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Thread: WACO YMF


  1. #15926

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    RE: WACO YMF

    Jaybird,

    I fly full scale as well. Much better than RC planes. Never wrecked one yet. I brought this up because I thought the subject has been ignored by the model side. Just balancing it isn't enough in my view. I would really like to know the theoretical approach needed to get the answers. Beside me is a text by Barnes McCormick,who was a prof at Penn State and a world class expert on Aerodynamics. I'm not about to grind through all of that, but would like a more simplified answer appropriate to RC planes.

  2. #15927

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    RE: WACO YMF

    Sorry, didn't mean to preach to the chior.

    I agree 100%...the model side of aerodynamics seems more of a mystery than full scale. I look at a big Telemaster for instance and notice that the stabilizer is a large flat bottom UPRIGHT airfoil just like the wing! How can that NOT produce upward lift all the time? I look at my 1/6 scale Concept Fleet and the stabilizer is also a flat bottom upright airfoil with positive incidence. That kind of puts the tail downforce out the window too, or at least would seem so.

    Calculating the information you are looking for is far beyond anything I could get even get close to.

    I do know the GP WACO ARF has -1 incidence on the top wing and +2-1/2 on the symetrically shaped stabilzer and it flies great!

    Good luck on your search. If you do find a answer please share it.

    Jaybird

  3. #15928
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    RE: WACO YMF

    ORIGINAL: Jaybird

    Sorry, didn't mean to preach to the chior.

    I agree 100%...the model side of aerodynamics seems more of a mystery than full scale. I look at a big Telemaster for instance and notice that the stabilizer is a large flat bottom UPRIGHT airfoil just like the wing! How can that NOT produce upward lift all the time? I look at my 1/6 scale Concept Fleet and the stabilizer is also a flat bottom upright airfoil with positive incidence. That kind of puts the tail downforce out the window too, or at least would seem so.

    Calculating the information you are looking for is far beyond anything I could get even get close to.

    I do know the GP WACO ARF has -1 incidence on the top wing and +2-1/2 on the symetrically shaped stabilzer and it flies great!

    Good luck on your search. If you do find a answer please share it.

    Jaybird
    All airfoils with the exception of an asymmetric airfoil require a AOA component to produce lift, when your flying your wing will assume it's own AOA needed to carry the load, but that doesn't necessarily mean that your horizontal stab is carrying any + or - AOA, it is really more of how the designer set up the aircraft, the chosen airfoil, the AOI in regards of wing, fuselage center line and horizontal stabilizer relationships and so on. In this picture you can clearly see that I set up the horizontal stabilizer with 3 degrees positive AOI, and had the wing set at 0 AOI in relation to the FCL. Note that the paint trim line is running parallel to the FCL.

    Bob
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    Fly It Like You Stole It!!!

  4. #15929
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    RE: WACO YMF

    The issue that we get into have to do with Reynold Numbers. Full Scale airplanes differ from models due to the effects of Scale Volume, not Linear scale. The bigger the model, the more like the full scale it becomes. For example, a cube that is 4"X4"X4" will have a volume of 64 cubic inches. (4X4=16X4=64) A quarter scale model of that cube is 1X1X1 which yields a volume of 1. Even though the linear scale is one fourth the size of the full scale, the volume is much different. Hope this helps you see the difference.

    Bill, Waco Brother #1
    Its easy, just glue all the pieces together, and sand off everything that doesnt look like an airplane.

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    RE: WACO YMF

    ORIGINAL: Stickbuilder

    The issue that we get into have to do with Reynold Numbers. Full Scale airplanes differ from models due to the effects of Scale Volume, not Linear scale. The bigger the model, the more like the full scale it becomes. For example, a cube that is 4''X4''X4'' will have a volume of 64 cubic inches. (4X4=16X4=64) A quarter scale model of that cube is 1X1X1 which yields a volume of 1. Even though the linear scale is one fourth the size of the full scale, the volume is much different. Hope this helps you see the difference.

