Help with motor selection!

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billeblurzz

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I’m looking to launch my Der Big Red Max that I beefed up with the Vandenburn parts. Was going to use the called for Estes F15-4 motor suggested for a stock build. My all up weight is 21.5 oz. The Estes motor chart lists the Max liftoff for the F15-4 at 21 oz. What do you think?
 
Mine came in at 20.3oz when finished. Mine has flown well on E30 motors several times. I'm launching off a 72" rod.

I just ran the sim again adjusting for your weight of 21.5oz. The F15 is showing only 18.1 mph off a 72" rod so that would not be enough motor to be stable. You really need to be pretty close or exceed 30 mph off the rod. I personally wouldn't use anything less than an E30 on a rocket that heavy. I can tell you that mine also really likes F44's. Tons of thrust off the rod but it burns out quick so you're only looking at around 500'.


DerBigRedMax Motors.jpg
 
Great!! Thank you so much. I’ll give it some thought for another motor. What do you think of an F26-6 or F67-6 of which I have?
 
F26 doesn't get you to that recommended 30 mph off the rod. Sim'd it's showing 26.2mph off a 72" rod. On a DEAD CALM day with the rod pointed straight up and no one around I might try it. If there was anyone nearby such as a club launch I wouldn't chance it.

The F67 is a great motor choice.
 
OpenRocket is free and easy to use, and also a good bit of fun to play around with. You can get up to G motors in the same length as the Estes 29mm motors, so you’ve got a lot of options to explore.
 
If you
View attachment 566127
2 good rockets 🚀…2 perfect flights!! A great day!
If you go to ThrustCurve.org and put the specs of your rocket in the program will tell you what is safe to fly with and give you all the motors that work. I have it set at 50fps off the rod. You can adjust that perimeter to what you want as a safe speed off the rail. Lots of good info on that site. Another site I use is a parachute calculator. You put the weight in and the size of chute you think might work and the program tells you what the decent speed is. It's call Decent rate calculator. Good luck.
 
Mine almost lawndarted on an E16-6 but worked well on a E16-4 about 300ft. The F15-4 worked better.



I also tried it boosted by epoxying the retainer to the booster. Mostly worked well but didn't go any higher.

 
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