Re: Centering Ring Placement


Gary Slater
 

The limitation is that I got only two with the kit. 

There are instances particularly in short, stubby high power rockets that recovery gear may have to be in the nose cone or somewhat wrapped around a motor that invades the airframe space. Just sayin. 

I prefer a centering ring at both ends of the fins if possible but I also realize the strength lies at the centering ring/fin tab interface. I often add that 3rd CR when I build a rocket with “short” fin tabs like the one in question because I want that extra little bit of airframe stiffness where the forward fin tip meets the tube. 

So my options are to make another,  buy another or do without.  This rocket airframe length and volume will accommodate the recovery even if I do add that forward ring. Even more so because the shoulder of the nose is open giving me an extra 3 1/2 inches of length/volume. 

For the record the kit in question is a Loc Minie Magg. I am removing the closed aft end of the nose. 

On Jun 10, 2021, at 6:19 PM, Kevin A <kauskings@...> wrote:


Is the limitation only having 2, or does something in the design prevent a 3rd?

On Thu, Jun 10, 2021, 6:11 PM Gary Slater <gws77@...> wrote:
Let me add some information. 
The motor tube option is to accommodate up to a 38/720 case. So about 14 inches. 
What I want is all 3 CRs but I only have 2. 

On Jun 10, 2021, at 5:50 PM, Greg Smith <gregs@...> wrote:



Agree completely with Mark. A third, forward ring is useful because it provides a convenient anchor point for a U-bolt or other recovery attachment, and it makes construction easier because it holds the motor tube in good alignment while you work on the internal fin tabs and fillets. But its structural contribution is minor.

 

- GDS

 

 

 

From: cia-rocketry@groups.io [mailto:cia-rocketry@groups.io] On Behalf Of Mark Joseph
Sent: Thursday, June 10, 2021 5:45 PM
To: cia-rocketry@groups.io
Subject: Re: [cia-rocketry] Centering Ring Placement

 

Interesting points, Kevin.

One concern in not having a truly "forward" centering ring has to do with conveniently and securely anchoring the recovery harness. If you've got that worked out in some other way, then I wouldn't give this a second thought. My opinion is that supporting the forward end of the motor mount (or even motor mounts long enough for the range of intended motors) is a somewhat overrated concept. I think that the structural integrity gained by creating the mechanical "system" of airframe/fin tabs/centering rings/motor mount/epoxy is the bottom line.

Thanks for letting me ramble. Again.

Mark

________________________________________
From: cia-rocketry@groups.io <cia-rocketry@groups.io> on behalf of Kevin A <kauskings@...>
Sent: Thursday, June 10, 2021 5:22 PM
To: cia-rocketry@groups.io Group Moderators
Subject: Re: [cia-rocketry] Centering Ring Placement

I would think at the top of the TTW fin tab would give the best support... But how far past that point does the MMT extend?

If that ring is not at least slightly past the midpoint of the MMT, I'd be looking at other options... Perhaps some shims at the leading end of the MMT tube vs a full ring?

Just my noob thoughts.

Cheers,
Kevin

._,_

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