    Bill, Waco Brother #1
    This is actually a good point to bring up, for the very reason that the effects of scale volume are not linear. The larger an airframe, the more efficiently it will carry weight, that is why lets say a full scale Extra 300 weighing in at around 1400 lbs. empty performs very well at that weight. Now take a half scale Extra 300 and weigh it down 700 lbs. and it is not going anyplace, in fact at half scale weighing it down to 100 lbs. and it is a real pig. Now lets get down to small aircraft anything 1/4 scale or less. The smaller the airplane the more important it is to build as light as possible, because the Reynolds numbers are working against you from a load carrying efficiency standpoint.

    Bob
    Fly It Like You Stole It!!!

  6. #15931
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    RE: WACO YMF

    This is a very interesting discussion. One thing does not change. The wing has to fly at an angle of attack (AOA) at any given speed that will allow it (the wing) to produce enough lift to support the weight of the aircraft..If the plane appears to be "dragging it's tail", but still maintinaing altitude, then lift vs weight (gravity) is balanced. The plane is either too slow, too heavy, or the wing is mounted at the wrong incidence angle on the fuse. What ever is going on with the stab/elevator is just what is neccesary to maintain that AOA.

    IF the aircraft is tail heavy, You just can't trim it out to fly in a stable mannor; ie, hands off. I was a commercial pilot, and on a charter flight Idid early on in my carrier, I flew a load of water bottles to a lab to be analyzed for a new treatment plant. I was in a Cessna 206. All of the seatswere taken out and the bottles, about ten gallons each, were spread out on the floor and strapped down with a cargo net. As soon as Ibroke ground, the nose pitched up. I went forward on the elevator, and it pitched down. This continued all the way for the 300 mile flight. Ipulledmy seat as far forward as possible, but it was not enough. I was afraid I would not be able to land as the oscillations continued all the way to touchdown. We had all assumed we would be OKwith the CG. Wrong,

    As for the lifting tails on some models, Guess what? Some models are designed with a very aft CG.Competation free flight models ,YES, often have aCG back around 50 to 60 percent of MAC, but they all have stabs that are a large percentage of the total area., and they produce lift.The idea is that it's more effecient to have all of the flight surfaces contributing to overall lift, rather than having the tail exererting a down force

    Iknow, this has not helped this discussion, but only muddied the water. It sure seems to me that a positive incidence on the stab (LEup), would seem to indicate a slightly aft CGby design. The large tail plane would seem to support that.

    Joe
    "When you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."

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  7. #15932

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    RE: WACO YMF


    ORIGINAL: sensei

    ORIGINAL: Stickbuilder

    The issue that we get into have to do with Reynold Numbers. Full Scale airplanes differ from models due to the effects of Scale Volume, not Linear scale. The bigger the model, the more like the full scale it becomes. For example, a cube that is 4''X4''X4'' will have a volume of 64 cubic inches. (4X4=16X4=64) A quarter scale model of that cube is 1X1X1 which yields a volume of 1. Even though the linear scale is one fourth the size of the full scale, the volume is much different. Hope this helps you see the difference.

    Bill, Waco Brother #1
    This is actually a good point to bring up, for the very reason that the effects of scale volume are not linear. The larger an airframe, the more efficiently it will carry weight, that is why lets say a full scale Extra 300 weighing in at around 1400 lbs. empty performs very well at that weight. Now take a half scale Extra 300 and weigh it down 700 lbs. and it is not going anyplace, in fact at half scale weighing it down to 100 lbs. and it is a real pig. Now lets get down to small aircraft anything 1/4 scale or less. The smaller the airplane the more important it is to build as light as possible, because the Reynolds numbers are working against you from a load carrying efficiency standpoint.

