Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Fasteners, Screws, & Bolts  
User currently offlinepropilot83 From United States of America, joined Jan 2001, 604 posts, RR: 0
Posted (4 years 8 months 1 week 18 hours ago) and read 9265 times:

My question is for the engineer who designs and/or builds airliners. This is a complex and sophisticated question. When you see a myriad of phillips screws bolted on wings of airliners or any other location of an aircraft, are those screws tightly installed until its tight like you would screw something around your house? Or are the screws different from the ones we use around the house? And also are those screws secured by snapping into a lock position, where you cant tighten it anymore to prevent metal fatigue around the aircraft? So basically, the question is when you screw something on an aircraft, does it snap lock into something where you cant tighten it anymore? Are there any charts/diagrams to better show a visual explanation?

31 replies: All unread, showing first 25:
 
User currently offlinefr8mech From United States of America, joined Sep 2005, 5657 posts, RR: 15
Reply 1, posted (4 years 8 months 1 week 12 hours ago) and read 9188 times:

Any threaded fastener used on an aircraft is torqued to a specified value. That's the book answer.

In reality, threaded fasteners that hold panels in place, assemble secondary structure, etc. are tightened until they are tight. They are not supposed to be hogged down by a gorilla.

In many applications, the AMM will specify a torque. Big things that come to mind are engine mount bolts, flight controls, bolted structural members, fuel tank access panels, among others.

For everything else, the AMM has generic charts that wll give you a torque based on size of fastener and application.



When seconds count...the police are minutes away.
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 2, posted (4 years 8 months 1 week 11 hours ago) and read 9168 times:

One thing that should be pointed out you will find very few screws on a aircraft. Those flush phillips head fasteners you see holding the wing panels on are "bolts".

Under the panel, attached to the structure, you will find a plate nut (nutplate) which is permanently attached. The bolt is threaded into plate nut and tightened.


User currently offlinexero9 From Canada, joined Feb 2007, 155 posts, RR: 0
Reply 3, posted (4 years 8 months 1 week 10 hours ago) and read 9139 times:

Just out of curiosity.. It's kind of on topic with this subject, but how many bolts hold things on such as an engine, a wing? Vital things like that. On say an A320, or 737?

I wanted to say a high number, but I'm actually thinking somewhere around 2-4? Would that be correct?


User currently offlinefr8mech From United States of America, joined Sep 2005, 5657 posts, RR: 15
Reply 4, posted (4 years 8 months 1 week 10 hours ago) and read 9110 times:

Quoting xero9 (Reply 3):
thinking somewhere around 2-4

Not quite that low, anymore. Higher thrust ratings require more fasteners. As an example, the JT8 equipped B727 has bolts/nuts. The JT9 (B747) has 5. I believe the CF6 equipped B767 has 8.

Quoting 474218 (Reply 2):
Those flush phillips head fasteners you see holding the wing panels on are "bolts".

I'm going to disagree, just a little, though it's just a point of symantics. There are plenty of places on the aircraft (and in the IPC) where a fastener is called a screw, not a bolt. But the same part number in a different application may be called a bolt.

[Edited 2010-04-22 08:18:52]


When seconds count...the police are minutes away.
User currently offlineGST From United Kingdom, joined Jun 2008, 938 posts, RR: 0
Reply 5, posted (4 years 8 months 1 week 10 hours ago) and read 9096 times:

Quoting 474218 (Reply 2):

Under the panel, attached to the structure, you will find a plate nut (nutplate) which is permanently attached. The bolt is threaded into plate nut and tightened.

In most of the cases I have come across servicing aircraft (admittedly all of them are gliders), the bolts are almost invariably locked in place with a wire.


