stuffer tubes?

[bjphoenix]

I saw a couple of ejection failures at our local launch today. My Estes Executioner on a D12 did not eject the chute. It blew off the nose cone but the chute and kevlar protector was half in the body and half out of the body. This is a fairly light and large rocket so it tumbled down sideways and landed on tall weeds with no damage. That's a big volume to pressurize and the D12 couldn't do it. I'm thinking about retrofitting a stuffer tube to reduce the amount of volume that the engine has to pressurize. Or I have to get my act together, find my 24/40 casing and fly the thing on reloads.

The other failure was a BT60, maybe BT55 rocket that was around 6' long. (Is this an old kit?) It looked like it had the chute all the way out at the nose cone which would also be a lot of tube to pressurize. This particular one didn't blow anything out and lawndarted which crunched the long tube in several places. I think this one needed to separate closer to the engine rather than at the nose cone, in effect built most of the rocket length as a payload section.

 

[teepot]

I think the long rocket might be a mean machine. After I had several failures to eject I stopped doing nose cone eject unless it was a short rocket. Anything over 4' I make the top section a payload bay and the lower section just big enough to hold the chute and shock cord. This also let me convert several rocket to dual deploy once I got some altimeters.

 

[dpower]

Stuffer tubes are good ideas for larger volume rockets flown on BP motors. Estes kits often have stuffer tubes a bit short. The current 3" diameter Der Big Red Max has only a 4.5" motor tube, I've bumped it up to 6", a reduction of about 20% in volume. I prefer to build Estes kits as close to stock as possible, keeping the cost and weight down, so a shock cord connected to the MM, and stuffer tubes are about the only things I may change.

 

[Bill S]

I put in a BT-60 stuffer tube in my Estes Executioner, ending it about 8" from the front end. Seems to work well. Adds a bit of weight, but stability is okay in Rocksim.

 

[MidOH]

Makes sure you pack the chute so that it fills up the tube. If its packed too tight gases blow right by it, inside of shooting it out.

Also consider more slippery nylon chutes and kevlar.

But yeah, a 24mm reload motor is priceless.

 

[neil_w]

Makes sure you pack the chute so that it fills up the tube. If its packed too tight gases blow right by it, inside of shooting it out.

Sorry, that's backwards. In an ideal deployment, the ejection blows out the nose cone, and the momentum of the nose cone pulls out the chute. The looser the chute is in the tube, the easier it will be pulled out by the nose.

Certainly it is possible (and even likely in many situations) for the ejection to also push on the chute as well, but it's not the primary mechanism to rely on.

 

[MALBAR 70]

The first flight of my Executioner went the same way, popped the cone off. but no chute deploy. At the time, I assumed the problem was the dreded "Big Daddy nosecone shoulder failure syndrome" , but it has flown many,many more time without an issue.
The idea of adding a longer stuffer tube is something I hadn't considered. I think it would help with not only ejection problem but strengthen the somewhat flimsy Bt80 as well.

 

[MidOH]

You also have to worry about a loose chute being thrust/yanked sideways, and jamming up.

Pack your chute less compact and longer might help. Can't hurt to try.

Unless the nt60 is weighted, it ain't going to have much pull. Especially if the flight is wonky.

Dont make it tight or anything. Just enough to fill the tube to get an extra boost. Done right, you might notice that it slides easier. Especially nylon and kevlar. Plastic and rubber are so sticky and need powdered.

 

[BABAR]

Sorry, that's backwards. In an ideal deployment, the ejection blows out the nose cone, and the momentum of the nose cone pulls out the chute. The looser the chute is in the tube, the easier it will be pulled out by the nose.

Certainly it is possible (and even likely in many situations) for the ejection to also push on the chute as well, but it's not the primary mechanism to rely on.

First, I agree you never want a tightly packed chute. For low powered, if you can’t blow out the chute and wadding with your breath it is too tight.

second, I think the “ejecting the nose cone to pull out the chute” vs “ejecting the whole wad of wadding,chute,and nose cone as a single action” may both have roles here.

