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Prop hub stud torque

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jill(at)m-14p.com
Guest

Posted: Tue May 10, 2011 6:06 am Post subject: Prop hub stud torque

Just saw this post and thought I should correct some bad information.  The

torque value specified in the Russian V-530 Overhaul manual (Dated 14 May

1975) for the six prop hub studs is 7 (+1) kgc-m.  (50 - 57 ft/lbs - if

Online Conversion is correct.)  This is significantly different than 87. 



 I have never heard of a stud breaking on a V-530 hub, but I have now.   



Jill

M-14P, Inc.

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wlannon(at)persona.ca
Guest

Posted: Tue May 10, 2011 6:03 pm Post subject: Prop hub stud torque

Hi Jill;



I believe Eric's 87 lb/ft for the V530 prop. retaining nuts is correct.

I use 82 to 93 lb/ft.  Can't remember where it came from but it fits for the 

bolt size and the engine HP.  Hartzells & McCauleys on 150- 180 HP require 

50 ft/lb.

MT propellors (for over 300HP and with 9/16" studs) require 100 to 110 

lb/ft.



57 lb/ft is the correct torque for the V530 and J9-G1 blade clamp nuts.



Walt



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heaysr(at)telus.net
Guest

Posted: Tue May 10, 2011 9:17 pm Post subject: Prop hub stud torque

Hi Jill,



Please post all the other propeller torque number that you quoted to me on 

the phone yesterday that came directly from the V-Perod Propeller overhaul 

Manual.



Safety is the name of the game here - Your reference to "bad" information 

is a euphanism for unsafe and dangerous information.



Gorillas at the end of torque wrenches may well lead to stud failure.



Please set the record straight for the misinformed.



Royden

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heaysr(at)telus.net
Guest

Posted: Tue May 10, 2011 10:16 pm Post subject: Prop hub stud torque

Dear Yaklisters



This is an appeal please to not rely on personal belief or equivalence to 

North American propellers/practice.



The Russians built these very successful and robust V-530 props for 

decades - let's go by their manual. That they have evidently been seriously 

over-torqued (~60%) in the USA without previous reports of failures is a 

testament to their robustness.



Jill's conversion is correct.



7 kg.m = 50.6 ft.lb

8 kg.m = 57.9 ft.lb



As for stud size: - what you see in NOT what you get. The stud nut is 22 mm 

and one sees only thread exposed when the prop is off the aircraft.



But being on the receiving end of a broken stud one finds a stud shank that 

is wasted to a diameter noticeably less than the inside diameter of the 

thread - and always hidden from view when normally within the prop flange.



Why the designers do that, I can only guess. Presumably because the spline 

carries all shear loads and the stud is designed to carry only tensile 

loads. By wasting the shank, it will not attract shear loads from the holes 

through which it loosely passes in the prop hub.



The specified torque must be based on the wasted shank diameter (normally 

hidden from view) and not the larger thread that is normally in view. Hence 

the deceivingly low torque values specified by the Russians for these studs.



 If Jill posts all the torque numbers, you will find the specified torque 

for the prop blade c clamps is higher than the for the flange studs (59 

ft.lb if I remember well). Maybe not surprising as the shank diameter for 

the C clamp bolt visually appears larger than the wasted diameter of the 

prop flange studs. (However, to be confirmed with measurements next 

weekend).



I also hope to get you some photos showing the failed stud by next weekend.



Please take care and be vigilant with your torque wrenches!



Royden



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Dale

Joined: 30 May 2007
Posts: 178

Posted: Wed May 11, 2011 6:04 pm Post subject: Re: Prop hub stud torque

Torque: MT Propellers only Not V-530



MTV-9 Propeller on M-14PF uses a SAE-2 hub with 1/2 in bolts.



