed by a Honda civic or a Cessna 172 in driving and respectively flying modes. A "flying car"...
  6. D

    Busted

    Romania, as well. One of the issues there was hard to defect as all of the surrounding countries were communist too. Most fled trough former Yugoslavia as it was less likely to be "returned" if caught.
  7. D

    Busted

    Wow! This resonates with me, I grown up in a communist country. Some of my friends defected using inflatable tractor tubes, me I dreamed of building a powered hand-glider and fly to liberty. Fortunately, there was a revolution, the country opened up and I was able to legally emigrate to Canada...
  8. D

    Contra rotating propellers

    This is exactly my point in post #70, and the main reason I think contra-rotating are less efficient aerodynamically for light loaded props; even without counting gearing/transmission looses.
  9. D

    Contra rotating propellers

    This is essentially correct, and F=2*rho*A*vi^2; but P=F*(vi+v0). For the first propeller the v0=0(static condition) but the second prop's v0 is "seeing" induced velocity from the first one, so the second prop needs more power for the same thrust. If you want to use two propellers, it's always...
  10. D

    Contra rotating propellers

    It looks similar to McCormick formula, I'll look into this, Henryk, give me a couple of days.
  11. D

    Contra rotating propellers

    From disk actuator theory, a "maximum value" of thrust can be easily calculated, and for a 100HP, 1.7m diameter propeller, a thrust "maximum value" of 319Kg is calculated. For a good propeller, you should get to 0.8-0.9 of that, that's about 270Kg thrust. So, as you are not even close to that...
  12. D

    Contra rotating propellers

    No, same solidity means same ratio of total blade area to the disk area. I assume you used same propellers for both tests, and that means for single prop you have only half solidity. To have same solidity, you should use a blade that is two times as wide (double cord) for the single rotor, same...
  13. D

    Contra rotating propellers

    In order to have meaningful results you should compare the rotors having the same solidity, otherwise you're not comparing apples to apples.
  14. D

    Contra rotating propellers

    For a ducted propeller, as I mentioned before, using contra-rotating prop doesn't make sense at all. The duct forces all the air to pass trough both propellers, there is no slipstream contraction, so no influx of fresh air into the downstream propeller, all the thrust advantage of coaxial rotors...
  15. D

    Contra rotating propellers

    Disk loading on the Henrik contraption I think is about 40kg/m2, on par with some helicopters. From Leishman - "Principles of Helicopter Aerodynamics" pg.69 swirl loss on a typical helicopter rotor is about 1%. Taking into consideration just that contra-rotating propellers blades are "seeing"...
Top