    Bob
    Using your example of the Extra 300 weighing 1400 lbs (power to weight ratio of 0.2143)... a third scale would theoretically be 1/27th (3x3x3) =51 lbs .. (mm a little heavy on the wing loading!) with 11hp (300hp/27) same power to weight ratio... will fly probably quite realistically compared to the fullsize in terms of take-off and stall speed performance. As modellers, Have we not just become more accustomed to having more power to weight (that 1/3rd scale Extra would typically weigh around 30-35 lbs) to get the adrenalin pumping? Peter, #224
    Peter du Plessis
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  8. #15933
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    RE: WACO YMF

    " The wing has to fly at an angle of attack (AOA) at any given speed that will allow it (the wing) to produce enough lift to support the weight of the aircraft"

    Only for symmetrical airfoils.

    Les

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    RE: WACO YMF

    ORIGINAL: peterduplessis


    ORIGINAL: sensei

    ORIGINAL: Stickbuilder

    The issue that we get into have to do with Reynold Numbers. Full Scale airplanes differ from models due to the effects of Scale Volume, not Linear scale. The bigger the model, the more like the full scale it becomes. For example, a cube that is 4''X4''X4'' will have a volume of 64 cubic inches. (4X4=16X4=64) A quarter scale model of that cube is 1X1X1 which yields a volume of 1. Even though the linear scale is one fourth the size of the full scale, the volume is much different. Hope this helps you see the difference.

    Bill, Waco Brother #1
    This is actually a good point to bring up, for the very reason that the effects of scale volume are not linear. The larger an airframe, the more efficiently it will carry weight, that is why lets say a full scale Extra 300 weighing in at around 1400 lbs. empty performs very well at that weight. Now take a half scale Extra 300 and weigh it down 700 lbs. and it is not going anyplace, in fact at half scale weighing it down to 100 lbs. and it is a real pig. Now lets get down to small aircraft anything 1/4 scale or less. The smaller the airplane the more important it is to build as light as possible, because the Reynolds numbers are working against you from a load carrying efficiency standpoint.

    Bob
    Using your example of the Extra 300 weighing 1400 lbs (power to weight ratio of 0.2143)... a third scale would theoretically be 1/27th (3x3x3) =51 lbs .. (mm a little heavy on the wing loading!) with 11hp (300hp/27) same power to weight ratio... will fly probably quite realistically compared to the full size in terms of take-off and stall speed performance. As modellers, Have we not just become more accustomed to having more power to weight (that 1/3rd scale Extra would typically weigh around 30-35 lbs) to get the adrenalin pumping? Peter, #224
    No, the smaller you go, the less efficient the lifting capacity is, your forgetting about the Reynolds numbers working against you the smaller you go.

    Bob
    Fly It Like You Stole It!!!

  10. #15935
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    RE: WACO YMF

    ORIGINAL: LesUyeda

    '' The wing has to fly at an angle of attack (AOA) at any given speed that will allow it (the wing) to produce enough lift to support the weight of the aircraft''

    Only for symmetrical airfoils.

    Les
    All airfoils need AOA to produce lift with the exception of an asymmetric airfoil.

    Bob
    Fly It Like You Stole It!!!

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    RE: WACO YMF

    Don't all airfoils need some AOA to the relative wind to produce lift?

    AOA (angle of Attack) happens during flight in relationship to the relative wind and is different than AOI (Angle of Incidence) which part of the structural design.

    What was the question again?


    Jaybird

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    RE: WACO YMF

    ORIGINAL: Jaybird

    Don't all airfoils need some AOA to the relative wind to produce lift?

    AOA (angle of Attack) happens during flight in relationship to the relative wind and is different than AOI (Angle of Incidence) which part of the structural design.

    What was the question again?


    Jaybird
    Yes, except an asymmetric/cambered airfoil. Don't take my word for it, Google it.

    Bob
    Fly It Like You Stole It!!!

