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Old Dec 22, 2009, 11:08 PM
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Xpress..'s Avatar
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You don't set the plane tailheavy, ever. You set the CG so it will fly perfectly upright and inverted, without the use of any elevator

Also, daoldguy, if it pitches towards the gear on KE, you might want to try moving the bottom wing down about an inch using an extention
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Old Dec 23, 2009, 05:26 AM
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United States, PA, Bellefonte
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Originally Posted by Xpress.. View Post
You don't set the plane tailheavy, ever. You set the CG so it will fly perfectly upright and inverted, without the use of any elevator

Also, daoldguy, if it pitches towards the gear on KE, you might want to try moving the bottom wing down about an inch using an extention
Power off, I can let go of the controls and it will just float to the ground, inverted, it needs a touch of down stick to stay level, indicating a little nose heavy to CG.

Your thought is the coupling is related to the bottom wing needing seperated from the fuse, moved down about an inch, extending the wing struts and having a cabane added below the fuse?
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Old Dec 23, 2009, 08:24 AM
Old skool speed freak!
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Napa, Ca
Joined May 2004
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I think daoldguy was refering to the typical short nose/long tail moment found on bipes. Make them hard to balance sometimes.I've had guys complain about having to put so much lead in the front, when I say, make it useful weight and put in a bigger motor

Ok, xpress says mount the lower wing an inch lower. I would think that would increase drag further below the thrust line myself, and make the problem worst. Could the landing gear be the cause? Have you flown it without the landing gear? This plane has a very good layout, I can't see why it would do what you say if everything has been done correctly.

Couple of things I'm thinking of, 1, these wings are flat foam I assume, no airfoil shape at all , right? So that wouldn't even figure into this.

2, These light little foamys are flown with fairly large props, could the "P" factor of the prop be a cause to this??? Especially with high alpha KE, such as pulling out of KE loop. I would think that to be a possibility.

Do a search on "P" factor of props if your not familiar with it.

Hmmmmmmmm, lol There are some things you cannot correct, for you will affect other parameters of the airframe that you don't want to change.

Like I said before, sometimes ya gotta live with it and mix it out!!

Vinmech
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Old Dec 23, 2009, 08:34 AM
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Originally Posted by vinmech View Post

Like I said before, sometimes ya gotta live with it and mix it out!!

Vinmech
Yes, these are flat plate wings with the typical habit of climbing <lifting> with higher throttles. My first one had no gear at all and still had the same coupling. There have hundreds of these built, scaled from 18" to 35" and the behavior follows. I even did a test with one of my to be decom's birds adding the KFm2 and KFm4 wings steps to simulate a airfoil. The tests validated the effects of speed verses lift, but she still couples.

One thing I can also point out. Some bipes require you fly all surfaces, to make a smooth turn you need ailerons and rudder to work together. This design is not at all like that, rudder turns will tip the wings and in a lower power the nose will drop.
I have to wonder if it is the canted rudder, I may try more a fishtail style rudder and see what happens.
Thanks
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Old Dec 23, 2009, 08:54 AM
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vinmech's Avatar
Napa, Ca
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Never hurts to experiment! That is how we figure stuff out sometimes.

Try an "X" tail, where the tail and rudder intersect at their mid point on the thrust line so that they are equal. May look weird on the ground, but in the air it may be beautiful!! lol You could make temp mods using thin lexan and clear tape.

Also, I know you said this is a common trait in this particular model, But are your servo's, linkages and control horns tight and return to same neutral point everytime? No binding or slop? This is for nubes, please don't take offense!

Good luck, post us with your findings.

Thanks,Vinmech
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Old Dec 23, 2009, 09:00 AM
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vinmech's Avatar
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Daoldguy, was just looking at your rudder design again and the easiest thing you could do would be to add another inch or so to the bottom of the rudder temporarily to see what effect it may have?

Vinmech
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Old Dec 23, 2009, 09:26 AM
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No offense taken, I am asking for any suggestions. I dont use the cheap 9 gram servos, I mostly use the Futaba or Hitec since I am very picky about control throws ans centering. Had an issue during the build of the silo with centering, 3D arms caused rods to bind on wood horns. YUCKY

The rudder is a simple blenderm tape hinge, I can change the rudder out very quickly, got EPP foam all over the place.

Any chance the offset of the top and bottom wing could be related since the bottom wing is aft between an inch or 2?
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Old Dec 23, 2009, 12:53 PM
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Xpress..'s Avatar
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Your thought is the coupling is related to the bottom wing needing seperated from the fuse, moved down about an inch, extending the wing struts and having a cabane added below the fuse?
Yes, i believe the problem lies with the fact that there isn't enough fuse down there, so it doesn't have enough area to support it. Also, try a symmetrical rudder too
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Old Dec 24, 2009, 10:48 AM
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Lost the silo today. Pretty windy flying, gust twisted her on take off, tried to correct but went down hard. Lesson learned.....

Still had 80 flights and learned so much, so can't really complain, removed all gear from airframe and will be building another in the New Year. Thanks for everyone's help and suggestions, cause now I will make the build a little different and do all the mods from the outset.

Try and keep her close to 15oz this time.

Cheers Y'all.

Andrew
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Old Dec 24, 2009, 10:58 AM
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vinmech's Avatar
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Originally Posted by littleoak View Post
Lost the silo today. Pretty windy flying, gust twisted her on take off, tried to correct but went down hard. Lesson learned.....

Still had 80 flights and learned so much, so can't really complain, removed all gear from airframe and will be building another in the New Year. Thanks for everyone's help and suggestions, cause now I will make the build a little different and do all the mods from the outset.

Try and keep her close to 15oz this time.

Cheers Y'all.

Andrew

Dam, Just in time for the after X-mas sales!!

Hey, second time around is better, you can do all the mods from the outset and make it that much better!
For me, when i lose an airplane, it is just an excuse to get another one!
whether it is the same one or different.

Take care Bro, Mikeeee
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Old Dec 24, 2009, 11:38 AM
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Originally Posted by littleoak View Post
Lost the silo today. Pretty windy flying, gust twisted her on take off, tried to correct but went down hard. Lesson learned.....

Cheers Y'all.

Andrew
Dang.... Sorry to hear that during the holidays. Well now you will have spare parts and patch material for the next one.

Happy Holidays Guys
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Old Dec 24, 2009, 01:06 PM
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Dang.... Sorry to hear that during the holidays. Well now you will have spare parts and patch material for the next one.

Happy Holidays Guys
As you know I am not flightless..... I still have 9 models on my DX6i..... But only one is a 3D plane. Scale flight for a couple of weeks.

Merry Christmas
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Old Dec 24, 2009, 01:16 PM
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As you know I am not flightless..... I still have 9 models on my DX6i..... But only one is a 3D plane. Scale flight for a couple of weeks.

Merry Christmas
Scale flight is still fun too
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Old Dec 24, 2009, 02:46 PM
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Here is one forsale in Dallas

http://www.rcgroups.com/forums/showthread.php?t=1163871

80 bucks ready to go.
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Old Dec 24, 2009, 05:21 PM
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Yep, good deal for someone - too far for me. I placed my order this afternoon. First week of Jan I'll be back in the air with a Silo No. 2.
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