NAS1097 vs MS20426
NAS1097 vs MS20426
(OP)
Hello,
can these be substituted for each other? ie. could MS20426 be installed in lieu of NAS1097 and vice versa?
can these be substituted for each other? ie. could MS20426 be installed in lieu of NAS1097 and vice versa?





RE: NAS1097 vs MS20426
The Nas1097 rivet has a smaller head than the MS20426 for the same shank diameter.
So you could not put an Nas1097 rivet in a hole where an MS20426 has been.
B.E.
RE: NAS1097 vs MS20426
RE: NAS1097 vs MS20426
Steven Fahey, CET
RE: NAS1097 vs MS20426
debodine
RE: NAS1097 vs MS20426
For example a -3 426 is knife edged in 0.036 sheet. A -5 1097 is knife edged in that same sheet and carries more load. More load and a better fatigue life.
All that varies of course with sheet thickness, assembly methods, hole size, driven condition, and prep.
RE: NAS1097 vs MS20426
On the subject of knife edging... as a general rule how much (of the thickness) uncut material be left on sheet... by this i mean can you punch to, say, 80% material thickness to countersink the head???
RE: NAS1097 vs MS20426
The NAS1097AD fastener is used through out the Douglas DC9 Fuselage to attach the skins to most underlying structure due to the thickness of the skin (0.050"). Using their countersink charts for the NAS1097 and their minimum sheet thickness requirements the % for the 5/32" dia. is 58%, for 3/16" dia it is 63%, and for 1/4" dia it is 74%. All of the previous percentages leave the fastener head a little high and then would be shaved flush.
So it looks as though 67% would be a typically value for countersink depth to sheet thickness.
Regards
RE: NAS1097 vs MS20426
RE: NAS1097 vs MS20426
I'm not structures, and don't know how well the topic is covered, but it's the first place I look for generic guidelines.
RE: NAS1097 vs MS20426
theNAS1097AD is not even mentioned in AC 43 13 1B change 1 The only countersunk rivet mentioned is the MS20426.
Also I do not think there is any reference to percentages of metal thickness on countersinks in that repair data.you would have to look elswhere for that
B.E.
RE: NAS1097 vs MS20426
there is also a practical aspect, in that you need to some straight shank to allow some tolerance on installation.
btw, LZ4s in 0.04" skin, pretty typical constrcution are just outside this guide (0.029" CSK in 0.04" thick). my approach is to treat these as "transition" knife edge and add a fudge factor into the fatigue analysis (Kt = 1.5) to account for this.
RE: NAS1097 vs MS20426
Douglas uses 70% csk depth. It seems that it is more dictated by specific program philosophies. One half dozen...
RE: NAS1097 vs MS20426
I would be careful of shaving NAS1097 heads, it's been awhile since I worked a Douglas aircraft (and I miss it!!), however, I thought there was a note in the SRM that restricted shaving NAS1097 heads.
RE: NAS1097 vs MS20426
an obvious design aspect of using 1097s is their reduced tension capability. i know you're not going to be designing them to carry tension loads, but the issue may arise when you've used them in a thin gauge skin which then buckles (under shear and compression). off the top of my head i don't remember how NACA TN2661 calculates the tension loading on the rivets due to buckles forming, but i think you'll need tension allowables which are going to be hard to find (but they are pretty easy to generate).
regarding planedr's post (back on the 15th), i'd wouldn't put a 1097-5 in 0.036" skin, nor a 426-3, and i'd never describe either as "better fatigue" ... both are going to very limited in fatigue life and i think the 1097-5 with it's higher static allowable might beguile the designer into thinking things are ok. if i had to use a CSK rivet (in 0.036" sheeet, primary structure) i'd opt for a 1097-3, but i'd rather a 470-4.
RE: NAS1097 vs MS20426
As for the NAS1097 vs MS20426 I can say this much. The 1097 does exhibit a big improvement in fatigue life because of the slight rise in the center of the head. For a 3/16 diameter the 1097 has a basic head height of 0.046 (vs 0.073 for 20425) and an additional 0.008 crown in the center. This crown results in better over bucking of the rivet and in swelling. Lockheed developed their own improved version of the 1097 and named it LS10052. The improvement is that the crown extends across the entire head rather than just in the center. If you look up AIAA Paper No. 72-776 entitled "Structural Development of the L-1011" by D.J. Mackey and H. Simons you will see a comparison of joint fatigue lives. The curves presents fatigue life comparisons of the MS20426, NAS1097 and LS10052. The data presented is for DD6 rivets but I have seen the remainer of the data and it is pretty uniform even for standard sizes and non-ice box rivets. Basically, the 1097 shows about a 5 to 1 improvement over the 20426 and the LS10052 shows an additional 1.36 over the 1097. This type of data has been developed over decades and has formed the basis of many OEMs methods alas no one is left alive to remember where it comes from.
As for shaving heads, dont do it without testing.
Hope this helps.
James Burd
Avenger Aircraft and Services
RE: NAS1097 vs MS20426
You missed the point completely. That was 100% countersink!
In a given sheet assembly you can use a bigger rivet period. The prefered failure method in primary structure is bearing. For that you need a bigger rivet.
The deeper the countersink the more likely fatigue cracks are going to start at the inner surface along the straight shank of the fastener hole. The reduced head size of a 1097 provides greater inspection ability for the eliiptical crack formations in the future.
If you are in a position where your repair parts will buckle your repair is inadequate. If you must still use that thin a gauge you should be using 470's or Hi-Loks.
I would never go more then 67%. Boeing AR's will not accept 80% even with a gun to their head. Put in a countersink repair washer and then use a button head rivet. An already fatigued skin will crack out way to quickly. Better yet after inspecting the hole you need to o/s anyway just go button head.
RE: NAS1097 vs MS20426
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: NAS1097 vs MS20426
RE: NAS1097 vs MS20426
James Burd
Avenger Aircraft and Services
RE: NAS1097 vs MS20426
I used Boeing Engineering Liaison Manual, Page 40.2.1. I figured NAS1097 and BACR15CE are equivalent but I could only find BACR15CE allowables in double sheer on Page 40.2.2. Since the material for BACR15BB and BACR15CE are the same, I used the allowable values for BACR15BB! I don't think my values are correct though.
I would appreciate any help you could provide. I've gone the Fsu and Fbru way but I want to be certain what I'm doing is correct.
Thank you.
Damineh
RE: NAS1097 vs MS20426
for 1097AD i use the table in mil-hdbk 5 (or ar-mmpds-01) for 1097E and derate for shear strength.
RE: NAS1097 vs MS20426
RB1957, I checked the numbers, and the Grumman allowables are more conservative than de-rating the "E" allowable.
Steven Fahey, CET
RE: NAS1097 vs MS20426
Thank you.
Damineh
RE: NAS1097 vs MS20426
If you used BACR15BB rivet allowables you need to go back and reduce your numbers.