Fasteners used in Formula 1

[riff_raff]

This is totally false in every way. Even with self lock fasteners they still use safety wire. Although not in the way that is shown in the picture that allows one screw to back out so much. Next time you go on a commercial flight look for an aircraft that has one of the engine cowlings open. You'll see tons of safety wired nuts and bolts in there. On the Turbomeca Arriel 2s2 and 1s1 engines that we operate in some of our helicopters some of the only critical components that aren't safety wired are the magnetic plugs in the oil system that pick up any metal shavings that happen to come off in the engine. These plugs have a safety feature that when pulled out self seals up the hole so even if one fell out in flight it wouldn't leak.

trinidefender-

I have worked as a mechanical systems engineer in the US aerospace industry for over 25 years. And on every system design I have worked on for most of that time, including commercial and military aircraft structures, commercial aircraft engines, manned space vehicles, and even a helicopter transmission designed to use a Turbomeca engine, we always made an effort to avoid using lockwire to secure fastensers. Lockwire would never be acceptable for use on high-speed rotating assemblies since it would create dynamic balance problems. Lockwire is also avoided for securing fasteners inside of mechanical systems, since there is usually metallic debris created when the lockwire is cut.

In the aircraft world, there are regulations requiring specific levels of fastener locking. Most fasteners require two independent forms of locking. The most common methods used are installed preload and a deformed thread device. The magnetic chip detector devices you describe are indeed now designed so that they do not require safety wiring. They use a push-turn bayonet type connection, and they also now have a dry-break valve that prevents oil leaking out when they are removed. This arrangement provides the necessary level of fault tolerance required without the hassle of lockwire.

On most aircraft, there a few flight critical fastener installations that require dual fault tolerance. But I have rarely seen even these fasteners use lockwire. More often they use something like self-locking castellated nuts and cotter pins.

[Lycoming]

What's the advantage of a castle nut + cotter pin over safety wire? I can't think of any major ones off the top of my head.

[braddock]

This is totally false in every way. Even with self lock fasteners they still use safety wire. Although not in the way that is shown in the picture that allows one screw to back out so much. Next time you go on a commercial flight look for an aircraft that has one of the engine cowlings open. You'll see tons of safety wired nuts and bolts in there. On the Turbomeca Arriel 2s2 and 1s1 engines that we operate in some of our helicopters some of the only critical components that aren't safety wired are the magnetic plugs in the oil system that pick up any metal shavings that happen to come off in the engine. These plugs have a safety feature that when pulled out self seals up the hole so even if one fell out in flight it wouldn't leak.

trinidefender-

I have worked as a mechanical systems engineer in the US aerospace industry for over 25 years. And on every system design I have worked on for most of that time, including commercial and military aircraft structures, commercial aircraft engines, manned space vehicles, and even a helicopter transmission designed to use a Turbomeca engine, we always made an effort to avoid using lockwire to secure fastensers. Lockwire would never be acceptable for use on high-speed rotating assemblies since it would create dynamic balance problems. Lockwire is also avoided for securing fasteners inside of mechanical systems, since there is usually metallic debris created when the lockwire is cut.

In the aircraft world, there are regulations requiring specific levels of fastener locking. Most fasteners require two independent forms of locking. The most common methods used are installed preload and a deformed thread device. The magnetic chip detector devices you describe are indeed now designed so that they do not require safety wiring. They use a push-turn bayonet type connection, and they also now have a dry-break valve that prevents oil leaking out when they are removed. This arrangement provides the necessary level of fault tolerance required without the hassle of lockwire.

On most aircraft, there a few flight critical fastener installations that require dual fault tolerance. But I have rarely seen even these fasteners use lockwire. More often they use something like self-locking castellated nuts and cotter pins.

Preload and deformed fasteners are the most common methods of locking on engines/accessories from what I have seen (for the most part, my experience is on Rolls-Royce engines). Lock washers are also quite common. I wouldn't go as far as saying that lockwire is rare though. A great deal of airframe fasteners will still use lockwire, particularly in blind installations.

[braddock]

What's the advantage of a castle nut + cotter pin over safety wire? I can't think of any major ones off the top of my head.

Horses for courses. Rarely, if ever, will they suit the same application.

[simieski]

What's the advantage of a castle nut + cotter pin over safety wire? I can't think of any major ones off the top of my head.

I believe the cotter pin provides more failure resistance. Lockwire is pretty easy to break, whereas you will struggle to loosen off a nut and bolt with a cotter pin installed. In my experience it is uncommon for larger bolts to be safetied with lockwire, they are either split pinned will have a retaining plate. The retaining plates themselves might then be safetied with lockwire.

[braddock]

What's the advantage of a castle nut + cotter pin over safety wire? I can't think of any major ones off the top of my head.

I believe the cotter pin provides more failure resistance. Lockwire is pretty easy to break, whereas you will struggle to loosen off a nut and bolt with a cotter pin installed. In my experience it is uncommon for larger bolts to be safetied with lockwire, they are either split pinned will have a retaining plate. The retaining plates themselves might then be safetied with lockwire.

