Converting a rear deploy rocket to regular forward deploy?

The Rocketry Forum

Help Support The Rocketry Forum:

billdz

Well-Known Member
Joined
Feb 11, 2017
Messages
1,282
Reaction score
79
Some may recall my prior thread about the 5.5" rear deploy rocket I acquired, see https://www.rocketryforum.com/threads/rear-ejection-and-payload-bay.160035/#post-2013537.

Using Tim VanMilligan's recommendation to wrap the chute and lines around the motor tube, I launched the rocket and it had a hard landing that damaged the nose cone, because the chute did not unwind off the motor tube. I've acquired a new NC and am ready to launch this rocket again, but I'm leery about this rear deploy, others have told me it can be unreliable. So I'm wondering if it might be a better idea to convert the rocket to regular forward deploy. As I as I can tell, this would require 1) gluing the motor tube to the airframe (that seems doable), and 2) removing the bulkhead above the motor tube (may be difficult but there must be a way).

Any thoughts on whether this is a good idea? I'd be happy to keep it as rear deploy if there's a way to load the chute so it will deploy reliably.
 

Cape Byron

The BAR formerly known as Skippy-2
TRF Supporter
Joined
Aug 4, 2019
Messages
1,530
Reaction score
1,557
Location
Northern Rivers, Australia
With rear eject I've found most failures I've had are due to residue in the body tube preventing the motor 'pod' from ejecting cleanly OR wrapping the chute too tightly on the pod tube. Loose is good. Canopy on top of shroud lines. Swivels are a must.

The pod is usually loose enough to want to fall out of the model when you're placing it on the rod. Use a good stand off like a used motor.

Then again, I can only speak of my experience with my own scratch builds.
 

billdz

Well-Known Member
Joined
Feb 11, 2017
Messages
1,282
Reaction score
79
With rear eject I've found most failures I've had are due to residue in the body tube preventing the motor 'pod' from ejecting cleanly OR wrapping the chute too tightly on the pod tube. Loose is good. Canopy on top of shroud lines. Swivels are a must.

The pod is usually loose enough to want to fall out of the model when you're placing it on the rod. Use a good stand off like a used motor.

Then again, I can only speak of my experience with my own scratch builds.
Interesting, thanks. My pod is not so loose it would fall out on the pad. On my one flight, the pod ejected perfectly, but the chute just never unwrapped from around the pod tube. Your suggestion to wrap the chute and shroud lines loosely around the pod tube accords with what Tim VanMilligan says, but it did not work for me, perhaps something got twisted. What is the purpose of wrapping the chute around the tube? Why not just place the chute and shroud lines next to the pod tube, between the tube and the airframe?
 

Cape Byron

The BAR formerly known as Skippy-2
TRF Supporter
Joined
Aug 4, 2019
Messages
1,530
Reaction score
1,557
Location
Northern Rivers, Australia
Wrapping the chute loosely around the pod lessens the chance of a 'balled' or wadded chute jamming between the pod and the body tube.

What type of chute were you using?
 

Cape Byron

The BAR formerly known as Skippy-2
TRF Supporter
Joined
Aug 4, 2019
Messages
1,530
Reaction score
1,557
Location
Northern Rivers, Australia
Okay, my morning coffee(s) have me thinking...

On our Apanina the shock cord from the main airframe attaches to the front centering ring of the motor pod rather than further down the pod, which may give some 'shake' for want of a better word when the pod ejects.

Maybe?

Where is the shock cord attached on your model?
 

billdz

Well-Known Member
Joined
Feb 11, 2017
Messages
1,282
Reaction score
79
Wrapping the chute loosely around the pod lessens the chance of a 'balled' or wadded chute jamming between the pod and the body tube.

What type of chute were you using?
The chute is 42" with 4 shrouds and a swivel. Shock cords are attached to eye bolts on the top and bottom of the forward centering ring.
 

Attachments

Cape Byron

The BAR formerly known as Skippy-2
TRF Supporter
Joined
Aug 4, 2019
Messages
1,530
Reaction score
1,557
Location
Northern Rivers, Australia
Okay, similar mounting system on a much bigger rocket.

Hmmm... Nothing to suggest at present, but plenty to think about. I'll get back if I can think of anything.
 

teepot

Well-Known Member
TRF Supporter
Joined
Dec 8, 2019
Messages
1,085
Reaction score
668
Location
Pahrump, Nevada
Can it go above the motor? That's what I did on a rear eject I built. But I put the motor mount into a coupler. And the coupler slides into a BT.
 

