Can we talk SC Precision / SCP thrust plates?

These look interesting, anybody got a comment or two?

I wonder especially about this statement on their web page: "eliminates shear loaded joints, and these can be removed and replaced to reconfigure your motor arrangement". Well, OK... but what does that mean? I'm struggling to imagine a fundamentally different way to assemble a motor tube, fins, and some centering rings. This sort of implies a different, alternative way exists? Can someone elaborate on this?

I'm all for buying one just because it looks cool. And I can see how it can couple most of the push to the entire circumference of the BT. It's the rest of the description that has me scratching my head.

(no surprise; I'm basically still in a turkey induced coma :smile: )

"shear-loaded joints" refers to the condition where the motor pushes on the MMT, which tries to slip inside the CR's, which themselves try to slip up into the airframe, and in doing so, drag the airframe upward; it's the fact that the force is in the same plane as the mating surfaces, trying to make them slip past each other were it for the glue.

It looks like an unnecessary and seriously heavy addition to the back of the rocket (worst place to be adding weight). I never have understood it.

It basically takes the load off of the centering rings so that you can use very lightweight ones.

I don't know what the net weight savings would be, especially since you'd be adding a hunk of aluminum at the very worst place for it, weight-wise: at the very back.

CCotner said:

It looks like an unnecessary and seriously heavy addition to the back of the rocket (worst place to be adding weight). I never have understood it.

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That depends entirely on how big your rocket is. I have one on my 87 pound (pad weight) 7.5 inch Kraken. On that rocket, the weight is completely negligible, and I like the fact that it eliminates shear loaded joints. It also makes the back of the rocket look nice - it's a lot easier to clean a whole bunch of charring off of an anodized aluminum plate than it is on most rockets. Finally, I like that it is pre-drilled and tapped to accept a 98mm Aeropack - that makes the alignment and assembly a bit simpler. Is it necessary? No, but it can be helpful.

I used one on my ultimate darkstar just to make it look good.

Also, shear loaded joints become a problem when you make very large rockets using spiral wound tubes (paper or phenolic; blue tube would be more resilient). The inner layers can delaminate, so the joint won't fail in shear but rather the body tube. This I presume would nearly eliminate that possibility.

They do add weight to the back end of the rocket. However, if the rocket is not marginal, it may not be a big deal.

From my perspective, they're just plain cool, and are a nice touch. I just put one on my new Formula 98, still in progress.

Rocket bling. We seem to be moving that direction. Cool looking plates, av-bay bulkheads, charge containers, etc. Is it needed? Not at all. But hey, it's fun! And if it excites you and fits your design/build without sacrificing safety, then why not? BTW, I have a 6" SCP plate / Aeropack combo ready and waiting for an upcoming scratch build .

Everyone has hit the nail on the head: transferring the load directly into the end of the tube instead of transferring the load through the motor mount, through the shear-prone epoxy joints, then into the tube.

Additionally, it protects the back end of the rocket on landing, looks much nicer, and can be drilled/tapped directly.

For my 4" Broken Arrow (Black Friday purchase) I will be turning all aluminum plates. A part of me is considering making centering rings out of aluminum due to their minimal web, but that is definitely overkill. Aluminum altimeter bay bulkheads are superior (IMHO) for the reasons stated above, as well.

I will try to remember to post pictures.

The weight of Scott's thrust plates is not even worth mentioning, there not meant for 2.1" paper BT. If that type of weight is going to make your rocket unstable you most likely have bigger problems. IMO these plate are awesome! They fit perfectly, come pre drilled and threaded to mount your Aero Pack without having to play with those inserts.

I have one on my VORLON 5 and love it.

Gary,where did you get the kool blue aeropacs?

I see how that doesn't cause any weight issues... for some reason I was imagining a skinny motor mount in a 12" rocket, which would add a good deal of weight.

jimzcatz said:

Gary,where did you get the kool blue aeropacs?

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Jim:
I ordered unanodized retainers and had them done on my own.

For the sake of discussion has anyone had a motor mount blow through a rocket?

I've just never heard of this specific case as an example.

I have seen it happen but not with high power.

bandman444 said:

For the sake of discussion has anyone had a motor mount blow through a rocket?

I've just never heard of this specific case as an example.

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I've seen an adapter shear off its thrust ring and fly up through a rocket.

Otherwise, no, except in the case of a CATO, at which point all bets are off, anyway.

-Kevin

I think these are cool looking - but there are other solutions to this problem. You could do a stacked ring design with an inner ring that fits inside the tube and has an inner opening that fits that motor tube; then another ring that is the airframe diameter and has a coupler sized opening rather than a motor tube sized opening so that the lip of the motor (or retainer) rests against the motor tube rather than being gluded in a way that could sheer. The thrust would be distributed out to the outside by the ring and transferred to the bottom of the rocket tube - the key here is that these rings would need to be very strong assuming that you wanted to remove the reliance on the centering rings farther up the tube. fiberglassed or aluminum honeycomb then the weight difference is likely to be low.

