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GT Propeller bolts and toque settings

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GT Propeller bolts and toque settings

Postby Anonymous » Tue Feb 10, 2015 10:14 pm

Posted by: DL on 11:54:19 01/01/15 Thu

Just thought I would make this one public as the problem seems to have been found on another aircraft.

The set of propeller bolts sold by sky-craft seem a tad long. When tightening prop nuts to recommended torque settings (12lb/ft) using one washer on swish plate and one on propeller guides, we ended up with bolt being thread bound. What is more worrying is that the old ones were thread bound before we took them off!

If you have a GT propeller on your jab, it is probably worth checking :

1. that propeller is correctly torqued up (12lbs/ft)
2. nuts are not thread bound (1.5 threads showing) use washers to achieve proper torque

I will be checking my propeller following this as I recently replaced my propeller bolts (i do so every 12-18 months).
Anonymous
 

Re: GT Propeller bolts and toque settings

Postby Anonymous » Tue Feb 10, 2015 10:14 pm

Posted by: Roger on 16:39:56 06/07/14 Sat

Dean,

You need to review the JSB on fitting the propeller.

The extra long bolts are used to allow for the additional tinnerman washers as recommended in the JSB.
Anonymous
 

Re: GT Propeller bolts and toque settings

Postby Anonymous » Tue Feb 10, 2015 10:14 pm

Posted by: DL on 17:13:47 06/07/14 Sat

JSB009-1 Click Here states :

Jabiru aircraft have developed an alternate propeller mounting system to allow an increase in inspection intervals for propeller mount bolts. This system is applicable only when using Jabiru 2-bladed wooden propellers. When using this propeller mounting system the propeller bolts should be checked after the initial 25 hours of engine running, then annually thereafter"

From this i conclude that it is only applicable to Jabiru wooden propellers (as they are made of softer wood than GT Propellers).

Jabiru propellers do indeed need belville washers and are torqued to a lesser 7-8 lbs/ft using AN4-37A bolts.

GT propellers are torqued 12 lbs/ft as stated on Sky-Craft website HERE. The recommended bolt for the GT propeller is AN4-36A which is still way too long and results in nut becoming thread bound when torquing up.
Anonymous
 

Re: GT Propeller bolts and toque settings

Postby Anonymous » Tue Feb 10, 2015 10:14 pm

Posted by: roger on 21:31:59 06/07/14 Sat

Sorry - I meant belville and not tinnerman.

Whether it is a hard or soft propeller, the principle of using belville washers works on both can swell and contract as the weather changes. It is far better to use these washers than without and risking bottoming out the threads.
Anonymous
 

Re: GT Propeller bolts and toque settings

Postby Anonymous » Tue Feb 10, 2015 10:14 pm

Posted by: DL on 17:20:54 06/08/14 Sun

Roger,

Jabiru specify using Bellville washers for mounting Jabiru propellers, because the wood they use is softer (relatively) than is used by other prop manufacturers.

The washers are made of spring steel and 'dished' so that when torqued correctly, they exert some axial load and therefore retain tension to accommodate the wood moving with changes in humidity etc. A stack of Bellvilles allows a
greater tolerance of movement.

In the case of the GT propeller, which uses a denser wood, you don't need them unless specified by GT. The same goes for all other prop. manufacturers; use their specified method of mounting which specifies a higher torque.

The higher torque will squash bellville washers making them pointless and without purpose on a GT prop but go ahead and fit them if you think it works better for you!
Anonymous
 

What's wrong with adding washers? Whatever the type?

Postby Anonymous » Tue Feb 10, 2015 10:15 pm

Posted by: Clive on 11:54:19 01/01/15 Thu

Can't see this is a big deal. I have worked on loads of Jabs and very few had the 'right' length bolts, they just had washers to put the nut on the right place of the bolt.

Regards, Clive

P.S. I think we have bigger issues to worry about
Anonymous
 

Re: GT Propeller bolts and toque settings

Postby Anonymous » Tue Feb 10, 2015 10:15 pm

Posted by: Steve on 12:24:31 06/08/14 Sun

Does anyone know the dimensions of the Belleville washers because, as usual, Skycraft seem constantly out of stock of them.

I had the same problem with my GT prop. The recommended bolts for the GT, according to Skycraft, are AN4-36A tightenened to a torque of 16NM. Even with the Skycraft recommended washers, which were not Belleville, the nuts stripped their threads at just over half the recommended torque as they had bottomed out on the thread. I had to use multiple normal washers to allow enough thread to tighten.

The ideal bolt would be a AN4-35A which would work without packing it out with loads of washers.
Anonymous
 

Re: GT Propeller bolts and toque settings

Postby Anonymous » Tue Feb 10, 2015 10:15 pm

Posted by: DL on 17:37:54 06/08/14 Sun

SOLON

I have a spead sheet that may help calculating type and how many belleville washers you should use depending on wood that is used on propeller. I am happy to share it.
Anonymous
 

Re: GT Propeller bolts and toque settings

Postby Anonymous » Tue Feb 10, 2015 10:15 pm

Posted by: DL on 22:44:27 12/17/14 Wed

Click Here
Anonymous
 

Re: GT Propeller bolts and toque settings

Postby Anonymous » Tue Feb 10, 2015 10:15 pm

Posted by: Gary on 08:33:02 12/18/14 Thu

Ive always done my prop to 11ft lb torque, I was advised this by Clive James, its a GT prop, in fact I checked the torque on it yesterday, 1 bolt needed a 1/4 turn to bring it back in torque.
So what is the correct torque

So far we have 8 ft lb
11 ft lb
12 lb
16 ft lb
Anonymous
 

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