User currently offlinedl757md From United States of America, joined May 2004, 1562 posts, RR: 17
Reply 6, posted (4 years 8 months 1 week 9 hours ago) and read 9082 times:

Much information on fasteners can be found in Chapter 7 of the AC 43,13-1b . It can be downloaded in pdf from the FAA website at http://rgl.faa.gov/REGULATORY_AND_GU...ac81b86256b4500596c4e?OpenDocument

DL757Md



757 Most beautiful airliner in the sky!
User currently offlinefr8mech From United States of America, joined Sep 2005, 5657 posts, RR: 15
Reply 7, posted (4 years 8 months 1 week 9 hours ago) and read 9045 times:

Quoting GST (Reply 5):
In most of the cases I have come across servicing aircraft (admittedly all of them are gliders), the bolts are almost invariably locked in place with a wire.

What 474218 is describing are nutplates. They are typically used under panels as part of the fastener system for the panel. No need for safety wire here. The nuts are self locking.



When seconds count...the police are minutes away.
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 8, posted (4 years 8 months 1 week 6 hours ago) and read 8931 times:

Quoting fr8mech (Reply 4):
I'm going to disagree, just a little, though it's just a point of symantics. There are plenty of places on the aircraft (and in the IPC) where a fastener is called a screw, not a bolt. But the same part number in a different application may be called a bolt.

Bolts differ from screw in that bolts have a "head-shank-threads". Screws have a "head-threads".

When installing a bolt you never want to end up with "threads in bearing" or threads that are below the surface, so bolts have a shank.

But it does get confusing when you have a long screw, which my have a shank. However, when a screw has a shank it has almost twice the number of threads a bolt will have.
Big version: Width: 900 Height: 900 File size: 180kb


[Edited 2010-04-22 13:15:22]

User currently offlineLarshjort From Niue, joined Dec 2007, 1526 posts, RR: 0
Reply 9, posted (4 years 8 months 1 week 5 hours ago) and read 8907 times:

A screw commonly used to install access plates on aircraft such as a Learjet 60 and Cessna Citation is a MS24693 which looks like this

Another screw commonly used is the MS27039



139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4,
User currently offlineHAWK21M From India, joined Jan 2001, 31712 posts, RR: 56
Reply 10, posted (4 years 8 months 1 week 5 hours ago) and read 8895 times:

The Panel screws of the exterior most normally screw into Nutplates held below.At most Check C,damaged or unserviceable plate nuts need replacement.
The AMM Specifies a torque with tolerance needed by the faster to be secured.

regds
MEL.



Think of the brighter side!
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 11, posted (4 years 8 months 1 week 5 hours ago) and read 8870 times:

Quoting Larshjort (Reply 9):
A screw commonly used to install access plates on aircraft such as a Learjet 60 and Cessna Citation is a MS24693 which looks like this

All the fasteners shown are "screws" and can only be used in non-structural installations, like interior trim, etc.

See the following:

http://www.airpartsinc.com/products/ms24693-machine-screw-p15.htm


User currently offlinepropilot83 From United States of America, joined Jan 2001, 604 posts, RR: 0
Reply 12, posted (4 years 8 months 1 week 4 hours ago) and read 8837 times:

I knew the answer to this question was going to be a little complicated, so what is an AMM? So basically concluding the answer to my question, when you install a flush phillip head screw on a surface of an airplane (i.e. spoilers, wing area, etc.) to attach to another component, does that specific screw lock into something else to prevent metal fatigue? Like for example, you know how if you tighten a screw too tightly....too much pressure will crack the surroundings like a wall, metal, etc, can this example be applied to an aircraft or no?

User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 13, posted (4 years 8 months 1 week 3 hours ago) and read 8759 times:

Quoting propilot83 (Reply 12):
I knew the answer to this question was going to be a little complicated, so what is an AMM? So basically concluding the answer to my question, when you install a flush phillip head screw on a surface of an airplane (i.e. spoilers, wing area, etc.) to attach to another component, does that specific screw lock into something else to prevent metal fatigue? Like for example, you know how if you tighten a screw too tightly....too much pressure will crack the surroundings like a wall, metal, etc, can this example be applied to an aircraft or no?

AMM is the Aircraft Maintenance Manual.

