Most times it is not the operation that is a challenge, but the technique.
If you wish to manufacture this, you may want to do this as an assembly with each plate modeled separately.
Here is a surface copied from the helix. It was merges as a complete helix (sometimes these surfaces disconnect). And then the trim made a 1/3 rotation of the 1st spiral. A point was added to the edge of the new quilt. The flatten quilt was used using the 1/3 rotation quilt and the point.
Since flatten quilt has to make some determinations, you will notice that the ends are somewhat distorted. Measure the length of the edges of the flat quilt to see if the outcome is what you expect from measuring the length of the original edges.
This was of particular interest to investigate further.
I used my own dimensions in order to understand the ramifications as this is quite important for such a large project. This is certainly worth creating a scaled mockup to test the validity of the data obtained form the CAD model.
In the video, I added a few techniques that will help assure proper development:
1) Distortion of Flatten Quilt is sufficient in this instance to change the straight forward technique.
2) Ensure the developed edge in the helix is the same as the developed edge of the flat pattern.
3) Use a single flatten quilt edge to develop the form with a consistent width using a second sweep.
The deformation of the initial quilt was significant. I opted to use only the interface edge between the helix and the barrel. Then confirm the edge length before sweeping the actual "shelf" width. This process should minimize the expected distortion. Talk with your fabricators and see if I'm on the right path.
I opted to flatten a complete 360 degree section... twice. If the intent is to only flatten 1/3 (120 degree) sections, this should be managed in a similar way by dividing the initial helix at each 120 degree segment. Don't try to do this on the 360 degree flat quilt. Smaller segments may be more accurate. I don't know the tolerable level of inaccuracy for this type of feature, or how the helix will be formed.
I know you are using an older version of Pro/E so adding the model won't help you. I believe all the features I am using are available in older versions. Some of the features are completely different in their usage (like the intent edge reference) but it is there under a different feature type. Regardless, I hope the intent of my usage for these features are clear if you need to find a work-around.
Making the drawing is another matter. I suspect you will need to create a DXF for the fabricators. You can move the relevant features to layers to manage the views. You can use the flat planes to create view orientations. Again, this is probably easier as an assembly.
I made this as a part. It did have some trouble merging the barrel with the helix. Too many coincident edges I presume. I finally used a revolve surface; offset surface; and thicken just shy of intersecting. See the last 3 features in the image below.
Good luck and let us know if you need more specifics!
The problem I found with making the inner and outer edge at the same time is that the overall width is not maintained. Flatten Quilt was developed to provide a flat version of a distorted quilt and in doing so, it does make a lot of assumptions that distort complex geometry. That is why in this case, I chose to use the interface edge to use as a master.
The tolerance you are considering may be much to tights for Creo to accurately interpret the surface. Even the material thickness will change the interface between the barrel and the helix. There will be a lot of "craftsmanship" involved in putting all this together. In general, weldments like this are quite tolerant in both design and manufacturing tolerances. Your drum is near 4 meters long and 2 meters in diameter. Roundness of these panels will never meet 1-2mm. interference of the edges of your helix may need to be considered:
Again, there is no true "radius" involved. It is some level of complex involute, not knowing a more precise term for this. I really don't know of a better approximation. Further investigation in using the Flatten Quilt feature may get you closer. I find the command very annoying when you try to use its higher level functionality.
You might consider a top-down design for this. You can reference things at an assembly level to create parts. This is all advanced techniques and sometimes it really gets frustrating when references get lost. If your design is stable, you could just copy the helix many times and work from that. You could work with family table to determine which segment you want to act on. The barrel can be associative to the helix through an assembly. There are just to many ways to do this to recommend any specific method. You have to look at what your end goal is for this and possibly future designs. A simple method could lead to sustainability issues... but if this is a one-off design, maybe a the quick method is right. This is not for me to say.
I am only suggesting DXF because that is what a lot of machine shops require to make patterns with using CNC. Somehow you need to get the flat pattern to the fabricators. This is more than just a simple drawing. You can provide a drawing, but I would highly recommend you reference a CAD model of some kind to give the shop something to go on. It is not unusual to do this. This is often controlled in a drawing by adding a note with regard to using a specific CAD file for programming.
Are you the lead engineer on this project? If not, I would suggest letting whoever is responsible know that this is a risk and should be validated prior to fabricating the actual unit. There is a lot of approximation going on in this method and some skills to consider from your fabricator, such as how to pull that helix from a flat plate. The welding process can make up for a lot of approximation but there are limits.
I fully appreciate how involved something seemingly simple can be. Do not underestimate the required effort to make this successful. There are a lot of functions that have a stake in this endeavor. ...and it begins with you 
