Decalage angle

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

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  1. Jan 21, 2020 #1601

    Doggzilla

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    Yes, changes in drag will change AoA.

    Reduction on the bottom will cause a slight nose up.

    And changing the angle of the engine may have a benefit, but it will only show in testing. Windmills actually work better with one side facing further into the wind, because it reduces tip vortices on that side. Forward sweep greatly reduces tip losses.

    But for a prop going a hundred times the RPM? I do not know.

    What I can say is that the blades being reclined backwards during high AoA is almost certainly not good for thrust.
     
  2. Jan 21, 2020 #1602

    Eugene

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    My God, so many things connected together!!! You changing one thing and everything else is changing!!! I have very long way to go before everything will work together perfectly. And maybe it never will??!! It's like moving target! This will be my first and my last airplane for sure. There is so much to do on this airplane, but so little time!

    Next question: in level flight attitude nose is very light, but as you dropping it down it's becoming unbelievably heavy. Is horizontal tail working hardest during landing?
     
  3. Jan 21, 2020 #1603

    Doggzilla

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    Heavy in which way? It may just be the static stability fighting you.

    Your elevator is only half moving, so the fixed part is going to fight you any time it’s at an angle. The higher the angle the more it will come close to matching the elevator itself.
     
  4. Jan 21, 2020 #1604

    TFF

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    The leverage point of the landing gear goes over center. From the CG it does not matter. Or at lest not the same.
     
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  5. Jan 21, 2020 #1605

    Eugene

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    That’s right, thank you! I don’t know what I was thinking. Completely forgot that airplane is balancing around 25% MAC.

    I should try to rephrase my question differently. Obviously CG is moving during takeoff and landing. Horizontal tail is responsible for balancing during extreme angle of attacks. Question should be like, how is Aircraft with obviously marginal tail size is handling large CG movements during takeoff and landing?
     
  6. Jan 21, 2020 #1606

    Eugene

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  7. Jan 22, 2020 #1607

    Eugene

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    I would like to know CG situation on your airplane and compare to my Skyboy.

    Skyboy CG range 21-36.6% MAC
    Solo CG at about 33-36% MAC
    With passenger CG at 25-28% MAC
    25-50 lb ballast is normally used by most Skyboy "light=170lb" owners with 912 engines for solo flights to move CG forward by 2-3% away from rear limit of 36.6%.
     
  8. Jan 22, 2020 #1608

    Eugene

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    image002.jpeg
     
  9. Jan 22, 2020 #1609

    TFF

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    Until the stabilizer is within about 2 deg of incidence of the wing cord line incidence, you are giving away all the speed you are chasing. You are making gains that are worthwhile but that is where your missing speed is. It will change the character of the plane, and you may not want that to change. The wing and tail are still a drag brake as set.
     
  10. Jan 22, 2020 #1610

    Tornado Flyer

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    Get you a Titan Tornado and FLY! You can keep the Skyboy to tinker with!
     
  11. Jan 22, 2020 #1611

    photocopter

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    I don't use MAC % for my c ofg calculations (I thought only airliners use it..) My question to calculate my aircraft's MAC: Do I include my flaperon trailing edge (hanging below the wing's trailing edge) to get my wing cord or do I just use the wing's leading and trailing edge to get my wing cord???

    When I fly (I only weigh 140Lbs) my Catalina is at the most rear C of G limit. I don't like to take ballast as long as I am within the limit.
     
  12. Jan 22, 2020 #1612

    Doggzilla

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    It does not look like you need to change the engine angle, but maybe have to adjust the elevator again.

    Just looked at your pics again from the previous page and something definitely seems a bit off. It does not seem to match any of the diagrams you posted on this page.

    When you leveled the aircraft the elevator appears near neutral angle compared to the main wing and thrust line of the engine.

    The elevator angle should be negative compared to the line of the engine thrust, so that when you add thrust it pushes nose up to counteract the nose down of the engine thrust.

    This should reduce the difference in trim between thrust settings. But the elevator controls will be heavier pulling back and lighter nosing down.
     
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  13. Jan 23, 2020 #1613

    Eugene

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    I have read this message dozen times by now, but still not sure if I understand correctly all of it. Really appreciate translation into plain English. Sorry, some Russians pretty slow.

    8A07C0DA-0F95-4272-B2C2-521BC113BCD3.jpeg

    I have received my explanation from Russia this morning. Wondering if everybody agree with it.

    - “ Picture above is correct for Aircraft with undersized horizontal tail. This is OK solution for low speed aircraft. But this solution is generating extra unwanted drag. For efficiency reasons and speed you should keep your engine exactly where it is. This way you have smaller moment between trust and center of mass. Smaller nose down moment. Smaller interference from fuselage and propeller is getting more clean air. Doesn’t interfere with horizontal tail and allows you to fly a little faster. So, keep it just the way you have and don’t blow on the tail at such aggressive angle.”

    C9828663-D415-477A-98BD-2BBB70DE6C64.jpeg

    Picture above is what I have right now if I make bottom of my wing level.
     
  14. Jan 23, 2020 #1614

    Eugene

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    if your wing is straight and has no positive or negative swept, then it’s very easy. I believe you mentioned ones that your wing is 48 inches wide. So this is 100%. 4.8 inches is 10% , 9.6 inches = 20% and so on. With zero at Leading Edge and hundred percent at trailing edge.

    this is not very important, I was just curious, that’s all

    7219B7D8-EA89-48F8-94D9-684A1DC315D7.jpeg
     
  15. Jan 23, 2020 #1615

    Eugene

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    I made that statement not out of frustration. Not at all. I said it because I am realizing every day how complex and interconnected everything on our flying machines. If you change one thing everything else is changing. Especially something like installing engine with two times more power. I really enjoying every minute of it and I do get that for normal person this kind of enjoyment very hard to understand. That’s OK with me. Still trying to find a way to go this summer to Oshkosh 1976.
     
    Last edited: Jan 23, 2020
  16. Jan 23, 2020 #1616

    Doggzilla

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    To be fair, your aircraft is much more complex than most other aircraft. This is why nobody uses large engines with it.

    The Lake LA-200 has a high pusher engine and it was extremely dangerous on landing. It had up to 250hp, and it made pitch control very dangerous. Anything over 250hp would probably be near impossible to control.

    So if you feel like this is very complicated, its because it is. Top pushers are very complex aircraft.
     
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  17. Jan 23, 2020 #1617

    Eugene

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    Here is my situation. Were are you sitting in reference to the wing?

    IMG_1246.jpeg
     
  18. Jan 23, 2020 #1618

    Doggzilla

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    Photocopter: Just use the wing itself. The additional area is negligible and would only move it an inch or two. If that is too much... there is a problem. The difference is so small that its equivalent to the pilot leaning forward. That's how little effect it has.

    If you have stalled the aircraft and not tumbled backwards... your CG is fine. If you feel the aircraft nosing upwards instead of downwards during slow flight... then its too far backwards. If its ahead of the center of lift it will want to nose down. Behind will want to nose up.
     
  19. Jan 23, 2020 #1619

    Eugene

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    I agree. If you try to do your weight and balance at different AoA (+ or - 3°) difference will be only 1% or so. I did it many times
     
  20. Jan 23, 2020 #1620

    photocopter

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    Hey Eugene, here the details of my Catalina




    img052.jpg
     

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