Decalage angle

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Eugene, May 29, 2017.

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  1. May 24, 2019 #881

    Eugene

    Eugene

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    Smoke generators!!!??? So cool!!! Why didn't I think about it with my Russian brain??? I will look in to it! Thank you!

    Sure I can make more VGs and install them on the belly. That is no problem.

    So, every time we asking horizontal tail to do its job in some terrible turbulent air flow, = effectiveness is going down hill and unbalanced elevators starting to dance up and down even at low speed? And 100% balancing does quiet them down? Do I understand this life correctly?

    45364219_315404335857774_9193682353866670080_n.jpg

    Picture with short rear cowling
     
  2. May 24, 2019 #882

    Eugene

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    Picture of Skyboy rear cowling

    qUgpKF61Twud7HJc67RePQ.jpg F8rzhmP2QJKC81wHHI%WWw.jpg pJWBelTDQsyuOIKXj13btQ.jpg
     
  3. May 24, 2019 #883

    proppastie

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    it does not make sense intuitively that flight without the rear cowl, would give better results, but it might be interesting to try it.
     
  4. May 24, 2019 #884

    Doggzilla

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    If it doesn't do anything at all that tells us it's either engine or prop related.

    It could also be creating a low pressure on the bottom center of the wing during fast flight, cancelling out some of the lift and causing lots of drag.

    There are so many possibilities that I don't think we will know without a detailed survey of airflow.
     
  5. May 24, 2019 #885

    BBerson

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    Intuitively yes, but truncated bullet shapes can be less drag. My car (CRX) is truncated. Certainly less aft weight.
     
  6. May 24, 2019 #886

    Doggzilla

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    They actually use that on airliner wings because it's actually more aerodynamic at the edge of flows with different speeds.

    The airflow on the top part of the wing can even go supersonic, and having a truncated trailing edge with "carrots" significantly improves stability and drag.
     
  7. May 24, 2019 #887

    Eugene

    Eugene

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    To my surprise smoke generators is not something I can purchased in Walmart for $19.99.

    I am not hundred percent sure, but I think I heard from somebody, who tried to fly without rear cowling. I believe it was very uncomfortable ride and conclusion was made not to try it again.

    It was probably very similar experience to my attempt to fly without counter weights on elevator. this was a recommendation from my designer. I barely made 300 feet, turn around and landed on taxi way. Will never do that again!
     
  8. May 24, 2019 #888

    proppastie

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    He is Polish and you are Russian? .....maybe he wanted to get rid of you.
     
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  9. May 25, 2019 #889

    AdvenJack

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    I'm reading through this 45 page thread with great interest as fast as I can,
    while being attentive to all details!!! I just read post # 372 (dated Jan. 9, '18)
    "Went for test flight today with straight wings (no forward swept).
    Big improvement = at least 10 mph faster. Result of CG movement
    from 36% to about 33.5% MAC. AOA looks normal now at 100 mph
    and no more ballast up front. Will try to post pictures."

    I became so happy on your behalf Eugene, that I had to pop in and say congratulations!!!
    Post # 422 is too funny, and post # 488 Mother-In-Law flight in your SkyBoy = Huge Victory!!!
     
    Last edited: May 26, 2019
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  10. May 26, 2019 #890

    Doggzilla

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    I missed that.

    Interesting enough, that agrees with our theories that it's low pressure behind the fuselage.

    With forward sweep the airflow reverses and flows towards the center of the wing, which happens to be aligned with the rear of the fuselage. It would exacerbate the low pressure already being created by the rear fairing.

    With forward sweep the vortexes also roll off the center instead of the tips, due to the reversed spanwise flow.

    Edit: and into the prop.
     
    Last edited: May 26, 2019
  11. May 26, 2019 #891

    AdvenJack

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    Hi Eugene,

    Regarding posts #s 510, 511 *These are Outstanding posts, except for the last line of
    Post 511 where you say "Sorry for waisting your time". I have learned a whole lot from
    this thread and I'm only a little more than half way through it. Reading this thread
    has been very intriguing and educational for me. If I lived near you, you'd never get
    rid of me. I'd be standing there holding the flashlight for you as you worked, and hand-
    ing to you, the next tool that you wanted, or whatever!
     
