Charles_McG
Ciderwright
In the Pro24,29, and 38 lines, which have offset cores? And is there a way to tell from the CTI website (as opposed to buying one of everything and looking)?
Yes. I've had some terrible wobbly flights on moonburners with rockets that were fine on BATES motors. The Pro54 J140 has been a particular offender for me.Are people really seeing odd/strange/wobbly flights with these motors?
look to the far right of each motor. it says long burn. (looking at the thrust curves looks like moon burners to me? I'm not sure what the grain geometry is with Mellow Yellow)
https://www.pro38.com/products/pro24/motor.php
https://www.pro38.com/products/pro29/motor.php
https://www.pro38.com/products/pro38/motor.php
Tony
Any thoughts on the stability of moonburners compared to the CP/CG ratio of the rocket? Was thinking larger fins might help keep the rocket going more straight?
View attachment 360294
Here is the Pro24-6G G-145 Pink core geometry, a cylinderical hole. So this one has centerline thrust.
The motor burn itself, I believe is offset from a cylinderical core. The rocket is stable CP/CG wise in a sim but unstable in actual flight due to a moment about an reference axis down the center of rocket as the thrust isn’t centerline compared to a center core variant propellant grain. It’s got a torque. Some lightweight rockets or large rockets have problems. Somebody with more experience might want to speak up. The propellant core geometry and how it burns is the issue and the manufacturer does not indicate core geometry before you buy.
Does anyone have any measurements of this torque or thrust vectoring from moon burning motors?
The trust is not angled, the mass in the motor is offset to one side and if the rocket spins you get the unbalanced washing machine effect. Rockets that spin very little are fine.
Did a moonburner cause this?
I'd bet more on coning...the thrust from a moon burner has to come out a hole in the center of the nozzle. Likely this rocket had coning happen.Did a moonburner cause this?
Someday I’d like to build a test stand to specifically look for a small off axis force.
You should try contacting the Florida Institute of Technology. They have a test stand that does this. I don't know if they have ever tested offset cores, but I would think it's likely. Maybe they can shed some light on this for everyone.View attachment 362116 View attachment 362117
That Pink motor is a Bates grain type configuration.The motor burn itself, I believe is offset from a cylinderical core. The rocket is stable CP/CG wise in a sim but unstable in actual flight due to a moment about an reference axis down the center of rocket as the thrust isn’t centerline compared to a center core variant propellant grain. It’s got a torque. Some lightweight rockets or large rockets have problems. Somebody with more experience might want to speak up. The propellant core geometry and how it burns is the issue and the manufacturer does not indicate core geometry before you buy.
There wasn’t a yellow offered in the Pro24-6G line. The G-65 was the longest burn option and its core grain option sucked. The G-65 is the only MPR load for that Pro24-6G casing. The rest are HPR.
I have second hand knowledge of the CTI Pro29-5G H-53 Mellow load working fine for multistage sustainers. It has slow burn no offset.
What I can do for the OP is crack open a new L-1 G-145 reload for the Pro24-6G and we all can see the grain geometry of the Pink load if anybody cares to start a list with motors lying around. Might be cheaper than buying one of all.
View attachment 360294
Here is the Pro24-6G G-145 Pink core geometry, a cylinderical hole. So this one has centerline thrust.
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