Already the 4th flight with my Intimidator 5 rocket on an experimental baby M-class sugar motor going to 2200m. This time on a KNSU PG reload.
For this flight I tried the KNSU + 1,9% propylene glycol mixture (1,9% is nett added mass) as I was looking for higher thrust and a shorter burn. With a higher thrust I can use the same motor as a booster in a 2-stage configuration – as well as the interesting outcome what different candy propellants do in the same motor / rocket. Propylene glycol was tried to improve pourability / casting and only added just prior to pouring. After simulating in SRM 2014 and reading up on KNSU on Scott Fintel’s site I got a little concerned on KNSU RIO Pmax so I conservatively tried KNSU + PG. Supposedly making no little to no difference in burn rate. SRM indicated a burn time of 1,6seconds for straight up KNSU.
- Attached the outcome of this flight on KNSU 1,9% PG. It is almost the same as straight up KNDX with a 3s burn time but much more tedious to melt / cast and lower desity. It requires continuous stirring to prevent caramelisation and I can only melt one grain / 850gr batch at a time in a electric pan. I ruined a perfectly good dedicated pressure cooker due to this.
- Isp is good and considerably higher than KNSB reloads.
- The propylene glycol used was 99,5+% pure and indeed is makes the propellant better pourable but did not have a noticeable effect on density – it sure fumes though.
- I also tried straight up KNSU as a test grain which actually gave a slightly better density. 80% of the batch could be poured in the casting tube and the remaining KNSU required scooping.
- In all cases the propellant was not vacuum cast due to the hazard of carmelisation but did used a spring loaded compression mould.
- Average KNSU PG density was steady 95,3% of ideal. Test grain of plain KNSU gave 96,3%.
Most likely I will not use this propellant in a future motor again. I pefer casting KNDX with better density any time for an equivalent thrust curve. The addition of propylene glycol improves pourability but any true benefits are questionable and it’s likely surpressing the burn rate of KNSU a bit (although I haven’t valided this with a KNSU reload).
Watch on Youtube: Intimidator 5 – experimental M class sugar rocket – Flight IV
Intimidator 5 – powered by an experimental 5700Ns KNSU 1,9% PG (propylene glycol) candy motor equivalent to a M1900. Peak altitude of 2200m and a maximum velocity of 846km/h.
Onboard electronics included a RDAS Tiny for flight control, back up experimental timer, Mobius action camera looking down with a 3D printed camera shroud. Payload comprising of a BigRedBee – Beeline 70cm GPS 100mW tracker. All fast but safely recovered under a 72″ Iris Fruity Chute.
The launch took place on 09/10/2015 at SLD 2015-2 in the Netherlands. Launch site: OTCVust (formally known as ASK ‘t Harde).
LD’s 100mm rocket the XOZ-XL going to 3726m on a similar motor with a KNSB RIO reload: