Recovery / ref 24-002
Wadding, streamers and the deployments we kept getting wrong
Out of 61 flights in 2023 we recorded nine recovery failures, which is a rate none of us were happy with. Seven of the nine came down to two causes, and both of them were things we were doing in the last two minutes before the rocket went on the pad.
01
Why the wadding is there at all
A low-power motor ends its flight with an ejection charge that pushes hot gas up the inside of the body tube to pop the nose cone off and pull the parachute out. That gas is hot enough to melt thin nylon and to scorch plastic sheet, so something has to sit between the charge and the recovery gear. In our club that is flame-resistant paper wadding, loosely crumpled, filling roughly two to three body-tube diameters of length above the motor mount.
We had three failures in 2023 where the parachute came out with holes melted through it and one where the shroud lines had fused into a lump. All four were traced back to the same thing: too little wadding, packed too tightly. Wadding that is compressed into a plug does two jobs badly at once. It lets heat through because it has no air in it, and it can resist the charge enough that the nose cone leaves late or, in one case, not at all.
Checklist as it stands
- Two to three tube diameters of wadding, crumpled loosely, never packed down
- Parachute folded and rolled, not stuffed, and never damp from the last flight
- Shock cord checked at both anchor points before every single flight
- A test fit of the nose cone: firm enough to stay, loose enough to pull off by hand
- Motor retention checked last, with the rocket pointing away from everyone
02
The nose cone that stayed on
The worst of the 2023 failures happened on the second launch day in June. The rocket boosted normally, the ejection charge fired at apogee, and nothing came out. It came down nose first from something over 130 metres and buried the top third of the airframe in wet stubble about forty metres from the pad, well inside the cleared area and with nobody downrange, because the range was closed. That is the only reason it was an equipment loss and not something worse.
When we dug it out the cause was obvious and embarrassing. The airframe had been painted at home the week before, and the paint had run into the joint between nose cone and body tube and glued them together. Nobody had test-fitted it afterwards. Since that day the flight card carries a line that the person preparing the rocket signs: nose cone pulled off and replaced by hand, at the prep table, within ten minutes of the flight.
03
Delay times, which we had been guessing
Commercial low-power motors come with a delay built in, marked as the number after the motor code, and that number is how many seconds pass between burnout and the ejection charge. The delay wants to fire at apogee, when the rocket has slowed almost to a stop. Fire it early and the parachute comes out at speed and tears; fire it late and the rocket is already heading down and gathering speed, which gives the same result for a different reason.
We had been picking delays from habit rather than from mass. A light airframe coasts longer than a heavy one on the same motor, so the same motor code wants a different delay depending on what it is pushing. Once we started writing the empty mass on the build note and the total mass on the flight card, we could look back through the log and see the pattern: our heavier kits were consistently deploying late on the longer delays and were fine one step shorter. Two seasons of cards turned a guess into a table we keep at the prep desk.
04
Streamers beat parachutes more often than we expected
The field is about four hundred metres across, with a pine plantation along the north-east edge and a drainage ditch on the far side. A parachute that works well brings a small rocket down slowly, and on any day with wind above about three metres per second that means a long, slow drift straight towards the trees. For our lighter airframes, a crepe paper or plastic streamer of about ten times its own width brings the rocket down faster, lands it much closer to the pad, and has never once damaged anything we fly.
We now make the choice on the day, by mass and by wind, rather than by what the kit came with. Under about 80 grams on a breezy day it is a streamer. Heavier airframes keep the parachute, and on the windiest days that still pass our limit we use a smaller canopy than the kit supplied, or roll the parachute so it opens partially. Recovery walk distances across the 2024 season dropped by roughly a third compared with 2023, which we mostly attribute to this.
05
What the card asks now
The recovery half of the flight card grew four lines after 2023: wadding quantity, recovery device and size, shock cord checked, nose cone fit checked. All four are ticked at the prep table by the person who packed the rocket, not by the range officer, and the card goes to the range officer with the rocket. It is a small amount of bureaucracy for a hobby and it has paid for itself.
In 2024 we flew 73 flights and recorded two recovery failures, one of which was a shock cord that parted at the anchor on a much-used airframe that should have been retired. The other was a parachute that opened cleanly and then collapsed in a gust twenty metres up. We logged both, and the first one produced the club habit of writing a flight count on every airframe and retiring paper tubes at thirty flights or the first sign of a soft spot at the motor mount.
Altitudes are barometric readings off the airframe unless the entry says they were estimated from the ground. Masses are measured empty on the club scale. Where a flight failed, the failure is recorded as it happened and the card number stays with it.