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View Full Version : Stuffer Tube Questions (your rationale)


Bob Thomas
02-27-2006, 09:48 PM
I have been searching for a guideline of when to stuffer tube and when not. I have only one experience with a burn through in 1976 with my Centuri SST on a C6-? From most of the chatter I understand that engine composition has changed, but I have been active for the last year and have not experienced any paint bubbling or blow outs through the D engine range. I have built in a removeable stuffer on my Cherokee E power and may insert liners in future upscales. This is only as a precaution, for now, because I'd hate to wreck a nice build due to short-sightedness. But the additional weight does take its toll on a light build.

Are the stuffers mainly for heat protection or ejection charge pressure? Is foiling your own an option? Will reynolds wrap melt in hot gasses? Has anyone tried stove painting a liner (like I'm trying if its a heat thing)? Will baffles exacerbate blow out problems?

Would you share your experiences?

barone
02-27-2006, 10:12 PM
I have been searching for a guideline of when to stuffer tube and when not. I have only one experience with a burn through in 1976 with my Centuri SST on a C6-? From most of the chatter I understand that engine composition has changed, but I have been active for the last year and have not experienced any paint bubbling or blow outs through the D engine range. I have built in a removeable stuffer on my Cherokee E power and may insert liners in future upscales. This is only as a precaution, for now, because I'd hate to wreck a nice build due to short-sightedness. But the additional weight does take its toll on a light build.

Are the stuffers mainly for heat protection or ejection charge pressure? Is foiling your own an option? Will reynolds wrap melt in hot gasses? Has anyone tried stove painting a liner (like I'm trying if its a heat thing)? Will baffles exacerbate blow out problems?

Would you share your experiences?


Hey Bob,

Stuffers are mainly for pressurization. Reduces the volume of area to pressurize to deploy the recovery system. Usually for those long BT-80 based rockets like the Super Big Bertha. In some instances, they can also prevent a change in your CP by keeping the recovery system forward instead of allowing it to slide backwards during launch (mainly a side benefit).
Now to my experience.......I've burned through my stuffer tube on my Super Big Bertha (because I like to fly it ALOT). Of course, I wasn't forward thinking enough to built for replacement so I slid some BT-50 coupler stock down through what's left of the stuffer tube. Didn't even bother to glue it in. Just let it sit againt the engine block. Of course, that makes it replacable now. As for foiling your own, I'm not really sure what you mean. Seems easier just to buy the foil lined tubes from Balsa Machining Services. You want the foil on the inside of the tube (where the flame from the ejection charge is) so I don't know how you would attempt to use the Reynolds wrap unless you plan to roll your own tubes. Same with the paint, got to paint the inside of the tube. Baffles would confine the extent of damage to below the baffles. Not sure how that would help though. My stuffer tube damage is within three or four inches of the engine. If you haven't experineced any mishaps yet with the ejection charges of of some of the Estes motors, feel lucky. I've had paint blister from a 1/2A ejection charge. And the body tube on my Oracle is already burning through after only three flights........but, I've heard that others aren't experiencing these type of problems. As to a good rule of thumb for using stuffer tubes, I wish I could help you. For me, if the parachute has a lot of play inside the tube, I'm going with a stuffer to make sure I've got enough pressure to get it out.

Don
NAR 53455

JRThro
02-28-2006, 07:38 AM
Hey Bob,

Stuffers are mainly for pressurization. Reduces the volume of area to pressurize to deploy the recovery system. Usually for those long BT-80 based rockets like the Super Big Bertha. In some instances, they can also prevent a change in your CP by keeping the recovery system forward instead of allowing it to slide backwards during launch (mainly a side benefit).
Now to my experience.......I've burned through my stuffer tube on my Super Big Bertha (because I like to fly it ALOT). Of course, I wasn't forward thinking enough to built for replacement so I slid some BT-50 coupler stock down through what's left of the stuffer tube. Didn't even bother to glue it in. Just let it sit againt the engine block. Of course, that makes it replacable now. As for foiling your own, I'm not really sure what you mean. Seems easier just to buy the foil lined tubes from Balsa Machining Services. You want the foil on the inside of the tube (where the flame from the ejection charge is) so I don't know how you would attempt to use the Reynolds wrap unless you plan to roll your own tubes. Same with the paint, got to paint the inside of the tube. Baffles would confine the extent of damage to below the baffles. Not sure how that would help though. My stuffer tube damage is within three or four inches of the engine. If you haven't experineced any mishaps yet with the ejection charges of of some of the Estes motors, feel lucky. I've had paint blister from a 1/2A ejection charge. And the body tube on my Oracle is already burning through after only three flights........but, I've heard that others aren't experiencing these type of problems. As to a good rule of thumb for using stuffer tubes, I wish I could help you. For me, if the parachute has a lot of play inside the tube, I'm going with a stuffer to make sure I've got enough pressure to get it out.

