'chute shelf..?

[Ron Soto]

in one of my posts i had mentioned that the CG in my zephyr is less than one tube length of 4" from the CP. a reply'er mentioned that a 'chute shelf could be added one tube length higher in the BT changing the CG more forward. I thought about that.. thinking that currently the CG is so far back there 'might' be a problem running a larger motor. currently there's about 3.5 inches between the CG and CP for the AT H100W.. so, placing a 'chute shelf made from a MM wouldn't add that much weight, and it would definitely place the CG higher so that a larger motor could be used without too much weathercocking. is this acceptable?

thoughts?

ron-

 

[DJRNY]

in one of my posts i had mentioned that the CG in my zephyr is less than one tube length of 4" from the CP. a reply'er mentioned that a 'chute shelf could be added one tube length higher in the BT changing the CG more forward. I thought about that.. thinking that currently the CG is so far back there 'might' be a problem running a larger motor. currently there's about 3.5 inches between the CG and CP for the AT H100W.. so, placing a 'chute shelf made from a MM wouldn't add that much weight, and it would definitely place the CG higher so that a larger motor could be used without too much weathercocking. is this acceptable?

thoughts?

ron-

Ron - I've been pondering laundry shelves and also am getting near the time to start building my Zephyr, so your question is timely. I have no answers but additional questions I hope can be answered here.

If one is retrofitting a finished rocket with a chute shelf, say made from a cluster MM ring glued in, wouldn't that be problematic if one wanted to replace the shock cord sometime in the future? On the other hand, the Zephyr has a coupler, so would it be necessary to glue in the laundry shelf? You could thread the shock cord through an opening in the MM and push it down to the top of the coupler. It should sit tight, but be removable. Would this work?

I have also perused the threads on connecting the recovery system. One school of thought is to connect the chute directly to the nose cone, and the Zephyr falls into that camp. If the chute is connected to the nose cone, packed and burrito'd in the chute protector, it seems to me it wouldn't fall down to the MMT during acceleration anyhow. In that case is a laundry shelf necessary?

Dave

 

[Ron Soto]

Ron - I've been pondering laundry shelves and also am getting near the time to start building my Zephyr, so your question is timely. I have no answers but additional questions I hope can be answered here.

If one is retrofitting a finished rocket with a chute shelf, say made from a cluster MM ring glued in, wouldn't that be problematic if one wanted to replace the shock cord sometime in the future? On the other hand, the Zephyr has a coupler, so would it be necessary to glue in the laundry shelf? You could thread the shock cord through an opening in the MM and push it down to the top of the coupler. It should sit tight, but be removable. Would this work?

I have also perused the threads on connecting the recovery system. One school of thought is to connect the chute directly to the nose cone, and the Zephyr falls into that camp. If the chute is connected to the nose cone, packed and burrito'd in the chute protector, it seems to me it wouldn't fall down to the MMT during acceleration anyhow. In that case is a laundry shelf necessary?

Dave

Dave, This is a great start to my CG problem.. if looking at the attached photo (that i just took), you can see the epoxy ring from attaching the coupler to the BT. by your thinking, a 'cluster' MM would basically pass the ejection charge through the MM without it 'popping out'. this said tim mulligan will be on youtube tomorrow. i'll ask him about doing this. as i mentioned, the CG is so far back that using larger motors will definitely close the gap between the CG and CP.. it's already only 3.5", which is less than a BT.

as for replacing my shock cord (SC) in the zephyr, that would be a very timely, and frustrating exercise. as i followed the building instructions pretty close, at this time to swap out the shock cord.. i'd have to reach down and seperate the blue tape i wrapped around 6" of doubled up SC, manage to actually undo the square knot (which i made super-tight), then try and thread the new SC in and re-tie a square knot. and do all of this w/o being able to see what i'm doing and one-handed in a 4" tube. definitely not impossible.. but i can feel my frustration levels going up just thinking about it..

thanks for replying,
ron-

 

[DJRNY]

as for replacing my shock cord (SC)

For using a cluster centering ring for a laundry shelf, you have the right idea of what I was trying to describe.

As far as replacing your shock cord, I wasn't suggesting it would be a fun way to spend an evening! I have read that nylon shock cords may get damaged over time from the ejection charges and may need to be replaced. I have no experience with that, but am just trying to think ahead. It seems to me a sharp blade would make disconnecting it at the eye bolt relatively easy, and a slip knot (or sewn in loop) would make attaching a new one simple. At least on paper!

Dave

 

[David Schwantz]

On several rockets I have glued another, smaller BT, onto the inside of the main BT. I pack the chute into this smaller tube. Not only does it keep it in place, but it keeps things neater and it also protects from BP charring.

 

[David Schwantz]

To replace shock cord, just reach down inside tube and cut it. Gotta replace it anyway. Now your new cord, either tie a loop or sew one into it. Drop a length of dental floss down tube and through your eyebolt. Pull it up and tie onto new shock cord and pull it through eyebolt. Now just run the end back through the loop you made and pull tight. Go fly.

 

[Ron Soto]

To replace shock cord, just reach down inside tube and cut it. Gotta replace it anyway. Now your new cord, either tie a loop or sew one into it. Drop a length of dental floss down tube and through your eyebolt. Pull it up and tie onto new shock cord and pull it through eyebolt. Now just run the end back through the loop you made and pull tight. Go fly.

thanks... totally appreciate the thoughts..
r-