View Full Version : FBL Furion Tail in-flight explosion

05-01-2009, 03:19 PM
Today was the first crash of the Stretched FBL furion. I guess 1 out of 16 ain't too bad. And it was mechanical. :YeaBaby:

Anyway, I just put on a set of CY 59mm CF tail blades and ran through a pack of just resetting the gyro and re-tuning the gain. All went well. The second pack I took it easy doing a few pitch pumps and circuits. By the time I got to the 3rd pack, I started doing some really FF runs up and down the field when I decided to do a giant loop. The heli came around and shot right up just like it always had.. as I was coming down and leveling off the loop at about 25-30 feet, I heard a snap and it went into a wild piro. I hit TH and it came down. The impact didn't look so bad but of course there is some damage.

Damage report:

CY 59mm tail blades
1 x HS5065MG stripped gear
1 x Servo Horn
Tail fin
1 x tail grip/hub and linkage


05-01-2009, 05:55 PM
Is that a broken bolt? What headspeed are you running?

05-01-2009, 05:58 PM
Yup.. broken bolt on both ends.. I went back to the field and located the other TRG and noticed that one of the bearings failed..

I'm running the 350mm blades with the 4400kv motor 80% flat throttle curve..


05-01-2009, 06:24 PM
Damn, bdp, I'm sorry to hear that. When you put on the Radix tail blades, were they stiff? I noticed mine were so I dremeled the blade roots down a bit so they would lead and lag properly, I should have mentioned that earlier. At high speeds, like the ones you were mentioning, there will be the tail rotor version of dyssemetry of lift, if the blades are stiff, than they cannot compensate for this very well. This will cause stress on all the tail rotor parts. I'm not sure how familiar you are with dyssemetry of lift, but on RC helis, their main form of compensation is the lead-lag effect allowed by the blade grips being a bit loose (they also "flap" which means go up on the advancing side of the rotor disc, and down on the retreating side). The advancing half of the rotor disc will lag (drag back due to increased air friction), and the retreating side will lead (go forward due to the centrifugal force bringing it back out). This allows for the retreating blades to have a bit more relative airspeed and therefore, lift. What might have happened is the stress caused that bearing and-or tail rotor hub and screws to fail.
See how the aluminum threaded extrusion on the tail rotor hub straight up broke off!!! This further supports my theory that the tail rotor hub should be made of steel. Normally no one ever thinks about having to replace a tail rotor hub (until now I never have, despite the countless crashes on my ex-rex), this design is too vulnerable at those extrusions.

05-01-2009, 06:32 PM
Interesting that you mention that because I was going to ask you if your blades were tight. I usually run mine a bit loose so I sanded them some. For fear of messing them up, I left them a bit snug cause I didn't want to sand too much off..

That very well could have been my issue..


05-04-2009, 02:35 PM
Back together again and about to sand down these CY's a little more to see if we can have a successful flight..

Stay tuned..

05-04-2009, 10:24 PM
Hopefully that cures it. Also make sure those exposed flanged bearings are well-locktited in place, I actually pushed them out and locktited the outer race myself just to make sure they were snug.

Caleb Phillips
05-04-2009, 11:09 PM
You def. tightened the bolts going into the hub too much. I had this happen to me twice before I asked Jeff Miller what the deal was and he informed me. Just use some good loctite and get the bolts snug, no more. Hope this helps.

05-05-2009, 05:24 AM
OK.. The flight went well but apparently the lighting and camera wasn't cooperating. I took it easy on the hub bolts and I gave the tail blades some wiggle room. I took it easy on the flight and tried staying close to the ground to take a quick peek at the tail a couple of times to make sure its was good to go..

Thanks for the tips guys..:thumbup:

Again, nothing fancy and the video is bad. It's also REALLY windy and a little drizzle..

[Furion Flybarless Test]

05-05-2009, 07:18 AM
Good to hear that she's back up and running, you're definitely running a higher head-speed than me!! After you make sure everything's good, she's going to make quite a big air flier (mine definitely is, it's my favorite aspect 350mm flybarless!!).

05-05-2009, 08:43 AM
yeah... I'm really enjoying it.. It does some seriously giant loops. Once the sky clears up, i'm going to have a ball.. 350's are :Bang

05-07-2009, 10:18 PM

YouTube - Furion SK360 tweaking..

A little dark but almost there..

YouTube - Furion SK360 tweak vid 2

05-08-2009, 04:55 AM
Damn that's some headspeed!! Are you running a -6? I thought you were running a -8. I see that the bird loves big air, that's my favorite part about the set up. Only thing is it's really hard for a regular camera to keep up. I can't wait to try the 6S set up but it's gonna be about 2 weeks from now because I'm gonna be at a field training exercise.

05-08-2009, 05:29 AM
Yup.. -6 in there and it screams and gains some altitude pretty quickly. I'm going to try and vid some FFF this morning if I can find someone to hold a camera for me. I actually need to get a better camera.. The big air is fun and I pretty much cured the squirrely behavior by lowering my dampening gain just a hair.

Have fun in the field, must be military :thumbup::thumbup:.. Been out in the field many, many times in my Army days. Stay safe..

05-08-2009, 08:52 AM
Yep, Army, it's an Apache gunnery so it comes with some pros of watching Apache's shoot.

05-08-2009, 09:01 AM
Yep, Army, it's an Apache gunnery so it comes with some pros of watching Apache's shoot.

:thumbup:... missle crew myself .. Air defense..