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XHELI.COM . Advantage Hobby . Revolution Models

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Got Jet Fuel? Turbine Helicopters > Ha ha, my Predator turbine build begins
 
 
Doug C
Senior Heliman
Location: Northern CA

My Posts This: Topic  Forum

Hazchem,

You appear to be missing a collet, the sequence of installation is, lower collect on shaft, fan hub, uppercollet on shaft, washer, nut, (tighten the whole package). Now if you have the NX, you will probably have the new "combo" upper collet (see picture)



In my case, I had to saw off the nut portion and revert back to the "old" version of seperate nut and collet) as when I mounted it onto the second stage shaft, it jammed against the unthreaded portion of the 2nd stage shaft and I couldn't get the whole thing tight enough (so much for product improvments)

oh, the starter shaft is retained and is used to align the clutch hub and clutch when you mount the upper and lower sections together and adjust the position of the turbine/second stage.

One mod I did to mine was to convert over to the Condor landing gear ans I felt the standard Predator gear legs were on the flimsy side given the weight of the bird and to give me an inch or so more ground clearence (did kind of scorch the grass when doing initial start up testing)

Doug C
09-05-2008 Over year old.
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hazchem88
Veteran
Location: W.Mids UK

My Posts This: Topic  Forum		I have the NX
so now I'm thinking
lower brass collet
, hub,
then new type upper collect (the one with the nut attached. I assume the cone part points down inside the fan hub).
Just those 3 things?
Looks like that might work!
09-05-2008 Over year old.
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Doug C
Senior Heliman
Location: Northern CA

My Posts This: Topic  Forum		Haz,

yup, your picture has the parts in the correct sequence and orientation, just replace the nut/washer with the combo nut/collet and you are good to go,

Note my comments about unable to fully tighten the new style collet/nut combo to where it securely clamps the hub to the shaft.

I found it difficult to hold everything while putting enough torque onto the nut, there is nothing to relly grab onto once you have the fan hub on the shaft, maybe BellBloke has some suggestions in that area

Doug C
09-05-2008 Over year old.
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hazchem88
Veteran
Location: W.Mids UK

My Posts This: Topic  Forum		thanks doug.
I'll report back if the nut needs shaving
09-06-2008 Over year old.
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Bell Bloke
Key Veteran
Location: ....

My Posts This: Topic  Forum		Hi Doug, yes I made a tool that bolts to the 4 hols in the hub, didn't take very long, made it out of 3mm ali sheet.
It gives one a bit more purchase on the job......
09-06-2008 Over year old.
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Doug C
Senior Heliman
Location: Northern CA

My Posts This: Topic  Forum		Bell,

How did you keep the second stage shaft from turning while torquing the nut??

I used a strap style pipe clamp on mine with the strap wrapped around the fan hub but I still had problems with the shaft turning, resorted to disassembling the 2nd stage and using the strap on the drive gear, then re-assembling.

DC
09-07-2008 Over year old.
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Bell Bloke
Key Veteran
Location: ....

My Posts This: Topic  Forum		This sounds a bit obb but to stop the shaft turning I cleaned the dottom brass cone andhub with a degreaser ie. meths. Then I applied Evo stick rubberised contact adheasive to both parts, let it go tacky and then clamped them up. The rubberised film in the cone produces enough friction to stop the shaft turning, and it saves taking your engine appart. When if ever you want to undo it it just comes straight off because rubberised contact glue doesn't stick to metal very well. I've done 2 Wren engines in this way and it works really well. The key to success is:
1. Degrease the cone
2. Only a little bit of glue on the brass cone and in the Ali hub
3. Let it get tacky

And that's it
09-07-2008 Over year old.
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hazchem88
Veteran
Location: W.Mids UK

My Posts This: Topic  Forum		I need a little help,
I'm buildind the tail.
I have the speed up gear.

Trying to figure out which gear is which,
what's confusing me is that the pictures in the manual appear to be inverted.
The standard black gear goes to opposite way to the pictures.
The speed up ones are both the same colour. With an apparent error in the manual, I'm not sure which gear goes where?

any help would be appreciated!
09-13-2008 Over year old.
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hazchem88
Veteran
Location: W.Mids UK

My Posts This: Topic  Forum		and another odd thing;

step 70;
press M5x13 bearing into the R hand tail gearbox,

I assumue another M5x13 (since I have been given 2) should go into the left tail gearbox (to support tail output shaft at the end).

But the M5x13 bearing will not fit into the recess in the L hand box. I assumue I need a smaller bearing, M5x10 or someting.
Was anyone else supplied the correct bearing? Just me that is missing it?!



I apologies if it seems a stupid question. I know the answer really, but I ask partly for reassurance, and partly to help others that go down this route.
If you build a raptor or trex, the instructions are generally explicitly clear, with excellent drawings. But this is a whole different ball game. You have a wren manual that is full of outdated info and needs updated, and a cryptic predator manual with dark small photos!
09-13-2008 Over year old.
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MattJen
Elite Veteran
Location: UK

My Posts This: Topic  Forum		Hi Haz

the bearings are different sizes, the one that acts as a tail out put shaft support, is smaller in diameter it is a 5x 11 x 4



IF YOU LOOK AT STEP 71 you will see the gear upgrade fitted, as it is not the black one.. and you will see a different bearing part number. part number CNBB511 £4.99 @ centruy UK - in stock..