3/8" 24 UNF bolts 25 - 27 ftlb

7/16" 20 UNF bolts 41 - 44 ftlb

7/16" 20 UNF stopnuts 33 - 35 ftlb

7/16" 20 UNF stopnuts:

A-flange on Centurion 2.0 mit 155 HP 40 - 42 ftlb

1/2" 20 UNF bolts (< 300 HP) 63 - 66 ftlb

1/2" 20 UNF bolts (> 300 HP) 90 - 100 ftlb

and SMA SR 305-230

1/2" 20 UNF stopnuts (< 300 HP) 63 - 66 ftlb

1/2" 20 UNF stopnuts (> 300 HP) 80 - 85 ftlb

9/16" 18 UNF stopnuts 100 - 110 ftlb



Note: Torque values are valid for dry, free-moving threads

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wlannon(at)persona.ca
Guest

Posted: Wed May 11, 2011 8:52 pm Post subject: Prop hub stud torque

Where to begin?



There appears to be a need for some understanding of what "torque" is all 

about and I guess I will bore everyone to tears.  My apology in advance!



1.  The prop. attach studs on the M14P are designed to carry tensile loads 

only.  There is of course a very high shear component but this is reacted 

solely by the mating hub and flange serrations. The proper mating of the 

serrations depends on the tensile load of the studs but does not transfer 

shear loading to the studs.

A shaft mounted propellor reacts shear loads directly and independently 

through the shaft SPLINES.



2.  The waisted (not wasted) part of the stud (usually referred to as a 

necked stud) is done for a specific reason.

A stud, or bolt, designed to carry tension loads must be STRETCHED to a 

tensile loading in excess of the loads expected to be encountered in 

service.  This is particularly critical for a joint subject to cyclic 

loading and unloading.

Of course the stretching must not exceed the elastic limit

of the fastener.

If not pre-stretched the fastener will be repeatedly stretched in service. 

Depending on the frequency and magnitude of this action the stud, or the 

structure it holds, will eventually fail due to fatigue.

If it is correctly stretched, within its elastic limit, it will never 

stretch in normal service and will not fail due to fatigue.



A necked stud has the diameter reduced to correspond with the thread root 

diameter so that this stretching is reasonably uniform throughout the length 

and does not focus the entire load in the thread root area.  In addition, 

highly loaded fasteners like this will have rolled threads.



In any event a fastener loaded in tension is stretched on the basis of the 

weakest part - usually the thread root dia.

A fastener loaded in shear, which implies a close tolerance fit, is graded 

on the shear strength of the full dia. shank.



3.  The Prop retaining studs and the blade clamping bolts have many 

similarities,  they are necked and they both appear to have rolled threads 

but they are very different in size.

The blade bolt is 10 mm compared to the stud which is 14 mm.  That is the 

nominal dimension, NOT the necked area.

The 10 mm bolt is carrying pure tension loads without cyclic loading and is 

torqued to 8 Kgm, 78NM or 58 lb/ft.  The limit is 57 to 63 lb/ft.



The 14 mm stud has approximately double the cross sectional area of the 

bolt, is also loaded in tension WITH

a cyclic factor and it is torqued to the same number?  Not a chance.



4.  What is torque as it relates to a fastener?   It is a simple, easy to 

apply  method of somewhat controlled STRETCHING of a fastener.  It is highly 

subject to errors due to thread condition, lubrication, etc.

It is not used in some very highly critical joints because of those 

limitations.  Instead a direct measurement of bolt stretch is done using a 

micrometer or ultrasound techniques.  The limits are given in actual bolt 

stretch.



5.  Torque (stretch) values are determined from the ultimate strength of the 

material (UTS),  the yield strength (upper elastic limit), effective cross 

section area, thread pitch and the expected service loading.

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stephenmorrey(at)gmail.co
Guest

Posted: Thu May 12, 2011 5:58 am Post subject: Prop hub stud torque

Can anyone tell me what the torque is for the 4 bolts in the balance weight bracket attachment.  I expect I need to pull the balance weight to dye pen the bracket attachment?



