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Does cold weather have any effect when launching a HP motor

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Five

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I was wondering if 35 degree weather has any effect on launching a I65 54mm? The temp varies from 35 degrees at night and 55 degrees during the day. Its been sitting in my garage for a couple days. I wasn’t sure since this is my first winter with a level 1.
 

Alan Whitmore

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There is certainly an effect of propellant temperature on burn rate and chamber pressure. The effect of air temperature at the time of launch is much less significant. If you look at figure 11-7 in Sutton's "Rocket Propulsion Elements" you can see an enormous difference when the burn time vs chamber pressure is charted for a "standard" propellant temperature of 70 F, versus +160 F and -65 F. I would not be attending a hobby rocket launch where the atmospheric temperatures are at either of those extremes. The difference in performance between a propellant temperature of 35 F and 70F would, of course, be much less dramatic, you might not notice the difference.
Even so, when attending a launch when the overnight temperatures are forecast to be below freezing, I usually bring my motors in to the hotel room overnight, and transport them to the field in the cab of my truck. Depending on the size of the motor, you might want to prep the rest of the rocket with the motor in an interior pocket of your clothing until it's time to install. I think an I65 would fit in a shirt pocket, IIRC.

Alan
 

BABAR

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If you look at figure 11-7 in Sutton's "Rocket Propulsion Elements" you can see an enormous difference when the burn time vs chamber pressure is charted for a "standard" propellant temperature of 70 F, versus +160 F and -65 F. I would not be attending a hobby rocket launch where the atmospheric temperatures are at either of those extremes.
Yeah, I am with you there, bro. I ain’t going to any launches in that weather, Covid or not!
 

jsdemar

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The overall total impulse doesn't change much but the burn time will be somewhat longer for cold-soaked propellant.

The delay grain burn is slower on a cold day and faster on a hot day. It's effect is more pronounced than the motor characteristics.

Small motors will warm up stored inside within a couple hours. For larger diameter it's best to store inside overnight. Leave wrapped in a blanked and load into the rocket onsite.

(Former resident of the Great White North). ;-)
 

aerostadt

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In general the burn-rate will be slower for cold propellant (or ambient air temperature if the motor is at ambient air temperature). However, the total impulse is about the same. This means that the total burn-time will be longer and the average thrust will be lower.
 

Five

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Thanks everyone for the advice. From now on, the motors are staying inside the house.
 

Neutron95

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I've actually considered cold soaking motors to increase burn times for altitude shots.
 
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