54 mm scratch build motor mount ??

[curtthedirt]

I'm almost ready to epoxy my 54 mm motor mount into the 5 1\2 inch tube. I know there are many different choices of motors , some longer ,some shorter. My question is how do I go about keeping the motor in the rocket under thrust ?? What if I want to use different length motor. I built & flew the ultimate endeavor 20 yrs ago , even still have the build instructions but they arent very clear & I can't remember.

 

[fyrwrxz]

Wow! 54mm! Maybe a little research is in order. Straight smoke and good chutes!
,

 

[waltr]

Thrust ring on the motor housing.

Now how are you retaining motor to prevent ejecting the motor instead of the chute?

 

[Antares JS]

Most motors nowadays come with a thrust ring that prevents it from shooting itself up into the tube.

However, I am disturbed that you are building a rocket with a 54mm motor mount and didn't know that.

 

[David Schwantz]

what's a thrust ring??

 

[jqavins]

what's a thrust ring??

(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.

I am disturbed that you are building a rocket with a 54mm motor mount and didn't know that.

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.

 

[Spitfire222]

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

I'm pretty sure he was being sarcastic, as there has been quite a few brand new members making their first posts about an L1 or HPR rocket and asking very basic questions that they should know the answers to before flying that kind of model.

 

[jqavins]

Ah, well, sarcasm works too.

I didn't notice that this was the guy's first post.

 

[David Schwantz]

Sorry,I could not resist. I'll shut up now

 

[jqavins]

No, no, don't stop on my account. Just because Thicky McThick III here didn't get the sarcasm doesn't mean you shouldn't use it. (Maybe scaring off a new member with a naïve question means that...)

By the way, do I remember right? Are you an LP guy?

 

[kalsow]

By the way, do I remember right? Are you an LP guy?

Not really. David is too modest to say. But, he's scratch-built and flown all sorts of amazing HPR rockets! If I remember correctly, his grain bin and Saturn V love K's and his V2 eats M's.

https://www.rocketryforum.com/threads/flying-silo.170206/post-2224678https://www.rocketryforum.com/threads/12-foam-nc.162415/post-2127493https://www.rocketryforum.com/threads/what-did-you-do-rocket-wise-today.48649/post-2000258

 

[David Schwantz]

Awe shucks Bill

 

[David Schwantz]

And wasn't trying to be negative. Was just getting at that I am sure I asked that same question 50 years ago.
The only stupid question is the one you DON'T ask.

 

[Zbench]

Come on guys. The OP asked an honest question and doesn’t deserve the snark. If this is to be a welcoming community to new comers then occasionally we collectively might have to answer basic questions. The I can’t believe you didn’t know that kind of stuff is petty and not useful. He did ask so as to seek to understand and that’s the point of the forum.

 

[jqavins]

Yes, it's better he asked than not. What I and others said is the this is so very basic that not knowing it is likely a sign of not knowing some other important things. And that makes us concerned for his and others' success and safety.

If I get into a car, eaver to start driving, and ask what that big foot pedal on the left does, I probably should go back to driving the lawn mower around the yard for a lttle while longer while reading a driver's manual.

 

[Zbench]

I understand your point jcavins, but everyone at one point asked what the gas pedal does. Further, just because his rocket has a 54mm mount does not mean he will be flying with a level 2 motor. Not carrying water for the OP, but we need to be more tolerant. If you only have flown BP motors and you are doing your first high power build, then perhaps you don’t know about the thrust ring. Pointing that out in a helpful way as opposed to belittling and criticizing is what I’m drawing attention to.

 

[OzHybrid]

Yes, it's better he asked than not. What I and others said is the this is so very basic that not knowing it is likely a sign of not knowing some other important things. And that makes us concerned for his and others' success and safety.

If I get into a car, eaver to start driving, and ask what that big foot pedal on the left does, I probably should go back to driving the lawn mower around the yard for a lttle while longer while reading a driver's manual.

