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  1. #1

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    Flying Horizontal Stabilizer

    I have just finished building a Gee Bee R3 Racer. I only bought the plane because it looks really cool (IMO). There have been many reports that this model (20cc 59 inch version) has numerous bad flight characteristics (ground handling, takeoff, snap tendencies, hot landings, etc). I have not flown the plane yet but I am very concerned about the maiden.

    After checking all of the building issues pointed out by other modelers, I discovered I made a huge building error. The horizontal stabilizer has a slight curvature on one side and virtually flat on the other side, making it a "flying" stabilizer with some lift during flight. My problem is that I INSTALLED IT UPSIDE DOWN. THE FLAT SIDE IS ON THE TOP AND THE CURVED SIDE IS ON THE BOTTOM.

    Although there is only a slight curvature on the upper surface, this stabilizer would be a lifting type stabilizer. The difference in the upper and lower surfaces are very minor which is why I did not notice it (dumb move in any case). I have been building and flying for over 20 years. This is a first for me and I am embarrassed to tell anyone about it. It will be an ugly job to remove the stabilizer and turn it over as I will have to remove one elevator half and cut out the stabilizer.

    My thoughts are that, if I fly it as is, the tail will tend to drop as speed is increased. This may be offset by the 5 degrees of down thrust in the motor. In any case, some up elevator will need to be applied to keep the model flying level. This may add to the snap tendencies of the plane in turns and slow flight.

    My question is, how will this affect the flight characteristics of the plane?
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  2. #2

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    RE: Flying Horizontal Stabilizer

    dude..flip it...i've made mistakes too and the only way to make all right is to make all right..your experience will nag you as to what ya gotta do to make the plane fly right..

    SLOPE FAST - SOAR DEEP

    guamflyer
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    SLOPE FAST - SOAR DEEP

  3. #3
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    RE: Flying Horizontal Stabilizer

    Chances are what will happen is the resulting elevator trim will be obvious to the naked eye. It also might change as the plane's airspeed varies. Then again, you might not notice much at all after you get the initial trim worked out. It depends on how effective that airfoil was on that layout, and whether or not it was actually effective on the model.

    Very often, scale models that faithfully duplicated the details of the full scale wound up not needing or not reacting to what the full scale had.

    I'd say you face an interesting situation and little more. The maiden won't be any more dangerous than probably half the maidens we see in the hobby. There are a LOT of models, especially now with so many models being ARFs, maidened every day with far worse aerodynamic problems than you face.

    I'd love to maiden your plane. And would put money on that sucker getting through the flight with only some dirt on the tires.
    Good flying wit ya today

  4. #4

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    RE: Flying Horizontal Stabilizer

    A tail that lifts down - you are not the first to do this. I believe if you check out a Lockheed C-130 carefully, they do it too. Actually most conventional aircraft have downforce from the tail when the aircraft is in level unaccellerated flight. Draw out the force diagram of the center of lift and the center of gravity and you will see which way the lift from the tail has to go.

    As far as a "scale"detail - Please. The R3 is fictional, never sprang forth from the Grandville Brothers shop.
    - Supplementary insipid innocuous inane vacuous proclamation

  5. #5
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    RE: Flying Horizontal Stabilizer

    A couple of thoughts.........

    If the camber had been enough to worry about, getting the stab into the ARF's perfectly dimensioned hole in the fuselage would have been a problem. From the picture, it doesn't look like there is much camber at all.

    The wing looks symmetrical. They don't create the pitching moments cambered tails were used to handle those moments. So what you lost wasn't needed at all.

    No matter what shape the tail is, adjusting trim with the elevator will trim the pitch. I'm guessing that it is probable there will be more trim drag than before, but there could actually be less induced drag. Whatever trim the plane wanted before, it will still want. Since it didn't need a cambered tail before, and certainly didn't need a lifting tail before, it won't need any of that now. Not having it won't matter. In fact, it wouldn't have wound up with a lifting tail as designed. The tail would have needed trim to get the tail to produce only what lift and in what direction that lift may or may not have been needed.

    I hope you give it a shot as is. Do what the shade tree aeronauts did back then. Run it around under power and feel your way into the air. They'd do a real short hop down the runway if they were really hesitant about things. Heck, I'd almost drive up there to see the maiden.
    Good flying wit ya today

  6. #6

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    RE: Flying Horizontal Stabilizer

    DA ROCK,
    Thanks for the reply. In my early days of flying, I let other more experienced pilots do my maiden flights. Sometimes, they were not successful and therefore, I got not time on the sticks. Now, I go out to the field very early before anyone gets there and perform my own maiden flights.

    Here is a closeup photo of the stabilizer. As you can see, there is very little difference between the upper and lower curvatures on the stabilizer. It will probably not make any difference in the flight characteristics (but you never no). As you said, it depends on how effective the stabilizer performs on this model.
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  7. #7
    Moderator da Rock's Avatar
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    RE: Flying Horizontal Stabilizer

    ORIGINAL: HighPlains

    As far as a ''scale''detail - Please. The R3 is fictional, never sprang forth from the Grandville Brothers shop.
    Sorry about that.... Lots of shade tree aeronautical engineers back then did cute tricks like lifting tails for dumb reasons. So the designer of the model did the same.....


