Design for accessibility: Minimal Torque swept

[JasminTH]

Hi Group

I have a question on Torque wrenches.
I'm wondering on the minimal acceptable torque angle in designing of complex product (in my case, a business aircraft)

I know that a 36points torque wrench clicks every 10 degres, but there is a certain travel (about 5-8deg) before it catches some torque to apply on the fastener
Is there a minimal angle for a proper torque to be applied?
If I'm stuck between two structures that gives me only 11 deg (for example), will I be able to torque my fastener by applying 1deg at a time until final torque?

Also, we design for fast access and ease, so we don't want the mechanics spending a lot of time on the fastener, especially if there is few of them

Thanks for the support!

 

[rb1957]

"applying 1deg at a time until final torque" isn't compatable with "fast access and ease, so we don't want the mechanics spending a lot of time on the fastener".

although if there are only a few of them, then the process time becomes less important.

clearly your design has painted itself into a corner, and something's going to have to give.

Why torque the fastener ? significant tension load ??
How often is this equipment removed ?
Access to both ends of the bolt are highly restricted ?

Quando Omni Flunkus Moritati

 

[JasminTH]

We're looking to define an internal standard for minimal torque swept for accessibility, which means we want to know what's «feasible» and what's «optimal».
It's for the maintenance context that this criteria is important, since you'll be stuck with several systems aroung you fastener and you don't want to remove anything to get to a component (example: bolted-on avionic controller unit).

In the business aircraft designs, you have to cope with restrained space, which makes important to know what is the gap between feasible and optimal.
We have some design requirement saying that an LRU (line replacement unit) which is suppose to be changed only once in the aircraft lifetime, but requires an access in 20min (Includes: open access, change, test, close)

We have best practices for torque application and we want to make an aircraft as accessible as possible for the maintenance. We want to make intelligent designs with a customer oriented focus, and this accessiblity criteria is important for us

For example, if we can say that having 30deg swept is good for accessibility and we're challenged for stress issues of this 30deg cutout, can we go down to x degres?

 

[rb1957]

first it's hard to write a minimum standard, because of the many conflicting requirements.

you could say typical practice is 30deg min, less acceptable with Chief Engineer buy-off. this could be a sentence added to the front of your standards ... "standards define a typical minimum acceptable for design; may be deviated from with Chief Engineer/Project Engineer buy-off."

you could say one side of the fastener must have 30deg min.

personally i'd say avoided torque requirements (usually only requried on tension bolts (for structural accplications: for system applications obviously different).

Quando Omni Flunkus Moritati

 

[JasminTH]

Thanks for the confirmation
30 degres is actually the informal minimum torque swept we use.
Your formullation is actually interesting since, at first in the design, we should aim for this 30 degres, then analyze the roadblocks of other departments can be resolved
This has to take account of the Mean Time before failure, Development stage of the aircraft, posture for the task, etc.

And yes you're right, a minimum standard statement cannot exist, since at some point other issues are more important than tool swept
But with your wording make sense: "standards define a typical minimum acceptable for design; may be deviated from with Chief Engineer/Project Engineer buy-off."