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Torquing prop bolts
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carlisle

Joined: 20 Jun 2009
Posts: 72
Location: Sioux Falls, SD

Posted: Wed Oct 21, 2009 5:44 am Post subject: Torquing prop bolts

Was surfing around and found this little note on another forum.  It applies to a Zenair but struck a note with me.  Every time I go to retorque my GSC 66" adjustable pitch prop, the bolts are loose.  The prop was just inspected and overhauled by GSC.  My torque wrench is calibrated, etc, etc.



Anyway, here's the topic:



-----------------------------------------------------------------------------------



Our CH601HD Zodiac with a Rotax 912S 100 HP engine has a 68-inch, 3-blade

GSC wooden prop.  In our installation, there is a prop flange extension.

The prop is held on by 6 1/4-inch bolts (3 through the aluminum blade

roots), and by 6 5/16-inch bolts onto the flange extension.  GSC Systems

says use 100 inch pounds of torque for the 1/4 inch bolts, and 140 for the

5/16; these values are critical.  Normally, with a washer under both the

head and the nut, one holds the bolt head stationary, and torques the

nylon lock nut; these nyloks are the preferred nuts recommended by GSC.

Because of the design of the prop flange extension, it is not possible to

get the torque wrench onto the nuts.  Thus, one holds the nut stationary,

and torques the bolt head.  THIS IS NOT THE SAME THING.  My son Peter

(co-builder of our aircraft, and a professional mechanical engineer) knows

from practical experience that putting the torque wrench on the bolt head

can undertorque the nut by possibly 20-30%, or even more.  It stands to

reason: the bolt shaft (or grip) inevitably experiences some friction in

passing through the parts being bolted together on the way to the nut.

There is a little part called a "crow's foot" to overcome this difficulty,

which goes over the nut, extends radially outward for about an inch, and

has a square hole for attachment of the torque wrench.  It happened that I

had always torqued the prop bolts on our aircraft.  In setting out to

retorque the bolts yesterday because the weather is now turning cold,

Peter realized right away that there was a problem.  I had never used a

crow's foot (I did not know of their existence!).  I'm guessing that many

others using this Rotax/GSC prop installation were also unaware of this

problem.  What have others done about this?  Were they aware of the

problem?



-----------------------------------------------------------------------------------



Anyone else run into this problem?



Chris

Model 2, 582

Sioux Falls, SD

bw12345(at)sbcglobal.net
Guest

Posted: Wed Oct 21, 2009 6:13 am Post subject: Torquing prop bolts

Using a crows foot or any extension of the torque wrench will change the torque that you read on the wrench. How much?



BOB



--- On Wed, 10/21/09, carlisle <carlisle_99(at)yahoo.com> wrote:

From: carlisle <carlisle_99(at)yahoo.com>

Subject: Torquing prop bolts

To: kitfox-list(at)matronics.com

Date: Wednesday, October 21, 2009, 9:44 AM




Was surfing around and found this little note on another forum.  It applies to a Zenair but struck a note with me.  Every time I go to retorque my GSC 66" adjustable pitch prop, the bolts are loose.  The prop was just inspected and overhauled by GSC.  My torque wrench is calibrated, etc, etc

Av8r3400

Joined: 22 Sep 2008
Posts: 83
Location: North Central Wisconsin (KRRL)

Posted: Wed Oct 21, 2009 6:43 am Post subject: Re: Torquing prop bolts

Check my reply here for a couple of good links on the torque error with a crow-foot socket.

_________________
Thanks,
Av8r3400

Kitfox Model IV-1200 W/912UL & IVO
Kitfox Model IV-1050 W/912UL & Warp
YouTube Videos

carlisle

Joined: 20 Jun 2009
Posts: 72
Location: Sioux Falls, SD

Posted: Wed Oct 21, 2009 8:14 am Post subject: Re: Torquing prop bolts

I guess my issue with the crow's foot is that it's imprecise.  The reason you should torque on the nut instead of the bolt head is that there are no other resistances.  If you're on the bolt head, one has no way of knowing how much resistance there is to torquing along the length of the shaft.  Therefore, it's anyone's guess as to just how much you should compensate.  I think that the 20-30% advocated in the original thread is an estimation and probably ok for non critical/structural applications.  Holding the propeller on the airplane is not one of these however.