    A tail that lifts down - you are not the first to do this. I believe if you check out a Lockheed C-130 carefully, they do it too. Actually most conventional aircraft have downforce from the tail when the aircraft is in level unaccellerated flight. Draw out the force diagram of the center of lift and the center of gravity and you will see which way the lift from the tail has to go.
    As for the tail of your model lifting down... or up.... or sideways.... don't assume that just because one side of the stab is fat that the plane is going to suddenly be carrying weight back there... or not carrying weight being upside down. It ain't how it works. We trim our models in flight to fly level. In fact, full scale usually does that too. What that level flight trim does is adjust the tail to produce whatever lift is needed to point the plane level. That lift might be up (don't bet on that however). It's usually down, but usually not enough to need special profiles. Since our models don't have much CG movement in flight, and aren't used anything like the Hercs are, with hugely varying loads from overloaded to empty, they don't have variable incidence or any major trim adjustments available or needed.

    Your tail isn't going to lift down more than it would with symmetrical tail after you've found out and dialed in whatever trim is needed. It might produce a bit more drag than it would with a symmetrical tail, but then, that's probable had it been glued in upright.

    Your model design didn't need the tail to lift up to begin with. If the designer of that fictional beast cared about the efficiency of his design, and still wanted the camber, he would have designed the angle of incidence of that tail to suit the demands, which would probably have negated the value of the stab camber.

    The negative camber on the Herc is there to deal with the massive pitch stability problem the design experiences when the wing has to produce massive lift to carry massive loads. And there is an extra trim device in that little monster to crank the LE of the stab up or down to suit the loading. They need to be able to fly the plane when it's empty and when it's overloaded. Their world is a lot more demanding than ours. You aren't planning to carry a tank in that model, or chute it off the ramp in flight. .... although that'd be sorta kewl to do with a model..... hmmmmm

    Good flying wit ya today

  8. #8
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    RE: Flying Horizontal Stabilizer


    ORIGINAL: iFLYrc_Vic

    DA ROCK,
    Thanks for the reply. In my early days of flying, I let other more experienced pilots do my maiden flights. Sometimes, they were not successful and therefore, I got not time on the sticks. Now, I go out to the field very early before anyone gets there and perform my own maiden flights.

    Here is a closeup photo of the stabilizer. As you can see, there is very little difference between the upper and lower curvatures on the stabilizer. It will probably not make any difference in the flight characteristics (but you never no). As you said, it depends on how effective the stabilizer performs on this model.

    Excellent photo of what most everyone of us opinionated guys would want to see. You're right about it not looking very cambered. I'd bet there won't be much trim needed. I gotta say it's probably going to be more exciting talking about it than flying it. And think about just hopping it in taxi testing on the first run.

    I got $20 says you're the best choice you'd have of who maidens the sucker. Saves me that long drive....

    Let us know.........
    Good flying wit ya today

  9. #9

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    RE: Flying Horizontal Stabilizer

    Thanks all for your comments and education on chambered stabilizers. I feel much better about the stabilizer installation and will leave it as it is.

    As for the maiden, I will definitely do some hop testing before taking to the air. The plan is to accelerate and keep it on the ground as long as possible before take off. Hot landings will be the norm for this bird as well.

    Thanks again guys (gals).
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  10. #10
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    RE: Flying Horizontal Stabilizer

    The airfoill used for the horizontal tailplane really means little -
    diamond - smooth teardrop (streamlined - flat stab /tapered elevator etc..
    really
    The sensitivity may change bu t structurally all you need is a setup which will not bend or twist.
    On some designs the sensitivity may be an issue and ideally you want the elevator to trail somewhat in line with the stab.
    But all in all the airfoil- a non issue.
    Libby is still watching you

  11. #11

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    RE: Flying Horizontal Stabilizer

    ORIGINAL: guamflyer
    dude..flip it...i've made mistakes too and the only way to make all right is to make all right..your experience will nag you as to what ya gotta do to make the plane fly right..
    Β*Β* SLOPE FASTΒ* - SOAR DEEP
    Β*Β*Β*Β* guamflyer
    guamflyer,
    Looks like you have been out numbered by the aerodynamic community. Most replies here and on other forums have report that the shape of the stabilizer on this model will make little or no difference in the flying characteristics of the plane. It may not look right, or follow the norm, but it does not matter. As a matter of fact, the different is so slight, that no one would ever notice it - you have to put a straight edge on it to see the difference. Can you see that it is installed upside down on the closeup photo in post #5?

    Thanks for your rep/y anyway.
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  12. #12

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    RE: Flying Horizontal Stabilizer

    yeah, I know whatcha mean man..lol..I guess it also depends on the final outcome and what will actually work, sometimes I've gotten away with a mishap.thats the thing I love about modeling...many ways and ideas to do things and with the scale we work with..it can go many ways...... outnumbered is a good thing, everyone is thinking hard....


    SLOPE FAST - SOAR DEEP

    guamflyer

    guamflyer P-40 Bro #5 guamflyer\'\'s Dad #6
    SLOPE FAST - SOAR DEEP


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