Attachments

jqavins

Helpful Smartass
TRF Supporter
Joined
Sep 29, 2011
Messages
5,388
Reaction score
2,502
Location
Howard, NY
For the original question, conversion, you shouldn't have to remove the bulkhead. You only have to remove some of the bulkhead. Get in there with whatever tool(s) will reach and cut/drill/break it apart until there's plenty of open area for the ejection gas to get through. And in a 5.5" airframe that doesn't have to be nearly all of it. Then cut the body tube somewhat below the nose cone shoulder and add a coupler for separation.

As for rear deployment, like you I would have thought that laying the parachute alongside the MMT would be the way to go. The answer above makes sense, and plenty of people, it seems, have succeeded that way, so who am I to argue? Still, if you want to try a different way, how about fan folding the parachute to a little less length than the space you've got, then laying it it?

Did I read you right that you've got a 42" chute with only 4 shroud lines? I've never seen fewer than 6 on any size chute, and surely more for one that big.
 

billdz

Well-Known Member
Joined
Feb 11, 2017
Messages
1,282
Reaction score
79
For the original question, conversion, you shouldn't have to remove the bulkhead. You only have to remove some of the bulkhead. Get in there with whatever tool(s) will reach and cut/drill/break it apart until there's plenty of open area for the ejection gas to get through. And in a 5.5" airframe that doesn't have to be nearly all of it. Then cut the body tube somewhat below the nose cone shoulder and add a coupler for separation.

As for rear deployment, like you I would have thought that laying the parachute alongside the MMT would be the way to go. The answer above makes sense, and plenty of people, it seems, have succeeded that way, so who am I to argue? Still, if you want to try a different way, how about fan folding the parachute to a little less length than the space you've got, then laying it it?

Did I read you right that you've got a 42" chute with only 4 shroud lines? I've never seen fewer than 6 on any size chute, and surely more for one that big.
Thanks for the reply, I had almost forgotten about my original question. I'm happy to leave it as rear deploy if that will be reliable. I'm thinking that those who wrap the chute around the tube are flying smaller rockets, so that if not wrapped the chute would be squished too tight and stop the motor tube from ejecting. I'm going to try a ground test with the chute laid to the side of the MMT, there's plenty of room.

I'm not sure why there is a nomex blanket on the top side of the MMT, on the shock cord that connects the MMT to the bulkhead.

If conversion is needed, the hardest thing will be getting a tool down to the bulkhead, it is 2 feet deep. The new NC is ready so I need to decide soon.

Yes, the chute has 4 shrouds. It appears to be commercially made but I don't see any name or logo on the chute.
crayon MMT and chute.jpg
 

Cape Byron

The BAR formerly known as Skippy-2
TRF Supporter
Joined
Aug 4, 2019
Messages
1,530
Reaction score
1,557
Location
Northern Rivers, Australia
Yes, the chute has 4 shrouds. It appears to be commercially made but I don't see any name or logo on the chute.
I wonder if you would have more success with a more conventional chute?

Ground testing is the best way forward, for sure.
 

jqavins

Helpful Smartass
TRF Supporter
Joined
Sep 29, 2011
Messages
5,388
Reaction score
2,502
Location
Howard, NY
I'd forgotten that you're replacing the nose cone, so don't need the cut and coupler I mentioned.

Part of my thinking is that with a 5.5" airframe tube, the tool doesn't need to be two feet long, 'cause you can reach your hand in. You could probably reach up inside with a small rototool (Dremel) in hand and have at it.
 

billdz

Well-Known Member
Joined
Feb 11, 2017
Messages
1,282
Reaction score
79
As for rear deployment, like you I would have thought that laying the parachute alongside the MMT would be the way to go.
I wonder if you would have more success with a more conventional chute?
Ground testing is the best way forward, for sure.
Successful ground test today, with the chute laid alongside the MMT!

I'm going to fly it again this way with rear deploy. I'm feeling pretty confident, but if I lose another NC it is going to be converted. When I acquired this rocket, the NC was glued to the body tube, but I'm thinking about a less permanent means of attachment, in case I later decide to do a conversion or some other mod. The shoulder of the new NC is so thick I can't use plastic rivets, maybe self-tapping screws?
crayon ground test.jpg
 
Top