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HomeTurbine✈️Aircraft🚁HelicopterTurbine Helicopters › Wren 2nd stage turbine removal
06-01-2015 09:11 PM  4 years ago
steph

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think I can see the light at the end of the tunnel its been a slow process now the rebuild

The world is round you can run but you will always end up where you started from
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06-01-2015 09:38 PM  4 years ago
dgoss999

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What front bearing preload did you choose?
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06-01-2015 09:58 PM  4 years ago
steph

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Not actually knowing what the preload is I went with rule of thumb as long as there is some preload so I went for around .5mm
we will soon find out if its enough
As I did not have any information I could not do anything else
The Depth of the space for the front bearing is 6.5 mm and the depth of the bearing is 6mm so only .5 mm to play with
The world is round you can run but you will always end up where you started from
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06-01-2015 11:50 PM  4 years ago
dgoss999

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On the 2 stage gearboxes I have, the preload on the front bearing is done by a moving sleeve held against it's outer race by a coil spring. The spring is retained just inside the rear bearing (Gear side) by a 'C' clip in a grove.

The distance between the bearings is about 50mm. The sleeve is about 30mm and spring takes up the remainder of the space. (this set-up allows for over 10mm of preload movement)

The Part 1 (home builder) Plans for the MW54 downloadable from the Wren WEB page shows the general Preload arrangement (No's 10 and 38 in the drawing). According to this drawing, the preload is 3.75Kg.

NOTE: On the Gearbox the preload acts on the front bearing and not on the rear one like in the Gas Generator.

http://www.wrenturbines.co.uk/plans...s_turbo_jet.pdf

DG
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06-01-2015 11:56 PM  4 years ago
MattJen

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i'm pretty sure it depends on what shaft tunnel you have as they upgraded it to steel on newer Mark3's and removed the need for the circlip as it was prone to failing in the early days. The steel one has a lip/line on the inside..All The Best
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06-02-2015 12:08 AM  4 years ago
dgoss999

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Matt - We are talking gearbox here not Gas Generator.

DG
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06-02-2015 12:59 AM  4 years ago
MattJen

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sorry seniour momentAll The Best
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06-02-2015 09:45 AM  4 years ago
steph

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Dgoss999 that's the plans for the Mw54 turbine shaft not the second stage shaft
Unless I'm missing something here

The world is round you can run but you will always end up where you started from
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06-02-2015 10:42 AM  4 years ago
dgoss999

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I used the drawing as example of how the Preload on the ceramic bearings can be achieved and what the bearing preload is.

This system IS used in the two 2nd stage turbine gearboxes I have running.

Sorry to confuse and maybe not explain myself clearly, this is why I put the following in my original comment..

"The Part 1 (home builder) Plans for the MW54 downloadable from the Wren WEB page shows the general Preload arrangement (No's 10 and 38 in the drawing). According to this drawing, the preload is 3.75Kg."

DG
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06-02-2015 10:44 AM  4 years ago
dgoss999

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sorry seniour moment
Spanish now eh?
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06-02-2015 11:12 AM  4 years ago
MattJen

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Might as well be in spanish trying to understand your post lol...
I was confused why you put the plans up of the Gas generator when trying to explain the pre load on gearbox.. ha ha

Hence why I mentioned about shaft tunnel upgrade.

Never mind that's what happens when trying to read posts at 1am..
All The Best
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06-02-2015 11:39 AM  4 years ago
dgoss999

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I have no plans with the this sprung preload arrangement.

The Gas Gen plan, with the explanation was my best alternative!

DG
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06-02-2015 01:56 PM  4 years ago
steph

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Ah now I understand,
I pretty much copied the shaft tunnel and made a identical one so all the tolerances should remain the same
The .5 mm on the front bearing is the amount it moves after the preload is applied.
Hopefully if I have got all my measurements correct it should be as it was we shall see
The world is round you can run but you will always end up where you started from
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06-03-2015 02:42 PM  4 years ago
steph

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After initial tries to start the turbine failed due to the start motor not getting up to speed I finally got it to run

Well the good news is the turbine starts and runs at idle power have not tried full power yet
second stage turbine seem to run ok without any undue noises or rattles and the gearbox runs ok
The only problem is the second stage insulation got really hot to the point it nearly caught fire the insulation smoked like it was on fire
I'm thinking the oil from the gearbox must have somehow leaked forward through to the second stage to cause the smoke ??
I'm going to have to take the turbine assembly apart to investigate and also check the gearbox for oil I betting there is no oil in there
Strange as there was no smoke from the exhaust and if the gearbox oil leaked through there would have been
Back to the drawing board

The world is round you can run but you will always end up where you started from
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06-03-2015 10:38 PM  4 years ago
steph

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There is oil in the gearbox so was not that on closer inspection i saw the cause second stageturbine wheel its just catching the side of the spider my tolerances on the tunnel not as good as they should have been as there was is side movement on the front ceramic bearing oh well if at first you fail give up lolThe world is round you can run but you will always end up where you started from
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06-04-2015 08:34 AM  4 years ago
steph

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I'm thinking if I bore out the front of the tunnel and fit a 7mm spacer with the correct inside dia 16mm to fit the ceramic bearing this will solve the problem

Or remake the tunnel to the correct size this would be the obvious and correct thing to do

so what do I do take the easy route bore out or remake ?? what do you guys think
The world is round you can run but you will always end up where you started from
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06-04-2015 09:57 AM  4 years ago
dgoss999

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Steph,

It could be the ceramic bearing preload which is letting you down.

Counter-bore the current tunnel to take the sleeve and spring arrangement to give the correct ceramic bearing preload. Ensure you have an Angular Contact bearing on the gearbox side to run with the preload on this bearing on the turbine end of the shaft.

The smoke you mentioned due to oil while running won't be visible once the turbine gets up to speed. You may just notice it if the gas plume is backlit (eg. by the sun) while you fly it. You could though see it at the start and end of each run.

/DG
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06-04-2015 01:09 PM  4 years ago
steph

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What's letting me down is I don't have anything to work from like the plans of the tunnel wren promised me
Only the damaged part I'm taking guess measurements to work from

The sleeve sits in the tunnel its an interference fit no need to counter bore just warm up the tunnel and tap the sleeve to move it

The preload probably is letting me down as I'm only guessing what I should have

The ceramic bearings seat is to blame as the second stage turbine hits the side of the spider I'm pretty sure this is what caused the fire/smoke
The world is round you can run but you will always end up where you started from
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06-04-2015 01:33 PM  4 years ago
dgoss999

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Check out the plans for the Turboprop gearbox on the Wren site.. Can you use the 2nd Turbine and tunnel drawings there?

http://www.wrenturbines.co.uk/plans...op_drawings.pdf

(I would avoid the crinkly washer for the Preload though!!)

/DG
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06-04-2015 03:53 PM  4 years ago
steph

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Thanks Dgoss999

But the plans did not help me much so I have reassembled the old tunnel and measured the preload and adjusted to suit on the new tunnel its around 4/5mm preload witch is much as I had anyway

ok with that sort of sorted now what do I do about the front bearing do I sleeve or not as I can't glue the dam thing in as its a moving bearing
Probably best If I make a new tunnel
The world is round you can run but you will always end up where you started from
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