PDA

View Full Version : To mount or not to mount


Veracity
11-26-2007, 09:28 PM
Hello again,

As I stated in an earlier post, I'm working on a BT80 E powered rocket. I have several E engine mounts...but because I'm going to use a stuffer tube (BT50), should I simply use the stuffer tube as the mount?

I was discussing this with a friend last night. Yeah, I could do it. Yeah, I think I did it with another of my D powered home built kits. Yeah, Estes' D powered Broad Sword is set up that way...but should I?

The thing is this, take Estes as an example....their E mounts are beefier than all of their other mounts. (Thicker tube)

They might have done this because of the extreme heat an E would put off.

What dost thou think?

barone
11-26-2007, 10:28 PM
Hello again,

As I stated in an earlier post, I'm working on a BT80 E powered rocket. I have several E engine mounts...but because I'm going to use a stuffer tube (BT50), should I simply use the stuffer tube as the mount?Well, that's the easiest thing to do. One single BT50 tube vs two.

I was discussing this with a friend last night. Yeah, I could do it. Yeah, I think I did it with another of my D powered home built kits. Yeah, Estes' D powered Broad Sword is set up that way...but should I?Sure, why not. If you want to use a seperate tube for the stuffer, then you have to get a tube coupler (which you could use instead of a motor block) but then again, why go through the trouble when a single peice of BT50 will do just fine.

The thing is this, take Estes as an example....their E mounts are beefier than all of their other mounts. (Thicker tube)

They might have done this because of the extreme heat an E would put off.

What dost thou think?Thicker tube for a motor mount doesn't make that much difference. Where the strength needs to be is in the joint between the motor tube and the centering rings and the centering rings to the body tube. Of course, the centering rings need to be strong too.

So, in short, go with a single piece of BT 50 for your motor/stuffer tube. If you can, coat the inside of the stuffer tube with CA or get some of the foil lined BT50 from BMS. Anything to protect it from burning. My Super Big Bertha (same as the Broadsword) stuffer tube has burned through and now whenever a kit has a BT50 stuffer, I just use the foil lined stuff. But, seems other folks don't have the burn through problem. Maybe mine have just had some pretty hot ejection charges. :rolleyes:

BMS is at http://www.balsamachining.com/

Veracity
11-27-2007, 02:06 PM
So, in short, go with a single piece of BT 50 for your motor/stuffer tube. If you can, coat the inside of the stuffer tube with CA or get some of the foil lined BT50 from BMS. Anything to protect it from burning. My Super Big Bertha (same as the Broadsword) stuffer tube has burned through and now whenever a kit has a BT50 stuffer, I just use the foil lined stuff. But, seems other folks don't have the burn through problem. Maybe mine have just had some pretty hot ejection charges. :rolleyes:


Thanks for the advice. I just ordered a foil lined BT50 from BMS.


Just curios, how did you see/notice that Super Big Bertha's stuffer had burned through? The stuffer I have in my home built D powered rocket looks pretty crusty. It also looks as if someone really squeezed it. That's what I meant when I wrote that it was caving in on itself.

barone
11-27-2007, 03:43 PM
So, in short, go with a single piece of BT 50 for your motor/stuffer tube. If you can, coat the inside of the stuffer tube with CA or get some of the foil lined BT50 from BMS. Anything to protect it from burning. My Super Big Bertha (same as the Broadsword) stuffer tube has burned through and now whenever a kit has a BT50 stuffer, I just use the foil lined stuff. But, seems other folks don't have the burn through problem. Maybe mine have just had some pretty hot ejection charges. :rolleyes:


Thanks for the advice. I just ordered a foil lined BT50 from BMS.


Just curios, how did you see/notice that Super Big Bertha's stuffer had burned through? The stuffer I have in my home built D powered rocket looks pretty crusty. It also looks as if someone really squeezed it. That's what I meant when I wrote that it was caving in on itself.
Burn debris when removing the motor. Then looked inside and you could see where the tube looked like it was caving in but it was actually burnt. I ended up shoving a piece of BT20 into the stuffer...not a great way to fix it but I could still fly. Had I known about the BT50 coupler stock, I'm not even sure it was sold then, I would have went that route. Just shove it end from the forward end until it hit the motor block.

As for the foil lined tube, I think it was Doug who said that the foil actual peels off from the ejection charge and you end up with just a body tube (like I said, I haven't launched one using it yet. But the foil lined tube is thicker than the reular BT50 and that may be enough to keep it from burning through.

I really don't understand why others aren't having this problem. My Oracle is the same way. Even though it doesn't have a stuffer tube, after 4 launches I have significant burning of the body tube just above the motor mount, I think the only thing holding it together is the decal wrap. Needless to say, the rocket won't fly again. The camera will on a different launch vehicle.

Mark II
12-06-2007, 09:58 PM
I really don't understand why others aren't having this problem. My Oracle is the same way. Even though it doesn't have a stuffer tube, after 4 launches I have significant burning of the body tube just above the motor mount, I think the only thing holding it together is the decal wrap. Needless to say, the rocket won't fly again. The camera will on a different launch vehicle.
Don,

I'm just wondering if you ever tried spraying the critical areas in your rockets' innards with high-temp spray paint (like the kind used to paint outdoor grills), appliance epoxy paint or auto engine paint?

I haven't seen any actual tube damage on any of my rockets (yet), but I have been finding the insides coated with an unusually large amount of ejection charge residue after some recent flights. - seemingly quite a bit more than I was getting in the recent past with black powder motors.

Mark

barone
12-07-2007, 09:39 PM
Don,

I'm just wondering if you ever tried spraying the critical areas in your rockets' innards with high-temp spray paint (like the kind used to paint outdoor grills), appliance epoxy paint or auto engine paint?

I haven't seen any actual tube damage on any of my rockets (yet), but I have been finding the insides coated with an unusually large amount of ejection charge residue after some recent flights. - seemingly quite a bit more than I was getting in the recent past with black powder motors.

Mark
No, never tried that. It sounds like an easy solution to current builds is the flash damper suggested earlier (ok, I like to make up names for things.... :o ). But future builds, I think I'm going to stick with running the coupler tubing inside the stuffer tube. Yep, adds weight but should get some longer performance.

Mark II
12-08-2007, 04:27 AM
No, never tried that. It sounds like an easy solution to current builds is the flash damper suggested earlier (ok, I like to make up names for things.... :o ). But future builds, I think I'm going to stick with running the coupler tubing inside the stuffer tube. Yep, adds weight but should get some longer performance.
Lining the stuffer with a length of coupler stock does make sense.

Thinking it through, I guess you could then just glue a motor block in at the upper end of the stuffer tube, and then trim your coupler stock to fit as a motor spacer. You would just insert the length of coupler stock into the mmt like you would for any motor spacer, and not glue it in. If you also epoxied a small loop of Kevlar or beading cable somewhere on the inside of the coupler, it would help you to be able to extract the coupler after every few flights so that you could inspect it for damage. You could then replace the coupler liner as necessary, and never again have to worry about seeing ejection charges burn through your motor mount. :)

Then either shave weight somewhere else to compensate for the increased weight of the mmt, or else use a bigger motor. ;) :D

Mark K.

Veracity
12-08-2007, 11:45 AM
Lining the stuffer with a length of coupler stock does make sense.

Thinking it through, I guess you could then just glue a motor block in at the upper end of the stuffer tube, and then trim your coupler stock to fit as a motor spacer. You would just insert the length of coupler stock into the mmt like you would for any motor spacer, and not glue it in. If you also epoxied a small loop of Kevlar or beading cable somewhere on the inside of the coupler, it would help you to be able to extract the coupler after every few flights so that you could inspect it for damage. You could then replace the coupler liner as necessary, and never again have to worry about seeing ejection charges burn through your motor mount. :)

Then either shave weight somewhere else to compensate for the increased weight of the mmt, or else use a bigger motor. ;) :D

Mark K.

Guys,
I like where this is going....
But tell me, what is coupler stock? What is card stock? I've read these things here but I havew never used them. I've certainly used couplers.

I'd love to retrofit my old homebuilt that's got some stuffer tube "burn/squeeze" going on.

Also, as the above post suggests, I love the idea of inspecting/replacing any shield that's put in place...but I can't see it. The above description sounds great...I just can't visualize it.

The shield has to be above that last motor mount ring 'cause that's where all of the evil hot stuff will be. So if it's lining the stuffer and it's above that last ring...how do you get it back out?

Sorry for beating this dead horse but the new rocket I'm building is something of which I'm very proud and I'd like to add this feature to protect it. I bought one of those foil lined BT50s just in case that helps. We shall see.

barone
12-08-2007, 04:05 PM
Guys,
I like where this is going....
But tell me, what is coupler stock? What is card stock? I've read these things here but I havew never used them. I've certainly used couplers.

I'd love to retrofit my old homebuilt that's got some stuffer tube "burn/squeeze" going on.

Also, as the above post suggests, I love the idea of inspecting/replacing any shield that's put in place...but I can't see it. The above description sounds great...I just can't visualize it.

The shield has to be above that last motor mount ring 'cause that's where all of the evil hot stuff will be. So if it's lining the stuffer and it's above that last ring...how do you get it back out?

Sorry for beating this dead horse but the new rocket I'm building is something of which I'm very proud and I'd like to add this feature to protect it. I bought one of those foil lined BT50s just in case that helps. We shall see.
Coupler stock is 34" lengths of body tube coupler...either 18mm or 24mm or 29mm, or centering rings, or motor blocks. What's good about using the coupler stock for retrofitting, in most cases you don't have to take your rocket ab part, just slide it into the stuffer tube from the forward end until it butts against your motor block.

As for inspecting, if you don't glue it in place, and you really shouldn't have to, you can remove the coupler stock every so often and check it for wear/burn through and then just replace it.

Now, keep in mind, it appears I may be the only one with a burn through problem so all this may be unnecessary.

Mark II
12-08-2007, 09:05 PM
Coupler stock is 34" lengths of body tube coupler...either 18mm or 24mm or 29mm, or centering rings, or motor blocks. What's good about using the coupler stock for retrofitting, in most cases you don't have to take your rocket ab part, just slide it into the stuffer tube from the forward end until it butts against your motor block.

As for inspecting, if you don't glue it in place, and you really shouldn't have to, you can remove the coupler stock every so often and check it for wear/burn through and then just replace it.

Now, keep in mind, it appears I may be the only one with a burn through problem so all this may be unnecessary.
Actually I was thinking of how to install it into a new build. My assumption was that the stuffer tube was just the motor tube, but with extra length. Instead of taking a standard issue motor tube and grafting on some additional length to make a stuffer, I just buy motor tubing in the length I need to accomodate the motor plus some extra length to serve as a stuffer. I think that this is a pretty standard technique.

Anyway, my thought was that you glue the motor block in at the top of the stuffer tube, and then insert a length of coupler stock with a length that is equal to the distance from the bottom of this motor block to the top of the inserted motor. You don't need to install a block right in front of the motor, because the coupler stock/motor tube liner will serve that purpose (i. e., it will prevent the motor from moving forward).

You then just need to slide in this motor tube liner in from the rear of the motor tube until it butts up against the block at the top of the stuffer tube, and then insert your motor behind it as you normally would. (I'm assuming that you wouldn't be using a motor clip.)

You would have previously epoxied in a small loop of burn-proof cord to the inside wall of the motor tube liner a couple of inches in from the rear of the liner, to give you something to grab onto when you want to pull the liner out to inspect it.

It's as simple as that.

I hadn't thought of installing the liner in from the top, as Don described, but his method would certainly be the way to go if you are retrofitting an already-built rocket. It would work exacly the same way as my idea, just being installed from the other end. With his method, you could still use a motor clip, and you would need to install a motor block in the conventional way, right in front of the motor. Installed in this way, the liner should stay in place and not be pushed out by the ejection charge.

Don, if I haven't seen any burn-through of my motor tubes, it may be due to to the fact that I haven't put any of my rockets through very many flights (I'm building them much faster that I can launch them!), Either that, or else I've just been lucky -- so far! :rolleyes:

Question: are you seeing this burn damage with rockets that fly on composite motors, or is it occuring with black powder motors?

Mark K.

Intruder
12-08-2007, 09:16 PM
Lining the stuffer with a length of coupler stock does make sense.