The big foot pedal on the left could be either a clutch in a manual gearbox vehicle or a brake pedal if it was automatic. So great question Joe.
Zbench, the pedal on the far right is the gas pedal. Not to be confused with the multiple operational capabilities of the left pedals...
Norm

 

[jqavins]

The clutch pedal is the same size as the gas and brake pedals on such cars. A big one on the left is always the brake.

Yes, snarkiness is the opposite of helpful. Look at post numbers 3, 4, and 6. And in case it wasn't clear, Thicky McThick III is a nicname I give myself when I'm being particularly slow on the uptake, not anything directed at the OP.

 

[OzHybrid]

The brake is the biggest. That does not mean the other left pedal cannot be big. And the clutch. Details Joe.....

 

[OzHybrid]

The amount of consideration you have to give this is proportional to the maximum number of G's your rocket will be subjected to with a consideration of the max takeoff thrust. Shock loading on. components is a lot harder than soft loading.
You may only need to spread the motor thrust on to the motor mount tube and allow the force to be distributed to the rest of the rocket through the glue of the mmt to the body or for high thrust shock loaded you might want to use a full size plate across the rear mmt out to the body tube to distribute the loading at that point rather than entirely relying on the glue of the bulkheads as a sole thrust transfer method. Some people foam the mmt in place to the body tube.
Whatever you do, good luck. Find a mentor.
Norm

 

[jqavins]

This picture is typical. The brake and clutch pedals are the same size. There is no "big pedal on the left". Any time the one on the left is bigger than any other, it's the brake.

 

[OzHybrid]

This picture is typical. The brake and clutch pedals are the same size. There is no "big pedal on the left". Any time the one on the left is bigger than any other, it's the brake.
View attachment 515169

Are there any African Swallows in the boot of the BMW?

 

[tsmith1315]

Are there any African Swallows in the boot of the BMW?

Nah, they're not migratory.

 

[David Schwantz]

But I did see a North Amercian Spotted Ferret Bat in there.

 

[OzHybrid]

Nah, they're not migratory.

I think the European Swallow is or was that the Norwegian Blue?

 

[tsmith1315]

I think the European Swallow is or was that the Norwegian Blue?

Definitely the European Swallow, the Norwegian Blue just pines for the fjords. Although, coconuts have been know to make a seasonal journey as well.

 

[jqavins]

OK, I guess we're done here.

 

[Hyak]

You guys are all wrong on what the pedals do!!!!

Left Rudder! Left Rudder!! (and pressing on the top of the pedal is left Brake)
( 'Gas' is usuually on the panel or in the Throttle quadrant!)

Geezzz fellows, how could you not know that?

Ok seriously, I agree with what someone else said earlier. The fellow was asking a question, which to most of us, wouild be basic. But rememebr we *ALL* had this question. and MANY more, once upon a time! We may have found the answer(s) by other metjods, but we ALL had them.

This is a great forum, lots of good knowledge, and everyone is helpful. (Honestly)

@curtthedirt - Welcome to the forum and dont be afraid to ask anything at all. The TRF is a great resource, everyone is great here, despite them being growly sometimes! There is a massive amount of knowledge end experiance here, but sometimes one has to have a bit of a tough skin!

This parrot is no more! It has ceased to be! It's expired and gone to meet its maker! This is a late parrot! It's a stiff!

 

[Spitfire222]

Come on guys. The OP asked an honest question and doesn’t deserve the snark. If this is to be a welcoming community to new comers then occasionally we collectively might have to answer basic questions. The I can’t believe you didn’t know that kind of stuff is petty and not useful. He did ask so as to seek to understand and that’s the point of the forum.

Counterpoint: This is more than answering 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. With no post history, it's difficult to ascertain their experience level, so it's usually best to err on the side of inexperience.

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. And sometimes, that involves not helping out someone who asks very basic questions, but advising them to step back and gain more experience in a more methodical manner.

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

 

[Hyak]

" 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'!