Red, White, and Blue Success! (Canted cluster MDRM)

[wfcook]

Hey Bill,,

What length motor tube did you use? Something different or is it just two more of the size that comes in the regular lit?

Thanks
Ed

As I recall, they are 190.5mm (7.5"), sized for three grain loads. I don't remember what comes in the kit right off hand, but for my canted Drei max I cut the motor tubes out of foil-lined MT stock from balsamachining.com

It can handle two 3G and single 4G load if you are ok with imbalanced thrust (I did this in June). You can't fit more than one 4G load in there without extending the tubes aft.

The key to the whole design, and the part most people miss when building a canted cluster rocket, is that the focus of the mount (the point where the centerlines of the MT's intersect) should be approximately halfway between the CG and the Cp. For the vast majority of rockets, that will give you the best chance of surviving if one motor doesn't light.

For this reason, the Drei Max actually has a fair amount of weight in the nose to move the CG far enough forward. If I were looking for performance instead of effect, I'd have smaller fins and bring the CG and Cp closer together. But then, it wouldn't be an MDRM, and that was sort of the point.

 

[race 58]

As I recall, they are 190.5mm (7.5"), sized for three grain loads. I don't remember what comes in the kit right off hand, but for my canted Drei max I cut the motor tubes out of foil-lined MT stock from balsamachining.com

It can handle two 3G and single 4G load if you are ok with imbalanced thrust (I did this in June). You can't fit more than one 4G load in there without extending the tubes aft.

The key to the whole design, and the part most people miss when building a canted cluster rocket, is that the focus of the mount (the point where the centerlines of the MT's intersect) should be approximately halfway between the CG and the Cp. For the vast majority of rockets, that will give you the best chance of surviving if one motor doesn't light.

For this reason, the Drei Max actually has a fair amount of weight in the nose to move the CG far enough forward. If I were looking for performance instead of effect, I'd have smaller fins and bring the CG and Cp closer together. But then, it wouldn't be an MDRM, and that was sort of the point.

Thanks Bill,,

I just opened the kit and the motor tube that comes with it is 8",, so you think you use 3 8 inchers instead of 7.5?

I also ordered the centering ring and fin kit from Wingarcher. What a nice guy to deal with,, thanks for sending me to him.

I should get started later next week on my build. I have decided to do the graphics different from what I first thought (Blue Max) I will post my ideas about it when I start the build.. 1st hint...it has something to do with Chicago.

Thanks
Ed

 

[wfcook]

Pretty sure I used 7.5" tubes. Just long enough to fit the 3G casings. The issue with longer ones is that the motor mass is quite large and I didn't want to drive the CG any further aft. However, as long as your design and build keep the focus of the mount about midway between Cp and CG you are all good.

Wingarcher is great to deal with. That was my best move on the whole rocket.


Sent from my iPhone using Rocketry Forum

 

[race 58]

Pretty sure I used 7.5" tubes. Just long enough to fit the 3G casings. The issue with longer ones is that the motor mass is quite large and I didn't want to drive the CG any further aft. However, as long as your design and build keep the focus of the mount about midway between Cp and CG you are all good.

Wingarcher is great to deal with. That was my best move on the whole rocket.


Sent from my iPhone using Rocketry Forum

Thanks,,, I'll make them 7.5, I was just curious

 

[race 58]

Lookee here what I got today from UpscaleCNC (Wingarcher here on TRF). :grin::grin::grin:

 

[race 58]

Bill,,

Do you happen to have a scan or copy of the template for the motor tube cutouts on the body tube?

Thanks
Ed

 

[wfcook]

Yes - I'll have to look it up tomorrow.

 

[marcusSRG]

Sweet.

 

[wfcook]

Bill,,

Do you happen to have a scan or copy of the template for the motor tube cutouts on the body tube?

Thanks
Ed

What is the actual, measured circumference of your body tube?

 

[race 58]

What is the actual, measured circumference of your body tube?

322mm

 

[wfcook]

322mm

OK, I'll have to wait until I get home to do it.

 

[CZ Brat]

Bill,,

Do you happen to have a scan or copy of the template for the motor tube cutouts on the body tube?

Thanks
Ed

Here is a simple way to do it. Take a scrap piece of MMT and cut it at the angle you want it coming out of the body tube. Position it where you want your MMTs to come out, then just trace it and cut it. I show this in the first post of the attached thread.

https://www.rocketryforum.com/showthread.php?67272-Estes-V2-Steam-Punk-Forward-Mounted-Canted-Cluster-build-thread

 

[wfcook]

Here is a simple way to do it. Take a scrap piece of MMT and cut it at the angle you want it coming out of the body tube. Position it where you want your MMTs to come out, then just trace it and cut it. I show this in the first post of the attached thread.

https://www.rocketryforum.com/showthread.php?67272-Estes-V2-Steam-Punk-Forward-Mounted-Canted-Cluster-build-thread

I've got a ready-made template calculated with all the math from Apogee peak-of-flight #363, so I'll just send him that as soon as I get home to do it.

