Boom broke in flight?

Dumb Thumbs · Posted: Sat Jun 26, 2010 4:34 am Post subject: Boom broke in flight?

I was playing around with my HK450 in the back yard, just to check trim etc before bringing it to the field in the AM. About three minutes in and about 30 ft. out I hear an odd sound coming from it. I brought it back in close and I see the tail boom is shaking like crazy. Somehow managed to land it OK and I find that the boom snaped clean apart at the boom block Surprised

.
I've taco plenty of Align booms in crashes in other birds, but never ever broke a one.
Anyone ever had a boom snap for no apparent reason?

Crashagain · Posted: Sat Jun 26, 2010 1:31 pm Post subject:

I have had one crack about 60% around before I found it.
Turns out that I had a vibration in the tail and over time it just fatigued the boom. Loose boom supports will allow this to happen too..
Glad you caught it before really flying it and watching it explode in mid flight..

Dumb Thumbs · Posted: Sat Jun 26, 2010 9:26 pm Post subject:

You hit it right on the head Crash about vibration issues. From day one I've had nothing but problems with blade tracking & vibration on this HK 450. I fixed the tracking by replacing all the ball links with Align links, new damper rubbers and went with some better quality CF blades, but still had the shakes. I replaced the drive gears with Align and I'd say 95% better now but I guess the boom had already had serious stress damage by then.
Oh well, it could have been a lot worse in so many ways Very Happy

The belt was the only thing keeping the tail on the heli when the boom parted.
Imagine the carnage if the sharp edges of the broken boom cut the belt and the boom went into the blades! Good news for my LHS, not so good for me.
So now I have one more thing to add to my pre-flight checklist (check boom to make sure it isn't about to go BOOM).

oldmanflyer · Posted: Sun Jun 27, 2010 1:19 am Post subject:

Yea, I'm learning all about the pre-flight check list the hard way.

Crashagain · Posted: Tue Jun 29, 2010 9:36 pm Post subject:

Don't beat yourself up to bad, oldmanflyer. We all have been guilty of that. You get comfortable and forget to check things. Before every flight, I tug on all of the linkages, wiggle blade grips, tail blades tug on the grips, and check the movement of everything. A couple of weeks ago I was flying mt 600 at the field and after a flight, I refueled and as it was filling up I started my routine of tugging on stuff... Shocked

One of my long links on the swash plate fell off right in my hand and I barely touched it.
It would have been a disaster if that flew off in the air. I would have lost all control of the head. Preflight checking saved my heli. Just force yourself to make it a habit..

oldmanflyer · Posted: Wed Jun 30, 2010 1:53 am Post subject:

Thanks Crachagain,
With all you guys helping us newbbies, it shortens the learning curve a lot. Now I check everything before each flight and put oil where needed to.

Crashagain · Posted: Thu Jul 01, 2010 9:34 pm Post subject:

Awsome. It's nice to know that all of my mistakes can help someone.. Laughing

oldmanflyer · Posted: Fri Jul 02, 2010 1:50 am Post subject:

Well I had 4 flights today in 14mph wind with gust, it was hard but I did not crash Smile

Crashagain · Posted: Fri Jul 02, 2010 7:56 am Post subject:

Good job...
Last sunday I was practicing funnels in 20mph winds..
I have learned to fly even if it's windy, it will make you a better pilot.
I don't recomend it for everyone, but if I waited for a non windy day, I would never get to fly..

Dumb Thumbs · Posted: Thu Jul 22, 2010 12:33 am Post subject: Stlll got vibration issues

I did a check flight late yesterday on the HK450 and all seemed well, but today at the field (local park) the vibration started in again. Got bad enough that the canopy fell off in flight! When I landed I found that the boom brace screws got loose on the bottom plate, allowing the struts to amplify the vibration until it shook the canopy loose.
I'll just ramble off where I'm at as of now with this:
This bird has never been crashed so I'm ruling out bent shafts or damaged bearings.
Main blades are mid quality CF and balanced (CG & total weight).
Tail blades were HK stock, so I'll try swapping them out for K&B blades.
Tail blade grips are Align with Chinese weight mod.
Tail shaft & output shaft replaced with Align. (stock had plastic pulleys)
Drive gears replaced with Align blue gears.
All stock links replaced with Align links.

All I can think of is there is too much slop in the head or the motor shaft is bent or the bearings are shot. The motor did come off my Rex450SEv2. It has seen some "less then perfect landings" and has many hours on it.
Anybody have any ideas about what I might be missing or what else may be causing the vibration???

tombo242 · Posted: Thu Jul 22, 2010 1:38 am Post subject:

Hi DT,
Just a thought, (well the only one I've had) but as your flying in the local park is there a possiblity of grass damage to the tail rotor. A bent shaft there is not easy to spot unless you are really looking for it, but it will cause vibration even if only slightly out.

Dumb Thumbs · Posted: Thu Jul 22, 2010 8:11 am Post subject:

Nope, tail has never hit the ground. There is a nice hard packed dirt patch that I fly from at the park and in the back yard I roll the BBQ out of the way and have a great concrete heli pad.
I'm really thinking more & more it's the motor shaft. I think it's time to shop around for a Scorpion motor Cool

.

Crashagain · Posted: Thu Jul 22, 2010 11:43 am Post subject:

It could be a combo of the dampers worn out and the bearings on the main shaft are worn too.
I had a vibration issue and it turned out to be the main shaft bearings. It's amazing how a little slop can escilate as it transfers thru out the rest of the heli frame.

Dumb Thumbs · Posted: Thu Jul 22, 2010 10:50 pm Post subject:

It's an almost new heli so I'd belive the bearings to be OK and I had replaced the damper rubbers wiith TrueBlood reds back when I couldn't get the blades to track right.
I took it out this morning with K&B tail blades in place of the HK blades, thinking if the stock blades were flexing it might set an harmonic inbalance going. Flexing one way then the other and the gyro trying to compensate.
Everything seemed fine enough just slowly flying around and thought I'd wring it out a bit more with some loops. Well I was so focused on the vibration issue I never went into Idle up before I started the loop low off the deck. I always like to start loops low and add lots of neg pitch on top to gain altitude, but being in normal mode you can guess how it ended Rolling Eyes

LAWN DART!
My inital NTSB investigation shows that I was sooo close to pulling out of it. Didn't even nick a blade. The nose took the brunt of the inpact, canopy, alum lower frames all bent up and battery a little tacoed.
Servos are fine as well as the ESC butthe battery now only reads 2 cells so it may be heading for a long soak in a salt bath. That's what hurts most, in was a fairly new Outrage pack.
Back to the vibration issue. While going over whats broke I found that the center ball in the swash is very very sloppy compared to a spare Align I checked it against. So I think I've finley found the vibration problem, but found it in a expensive sort of way.

pjdog · Posted: Thu Jul 22, 2010 11:14 pm Post subject:

Wow DT, That really sucks when the Brain servo lets you down.

Sorry about the repair. But there is the bright side. Looks like you found the vibration problem.

I guess I glad that I'm not up to the aerobatic flying yet. That's when the real crashes start. It's allot harder to get in trouble when your just trying to hover around the yard and not hit anything. I seem to be at my limit right now. Helicopters are so much harder to control than airplanes and submarines. Airplanes are like riding a bicycle.

Jack