Lucky escape.. bruised arm after Mini Titan flybar oscillation and destruction

[liaan]

hi all

While i was trying to get my tracking correct on my mini titan, stock everything, (holding heli down with hand on skids) i noticed major oscilation of the paddles.

By the time i was able to hit the throttle hold, the heli was lying on its side... the landiing skids still semi in my hand.. (1 screw actually torn out and cause the heli to tilt over,will upgrade those screws soon!)

Damage: blades, main shaft, feathering shaft, upper mixing arm, flybar, stripped forward servo gears.. and VERY bruised arm..:(

I think the damage was caused by the oscillation of the paddles, which actually hit the battery, and then naturally caused everything to hit everything else..( the rotor disc also tilted forward to scary angle)... blades broke at the point of hitting the paddles...... or my arm..

can anyone maybe tell my what will make the paddles oscilate so much? this was at +- 2 degrees positive pitch, and 90% throttle..... did not touch any of the other sticks.....

i've balanced the whole head without blades, and blades balanced as well.. still did not cure the vibration at low rpm...

i've noticed this flybar oscillation before with other blades, but never this bad....
no crashes before this one... well, if one can call this a crash seeing it never left the ground :wink:


any thoughts/ideas...:confused::confused::confused:

and now i learned.. never trust the skids when holding down your heli unless they properly bolted on!!! lesson learned..

cherio

L:

[istandalone]

:Pics

[liaan]

:Pics



there are kids reading this as well :lol:

[MarkD]

there are kids reading this as well :lol:

If they see the pics maybe they will then learn from OUR mistakes :thumbup:

[liaan]

If they see the pics maybe they will then learn from OUR mistakes :thumbup:
will wait day or 2 for blue/blackness to settle in.. at the mo its just red, swollen and 3 nice blood/red strikes on forarm close to elbow... not very impressive as yet ;-)

[cudaboy_71]

any thoughts/ideas...

and now i learned.. never trust the skids when holding down your heli unless they properly bolted on!!! lesson learned..

i think your first mistake was spooling up a heli within arms reach. that's just dangerous. if there was a serious vibe in the heli, it only exacerbated by holdinding it firmly to the work surface (ground resonance???)

lesson learned should be: never spool up a heli on the bench. you should track your blades in the air.

[kevntri]

Dude....
Use a broom stick or something if you have to hold it down.
I use a piece of PVC pipe and duct tape it down and then stand on one end.

[liaan]

What will you guys say is the best way todo the tracking?

i did notice that tracking is off while hovering, but how do you determine which blade is which? i don't hover that close to me :wink:

i always seen people do the hold on ground technique till tracking fine, then do test hover and recheck....

never thought about the ground resonance... must have been the cause, for when i spool down in normal mode, the heli always gets the shakes on hard surfaces...

hopefully the vibration/resonance will be resolved with all the new parts... pitty its weekend, all shops closed...:(

L:

[MarkD]

Mark one blade/grip as the master with tippex or similar. Use dark coloured (if the blades are white or white if the blades are black) tracking tape or insulation tape taped to the end of this blade. Spool up to just below hover and you will see that one blade looks shorter to the other when looking edge on. Make adjustments to the unmarked blade to bring it in line with the Master. Remove tape and fly :D

BTW the master blade should have been bench set to 0deg at mid stick

[liaan]

Mark one blade/grip as the master with tippex or similar. Use dark coloured (if the blades are white or white if the blades are black) tracking tape or insulation tape taped to the end of this blade. Spool up to just below hover and you will see that one blade looks shorter to the other when looking edge on. Make adjustments to the unmarked blade to bring it in line with the Master. Remove tape and fly :D

BTW the master blade should have been bench set to 0deg at mid stick

Sorry to be all technical here.....
don't sticking tape on 1 blade cause lots of vibration:confused:

i've tried standard blue/red tracking tape.. man its hard to see in contrast to the stock woodies...

will try and get some black and white tape..



thanks
L:

[OHIOBOWHUNTER]

best tracking tape made is none at all ! use a magic marker...usally comes off completely with denatured alcohol although my set of white mavericks are permanently stained :bawl the best part of useing magic marker is no out of balance effect :wink:

[cmb2003svt]

1st,
Glad you came out unharmed.
2nd,
As cudaboy_71 stated that is a big No No.
3rd,
Like OHIOBOWHUNTER i use a silver marker. Even if you were concerned with the weight of tape it is such a small amount that it wouldn't even cross my mind to care.
4th,
Sounds like a bent feathershaft.
5th,
Like other have said track your blades in the air or build the below.

http://www.helifreak.com/showthread.php?t=56617&highlight=tripod

[liaan]

Thanks cmb2003svt (http://www.helifreak.com/member.php?u=29639)

well, after full inspection.. following found... loose rotor hub on shaft, worn out top main shaft bearing (lots of play).. and many worn out balls/links., swashplate LOADS of play...... this after about 40 flights.. well more like hovers / figure 8's...

now at least get to replace all of it...

fly safe..