A flush head bolt is installed in a plain countersunk hole. Simple as that.

Aircraft mechanics are expected to know how to install bolts correctly without damaging the attaching parts.


User currently offlineAirframeAS From United States of America, joined Feb 2004, 14150 posts, RR: 24
Reply 14, posted (4 years 8 months 1 week 3 hours ago) and read 8732 times:

Quoting xero9 (Reply 3):
but how many bolts hold things on such as an engine, a wing?

On our A318's, A319's and A320's at F9, all of the CFM's have 8 HUGE bolts attaching the engine to the pylon each. I am pretty sure that is standard for all the A320 family aircraft regardless of engine.



A Safe Flight Begins With Quality Maintenance On The Ground.
User currently offlineChese From United States of America, joined Sep 2006, 29 posts, RR: 0
Reply 15, posted (4 years 8 months 6 days 22 hours ago) and read 8648 times:

Quoting propilot83 (Reply 12):
when you install a flush phillip head screw on a surface of an airplane (i.e. spoilers, wing area, etc.) to attach to another component, does that specific screw lock into something else to prevent metal fatigue? Like for example, you know how if you tighten a screw too tightly....too much pressure will crack the surroundings like a wall, metal, etc, can this example be applied to an aircraft or no?

This absolutely does happen although the first thing I thought of was screws in acrylic windows. They can cause small cracks that won't appear initially. There really isn't anything to prevent metal fatigue like say with a washer under the head of a nut, as screws are used primarily in panels that are removed fairly often.



Note to airliners.net admins, I will not like you on Facebook.
User currently offlinepropilot83 From United States of America, joined Jan 2001, 604 posts, RR: 0
Reply 16, posted (4 years 8 months 6 days 19 hours ago) and read 8602 times:

Quoting Chese (Reply 15):
This absolutely does happen although the first thing I thought of was screws in acrylic windows. They can cause small cracks that won't appear initially. There really isn't anything to prevent metal fatigue like say with a washer under the head of a nut, as screws are used primarily in panels that are removed fairly often.

So I guess this answers my question then, when you install a screw into any part of an aircraft, it does not lock into something else, you have to tighten it until it gets real tight???? This is no different than using screws around your house then, like causing cracks around a screw while tightening it too much around walls, and other metals??? If this is true, then its surprising, because an airplane expands and contracts like a balloon every time it takes-off and lands, the airplane goes through metal fatigue.


User currently offlinefr8mech From United States of America, joined Sep 2005, 5657 posts, RR: 15
Reply 17, posted (4 years 8 months 6 days 13 hours ago) and read 8506 times:

Quoting propilot83 (Reply 16):
So I guess this answers my question then, when you install a screw into any part of an aircraft, it does not lock into something else, you have to tighten it until it gets real tight????

No, you do not tighten until it gets real tight. There is a torque value. Now, most folks don't use a torque wrench on a simple panel, but, as 474218 stated, aircraft mechanics are expected to know how to install a panel screw, or bolt, without damaging the panel. There is no fail safe. If you have a gorilla installing fasteners, you may have an issue, as we have all seen.

Now, to be sure you understand, the fastener does not go into the metal below the panel (like a stud in a wall), it has a receptacle, commonly a nutplate, that accepts the fastener. This is what the fastener is torqued against, along with the panel.



When seconds count...the police are minutes away.
User currently offlineTristarsteve From Sweden, joined Nov 2005, 4070 posts, RR: 33
Reply 18, posted (4 years 8 months 6 days 10 hours ago) and read 8474 times:

I think that installing scres and bolts is about the most important thing you learn when you are an apprentice. Anyone can tighten a bolt 'real tight', it takes skill to tighten it correctly. And there are many that overtorque panel screws. If you have a wing access panel with 50 bolts in it, it is unusual to remove all of them without difficulty. There is always one or two that are too tight, or have damaged heads, then you need to drill them out. I'm lucky. I work on the ramp nowadays, and don't do it often, but when I have to remove a big panel I know there will always be a problem.
Too many mechanics use power tools to fasten screws, which gives the next guy a problem.