On Thu, May 12, 2011 at 12:49 AM, Walter Lannon <wlannon(at)persona.ca (wlannon(at)persona.ca)> wrote:

 [quote]--> Yak-List message posted by: Walter Lannon <wlannon(at)persona.ca (wlannon(at)persona.ca)>

  



 Where to begin?

 

 There appears to be a need for some understanding of what "torque" is all about and I guess I will bore everyone to tears.  My apology in advance!

 

 1.  The prop. attach studs on the M14P are designed to carry tensile loads only.  There is of course a very high shear component but this is reacted solely by the mating hub and flange serrations. The proper mating of the serrations depends on the tensile load of the studs but does not transfer shear loading to the studs.

  A shaft mounted propellor reacts shear loads directly and independently through the shaft SPLINES.

 

 2.  The waisted (not wasted) part of the stud (usually referred to as a necked stud) is done for a specific reason.

 A stud, or bolt, designed to carry tension loads must be STRETCHED to a tensile loading in excess of the loads expected to be encountered in service.  This is particularly critical for a joint subject to cyclic loading and unloading.

  Of course the stretching must not exceed the elastic limit

 of the fastener.

 If not pre-stretched the fastener will be repeatedly stretched in service. Depending on the frequency and magnitude of this action the stud, or the structure it holds, will eventually fail due to fatigue.

 If it is correctly stretched, within its elastic limit, it will never stretch in normal service and will not fail due to fatigue.

 

 A necked stud has the diameter reduced to correspond with the thread root diameter so that this stretching is reasonably uniform throughout the length and does not focus the entire load in the thread root area.  In addition, highly loaded fasteners like this will have rolled threads.

  

 In any event a fastener loaded in tension is stretched on the basis of the weakest part - usually the thread root dia.

 A fastener loaded in shear, which implies a close tolerance fit, is graded on the shear strength of the full dia. shank.

 

 3.  The Prop retaining studs and the blade clamping bolts have many similarities,  they are necked and they both appear to have rolled threads but they are very different in size.

 The blade bolt is 10 mm compared to the stud which is 14 mm.  That is the nominal dimension, NOT the necked area.

 The 10 mm bolt is carrying pure tension loads without cyclic loading and is torqued to 8 Kgm, 78NM or 58 lb/ft.  The limit is 57 to 63 lb/ft.

 

 The 14 mm stud has approximately double the cross sectional area of the bolt, is also loaded in tension WITH

 a cyclic factor and it is torqued to the same number?  Not a chance.

 

 4.  What is torque as it relates to a fastener?   It is a simple, easy to apply  method of somewhat controlled STRETCHING of a fastener.  It is highly subject to errors due to thread condition, lubrication, etc.

 It is not used in some very highly critical joints because of those limitations.  Instead a direct measurement of bolt stretch is done using a micrometer or ultrasound techniques.  The limits are given in actual bolt stretch.

  

 5.  Torque (stretch) values are determined from the ultimate strength of the material (UTS),  the yield strength (upper elastic limit), effective cross section area, thread pitch and the expected service loading.

 .

 6.  I would hope someone could find a published torque value  for the V530 nuts that make sense.  57 lb/ft does not.

 Fasteners do fail from over tightening.  There is always a limit.  But more often they fail from under tightening and subsequent fatigue.

 

 Cheers;

 Walt

 

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wlannon(at)persona.ca
Guest

Posted: Sat May 14, 2011 12:09 pm Post subject: Prop hub stud torque

Stephen;

  

 I can not tell you what that torque should be since  I have never seen the Yak 52 elevator bellcrank or the attached balance  arm.

  

 One of these bellcranks was just recently found  cracked in my local area.

  

 Visible (red) dye penetrant inspection may well  reveal a crack but will not guarantee that there is no crack.

 Fluorescent dye penetrant inspection (FLPI) is far  better but is still subject to factors that could hide a very small  crack.

  

 Assuming that there is reasonabe  access the best inspection method is Eddy Current.  This  could possibly be done without removing the balance arm.

  

 I would suggest you contact a reputable NDT company  in your area for advice. 

  

 Walt

  

  

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