L:

[kevntri]

a marker and hit the tip of one blade

[istandalone]

yup, just permanent marker here. i tape off one blade, use masking tape to make a stripe mask. that way any weight gain on one blade is negligible and it's permanent. i'll never have to draw another stripe for the life of the blade, or stop what i'm doing to tape off a blade.

[lperagallo]

Liaan,
Don't ever try to hold down a heli and spool up. As you now know, it is very dangerous. Even though they are small they can generate some pretty awesome power. I've heard of all sorts of ways to hold down a Heli, but if anything breaks that's holding it down, you've got a wild beast potentially going everywhere.

Blade tracking can be done without lifting off if you must by spinning up the blades with zero pitch. Crouch down on the ground (away from heli) and look at the blades. Then spool down and make your adjustment. You should be able to get the tracking down to a turn by setting the pitch on teh bench. The worst I've ever had to move a blade is two turns and most of the time it's spot on. Of course, worn parts will make it impossible to track regardless of the method used. One flight it might be good, the next off and so on.

This is very important......Make sure that you do pre and post flight checks on all critical parts, especially the head and swash, but also check all servos and linkages for slop. Good safety will save your butt and your precious machine.

Lou

[JasonJ]

I strap my helicopters to my rolling welding bench, stand well back, spool up and give just enough collective to get blade cone, and adjust from there. Even my way isn't the safest, but since I am alone it is more safe than trying to hover eye level and check tracking at the same time. I also use the master blade/sharpie technique.

[hornet dave]

tracking adjustments - all I do is adjust one of the blades, it doesnt matter which one. If the tracking gets worse as a result, adjust it the other way. No tape or magic markers or anything required, just keep track of which blade you make adjustments to.

[invertmast]

i think your first mistake was spooling up a heli within arms reach. that's just dangerous. if there was a serious vibe in the heli, it only exacerbated by holdinding it firmly to the work surface (ground resonance???)

lesson learned should be: never spool up a heli on the bench. you should track your blades in the air.

Dangerous.. more like stupid. best way to check the tracking is flying the thing. Is it just me, or are posts like this becoming more and more frequent since winter weather has set in. I honestly thing it may be time for us to put up a
"stupid ideas, DONT try these" sticky at the top of the general and newbie forum.

[Sonny]

tracking adjustments - all I do is adjust one of the blades, it doesnt matter which one. If the tracking gets worse as a result, adjust it the other way. No tape or magic markers or anything required, just keep track of which blade you make adjustments to.

I was going to say. This is easy. If you increase the pitch on the blade by a turn and traking looks good, but heli seems to want to hover at a lower stick level. Then turn both back down one turn. Or vice versa.

[liaan]

"stupid ideas, DONT try these" sticky at the top of the general and newbie forum.

Thanks all for you replies....
I purposfully posted this little stupid/dangerous incedent of mine... i've been reading forums/web pages daily for last 3 months, and actually never found a what not todo list....

i'll of course never do this again, and would like other people to learn from my mistakes...

can Helifreak not create a new forum or sticky as suggested about best practices.:confused:.. ie, don't fly in parking lots, home, close to other people etc etc...

L:

[cmb2003svt]

Agreed but there is a forum called Helicopter Safety. I haven't gone through each one but i can bet your incident is there somewhere. Regardless glad you are OK.

[OrcaSea]

In full scale helis there is a phenomenon called 'ground resonance' that, as i understand it, can shake a heli to peices. I think the same thing can happen to small helis.

I was checking tracking on my coaxial and came up with a cunning plan to hold it down while I observed and run the sticks. It shook like crazy and the tracking was all over the place. Luckily, it is small enough that I can hold it in my hand safely, and when I ran it up it ran smooth as silk and tracked perfectly.

[liaan]

In full scale helis there is a phenomenon called 'ground resonance' that, as i understand it, can shake a heli to peices. I think the same thing can happen to small helis.

.

just did google for ground resonance... loads of answers, quote from one site:

"Ground resonance happens in helicopters with lead-lag hinges. It occurs only on the ground. It starts when the blades "bunch up" on one side of the rotor disc where they generate an unbalanced centrifical force that gets in phase with the natural frequency of the aircraft rocking on it's landing gear. Modern helicopters avoid this by using dampers on the blades and on the gear (shock absorbed struts). It is less prominent on wheeled helicopters although can occur. The emergency action is to lift the aircraft to a hover.

Ground resonance has not been "solved", and is still a big concern for anyone who flies a helicopter with a fully-articulated rotor system. It basically is an out-of-balance condition in the rotor system of a helicopter on the ground that rapidly increases in frequency until the helicopter shakes itself apart. It is usually caused by a hard ground contact, and is much more likely in aircraft with improperly maintained landing gear (deflated oleo struts, for example). "

and as we know ,the Mini Titan don't have anything close to "solid" landing gear.. very soft and flexible and this will be the same as the defalted oleo struts mentioned above..

L:

[Sonny]

The bolt thru the blade root is basically a lead drag hinge. Assuming it's not too tight.