Thinking it through, I guess you could then just glue a motor block in at the upper end of the stuffer tube, and then trim your coupler stock to fit as a motor spacer. You would just insert the length of coupler stock into the mmt like you would for any motor spacer, and not glue it in. If you also epoxied a small loop of Kevlar or beading cable somewhere on the inside of the coupler, it would help you to be able to extract the coupler after every few flights so that you could inspect it for damage. You could then replace the coupler liner as necessary, and never again have to worry about seeing ejection charges burn through your motor mount. :)

Then either shave weight somewhere else to compensate for the increased weight of the mmt, or else use a bigger motor. ;) :D

Mark K.

Instead of using your precious Kevlar cord, you could just tape the coupler stock to the motor, like you would if you were staging, and slide the who thing in that way. Or do you think the ejection charge would case the tape to fail.

barone
12-08-2007, 10:37 PM
Actually I was thinking of how to install it into a new build. My assumption was that the stuffer tube was just the motor tube, but with extra length. Instead of taking a standard issue motor tube and grafting on some additional length to make a stuffer, I just buy motor tubing in the length I need to accomodate the motor plus some extra length to serve as a stuffer. I think that this is a pretty standard technique.

Yes, exactly. This is standard.

Anyway, my thought was that you glue the motor block in at the top of the stuffer tube, and then insert a length of coupler stock with a length that is equal to the distance from the bottom of this motor block to the top of the inserted motor. You don't need to install a block right in front of the motor, because the coupler stock/motor tube liner will serve that purpose (i. e., it will prevent the motor from moving forward).

You then just need to slide in this motor tube liner in from the rear of the motor tube until it butts up against the block at the top of the stuffer tube, and then insert your motor behind it as you normally would. (I'm assuming that you wouldn't be using a motor clip.)
Yes, this works as long as you're not looking at using a clip for motor retention as you state. However, if you want to use a clip, just assemble the stuffer tube as the instructions say, then slip your coupler stock in from the front, butting it against the motor block. The ejection charge should pass through it without blowing it out (of course you could always add some tape to make it a tighter fit).

You would have previously epoxied in a small loop of burn-proof cord to the inside wall of the motor tube liner a couple of inches in from the rear of the liner, to give you something to grab onto when you want to pull the liner out to inspect it.

It's as simple as that.

I hadn't thought of installing the liner in from the top, as Don described, but his method would certainly be the way to go if you are retrofitting an already-built rocket. It would work exacly the same way as my idea, just being installed from the other end. With his method, you could still use a motor clip, and you would need to install a motor block in the conventional way, right in front of the motor. Installed in this way, the liner should stay in place and not be pushed out by the ejection charge.

I'm thinking from a retrofit prospective, sliding the coupler stock in from the front is the easiest way to do it.

Don, if I haven't seen any burn-through of my motor tubes, it may be due to to the fact that I haven't put any of my rockets through very many flights (I'm building them much faster that I can launch them!), Either that, or else I've just been lucky -- so far! :rolleyes:

Question: are you seeing this burn damage with rockets that fly on composite motors, or is it occuring with black powder motors?

Mark K.
I'm getting burn through from both...composites more rapidly. As a mater of fact, I flew a 18mm D from Apogee in a paper shroud egglofter....the ejection charge set the rocket on fire :eek: Needless to say, it DQed :(

Mark II
12-08-2007, 10:56 PM
Yes, exactly. This is standard.
Yeah, my lengthy explanation was to help Veracity visualize what you and I had described.

I'm getting burn through from both...composites more rapidly. As a mater of fact, I flew a 18mm D from Apogee in a paper shroud egglofter....the ejection charge set the rocket on fire :eek: Needless to say, it DQed :(
Interesting that you mention this problem with an Apogee motor - have you read TVM's article about the so-called "hibachi effect"?

http://www.apogeerockets.com/education/newsletter28.asp

This is why I was wondering if you saw the problem more with composite motors.

Mark

barone
12-08-2007, 11:17 PM
Yeah, my lengthy explanation was to help Veracity visualize what you and I had described.


Interesting that you mention this problem with an Apogee motor - have you read TVM's article about the so-called "hibachi effect"?

http://www.apogeerockets.com/education/newsletter28.asp

This is why I was wondering if you saw the problem more with composite motors.

Mark
Yes, saw that but others might be interested in it also. Somewhere there is a video of one of their 18mm Ds on a test stand. Apparently, I haven't seen it, it shows a rather sustained flame of about three inches in length when the ejection charge went. My paper shroud didn't stand a chance.... :rolleyes: