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Dzus spring loaded cowl fastenings for a savannah cowl


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Savannah supply homegrown aluminium fasteners that can bind and spread.
I replaced all mine with steel Dzus from Aircraft Spruce:

 
Model                           Cat #                   Quantity
121J-540-Z3C             AJ5-40                    13
121J-545-Z3C             AJ5-45                    3
 
That includes a couple of spares, though I have learnt to be really careful taking them out when on grass.
 
 
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11 minutes ago, facthunter said:

You shouldn't work on planes when you are ON grass. Nev

It's also challenging for those of us with more than the usual pair of thumbs, Nev.....)

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Thanks for info.  My mate chose to place cowl on outside of fuselage; so a little harder.  The side top to lower is all good; but the corner overlap needs longer than the .50 size; needs an extra 3mm so needs the .625 so he will get some .650 size  (2 needed ex Adelaide so 10 to 14 days delivery)   

 

I suggest he lengthens to of the .40 size, drill tap thread set a counter sunk metal thread into the fastening then cut through and add a lengthening collar of 3mm plus the cut off wheel thickness and loctite together.  Will allow trial fit while waiting for new ones.  I had things on so up to him to decide.

 

If I fitted one again to outside I would fit the top piece; then cut the lower piece down its middle then mount to front fuse skin side and fit side top to lower dzus fastenings and resin/ mat the lower half join gap.  (No worries to do this perfect and whit correct resin and mat layup.

 

Thanks for info and was just trying to get a couple of correct lenght Dzus by end of week if possible.

 

Cheers.

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PS for anyone building: due to variations in cowl thickness, some adjustment of the individual fasteners will probably be required. I did this by  reworking (okay, bending) the springs, and in some cases by packing under the spring where it is attached to the inner cowl.
As with all cowl fitting, this really needs to be done before the paint.

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1 minute ago, IBob said:

PS for anyone building: due to variations in cowl thickness, some adjustment of the individual fasteners will probably be required. I did this by  reworking (okay, bending) the springs, and in some cases by packing under the spring where it is attached to the inner cowl.
As with all cowl fitting, this really needs to be done before the paint.

Plus take the time needed.

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Blueadventures, my cowl is inside and I would do the same again.

The purists would say it is less streamlined, but this is not a streamlined aircraft and I can't see the overlap making any difference.
I also like the idea that my cowling is more likely to stay with the aircraft, tucked in as it is......)

My understanding is that it used to be a struggle to fit some cowls this way, but for me it went very easily. Maybe this is a feature of the XL and S, probably also it is due to the corrugated steel hoses that allow very tight smooth bends without flattening.
 

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Any chance someone would have two complete Dzus fasteners of the ' smallest size '  out there, to join two thin alloy parts. ( not structural ).

I,m using two 3/32" nuts & bolts at the moment.

The sizes have me bamboozled

spacesailor

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1 hour ago, spacesailor said:

Any chance someone would have two complete Dzus fasteners of the ' smallest size '  out there, to join two thin alloy parts. ( not structural ).

I,m using two 3/32" nuts & bolts at the moment.

The sizes have me bamboozled

spacesailor

Camlocs are worth considering for the job, they are my choice.

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Blueadventures, 

I checked them out !,  ( camlocs )

But

The same thing aplies.  Even in their literature it says ( can,t find that site now, so as l remember it )

" we don,t use size but serial numbers ".

So to fasten a ten-thou" inspection door closed l use a couple of nuts & bolts.  And some are in French ! The rest American.

spacesailor

Edited by spacesailor
Missed word
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Give us a clearer idea of what you are trying to do Spacesailor.
My aircraftt has Dzus for the fg cowlings (higher load, greater weight) and camlocs for oil inspection and belly hatches.
Different fasteners will be more appropriate in different applications.
In all cases there will be lookup tables identifying the sizes and how they are measured. It's just you sometimes have to do your own homework finding the appropriate table. And you have to know how they are measured, or you're just guessing.

I would guess Aircraft Spruce only take orders for part numbers to avoid arguments with folk who guessed, then didn't get what they wanted.

 

Camloc info is here: scroll to the bottom and it says how to measure for them:
https://www.aircraftspruce.com/catalog/hapages/camloc4002.php

It doesn't look as if they carry the shortest size.

 

If it helps, the shortest (slotted head, undercut) Dzus is the AJ3-25 for 3/16" diameter or AJ4-25 for 1/4" diamrter.
(So the first part of the number is diameter in 16ths and the last part is the length in decimal....gotta love this stuff!)
They have a length of .25 or 1/4".
If they are still too long (or if you have to buy the next size up which is AJ3-30 or AJ4-30) all you do is pack and/or rework the spring they get hold of.
 

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As the '  fuelcap cover is 0.8mm & the base is the same !. ( just went out & measured it  ).

Then 2 mm thickness of material, is a bit small. The reason, l asked for a couple of the smallest, will give me an idea how Big the smallest is.

There are bigger RC models than the HummelBird,  And with bigger engines.

spacesailor

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22 minutes ago, spacesailor said:

As the '  fuelcap cover is 0.8mm & the base is the same !. ( just went out & measured it  ).

Then 2 mm thickness of material, is a bit small. The reason, l asked for a couple of the smallest, will give me an idea how Big the smallest is.

There are bigger RC models than the HummelBird,  And with bigger engines.

spacesailor

Camloc  -4 will fit and may be even a -3  (I'd say a -3 will do the job  also can get with either a screw driver slot or a wing nut type piece attached.)  I also place a thin nylon washer under mine to protect the fibreglass.

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It does sound like the Camloc would be your better option. That's what I have on my oil inspection hatch, which is opened every preflight. I think they are better suited to that sort of constant use.

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1 hour ago, IBob said:

It does sound like the Camloc would be your better option. That's what I have on my oil inspection hatch, which is opened every preflight. I think they are better suited to that sort of constant use.

Agree Bob; thinking its a small hatch so a small lock like camloc would suit and its receptacle is small in size as well.

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Jabs magnetic trick should stick !.

BUT

The compass is much closer  on a HumelBird, I,m saying 5 or 6 inches. After all the length is 14' ( feet ).

I guess  l,ll have to keep screwing away with thoe two 3/32 bolts. 

It,s just the thought of dropping one  ( or both  ) in the airfield grass !, never to be found again.

spacesailor

 

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