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  12. May 27, 2019 #892

    Eugene

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    https://drive.google.com/file/d/1TLkJZ1G0hHS4wuQxqCamFLw3h9CxSfDp/view?usp=sharing

    This is flight from this morning after removal additional plates from elevators. Everything is back to normal and control stick is not dancing back and forth in my hand anymore. You can see on this video little vibration, but I am sure it is normal for pushers.

    Screen Shot 2019-05-26 at 19.58.50.png

    Still need a lot of nose up trim, as you can see on this picture. That is surprising because stabilizer has additional 3.2 sq. ft. of additional area. That is about 15% increase for whole horizontal tail.
     
  13. May 27, 2019 #893

    Eugene

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    Screen Shot 2019-05-25 at 22.14.17.png

    Maybe I should copy as much as possible from this airplane. Sounds like very good flying machine. Only difference is tail higher. Something I am not able to change.

    IMG_2557.jpg

    My tail positioned inside of bumpy air flow created by wide cabin.
     
  14. May 27, 2019 #894

    Doggzilla

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    Note the difference in shape of the rear fuselage. Much thinner on the top, but much wider as it meets the tail boom at the bottom.

    I wonder what the effect of moving the engine a foot to the rear would do. If that would help allow the prop to get better flow instead of having to pull directly off of the boundary layer of the fuselage and wings.
     
  15. May 27, 2019 #895

    Eugene

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    Impossible experiment from CG standpoint
     
  16. May 27, 2019 #896

    Doggzilla

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    Not really. It's maybe a quarter the total weight, moving it a foot would only move the CG a few inches at maximum.

    Much less than your nose ballast has moved it forward.
     
  17. May 27, 2019 #897

    Doggzilla

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  18. May 28, 2019 #898

    Eugene

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    3" prop expansion already installed. But gearbox on 912 engine doesn't like them at all. My engine have only 1114 hr but on 3 rd gearbox already.

    Here is another prospective from my russian friends.

    fullsizeoutput_1706.jpeg

    This inside corner needs to be round like on Seamax

    fullsizeoutput_1709.jpeg

    Yes fuselage is very wide on the bottom and needs to be longer to prevent flow separation. But on top looks relatively narrow very similar to Seamax.

    fullsizeoutput_1705.jpeg


    New 70" prop vs 62" original already getting enough clean air and have OK efficiency. That is why new prop pitched to only 13° vs 18°on old one. Propeller area close to the center not doing much anyway and that is why moving muffler down didn't give any effect at all.

    fullsizeoutput_1707.jpeg

    Of coarse engine cowling will do something. So is everything else. 20% horizontal tail area increase needs to be done by increasing it's span to get outside of turbulent air created by low part of fuselage.
     
  19. May 28, 2019 #899

    Doggzilla

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    Looks like you are ahead of me then.

    When you changed the sweep of the wings and gained that speed, did you notice a change in vibrations?

    I wonder if those gearbox failures were exacerbated by the prop being fed uneven air and having unusual amounts of vibrations. Off center loading of props is really bad for gearboxes.
     
  20. May 28, 2019 #900

    Eugene

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    Gear box problems, I was told, all related to 4-blade Warp drive with very heavy hub. So heavy, that they don't make them anymore.

    Removing forward wing swept resulting in CG movement about 2.5% forward. This airplane with passenger or ballast will fly a little faster, smaller AOA, will need more UP trim with tail becoming loaded at that point with no vibrations at all, but very lazy maneuvering with overloaded feel.

    fullsizeoutput_170c.jpeg

    Maybe inside of new rear cowling I can have some reinforcements for tail boom. Or cowling itself can be made strong enough to act as structural part.
     
    Last edited: May 28, 2019

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