Decalage angle

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

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  1. Mar 9, 2019 #801

    Eugene

    Eugene

    Eugene

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    Peter,

    Forgive me if I asked this question before. I looked in old messages, but didn't see it.

    In the past 2 years I talked to different Skyboy owners and they all confirmed to me that this airplane flies completely different with passenger vs solo. Best way to describe is to say, that with passenger airplane feels overloaded. You need much more nose up trim. Trim is not sensitive anymore. You can move trim lever back and forth by 1/2 inch and feel very small gradual changes in climb or descent. Otherwise flying solo aircraft would respond immediately with up or down by 500 ft/min.

    In addition ailerons with passenger becoming very lazy and wiggling your wings will turn in to slow motions. I call it flying cow. One time I was flying C-172 with 200 lb over-gross and 160 HP with very similar feel in controls.

    I was told by some engineers that this kind of behavior is direct result of under sized horizontal tail. Wondering what do you think.

    Thank you!



    Peter Garrison
    12:46 AM (1 hour ago)

    to me

    Eugene,

    The lack of trim effectiveness would be expected if the horizontal stabilizer were already operating near its maximum ability with two aboard. Do you have any photos of the empennage in flight while carrying two people? Is the 2-person loading the most forward CG case? It would then be the most statically stable, meaning that stick forces would become heavier. There would be some diminution in roll response because the moment of inertia about the longitudinal axis would be greater, but I'm surprised that the effect would be as large as you describe.


    Peter,

    This picture was taken with 200 lb lead ballast on passenger seat, at 85 MPH, CG at about 23% MAC, stabilizer at about negative 8° AOA and elevator at 10-11° AOA.

    This aircraft was certified in Germany with CG limits 21% - 36.6% MAC. This is same CG range as Aeronca Champ with same NACA 4412 wing and you feel very little difference between solo flight and with passenger. Aeronca empty about 100 lb heavier and same cruise speed with 85 HP engine. My Skyboy has 100 HP engine.

    I remember during our first flight with LSA instructor right after takeoff he decided to abort our lesson. On downwind he was telling me that something is wrong with this airplane and he not comfortable flying with me and checking me out in it. To prove his point he was moving stick left and right with 6" spread, but aircraft was flying straight and didn't respond.

    Only later after talking to different Skyboy owners I found that this behavior is normal for all Skyboys and we start flying again.

    Thank you!





    fullsizeoutput_1362.jpg
     
  2. Mar 11, 2019 #802

    Eugene

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    Peter,

    Just wanted to add something, that I think it's important. Skyboy was going through German certification in 1992 as ultralight with 50 HP engine, larger wing 168 sq. ft. with different P3 airfoil.

    For American market 100 HP engine was installed with smaller wing 139 sq. ft. and 4412 airfoil.

    Same 5 ft chord was used on both wings and same empennage without changes.

    Thank you.




    Peter Garrison
    2:21 PM (6 hours ago)

    to me

    Eugene,

    Reducing the size of the wing while keeping the horizontal stabilizer the same would normally be expected to increase longitudinal stability. On the other hand, I am inclined to think that power is destabilizing in this airplane, and so reducing power would increase stability and reduce the balancing load required because of the high thrust line. But I cannot guess the magnitude of either change.

    Lack of roll response, with a large dead band in the middle of the stick travel, is not uncommon, and can be due to adverse yaw or to poor aileron design. Many airplanes, especially older ones, required rudder to initiate a turn, with ailerons later adjusting for coordination and maintaining back angle.




    Peter,

    Ok, I will not worry about slow roll response anymore. On the other hand, it's only slow with passenger.


    So, with engine above the wing, more power should be compensated with larger horizontal tail. This is what I understand from your message. With reduced power down to 50-60 HP or so, airplane very stable, slow 65-70 MPH, with 6-8° AOA and very relaxed. Because at that point aircraft in its design configuration.

    I was trying to find what needs to be done to match this aircraft to 2 times larger 100 HP engine. I was told by many that correctly designed 100 HP - 100 MPH, LSA aircraft should have decalage of 4-6°, and not 10-12° like on my Skyboy. Without knowing any better I was after decalage.

    Someday I will try to convert my flat tail to 0009 airfoil with increased area by 20%. Hopefully it will make some difference.

    Thank you very much for your help!
     