My A&P mechanic buddies say that a crow's foot is not designed for this.  They also say that a little loosening of the prop flange bolts is normal and 'figured in' when determining the correct torque settings, especially with a wooden prop where expansion/contraction has to be taken into account.



Chris

Tommy Walker

Joined: 12 Jan 2006
Posts: 442
Location: Anniston, AL 36207

Posted: Wed Oct 21, 2009 12:09 pm Post subject: Re: Torquing prop bolts

Hi,



Just wondering.  Is there a FAR that requires that bolts go from front to rear?  Could the bolt head be placed in the rear and the nut in front.  I had a Warp Drive prop on a 912, and I believe the instructions for assembly of the prop and hub specified this.



Tommy Walker in Alabama

Do Not Archive.



 	  carlisle wrote: 	
		  Was surfing around and found this little note on another forum.  It applies to a Zenair but struck a note with me.  Every time I go to retorque my GSC 66" adjustable pitch prop, the bolts are loose.  The prop was just inspected and overhauled by GSC.  My torque wrench is calibrated, etc, etc.



Anyway, here's the topic:



Chris

Model 2, 582

Sioux Falls, SD

_________________
Tommy Walker
N25A - Anniston, AL

helili(at)chahtatushka.ne
Guest

Posted: Wed Oct 21, 2009 2:41 pm Post subject: Torquing prop bolts

Nope.  It's not a FAA/PMA prop. No FAR specifies which way bolts are

installed.  There are Advisory Circulars that recommend certain ways to

install bolts, but manufacturer's recommended procedures take precedence

over AC recommendations, even in the case of FAA/PMA approved products.



John Hart

KF IV, NSI Subaru

Wilburton, OK 



--

Tom Jones

Joined: 12 Mar 2006
Posts: 752
Location: Ellensburg, WA

Posted: Wed Oct 21, 2009 3:53 pm Post subject: Re: Torquing prop bolts

Carlisle wrote:

 	  Quote: 	
		  Every time I go to retorque my GSC 66" adjustable pitch prop, the bolts are loose. The prop was just inspected and overhauled by GSC. My torque wrench is calibrated, etc, etc. 	




Chris, which bolt circle do your prop bolts use on your 582 prop flange and are they threaded?  Some people have been known to use 5/16 bolts in the holes that are actually 8mm.  5/16 is a hair smaller than the 8mm.  If the bolts are correct and you use either saftey wire through the heads or nylock lock nuts on the bolts I would say, if they are loose, the prop has shrunk.

_________________
Tom Jones
Classic IV
503 Rotax, 72 inch Two blade Warp
Ellensburg, WA

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Wed Oct 21, 2009 4:42 pm Post subject: Re: Torquing prop bolts

Here you go. See attached for Crowsfoot torque calculation. It's not a huge change, just a slight one. Play with the calculation it isn't hard. Just kind of fill in the blanks and a simple math problem.

Torque with a crowfoot calculation.pdf

Description:

Crowsfoot Calculations

Download

Filename:

Torque with a crowfoot calculation.pdf

Filesize:

26.27 KB

Downloaded:

503 Time(s)

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

Av8r3400

Joined: 22 Sep 2008
Posts: 83
Location: North Central Wisconsin (KRRL)

Posted: Thu Oct 22, 2009 3:08 am Post subject: Re: Torquing prop bolts

Check this out.



This was part of my response to the original poster on the Team Kitfox Forum.

_________________
Thanks,
Av8r3400

Kitfox Model IV-1200 W/912UL & IVO
Kitfox Model IV-1050 W/912UL & Warp
YouTube Videos

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Thu Oct 22, 2009 12:36 pm Post subject: Torquing prop bolts

Changes in torque can be significant especially when torquing composite and

wooden props.  The easiest way to eliminate and deviation in torque form

what is delivered by a properly calibrated torque wrench is to always apply

the final torque with the crows foot at 90 degrees to the torque wrench.

