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  1. #1
    Ernie Misner's Avatar
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    Side Force Generators question (SFG's)

    I posted this in the 3D forum too...... >>> I have the new UCanDo SF and just started the build. It has SFG's that bolt to the wingtips, nothing unusual here. What is odd though is that the SFG's and wingtips are not parallel to the fuselage. The SFG's (and wingtips) point in towards the nose of the airplane quite a bit, maybe more than 5 degrees. What are they thinking? Anyone ever seen SFG's that have tow in like that? Looks like it would cause a lot of drag in straight flight! Ideas anyone? Thanks. >>>

  2. #2
    Hi Ernie , I have only one plane with SFGs , it is an "E Flight mini funtana X" , and it's SFGs are both in perfect relationship with the vertical stabilizer . They are neither "toed in" nor "toed out" , just facing perfectly straight ahead as the vertical stabilizer does . Due to the tremendous drag it would cause to have them as you describe , and the fact that any other plane I've ever seen with SFGs was like mine , I would guess that there is something wrong with the mounting of them that you have encountered . I wonder , are there any kind of spacers with the kit that may be to align the SFGs ?

  3. #3
    Ernie Misner's Avatar
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    Thanks for the thoughtful reply. What you are thinking all makes sense, but no spacers. The SFG's are definitely towed in. Take a look at the pictures, number 2 I think shows the angles. When you see my wing it is more obvious. http://www3.towerhobbies.com/cgi-bin...DUJC&P=ML#tech

    Well clearly the engineers for Great Planes did have something in mind. We will see. People so far says it is a terrific flyer. The tow in sure looks draggy to me though.

  4. #4
    scale only 4 me's Avatar
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    Not a plane designed for high speeds so the benefit of stability out weighs the negative effect of additional drag,, fly with and without,, see which way works for your flying style
    You're so smart,, you figured out how to read this!! Or maybe ya just got lucky??

  5. #5
    Hi Ernie , Thank you for the link to the photos of your plane . I can see where there would be no spacers required since those SFGs don't extend beyond the wing to the aileron as mine do . You see , if it weren't for the spacers on the Funtana the ailerons would bind on the SFGs . I would like to hear of your experience with flying it both with and without to see what you think of them when you get to flying it . I will say that although they didn't seem to improve what I call "prop hanging" (hovering the plane in a vertical stationary position) much , they most certainly did improve the Knife Edge maneuver quite well . What I did was a couple of flights with , then a couple without , back and forth , I installed and removed them around 6 or 7 times and by far it was the Knife edge that was most improved . I never noticed any reduction in speed or need for additional throttle to maintain approx. the same speeds with or without them but then again they have no tow in like yours do . Scale also makes a good point in that these twisty acrobatic types really aren't about top speeds , and so a bit of drag in exchange for maybe a slightly greater stability may be an acceptable trade off .

    PS , Sorry for the crappy cell phone photos , but I figured I'd throw a couple of shots of the Funtana's SFGs in just for grins
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  6. #6
    Ernie Misner's Avatar
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    Thanks for the great replies and photos guys! The consensus seems to be that a little drag will not hurt slow flying 3D planes. Foamies even have drag plates installed on the ailerons sometimes. Yes, sure will fly it both ways whenever I get it going. init4fun, I am hearing that besides knive edge, the SFG's do help with high alpha harriers a lot too. One friend said they hinder the roll rate. Anyway I'm getting used to the idea that they are towed in and guess I'm the only one who noticed that so far......

  7. #7
    Hoghunter12's Avatar
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    There is toe-in and here's the reason why..............Click image for larger version. 

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  8. #8
    tailskid's Avatar
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    Good catch!
    # 93 in Club Saito; Carl Goldberg Ultimate Brotherhood # 12; Pulse brother # 2;Hellcat Brotherhood #8;P-47 Thunderbolt Brotherhood #18

  9. #9
    Ernie Misner's Avatar
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    Hoghunter (really?), great job of diagramming that for us. Thanks!

  10. #10
    scale only 4 me's Avatar
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    Quote Originally Posted by Hoghunter12 View Post
    There is toe-in and here's the reason why..............Click image for larger version. 

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    You're so smart,, you figured out how to read this!! Or maybe ya just got lucky??

  11. #11
    Quote Originally Posted by scale only 4 me View Post

    As Scale has so nicely pointed out here , yes it would be obvious that the tow in is the result of the leading edge being shorter than the trailing edge . But , this only explains the physical reason for why the SFG is toed in and does not explain WHY it's been positioned as such . As with all things of this complexity , those were engineered in that way for a certain , specific , aerodynamic reason .

    And I'd like to know what that reason is

    PS , I have done a bit of searching and have seen some small acrobatic foamies with the multiple SFGs / air brakes mentioned in post #6 by Ernie . They look kinda cool in a star wars ish kinda way

  12. #12

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    Perhaps it was done to keep the model from over-speeding. If this one is built anything like the .46 and .60 examples, it is uber-light to the point of fragility. Those examples have a specific warning in the manual to not fly the model fast; period.

    The one model I have with SFGs has them parallel to the thrust line. But I haven't installed them. As I understand it, they are primarily to assist in 3D manuevers; I don't do 3D.

    .

  13. #13
    Moderator daveopam's Avatar
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    Mine are all straight Ernie. In knife edge it would make the upper SFG closer to inline with the path of the plane but make the lower one have a higher AOA.I cant see how this would help any in KE flight. Now in HA flight, like in a Harrier this would make a low pressure area at the tip of the wing in the AILE area. Would this improve wing rock problems??
    Don't really know just spit balling.

    david
    I never want to see a crash. But I don't want to miss one either.

  14. #14

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    I think there are a lot of misconceptions about SFG's in the modeling community. Upon seeing a SFG mounted to a model aircraft for the first time, one might think its purpose was to merely increase surface area during KE flight.

    In actuality, there are many aerodynamic forces working at/around the wingtips of our models, changing with each change of speed, pitch, roll and yaw that most of us don't understand or consider when looking at a static model sitting on the flight table at the field.

    While I don't claim to be an expert, or to know and understand ALL of the effects that SFG's have on our models, this explanation helps to wrap one's brain around the various aerodynamic principles that are in play and how SFG's may (or may not) affect the flight characteristics of our models.

    http://en.wikipedia.org/wiki/Wingtip_device

    Regards,

    Astrohog


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