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  1. #1

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    Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    I have noticed that some models have the engine and wing on a common centerline on the fuse while the horizontal stab is sometimes on that line or above that line in varying amounts. What are the advantages of having the stab in line or above the wing / engine center line.

    Also what advantages are derived from having elevators and rudders with those counterfoil sections.

    Karol
    When inverted always remember that down is up and visa versa

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.


    ORIGINAL: karolh

    I have noticed that some models have the engine and wing on a common centerline on the fuse while the horizontal stab is sometimes on that line or above that line in varying amounts. What are the advantages of having the stab in line or above the wing / engine center line.

    Also what advantages are derived from having elevators and rudders with those counterfoil sections.

    Karol
    What is a counterfoil section?

  3. #3

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    Counterfoil or counter balance, it's the end section of the elevator forward of the hinge line at both ends of the horiz. stab and the top section of the rudder forward of the hinge line above the vert. stab

    Karol
    When inverted always remember that down is up and visa versa

  4. #4
    Moderator da Rock's Avatar
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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    In full scale use, those tabs lessen the stick loads for those surfaces. They also provide a convenient place for counterweights. The weights help balance the mass of those surfaces. When the surface is balanced it is less apt to flutter.

    For models, they're not as important as we have zero stick load feedback. Our systems are driven by servos and there is no free movement possible.
    Good flying wit ya today

  5. #5

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    Most control line stunt airplanes have the stab and elevator above the wing center line. For one thing it is easier to get the pushrod and control horn on the elevator where you want them The thrust line and wing center line may be the same or not. I get the impression that the engine is often placed where the wing centerline goes through the CG of the engine, at least that is how I have designed CL stunt airplanes. There are very successful stunt airplanes: however, which have the thrustline, wing centerline, and stab-elevator in line.

  6. #6

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    ORIGINAL: da Rock

    In full scale use, those tabs lessen the stick loads for those surfaces. They also provide a convenient place for counterweights. The weights help balance the mass of those surfaces. When the surface is balanced it is less apt to flutter.

    For models, they're not as important as we have zero stick load feedback. Our systems are driven by servos and there is no free movement possible.
    I am aware of the use of counterweights on control surfaces to offset the possibility of flutter but thought that there was some other flight enhancing reason for having the tabs on our models.

    Karol
    When inverted always remember that down is up and visa versa

  7. #7

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    I have run into trouble with two of my own design models that had their symmetrical-airfoiled, non-dihedraled wings and horizontal stabs in line. The symptom was a sudden uncommanded pitch up or down. I think that the cause was that the stab was in airflow that was split by the wing, with a thin, slightly lower velocity, turbulent flow sheet hitting the stab right on its airfoil centerline.

    I think that if this lower velocity flow regime shifts just slightly up or down due to a slight change of wing lift coefficient, the stab suddenly sees higher velocity air above or below it, which tends to abruptly raise or lower the stab. I fixed the problem by increasing wing incidence by about half a degree, which avoided having to relocate the stab. I now make sure that the stab is at least a half inch above the wing airfoil centerline. Stab dihedral or anhedral would also probably fix this problem.

    I suspect that for non-symmetrical wings, the stab should be slightly above or below the airfoil zero-lift line.

    Many of my control line models had their symmetrical wings and stabs in line. without any sudden pitch problems, possibly because slight building errors moved the stab slightly out of line with the wing.

  8. #8

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    I am currently doing an own design profile model based on a set of 66" span Katana wings I was given hence my post as I have been deliberating on just where to locate the horiz. stab in relation to the wing/engine thrust line. I had assumed a stab location of 3/4" above the wing/engine centreline and based on your comments regarding your experience in this area I will use that position.

    Karol
    When inverted always remember that down is up and visa versa

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    Hi Karol, I applaud your project. I did a similar last winter and went through some of the thought processes you narrate. My thinking was that drag forces should be balanced on the thrust line to avoid drag induced pitch. The three biggies are stabs, wing and undercarriage. In my case, I laid the horizontal sheet stab as one would do on an inverted stick fuselage. I guessed that the stabs would have a fair amount more drag than the undercarriage so that meant dropping the wing (by far the greatest drag factor) slightly below the engine thrust in hopes of having better drag balance. IIRC, the wing is 5/8" below thrust line and the horizontal stab is 1.75" above.

    I don't know that there are any magic numbers but for good flight manners... some thought might help. An example of poor would be a Spacewalker I built. The engine is high, and it has a large low wing and center stab. That means that the big three drag factors are all well below the engine thrust line and considerable lever arm on the high drag of the wing. It was no surprise that the plane required a lot of up trim even though engine, stab and wing were all carefully set zero. Ultimately, I had to adjust the wing incidence positive to get the power on/off trims into alignment.

