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rowlandcarson(at)gmail.co
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 Posted: Fri Feb 24, 2017 12:18 pm Post subject: fastening duct to firewall/footwell |
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The sides of the cooling duct (CD2 & CD3) are attached to the inboard faces of the footwells by AN3-5A bolts. The manual calls for the corresponding anchor nuts to be installed in reverse to make them nearly flush with the surface inside the cockpit.
I can’t see any reason why they need to be flush - they will be in the area beyond the rudder pedals and quite low down, so should not interfere with anything. I guess if they are fitted the normal way round, longer bolts will be needed.
Anyone know of a good reason to stick to the reverse installation of the anchor nuts? It seems less bother to fit them the normal way round, but I thought I’d check that I’m not missing a really stupid gotcha by ignoring the manual on this point!
in friendship
Rowland
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alan.twigg775(at)gmail.co
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| Posted: Fri Feb 24, 2017 1:45 pm Post subject: fastening duct to firewall/footwell |
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Since Rowland and I are at the same point, I would also like to know.
Alan
Sent from my iPad
| Quote: | On 24 Feb 2017, at 20:17, Rowland Carson <rowlandcarson(at)gmail.com> wrote:
The sides of the cooling duct (CD2 & CD3) are attached to the inboard faces of the footwells by AN3-5A bolts. The manual calls for the corresponding anchor nuts to be installed in reverse to make them nearly flush with the surface inside the cockpit.
I can’t see any reason why they need to be flush - they will be in the area beyond the rudder pedals and quite low down, so should not interfere with anything. I guess if they are fitted the normal way round, longer bolts will be needed.
Anyone know of a good reason to stick to the reverse installation of the anchor nuts? It seems less bother to fit them the normal way round, but I thought I’d check that I’m not missing a really stupid gotcha by ignoring the manual on this point!
in friendship
Rowland
| Rowland Carson ... that's Rowland with a 'w' ...
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JonathanMilbank
Joined: 14 Apr 2012
Posts: 395
Location: Aberdeen area
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| Posted: Fri Feb 24, 2017 2:04 pm Post subject: Re: fastening duct to firewall/footwell |
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Hi Rowland,
Having just done the same task a few weeks ago, I'll attempt an explanation. Forgive me if some of my explanation is something you already know and understand.
The rudder pedals are secured to a little plywood floor bonded into each foot-well. Underneath this floor is a "blind" void which has a flat vertical wall as part of each foot-well on the inboard side. It is these walls to which my captive nuts are attached and consequently it's impossible to secure captive nuts in the normal way, unless the captive nuts were to be installed before the floor got bonded in.
Therefore once it has been decided where to position each captive nut, they should only be secured as described in the XS engine installation manual. Hopefully the walls of the duct will fit snugly in contact with the nuts, but mine didn't. There was a small gap of 3 or so millimetres on each side. Because I didn't want my duct walls to be tensioned outwards with the AN3-5A bolts and therefore constantly straining to pull out the captive nuts which are only held by their little rivets into the foot-well vertical sides, I riveted a penny washer to each side of the duct to act as spacers.
The captive nuts should be installed as described in the manual for another reason, which is to cope better with shear loads at least until the bolts fastening the duct to its brackets can take the strain off the captive nuts. If you found that there was enough of a gap on each side of the duct to allow orienting the captive nuts so that they weren't embedded in the foot-well sides, then they would probably cope poorly with shear loads and would quite easily tear out their rivets.
Or so it seems to me.
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dpark748(at)icloud.com
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| Posted: Fri Feb 24, 2017 2:17 pm Post subject: fastening duct to firewall/footwell |
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If the installed fixed nut became loose then the fixed nut could be installed higher up in the footwell conventionally attached to a washer bonded to the inner footwell wall out of the way of the rudder pedals.
A bracket could be attached to the cooling duct to accomodate the new position?
Any comments???
Dave Park
| Quote: | On 24 Feb 2017, at 22:04, jonathanmilbank <jdmilbank(at)yahoo.co.uk> wrote:
Hi Rowland,
Having just done the same task a few weeks ago, I'll attempt an explanation. Forgive me if some of my explanation is something you already know and understand.