Consider what each achieves. A cotter pin/castle nut combination will secure a bolt/stud and a nut together, for example in a mechanical linkage. Lockwire will secure components together; be they any combination of screws, bolts, nuts, jamnuts, AN fittings, cannon plugs, filters, plugs or the airframe/engine/component itself.

When fitting a castle nut and cotter pin, the fasteners are torqued to spec and then the nut is backed off to align the castle nut with the hole in the shank of the bolt/stud to allow fitment of the cotter pin. This allows movement in a linkage, but is unsuitable where a specific clamping force is required or where a nut does not exist. The bolt/nut combination will allow movement, but not movement relative to each other.

Ignoring substitution of cotter pins for lockwire in a castle nut application (perhaps where access is poor); when lockwiring, a fastener or other component is torqued to spec and then secured in that position with lockwire - tending to tighten. This serves to maintain preload and serves as a secondary locking device. In mechanical linkages, however, this could lead to binding or damage to bearings.

A bolt and nut both drilled for lockwire will either have to be lockwired to each other, or to other components separately for lockwire to be effective. Although there is no real reason not to do this, there are far simpler secondary locking devices available; such as nylock or deformed nuts.

Lockwire done to spec will not provide any diminished failure resistance. The only broken lockwire I have seen recently was as a result of repeated, direct (9" from the ground) exposure to landings on unprepared runways.

[trinidefender]

This is totally false in every way. Even with self lock fasteners they still use safety wire. Although not in the way that is shown in the picture that allows one screw to back out so much. Next time you go on a commercial flight look for an aircraft that has one of the engine cowlings open. You'll see tons of safety wired nuts and bolts in there. On the Turbomeca Arriel 2s2 and 1s1 engines that we operate in some of our helicopters some of the only critical components that aren't safety wired are the magnetic plugs in the oil system that pick up any metal shavings that happen to come off in the engine. These plugs have a safety feature that when pulled out self seals up the hole so even if one fell out in flight it wouldn't leak.

trinidefender-

I have worked as a mechanical systems engineer in the US aerospace industry for over 25 years. And on every system design I have worked on for most of that time, including commercial and military aircraft structures, commercial aircraft engines, manned space vehicles, and even a helicopter transmission designed to use a Turbomeca engine, we always made an effort to avoid using lockwire to secure fastensers. Lockwire would never be acceptable for use on high-speed rotating assemblies since it would create dynamic balance problems. Lockwire is also avoided for securing fasteners inside of mechanical systems, since there is usually metallic debris created when the lockwire is cut.

In the aircraft world, there are regulations requiring specific levels of fastener locking. Most fasteners require two independent forms of locking. The most common methods used are installed preload and a deformed thread device. The magnetic chip detector devices you describe are indeed now designed so that they do not require safety wiring. They use a push-turn bayonet type connection, and they also now have a dry-break valve that prevents oil leaking out when they are removed. This arrangement provides the necessary level of fault tolerance required without the hassle of lockwire.

On most aircraft, there a few flight critical fastener installations that require dual fault tolerance. But I have rarely seen even these fasteners use lockwire. More often they use something like self-locking castellated nuts and cotter pins.

Well on the entirety of the gearbox bolts going around are lockwired, the rotor mast has many bolts with the same. You mistake me. Not in the engine internals of course there wouldn't be lock wire but for many applications where there is a circle of bolts holding on a plate or what have you they will still be lock wired. For sure the overall use has decreased somewhat but looking around our aircraft I wouldn't say that it is outdated. Still pretty common to see here

[flyboy2160]

But when's the last time any of you guys remember seeing safety wire on a modern F1 car? Maybe in an old picture from the 60s? Given how often the cars are disassembled, checked, adjusted, and reassembled, safety wire would seem to be prohibitive.

[Lycoming]

But when's the last time any of you guys remember seeing safety wire on a modern F1 car? Maybe in an old picture from the 60s? Given how often the cars are disassembled, checked, adjusted, and reassembled, safety wire would seem to be prohibitive.

I want to say 80's, but this is true.

[PlatinumZealot]

I am seeing more common use of hollowed out bolt caps. Think hex/torx bolts with the cap hollowed out like an Allen bolt.

[flyboy2160]

I am seeing more common use of hollowed out bolt caps. Think hex/torx bolts with the cap hollowed out like an Allen bolt.

That dished out hollow is a standard design feature of NAS close tolerance bolts. The shank diameters are held to much tighter tolerances than standard bolts.

[riff_raff]

What's the advantage of a castle nut + cotter pin over safety wire? I can't think of any major ones off the top of my head.

For a bolt loaded in double shear (like a clevis attachment) the self-locking castle nut and cotter pin will still permit the bolt to rotate while providing the required level of fault tolerance for the thread locking function.

[riff_raff]

Well on the entirety of the gearbox bolts going around are lockwired, the rotor mast has many bolts with the same. You mistake me. Not in the engine internals of course there wouldn't be lock wire but for many applications where there is a circle of bolts holding on a plate or what have you they will still be lock wired. For sure the overall use has decreased somewhat but looking around our aircraft I wouldn't say that it is outdated. Still pretty common to see here

trinidefender-

Here is a picture of the AH-64 MRGB that is capable of mating with the Turbomeca RTM322 engine. Can't see any lockwire being used on the gearbox fasteners.