Cold weather ignitions

After thawing out from yesterday's launch I got to thinking on whether
temperature has any noticable effect on igniting motors. If there's
clear weather the local club will fly year round. And since I'll have
the free time since I won't be working much for the next 4 years I might
find myself launching in below freezing conditions. Since in other
genres, welding, starting bonfires, etc I know "just a few degrees" can
make a very noteable difference in the outcome. Anyone have
experience/advice/opinions on this?
Chuck
Reply to
Zathras of the Great Machine
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I don't know if there is a difference in how hard or easy it is the ignite the motors. However batteries tend to perform less well in the cold so it can be possible to get less current going through your igniters. Thus it may take longer for them to ignite.
Jonathan ----- Jonathan Sivier Secretary, Central Illinois Aerospace jsivier AT uiuc DOT edu NAR #56437 Tripoli #1906 CIA Web Site:
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"Remember to always keep the pointy end up."
Reply to
Jonathan Sivier
Estes igniters on a 12 volt relay system have no problem up to 10 degree weather. Zak Orion Will probably correct me on this, as I don't keep accurate details.
We've also used other igniters, but not as many as estes, So I can assume there is no problem with them.
I will note that cold weather tends to chill fingers which converts them to thumbs when installing igniters, causing problems.
Reply to
tater schuld
Ambient temperature does have an effect on the burn rate of AP based propellants, at least. How much of an effect depends on the propellant formulation. Those with a high burn rate coefficient (a) have higher temperature/burn rate sensitivities.
Reply to
Greg Deputy
Same for BP. The initial temperature of BP affects burn rate.
Try flying at -25C or so with BP motors, and you'll notice that they burn slightly longer. On such cold days, you *want* your rocket to land very far away, in order to improve the circulation to your limbs during the long walk to find it :-)
Have flown rockets with icicles forming on my goatee...:-) [and no smartass remarks about getting caught in some venting N2O during the summer :-) ]
Reply to
Marcus D. Leech
"Marcus D. Leech" wrote in news: snipped-for-privacy@nortelnetworks.com:
I'm a member of the Champlain Region Model Rocketry Club (CRMRC), and it flies out on the frozen bays of Lake Champlain in February and March. I joined them last year.
I flew stock standard Estes B's and C's with Estes igniters on a 12Volt vehicle battery system. Other folks were flying AP reloads from Aerotech and Pro38. Reliable ignitions had by all in the 0F temperatures.
A bigger problem is in the fit of assemblies with tight tolerances. Things that fit well at 80F may not go together at all at 0F. Different types of material, and different shapes, react differently to the cold.
One flier had to peel several layers off an Estes D to get it into the engine mount. I suspect that's because the rocket was at air temperature, but the engine had been in his warmer range box and pocket.
ScottE
Reply to
ScottE
Here in Canada about half of our launches are "cold weather" launches by default. Luckily it doesn't make too big of a difference, but the cold can cause a few problems. The biggest problem is with batteries - regardless of battery type there will be some current loss as the temperature drops. On the ground this usually means that you have to hold the launch button a few extra seconds to light the ignitor. But this can become a problem if you are using electronic recovery systems - I've lost a few rockets because the battery couldn't provide enough juice to ignite the recovery charge. Generally speaking you can keep the juice up by keeping the batteries warm (i.e. in an inside pocket), and install them just before launch. On extremely cold days some people up here will use those chemical hand warmers to keep the batteries warm. I can't comment on how well this works as I've never used these before.
Another problem, which has already been mentioned, is uneven thermal contraction. As things cool they shrink, but if your rocket is made of different materials some parts may shrink more then others. So what may be a good fit at room temperature may be too loose or too tight at cold temps. I always carry a little masking tape and some sand paper to adjust for this.
But the biggest problem I've run into is with my body. Launching rockets can involve a lot of standing around, and if it's real cold life can become miserable. A thermos of coffee goes a long ways towards fixing that. I've also found that huddling over the burning, shattered remains of a crashed rocket can also keep you quite warm - but that's another story. . .
Bryan
Reply to
Bryan Heit
If you're flying in sub-zero (F) weather and letting the motors cold soak down to ambient temp, it's not unusual to see delay time wander, since the pressure exponent and temperature sensitivity coefficients of the propellant and delay are usually different.
Reply to
Mike Dennett
Nope, and don't plan to find out, either... I am *not* a cold weather person. And I live in Michigan, go figure...
Eldred
Reply to
EldredP

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