The rudder pedals are secured to a little plywood floor bonded into each foot-well. Underneath this floor is a "blind" void which has a flat vertical wall as part of each foot-well on the inboard side. It is these walls to which my captive nuts are attached and consequently it's impossible to secure captive nuts in the normal way, unless the captive nuts were to be installed before the floor got bonded in.
Therefore once it has been decided where to position each captive nut, they should only be secured as described in the XS engine installation manual. Hopefully the walls of the duct will fit snugly in contact with the nuts, but mine didn't. There was a small gap of 3 or so millimetres on each side. Because I didn't want my duct walls to be tensioned outwards with the AN3-5A bolts and therefore constantly straining to pull out the captive nuts which are only held by their little rivets into the foot-well vertical sides, I riveted a penny washer to each side of the duct to act as spacers.
The captive nuts should be installed as described in the manual for another reason, which is to cope better with shear loads at least until the bolts fastening the duct to its brackets can take the strain off the captive nuts. If you found that there was enough of a gap on each side of the duct to allow orienting the captive nuts so that they weren't embedded in the foot-well sides, then they would probably cope poorly with shear loads and would quite easily tear out their rivets.
Or so it seems to me.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=466601#466601
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JonathanMilbank
Joined: 14 Apr 2012
Posts: 395
Location: Aberdeen area
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| Posted: Fri Feb 24, 2017 2:42 pm Post subject: Re: fastening duct to firewall/footwell |
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The way I see this matter is that the captive nuts with their AN3-5A bolts don't do very much load bearing after the duct gets secured to the brackets affixed to the front faces of the foot-wells. However quoting Nev Eyre, the captive nuts and their bolts are there to help minimise the tendency of the duct to "nod".
This seems all the more a good reason to install them as per the manual in the first place and to mount them in the most effective way (as per the manual) to resist shear loads effectively.
Mounting them higher up as you describe would probably work depending on the new position, but why have that bother when all it takes is a little care to install them correctly in the first place?
If the front of the duct rests on the top of the intake "gob" in Nev's excellent cowls, then the "nod" consideration is pretty much dealt with.
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rowlandcarson(at)gmail.co
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| Posted: Fri Feb 24, 2017 2:56 pm Post subject: fastening duct to firewall/footwell |
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On 2017-02-24, at 22:16, david park <dpark748(at)icloud.com> wrote:
| Quote: |
If the installed fixed nut became loose then the fixed nut could be installed higher up in the footwell conventionally attached to a washer bonded to the inner footwell wall out of the way of the rudder pedals.
A bracket could be attached to the cooling duct to accomodate the new position?
|
Dave - for some reason I did not receive the posting from Jonathan to which you are replying (yes, I have checked my gmail and local spam folders).
His description reveals that I have not understood the manual correctly.
I thought the anchor nut was to be fitted on the _cockpit_ face of the footwell inboard side, above the heel support. I see now it is intended to be fitted lower down (and thus probably further aft to give a longer moment arm from the CD4/CD5 brackets) but on the _tunnel_ face of the footwell inboard side (because there is no access to the cockpit side at that level). This of course explains why it has to be flush-fitted.
It never occurred to me that it was only held in by the rivets, so could not take any real load in tension - and its ability to take shear load depends on a good fit in the recess, as well as those rivets.
Thanks very much to Jonathan for his good explanation, and to Dave for responding to it, or I’d never have seen it!
in friendship
Rowland
| Rowland Carson ... that's Rowland with a 'w' ...
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dpark748(at)icloud.com
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| Posted: Fri Feb 24, 2017 3:24 pm Post subject: fastening duct to firewall/footwell |
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During build do it as in manual. I was only suggesting a possible maybe better repair if the imbedded anchor nut fails. It will not take much torque when tightening bolt? Make sure bolt thread does not reach unthreaded part when installing.
Dave Park
| Quote: | On 24 Feb 2017, at 22:55, Rowland Carson <rowlandcarson(at)gmail.com> wrote:
> On 2017-02-24, at 22:16, david park <dpark748(at)icloud.com> wrote:
>
>
>
> If the installed fixed nut became loose then the fixed nut could be installed higher up in the footwell conventionally attached to a washer bonded to the inner footwell wall out of the way of the rudder pedals.