I always use a torque wrench for engine mount bolts, and wheel nuts. But not much else.
I find it amazing nowadays how few bolts have secondary locking. You still see split pins used in some flying controls, and occasionally have to wirelock a bolt, but not often, except on engines, and bolts on wheel cover plates.(The B737 is a pain.)

I am British. To me a screw has a point on the end, and is usually used in wood. A bolt has a flat end and normally goes into a nut.


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 19, posted (4 years 8 months 6 days 8 hours ago) and read 8434 times:

Quoting fr8mech (Reply 17):
Now, to be sure you understand, the fastener does not go into the metal below the panel (like a stud in a wall), it has a receptacle, commonly a nutplate, that accepts the fastener. This is what the fastener is torqued against, along with the panel.

Addtionally, every nutplate I have ever seen are self locking. The nut portion is crimped making it slightly oval or triangular which adds in bolt retention.

And just as bolts have a specific torque. The nutplate has a running torque or a point where it should be replaced if the bolts can be installed to freely. As an example a 3/16" diameter bolt with 32 threads per inch (10/32) should be torqued to 30 to 35 inch pounds. The running torque for a 10/32 nutplate should be 10 to 12 inch pounds.


User currently offlinepropilot83 From United States of America, joined Jan 2001, 604 posts, RR: 0
Reply 20, posted (4 years 8 months 6 days 6 hours ago) and read 8380 times:

Quoting fr8mech (Reply 17):
Now, to be sure you understand, the fastener does not go into the metal below the panel (like a stud in a wall), it has a receptacle, commonly a nutplate, that accepts the fastener. This is what the fastener is torqued against, along with the panel.

Okay, so basically its like this then, when you install a screw into a wing panel, etc., inside that area where you install the screw, there is another bolt or something like an "anchor" to install the screw into to prevent damage like metal fatigue or cracks?? Just like for example, when you install an anchor into a wall and then install a screw into it?


User currently offlineHAWK21M From India, joined Jan 2001, 31712 posts, RR: 56
Reply 21, posted (4 years 8 months 6 days 5 hours ago) and read 8354 times:

Quoting Tristarsteve (Reply 18):
Too many mechanics use power tools to fasten screws, which gives the next guy a problem.

Its Important to think of the Removal when Attaching screws to a panel.The Bloke could be yourself.Do not use damaged head screws & if possible use a light spot of grease especially if installation is done during rain.It helps in preventing corrosion & getting tight.

regds
MEL.



Think of the brighter side!
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 22, posted (4 years 8 months 6 days 5 hours ago) and read 8354 times:

Quoting propilot83 (Reply 16):
So I guess this answers my question then, when you install a screw into any part of an aircraft, it does not lock into something else, you have to tighten it until it gets real tight????

It locks into a threaded receiver...usually a nutplate, occasionally an embedded nut.

Quoting propilot83 (Reply 16):
This is no different than using screws around your house then, like causing cracks around a screw while tightening it too much around walls, and other metals???

Correct. If you overtighten an aircraft screw you can damage the structure, just like in other applications. However, aviation metals are very tough and fracture resistant...the most likely result of overtorquing is a stripped head and great difficulty removing the fastener later.

Quoting propilot83 (Reply 16):
If this is true, then its surprising, because an airplane expands and contracts like a balloon every time it takes-off and lands, the airplane goes through metal fatigue.

Screws and bolts don't really contribute to metal fatigue because the clamped material is in compression. You can only get fatigue cracks when you go into tension. The *holes* you make for screws and bolts can be huge fatigue sources (stress concentration around the holes), but that's designed for in both how you handle hole spacing and size, and how you prepare the hole (e.g. cold working).

Quoting propilot83 (Reply 20):
Okay, so basically its like this then, when you install a screw into a wing panel, etc., inside that area where you install the screw, there is another bolt or something like an "anchor" to install the screw into to prevent damage like metal fatigue or cracks??

