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Old Dec 03, 2012, 03:34 PM
Don't take your guns to town
vespa's Avatar
Thousand Oaks, CA
Joined Mar 2004
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Actually when DSing a plane like the Ceres at a big hill you have to make huge laps at zero lift most of the time in order to keep the speed down. And though loading the wing reduces the flutter tendency you certainly can't count on that as there are plenty of times where the elevator must be released for path control.

3421's are great but I don't think they're any stiffer than your MKS and that's all that matters. Also note that due to the thickness of the 3421 you'll get far less flap travel unless you switch to a bulged cover.
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Old Dec 03, 2012, 06:52 PM
Detail Freak
target's Avatar
Harbor City, CA
Joined Oct 2003
21,672 Posts
My Ceres (with the 3421's) has flat covers, and no bearings. The bearings can only help.

Also, I have a reasonable amount of flap throw (70-75* down, and about 10* up), so maybe thats the difference, but I didn't need bulged covers, at any rate.
Basically, I think part of the difference between Chris' Ceres and mine is his is a B layup, and mine is an F...
Could it be that just the flap itself is fluttering, and maybe you have a delam somewhere? If that is the case, it won't matter if you pot the servo in with solid epoxy, your problem will persist I think.

Chris-
Please check your plane's flaps closely and see if you can find any clues with regard to that. If you have already, just disregard....

R,
Target, the other Chris.
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Old Dec 03, 2012, 11:12 PM
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Australia, QLD, Gold Coast
Joined Sep 2008
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Quote:
Originally Posted by vespa View Post
Actually when DSing a plane like the Ceres at a big hill you have to make huge laps at zero lift most of the time in order to keep the speed down. And though loading the wing reduces the flutter tendency you certainly can't count on that as there are plenty of times where the elevator must be released for path control.

3421's are great but I don't think they're any stiffer than your MKS and that's all that matters. Also note that due to the thickness of the 3421 you'll get far less flap travel unless you switch to a bulged cover.
mine DS'd to 169mph and looked solid, was wanting more wind..... tight laps / big laps all great. i have just given it a new paint job I will post some pics
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Old Jan 06, 2013, 01:45 AM
Thermal Wrangler
DrFragnasty's Avatar
Launceston Tasmania
Joined Mar 2004
2,116 Posts
Anti-Flutter League

I think It's sorted. The flutter that is.

I fixed the flap servos to the opposite skin and flew "the ring off it" at Braddons lookout; a slope site notorious for turbulent thermal / slope lift and also from "some height" at the flat field and it still fluttered. I'm not saying that bonding the servo to the opposite skin doesn't work but if you have servo frames I suspect you don't have to go the extra effort.

By process of elimination I suspected the ailerons so replaced one 4-40 clevis which looked very 2nd hand which was only kept closed thanks to a wind of cotton. The JR 171s had a little slop but not significant.

Still fluttered though. Thankfully no destruction of hinges or any other structure.

Blamed the MKS 6125s but they showed no sign of any defect until last week when I noticed a flat spot at deflection on one flap servo.

I replaced the entire gearset although I still had to leave one ball-race in situ in the case because it proved too hard to remove and simply removed the corresponding one from the new output shaft. Also zapped the clevises again and there's not slop. None.

Took it out today in stifling, hot windy turbulent weather and apart from the first launch off bungee it took several launches to find any lift to work with. Ran 600g wing ballast. There were some freakish thermals passing through today; small radius and rapidly moving skywards. To use them you had to bank and crank. It wasn't pretty.

The sky was cloud-free and made visibility at height tough.

However, several pin-drops from height didn't induce flutter so for the mo' it's looking good.


Chris.
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Old Jan 22, 2013, 05:35 AM
Thermal Wrangler
DrFragnasty's Avatar
Launceston Tasmania
Joined Mar 2004
2,116 Posts
Anti Flutter League

Took the Ceres for a spin last Sunday in very thermic weather, 600g ballast; small but powerful thermals were everywhere.

On one speed run at the end I peeled off left and hit massive sink so darted right, still with a fair amount of speed and hit a massive boomer. It took three or so tight turns to gain around 300ft. It was like having an engine in the nose.

Overall great fun but it still fluttered diving at speed ( from significant height) So I got home and jumped into a mod. using slightly taller horns (see photos).

The hard part was removing the horns and making a slot. A 2mm drill bit and the trusty Dremel removed all the material and the new horns bogged-in.


Chris.
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Old Jan 22, 2013, 06:57 AM
Detail Freak
target's Avatar
Harbor City, CA
Joined Oct 2003
21,672 Posts
I'm certain that will help, but what was the servo arm length??
I think the instructions call for a 6mm arm, and that means drilling a hole closer to the center of the output shaft in every brand of servo's arm.
If I recall correctly, even with the 6mm arm, I never used 100% of the normal servo travel, so a bigger horn in the surface may be the hot ticket.
Just curious what was there.
Sounds like fun flying conditions!

