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BMJR Model Products Geef 250 by pfinn. Viewed 1624 times.
Build Thread
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| Image Comments |
| pfinn | 11-Oct-09 20:33 | | The GEEF! It's ALIVE! http://www.youtube.com/watch?v=SvRZGOgvt_c |
| mleduc | 11-Oct-09 20:56 | | Awesome flight! I don't know if that was your first one or not. I assume you are playing with the CG at this point. That battery pack may have to move a hair :-) . This ship reminds almost exactly (or sort of) of a free flight plane I saw in an old family friend's book, except it had a saucer airfoil on top, like the Vought "Pancake" I guess. Same sort of attitude. In any event, congrats. Hoping you might be willing post your setup and your opinions on whether it would you think it would work for a Guillow's Arrow. (long shot :-) ) |
| pfinn | 12-Oct-09 00:47 | | mleduc, This is a repro kit of a 1949 comp. design. Awsome kit by the way. As far as CG, there's a long story on that one on a previous post in this build. With a lifting stab like this and your Arrow (I know that model because my son, jfinn, is slowly but surely building one here, see his hanger) the flight characteristics change quite dramatically with change in airspeed. The faster the plane travels, the more lift the stabilzer creates and hence more nose down pitching. As a freeflight, and this goes with most "Lifting Stab" equipped models of this sort, the CG is way back. See the white mark on the wing saddle (the one very close to the wing)? That's more or less it on this airplane. It was designed to ascend rapidly under power at a high angle of attack at high speed, engine quits and then transitions into a very slow floating glide. The model is actually using the the stabilizer as a lifting surface so the CG is moved rearward in relation to the main wing because the "Center of Lift" has been shifted rearward by the lifting stab. The CG and CoL relationship directly contributes to stability. Could go on, but I won't (phew!).
As an RC, the Lifting Stab makes for a... unique...flying experience. Lots of varialbes to contend with during flight. Personally, I like it, keeps you on your toes. For a more conventional flight characteristics I would definately go for a "Plank" non-aifoiled built-up style horz. stab., put the CG at 25-30% and go from there. That's what Jimmy is going to do with his although he did build the stock stab too. "Droid", here at VA also RCed an Arrow. He has some good insights as well pertaining to the Arrow in particular. The prop in this picture was totally wrong. Too much tourque ("P" factor).Currently using a 6-4 Master Airscrew. Very small rudder movement is needed with a poly wing. I've got only 1/4" throw either way. In a glide it's almost not enough, under power, it's almost too much. Elevator throw is 1/2" up and down and not as sensitive. Right now I'm also deciding if I prefer the way it flys with either three pennies of nose weight or five. My friend flew the Geef after the video and said that this is the type of plane you might need to change your shorts after flying. He just wasn't used to it! Hope this helps and sorry every body for the "Longwindedness". Phil
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| mleduc | 12-Oct-09 14:27 | | No Pfinn, I very much appreciate the detail. I have been building an Arrow in my mind for some time since I saw the Purple/Yellow one (Droid's I believe) and definitely see some similarities to this bird. I'm collecting parts and checking in at RC groups for info as I'm more or less waiting for a stable housing situation to get going on my project. Thanks very much for the run through. Since I'm a novice at flying I very much appreciate your advice on the horizontal stabilizer factor. ML |
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