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Servo in tail

Old 03-10-2004, 09:07 AM
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Speedo125
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Default Servo in tail

Hi guys:
Forgive me if you've discussed this before. I've been away for a while. I'm building (OK, re-building) my NES Victory open class ship. At this point in it's life it'll only be used for easy recreational flying. Rather than the usual full-flying stab/elev, I'm going with a conventional fixed stab and elevator. I already have a carbon pushrod running back to the rudder, but was thinking of putting the mini elev servo in the fin. Yeah, I know about the weight situation, but I've done some weight tests with a digital scale, and the difference just isn't that significant. ANYWAY, my question is: Should I be concerned about radio interference with that long servo lead running down the fuse' in close proximity to the antenna? I can change that rudder pushrod to something else if you think that could be a problem.
Thanks,
Thom
Colorado
Old 03-10-2004, 11:31 AM
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Tall Paul
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Default RE: Servo in tail

There's pros and cons about radio interference with long servo leads and antennas.
I use long leads with the antenna right next to them, with no detectable interaction in several planes.
Old 03-10-2004, 11:37 AM
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Landi
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Default RE: Servo in tail

I would not worry about.

You could run your antena in a tube as far as possible from the rod as possible.

Aslo make sure u twist your servo cables this will reduce the probability of interfearence and if u want ot go really sure u can buy a servo amplifier. Servo City has some about $13 plus shipping.

I run 6 feet long servo leads from the ruder of my big glider all the way to the reciver and I dont have any problems.

Saludos

Landi
Old 03-10-2004, 01:05 PM
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MTT
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Default RE: Servo in tail

I agree with Landi, you won't have any problems there !
On my Cumulus E e-powered sailplane, I even have both the elevator and rudder servos back in the tail.

And on my 1/4 scale Ka8, it's also in the tail.
I don't use any servo amplifiers, just twist the long leads, I also do that on the long leads which run out to the aileron servos.

Never had any problems so far.

Michael
Old 03-11-2004, 08:54 AM
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Speedo125
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Default RE: Servo in tail

OK, thanks guys. You've really been helpful. I'll slip my servo in the tail and go for it.
Thom
Old 03-11-2004, 12:01 PM
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FHHuber
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Default RE: Servo in tail

On a sailplane... your mainproblem might be... having the servo way back near the tail will require up to 3 times as much ballast in the nose. (the tail is usually much longer than the nose...)

Its something to consider about the effects of the change.

If the long lead does cause a problem... te amplifier/glitch buster circuits do a great job of cutting it down... and you can always run the antenna in a tube in the wing to get it away from the servo lead.
Old 03-11-2004, 01:57 PM
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Landi
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Default RE: Servo in tail

@FHHuber

U are rite about the increase of weight in the nose to compensate for the servo. But if u run the numbers for a open class ship which I imagine would be at least 3 m the weight of a standard servo 51 g length of the fuse 2m, the cg at 50 cm from the nose and aft 150cm to compensate this u would need M = (51 x 1.5)/0.5 = 153 g as u can c u are completly rite about the 3 times to compensate but on a big ship a additional weight of 102 g (which is only 2 times ) does not make much diefference. with the big advantage that u will have very short arms to control your surface wich will give u less probability of having slope in your controls.

If u have the antena in the wing u will have even more cables to cause interference (A, F and S) this make up nine cables instead of three cooming from the tail also u will have to pull the antena out of the wing evrey time u pack your plane with the danger of damaging the antena wich could cause some serious interfeerence.

Saludos Landi
Old 03-11-2004, 05:12 PM
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MTT
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Default RE: Servo in tail

I'm with Landi on this, on the bigger ships, you won't notice the difference. Especially modern type scale sailplanes often times will fly even better with a little bit more wing loading.
I initialy had my Flair Ka8 equipped the traditional way, with the servo up front, but later moved it into the tail for more precise elevator control, and easier assembly at the field.
However I could not detect any change in the flight characteristics of the Ka8.
Except the more precise elevator control, of course !
IMHO, the benefits fo a short, slop-free elevator system outweigh the drawback of the weight increase, except maybe on all out F3J/floater sailplanes, where absolute minimum sink is the goal.

And on e-powered sailplanes, it is even less of an issue, since you compensate by moving the drive battery, so you don't have any weight increase at all.

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