R,
Target
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Old Jan 24, 2013, 02:42 PM
Thermal Wrangler
DrFragnasty's Avatar
Launceston Tasmania
Joined Mar 2004
2,116 Posts
Old Skool

Hi T,
Longer horns need a small blister cover but overall it's very solid. A far more positive movement with little "spongy" play.

Old skool but hopefully that's the flutter gone.
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Old Jan 24, 2013, 06:35 PM
Detail Freak
target's Avatar
Harbor City, CA
Joined Oct 2003
21,672 Posts
So, then you are using the same length servo arm and more travel from the servo?
Or, did you have to go to a longer servo arm??
Just curious....
Probably not as draggy as you think, I think.

R,
Target
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Old Jan 31, 2013, 07:46 PM
Thermal Wrangler
DrFragnasty's Avatar
Launceston Tasmania
Joined Mar 2004
2,116 Posts
Cold Chisel

Longer servo arm T and bubble covers.

Anyhoo I just wanted to share my pain; for ailerons, previous owner epoxied the 171s (noisy, lots of play most likely responsible for flutter) into the wing.

With lots of epoxy.

I can't budge it so it looks likely a Dremel job dammit.

Will replace with 761s and servorahmen frames.
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Old Jan 31, 2013, 08:12 PM
Don't take your guns to town
vespa's Avatar
Thousand Oaks, CA
Joined Mar 2004
2,607 Posts
These usually come out easily. Use a square-tip Dremel to remove part of the glue fillet, drop a razor blade in there, tap with a hammer, and it'll come right out without stressing anything. Rest the wing on foam so it doesn't get scratched. The key is to use something heavy that fits the razor blade very well -- the standard-size needle nose pliers in my pics are the best I've found.



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Old Jan 31, 2013, 08:52 PM
Thermal Wrangler
DrFragnasty's Avatar
Launceston Tasmania
Joined Mar 2004
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A degree in cunning from Oxford

You're as cunning as a fox with a degree in cunning from Oxford.
Thanks for sharing Vespa, I'll give it a go.
Chris.
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Old Feb 02, 2013, 04:10 PM
F3B and F3K
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United States, TX, Dallas
Joined Mar 2009
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Chris,

I question that you need larger servo arms and bulge covers, you just need to use ALL available servo throw.

An important thing to get enough deflection with short servo horn and large flaperon horns:

You need to electronically offset the servo (with the TX) ,not mechanically. When the transmitter trim is neutral, the flap is already say 30% deployed. You then trim the flaps flush in every flight mode. In my F3B planes this can be the maximum subtrim that is available.

This makes sure that you get most of the available servo throw for deflecting the flaps down (you can't use all of that throw if you mechanically offset the servo arm forward, because then a lot of throw is unused, i.e. movement into the wing).
That way I get enough throw with hidden servo arms using large sized flap horns.

Reto
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Last edited by RetoF3X; Feb 02, 2013 at 05:49 PM. Reason: typo
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Old Feb 02, 2013, 06:30 PM
Thermal Wrangler
DrFragnasty's Avatar
Launceston Tasmania
Joined Mar 2004
2,116 Posts
Gentle Persuasion

Great explanation Reto, thanks.

Servo popped-out thanks to the scraper blade trick but mostly from leverage using the M3 allen bolt and gentle persuasion and colourful language. Words like "Crikey!" and "Cripes!".

Here's a tip; take a chisel blade, heat with butane torch and use the reverse-side to remove epoxy. Use gingerly and keep the blade moving to prevent any heat damage. Much less hassle than the dremel grinding and in my case, didn't affect the top skin at all.
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Old Feb 03, 2013, 12:35 AM
Build A Rocket Boys!
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Portland, Oregon
Joined May 2002
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Another option is a Hobbico Hot Knife with a chisel blade to remove epoxy. I always place a cold rag under the skin and take it slow but I can make a servo bay look virgin again with this method.
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Old Feb 04, 2013, 06:21 PM
Thermal Wrangler
DrFragnasty's Avatar
Launceston Tasmania
Joined Mar 2004
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Hot knife sounds a good option PDX. I came pretty close to removing all epoxy using my chisel butane torch combo.


Thanks for the "offset" tip Reto. I'd forgotten about that on my last 2 gliders but they had conventional horns so had plenty of down flap. I remember doing it previously but haven't worried about it until now.

On the JR9xv2 (9303) I tweaked the sub-trim to -220 and + 220 for left and right flap (as per the manual although they mention -225, 225) then adjusted offset to 170 in the Butterfly menu then adjusted the linkage and hey presto! Heaps of flap and adequate up travel too.

The bigger flap horns resist "blow-back" a lot. compared to before.

Ailerons are now mint. 94761s are in frames, the linkages are now 2mm rather than 4-40 and use subsequently smaller clevises. No play and lots of friction-free travel.

Both flap and aileron servo covers now have a bump (estrella covers on ailerons) and custom on flaps. My next F3B ship will have RDS ailerons and conventional on flaps.
I'm surprised F3J ships haven't moved to RDS ailerons.

Flaps are still 4-40 linkage.

Despite the abuse the top skins are still pristine.

I'll thrash it around Braddon's Lookout and see if it flutters now.
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