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Old Apr 14, 2012, 02:53 PM
Build A Rocket Boys!
PDX Slope Pilot's Avatar
Portland, Oregon
Joined May 2002
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Thanks for that info Jon! I may need to try a Cyril out at some point.
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Old Apr 18, 2012, 07:25 AM
Thermal Wrangler
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Launceston Tasmania
Joined Mar 2004
2,145 Posts
Dives from insane heights = ludicrous speed

Flew on the weekend off the slope at Devonport, Tas. Amazing lift all day.

John & Florian had their FOSAs tearing around (Florian 1.3Kg ballast) and I ran the Ceres with 1.5Kg in the wing. Dives and speed runs from insane heights (8-10 sec dives) were spectacular. Fastest I've seen gliders go in the flesh and that includes DSing.

Verdict: I could have used more lead (the lift was that good) and I may have to get a FOSA; they proved faster than the Ceres.

Stripped the gears on one flap servo on landing. A pretty innocuous bump it was too but the MKS mini didn't like it and despite the ball-races and metal gears and shiny metal case it was busted. 2 sets of gears are ordered and en route.

Expected more from these servos. I've only ever stripped a flap servo once and that was a cheap HiTec 65HB in a 60" sloper. I've never stripped any other make.

Still, the decision to use the servo frames is valid IMHO. Undo a clevis, 2 allen bolts and remove it. Simple.
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Old Apr 18, 2012, 07:34 AM
registered user
Australia, QLD, Gold Coast
Joined Sep 2008
2,511 Posts
I really like and have never stripped a 94761 and now with the bearing kit there even better. I dont get enough time to fly my Fosa but its the Queen in my hangar . . Makes me fly my Ceres like its stolen now
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Old Apr 18, 2012, 12:12 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
21,862 Posts
Chris-

A spare servo is also a great addition to your flight box. Would make your day not end in that situation...

I too, love the smartmodel frames. I have not had need to remove a servo from one, yet.

R,
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Old Dec 01, 2012, 07:48 PM
Thermal Wrangler
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Launceston Tasmania
Joined Mar 2004
2,145 Posts
Ceres Flap Flutter Returns

Flutter Returns
A day of big slope lift at Braddon's Lookout in Tas. saw the heavy artillery come out. Vikos with wing and fuz ballast was around 3.6Kg and super fun.

John with Fosa Lift with max ballast practiced F3B speed out the front in amazing air and after 20 laps it still didn't slow down.

Energetic air was everywhere and thermalling to height over the back and diving into the valley

Ceres was loaded with 1.5Kg and was fun until one high-speed dive made it flutter. Land and post-mortem revealed no damage. John spotted the servo flexing the upper skin just barely so we reckon that's the cause.

On return home, cobbled together a couple of struts tied to the top skin (see photo) and a couple of drops of zap to the servo. I'll see if it holds up if I can thermal out to height off the winch this afternoon.
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Old Dec 01, 2012, 08:51 PM
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You should perhaps try to slide in a rib at the servoshaft side of the servobay.
5mm vertical grain balsa just in between the top and bottom skin more or less directly beside the servoshaft/pushrod should lock the skin movement.

Regards
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Old Dec 01, 2012, 09:39 PM
launch high, go fast
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Australia, TAS, Devonport
Joined May 2008
152 Posts
Yes, I'll second that.

Not sure about the Ceres, but both the Fosa, and Fosa lift have ribs tying the top and bottom skins together. They're all Baudis models (did I mention how good they are??), so maybe the Ceres is the same?

Ribs reduce the length over which the skin can flex. If your model has ribs, I would check their bond to the inner skins. Then check the softness of the skin where the servo is attached. If the carbon rohacell skin has delaminated it will be too springy. Check also the bond of the flap subspar to the skins. Check the servo frame is properly attached to the top skin.

Maybe this was unseen damage from the broken gears earlier? It takes a lotta force to break metal gears!

John
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Old Dec 01, 2012, 09:41 PM
Thermal Wrangler
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Launceston Tasmania
Joined Mar 2004
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Hi ibuild,
Good point.

There's a full-chord rohacell rib just slightly out of view on that side and the ballast tube fabric on the root-rib side; I didn't think it would make much difference adding another rib but you never know; if this strut doesn't work it's worth a try..


