Rear deployed chute

[Ctbch05]

How would I go about a rear deployed parachute? Not any particular build or rocket just in general. Would it involve redirecting the ejection charge blast with an mushroom or inverted funnel type shape?

 

[sharkbait]

How would I go about a rear deployed parachute? Not any particular build or rocket just in general. Would it involve redirecting the ejection charge blast with an mushroom or inverted funnel type shape?

My big saucers, big Sputniks, and my Flying Pumpkin all have rear eject. Simply have a solid bulkplate somewhere above the motor mount tube, don’t glue the motor mount centering rings to the airframe, blow the entire motor mount out the rear along with your recovery gear.

 

[lakeroadster]

How would I go about a rear deployed parachute? Not any particular build or rocket just in general. Would it involve redirecting the ejection charge blast with an mushroom or inverted funnel type shape?

A motor / parachute spool.

I love rear eject chutes... Check out my Red Columbine or Warhawk build threads.

 

[Ctbch05]

My big saucers, big Sputniks, and my Flying Pumpkin all have rear eject. Simply have a solid bulkplate somewhere above the motor mount tube, don’t glue the motor mount centering rings to the airframe, blow the entire motor mount out the rear along with your recovery gear.

So have a shockcord and parachute like kindof wrapped around the mount assembly? So that when it gets blown out, it drags along and unspools to deploy sorta? I'm bad at explaining things lol

 

[sharkbait]

So have a shockcord and parachute like kindof wrapped around the mount assembly? So that when it gets blown out, it drags along and unspools to deploy sorta? I'm bad at explaining things lol

Thats exactly how my saucers are set up.
The Sputniks and flying pumpkin have the chute and gear in the space above the MMT

 

[Ctbch05]

Thats exactly how my saucers are set up.
The Sputniks and flying pumpkin have the chute and gear in the space above the MMT

Okay thankyou so much bc I was wondering how to do it. Yall are awesome with all the quick advice and stuff. I really appreciate it.

 

[Padruig]

Another option is like what is setup on the Estes Gemini DC. Two outer tubes attached to the main tube with cutout holes passing between the two. All three tubes have glued in nosecones, restricting forward gas movement. The gas vents out the sides of the main tube into the side tubes and pushes the parachute out the back of the tubes.

https://www.rocketreviews.com/gemini-dc-7633.html

 

[Cape Byron]

Go to the Apogee Rockets website and look for the Peak of Flight newsletters. You should be able to search for the one on rear-eject. That will tell you all you need to know.

I’d post a link, but my phone is about to cut out.

 

[JimByrne]

Does anyone else have photos that they can share, showing their lay out of motor mount & parachute?

 

[David Schwantz]

/this is bomb rocket. Rear eject. 1st pic all stowed away. 2nd starting to deploy. 3rd pilot chute showing. 4th pic, deployed. 5th pic you can see main just starting to come out.

 

[Cape Byron]

Found the Apogee newsletter.

https://www.apogeerockets.com/education/downloads/Newsletter439.pdf
Pod Prep page from our Apanina kit instructions (Attached).

 

[BABAR]

lots of good ideas Already mentioned.

few more of tricks.

1. the downside of rear eject pods is space can be at a premium. With fat bodied rockets, not as much of an issue. With medium or relatively narrow body rockets, like BT-20 to BT-50, it can be both tight and a PITB to back.

you CAN downsize the central tube BELOW motor mount diameter, for example you can use a BT-20 motor mount and extend the tube up the middle using a BT-5. the BT-5 to BT-20 centering ring will serve as a centering ring and a motor block. Put a rolled up piece of aluminum can or smear the inside first 3 inches of the BT-5 to prevent burn through. Make sure to attach your shock cord and chute to the motor mount end of the tube, you may need to route the rocket body attachment through a channel in or through the forward centering ring, or use an external mount. This will greatly increase the room for chute packing. Nice thing about rear eject is no wadding needed to for chute, may want some for shock cord if it is stowed anteriorly,

2. Nose weight. You can use your pod to carry the nose weight, especially for hollow plastic nose cones. You can cut Base of the nose cone (the bulkhead, if you prefer) off and extend the central motor pod tube well into the nose. Now attach Your nose weight to the front tube of the motor pod forward of the forward centering ring. At ejection, this is less weight in the body section of the rocket on descent, which is kind of a good thing since it is going to land pointy end first, so keeping that section as light as possible helps. It is ESPECIALLY helpful with internal pop pod gliders, as you have the nose weight where you want it for boost and you literally eject it (with a streamer or chute of course) from the glider segment at apogee, so it is win-win,

3. Consider using a rounded tip nose cone, as rear eject models coming in nose first can be a bit tough on the nose, especially if landing on hard surfaces like asphalt, concrete, playa, rocks, etc. consider also at launch putting a little piece of masking tape on the nose to protect the paint, pull it off carefully on recovery.

hope these are helpful.

