Decalage angle

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

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  1. Jul 15, 2019 #1201

    proppastie

    proppastie

    proppastie

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    You need the elevator/tail to keep you level.....if the boom bends it all comes out in the wash. You will still have the same amount of drag to keep the aircraft level, and you still will go the same speed. Changing the W&B so there is less deflection needed probably will allow you to pick up a little speed, but with the drag of the engine, and shape of the fuselage it will not be much. If you do that you will sacrifice stability.
     
  2. Jul 16, 2019 #1202

    Eugene

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    OK, just wanted to make something clear. This is not about speed increasing or drag reduction at all.

    From the very beginning of Skyboy production this airplane with big engines was developing some kind of elevator vibration. Nobody could explain what it is and some people call it flutter. Factory in Europe did a lot of research and best they can do is issued AD to install bigger and heavier elevator ballasts. This heavy counterweights really do suppress that vibration to the minimum, but you constantly feel it with your hand in flight. If God forbid you have a loose connection somewhere it will progress to something like I showed on my video.

    After talking to many people I made a conclusion that very good recipe against any kind of a flutter or vibration is to make sure that everything is very rigid without any play.

    Well, recently I learned that whole empennage on my airplane is very flexible and nothing I can do about it. I know now that angle I see on my horizontal tail on the ground is different from angle I have in-flight. Angle itself doesn’t make me nervous. I wanted to know if this is OK to have such flexible tailboom.

    If they all do that and this is nothing to worry about, then I will forget about it and start concentrating on my trip to Oshkosh.
     
  3. Jul 16, 2019 #1203

    TFF

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    You have the type of airplane you have. I find it interesting that you experiment. You seem to be learning a bunch. You still are not going to create a new airplane out of it. It will always be what it is. I think also the other model you keep trying to match probably struggles to get the performance numbers you are after, and probably more like what you are flying than not. There are a lot of airplanes that have multiple aircraft on one certification. It means there is a common base but each model has to match its specs. 172s,Mooneys,Piper. Just about every airplane company does that.
     
  4. Jul 16, 2019 #1204

    Eugene

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    So, in plain English, what I read between the lines is - what I have is not ideal and far from perfect. After all every airplane is a compromise. 1.5° deflection under 50 pounds load is not a very good thing but it’s not dangerous either.

    I simply didn’t know, this was a new finding for me. I will do my best not to think about it during my flights. But I can’t promise that I can make it happen. It will be very hard to do.
     
  5. Jul 16, 2019 #1205

    proppastie

    proppastie

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    From FAA Glider Criteria limit load on horizontal tail ......if it survives limit which includes gust loading you should be good to go. Need to calculate the area and use the chart to get the load. Down load full book my site or google....you also could calculate the strength of your boom first before you break your airplane.
     

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  6. Jul 16, 2019 #1206

    Eugene

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    I am not afraid to brake my tail boom. I was under impression that whole empennage structure needs to be rock-solid to prevent any play during load changes in flight.

    Tail boom flexibility = its what was making me nervous and I was trying to solve that on paper with aluminum tubes or so. Cables only good for load distribution.
     
  7. Jul 16, 2019 #1207

    Eugene

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    Screen Shot 2019-07-15 at 21.34.19.png

    So, I will keep my speed under 190 MPH from now on
     
  8. Jul 16, 2019 #1208

    Eugene

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    40ABD493-B774-459A-8E19-618E557C1F74.jpeg 60EB0FE6-9E07-4BEB-BE4E-45B9E2C5971D.jpeg 108A1EA5-2E37-4118-B570-C337C928E927.jpeg

    From Peter:

    Eugene,

    Since the load that seems to be of concern is downward on the horizontal stabilizer, I don't see why tubes would be an improvement on cables. As far as the attachments are concerned, you would like a line projected along the cable/tube to intersect the center of the wing spar to which it is attached. The additional diagonal brace within the wing is a good idea.

    But is all this really needed? In photographs of your horizontal tail in flight, there does not seem to be an excessive amount of up elevator.
     
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  9. Jul 16, 2019 #1209

    BBerson

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    Peter is usually right.
    Another 6" X 3 foot tube could be slipped over your boom tube at the fuselage. That would reduce the deflection substantially.
    I think several do that.
    Your brace will just bend the rear wing spar down at that point. Needs to be at the rear strut point same as your cable were.
     
  10. Jul 16, 2019 #1210

    Eugene

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    Wow, I didn't know! Can you give me some examples?
     