The problem (as is often the case in HPR) is that many of these rockets are overbuilt. This type of plate is great for looks and for function - but my guess is most are using it for looks and trying to justify it by function and a few are actually benefiting from the function directly.

These definitely fit into the category of 'want', not 'need'. Gary didn't need blue anodizing - but now how many of you are jealous and now want to choose a color for your retainers? ( I need red ones to match my cool thrust rings!)

Scott, want to start taking custom orders for your anodizing shop? :grin:

The only part I'm not clear on is the retention for the thrust plate.

...Wood screws? Tee nuts? PEM nuts?


All the best, James

GaryT said:

The weight of Scott's thrust plates is not even worth mentioning, there not meant for 2.1" paper BT. If that type of weight is going to make your rocket unstable you most likely have bigger problems. IMO these plate are awesome! They fit perfectly, come pre drilled and threaded to mount your Aero Pack without having to play with those inserts.

I have one on my VORLON 5 and love it.

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get some respectable rockets MAN!

Very nice...!!!!!

I bought one for my PR Madd Max. 8" tube 4" hole. The plate weighs one pound exactly. Do I need it. No. Will I use it. Probably. The first one he sent me was 7.5"x4" fits PML tube. Since I have a PML 1/2 scale Patriot, I just kept that sucker, and had him ship me the correct one. Haven't weighed the 7.5"x4" yet. Gotta be close to that 1 pound, I assume.

Adrian

UncleVanya said:

The problem (as is often the case in HPR) is that many of these rockets are overbuilt. This type of plate is great for looks and for function - but my guess is most are using it for looks and trying to justify it by function and a few are actually benefiting from the function directly.

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Brad, we are in 100% agreement on the overbuilding!

The metal plates do look cool. Darned cool. But they're not necessary.

-Kevin

Theres nothing wrong with building a stronger rocket. It all depends on what the builder wants out of HIS rocket AND how long he wants to keep it for. Can a paper BT stand up to an M? Yes! Can it be built with Elmer's wood glue and still fly an M? Yes! Can you use standard rail buttons on a 60lb rocket? Yes!

BUT! I can guarantee you this your rocket will last 10 times longer and fly MANY more times if over built by even little. Personally I'd MUCH rather fly my rocket longer than use inferior materials in its build just because I can.

To Gary's point, it's a matter of what makes the flier happy -- if it's within the safety code, and it makes the flier happy, then it's the right materials for the job.

-Kevin

Worsaer said:

These definitely fit into the category of 'want', not 'need'. Gary didn't need blue anodizing - but now how many of you are jealous and now want to choose a color for your retainers? ( I need red ones to match my cool thrust rings!)

Scott, want to start taking custom orders for your anodizing shop? :grin:

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Sign me up!!!!

Well I'm sold. I ordered a ring last night for the 6" Darkstar I got from Tim's BS sale.

GaryT said:

Theres nothing wrong with building a stronger rocket. It all depends on what the builder wants out of HIS rocket AND how long he wants to keep it for. Can a paper BT stand up to an M? Yes! Can it be built with Elmer's wood glue and still fly an M? Yes! Can you use standard rail buttons on a 60lb rocket? Yes!

BUT! I can guarantee you this your rocket will last 10 times longer and fly MANY more times if over built by even little. Personally I'd MUCH rather fly my rocket longer than use inferior materials in its build just because I can.

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This could head downhill fast so I'll just suggest that we agree on some points and disagree on others... no that's not sufficient.

My saying that someone is overbuilding a rocket is guilty of making an assumption - the assumption is that they have no need for the extra strength - which could be wrong. "Need" can be defined a lot of ways. Your statement that there is nothing wrong with building a stronger rocket is also wrong - a stronger than needed rocket has increased safety risks. Imagine building rockets that survive a ballastic fall from apogee - who hasn't seen one of these? Now imagine it hits something we don't want hit? Luckily this is a very low likelyhood due to the "needle in a haystack" type problem of a falling rocket hitting something.

What I guess bothers me - isn't someone like yourself - you took the time to make a concious decision to build things stronger, you understand that lighter methods can be used safely. The problem I have is with people who think their rocket should be built to withstand their F250 running over it before it can handle a baby J motor!

If we all spent more time on ensuring successful recovery maybe we would spend less time overbuilding the structure of the rockets.

UncleVanya said:

What I guess bothers me - isn't someone like yourself - you took the time to make a concious decision to build things stronger, you understand that lighter methods can be used safely. The problem I have is with people who think their rocket should be built to withstand their F250 running over it before it can handle a baby J motor!

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My concern is a variant of that, but not related to this specific topic.

Instead, I get worried when people justify the "need" to cover everything with carbon fiber, or build fiberglass rockets, "Because mine fell from 5,000 feet without a parachute and wasn't scratched."

So, they fix their recovery problems by building a bullet proof rocket, rather than fixing the problem that prevented the parachute....

-Kevin

overbuilt or not, that blue thrust plate/retainer combo looks great!

Derek
Neither Kevin or UncleVanya were saying mine was over built, we where just talking about over building in general. But I agree it looks awesome. Thanks!