Tail feather Gussets

[scottiniowa]

Are you coping the aluminum at these areas? I would think this would weaken the ends of the aluminum sine they are not welded and the placement of the rivets at the ends would not help, would it be better to move them outward away from any coping. I'm just wondering since we are discussing this here.

a good point Joe.  Not often I would defer a question, but this one I will.  as you estimated, I have coped the ends. And this may/may not make your argument true. As inside with NO coped ends, would not have any leading or trailing edge support vs coped. That being said, your statement is also true.

To date, NO one (designer or builders)  has said, yeah or nah on this.  NON- Coped certainly would be easier...to make and draw.

Completely open on this.- depending on what is suggested with facts/theory this will slightly alter the look of the gusset by 1/2 the D of the tube. (larger) 
Scott

[joecnc2006]

I would vote for non coping the aluminum since we are using the gussets. easier build and a little less weight on the aluminum tubs although the larger gussets may negate this. 
There are two reason I look at it this way.
1. The fuselage is coped but they are welded no gussets.
2. The wing ribs are built with no coping but uses gussets to compensate the void area.

[liteflyt]

Scott, your A-5 drawing shows the tube ENDS protruding Into the joining tube...probably not a good idea....
suggest you redraw showing what you really mean.   Got my "cheaters" on now.....  ;^)

[joecnc2006]

Scott, your A-5 drawing shows the tube ENDS protruding Into the joining tube...probably not a good idea....
suggest you redraw showing what you really mean.   Got my "cheaters" on now.....  ;^)

As he mentioned before the tubes do not protrude into the adjacent tubes they are intended to be coped around them.

[scottiniowa]

Though it may appear through the use of Jpegs that a part extends into another, I can assure I don't have this done.  Most likely if I have ghosted a part to better show a internal view, it can often appear that the lower side of a coping is poking into  the exterior frame.  This is really true if you were looking at coped frames.

But, with recent talk, about doing the extra work for coped ribs and using gussets, the need for coping is probably nil. 

When I can get back to by guide, I will take the coping out of all alum ribs, re-space rivet edge clearance, which in turn will cause a reshaping of the actual gusset.  Certainly the case where one change makes 10 more.  I will stick with my three rivet rule, and if someone wants to make it smaller, it is simply a matter of reducing size by one out rivet per intended area of reduction.

thanks for checking things out.

[scottiniowa]

As he mentioned before the tubes do not protrude into the adjacent tubes they are intended to be coped around them.

Tube to the right  of my  jpeg photo, is in fact a tube  See your drawing sheet #1 upper left
The other two items, which appear to be tubes are in fact coped ribs and do not protrude into the main tube.
I could have and should have supplied more photos to show this better, but thought 4 top views were enough to get started.

As stated just a note or two ago, I can and will reduce this same ribs and even at that, if the jpeg was viewed looking aft, would still appear they were protruding
Had I made this jpeg with hidden lines show, it would have been very busy, but dashed lines.  Or with lines hidden, would appear they were hiding inside of the tube.

Only way to win on that would be to show top-side and front views.

cheers

[joecnc2006]

Any further words on this.

[scottiniowa]

Any further words on this.

Hi Joe,
   I certainly did learn that there was a difference of opinion out there, but most of the time those differences are expressed only after a part is said to be made a certain way. LOL  Nothing wrong with that, but it sure seems to be the case.
    I got hired on a another project, so got pulled away (for pay) but soon to be back to this.

As per the first line- I am almost certain, no matter what shape/pattern I show, someone will certainly say it is not correct, and that is ok too. As they will be strictly offered as ONE possible shape/form for these gussets. If I error, it will be towards the safe side. So with that in mind, I will have NO runs of rivets of 2 only.   I will always have 3 or more.  Edge distance has been established  (2 x dia. of hole size)  as well as min/max spacing. I will use .750" spacing.

cheers
Scott

[Aerodude45]

I like the idea of using number of rivets and edge distance between rivets as a way to determine rivet size. I'd like to propose an experiment, which I have the means and materials to try. Please let me know if you think this is worthwhile or would like to see a different methodology.

