tensioning drag/antidrag wires

[Bitshifter]

I noticed that you assembled and rigged the Hatz before covering the wings. I am wondering if you happened to check the drag / antidrag wires at that point. I wonder if the flying wire rigging may have "tweeked" the wings a bit. I am interested in this answer since I will be doing it at some point in the future. I was also wondering if the tabs on the compression struts were just a little off angle then the tension would be reduced as flying stress created the proper angle.
Please continue to post your findings and experiences as I find them to be very helpful.

Thanks
Ed

[Mark K]

I'm assembling my first wing and wanted to trammel the wing before I glued up the ribs. I'm building the classic with tabs on the compression struts. I made my antidrag wires from round stainless clamped in a bench vise with aluminum stock to protect the wires as I cut the threads, worked great.

My question is how do I grip the anti drag wire in the tensioning process now that its in the wing?
- Can I file flats for a small wrench to fit without weakening the wire?

In an earlier post Hans and Sam have beautiful wires that are square, can I do that in a small section without compromising the wires? How do the guys with round wires grip the wire without maring it? Once covered I'd have to be able to adjust the tension through an inspection cover right?
Thanks
Mark

[alvinsager]

Hi,
I made a pair of hardwood jaws for a small vise-grip that had a groove for the wire. Worked fine.
Al

[Mark K]

Thanks for the reply Al, That sounds easy enough. I'll give it a try.
Thanks Again
Mark

[JBMoore]

I had a two sets of aluminum jaws made that were held together by a 10-32 screw.
They were big enough for me to use an adjustable wrench and I put one set on each end of the wire so I didn't introduce any twist.

Jeff Moore

[mmarien]

My neighbor said the formula was 25 lbs to deflect the anti/drag wire 1/4". I tried it. It seemed like a lot of pressure on the wire. So I did some digging. I found a couple of things. The first was this formula:

T = (L * F) / 4 * X where

T is the tension on the wire.
L is the length of the wire.
F is the force in lbs applied at right angles at the mid point of the wire.
X is the deflection of the wire

There are some caveats. The diametre of the wire needs to be much smaller than the length so the stiffness of the wire is not a factor. The force is applied at right angles at the midpoint of the wire. And the force is small compared to the tension of the wire, ie: the deflection should be much much smaller than the wire length.

So plugging in what my neighbor gave me resulted in a tension of 1000 lbs = (40 * 25) / 4 * 0.25. It didn't make a lot of sense. I found this for a Stinson:

Screenshot 2021-04-06 134748.jpg (178.16 KiB) Viewed 823 times

The tension was about a tenth of what I was told!! On some cub forums the number 1/2" deflection with 12-15 lbs of force was repeated several places. Dakota Cub was mentioned as the source. This comes out to about 240 - 300 lbs tension. My neighbor is building a J3. His wires are smaller than 3/16" I hope he doesn't have 1000 lbs tension on them.

So between the Stinson diagram and what Juerg Mueller said above makes a lot of sense.

PS: for those with a good ear, someone on the Internet said that the twang the wire makes should be "G" on a musical scale. I'm going to use my fish scale and 5 lbs force with 1/2" deflection which would put about 100 lbs tension of the wires. I also may check the twang. You never know. Build a Hatz is probably part artistry.