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Nov 11, 2009, 02:05 PM
agony sweetns the victory
atjurhs's Avatar
Discussion

new vs. tradtional servo layout for lite weight


Hey guys,

I'm in the middle of building a Skua 1500, and I want to keep it lite. I'm thinking about using some cable or otherwise flexible pushrods and re-locating the servos in front of the CG instead of behind the CG, and that way hopefully reduce some nose weight.

What do you think are the CONS to doing this?

Thanks, Todd
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Nov 11, 2009, 02:15 PM
Phil.T-tailer
Phil.Taylor's Avatar
slop/backlash in the cables/pushrods - cos of the bends
when CofG'd right - you'll need very little elevator movement, and slop will have a disproportionately large effect. might work OK on a Zagi, but not an S15
YMMV
Phil.
Nov 11, 2009, 02:22 PM
altitude adjustment
thumbhead's Avatar
I've tried the same thing on a combat wing years ago by using Golden Rod flexible pushrods and could not get it to work without slop. The transition between push and pull going around an arch like that would create a tiny bit of slop. I ended up pulling it all out and going with tradition pushrods.

mark
Nov 11, 2009, 03:03 PM
__Jackass Savant__
theBOZman's Avatar
what about moving the servos from the stock layout to the root of the outer panel "where the panels join" right on the CG?
Nov 11, 2009, 03:38 PM
Composites Kid
Alex.Schweig's Avatar
SLOP!

Lots of it! Every time you use a flex rod for a curve like that, you'll end up with slop.

And on a plank, you definitely want the most rigid setup you can install.
Nov 11, 2009, 03:39 PM
agony sweetns the victory
atjurhs's Avatar
Thanks guys for the inputs! Guess I won't do it as I know slop is really bad on a plank.

BOZ, that's right where the fins go, and that wouldn't really get you in front of the CG anyways, but thanks for the thought.
Nov 11, 2009, 03:54 PM
__Jackass Savant__
theBOZman's Avatar
at least on the CG wouldn't require a counterweight. They would just be ballast. And the fins are surface mounted, right?? You could even run the rod trough the fin and have the control horn inline with the fin. It would be aerodynamically cleaner.

But that might require thinner servos, so you would have less torque and durability.
Last edited by theBOZman; Nov 11, 2009 at 04:01 PM.
Nov 11, 2009, 04:03 PM
__Jackass Savant__
theBOZman's Avatar
Maybe composite vertical stabs as well. use lighter material behind the CG. Is there any way to lighten the TE build up or the elevons?
Nov 11, 2009, 04:34 PM
agony sweetns the victory
atjurhs's Avatar
because of the spar location and CG location, you'd have to mount the servos 1/2 span-wise down the center panels in order that they are aligned with the CG and become "ballast" but then there's no way to run linkage to the elevons without flexible cables and we already decided not to do that because of slop. I'll locate as per the instructions. I'm using BB380 Max servos, they are fairly light and have plenty of torque.

I have been thinking about cutting large "lightening" holes in the elevons before covering with ultra-cote. That would reduce weight aft of the CG, but not sure how "flexy" the elevons would then become? Maybe competition grade balsa as a replacement for them instead???

I'm not sure what material I could use that would lighten the vertical fins much. They are currently made out of 3mm coroplast. I suppose I could look into competition grade balsa as a replacement for them too???
Nov 11, 2009, 06:44 PM
Taranis Tyro...
MattyB's Avatar
Honestly, I really wouldn't bother moving the servos from their stock positions. I personally never fly my S15 with less than half ballast - it won't really fly below 5mph on my regular (fairly average sized) slopes, and above 5 the ballast goes in as I think it improves efficiency. The only mod I'd make if I built another would be lightweight bagged fins to replace the correx ones and an extra ballast tube - it's too light above 15mph even with full ballast.


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