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SAB Goblin 500/570 SAB Heli Division - Goblin 500/570 Helicopters |
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09-10-2014, 11:40 AM | #1 (permalink) |
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Join Date: Jan 2009
Location: NorCal
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Goblin 570 Tail "Groans"
For lack of a better word my 570 makes a "bad" groan sound when the tail has high pitch in the clockwise direction. I hear groans during hard stops (flicking collective generating high tail pitch to counter torque), during extreme high speed funnels, or nose in sideways loops at higher speeds.
My working theory is that by designing in a damped tail there are now lots of possible resonances causing a groan sound or buzzing. The ability for a tail blade to flap is not a good thing. I don't see any engineering merit in the damped tail design. There is no vibration problem to solve here. Any ideas to make the tail rigid? Or know some stiffer tail dampeners? I swapped on some rail blades to see if there is less groaning. Next I'll swap in my g500 tail which seems to have stiffer dampening compared to my 570. |
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09-10-2014, 11:44 AM | #2 (permalink) |
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Maybe try pre loading the tail dampers a little with some 0.1mm or 0.2mm shims? not sure if this will help, but might be worth a try.
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09-10-2014, 11:45 AM | #3 (permalink) |
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09-10-2014, 11:57 AM | #4 (permalink) |
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Location: NorCal
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I though of that, but seems like a bad idea when you mechanically need a tail that's smooth with no mechanical resistance?
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09-10-2014, 12:12 PM | #5 (permalink) |
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There should not be any more resistance other than stiffer dampening, the bearings will still work like they do now, it would be the same as doing this to a main blade head(which is very common practice on many models), when shimming the main blade dampers, the head still rotates freely, unless you go crazy with shims, but I doubt a 0.1mm shim on both sides will do any harm.
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09-10-2014, 12:33 PM | #6 (permalink) |
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Location: NorCal
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So the link DavisBladeWorks sent is exactly the same issue as mine. Looks like he worked insanely hard to solve the problem but gave up and got a new kit. :-/
Looking through his experiments, I don't see where he tried a rigid tail. So it seems like the right direction to go and solve this. |
09-10-2014, 02:36 PM | #7 (permalink) |
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Join Date: Jun 2014
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Have you tried installing the original 22T tail pulley? Maybe perhaps the very high tail speed is not meant for the stock dampers?
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09-10-2014, 03:51 PM | #8 (permalink) | |
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Quote:
I have a flight video of the groaning with a tight in sideways loop. Will post it shortly. It has zero impact on flight performance, so I'll probably just let it go. |
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09-10-2014, 04:53 PM | #9 (permalink) |
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09-10-2014, 05:35 PM | #10 (permalink) |
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I hear what you mean.. Sounds like a resonance of some sort, but only when the blades are pitched hard at extreme loads, hard one to pin down. Really curious to what ends up fixing this.
Running the 21T on the tail with higher hs's may be the issue, but as you saidit happens at lower speeds too., could be the dampers are just wore in, or to soft and need a little pre load to stiffen the grips as well. At least those are the only things that make sense, presuming all mechanical is A ok. I would think that if the tail blades were out of whack balance wise it would be making that sound way more often. Seems to be when the tail is under extreme load only, so I still think shimming may help.
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09-10-2014, 06:04 PM | #11 (permalink) | |
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Quote:
I'll have a look at shimming though on the tail dampeners. I still really think a damped tail is cool in theory but a bad idea in practice since it opens the door to major resonance problems. And I think this is what's happening here. The tail shaft moves easily. It's not stiffly damped at all. Very little force to make it teeter back and forth. I tried rail tail blades in that video, and you can see that it had no impact. It also groans sometimes in hard stops etc. Kinda cool to know when you're hitting that max tail pitch level. :-P |
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09-10-2014, 10:58 PM | #12 (permalink) |
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Join Date: Jun 2014
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Have you checked your tail belt tension? I believe your kit is relatively new so your belt may require re tension every so many flights. When I first got my G570, I flew it several times and heard the belt slapping the boom during funnels. I checked the tension and it had a lot of slack. I had to re-check four times to get it to stay at a constant tension. When you hear this "groaning" sound the belt may be rubbing against the boom and or tail push rod guide. Anyway, hopefully you get this all resolved, and BTW that was some insane flying! Been flying for four months now and I wish to eventually fly like you!
EDIT: BTW, I put A LOT of tension on the tail belt! Easier to achieve with an extra hand. I fly 2650HS and no more noises coming from the tail. |
09-10-2014, 11:02 PM | #13 (permalink) |
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Location: NorCal
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Thanks!
Yes was running it very tight in the video. Tighter than normal as I debug this. The 22T tail pulley is in. Will see if it changes things. If this fails I'll just keep flying my groaning 570. It flies awesome and other than a bad sound it has zero impact. |
09-10-2014, 11:31 PM | #14 (permalink) | |
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Join Date: Jun 2014
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Quote:
Let me know the flight difference between the two pulleys!.. I was gonna pick up a 21T today but decided to hold off on it because I read that max HS with a 21T pulley is 2400. Too low for my liking. After seeing you overspeed the crap out of your G570 I'm confident that the tail will hold strcturally at such high HS!... |
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09-11-2014, 02:27 AM | #15 (permalink) |
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Join Date: Jan 2009
Location: NorCal
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Another video with a groan.. If you listen during the piro reversal at 1:55 you can hear a little short groaning. :-)
[ame]http://youtu.be/sPb_8sM5lP8[/ame] |
09-11-2014, 04:34 AM | #16 (permalink) |
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Join Date: Oct 2011
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maybe should try to move back to the stock tail blade and try again?
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09-11-2014, 01:06 PM | #17 (permalink) |
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Join Date: Jun 2014
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I think you should just neglect the sound and enjoy the machine as it is. Damn u beat the crap out of that! Lol. Notice a difference with the stock tail pulley?
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09-11-2014, 01:20 PM | #18 (permalink) |
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Join Date: Jan 2009
Location: NorCal
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" Damn u beat the crap out of that! Lol. "
That's why I love flying Goblins. They hold up to it all. It's not a common trait among models out there. The engineering is just exceptional. I don't say this lightly. I've owned A LOT of different models. 8 different types of 700's, 6 600's, etc. Stock pulley is in now, and I also pulled off the Lynx metal tail pitch arm and metal pitch slider from my Goblin 500 and mounted it on the 570. I'm wondering if any flex in the stock plastic pitch slider is the culprit here? The top pin was very easy to bend. The plastic is flexible instead of stiff! So now it's all rigid metal. So trying 3 things at once here. 22T pulley, all metal tail pitch control. Not very scientific, but if it works the solution is in there somewhere. :-P Will report back. |
09-11-2014, 02:56 PM | #19 (permalink) |
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Join Date: May 2012
Location: Southeastern Massachusetts
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"Damn u beat the crap out of that!"
Especially on the maiden! I'd like to see how you rip on it after you feel comfortable with the machine! LOL.
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