54 mm scratch build motor mount ??

[Spitfire222]

And I absolutely agree with the "good stewadship" part. But prehaps gently following up and advising that prehaps a 54mm might not be the best HPR entry motor size...or something like that...

We dont want to scare people off! This is a great hobby!
Cheers'!

I complete agree with this, and definitely don't want to scare someone off. I guess my thinking is, if we provide the answer while also advising them to reconsider 54mm, etc, I seriously doubt they will actually heed the advice since they got the answer they're looking for. If we refrained from providing the answer outright, it might incentivize someone to look into it more and do their own research, learning other things in the process.

I maintain that asking this level of question for an HPR build should raise some eyebrows. Yes, we all started from scratch and learned, but I think most of us do it methodically beginning with LPR, where mistakes and learning experiences generally are more forgiving than HPR.

@curtthedirt Check out Apogee Rockets if you haven't already, for lots of informational content on all aspects of rocketry.

 

[jqavins]

This hobby can be contentious with the general public and power that be because it involves deliberately lighting things on fire to make them go really fast. Understandably, it makes some people nervous, so we have to be good stewards of the hobby to not give motives to those who'd prefer to shut down all rocketry activity...

Also, jeez, I'm continually impressed at this forums talent at going way off-tangent from a thread's topic.

Speaking of tangents, I need to get this off my chest.

I am a little tired of the cautions about public perceptions of safety and "shutting us down". Of course it's a valid point, but sometimes it seems to take up more conversational space than the more important actual safety. If there is an increase in injuries and property damage, and it leads to tighter regulations, which is more important: the regulations or the injured people?

It reminds me of something I encountered in the community where I bought my first house. There were sidewalks heaving and some people were injured when they tripped on them. The HOA board considered this a very serious matter because it drove up the association's insurance rates. They wanted to add some sort of waiver to the policy because they were more concerned with keeping the rates down than with fixing the sidewalks.

They were more concerned with the secondary effect of a safety issue than they were with safety. When the public perception and regulation is brought up first and more often than real safety it feels very much the same.

OK, my chest has been cleared. Thanks for listening.

I guess my thinking is, if we provide the answer while also advising them to reconsider 54mm, etc, I seriously doubt they will actually heed the advice since they got the answer they're looking for. If we refrained from providing the answer outright, it might incentivize someone to look into it more and do their own research, learning other things in the process.

With all due respect, I think that's bass ackwards. You get people to listen to you by engaging with them where they are. Refusing to answer and lecturing instead will only alienate someone.

 

[Zbench]

With all due respect, I think that's bass ackwards. You get people to listen to you by engaging with them where they are. Refusing to answer and lecturing instead will only alienate someone.

Truer words were never spoken. In this case, I think that’s happened. The OP has not been back since the vigorous chastisement that was delivered. On his first ever post no less. That’s a shame.

 

[curtthedirt]

(David, if I remember right you're an LP guy and it's fine if you need to ask this.)

The aft closure has a bigger diameter than the tube, which creates a lip that keeps the motor from pushing up inside. The figure below is for a CTI motor; AT cases and SU motors are similar. (I find it odd that only a maximum diameter is given for the closure. Trust me, the minimum diameter is adequate for the purpose.) The aft edge of the MMT must be strong enough to handle the peak thrust from the motor.
View attachment 514917
Yeah, that.

Seriously @curtthedirt, you should understand that the change from an engine block to a thrust ring is the least of your worries among the differences in the necessary build practices and flight day practices between something that uses an F15 (the biggest engine I know without a thrust ring) and something that uses an I120 or I150 (the lowest thrust and lowest impulse of all CTI 54 mm reloads; with AT motors there are others that may be lower, but not by a whole lot).

Please consider the figure below, which is an overlay of the thrust curves of the motors I mentioned above. I hope this gives you pause.
View attachment 514919

You answered my question - thanks. It's been a decade since I kinda semi retired the rocket hobby & I just needed a little refreshing.

 

[curtthedirt]

" basic questions from someone just starting out in LPR. This is someone asking an HPR-related question that they absolutely should know if they are dealing with 54mm motor mounts "

You're right, he should know, and that is EXACTELY my point: He DID ask the question, because he wanted/needed to know.

And I absolutely agree with the "good stewadship" part. But prehaps gently following up and advising that prehaps a 54mm might not be the best HPR entry motor size...or something like that...

We dont want to scare people off! This is a great hobby!

REMEMBER, no matter how long one has been in this hobby, (or anthing really) Once upon a time, every one us didn't know the answers. We all started from scracth. We all had to learn, - by overt or subtle means, somehow, one way or another.
So what seems like a basic question to one person, may not be for another.

Anyway, TRF is a great place, and has great, knowledgable folks here at ALL experiance levels - so there will be questions at all levels!

Cheers'!

Geeze , after not flying hpr for a decade , closer to 2 decades actually , I was just making sure I didn't epoxy in my mmt & then remember something I should've done first. It was a newbie question but whatever. I attempted level 2 certification in 2001 @the black rock desert about 2 months before 9/11
Ultimate endeavor on a K-550 W. Unfortunately the chute didn't deploy & it came in ballistic. It lived to fly again (after ordering the top bt & nose cone. I will be attempted level 2 again @ LDRS 40 in June w/my scratch build. The pictures are of my ultimate endeavor. Thought I had pic. of current build but apparently not.

 

[jqavins]

Geeze , after not flying hpr for a decade , closer to 2 decades actually , I was just making sure I didn't epoxy in my mmt & then remember something I should've done first. It was a newbie question but whatever.

Glad to learn it was just a refresher question. I hope you understand why it raised such concern.