  11. Jul 16, 2019 #1211

    BBerson

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    Try Earthstar. Maybe Kolb.
     
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  12. Jul 17, 2019 #1212

    Eugene

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    Peter,

    Does it really need it? I don’t know, and this is what I am trying to answer.

    What I do know that airplane in level flight has some kind of isolations that I can’t explain. You can experience that when driving small car and pulling big heavy trailer. Situation when trailer will be constantly jerking the car back-and-forth.

    I feel something very similar in level flight in my airplane on control stick.

    Just a little reminder that airplane was certified with 50 hp engine and P3 airfoil. Right after factory started shipping this airplanes with 100 hp engines and 4412 airfoil, they started developing some problems . They didn’t know what it is and where it’s coming from. Some people call it elevator buffering, some call it flutter, some call it vibrations . They really didn’t know how to fix it, but after series of experiments they discover that larger and heavier elevator ballast seems to suppress this buffering to relatively acceptable level.

    Everybody I talk to they always stressed importance of everything needed to be solid and rigid on your aircraft to avoid flutter. Recently I discovered that my whole empennage has the flexibility to deflect in flight possibly up to 2°.

    But if you telling me that I am worrying about nothing, then I will get that out of my head. This was simply attempt to make tail rigid so doesn't move up and down under load changes during flight.

    Peter Garrison
    3:22 PM (4 hours ago)
    [​IMG]
    [​IMG]
    to me

    Eugene,

    I think that what you are feeling is the turbulent wake of the fuselage and propeller buffeting the elevator. I doubt that flutter could occur at the speed at which you are flying. Has there ever been a case of a Skyboy losing its tail in flight?
    [​IMG]
     
  13. Jul 17, 2019 #1213

    Eugene

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    "As far as the attachments are concerned, you would like a line projected along the cable/tube to intersect the center of the wing spar to which it is attached. The additional diagonal brace within the wing is a good idea."

    I don't have clear picture about what is Peter trying to say. Can someone help me please ?
     
  14. Jul 17, 2019 #1214

    proppastie

    proppastie

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    think you need a fitting from top cap to bottom cap of the spar and attach to the middle of the spar....so you do not twist the spar or wing by pulling the top or bottom of the spar.

    not knowing how you spar is made so it is just a guess, if the spar is round would need a fitting around the spar and attach a the center of the spar...still just a guess
     
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  15. Jul 19, 2019 #1215

    Eugene

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    33C140C8-83BB-432D-93C0-07339F318151.jpeg

    Wondering if this is correct picture
     
  16. Jul 19, 2019 #1216

    Eugene

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    Screen Shot 2019-07-16 at 21.42.13.png
     
  17. Jul 19, 2019 #1217

    Eugene

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    Screen Shot 2019-07-18 at 22.32.44.png Screen Shot 2019-07-18 at 22.32.13.png

    Found something interesting. Pictures above about Aeronca Champ with tandem seating and large CG movements (18-36%). Stabilizer incidence set for 5° and wing for 1°.

    Pictures below about Aeronca Chief with side-by-side seating and very small CG movements (23-25%). Stabilizer set for only 3.5° and same 1° for wing.

    This airplanes with about same weight and same wing, flying with same 60 HP engine at 75% power = 47 HP and going at same speed of 90 MPH.

    So, looks like at this kind of speed 5° tail vs 3.5° not making any difference at all. Theoretically for tandem seating they should of installed larger tail, but instead they made incidence by 1.5° larger. And it works!!!

    This airplane moves at 90 MPH on 47 HP. My engine need to make 90 HP for this speed.

    Screen Shot 2019-07-18 at 22.30.18.png Screen Shot 2019-07-18 at 22.29.34.png
     
  18. Jul 25, 2019 #1218

    Eugene

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    fullsizeoutput_1776.jpeg fullsizeoutput_1775.jpeg

    Flying home from OSH I found myself holding right rudder in order to keep boll in the center. I am sure it was always like that, but for my short flight , I didn't pay attention to it.

    On the ground I moved pedals in to same position and you see pretty big rudder deflection.

    Aircraft is 100% symmetrical from left to right. I was making sure of that with many diagonal measurements during process of changing wing swept.

    Can someone explain to me what is going on? Engine installed with 1.5° angle.Thank you.


    IMG_1958.JPG
     
  19. Jul 25, 2019 #1219

    proppastie

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  20. Jul 25, 2019 #1220

    BBerson

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    The prop wash rotates and hits the tail on one side. It varies with power level.
     

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