John,
Gears seem ok, they were replaced previous except for the main output shaft. Servo frame is solidly bonded to carbon patch. It's likely the rohacell has delammed from the outer skin though.

Right. I'm off for a fly.
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Old Dec 02, 2012, 10:19 AM
Detail Freak
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Harbor City, CA
Joined Oct 2003
21,862 Posts
On my F3F Ceres's, sometimes the drag spar became de-bonded from the bottom skin right about where the flap servo is.
You might look for that, especially if the surface has fluttered.
My surfaces never fluttered, but I had some double centering because of the debonded section. This was probably due to less than perfect ballasted landings.



R,
Target
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Old Dec 03, 2012, 04:33 AM
Thermal Wrangler
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Launceston Tasmania
Joined Mar 2004
2,145 Posts
There was a purple patch of lift for about 15mins around 2pm yesterday.

Prior to that it was all over the place, I couldnt find lift from a lot of launches. Even the Xplorer struggled. It's the sort of air where you check to see if the cg hasn't shifted or the radio is playing up because flying is so erratic and ultimately fruitless. Big handfuls of sink mixed with tiny thermals.

Then it went still and warm and I launched the Ceres hoping to snare something and happened to zoom straight into a monster. Two mins later it was 1 km downwind and a tiny speck. Cruised back overhead maintaining height then vertical for 5-6-7 secs. The velocity was quick enough to induce flutter.

Again no delam or other damage. MKS flap servos seem unfussed. 171s ailerons same. Ruddervators same...all solid.


I'll add some ribs see how that helps.
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Old Dec 03, 2012, 06:48 AM
launch low, fly high
New Zealand, Hawke's Bay, Havelock North
Joined Dec 2004
1,883 Posts
The ribs are unnecessary once you have connected the servo to the lower skin. This is something that I do on every aircraft I build so that the servo loads do not result in flexing the upper wing skin.

On my Ceres, I have bearings above the servo horns. I thought that Juri provided these bearings with the airplane... I did a test when I installed the servos, and did not glue down the bearing mount initially. I checked the control surface for stiffness, and it was a bit floppy. After I bonded the bearing mount, the controls got a more rigid! One caution, the servo horn screw can slowly back out over time, you can guess how I discovered this little tidbit.
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Old Dec 03, 2012, 08:58 AM
F3B and F3K
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United States, TX, Dallas
Joined Mar 2009
1,638 Posts
Tiny surface horns (like on the Ceres) are evil too and more prone to flutter (more slop coming from clevis and axial play of servo, more load on servo, skin and hingeline...).

For a slope ship, I would use larger horns on the surfaces than originally designed for the Ceres.

Reto
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Old Dec 03, 2012, 11:25 AM
Detail Freak
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Harbor City, CA
Joined Oct 2003
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I never had a problem with flutter on mine, just the small issue I mentioned above.

Could the servo arm be a problem, Chris?
I used 3421JR's for the flaps of my 2 Ceres'.

R,
Target
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Old Dec 03, 2012, 02:05 PM
War is over (if you want it)
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Thousand Oaks, CA
Joined Mar 2004
2,665 Posts
The most effective (and easiest and lightest) method I have found for skin stiffening is to simply add a tiny section of vertical grain balsa rib between the drag spar and the rear servo lug. It's just a simple wedge shape with a loose fit and a light mixture of microballoons to secure, it needn't contact the drag spar or the servo and need't be very thick or heavy (1/8" balsa is fine). It functions as a shear web between top/bottom skins creating a non-deformable region of wing skin as close as possible to the rear servo corner. The front servo corner is already perfectly rigid due to it's proximity to the spar so all that's needed is to support the rear.

This works great on my Ceres and I DS that plane way faster than anyone has ever taken one on the front side. Flaps go 20 deg up and just over 90 down with stock horns and sloppy 761 servos and 3rd bearings. Pic below is my Tanga J showing the setup with lighter servos.
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Old Dec 03, 2012, 04:04 PM
Thermal Wrangler
DrFragnasty's Avatar
Launceston Tasmania
Joined Mar 2004
2,145 Posts
Thanks Vespa, that looks a good solution.

DSing is different; there's always a positive pressure on the system. Vertical dive however doesn't provide that pressure so there's a trend to oscillation.

My gut feeling is 3421s are the panacea.
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