RunRyder - Xcell Gas Incident and Questions

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Gasser Model RC Helicopters > Xcell Gas Incident and Questions

caiman
Heliman
Location: Monterrey México

I just test flown a XCell gas graphite that I purchased from a friend.

During flight, I noticed some abnormal shaking of the whole helicopter when at low RPM and then some vibration on the tail at high RPM and a noise that I think might have come either from the rudder torque tube or from the main gear. Even with the vibration, the Gyro made a good job holding the heading.

The previous owner replaced the rudder control plastic clevis with a welded bronce adaptor and a ball link on the rudder servo. This ended up not being a good idea, since on my second hovering flight the bronce adaptor broke, maybe due to vibration or to the increased torque and speed of the Hitec servo I installed together with my 401 Gyro. Fortunately I could land it without any damage (except for a slight dent on the maing gear) but it surely wasn't a glad experience.

Apparently this helicpter have had a similar incident a while ago, but according to the previous owner that time the opressors on the tail rod pinnion got loose even though they were installed with red loctite. I think the problem might have been that the pinnion was not installed so that the oppressors would enter the notch on the shaft. At that time, my friend did crashed it and had to replace the main blades and tail boom. He didn't remember if he did changed the main shaft and the blade shaft as well, so that makes me believe maybe he did not, and that might be causing the vibration and the shaking.

When I first inspected the helicopter, I discovered that the friction on the collective control was much larger when on negative pitch that when on positive pitch so I had to slightly sand the main shaft on that part and lubricate it thorughly. Could that be caused by a slighlty twisted main shaft due to my friends' crash???

Anyways, I already ordered a new main gear and a new main shaft, but unfortunately forgot to order a blade shaft in case my friend didn't changed it. I will inspect it and if it's bended I will order it too.

Now, I am very concerned about that damn tail rotor, how can I make sure that the shaft pinnion opressors wont get loose, would locktite be enough? what kind of locktite red or blue? after his crash, my friend used instant glue (CA) on them but I think locktite would be better, what do you think?

I also ordered a new tail control rod extension so I can screw on a new plastic ball link conector on the tail control rod. I want to stay away from bronce parts because I think plastic will withstand more vivration than broce, do you think that would work fine? (The tail rod has no bendings and it moves very smoothly).

Also, how should I adjust the correct mesh between the main gear and the tail pinnion, as well as between the maing gear and the engine gear?

This helicopter had a collar on the lower part of the main shaft (just below the main gear) and it didn't have any bolt inserted on the hole located on the bottom of the shaft, is that normal? should I install a flat washer and a bolt and lock nut instead of the collar?

I already installed the heavy duty tail drive upgrade as recommended by some of you, however I think my emergency landing was hard enough to slightly dent the main gear anyway.

I am using carbon blades and haven't had a chance to check there balance, they don't have any stickers so I think they were never balanced, do they normally come well balance from the factory or not?

I appreciate your comments regarding the recomended setup for the rudder linkage, pinnion gear oppresors, gear mesh procedure, the collar or bolt on the main shaft, as well possible causes for the shaking and vibration and any other comments or suggestions you may have.

Thanks.

07-01-2008 02:25 AM

rbort
Elite Veteran
Location: Franklin, MA - U.S.A.

Answers for you

Vibration is a hard thing to diagnose remotely. As usual, balance the blades (no they are never perfect from the manufacturer), center the flybar 100%, put the paddles on the same distance into the flybar, balance the main gear, balance the fan and all this will help. Get a koll rotor pro blade balancer, and a high point balancer to do this. For the main gear try it in all 6 positions on the auto hub, one of the 6 positions will balance while some of the others will throw it off bad. Also check to make sure the main shaft and head axles aren't bent by taking them out and rolling them on a table while watching the gap between them and the table as they roll. Most likely the tail rotor shaft will not be bent. They survive many crashes. A good way to check it also is to spin the tail rotor and look at the pitch slider and see if its wobbling. Same goes for the main shaft, spin it and look at the swashplate and see if its wobbling. Try is at full collective up and down, also same full travel on tail pitch slider and look for wobble. If you see any, replace the shafts.

I wouldn't go with any welded brass piece on the tail pushrod. Its threaded so just add either a ball link end of a clevis type end to attach it to the servo.

Adjust the mesh so that there is no play at the high point, and only little play at the low points. Even putting a piece of paper in the gears and pushing them hard together and tightening then taking the paper out gives you a good mesh.

There should be something with a screw or pin through the hole in the bottom of the main shaft. If you don't have that you can replace the collar with a washer and then a bolt with a nylon lock nut and that will be fine.

I don't understand what you mean by "pinnion gear oppresors"

-=>Raja.

1005 Xcell Gas, BHH G26 3D Plus, Jewel Generator
Spectra-g, BHH G26 3D Plus, Jewel Generator

07-01-2008 03:26 PM

caiman
Heliman
Location: Monterrey México

By opressors I meant the allen set screws (similar to the ones used on collars). The pinion gear (part #0231) is the one that transfer power to the tail rotor and meshes to the main gear and it's attached to part number #0832-3 by means of one or two set screws.

The guy that sold me the helicopter told me that the set screws on the pinion gear got loose and he lost tail rotor power. He had used red loctite and after the incident he applied CA instead of loctite.

If I remember correctly, part #0832-3 has a small notch where the set screw should be tightened to prevent the pinion gear from rotating, am I correct? If so, maybe my friend positioned the set screw outside that notch and that was what coused the fealure?

Have you heard of other rudder fealures like the one described on this model?