I often fly rockets with stock nose cones with no added weight. These carry very little kinetic energy even if forcibly ejected, and are unlikely to drag the chute out with them.

second, choice of wadding may make a difference. Again you never want to tightly pack wadding. Paper wadding should be loose, but may provide enough of a seal that it acts like a piston, the ejection charge shoves it forward and in turn shoves everything else in front of it (chute, the length of shock cord, and cone) out the front. Not sure if Dog Barf works this way, as it is more particulate.

perhaps the distinction can be in part made by examining the rocket at recovery. Under the “nose cone ejection drags everything with it” theory, I would expect the cone, length of shock cord, and chute to eject. But the WADDING which is NOT attached should stay in the rocket. In my “non weight augmented nose cone” models, with successful deployment the wadding is just about always ejected. On the other hand, on those same models during my fortunately uncommon failures, most commonly the nose is out dangling but the chute and cord are fouled up, often just BARELY at the forward edge of the tube. I attribute those failures to too tightly packed wadding or more commonly chute, sometimes shock cord.

YMMV

 

[Back_at_it]

I learned the hard way after a few less than perfect ejections with an Alien Space Probe back in my youth that Stuffer tubes (or bigger motors in this case) were often a necessity. When I built my Executioner I looked at the stock stuffer tube and knew it wasn't enough. My initial though was to extend it up past the coupler but that was right about the time I started putting baffles in everything so I extended it to 11.5 inches. I then used the stock coupler and put baffle plates in it. That Executioner has flown a dozen times without an ejection issue.



As for the Mean Machine that was mentioned. I'm not sure what Estes was thinking. Mine didn't come with a stuffer tube at all. Nada, Nothing. Just a Standard 24mm "D" engine mount. I'm sure this was a cost concern but I too have seen them built stock and fail to deploy. Thankfully It's never happened to mine but I have seen at least two hit the ground with with just the nose cone out.

When I built mine, first thing I did was throw that stupid twist together coupler and all of the other short couplers in the trash and add my own 4 inch pieces of coupler. I added a stuffer tube that stopped 2 inches below the bottom of the second coupler. The center coupler was turned into a 4 in baffle and the rocket was modified to separate between the third and fourth tubes.

 

[bjphoenix]

I put in a BT-60 stuffer tube in my Estes Executioner, ending it about 8" from the front end. Seems to work well. Adds a bit of weight, but stability is okay in Rocksim.

I'm thinking about doing this to mine. I still want to try it on a D or E reload and I might just dedicate it to composite motors, but D12s are just too convenient.
Built stock the Executioner is fairly large and lightweight, if you are flying it on grass there isn't much need for a parachute, I was surprised how slowly it came down without the chute out. I was sure that it would not be damaged on landing and it wasn't.

 

[4regt4]

I'm just starting an Executioner build. I've become a fan of both baffles and stuffer tubes. Here's what I'm thinking:

1. Long BT-50 stuffer tube with baffle in the end - up to near end of body leaving a comfortable amount of room for chute, etc. -- or --
2. Use the stock MM tube, couple an upsized BT-60 stuffer to near the end of body with baffle. Thinking here is that the baffle would be larger and less restrictive. -- or --
3. Stock MM tube (maybe extend it a bit...) with baffle. But, break the rocket in half with a bulkhead at the coupler putting the chute in the middle of the rocket. Possible disadvantage is if the Cg gets shifted too far rearward. But if it seems to sim OK, this would definitely decrease the interior volume needed for the ejection charge to "fill".

Thoughts?
Hans.

 

[Back_at_it]

I have two and both were built the same way. Difference is that one has a 29mm mount while the other is stock 24m.

When I built them I extended the motor mount tube to 11.5 inches. This placed the top centering ring at about 1.5 inches below the tube coupler. I used a 4 inch section of coupler and created a 4 plate baffle inside the coupler as shown below.

Mine still separates at the nosecone. Between the two of them, I have about 15 flights with no failures.



Inside look at the baffle design for reference.