Modern day "motorcycle of the air" aircraft class?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by cluttonfred, Oct 3, 2015.

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  1. Mar 18, 2019 #2121

    Victor Bravo

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    Were you asking me or Erkki?

    Speaking only for me, I don't really like the small tip plates on the end of the rear wing, they will not provide anywhere near as "solid" of yaw stability as larger and higher aspect ratio fins. Taller, narrower fins on the outboard end of the rear wing can work (Ercoupe), but you give away any and all benefit of the prop blast. The prop blast on a large central rudder will be a big deal on a mono-wheel landing gear like what your rendering shows. Even if you have nosewheel steering forward of the main gear, once you raise the nosewheel off the ground during the takeoff roll, you'd be relying on rudder authority from then on. Having the rudder in the prop blast will increase that authority.

    If you are referring to the Spratt wing specifically as a free-wing with no direct control input to it, I don't like it at all. The Mignet system of a direct control linkage from the stick to the forward wing for pitch control, I can live with.
     
  2. Mar 18, 2019 #2122

    erkki67

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    The Ultralight Spratt103 had direct control to the front wing like the Flea
     
  3. Mar 18, 2019 #2123

    Sockmonkey

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    I appreciate input from either of you.

    As erkki said, a spratt wing is essentially a Mignet type system only with two control linkages so the left and right halves of the wing can be pitched separately when you move the stick side to side. Two-axis with fewer parts than a moving rudder and moving wing would need.
    Now, I was under the impression that having the rudder out of the propwash was a good thing since the wash introduces asymmetrical forces on it so you need input to counter it.
     
  4. Apr 7, 2019 #2124

    ultralajt

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  5. Apr 7, 2019 #2125

    cluttonfred

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    Yikes, those intakes seem to be placed in unfortunate proximity to the pilot's...ahem...cockpit. ;-)
     
  6. Apr 7, 2019 #2126

    FritzW

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    I wanted to mention something about that but I couldn't find a way to say it that didn't sound dirty.
     
  7. Apr 8, 2019 #2127

    pwood66889

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    Fred Weick worked a long time at ERCO to get the independent yaw control removed. It involved canting the engine, and moving the "verticle" to the end of the elevators.

    " I was under the impression that having the rudder out of the propwash was a good thing since the wash introduces asymmetrical forces on it so you need input to counter it."
    Correct, Sock. But wash amount effects control; yet one's throttle may not agree with what one needs from the aircraft.

    The `coupe does approach a "motorcycle of the air." "Ask the person who owns/has flown one."

    Percy in NW FL, USA
     
  8. Apr 8, 2019 #2128

    Sockmonkey

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    To make sure I'm getting the idea across, The broomstick would be two-axis, using the two halves of the main wing for pitch and roll control. The rudders would be fixed, and only there for yaw stability.
     
  9. Apr 8, 2019 #2129

    Vigilant1

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    Not to be pedantic, but then they aren't rudders. They are vertical stabilizers.
     
  10. Apr 8, 2019 #2130

    blane.c

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    Interesting engine about the right size.
    BJC.PNG
    J&AS ENGINE.PNG
    J&AS ENGINE SPEC.PNG
     
  11. Apr 8, 2019 #2131

    Hot Wings

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    Yes it is interesting. Looks kind of like a Honda version of the Suzuki 1L. 50 Hp from the same displacement as the Briggs vertical engines. Being a marine engine it's probably rated for continuous operation?
    Nice OEM bosses that could be used for the PSRU mounts.
     
  12. Apr 8, 2019 #2132

    blane.c

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    2 Blade Propeller dia. = 1.83 times the cube root of the bhp.
    3 Blade Propeller dia.= 1.5 times the cube root of the bhp.
    Does anyone know for a 4 Blade Propeller dia the multiplying factor of the cube root of the bhp?
     
  13. Apr 8, 2019 #2133

    Vigilant1

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    Maybe a hint or clue about where this comes from? Is this some sort of rule-of-thumb for picking a prop diameter? I would think airspeed would need to be included somehow for this sort of thing to be useful.
     
  14. Apr 8, 2019 #2134

    ultralajt

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    :)
    Yes , I was about to say: "this design sucks!" :)
     
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  15. Apr 8, 2019 #2135

    blane.c

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    Dan Raymer's SIMPLIFIED DESIGN FOR HOMEBUILDERS page 23. And yes there is another formula with airspeed to check tip speed on the same page.

    I believe what he his saying is that these are the practical diameters the hp is going to be able to use. Then check to see if it works with the airspeed.

    I don't think airspeed is all that much of an issue in practical terms for what I am playing around with, it is mostly if I can reduce propeller dia. and also it may just be easier to build a four blade prop than a three blade prop. A four blade prop can be as easy as laminating two, two blade props together. Then it becomes whether they are more efficient parallel like the Lazair's or placed in some kind of X configuration or just plane ol' square to one another.
     
  16. Apr 8, 2019 #2136

    Sockmonkey

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    Ah, thank you. In this case it's not pedantic since it's a specific design factor.
     
  17. Apr 8, 2019 #2137

    Vigilant1

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    Thanks for the reference. It is probably a useful starting point, but maybe not equally applicable across all HPs. For example, for a 75HP engine and a 2 blade prop, it gives a result of 7.7. If that is "feet" then it would be a 92" diameter prop, and there's no 75HP engine I know of that turns a prop that long.

    With regard to helical tip speed, we do care about it, but doesn't change a >whole< lot with airspeed. The circular speed of the prop continues to be much more important in this regard than the speed of the airplane for most GA applications.
     
  18. Apr 9, 2019 #2138

    BJC

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    My copy (this is the first time I’ve referred to it - need to scan it soon) says the fourth root rather that the third. That is better. The 10 foot diameter for my airplane would necessitate an entirely new landing gear.


    BJC
     
    Last edited: Apr 9, 2019
  19. Apr 9, 2019 #2139

    blane.c

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    Sure but he is saying 7.7 feet is the biggest dia. that in practicality a 75hp engine is going to turn, then check tip speed and reduce dia.

    V (tip) = The square root of (V squared + {[pie x n x D]squared}) ; D in feet, V in feet per second, n=RPM/60.
    Crap is says to the fourth, I was looking at the fourth, guess I was interpreting square (four sides) to cube or something equally silly. It would be easier if I could type the proper formula instead of having to word it.
     
  20. Apr 9, 2019 #2140

    Dart

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    I'll start by pointing out that I'm ignorant of the facts around prop design, but have some impressions that are not aligned with what I'm reading here. I'd thought the general assumption was that a larger prop, aerodynamically is always better, and for practical reasons they are sized down? Moving lots of air more slowly and all that?
     

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