I don't know if I could explained myself.

I ball link connector would be better than a standard clevis type connector for the rudder control rod correct?

Thanks.

07-01-2008 07:23 PM

rbort
Elite Veteran
Location: Franklin, MA - U.S.A.

Ok I understand now

The pinion that drives the tail will never get loose. I've been flying 10+ years over 2300 flights and never had an issue with that. If you tighten one setscrew on the flat and the other down pretty snug, its permanent until you try to break it free. Even loosening the screws later it will be hard to free the gear as it will seize itself over time on the shaft though not impossible to do.

Standard Minair setup came with clevis type for the rudder but I use ball link on all my stuff. I think its better though watch your links and replace them if they get too sloppy before they can pop off in flight.

You're very welcome!

-=>Raja.

1005 Xcell Gas, BHH G26 3D Plus, Jewel Generator
Spectra-g, BHH G26 3D Plus, Jewel Generator

07-01-2008 07:35 PM

caiman
Heliman
Location: Monterrey México

Did you use red or blue loctite? which one is supposed to be stronger?

07-01-2008 10:16 PM

pgkevet
Veteran
Location: surrey UK

blue is threadlock. Red is studlock and 'stronger' although if memory serves it is possible to design threadlocks for specific vibration frequencies and ranges. And green is bearing-lock.

pgk

07-01-2008 10:21 PM

caiman
Heliman
Location: Monterrey México

So which one would be best for the tail rotor pinion set bolts?

07-01-2008 10:37 PM

pgkevet
Veteran
Location: surrey UK

blue should be adequate and allows undoing by hand. Red usually needs the application of heat to undo.. it's use on studs allows one to add to those studs with blue threadlock and still undo it. Green if you never want it to shift without serious effort and heat

pgk

07-01-2008 11:10 PM

rbort
Elite Veteran
Location: Franklin, MA - U.S.A.

Red is considered permanent.

Use blue for all screws, green for bearing to lock them to the shafts. Red is not used at all.

-=>Raja.

1005 Xcell Gas, BHH G26 3D Plus, Jewel Generator
Spectra-g, BHH G26 3D Plus, Jewel Generator

07-02-2008 01:16 AM

GREYEAGLE
Key Veteran
Location: Sioux City IA

Maybe these will help

If we can help just ask, weve already been their, I suspect a tweaked main shaft or a feathering spindel in the head block.

Pull one blade, and rotate the spindel with your allen wrench to se if the other blade teeters up and down a bit indicating a bent spindel.

If the swash has a tight spot at the top of the throw it's maybe a indicator also.

Last check to see if you have perfect static blade tracking / its set and maintained by the two opposing set screws in the little brass knureled nuts pressed into the bottom of the plastic head block.

Be patient young gass hopper : Your gona love it !

Opp's forgot : Typewriter white out is great for reading the high spot on your gear, just a liitle touch in the area when you feel it go by, then read the contact pattern.

greyeagle

07-02-2008 02:17 AM

caiman
Heliman
Location: Monterrey México

I don't have the original manual, so I have two more questions:

1)- Should all ball bearings be attached to their shafts with green loctite or can I just leave them in their respective position slots without permanently attaching them to their shafts?

2)- What kind grease should be used on the main gear and on the tail rotor assembly? would low viscosity silicon grease be ok?

Thanks.

07-02-2008 07:49 AM

rbort
Elite Veteran
Location: Franklin, MA - U.S.A.

Answers

Locktiting bearings to sharts especially on the tail transmission (0832) prevents the bearings from cutting a groove into the shaft. You don't need to do this for the main shaft bearings. Also on the tail box itself bearings I haven't had this issue either so #1 is the 0832 shaft with its bearings.

No grease should be used on the main gear.

Pack the tail box with a good quality grease.

-=>Raja.

1005 Xcell Gas, BHH G26 3D Plus, Jewel Generator
Spectra-g, BHH G26 3D Plus, Jewel Generator

07-02-2008 03:14 PM

caiman
Heliman
Location: Monterrey México

On the 0832 green locktite would be needed only on the small bearing not the large one that supports the main shaft, correct?

I already installed the 0832 and had to open the frames and everything, I would preffer not to do that again, could I add green locktite without unassembling everything?

07-02-2008 10:12 PM

rbort
Elite Veteran
Location: Franklin, MA - U.S.A.

0832

Is the tail drive shaft that couples to the torque tube in the boom on the front end. You'd need to locktite all 3 bearings so the shaft will last longer and not have the bearing wear a groove in it.

You can pull out the whole transmission to the rear if you remove the boom and the clamps without disassembling the frames.

Is it really important? No, may not be worth your effort as it will last a while before it wears down. Up to you whether you want to tackle it or not.

No green locktite is needed on the main shaft bearings, hoever, come to think of it, the clutch bearings can use some as the clutch shaft can get grooved over time as well.

-=>Raja.

1005 Xcell Gas, BHH G26 3D Plus, Jewel Generator
Spectra-g, BHH G26 3D Plus, Jewel Generator

07-03-2008 04:10 AM

caiman
Heliman
Location: Monterrey México

If the whole transmision can be pulled to the back without unassmebling the frames that makes it a lot easier.

The locktite should be applied between the shaft and the bearing correct? I assume just a little amount should be applied and it gives you enough time before it dries to adjust everything properly (specially how much 0832-3 should be inserted inside 0832-2 so that it seats and meshes properly on top of the main gear)?

Thanks.

07-03-2008 07:06 AM

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Gasser Model RC Helicopters > Xcell Gas Incident and Questions

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