As to which gear goes where, the 13 i put on the tail output shaft..

i personally dont think it matters, the only thing that confused me was the normal gear set had 2 grub screws locking each gear to the input/output shaft, when i bought the upgrade gear set, it only has 1 grub screw on both gears to fit them to the input/output shaft, which seems a bit daft for a set of gears that speed up the tail..

So far after 7 flights no problems , so it must be ok

Manual
I have the manual in PDF formatt, the pictures are much easier to see and lighter, Pm me your email address and i will send it to you.
I also found the standard one hard to read..

Matt
09-13-2008 Over year old.
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Bell Bloke
Key Veteran
Location: ....

My Posts This: Topic  Forum		Yes it does matter which way the gears go.....
The one with the greater number of teeth always drives the one with less/ That's a speed up gear box.
ie. your imput has 14 teeth (drive from bevel crown gear)
And your output to the tail blades is the 13 tooth one.
Don't forget to shim your gearbox to make it run smooth.
09-13-2008 Over year old.
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MattJen
Elite Veteran
Location: UK

My Posts This: Topic  Forum		Good point Bell Bloke,

thanx for the info i understand why i put the 13tooth on the output shaft.... i did it wihtout thinking...

But just for info, why does 14tooth drive the 13 tooth and not the other way round >

matt
09-13-2008 Over year old.
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coolice
Key Veteran
Location: Northamptonshire, England

My Posts This: Topic  Forum		Hey Matt,

The tail speed up gears can be likened to a pinion & spur gear of say a model car as an example.
In order to go faster in a straight line you need a bigger pinion gear (drive gear) meshed to a smaller spur gear (driven gear).
Thus the driven gear rotates faster in relation to the pinion as it has lesser teeth to rotate over a complete revolution if you like.
A crude way of making an example of it but it give you the general idea.

Another good one is a bicycle with multiple gears, you change up to a bigger sprocket at the pedal end and a smaller sprocket back at the rear wheel to go faster.

With RC cars we divided the number of teeth on the spur gear by the number of teeth on the pinion to give us the gear ratio, liek we do with our heli's main gear & clutch pinion to know our gear ratio.

In the Tubines case, some of us have lowered the tooth count on the clutch bell and increased the number of teeth on the main gear.
Thus the clutch bell has to rotate more times to get the main gear to complete one revolution, allow us to rev the Turbine higher to achieve the same head rpm.
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Ian Contessa
Team Robbe SchluterUK
Midland Helicopters
09-14-2008 Over year old.
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hazchem88
Veteran
Location: W.Mids UK

My Posts This: Topic  Forum		thanks for all that info, all explicitally clear now.
I'll order that missing bearing.

Did you guys have to trim '3-4mm' off the backs of your carbon tail blades as shown in the manual? Mine look like they won't need trimming, or possibly only 0.5mm at the most. Glad I didn't trim them before trial fitting!
09-14-2008 Over year old.
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coolice
Key Veteran
Location: Northamptonshire, England

My Posts This: Topic  Forum
Quote 
Did you guys have to trim '3-4mm' off the backs of your carbon tail blades as shown in the manual? Mine look like they won't need trimming, or possibly only 0.5mm at the most. Glad I didn't trim them before trial fitting!

Hey Matey,

Yes, I did on my model and also on the nitro Predators I had as well.
I took a Dremmel sanding drum to the backs of the blade root on mine and sanding it into a nice round shape so as to allow the blade to swing full in the tail grip.
It doesn't really need to able to swing fully but I find when packing the model in the car, being able to swing the tail blades together helps
.

Ian Contessa
Team Robbe SchluterUK
Midland Helicopters
09-14-2008 Over year old.
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Bell Bloke
Key Veteran
Location: ....

My Posts This: Topic  Forum		Don't forget to ballance them, Quick UK do the best one I have ever used.
09-14-2008 Over year old.
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MattJen
Elite Veteran
Location: UK

My Posts This: Topic  Forum		Don't forget to ballance them, Quick UK do the best one I have ever used.

Bell,

Best what ? Balancer ?

matt
09-14-2008 Over year old.
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hazchem88
Veteran
Location: W.Mids UK

My Posts This: Topic  Forum		balancing tail blades; can you really get that much accuracy balancing something so small and light as a pair of CF tail blades? And will it really make that much difference?
Surely just a spec of one dust on one blade might be enough to tip the balance?
09-14-2008 Over year old.
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Bell Bloke
Key Veteran
Location: ....

My Posts This: Topic  Forum		Yes, balance on the tail is most important because although an out of balance tail is hard to see, vibration from it will cause early failures on the tail servo. Servos don't, as you know like vibration. Dust on the blades could put them out of balance but since they both get the same amount on they I think you could work with the theory of all things being equal
Tail bearings also suffer massively, the better everything is balanced the longer it will last and the fewer problems you will have.
Matt, the quick unit we finally used on you main blades is the best I've seen so far, short of using those chemical or paint scales.
09-14-2008 Over year old.
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MattJen
Elite Veteran
Location: UK

My Posts This: Topic  Forum		thanx Bell

I will then start to balance my blades both tail and mains

Matt
09-14-2008 Over year old.
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Got Jet Fuel? Turbine Helicopters > Ha ha, my Predator turbine build begins
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