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HelicopterMain Discussion › Start shaft broke off in flight
11-07-2016 04:49 AM  18 months agoPost 1
honda411

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Surprise, AZ USA

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So I was flying my Trex 700 nitro and about 30 seconds into the flight the start shaft snapped and the start cone was bouncing around on the main gear. If it were to have broke while starting it, it wouldn't start. And it would have fell right off since it was a clean break. It broke off just under the set screws. How is this possible? Never seen it before. Or what would cause such a thing. I don't think or see the cone engaging and spinning fast after I start it so the one way bearing should be good.

HeliDirect Field Rep, Synergy N7 w/ OS 105, Torq Servos, Cyclone/ Rail blades

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11-07-2016 02:05 PM  18 months agoPost 2
albertoc

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Madrid-Spain

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Hi,

Never happened to me in +1000 flights with T700n, its the only model I flew latest 3 years every single weekeend.

In which point approx the shaft was snapped?

BR

Alberto.-

Respect and fly safe

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11-07-2016 02:58 PM  18 months agoPost 3
Tyler

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Chicagoland area

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How powerful is your starter and how much compression foes your engine make? Hydrolock history?

Our modern starters and engines can create a lot of torsional stress.

Enjoy things that money can buy IF you don't lose the things money can't buy.

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11-07-2016 03:38 PM  18 months agoPost 4
junkpilot

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Alamogordo N.M.

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Broke!
A bent start shaft or an out of balance cone could do that easy!
Junkpilot

When you fly JUNK it's hard to tell when you've crashed!

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11-07-2016 04:08 PM  18 months agoPost 5
Jeff polisena

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westpalmbeachflorida usa

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It twisted and held by a small amount of material and after you started , spinning of shaft finally let it go . Never had this happen but its not impossible .

I stole it ,flew it and gave it back ;)

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11-07-2016 04:09 PM  18 months agoPost 6
honda411

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Surprise, AZ USA

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It did act as a hydrolock at one point when the old engine was locked solid from rust when I bought it. So that could have helped it. 3s lipo battery starter. I'll try to post a pic

HeliDirect Field Rep, Synergy N7 w/ OS 105, Torq Servos, Cyclone/ Rail blades

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11-07-2016 09:43 PM  18 months agoPost 7
Todd74

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PA, USA

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I know a guy who broke several start shafts, but it was a 600N, and it happened when starting, and he was using a drill as a starter.

I've personally never broken one on a 600N or 700N in approximately 1 zillion flights.

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11-07-2016 09:46 PM  18 months agoPost 8
Tyler

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Chicagoland area

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Which starter was used?

Enjoy things that money can buy IF you don't lose the things money can't buy.

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11-08-2016 02:30 PM  18 months agoPost 9
Four Stroker

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Atlanta

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"using a drill as a starter"

Jack hammering might break one that was flooded. But usually the set screws strip and pop out.

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11-08-2016 02:39 PM  18 months agoPost 10
Tyler

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Chicagoland area

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The align starter and most gear reduced gears often hammer excessively.

Enjoy things that money can buy IF you don't lose the things money can't buy.

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11-08-2016 02:47 PM  18 months agoPost 11
Four Stroker

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Atlanta

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They will also destroy the one-way in the clutch.

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11-08-2016 03:21 PM  18 months agoPost 12
KingCobra Heli

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MA-USA

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Starter
What is the best starter setup to not cause damage to anything?

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11-08-2016 03:31 PM  18 months agoPost 13
Four Stroker

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Atlanta

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Well you don't want more starter for an application than you need. If the engine floods you actually want the starter to stall !

Get a Sullivan Dynatron OR just the regular Sullivan and only put as many cells on it as you need. The Torq Master also works fine. I would probably try 3S on a Dynatron first and if that don't go try 4S. I have seen the small Sullivan crank a 700 fine on 4S.

Don't hold the switch down more than 3 seconds at a time !

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11-08-2016 06:52 PM  18 months agoPost 14
utahbob

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St. George Utah

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could be a bad heat-treat
Does the break area look cyrstallalized? With those divots for the set screws closeby and the material being brittle that could cause it..My flying buddy and I have trouble starting our 700's in cold wheather..so I made a couple of experimental start shafts out of Oil hardening tool steel with the cup that engages the one-way .001 larger..then I flame hardened just that area..they work better than the stock shaft.

I do a great decending funnel!

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11-08-2016 09:08 PM  18 months agoPost 15
honda411

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Surprise, AZ USA

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Hey sorry everyone for not getting a picture up yet. Completely forgot last night to take one or two.

I use the great planes starter and have the heli starter adapter instead of the cone it came with.
The picture I will post later tonight should give you all the information where the break was

HeliDirect Field Rep, Synergy N7 w/ OS 105, Torq Servos, Cyclone/ Rail blades

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11-09-2016 03:37 AM  18 months agoPost 16
honda411

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Surprise, AZ USA

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Pics up
And correction. It's the hangar 9 12 v red and black starter

HeliDirect Field Rep, Synergy N7 w/ OS 105, Torq Servos, Cyclone/ Rail blades

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11-09-2016 06:13 AM  18 months agoPost 17
Tyler

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Chicagoland area

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The best news is how inexpensive this repair will be. Great opportunity to replace starter assembly bearings, coupler, etc.

Enjoy things that money can buy IF you don't lose the things money can't buy.

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11-09-2016 04:06 PM  18 months agoPost 18
honda411

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Surprise, AZ USA

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Yeah I'm going to put in a lynx clutch and new bearings and such.
The bad news is how much of a pain to split the frames to get the assembly out

HeliDirect Field Rep, Synergy N7 w/ OS 105, Torq Servos, Cyclone/ Rail blades

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11-09-2016 05:27 PM  18 months agoPost 19
Todd74

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PA, USA

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You don't really need to split the frames. Take two thin screwdrivers, like the shirt pocket type, and wedge them in between the frame sides and the bearing block, which bows the frame out enough to clear the locating tabs on the block, then wiggle the block up and out through the top. I've done this countless times.

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11-09-2016 06:15 PM  18 months agoPost 20
icanfly

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ontario

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interesting, the repeated twist of the starter would fatigue the weakest part, where the set screw is on mild steel or simply wire stock. The way a metal is drawn upon manufacture determines it's molecular arrangement with it's alloying additives and ultimately it's workload and duration before fail, the shaft met it's due date. If perhaps the set screw was torqued down really hard it would begin a molecular deformation of the material around it due to mashing and rebound characteristics inherent in metals (similar in many ways to a golf ball in impact, now twist while it's deformed and it will tear away more easily than when fully orbital). Add some high frequency vibes in there and,,,. The starter kicks into spinning as soon as the e is applied,

if it had a soft start the shaft might live longer and or might not be broken at all.

Engineers stuff, thanks for the lesson as it's something to be aware of with all shafts put under stress loads.

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HelicopterMain Discussion › Start shaft broke off in flight
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