Poor man's disk gap band drogue

[robopup]

Drogues have been kind of an afterthought for me for a long time - basically I would just look at descent rates and call it good. And always on 29mm, often for 38mm, and sometimes 54mm, I would just fly drogueless. I had a higher flight this fall which got me more interested in drogues - on its descent the second stage transitioned several times between some pretty violent horizontal spinning and ballistic descent, towing the nosecone behind it, captured with onboard video. This rocket had a simple, small streamer for a drogue.

I've had a lot of forced downtime this fall, so I've been spending some of that time playing around with parachutes and noodling on drogues. I sewed 6 torroidal mains (4 30in, 2 48in) following this tutorial (it's amazing) to practicing hemming, french seams and to stock up for the next season or two. I also found this article with a write up and design and disk gap bands, and noticed Curt von Delius used one for his large 2 stage recovery so I figured I'd give 'em the 'ole college try.

Since I'm looking to recover smaller rockets - 54mm and 75mm min diameter, these drogues are going to be quite a bit smaller than the apogee article. I've been playing mainly with 7in diameter for the 54mm (and I'll likely go a bit smaller yet for final, TBD...), and was really struggling to follow the apogee article build steps with something so small. Among other things, keeping a consistent gap distance and sewing shroud lines to the small gap section were challenges. To try and figure this out, I've been playing around with making them the same way I've been making mains, and cutting the gap out of each gore before hand. After some strikes and gutters, I'm getting closer to a process:

I'm using this site to generate my patterns - 8 gores, 7 in diameter hemispherical. The apogee article disk is just a flat circular piece of fabric, so I'm setting the program's ellipse "eccentricity" to 0.9 (if I'm interpreting this input correctly) so that the disk is about the same diameter as the band. Each gore is cut out with a soldering iron - I'm using 1oz fabric from Ripstop by the Roll.

Then I slice down the center of the gap, hem each side (there isn't enough fabric in the gap width to fold the material edge twch), and hem the top. (messy cuts, these are scraps from a larger project):


These gores get sewed together using the linked tutorial above:


All gores sewn and bottom hem complete. Note I'm simply leaving the seams connecting the disk and gap:


Shroud lines on, from the bottom of the gap to ~1.5 in up the disk. These chutes are pretty small so I'm only using 8 lines:


Complete:


I'm still playing around with how to pack these - when you fold all the gores in on each other like a normal torroidal/hemispherical chute, the gap and band just look like they're going to tangle on each other. It does pack pretty small though:


I'm getting to the point now where I think I'll fly a few and see how they do!

 

[sriegel]

Cool project.

You might save some effort by eliminating that little strip of fabric between the disk and band. You already have the suspension line spanning the gap. Stitch the line to the band, mark the gap distance, stitch the end to the disk.

Have you obtained any flight data?

 

[sriegel]

IIRC, a true DGB is literally a flat disk with the band. Your gores could be simple triangular wedges (nice cutting efficiency there!) and the band rectangular pieces.

 

[robopup]

@sriegel - Thanks! Yes, I played around with the design in the Apogee article (flat circle, disk), and made a couple chutes that are sort of usable with this method. I specifically had trouble getting the gap right and lines attached with the chute diameter being so small, which is why I went to the alternative in my OP. It was much easier to sew lines on with a consistent gap distance (which results in the small strip of fabric you mention) with a single pass than to sew individual sections on the disk and the band. Having said all that, I'm not much of a seamster (your stuff is amazing!) so YMMV.

Looking to get some test flights up this spring!