This is easy to verify by simply torquing a nut and bolt put through an old

piece of scrap steel.  Then checking the torque without the crow foot.  For

those of you worried about a crow foot slipping you can also use a cable or

hose wrench.  It looks like a cross between a crow foot and a ring wrench.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

carlisle

Joined: 20 Jun 2009
Posts: 72
Location: Sioux Falls, SD

Posted: Thu Oct 22, 2009 3:58 pm Post subject: Re: Torquing prop bolts

Tom...I'm not sure what you mean by 'prop circle'.  The bolts that attach the prop hub to the flange ARE threaded, there are 6 of them, and there are 6 studs that are also threaded into the prop flange and fit into holes in the back of the hub to relieve torsional loads on the prop.  In addition, there are 2 'pinching' bolts for each of the 3 blades that squeeze the hub onto the molded neoprene blade roots.  They do not pass through to the flange on the transmission.



Chris

Tom Jones

Joined: 12 Mar 2006
Posts: 752
Location: Ellensburg, WA

Posted: Thu Oct 22, 2009 5:04 pm Post subject: Re: Torquing prop bolts

 	  Quote: 	
		  Tom...I'm not sure what you mean by 'prop circle'. The bolts that attach the prop hub to the flange ARE threaded, there are 6 of them, and there are 6 studs that are also threaded into the prop flange and fit into holes in the back of the hub to relieve torsional loads on the prop. In addition, there are 2 'pinching' bolts for each of the 3 blades that squeeze the hub onto the molded neoprene blade roots. They do not pass through to the flange on the transmission.



Chris 	




My original post was to alert you incase you had a prop that uses 8mm bolts into the threaded 8mm holes so you could be sure someone had not put 5/16 bolts in.   



If it is a Type-B drive:

The prop flange has 1/4 inch and 8mm holes arranged on a 75mm circle.  On older Rotax prop flanges the 1/4 inch are threaded to 1/4-28.  On newer flanges the 1/4 inch holes have no threads and you use lock nuts on the prop bolts.  On both old and new types the 8mm holes are threaded  and those are the holes the 8mm studs are threaded into.



If it is a Type-C drive:

There are two different diameter bolt circles.  A 75mm bolt circle (same as the Tyle-b drives) and a larger 100mm bolt circle.  the 100mm bolt circle is always 8mm and untapped. If a prop is designed for the larger circle it is attached with 8mm bolts.



If your GSC is the same as the one I used all the bolts are 1/4 inch and the 6 8mm studs in the threaded 8mm holes.  Some use a drilled head bolt and safety wire and some installations use lock nuts on the bolt.



Wow, I hope I didn't confuse yoy with all this but I think from what you say in your last post your installation is correct.

_________________
Tom Jones
Classic IV
503 Rotax, 72 inch Two blade Warp
Ellensburg, WA

carlisle

Joined: 20 Jun 2009
Posts: 72
Location: Sioux Falls, SD

Posted: Thu Oct 22, 2009 6:32 pm Post subject: Re: Torquing prop bolts

Tom...Wow, very complicated indeed.  But thanks for the explanation.  I had no idea there were so many variants.

Mine's a B gearbox.  The 6 through bolts that attach the prop are special high grade bolts supplied by Skystar, way back when I built the plane.  They have about 150 hrs on them and my A&P mechanic friends say they're in good shape so I don't need to replace them.  I'm not exactly sure their diameter or thread pitch and can't remember the markings on the head.

Interestingly, when I had the prop overhauled by GSC, I asked for new bolts anyway and they said that they recommend standard AN hardware for mounting now.  

Anyway, I have another question.  Does anyone use threadlock?  Not the strongest kind (red I think), but just something to make the bolt a little more secure.  Is thread lock a no-no in aviation applications?



Chris

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Oct 23, 2009 12:27 pm Post subject: Torquing prop bolts

This is true... Recommendations are; the prop be bolted on to specified

torque and lockwired, however, Ivo requires you NOT lockwire the bolts.

When I asked why I was told it was because people didn't like to cut the

lockwire to check torque on the scheduled basis.  Even though I prefer to

see lockwire on a prop I did not drill and wire mine.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Oct 23, 2009 2:39 pm Post subject: Torquing prop bolts

The problem with threadlock , there are aviation specific threadlocks

available, is it makes it impossible to check the torque on the bolts.  You

will literally have to remove the bolts clean them and the holes they went

into and re-torque them just to check torque.  Nyloc nuts are a lot better

answer...  and lockwire is better again if you don't mind cutting a bit of

wire at prescribed intervals to check your torques.  If you have an all

metal fixed pitch prop then you can torque, lockwire and basically forget

about it for a long time.  



