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New Beginner to Model Helicopters


Malcolm Smith 9
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I have been given a Art Tech Mini Pred v2.4G helicopter and although there was a few things wrong with it I have managed to get it running and the control functions seem to be working normal.

There is however quite a lot of vibration when held down on a table with somewhat less when it is hand held.

I have a set of new blades but the vibration is just the same. Can anyone please let me know if this is normal before I commence flying trials?

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Posted by Malcolm Smith 9 on 10/06/2020 16:05:40:

I have been given a Art Tech Mini Pred v2.4G helicopter and although there was a few things wrong with it I have managed to get it running and the control functions seem to be working normal.

There is however quite a lot of vibration when held down on a table with somewhat less when it is hand held.

I have a set of new blades but the vibration is just the same. Can anyone please let me know if this is normal before I commence flying trials?

You may find it's the blade 'tracking'. Put it on the table with a long heavy weight across the skids and some positive pitch on, look at the main rotor 'edge on', rev it up to a highish speed and see if the blade tips are at the same level.

If not adjust the final links to the blades so they are. You might be able to check the tail rotor the same way. but it's less likely to go out of alignment.

(In 'real life' if they have a vibration problem they get a brave guy who very carefully holds up a whitewashed broom to check this )

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Malcolm,

I have been flying, crashing and repairing helicoptersfor over 10 years and the main reasons for bad vibes are a bent main shaft, bent feathering shaft or if it is flybarred, a bent flybar or non centred paddles. Then you can add on out of balance main blades, bad tracking main blades or tail blades or any of the bearings associated with the head and mainshaft. The best advice I can give to anyone starting out in helicopters is to find a local club with a helicopter expert to check it over for you, as these are difficult enough beasts to master and it is made much more difficult (and expensive!) if you are learning on the job, but well worth the effort when you finally do.

Barry

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Thank you all for your replies. I have had the helicopter in my workshop and spent a lot of time looking at the control functions servo and all appears OK. I moved the the rear drive shaft clear of the main cog and found that even with this disconnected there was still the massive vibration. However when the rotation stopped I noticed that the smaller rotor was sitting out towards one side and not central as I thought it should be. It therefore seems that this is the cause of the out of balance. All the links are in place and there is free and full movement of all parts. Any thoughts please.

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Ho Malcolm

When you say the smaller rotor was sitting out towards one side, do you mean the slider which runs in and out along the tail rotor shaft?

If so, this is perfectly normal, and if you have Heading Hold on your gyro, the slider could be completely to one side.

Certainly not the cause of your vibration.

I would go with the others and suspect a bent main shaft or feathering shaft, but also possible out ob balance main blades.

Do you have a blade balancer? if not, they're not expensive and well worth having in your tool box.

Other than that, to check main shaft, pull the head off completely then spin the model up, looking at the top of the shaft from above. Easy to spot if the shaft is not running true.

Bent feathering shaft is a little more difficult, but there is an easy way. Pull one of the blades off. Inside the blade holder you will find a cap head screw that holds it on. Turn that screw with an allen key while watching the other blade holder.

If, as you turn, the other holder moves in a circular motion, then you have a bent fs.

Try these checks first then post back

Cheers

Jeff

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H Jeff

Its the small rotor which sits directly under the main blades which shoots out to one side. If I prevent the sideways movement by using an elastic band the vibration goes away.

I cant find a way to add a picture of the issue

Are you aware of any members living in the Ashford Kent area who perhaps I could go and see?

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Hi Malcolm

Colin beat me to it by a short head.
Yes, what you refer to as the small rotor is the flybar.
This goes through a square frame either side of the head. Where the flybar goes through the frame there should be two grubscrews to lock it in place.
Either these screws are loose, or missing altogether.
If they're only loose, tighten up with an allen (hex) key.
If they're missing altogether you will have to source some replacements.
I'm guessing they are 3mm, so here's the place to go.
http://www.modelfixings.co.uk/steel_grub_screws.htm
What you need are MF-GS31
Anyway, here's the procedure.
I'm guessing there are two small blades on the end of the flybar. These are called 'paddles' and need to come off.
No biggy, they only screw on.
With those off, measure from the flybar frame to the outer end of the flybar.
Actual distance is not important, but they must be identical each side.
Once they are, tighten up the grubscrews, preferably using a touch of threadlock to retain them.
Now you can screw the paddles back on. There is a thread on each end of the flybar. Screw the paddles on until you can't see the thread any more.
The paddles should also be the same distance out from the frame on each side, But when you have got them as close as possible, you need to check the paddles are parallel with the flybar frame.
Look across the top of the paddle and sight it visually with the frame. Might need to turn the paddle slightly, but getting them parallel is most important.
Easier to do than to describe, but it should get you in the ballpark.

Let us know how you get on

Jeff

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Hi Jeff/Colin.

Thank you for your replies. The handbook is the same as i have for the helicopter.

Colin you have just put your finger on the problem. I have had a close look at the assembly detail in the manual and see that the part identified as 030 has not been installed. The part does not have the grub screw provision and therefore the problem has existed from the original purchase of the helicopter. I spoke to my son today who owns the helicopter who told me he never actually managed to fly it. Now we know why.

I have ordered two collars and see what happens when they arrive.

Thanks again for your help.angel

Stay safe.

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Hi Malcolm, now you have me puzzled.

When you say part 30 is not installed, does that mean just not fitted or missing altogether.
if it's missing altogether, how do you know it does not have grubscrew provision?
However, the problem may be more than that.
Again from the diagram, mixer arm, part number 007 has a bolt going through it which then screws into part 30 and it's this that locks the flybar in place.
If part number 30 is missing then there is nothing to bolt the mixer arm to, which means either it is floating about in mid air, or it's missing as well.
Without that part, and its associated parts, there is no link from the swash to the head, and it will never fly.
Is there any way you can get a photo of your head (the heli, that is) so we can look at what you have?

Sorry if this compounds the problem

Jeff

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