> A bracket could be attached to the cooling duct to accomodate the new position?
Dave - for some reason I did not receive the posting from Jonathan to which you are replying (yes, I have checked my gmail and local spam folders).
His description reveals that I have not understood the manual correctly.
I thought the anchor nut was to be fitted on the _cockpit_ face of the footwell inboard side, above the heel support. I see now it is intended to be fitted lower down (and thus probably further aft to give a longer moment arm from the CD4/CD5 brackets) but on the _tunnel_ face of the footwell inboard side (because there is no access to the cockpit side at that level). This of course explains why it has to be flush-fitted.
It never occurred to me that it was only held in by the rivets, so could not take any real load in tension - and its ability to take shear load depends on a good fit in the recess, as well as those rivets.
Thanks very much to Jonathan for his good explanation, and to Dave for responding to it, or I’d never have seen it!
in friendship
Rowland
| Rowland Carson ... that's Rowland with a 'w' ...
| <rowlandcarson(at)gmail.com> http://www.rowlandcarson.org.uk
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JonathanMilbank
Joined: 14 Apr 2012
Posts: 395
Location: Aberdeen area
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| Posted: Fri Feb 24, 2017 3:43 pm Post subject: Re: fastening duct to firewall/footwell |
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You have a good point, which is why I didn't use bolts but rather screws of the type which hold my spinner to its backing plate. They're threaded all the way up to the head and tightening with a screwdriver minimises the possibility of over-torqueing. After all, they really are needed only to tolerate loads in shear and shouldn't be tensioned out by the duct sidewalls.
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grahamsingleton(at)btinte
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| Posted: Sat Feb 25, 2017 3:10 am Post subject: fastening duct to firewall/footwell |
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Rowland
Aren't the anchor nuts fitted on the outside surface of the footwell? In several positions it must be nearly impossible to fit the anchor nuts in the normal way.
Graham
On Friday, 24 February 2017, 23:25, david park <dpark748(at)icloud.com> wrote:
--> Europa-List message posted by: david park <dpark748(at)icloud.com (dpark748(at)icloud.com)>
During build do it as in manual. I was only suggesting a possible maybe better repair if the imbedded anchor nut fails. It will not take much torque when tightening bolt? Make sure bolt thread does not reach unthreaded part when installing.
Dave Park
| Quote: | On 24 Feb 2017, at 22:55, Rowland Carson <rowlandcarson(at)gmail.com (rowlandcarson(at)gmail.com)> wrote:
--> Europa-List message posted by: Rowland Carson <rowlandcarson(at)gmail.com (rowlandcarson(at)gmail.com)>
> On 2017-02-24, at 22:16, david park <dpark748(at)icloud.com (dpark748(at)icloud.com)> wrote:
>
> --> Europa-List message posted by: david park <dpark748(at)icloud.com (dpark748(at)icloud.com)>
>
> If the installed fixed nut became loose then the fixed nut could be installed higher up in the footwell conventionally attached to a washer bonded to the inner footwell wall out of the way of the rudder pedals.
> A bracket could be attached to the cooling duct to accomodate the new position?
Dave - for some reason I did not receive the posting from Jonathan to which you are replying (yes, I have checked my gmail and local spam folders).
His description reveals that I have not understood the manual correctly.
I thought the anchor nut was to be fitted on the _cockpit_ face of the footwell inboard side, above the heel support. I see now it is intended to be fitted lower down (and thus probably further aft to give a longer moment arm from the CD4/CD5 brackets) but on the _tunnel_ face of the footwell inboard side (because there is no access to the cockpit side at that level). This of course explains why it has to be flush-fitted.
It never occurred to me that it was only held in by the rivets, so could not take any real load in tension - and its ability to take shear load depends on a good fit in the recess, as well as those rivets.
Thanks very much to Jonathan for his good explanation, and to Dave for responding to it, or I’d never have seen it!
in friendship
Rowland
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