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

msm_9949(at)yahoo.com
Guest

Posted: Fri Oct 23, 2009 3:21 pm Post subject: Torquing prop bolts

I could be wrong Chris, and someone will surely jump me if I am, but since those bolts must be retorqued at least annually during your condition inspection, and since they will be safety wired, thread lock isn't necessary or desireable. At least I don't do that with mine.

  

 Marco Menezes N99KX

 Model 2 582-90 C-Box 3:1 w/clutch



--- On Thu, 10/22/09, carlisle <carlisle_99(at)yahoo.com> wrote:



  	  Quote: 	
		  

From: carlisle <carlisle_99(at)yahoo.com>

Subject: Re: Torquing prop bolts

To: kitfox-list(at)matronics.com

Date: Thursday, October 22, 2009, 10:32 PM



 --> Kitfox-List message posted by: "carlisle" <carlisle_99(at)yahoo.com (carlisle_99(at)yahoo.com)>



Tom...Wow, very complicated indeed.  But thanks for the explanation.  I had no idea there were so many variants.

Mine's a B gearbox.  The 6 through bolts that attach the prop are special high grade bolts supplied by Skystar, way back when I built the plane.  They have about 150 hrs on them and my A&P mechanic friends say they're in good shape so I don't need to replace them.  I'm not exactly sure their diameter or thread pitch and can't remember the markings on the head.

Interestingly, when I had the prop overhauled by GSC, I asked for new bolts anyway and they said that they recommend standard AN hardware for mounting now.  

Anyway, I have another question.  Does anyone use  threadlock?  Not the strongest kind (red I think), but just something to make the bolt a little more secure.  Is thread lock a no-no in aviation applications?



Chris





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=269tronics.com/Navigator?Kitfox-List"  --> http:========================



	


         [quote][b]

pwmac(at)sisna.com
Guest

Posted: Fri Oct 23, 2009 3:25 pm Post subject: Torquing prop bolts

Nylocks introduce a torque variable. One must do lots of tests to be 

able to get the proper torque has to include the torque resistance of 

the nylock. I know many use the nylock nuts but to be correct and 

precise use a regular nut and lock wire. Always unscrew the nut then 

re torque to get a correct reading.

Standard practice.

Paul

=============



At 06:05 PM 10/23/2009, you wrote:

[quote]



The problem with threadlock , there are aviation specific threadlocks

available, is it makes it impossible to check the torque on the bolts.  You

will literally have to remove the bolts clean them and the holes they went

into and re-torque them just to check torque.  Nyloc nuts are a lot better

answer...  and lockwire is better again if you don't mind cutting a bit of

wire at prescribed intervals to check your torques.  If you have an all

metal fixed pitch prop then you can torque, lockwire and basically forget

about it for a long time.



Noel



--

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Fri Oct 23, 2009 3:26 pm Post subject: Torquing prop bolts

At 07:32 PM 10/22/2009, you wrote:

 	  Quote: 	
		  Anyway, I have another question.  Does anyone use threadlock?  Not 

the strongest kind (red I think), but just something to make the 

bolt a little more secure.  Is thread lock a no-no in aviation applications?


	


I use six 8mm bolts threaded into the flange, torqued, then backed by 

six nylocks. I also safety wire. Ain't no way that prop's comiin' off.

Guy Buchanan

San Diego, CA

K-IV 1200 / 582-C / Warp / 400 hrs. and counting

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Oct 23, 2009 3:56 pm Post subject: Torquing prop bolts

What kind of blades do you have Guy?  Most departures I've heard of have

most of the root left in the hub when the blade departs.  I don't think I've

ever heard of a hub departing.



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Oct 23, 2009 3:58 pm Post subject: Torquing prop bolts

For the nyloc you use friction torque...  That requires the use of a torque

meter or beam type wrench to measure the friction of the nyloc.  That

friction is then added to the torque requirement...  I prefer your method

with the lockwire but do as the manufacturer instructs me to do.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

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