  3. Mar 16, 2019 #803

    BBerson

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  4. Mar 16, 2019 #804

    Eugene

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    Its hard to tell exactly on this picture were to measure angle for horizontal tail. Thank you. Very interesting airplane!
     
  5. Mar 18, 2019 #805

    Eugene

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  6. Mar 18, 2019 #806

    Eugene

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    000F439E-7AB1-40A5-979E-B29DE7B84CC2.jpg

    Seems to me that during level flight horizontal tail will be above and outside of turbulence that generated by wide cabin and above wing down the wash. From that standpoint looks like a very good design
     
  7. Mar 18, 2019 #807

    BBerson

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    Yeah. The tailboom is angled upward.
     
  8. Mar 18, 2019 #808

    BJC

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    Down was comes from above the wing too.


    BJC
     
  9. Mar 30, 2019 #809

    Eugene

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    Exhaust is all done, muffler feels rock solid with no movements at all. So, no support brackets needed.
     

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  10. Apr 13, 2019 #810

    Eugene

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    I have decided to do painting after the test flights. There is good chance that something will be changed. Now I understand why I have seen at Oshkosh year after year so many unpainted airplanes.

    Every little wing turns out to be 4.4 pounds each, with total 8.8 pounds additional weight on the tail. This will move my CG during solo flight with full tank from 34.1% back to 35.9% MAC. Looks like 20 pound ballast on the passenger side will fix that back to normal.
     

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  11. Apr 19, 2019 #811

    Eugene

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    Here is my first test flight report.

    Did go for short 30 min flight, just to see that everything is working OK. Was pretty bumpy, airplane didn't feel any different at all and pretty much same speed. Except trim lever moved forward to more or less normal and usual position. Next time I will go with camera to see elevator position in level flight.

    I do have another question.

    After I did my weight and balance turns out that CG during solo flight with full tank will be at 36.6% MAC. Witch is my rear limit on Skyboy. So, to be safe I put 25 lb in front of rudder pedals on passenger side and that moved CG forward by about 2% to 34.6% MAC. I heard somewhere that ideal CG position is at 28-30% MAC. If that is true, then I need 75-90 lb ballast.
     
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  12. Apr 19, 2019 #812

    proppastie

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    I think 25% is considered the best very safe......28-30% is not far off. If you were able to sit farther forward somehow (move the seat?) perhaps it could be done without the ballast. Probably a major project though. I know with my bird I will not cut/mount in the control stick until I have all the weights measured because where I sit will determine where the CG is.
     
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  13. Apr 19, 2019 #813

    Eugene

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    My seat doesn't move. That left me with 2 options:

    #1 - using ballast on passenger side

    #2 - to do positive wing swept by 2° or so to move CG forward


    Screen Shot 2019-04-18 at 10.18.49.png Screen Shot 2019-04-17 at 22.27.29.png
     
  14. Apr 19, 2019 #814

    Eugene

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  15. Apr 19, 2019 #815

    BJC

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    Have you determined the location of the neutral point?

    A good starting value for the minimum static margin is 5%, but you may be comfortable with less after a careful series of flight tests.


    BJC
     
  16. Apr 19, 2019 #816

    Eugene

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    No, I don't know how to do that. Need to do my homework.
     
  17. Apr 19, 2019 #817

    proppastie

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    if you can build a new tail you can move the seat....check out what 10" forward for your weight does to the CG...You could extend the Pod forward to do the seat movement, or just bend your knees more. Might make only the pilot seat move forward and if you have a passenger move it back to the existing position.
     
    Last edited: Apr 19, 2019
  18. Apr 20, 2019 #818

    Eugene

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    I am 6 foot 1 and running out of legroom already. But even if I can find the way to move myself forward by 6 inches, CG will move forward only one 1.5%.

    I already put 65 pounds ballast in my airplane and it's all ready to go for test flight tomorrow morning. This will give me CG position at 30.7%.
     
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  19. Apr 20, 2019 #819

    BBerson

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    Flight testing the aft limit should be with a parachute. In case of unrecoverable spin.
     
  20. Apr 20, 2019 #820

    proppastie

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    See how it flies if you like it great....I did not do any calculations till now but should you want a major winter project.....moving your pilot to -30 will bring you into 30% MAC

    assuming everything else is the same,...not possible because as you move the structure/pod forward you are moving more weight forward and you will not have to move the seat that much. Certainly not an easy fix, but you seem to like working on this.
     

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    Last edited: Apr 20, 2019

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