My hypothesis is that 6D rivet-spacing with 2D edge distance with each run having 3 rivets and with the tubes coped is the lightest option that will result in adequate strength. My assumption for adequate strength will be tube failure before gusset failure when the tubes are loaded in bending with the load force applied perpendicular to the tube and parallel to the plane of the gusset. (I welcome any arguments against this assumption; I don't know if that determines what is adequately strong. I also seem to recall my professor in A&P school last year saying failure in shear just before failure in bearing is preferred, but have not found anything online to corroborate this.) This force will be applied so that the gusset is loaded in tension (obviously in compression a .020" gusset will buckle). I will use the same 90 degree test joint configuration for all test pieces, and will test the configuration that is most successful in a 3/4"OD .035"wt to 3/4" .035"wt joint on the other joint-dimension configurations found in the plans (.020" C-channel to 3/4", .020" C-channel to 3/8", 3/8" to 3/4"). My joint configuration is detailed in the attached drawing.
 
(X4) 3/4" to 3/4" .035 joints (1 pair coped vs uncoped, 1 set 3D and 6D rivet spacing)
(X1) 3/4" to 3/8", most successful configuration from above
(X1) 3/4" to .020" Channel, same config
(X1) 3/8" to .020" Channel, same config

I have some spare aluminum tubing and .020" gusset material. I was going to make my gussets by drawing the tail in AutoCAD, using rivet spacing and number of rivets to determine gusset dimensions, drawing a circle with a radius of 2D around the last rivet, then drawing lines tangent to those circles much like what was mentioned above. I was also planning on coping. Hopefully this experiment would allow an "official" conclusion to be reached.

[s johnson]

Jakob,

Seems to me the FAA has already done extensive testing and pretty much states what should be used as far as spacing requirements in AC43-13 . You must be bored. Hurry up and get your bird rebuilt so we can go flying together this spring/summer  :-)

Scott J.

[scottiniowa]

I like the idea of using number of rivets and edge distance between rivets as a way to determine rivet size. I'd like to propose an experiment, which I have the means and materials to try. Please let me know if you think this is worthwhile or would like to see a different methodology.

 

Aerodude45,  Though it may be true, I have not seen using the number of rivets and edge distance calculation to determine rivet size.  I would have a hard time to find any where on this aircraft that 1/8th stainless rivet won't do the trick. And yes, 2D for edge clearance,  and as many books show, the spacing can very a fair bit, but using min and max, will determine much.

You had a fair bit of formula stuff, but I couldn't determine to what/which it was going to be used.  It looks like you want to do testing, I'm sure the group would be interested in your findings.  I am pretty sure in the time to do "proper" testing, the entire tail structure could be built and well on your way to having aircraft done. 

cheers
Scott

[Aerodude45]

Scott, that was a typo. I meant "gusset size", not "rivet size". Sorry about that.

[joecnc2006]

Here is some text on rivets.

EDGE DISTANCE.— 2x rivet diameter but not > 4x rivet diameter. The edge distance for all rivets, except those with a flush head, should not be less than twice the diameter of the rivet shank nor more than four times the diameter of the rivet shank. Flush-head  rivets  require  an  edge  distance  of  at  least 2 1/2 times the diameter. If rivets are placed to close to the edge of the sheet, the sheet is apt to crack or pull away from the rivets. If they are placed too far away from the edge, the sheet is apt to turn up at the edge.
RIVET PITCH (SPACING) — (4 to 6 times rivet diameter) 1/8 rivet = ½ to ¾ inches.
  Rivet    spacing    (pitch) depends  upon  several  factors,  principally  the thickness of the sheet, the diameter of the rivets, and the  manner  in  which  the  sheet  will  be  stressed.  Rivet spacing should never be less than three times the rivet diameter. Spacing is seldom less than four times the diameter nor more than eight times the diameter
 
TRANSVERSE PITCH.—  (75 percent of existing rivet pitch ) 1/8 rivet = 9/16 inch.
 When  two  or  more rows  of  rivets  are  used  in  a  repair  job,  the  rivets should  be  staggered  to  obtain  maximum  strength. The  distance  between  the  rows  of  rivets  is  called “transverse   pitch.” Transverse  pitch  is  normally 75 percent of existing rivet pitch, but should never be less than 2 1/2 times the diameter.