Don
NAR 53455
Don,

Thanks for your post. My next project is likely to be a fairly long BT-80 model (Fat Boy kit plus another 14" tube), so it sounds like I'll need a stuffer tube.

If you were to build a replaceable stuffer tube, how would you (and anyone else) do it?

Doug Sams
02-28-2006, 05:32 PM
Seems easier just to buy the foil lined tubes from Balsa Machining Services. BMS has foil lined tubes? I knew Totally Tubular did, but wasn't aware that Bill had them.
Doug

Doug Sams
02-28-2006, 06:49 PM
Is foiling your own an option? Will reynolds wrap melt in hot gasses? Has anyone tried stove painting a liner (like I'm trying if its a heat thing)? My take is the foil lined tubes are over rated. I've used them, and all that happens is the foil quickly peels away just ahead of the motor where the ejection charge is hottest. If you then try to slide in a longer motor such as an Estes E after having flown a 2.75" long motor, the peeling foil tends to make for a tighter fit, but it's nothing that can't be fixed by sanding out the tube.

Punchline: The foil in the foil lined tube is superfluous. The thicker walled tube is the real improvement, and you can get thicker walled 24mm tubes from BMS among others. Several guys offer rings designed to fit around them, although standard rings (ie, with BT-50 openings) can be sanded out in a pinch.

I think LOC has a thicker walled 18mm motor tube, and pretty much all 29mm tubes come in either thick or thicker.

What I've been told ruins the motor tubes - and I'm inclined to agree - is condensation settling in the tube after ejection. One technique is to apply an ablative coating from the forward end of the motor, forward a few inches. Basically, just smear some thin CA in, then sand it smooth. Recoat occasionally. Another ablative technique has been mentioned sort of, but instead of using a coupler, just use some card stock and roll up a ~3" length to insert ahead of the motor. This will protect the motor tube and is easily replaced.

I should point out that both these techniques presume you don't have a thrust ring or the forward tab of the engine hook. I pretty much use tape rings on the aft ends of all motors in lieu of motor blocks - it allows any length motor to be used. And I rig the motor hooks so that they don't stick thru the motor tube wall on the forward ends. So it's easy for me to gain access several inches into the motor tube.

Lastly, yes, you can foil your own tubes. I did it once on my L'il Augie. That's one of the reasons I now advocate coating with CA instead.

HTH.

Doug

barone
02-28-2006, 08:04 PM
BMS has foil lined tubes? I knew Totally Tubular did, but wasn't aware that Bill had them.
Doug


Sure....check out their web page http://www.balsamachining.com/CATALOG.htm and item number T50MF-34. 34" length of metal lined BT-50 for $3.

The thicker walled tube is the real improvement

I agree.

If you were to build a replaceable stuffer tube, how would you (and anyone else) do it?

I don't know if you've seen how Carl (Semroc) did his interchageable motor mounts for the SLS Laser-X, but that's the best way I've seen yet. Through the wall fins that the motor mount locks on to. You may get some bypass but I think it would work just as well adapted for removable stuffer tube, or in your case, the engine mount stuffer tube assembly.

Don
NAR 53455

jflis
03-01-2006, 09:23 AM
What I have done in the past to protect stuffer tubes is to use a long stage coupler as the Engine Block. If I am overly concerned (common with 24mm motors) I may even double up and put two couplers, end to end. I find the fish-paper of the couplers to be tough with regard to ejection particles and heat.

Anyone else ever tried this? I've got models with stuffer tubes that are over 20 years old with many dozens of flights with no noticible wear...

Ltvscout
03-01-2006, 05:44 PM
What I have done in the past to protect stuffer tubes is to use a long stage coupler as the Engine Block. If I am overly concerned (common with 24mm motors) I may even double up and put two couplers, end to end. I find the fish-paper of the couplers to be tough with regard to ejection particles and heat.
I've never done that but it is a great idea!

Bob Thomas
03-01-2006, 07:15 PM
Great info guys, thank you. As I noted, the only stuffer I made was for the Cherokee for E motors. The bt 50 sized Hand-rolled tape reinforced ugly stuffer weighs in just less than a commercial heavy weight tube, but I added a slip over coupler (ST10 tube) that fits over the forward engine tube. The stuffer ends at the forward end about 3 inches before the nose cone with a BT 55 coupler using a few toothpicks to center it. It is not a baffle, but the wadding sits well, inside the forward coupler. The shock cord comes up through the the gap made by the toothpicks, making it secureable if ejected. The stuffer is centered at the bottom by a notched centering ring, sanded for a loose fit. It hasn't burned out or blown through after its first two flights. As for foiling, I did it with reynolds on the inside, tacked with 3m. I know it helps with hot ejection gases, but the gaps probably defeat any gas pressure damage. I'll keep experimenting, or wait until the flaming indian crashes!