 

[kuririn]

The only thing I would add is do not wrap the chute and shroud lines around the motor tube, just lay it on the side.
Otherwise you increase the risk of your recovery device not unfurling.

 

[BABAR]

The only thing I would add is do not wrap the chute and shroud lines around the motor tube, just lay it on the side.
Otherwise you increase the risk of your recovery device not unfurling.

Definitely. Also not the best “spike and fold” solution. There are lots of ways to skin this cat, here’s one:

ideally dust it with non-cornstarch baby powder before starting.

assuming a hexagon or octagon ParaSheet (typical low power kit or homemade chute),

fold in half so shroud line attachments meet (1/2 hexagon or octagon)

fold 90 degrees (1/4)

if width from side to side (not tip to edge) is still wider than length between centering rings, fold once more to 1/8, the OPPOSITE DIRECTION of previous fold. You want an accordion, not a burrito. hopefully this should be enough to fit Between rings. Keep shroud lines straight, out of the chute at this point.

now fold tip to edge. If remaining LENGTH of your truncated triangle is still more than one wrap around the central core tube, fold again in opposite direction. Keep folding (should only take three or at most four folds), on last fold tuck shroud lines in the fold. Definitely no shroud lines around the chute, I think you can wrap around the tube as long as there is little overlap, definitely not more than 1 1/2 wraps.

you Should still have a fairly FLAT bundle that you can wrap around the central tube, should wrap around once, definitely not more than twice.


i would be curious to know how others deal with shock cord attachments to the rocket For these, my tendency has always been to use this for glider central pop pods so there IS no attachment.

issues I see is that a forward stowed cord (between forward ring and base of nose cone or, if hollowed out and extended, the internal surface of the nose cone itself) is subject to ejection blast, so challenging to protect.

other attachment points, including external, have to run between centering rings and body tube. Maybe a notch in the rear centering ring? a Trifold mount BETWEEN rings would likely bung up sliding the mount in and out.

BTW, if you do cut off the basal bulkhead of a hollow nose cone. Put some glue (JB weld is ideal, but even a couple layers of white glue is probably adequate) on the inside of the TIP of the plastic nose cone, as it is gonna get a direct hit of ejection blast and particles.

also, classic construction is to glue the nose cone in place. This definitely works. Option for inspection or replacement or otherwise access to forward body tube is to secure the cone with an external tape wrap. This is aerodynamically suboptimal as it does create two small circumferential ridges and a seam, but if you were an altitude junkie you probably aren’t going To use rear eject anyway. Mylar tape works well, isn’t too thick, and comes in nice shiny colors so maybe it will spruce up your paint scheme rather than mess it up. Electrical/Vinyl tape also works well, you can stretch it so it holds tighter, also comes in a few colors (I have seen white, yellow, red, blue, green, and purple in addition to classic black.). In either case, not a bad idea to put a layer or Scotch or generic cellophane tape around both the outer base of the nose cone (just above shoulder) and the forward edge of the body tube AFTER painting, BEFORE putting on Securing tape. Wrap it the OPPOSITE direction of your Securing tape wrap. This will allow you to remove the Securing tape more easily WITHOUT pulling off the paint or worse delaminating the tube.

 

[BABAR]

Also (yeah, I know,’nuff already), unless you have a ton of space, these are best packed soon ideally just before flight, and really need to be able to slide in easily. After packing, the recovery device tends to spontaneously try to unwrap, leading to more friction at deployment. Longer it is stored, the more it unwraps. Rear pop pods need to be on the looser side, as unless the whole pop pod comes out, they don’t function well.

 

[BABAR]

A motor / parachute spool.

I love rear eject chutes... Check out my Red Columbine or Warhawk build threads.

View attachment 554346View attachment 554347View attachment 554348View attachment 554349View attachment 554353

there is a modification that may minimize impact on nose.
longer shock cord, with the motor mount attachments separate from and longer than the body tube attachment , ideally several feet.

motor mount lands first, the decreased mass on chute slows both chute and body tube descent rate, so body tube/nose cone impact is a bit lighter.

you sometimes see this on high power launches were multiple segments come down under one chute, the first segment impacts and the others slow down a bit before THEY impact.

 

[shockie]

Here's an oldie but goldie: Minimum diameter model with a rear ejection clip made out of a safety pin. I actually used one of these in my NARAM-12 Design Efficiency model. The model was made from an Estes Bt-10 mylar plastic tube (from their Streak kit) and a CMR plastic nose cone. It kinda melted both going up and coming back down.

 

[BABAR]

Here's an oldie but goldie: Minimum diameter model with a rear ejection clip made out of a safety pin. I actually used one of these in my NARAM-12 Design Efficiency model. The model was made from an Estes Bt-10 mylar plastic tube (from their Streak kit) and a CMR plastic nose cone. It kinda melted both going up and coming back down.

I love this. Been thinking a long time how to do it, this is simple and brilliant. Thanks.

Now problem is how to use it? What happens to rocket body once motor ejected, at least if no electronics on board?