  13. #15938

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    RE: WACO YMF

    Who is this guy Reynolds??? Why did he screw everything up??? Lift generation??
    According to the Bernoulli venturi principle it's the "separation of air molecules" allowing a low pressure area on the top surface of the wing????? That's what I taught when I was a certificated flight instructor....how many years ago was that???
    Just kidding around. The whole basic aerodynamics discussion is fun. Mitch

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    RE: WACO YMF

    Almost as much fun as the "why don't people build kits anymore" converstion on the other thread!

    Jaybird

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    RE: WACO YMF

    Hi Joe,

    symmetrical airfoil was chosen to have a better inverted flight performance. If you fly upside down with Clark Y your AoA has to be awfully high which in my opinion does not look nice. With the symmetrical airfoil you AoA is much lower and your nearly can fly straight and level. That was the reason for this airfoil. A customer did built it with the Clark Y flies good as well but inverted see above.

    Peter

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    RE: WACO YMF

    Barry,

    sorry fro not mentioning the CG in the plans but the CG is max. 2 cm in front of the aft cabane struts on the upper wing center section if you weight it in more to the front it is nose heavy which is not such as critical as tail heavy but....


    Peter Waco brother #170

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    RE: WACO YMF

    To All,

    just to make it clear:

    upper wing 0 to minus 2 degrees
    lower wing 0 degrees
    horizontal stab 2 degrees leading edge up
    CG just in front of the aft cabane strut about one to two fingers width.

    That's how the Barth Wacos should fly and I do fly them.

    Peter

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  18. #15943
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    RE: WACO YMF


    ORIGINAL: FMBB

    Hi Joe,

    symmetrical airfoil was chosen to have a better inverted flight performance. If you fly upside down with Clark Y your AoA has to be awfully high which in my opinion does not look nice. With the symmetrical airfoil you AoA is much lower and your nearly can fly straight and level. That was the reason for this airfoil. A customer did built it with the Clark Y flies good as well but inverted see above.

    Peter

    Waco Brother #170
    Thanks, Peter,

    Iassumed it had to do with aerobatic preformance, but Iwanted to make sure Iwasn't missing something.

    Joe

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  19. #15944
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    RE: WACO YMF

    The designer bearers the burden of making all these structural and aerodynamic decisions, and he must consider many tradeoffs along the way.[8D]

    Bob
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    RE: WACO YMF

    jaybird,What is the incidence of your bottom wing.?

    Bill

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    RE: WACO YMF

    Jaybird, I think the reason young men aren't building is they have more money then time .
    Plus look at the quality of the ARF's.
    I belong to a club of about 60 members and there may be 2 or 3 guys who build.

    Bill
    WB126

  22. #15947
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    RE: WACO YMF


    ORIGINAL: nine o nine

    Hello Albert, You've done some BEAUTIFUL work! I see on your landing gear profile you may have done what some kit makers have done... that the rear edge should end up behind the wing leading edge. That makes the whole triangle shape different. If you're not after 100% scale accuracy it'll be fine and much easier from an engineering standpoint.
    I love the build. Mitch
    Hello Mitch,

    A few new pics ...Of course I saw that the original chassis are made differently. But, it is quite difficult to run ...So I did just that. Has probably become, when I will make a 40% scale model I will try to make an absolutely exact copy.

    Albert
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  23. #15948

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    RE: WACO YMF

    FMBB, Thank you sir. I had missed your post on my 1st read after being gone awhile.

    Bill
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    AMA6416 and waiting for Bill WB#1 to tell us again his AMA#?

  24. #15949
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    RE: WACO YMF

    Please let's let this be the end of the Building vs Arf thing. We have both here and both are welcome.

    Bill, Waco Brother #1
    Its easy, just glue all the pieces together, and sand off everything that doesnt look like an airplane.

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    RE: WACO YMF

    Sorry, sorry, sorry! It was meant as a joke as it is another subject that gets everyone worked up.

    Besides, I didn't actually ask the question, I just noted that it too has a lot of strong opinions.

    I worked on adding the javelins to the new flying wires on my GP WACO ARF last evening and should have it finished tonight.

    Jaybird
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