 

[wfcook]

Here is a simple way to do it. Take a scrap piece of MMT and cut it at the angle you want it coming out of the body tube. Position it where you want your MMTs to come out, then just trace it and cut it. I show this in the first post of the attached thread.

https://www.rocketryforum.com/showthread.php?67272-Estes-V2-Steam-Punk-Forward-Mounted-Canted-Cluster-build-thread

Just in case anyone is interested, here is my spreadsheet for doing canted-cluster calcs. The explanation is in Apogee Peak Of Flight #363.

View attachment CenteringRingCalcsFinal2.xlsx

 

[rstaff3]

I have to admit I didn't follow the details when I read your article. Methinks if I want to build a canted motor cluster with the motors pointed at the correct spot, I'll just clone your awesome rocket. :dark:

 

[CZ Brat]

Just in case anyone is interested, here is my spreadsheet for doing canted-cluster calcs. The explanation is in Apogee Peak Of Flight #363.

View attachment 180962

Thanks for sharing that. I might try the "correct" way next time.

 

[wfcook]

Thanks for sharing that. I might try the "correct" way next time.

I don't know that I'd go so far as to call a particular way "correct"...but it does produce a fairly precise fit.

 

[wfcook]

I have to admit I didn't follow the details when I read your article. Methinks if I want to build a canted motor cluster with the motors pointed at the correct spot, I'll just clone your awesome rocket. :dark:

I'm sure Nat would love to sell you a set of centering rings ;-)

 

[race 58]

I'm sure Nat would love to sell you a set of centering rings ;-)

Yes he will.... and they are very nice along with his fins to go with it. See Post #35

 

[wfcook]

322mm

Here's the 322mm cut template. If it doesn't quite fit let me know and I can adjust.

The mount is designed to install with the aft CR flush with the aft end of the BT. This makes motor retention a lot easier to fabricate. Note that I drilled holes and installed weld nuts for motor retention before installing the mount. You could use threaded inserts after the fact, or design something different from what I did.

View attachment Mega Der Drei Max cut template 322mm.pdf

 

[RochonRockets]

Here is a link to my Build thread based on the cluster mount from Bill.

https://www.rocketryforum.com/showt...ei-Max-(a-canted-cluster-version-on-the-MDRM)

Awesome rocket by the way.

 

[race 58]

Here's the 322mm cut template. If it doesn't quite fit let me know and I can adjust.

The mount is designed to install with the aft CR flush with the aft end of the BT. This makes motor retention a lot easier to fabricate. Note that I drilled holes and installed weld nuts for motor retention before installing the mount. You could use threaded inserts after the fact, or design something different from what I did.

View attachment 181096

OK Thanks

Right now it's printing on only one page and it will need to be printed on 2 and taped together to go all the way around the tube, 1 sheet is about 3" short.

I'm trying to figure out how to print it to the size I need. A little tinkering and I'll get it.

Thanks for posting it.
Ed

 

[wfcook]

OK Thanks

Right now it's printing on only one page and it will need to be printed on 2 and taped together to go all the way around the tube, 1 sheet is about 3" short.

I'm trying to figure out how to print it to the size I need. A little tinkering and I'll get it.

Thanks for posting it.
Ed

If you can print on legal-sized paper (8.5x14) it should work on one sheet.

 

[Wingarcher]

Thanks for all the kind words guys.... now, get to work! Build that thang!

Nat Kinsey
UpscaleCNC

 

[race 58]

Pretty sure I used 7.5" tubes. Just long enough to fit the 3G casings. The issue with longer ones is that the motor mass is quite large and I didn't want to drive the CG any further aft. However, as long as your design and build keep the focus of the mount about midway between Cp and CG you are all good.

Wingarcher is great to deal with. That was my best move on the whole rocket.


Sent from my iPhone using Rocketry Forum

I'm gathering up the additional parts I need and forgot to ask you Bill about the motor tubes.
Did you use reg wall, thick wall or blue tube for your motor tubes?

Thanks
Ed

 

[wfcook]

I'm gathering up the additional parts I need and forgot to ask you Bill about the motor tubes.
Did you use reg wall, thick wall or blue tube for your motor tubes?

Thanks
Ed

I used BalsaMachining.com T52HMF-34 (foil-lined heavy paper tubes), mainly because that's what I had on hand. The tubes are pretty well protected from impact by the fins and the motor casing that keeps them from bending, and given that there is so much weight in the back end that you have to add weight to the nosecone, I was trying to save a little mass aft. The dimensions of the BMS tubing are roughly the same as the LOC 29mm motor mount tubing, which I believe would also work fine.

 

[race 58]

I used BalsaMachining.com T52HMF-34 (foil-lined heavy paper tubes), mainly because that's what I had on hand. The tubes are pretty well protected from impact by the fins and the motor casing that keeps them from bending, and given that there is so much weight in the back end that you have to add weight to the nosecone, I was trying to save a little mass aft. The dimensions of the BMS tubing are roughly the same as the LOC 29mm motor mount tubing, which I believe would also work fine.

Thanks Bill