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  1. Blackburn Mark

    Propeller size conundrum

    Got a response from E-Prop regarding swinging one of their 150cm or 160cm pitch adjustable props with such marginal power (15~20hp) They advised the 160cm (63") for better efficiency. Ordered one of those. Just need to work out how much reduction I want to run (tip speed)
  2. Blackburn Mark

    Propeller size conundrum

    With operating at a lower speed and power than a Quicksilver mx, I am hoping I will be no worse off than one of those :) In fact, if I can swing a 160cm, I am hoping to be quieter than I am now with a 130cm.
  3. Blackburn Mark

    Propeller size conundrum

    These props (paramotor prop) run in pretty messy air, very close to the pilot, cage, netting... The prop on this design has an easier life in that regard unless what spills of the wing is going to interfere. I could possibly even skin the rear of fuselage with untreated polyester for a nicer...
  4. Blackburn Mark

    Propeller size conundrum

    Scout Paramotors uploaded this yesterday, an interesting insight into the gap between launch and cruise for us slow fliers.
  5. Blackburn Mark

    Propeller size conundrum

    Its not something I had any desire to grapple with, the spine behind this particular project was to take the results of other peoples success and juggle them into a goal that wouldn't require a degree in fluid dynamics', structural engineering or infinite navel gazing. I'm not a skilled aircraft...
  6. Blackburn Mark

    Propeller size conundrum

    There are paramotors that will fly at 50mph+, faster than I will be flying at, the paramotor I have now will do 30mph+ but is most efficient at 25mph (ish) so we are not looking at any vast departures regarding "designed for flight speeds". Ascertaining the suitability of the DT-Propeller's...
  7. Blackburn Mark

    Propeller size conundrum

    So correct me if I am becoming more lost: "IF" we maximize diameter to gain the associated advantages, we reduce the size of the window in which those advantages sit (it becomes a more precisely "single speed" aircraft and any deviation from that speed window "more" quickly becomes a...
  8. Blackburn Mark

    Propeller size conundrum

    Ahhhhh..... I think a bell just rang in my head! I assume, inversely, if I tune for max static, at cruise the prop may be close to free-wheeling at 80% :) I'm going to have to ponder this... It felt like a gamble might be on the cards with a 160cm but the power is so marginal, I would like the...
  9. Blackburn Mark

    Propeller size conundrum

    I am struggling to grasp what you are trying to say, I just attempted to download the software so I could have a play but my connection is really bad at the moment and I keep getting a 404 Are you saying we have some evidence that the 130cm is a better option?
  10. Blackburn Mark

    Propeller size conundrum

    I always thought the adage was "keep the propeller as long as possible for as long as possible"... ? I thought it was a play on // Make it as long as you can but not so long you shorten it via a prop strike..... I'm happy to be corrected if there is more to the saying. I have managed to acquire...
  11. Blackburn Mark

    Propeller size conundrum

    They are pretty gutless but despite enjoying more power and a snappy propeller mass (E prop), my usual operations tend to be at least a two hour meander (up to four if its warm and I'm not fighting my wing) so the fuel burn is a big feature for me. If I fail to make the 70kg weight, I can always...
  12. Blackburn Mark

    Propeller size conundrum

    Using E Prop's calculator: I think that would leave me with 31.9kg thrust at 80%rpm at a 30mph cruise speed (160cm prop) // (130 prop = 28.6kg) Full power static (160cm=74kg) (130cm=64kg) I don't trust that last number, I run a 130cm now and I'm 99% sure I'm not getting 64kg static, even...
  13. Blackburn Mark

    Propeller size conundrum

    Still no word from E Prop but I think I have found a hint on their site: The 160cm on this graph seems to "just" place me within the lower end of their spec at 20hp 8000rpm 1:4 reduction (2000rpm) I might lose something at 80% but I cant see their being any wild kinks in that curve bellow 20hp.
  14. Blackburn Mark

    Propeller size conundrum

    I stand corrected, I always assumed it was to prevent aerodynamic forces twisting the blade.
  15. Blackburn Mark

    Propeller size conundrum

    The Helix has quite a meaty mounting center, 75mm hole pattern.... The passthrough needs only be 40mm plus a touch for clearance so I am reasonably confident I can bore the required extra without too much drama.
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