Glider? Dumping motor definitely drops unneeded weight, but CG shift is wrong (hmmm, unless it flies backwards….. that has potential…….)


Helicopter? Definitely do—able. Just need a mechanism to deploy rotors, Lots of ways to implement that.

Of course, both above can be done with simple motor eject. But this addition might make such more acceptable in certain fields or high wildfire risk areas where motor eject might make flyers or RSOs itchy or where unretarded motor eject is forbidden.

There must be other options I am just missing.

 

[JimByrne]

I love this. Been thinking a long time how to do it, this is simple and brilliant. Thanks.

Now problem is how to use it? What happens to rocket body once motor ejected, at least if no electronics on board?

Glider? Dumping motor definitely drops unneeded weight, but CG shift is wrong (hmmm, unless it flies backwards….. that has potential…….)


Helicopter? Definitely do—able. Just need a mechanism to deploy rotors, Lots of ways to implement that.

Of course, both above can be done with simple motor eject. But this addition might make such more acceptable in certain fields or high wildfire risk areas where motor eject might make flyers or RSOs itchy or where unretarded motor eject is forbidden.

There must be other options I am just missing.

The body & motor tube (with motor in it) are all attached together with the harness and will land together. The motor does not eject from the motor tube. The CG doesn't matter after ejection since it is all hanging under the parachute.

 

[BABAR]

The body & motor tube (with motor in it) are all attached together with the harness and will land together. The motor does not eject from the motor tube. The CG doesn't matter after ejection since it is all hanging under the parachute.

Can't argue with success, but seems a bit counterintuitive.

I can buy a metallic wire running from the attachment device to the recovery streamer or chute, maybe with a small wadding or nomex burrito. Problem is that ejection charge initially will ram everything in front of it FORWARD, so you have to rely on kinetic energy/inertia of the two parts, motor going back and "kicked" rocket body forward, to pull the rammed chute and wadding back OUT after ramming it forward initially. Would require some very loose packing.

Another option would be a piston just above the motor, with a "piston block" (equivalent of motor/engine block.) Ejection charge fires, blows motor out, blows against piston but piston can't go forward because of piston block, inertia of motor ejection (particularly with Estes (in)famous "shotgun" ejection charges then pulls out the piston and the laundry attached forward to it. Hmmm, the piston block MIGHT catch on the chute or streamer, so the "piston block" might be made as a long TUBE (basically same body tube as the body tube, cut out a long sliver that when taped leaves it JUST barely able to slide into the main tube. Make it long enough to hold your shock cord and chute. Costs you a little bit if diameter (two wall thicknesses), which isn't too bad, and leaves a smooth surface for the laundry to slide out. Bonus, the piston protects the chute from the ejection charge, no wadding needed. I like this. The piston doesn't even have to be that long, could probably do it with just a bulkhead. Hmmm, I can see this working very well for a minimum diameter 24mm version of the Buillet Bobby. Specially SMALL short stubby rockets with bulbous hollow plastic nose cones, maximized the space for the chute (cuz you can cut the bulkhead base off the nose cone, glue the shoulder in, and can use the nose cone itself as space for your recovery gear.

Would work nicely for downscale Gooneys.

One issue I can see with the attachment hook, fully packed motors (like the C6-5 and the C5-3) may not have a lot of space in the forward end of the actual motor to put the hook. Should have plenty of room on 18 mm black powder A and B and 24 mm black powder C motors.

 

[RocketRev]

My level 1 cert was a 4" diameter LOC parts scratch built rear ejection. Worked great for several years. I epoxied a 4"x54mm centering ring about 16 inches up into the rear of the fin section. The motor mount tube slid up in to aft section and had another CR epoxied on its end. Plenty of room for recovedry harness and parachute. All but the last flight were with 38mm motors and a 54/38 motor adapter.

When it worked, deployments were smooth, gentle, and seemed to be unhurried. I really ought to build another one. Maybe 5.5" this time.......hmmmmmmmmmm.......thinking........

On several flights I did have a problem with the slip-stream being so smooth that the parachute just sat against the motor mount tube after ejection and did not deploy. I was working on a fix to destablize the smoothness of the airstream during descent when the rocket was destroyed by shredding the unfiberglassed 1/8" thick plywood fins on a K-550 trying to go thru mach. I learned a lot that day including not to try to break mach with unprotected plywood fins. I never rebuilt it, so I don't even know if my fix would have worked. But an overly smooth slipstream after deployment might be something to watch out for in rear deployment. At least that was my observation back in 1992 and 93 when I built and flew that beauty.

I almost forgot to mention my "fix" which was in fact two fixes. The first was simply to increase the length of the harness cord between the airframe eyebolt in the internal epoxied centering ring and the centering ring on the MMT. The second was to add a small drogue chute on the top of the parachute to pull the parachute away from the MMT in order for it to deploy.

Well there you have my two small solutions to the smooth slip stream problem that I found.

Brad