First Forward Flight & Failed Tail

[shuglu]

Hi All

Had my first forward flight on my knight today and what a machine. Large figure eights and stall turns, loads of fun. Three tanks and no problems.

Fourth flight and half way though the tank, was hovering three foot off the deck and the tail let go. Hard landing, minimal damage. Broke one landing gear strut and the tail shaft.

It all happened very quickly, but as far as I can remember, the piro was to the left and no tone change from the motor could be heard.

My question is. Did the shaft fail and cause the tail the let go or was this a glitch and a hard landing which broke the shaft. The vertical tail fin isn't damaged and the tail blades show no signs of a ground strike but the shaft is broken at the point it leaves the tail assembley. Could the force of the landing have broken the shaft and spared the plastic fin.

The quality of the Knight is good, so find it hard to believe the shaft would just fail.

Cheers

Justin

[robgt]

Sounds like the shaft failing lost you all tail authority and it went into a spin.
Glad you didn't get much damage!
Cheers,
Rob

[shuglu]

Thanks robgt, she's a tough bird.

I'll soon know. Spares from skyline, repair, and fly again next weekend. Hope it's not that damn glitch again.

Justin

[Ade_Law]

see if you can remember the sequence of events. were there any nasty noises from the tail as it started piroing?

if not the tail shaft probably broke when it hit the ground. Tail shafts are weird things, you can hit them hard and not bend em. then another crash it wont touch the ground and come out bent or broken!

have you checked the tail counter gear? the small gear on the shaft that is driven by the lower half of the main gear.

Ade

[shuglu]

Hi Ade

No weird noises or any sign of impending failure but it did happen very quickly and I could have missed it. Also checked the tail counter gear, meshing fine and all teeth present. Belt also OK. I worked through the previos glitch issue also. Tightened belt tension, Anti static spray on belt, aluminium plate between gyro and mount, and four and a half flights before this. Could this still be a glitch issue?

Justin

[simon_s]

What tail servo are you using? I have had 9254s go to maximum movement in one direction and lock out.

[shuglu]

I'm using 401/9254.

[simon_s]

I have read on the net that if you wiggle the wires on your servo sometimes you can find a loose connection; it may be worth having a look at that.
Before the servos have locked out on mine (and other club members) they sometimes glitch/kick when you are flying and generally don’t feel right. I have had three problems with 9254s and all have been replaced, if it happens to me again I will change servos.
I’m not saying this is the problem but it may be something to think about

[bladetrasher]

Did you check the voltage of the battery under load after the crash???
It is known that sometimes the 401 gyro can cause the servo to go hard over in a low voltage situation

[shuglu]

Hi Bladetrasher

I have a fromeco regulator installed and checked the voltage just prior to flight at 7.8v. I am going to get another 9254 and see if it sorts this out. I might not be as lucky next time.

Justin

[SRH990]

I've had two 9254's fail on me too, they were both boom mounted on a Raptor 50. The third 9254 went back where it was intended, inside the canopy and I had no more problems.

[simon_s]

All mine failed while using a quick UK rear mounted servo upgrade. I am now using the titan push rod kit which is supported on the boom so maybe doesn’t allow as much vibration to reach the servo.

[Ade_Law]

the standard v2 pushrod is cheap and reliable if loctited correctly. Only trouble is that the titan's half arsed push/pull uses the rudder servo mount.

Ade

[helihead]

hi shuglu.
i would agree with ade a would suspeect something els failed before the tail output shaft broke, so be very carefull with the next fight ,,i hate incedents that can't be easly recognissed. broke three furys before i realised the campac was faulty 2 years ago..but out of too many crashes i have never broke a shaft.. good luck m8

[shuglu]

Hi helihead

I agree. I Have a new 9254 coming and the old one going back to ripmax. I'm not leaving it to chance again. I was just settling down to the idea that the knight was nice and stable and I could relax and enjoy just flying, but this is how you gain experience.

Justin