I am wondering if some of your problem might also be humidity. I live in the
desert and we generally have no problem igniting our motors, even in the winter
when temps are in the 30-40s F.
I have noticed motors are harder to start when either the humidity is high
(rare here) or it is raining.
Here's an example: at 8:50 the SpaceX interns launching with my 75mm sugar had
no problems with ignition before the rains came but at 11:10 in the video, the
same motor reloaded but out in the rain on the test stand was a different
story, took 3 tries (two shown in video).
Friends of Amateur Rocketry May 7, 2016 rocket launches and tests
|
|
|
| | |
|
|
|
| |
Friends of Amateur Rocketry May 7, 2016 rocket launches and tests
These are most of the flights and static tests conducted at the Friends of
Amateur Rocketry (aka the FAR site) o... | |
|
|
We now generally don't use any primer to start our motors 'slowly' to avoid
cracking grains. The first attempt failed, there was rain water on/in the
nozzle, and so we beefed up the second igniter with some additional APCP
shavings attached to it and it 'fired' though not the best.
I might be worth while to thoroughly document the humidity conditions from
casting day to firing day and what steps are taken to protect the propellant
from moisture.
Rick
On Friday, September 22, 2017 10:12 AM, Richard Nakka
<richard.rocketry@xxxxxxxxx> wrote:
The Primer is described here:
http://www.nakka-rocketry.net/ignexp.html
Consists of 80/20 mix of potassium nitrate and charcoal mixed with 70%
isopropyl alchohol. Painted on all exposed grain surfaces.
On Fri, Sep 22, 2017 at 11:11 AM, Bdale Garbee <bdale@xxxxxxx> wrote:
Richard, what do you use as a primer? My sorbitol formula with a little RIO
lights easily, but I'm still struggling with erythritol...
Bdale
On Sep 22, 2017 7:35 AM, Richard Nakka <richard.rocketry@xxxxxxxxx> wrote:
Nikolai,
I've only recently begun using xylitol based propellant, but have had no
problems with igniteability. However I always prime the surface (I mainly use
it for a smoke tracking charge). As with sorbitol, xylitol does not caramelize
when heated, and this likely is what makes these more difficult to ignite.
Adding a primer makes a huge difference as the primer material readily absorbs
heat and quickly heats the underlying propellant to ignition temperature.
I also prime my KNDX grains, even if it is strictly speaking not necessary, as
dextrose does caramelize.
Richard
On Fri, Sep 22, 2017 at 8:18 AM, Nikolai Nielsen <nielsen.nikolai86@xxxxxxxxx>
wrote:
i made a small motor yesterday using xylitol and when the motor started up it
looked like it was going to burn nicely with the fuel being burned in a short
amount of time(it was a core burner) but when it lit, i could see that it was
building up pressure but then it suddenly slowed down and proceeded to burn for
another 20 seconds or so. this is what i imagined what happened(see picture)
and then today i remembered that when i lit some of the left over fuel, it
took a lot longer to ignite than my other fuels and i then realised that unlike
the KNSU motors, the KNXY motor wasn't burning all the available surface up,
just the surface that was currently burning and i believe this is due to the
difficulty of igniting the fuel so maybe the heat inside the motor isnt
igniting the rest of the fuel as it does in other motors(i think this is also
what happened to my rocket launch day 2 video). this then made me remember this
video at 0:29 https://www.youtube.com/w atch?v=BmhnronPiYE and i saw he had a ;
black fuel grain which he said in the comments was KNSB that was primed. I
found a page on Richards website that details this so im going to try that next
time i use xylitol fuel, hope it will work.this is the video of the burn
https://youtu.be/xPuqFZ0k T_QNikolai Nielsen