    I considered my project a great success as the plane required only two clicks of down trim and no roll trim on maiden. If the wing had been left on thrust center line where first drawn... no doubt more down trim would have been needed. Offsetting it 5/8" down from thrust line countered most of the stab drag.

    Finally, the project was a real thrill beyond any previous build. Part of that was because the plane was designed around what tickled my gizzard the most, it was my creation. And.... it was my responsibility to ensure it would be a success and that forced a lot of thought and effort beyond what one normally puts into a kit or built to another's plans.

    Wishing you a lot of fun and enjoyment in your effort. I'd concluded even if it didn't fly great and perhaps turned out to be the field ugly duckling the experience was worthwhile but when it looked good and flew great, the satisfaction of accomplishment was overwhelming. I love to fly the plane.

    PS: I'd drop your wings to about 1/4-3/8" below thrust line if the stab is 3/4 or so above.

  10. #10

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    Thanks for your words of encouragement as I am even surprising myself at the level of enthusiasm doing this has generated in me, plus just the knowledge that I am using my very own parameters to accopmplish this is just the icing on the cake. Your suggestion regarding the postion of the wing and stab in relation to the engine thrust line is food for thought and one that quite possibly I will incorporate in my design. Hopefully like you I will be successful in this undertaking and end up with a nice flying model.

    Karol
    When inverted always remember that down is up and visa versa

  11. #11

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    AA5BY, your mention of the possibility of no magic figures existing I got the bright idea of checking on the stats of some sport models that in my opinion fly great which are, Kaos , Super Sportster, Goldberg Extra, Davey Models Hammer 40 and MW Extra 300 and noted that the only common denominator among them was that all had the stab above the engine and wing center lines but in varing degrees, so now the plot thickens

    Karol
    When inverted always remember that down is up and visa versa

  12. #12

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    Planes like the Kaos .40 are of the size that the drag couple is probably not an issue to be of much concern.

    When entering the world of giant... drag couple becomes an issue. My initiation to it happened with the BUSA Phaeton .90. The greater drag of the upper wing and longer lever arm compared to the bottom wing had the plane climbing badly, which had to be countered by some negative wing incidence. On the Spacewalker, the drag problem was opposite and pitching the plane down.

  13. #13

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    I have had good success using balance tabs (never ever heard of them being called counter foils in some 30 years of modelling) on my larger models. Back when a big servo only put out about 30 inch/oz of force, they let you drive large surfaces with those servos. I also had good success with boost tabs where it was not so easy to add balance tabs. Just limit the size of either boost tabs or balance tabs to 10% or less of the total moveable surfaces.

  14. #14
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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    ORIGINAL: karolh

    I have noticed that some models have the engine and wing on a common centerline on the fuse while the horizontal stab is sometimes on that line or above that line in varying amounts. What are the advantages of having the stab in line or above the wing / engine center line.

    Also what advantages are derived from having elevators and rudders with those counterfoil sections.

    Karol
    A good aerobatic setup can have variance on wing/stab power placement -
    keeping em all reasonably close to a common line is a good idea but NOT mandatory
    balance tabs? only if you just want to play with em.
    it's all fun.
    We could go on n on but the single most important goal?
    keep the wing loadings down and make the control surfaces as light as practical and balance em as close as practical to hinge line
    this eliminates possible flutter if done correctly .
    Libby is still watching you

  15. #15

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    A big thank you to all who offered opinions and suggestions on this, several of which have had some influence on my final design. For what it's worth I am using an arrangement that has the wing c/line at 3/8" below the engine's thrust line and the stab at 1.25" above, with all set at 0 deg. Hopefully it will fly but just how good remains to be seen, but I am being quite optimistic

    Karol
    When inverted always remember that down is up and visa versa

  16. #16
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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    Nothing wrong with those basic numbers - 5 pounds to 40 pounds - same setups are common.
    Libby is still watching you

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    An old pattern plane - the Eyeball - had no dihedral and the engine, wing and stab all on the same line. It flew well.

    Paul
    Gosh, model airplanes are not a matter of life and death - they\'\'\'\'\'\'\'\'re more important than that!

  18. #18
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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.


    ORIGINAL: karolh

    A big thank you to all who offered opinions and suggestions on this, several of which have had some influence on my final design. For what it's worth I am using an arrangement that has the wing c/line at 3/8'' below the engine's thrust line and the stab at 1.25'' above, with all set at 0 deg. Hopefully it will fly but just how good remains to be seen, but I am being quite optimistic

    Karol

    Pictures?

    (IMHO, the stab should be located to minimize Yaw-Pitch coupling)
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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    ORIGINAL: mithrandir


    ORIGINAL: karolh

    A big thank you to all who offered opinions and suggestions on this, several of which have had some influence on my final design. For what it's worth I am using an arrangement that has the wing c/line at 3/8'' below the engine's thrust line and the stab at 1.25'' above, with all set at 0 deg. Hopefully it will fly but just how good remains to be seen, but I am being quite optimistic

    Karol

    Pictures?

    (IMHO, the stab should be located to minimize Yaw-Pitch coupling)
    Where would you suggest it be located ?? No pictures just yet.

    Karol
    When inverted always remember that down is up and visa versa

  20. #20
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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    if you send me drawings, I can model it up in CAD and run a CFD case to determine the theoretical null position....

    but on the "Typical" plane, located about halfway doen the fuselage, (Vertically speaking, or Mid-location) is about right....
    high mounted stabs pitch down and bottom mounted pitches up with yaw
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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.


    ORIGINAL: mithrandir

    if you send me drawings, I can model it up in CAD and run a CFD case to determine the theoretical null position....

    but on the ''Typical'' plane, located about halfway doen the fuselage, (Vertically speaking, or Mid-location) is about right....
    high mounted stabs pitch down and bottom mounted pitches up with yaw
    I'm failing to grasp why that is true. A high mounted stab will add a drag couple above the thrust line that pitches up to my way of thinking.

  22. #22
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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    The position of stab-wing -and thrust lines are all COMPROMISES
    all on CL is not necessary - but it works well for many models - I never liked the Eyeball - -
    One design - the ZLIN has engine-(prop) up high -wing on bottom of fuselage and stab up high
    setup correctly these are fantastic flyers - been there
    My own favorite "all around setup is almost exactly as you first noted
    - the pitch due to stab location- has some merit -on some designs but for the most part the CG is more critical in this respect.
    All on one line is fine -just not manadatory.
    Too many factors at work
    Libby is still watching you

  23. #23
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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.


    ORIGINAL: AA5BY


    ORIGINAL: mithrandir

    if you send me drawings, I can model it up in CAD and run a CFD case to determine the theoretical null position....

    but on the ''Typical'' plane, located about halfway down the fuselage, (Vertically speaking, or Mid-location) is about right....
    high mounted stabs pitch downand bottom mounted pitches up with yaw
    I'm failing to grasp why that is true. A high mounted stab will add a drag couple above the thrust line that pitches up to my way of thinking.

    The key is the "with yaw" part. In level flight it's not an issue as any slight drag couple is masked within the overall pitch trim. But when a pattern model yaws such as in wing overs or during knife edge flight the vertical location of the stabilizer has some odd coupling that promotes some pitching. I suspect that it's related to the "low aspect ratio vortices" that flow around the fin when it's lifting strongly to the side with full or nearly full rudder application hitting the stabilizer more strongly one way than the other. But that is pretty much a WAG on my part. I do know from reading the articles found in magazines from the 60's and 70's on pattern designs that the location of the stabilizer vertically was set specificaly to correct such yaw related issues back in the days before it was simpler to adjust in a mix at the Tx.

    In one notable case, and Richard can likely remember the design, the article discussed how the stabilizer was set too high and the model had a massive amount of pitch during knife edge. A big meet was coming up quickly and the designer had no time to chop and rebuild the whole tail to lower the stabilizer. So what he did was to simply cut off the stab halves and glue them back on with a fairly gross amount of anhedral. That fixed the issue well enough that he went on to win or place well in the Nats that year and the design was published in MAN or RCM with the drooped stabilizer as a "feature" rather than a "fix"... It was even kitted with the anhedral stabilizer if I recall correctly. And likely it spawned a few copy cat designs since I seem to remember seeing lots of anhedral stabilizer pattern models for a few years after that.

    Richard, do you recall the name of that original design?
    Witty saying to be plagarized shortly.....

  24. #24

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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    I don't know if it was the original design you are thinking of but one pattern plane of note that had an anhedral stab was the Curare.

    Karol
    When inverted always remember that down is up and visa versa

  25. #25
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    RE: Having engine, wing and horiz. stab on a common centerline as opposed to having it otherwise.

    I believe it was the Curare that made the Anhedral stab fashionable....

    where is Hanno these days??? does he have a facebook page?
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