There is an "anchor" (the nutplate or embedded nut). It's not there to prevent damage like metal fatigue or cracks, it's there to provide the screw something to thread into. Fatigue/crack resistance is built into the design of the thing you're screwing through.

Quoting propilot83 (Reply 20):
Just like for example, when you install an anchor into a wall and then install a screw into it?

Basically, yes.

Tom.


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 23, posted (4 years 8 months 6 days 4 hours ago) and read 8332 times:

Quoting propilot83 (Reply 20):
Okay, so basically its like this then, when you install a screw into a wing panel, etc., inside that area where you install the screw, there is another bolt or something like an "anchor" to install the screw into to prevent damage like metal fatigue or cracks?? Just like for example, when you install an anchor into a wall and then install a screw into it?

No. There is a hole through all the parts with a nutpate on the bottom side of the lowest part. The bolt passes through all the parts into the nutplate. The bolt is turned until the proper torque is reached.

Simple as that. Nothing but panel, sub-structure, nutplate and bolt.

Below is how flush rivets can be installed. A bolt would be the same, with the rivet the rivet's manufactured head and its shank being the bolt and the rivet shop head being the nutplate.





User currently offlinepropilot83 From United States of America, joined Jan 2001, 604 posts, RR: 0
Reply 24, posted (4 years 8 months 6 days 2 hours ago) and read 8281 times:

Thanks guys for answering my question, mostly to you tdscanuck. I know this question was very sophisticated and complex, however the answers were as well, but I believe I've figured it out now.

25 Post contains images soon7x7 : Get ready for a picture storm on fasteners, I just happened to have a bunch sitting on my desk...The first overview shot will help you to scale the la
26 Post contains images soon7x7 : Crap...the overview image didn't load...here you go... Image "E" are stainless steel washers that usually find their way onto countersunk phillips scr
27 web500sjc : How many bolts hold on a 777 engine
28 soon7x7 : Can't find the answer...It's sort of a trick question as the engine has anti sway yokes which technically add to the number of mounting hardware but
29 Tristarsteve : Sorry don't know either, but a RR RB211 has eight bolts. There are four on the fwd mount, and four on the aft mount. They are critical because they a
30 soon7x7 : Wasn't the RB211 an exceptionally heavy engine for its size, something to do with three shaft configuration?
31 474218 : The RB-211 QEC depending on the model weighs between 12,900 and 13,700 lbs. This weight includes all cowlings, ducting and thrust reverser. The CF-6
Top Of Page
Forum Index

Reply To This Topic Fasteners, Screws, & Bolts
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
Aircraft Fasteners - Update posted Thu Nov 9 2006 13:48:52 by HAWK21M
Engine Mount Bolts DC10. posted Wed Oct 26 2005 12:35:12 by HAWK21M
Replacement Of H-11 Bolts By Inconel 718 Bolts posted Fri Jun 17 2005 11:06:40 by HAWK21M
Explosive Bolts On 747 Engine Pylon posted Sat Dec 6 2003 21:51:44 by GrandTheftAero
"Use Correct Length Fasteners" posted Fri Oct 27 2006 22:25:48 by Andz
Triwing Screws posted Thu Feb 22 2001 23:24:09 by Avt007
Engine Mount Bolts posted Mon May 22 2000 18:54:36 by HP-873
Replacement Of H-11 Bolts By Inconel 718 Bolts posted Fri Jun 17 2005 11:06:40 by HAWK21M
Explosive Bolts On 747 Engine Pylon posted Sat Dec 6 2003 21:51:44 by GrandTheftAero
"Use Correct Length Fasteners" posted Fri Oct 27 2006 22:25:48 by Andz
Triwing Screws posted Thu Feb 22 2001 23:24:09 by Avt007
Engine Mount Bolts posted Mon May 22 2000 18:54:36 by HP-873

Sponsor Message:
Printer friendly format