Advice About Disposable Wadding Alternatives in LPRs

[John Taylor]

I just purchased a large piece of Nomex cloth off of Amazon. It will make a bunch of protectors. I just cut to size, cut a small hole for the shock cord to go thru.
I also use dog barf in certain applications. It works great.

 

[BABAR]

Something I think doesn’t get considered in wadding use (especially with blankets) is protecting the shock cord.

parachutes are mostly either plastic or nylon. neither tolerates ejection charges well,

shroud lines are often cotton thread (I have heard some also use various fishing lines). These also are not heat tolerant,

low power shock cord are usually made of either elastic or Kevlar. Elastic is poorly tolerant of heat. Kevlar does much better, but is NOT BURN PROOF.

shock cord protection has at least two techniques. One is a forward mounting, often just below the level of the inserted nose cone shoulder, think classic Estes tri-fold. Even WITH this, when PACKING may bring this cord close to the forward end of the motor mount without wadding. (What I don‘t like about the tri-fold is that it breaks up the smooth forward inner surface of the tube and can hang up your chute.) I like attachments near the motor mount, but it puts the first few inches near the hottest part of the ejection blast. You can use @hcmbanjo ‘s replaceable technique for non-minimum diameter rockets which gives you a chance to inspect or replace. For minimum diameter I have had a number of rear mounted shock cords burn through after a number of flights.

second option with motor mount attachment is either heat shrink tubing around it, some other protection, or a wire leader. Wire leaders are kind of awkward

 

[SolarYellow]

I just unpacked some motors that came with biodegradable foam peanuts. I have read about them suggested as a potential wadding alternative. So after I carefully saved them in a big ziploc, I took one out to the driveway with a lighter to see what would happen when it was exposed to flame. I was surprised when in a fairly short time, it caught and sustained a flame. Not just a little, that sucker wanted to burn. It would make a halfway decent fire starter when camping. It smelled slightly like burning marshmallows, and kinda acted like a lower-density, more air-filled version of a marshmallow on fire. It disappeared almost completely, but at the end, there was a glowing ember on the concrete about the size of a kernel of corn. I know people have used them successfully, and the ejection charge is probably in contact with it not enough time to light it, but remember people also used regular paper to make parachute protectors back in the early days. I would not do the packing peanuts.

Since I had the lighter out and was thinking about it, I took a square of Estes wadding bought some time in the last three months and a Decopuff out to the driveway and hit them with the lighter. The Decopuff was clearly even more flame resistant than the Estes wadding. The treated TP would get a flame going that would take a few seconds to extinguish after the lighter was gone. The Decopuff could maybe get a flame going, but I was never sure whether it was the Decopuff or just the lighter flame interacting and following the material. Either way, the flame would always be gone immediately without propagating in the material at all that I could see as soon as the lighter was taken away.

 

[mh9162013]

Keep in mind a concern from my original post: avoiding the use of any material that could be lost during the launch, ie become litter.

In case any one was wondering, I've concluded that a baffle + attached semi-resusable wadding (such as untreated denim) works great for me. The denim wadding is attached on the shock cord and is really only there to keep the parachute clean. It also provides an added layer of protection for times when the ejection charge "fizzles" instead of "pops" and the parachute gets exposed to additional heat.

I could also replace the denim with a nomex or other "formal" parachute protector. But I have more spare denim than I can ever use (or wear), so I'll go with what's free.