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Old Dec 31, 2012, 05:49 PM
RIP MC
fnnwizard's Avatar
United States, CA, Midway City
Joined Dec 2003
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Quote:
Originally Posted by ak79 View Post
I felt as if my x2 3.8 flew better than my 3.5, almost identical settings. So I checked CG's again and the 3.8 is at 123, where the 3.5 was at 118. So I think Web is right on the CG thing, for my tastes anyway.

I was able to shift my 3.5 CG back to 121 with a lighter fuse harness, but I will have to add tail weight or ditch my switch to do it without adding weight. Looking forward to flying them back to back soon.
AK, how about trying the 3.8 with the 3.5 stabs. See where the new cg is (I would recommend 118-120). I would love to hear your flight reports on this setup.

To date, I have only read from Webbie on his experience, but I think he had the cg far too forward at the time he tried it to get best use out of it.
Thanks.
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Old Dec 31, 2012, 06:17 PM
Win=span\massXpractice+lu ck
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Joined Jul 2007
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Quote:
Originally Posted by fnnwizard View Post
AK, how about trying the 3.8 with the 3.5 stabs. See where the new cg is (I would recommend 118-120). I would love to hear your flight reports on this setup.

To date, I have only read from Webbie on his experience, but I think he had the cg far too forward at the time he tried it to get best use out of it.
Thanks.
is there a 4th set of stabs out there or what ?

I have the molded set that came with my 3.5 - I have a molded set that came with my 4.0 - I have the foam sets from the SL series for the WC - those are the same size (PLANFORM) as the 4.0 -

So is there another size just for the 3.8 because I was not aware of that.
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Old Dec 31, 2012, 06:32 PM
RIP MC
fnnwizard's Avatar
United States, CA, Midway City
Joined Dec 2003
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Originally Posted by webbsolution View Post
is there a 4th set of stabs out there or what ?

I have the molded set that came with my 3.5 - I have a molded set that came with my 4.0 - I have the foam sets from the SL series for the WC - those are the same size (PLANFORM) as the 4.0 -

So is there another size just for the 3.8 because I was not aware of that.
No, just the original 3.5 stabs which is the one I always refer to as the smaller stabs.
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Old Dec 31, 2012, 07:00 PM
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I may try the smaller stabs on the 3.8 next time out. But then I won't be color coordinated.
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Old Jan 02, 2013, 12:18 AM
RIP MC
fnnwizard's Avatar
United States, CA, Midway City
Joined Dec 2003
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Ok, finally had some time to work on my fuses and I am thinking about this mod.
Using just a kevlar string in the pushrod guide to actuate the Hstab for up and an extension spring for down.
It looks to save a net of 12g of which most is towards the rear of the fuse.
The srping pulls about 8oz of tension on the ele servo in neutral and 12oz at full up ele so the servo works all the time. So far that is about the only negative I can think of.
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Old Jan 02, 2013, 04:33 AM
In F3J size does matter!
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Israel
Joined Nov 2006
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Pull-spring works well in DLG but I'm not sure I would use it in an F3J model, the loads during an aggressive launch might mess up your launch trim.
If you do decide to try pull-spring, use a very strong spring, you can add a counter spring on the servo side to balance the load on the servo so that no force is applied on the elevator servo at the neutral position. I've use this with great success in DLG when a stronger spring was needed. This will also reduce power consumption and prevent the servo from heating which will extend the life of the servo etc.
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Old Jan 02, 2013, 07:27 AM
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Quote:
Originally Posted by fnnwizard View Post
Ok, finally had some time to work on my fuses and I am thinking about this mod.
Using just a kevlar string in the pushrod guide to actuate the Hstab for up and an extension spring for down.
It looks to save a net of 12g of which most is towards the rear of the fuse.
The srping pulls about 8oz of tension on the ele servo in neutral and 12oz at full up ele so the servo works all the time. So far that is about the only negative I can think of.
Tuan,

From an engineering perspective, I don't see this as being worth the risk to save 1/3 of an ounce. If you really want to save some weight, consider building a lighter stab. The big solid core stabs Nan made for the World Championship models weigh around 30-35 grams. Bagged 3.5 size stabs could be lighter if done right. Depending on how much nose weight you have, this could knock off a full ounce or more. Much better return on investment with lower risk IMO.

Anyway, the stock models I think are light enough as is.

Tom
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Old Jan 02, 2013, 10:55 AM
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United States, CA, Midway City
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Originally Posted by Kiesling View Post
Tuan,

From an engineering perspective, I don't see this as being worth the risk to save 1/3 of an ounce. If you really want to save some weight, consider building a lighter stab. The big solid core stabs Nan made for the World Championship models weigh around 30-35 grams. Bagged 3.5 size stabs could be lighter if done right. Depending on how much nose weight you have, this could knock off a full ounce or more. Much better return on investment with lower risk IMO.

