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Devin McGRath
Mar 08, 2006, 09:33 PM
Well I had made this shocky about a month and a half to two months ago and haven’t had much time to post about it so I had some spare time and wanted to be able to contribute to this forum so here we go...

components

AXI 2204/54
CC10 amp
FMA direct M5 V2
Kokam 2 cell 340
Futaba 3110 servos
AUW 5.7 oz ( I did not go all out on this one for lightening because it was purely experimental)

I made a few different modifications to this one as you might be able to tell by the pictures ;) I made two counterbalances in the wing on this one. I was trying to achieve a faster roll rate. It did not to much at all. It did however make the plane roll perfectly axial at every aileron position before with my older ones they would start to loose there axial roll at extremely high deflections this one did not. These counter balances did not give the plane any bad characteristics at all. It did not hurt the precise aspect of the plane in any way. I also may little air dams right in front of the counterbalances that would block the airflow from catching the counterbalances at neutral and just around neutral because it is nearly impossible to get the entire aileron to center correctly when you are dealing with foam (these did add drag to the plane as well). On my previous F3A I had 90 degree pieces of foam off of the SFG’s to add drag I left them off on this one because of all of the extra drag created by the counterbalances and air dams.

Overall this F3A I think is a great flyer and an improvement on the original in every way except for the slight added weight of extra glue, carbon fiber, and probably the biggest downside would be the build time lol. Took a ling time to do.... one of the major lesson learned here is that round swept counter balances are inefficient. But it does look cool doesn’t it !

I can't get any detailed pictures of it for you guys right now but I do have these ones from the night I finished it. ( It's on its way to Memphis right now). Let me know what you guys think :) BTW the pieces on the leading edge are top secret as Jurgen might say.

byoung
Mar 09, 2006, 06:34 AM
Devin,
What are you using for your tensioning string to prevent twisting? I tried using natural kevlar but it keeps snagging and tangling.

Brad

Devin McGRath
Mar 09, 2006, 07:17 AM
I am using 17lb test low stretch fishing line. I also just run it all the way through and keep tightening it until it is as tight as I want it. You want it to stretch a little bit so it will not get to tight or loosen up when the foam expands or contracts.



Devin McGrath

byoung
Mar 09, 2006, 09:51 AM
Anything special about this fishing line? Is it spiderwire or normal monofilament? Does CA stick to it well enough to secure knots?

Thanks,
Brad

David Kyjovsky
Mar 09, 2006, 10:10 AM
I like to hear that it "axialized" your rolls. I have put similar (much more modest) counterbalances on my first Focus with exactly this idea. And it worked... I mean, it rolled very axially but there was nothing to compare it to.
It weakened the wing structurally, so with my next plane, I dropped the idea. And then it suddenly took more playing with differentials etc to achieve rolls as good..

Flying as slow as we do indoors, you have normally a high alpha situation where the coupling from ailerons to yaw is the strongest.. because the down going aileron gets much more "buried" in the airflow and hence the increased drag >> yaw coupling (opposite to your rolling direction). The counterbalances help by creating similar drag on the up-going aileron.

Thinking of it, axial rolling might be the idea behind Martin Müller's canted SFGs on the Manta ... the down going one gets always more airflow, it is aft of the CG and canted , so it might (just might) work against the "negative yaw coupling". Its airbraking is just another bonus for F3P...

Malves
Mar 09, 2006, 05:25 PM
Sick!:) What did you use for hinges?

Devin McGRath
Mar 09, 2006, 05:34 PM
byoung, it is regular monofilament it is kind of slippery but you can glue to it it will never let go in a knot with CA but I still do three knots just to be absolutely sure. I have never had a problem with it yet.


David, you could be right about the Manta you have a very good point. Also If you notice I have extra bracing on my wing across the SFG's to make the wing stronger the 64th plywood in front or the counter balances add strength. There is also a piece or carbon fiber in the aileron which makes it even stronger. It is just as strong as my old ones if not stronger.


Devin McGrath
www.devinrocks.com

Devin McGRath
Mar 09, 2006, 09:03 PM
Those are regular tape hinges ;)

byoung
Mar 13, 2006, 11:18 AM
Devin,
Good News your MicroRex motor is coming with the rest. :D I sent a PM to Jeff about it.
Back to this Modified F3A...what prop do you like with the 2 cell 340's; have you checked the current draw?

Thanks,
Brad

Devin McGRath
Mar 13, 2006, 11:30 AM
I like the 9x4.7 on two cells. The current is right at 6.4 amps


Devin McGrath

byoung
Mar 13, 2006, 01:19 PM
Devin,
Have you tried the GWS 9x5HD on two or three cells? How did it compare to the 9x4.7?

Thanks,
Brad

dorjes
Mar 13, 2006, 02:30 PM
Devin , how do you get these Shockies so light ? I just finished a Yak with 2204 Axi , CC Phoenix 10 , 1 Futaba 3110 , 2 bluebird 303s , TP 2s 480 pack , and it weighs 178 grams ready to fly with APC 8 x 3.8.

I know you string 'em up , and I think you delete the foam stiffeners on the bottom of the fuse , but I wondered if you used a different size carbon for the wings , or if you left out some of the carbon.

Thanks, Dorin Luck

Devin McGRath
Mar 13, 2006, 02:32 PM
It does not seam to be as responsive and flexes off of the hub more.



Devin McGrath

Devin McGRath
Mar 13, 2006, 02:34 PM
Yea I do everything I can to lighten them up.... lighter carbon different hardware and allot of other little things.... pull pull does save a good amount of weight as well. Half of the fun is figuring out where to save weight.


Devin McGrath

Aio_1
Mar 13, 2006, 02:40 PM
It does not seam to be as responsive and flexes off of the hub more...
I'd expect the 9x5DD to change speeds a little bit slower due to being a bit heavier but what do you mean about the flexing?
The 9x5 is a MUCH stiffer prop. I would think there's no way it would flex at that power level (do the slowfly props?)

Aidan

Devin McGRath
Mar 13, 2006, 03:32 PM
I did not meen to say flex I ment to say slip It seams to move off of the hub thus changing the direction of the trust.


Devin McGrath

Aio_1
Mar 13, 2006, 03:58 PM
Ah, I see.
I presume that's because the prop adapter doesn't fit the prop hub as neatly as the slowfly GWS hubs? I've noticed the different hub on the DD props don't always sit quite right on the prop-saver type adapters.

Aidan

byoung
Mar 14, 2006, 04:37 PM
Did anyone get the aluminum adapters that Hobby lobby shows on the web site for the 2204/54? It looks like there should be one for GWS HD props and another for APC SF props. My motor was second hand and I don't have them.

Brad

Devin McGRath
Mar 14, 2006, 09:11 PM
I got them with all of my motors.

Devin McGrath