When the chart specifies the Est. Max. Lift Wt., does that mean the weight of the rocket without the engine - or the weight of the rocket with the engine?
Estes Engine Performance Chart - A Basic Question
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https://www.rocketryforum.com/threads/how-to-interpret-the-max-liftoff-wgt-on-packaging.178912/
https://www.rocketryforum.com/threads/how-to-interpret-the-max-liftoff-wgt-on-packaging.178912/
Accepting that as gospel per Estes, and you have a model that is slightly over the limit - such as a 4.10 oz model launching on an Estes motor with a 4.0 limit - is that estimate mitigated by factors such as an extra-long launch rod, or by anything else?
Scott_650
Well-Known Member
Take that max lift off weight data with a healthy grain of salt - it’s more a rule of thumb than empirical data. A simulation run in RocSim or Open Rocket or even on Thrustcurve is going to give you a better picture of any given rocket’s performance on any given motor.
Do atmospheric conditions make a difference?
astronwolf
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Of course. Ever see a rocket weathercock in the wind? Slow, heavy rockets are the worst!
Got it. But I'm thinking of barometric pressure, humidity and temperature also.
Then use a Sim you can change those items on. most of those above effect light fast rockets not heavy ones.
Got it. I can take it from here.
Thanks for all the help, guys!
cfb_rolley
Well-Known Member
Barometric pressure definitely has an effect. I haven't noticed major differences in swings of like 5-10 mb at ground level, maybe a difference of a few meters in apogee. you would certainly see differences when comparing a launch at sea level vs a launch at 1000ft elevation though. In general, less dense air means there's less for the rocket to punch through, but also make the fins less effective.
For humidity, the value you'd want to monitor is water grains per pound of air, rather than relative humidity. Relative humidity changes with air pressure and temperature, whereas water grains is an absolute measure of how much water is in the air. Again, less water in the air = less to punch through, but I'm not sure how much of an effect this has.
But like Art said, just whack it in to a sim and play around with the numbers to get an idea of what those variables do.
Ez2cDave
Well-Known Member
Estimated Maximum Liftof Weight means "Climbing up the Launch Rod, with FIRE coming out of its behind" !
LOL !
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You can do a sim with your actual rocket, weight and conditions including launch rod length and see what the velocity is coming off of the rod. This is important to a successful launch. Consider the wind because a rocket that has a good stability margin, coming off of the rod in a good amount of wind, will likely weathercock. The delay time is also important. If a rocket goes straight and you have too much delay, it might get back too close to the ground before it deploys. If it weathercocks it may not get very high off the ground and it will definitely be too low when it deploys, plus it can be far away from the launch point.
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