Anyway, the stock models I think are light enough as is.

Tom
Happy New Year Tom!
Yeah, you are probably right. I am "thinking out loud" about this mod because the way the linkage/stab is setup, it is very condusive to the spring thing.
I am definitely looking at the possibility of lighter stabs too. Hmm.. what if both were done .

Quote:
Originally Posted by roydor View Post
... you can add a counter spring on the servo side to balance the load on the servo so that no force is applied on the elevator servo at the neutral position. I've use this with great success in DLG when a stronger spring was needed. This will also reduce power consumption and prevent the servo from heating which will extend the life of the servo etc.
Great idea, thanks Roy!
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Old Jan 02, 2013, 02:55 PM
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Warwickshire, England
Joined Sep 2006
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You'd need tail weight to balance it....
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Old Jan 03, 2013, 01:58 PM
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United States, CA, Midway City
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Originally Posted by satinet View Post
You'd need tail weight to balance it....
I think we'll be alright, I noticed on the current fuses, there is very little nose weight (lead shot) built in so not much work to dig em out if needed. If that is not enough, I'll move the battery back.

So why am I oing this? Well, the biggest reason is to get rid of any slop in the stab linkages. I tested the setup last night and have 100% faith in it.

The stab on the X naturally wants to deflect down in every case due to the cg of the stab behind the pivot (and to a slight degree the pivot being in front of its a/c) and the added weight of the connecting rod on the bellcrank. So, if the spring breaks in normal flight, I am sure the plane will still be flyable and landable.

I can only imagine the response from ele input will be better and if I can throw on lighter stabs from the factory (or another source) it would be amazing... provided your ele servo has capable resolution .
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Old Jan 03, 2013, 02:13 PM
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Yes but the down side is you will have to butcher a fuse to set it up.
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Old Jan 03, 2013, 02:46 PM
RIP MC
fnnwizard's Avatar
United States, CA, Midway City
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Originally Posted by ak79 View Post
Yes but the down side is you will have to butcher a fuse to set it up.
Yeah, you do have to do some minor surgery. 10 minutes top if doing precision work, and maybe 3 minutes butchering .

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Old Jan 03, 2013, 02:56 PM
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San Diego
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Quote:
Originally Posted by fnnwizard View Post
I think we'll be alright, I noticed on the current fuses, there is very little nose weight (lead shot) built in so not much work to dig em out if needed. If that is not enough, I'll move the battery back.

So why am I oing this? Well, the biggest reason is to get rid of any slop in the stab linkages. I tested the setup last night and have 100% faith in it.

The stab on the X naturally wants to deflect down in every case due to the cg of the stab behind the pivot (and to a slight degree the pivot being in front of its a/c) and the added weight of the connecting rod on the bellcrank. So, if the spring breaks in normal flight, I am sure the plane will still be flyable and landable.

I can only imagine the response from ele input will be better and if I can throw on lighter stabs from the factory (or another source) it would be amazing... provided your ele servo has capable resolution .
What if the pull cord breaks? Probably not likely, but something to think about.

I also wonder about the flutter response of such a soft system.

I also wonder about the power of down input - especially at full down. It would suck to soften the down response when you push into the bucket before the zoom.

I know you're going to do it anyway but I'm still not sure what problem it will solve (the linkage on my Xplorer stabs is plenty tight).

Let us know how it goes!

Tom
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Old Jan 03, 2013, 03:35 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
20,851 Posts
You will save more weight by simply ripping out the (IMO heavy-ish) stock pushrod housing and replacing the whole shooting match with some etched teflon tubing and a small-ish diameter CF rod (maybe .050"?)...
If you want to run a light spring also, then you will eliminate any possible (but likely improbable) double centering, and STILL have the capability of pushing with the linkage if the spring ever comes loose or breaks.

My 2 cents.

R,
Target
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Old Jan 03, 2013, 03:56 PM
LSF V aspirant
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United States, CA, Orange
Joined Oct 2006
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Quote:
Originally Posted by Kiesling View Post
but I'm still not sure what problem it will solve
+100. This is a high-risk, very low-return modification (I would even argue that someone flying a properly set up stock plane and one with this setup could not feel a performance difference, in any way). In addition, most of the fields we fly in SoCal are surrounded by residential areas. I would hate to see a plane go in to one as a result of a quest to drop a few grams from an 1,800 gram airframe.

Tom
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