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adding switch band to Tomach 54mm

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jkovac

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I'm building a fiberglass Madcow Tomach 54mm. My intention is to get a rocket with an onboard video camera, with the camera lens pointing down, as high as possible. I was planning to have a Mobius in the AV bay and use a lens cable to place just the lens on the outside of the switch band, pointed down, with a small shroud around it.

Having now received the Tomach kit, I see that the design for the AV bay does not use a switch band, it inserts fully in both the booster and payload sections. So I am thinking of adding a switch band, and wanted to see if anyone had any thoughts on that. I have looked at all of the Tomach build threads I can find, but I don't see that anyone has done this. It would obviously give 1/2" less purchase into the tubes on each end, and assuming I added a 1" band instead of cutting one from one of the existing tubes, it would make the rocket one inch longer.

It seems pretty straightforward, but I have thought that before about things, only to wish later that I'd posted a question a question on here first. Any input greatly appreciated.
 

Bat-mite

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DISCLAIMER: I don't have a Tomach and don't know any specifics about them. So this is just some general fodder for thought.

Adding an inch won't hurt anything. In fact, it will increase your stability a bit.

As for losing 1/2" on each side of the coupler, here's what you want to do. Don't put the switch band in the exact center. Offset it a bit so that you have a longer end and shorter end.

Screw or rivet the shorter end to the payload tube for flight, and that leaves the longer end in the booster, where your separation occurs and shear pins go. That way you add support where you don't have it screwed/riveted to the body.
 

NateLowrie

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As a general rule of thumb, you want at least 1 caliber of coupler length on each side. It looks like the coupler extends 3.5" into each tube which is well past 1 caliber. You should be able to install a switch band without compromising coupler integrity.
 

rc dude

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You could also get a longer coupler. I put an 8 inch coupler in mine to accommodate more electronics.
 

FredA

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Unless you are deploying off each side of the coupler, you can short the bolted-in end an keep a full 1-caliper length on the deploy end.....
 

mpitfield

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I have a 54mm Tomach however it is very different from the fiberglass one. It is the carbon fiber one which has a switch band, is loner and has no MMT so it is a MD. I would say first off get a profile setup in OR and run some simulations. If you don't want to change the overall dimensions you could always take away from either the booster and or payload tube whatever you add for your switch band. However my guess is that it would only make a difference on a profile that was right on the edge of stability.

RC dude has the 54mm fiberglass so you might want to ask him if he has any OR files that he can share, or look for them on-line. I am more than happy to share mine but you would have a lot more work to adjust it for your rocket.
 

jkovac

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Thanks all for the info. I will come back and post whatever I end up doing here.
 

watermelonman

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The Tomach is not a particularly high performance design. It is a cool rocket, looks great, and lots of us fly them high in 54mm minimum diameter form, but the aerodynamics are not exactly optimal. I would not hesitate to lengthen it if that gets you the flexibility you want, an inch or so is not going to cost you.

That said, the way I pack mine, there is tons of extra space in the payload bay. If I wanted a switch band I would pull it all off that tube.
 

jkovac

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The Tomach is not a particularly high performance design.
Do you know of any other 54mm MD rockets in kit form that are higher performance, or are we talking custom-built? I am new to this and still trying to learn the secrets of minimum diameter.
 

mpitfield

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Do you know of any other 54mm MD rockets in kit form that are higher performance, or are we talking custom-built? I am new to this and still trying to learn the secrets of minimum diameter.
Where do you fly? I have pushed my Tomach to just shy of Mach 2 @ just under 17,000AGL. I have other motor options, including the Loki L1040 that will push to over 23,000AGL, but no local field to do this at.

If you were to shorten the body or even do away with the payload bay, put your electronics in the nosecone then you can achieve even more numbers. But then it's not a Tomach anymore and this is a design change that would require some knowledge and experience that you may not have yet. There are other changes you would consider if you were focused on performance, such as the fin design, but again this is getting into more advanced areas. That is not to say these challenges are out of your reach, but easing into it may be a more enjoyable way to go...well it has been and continues to be for me.

To give you can idea on how design changes can affect the performance, try playing around with the fin design, fin location, BT lengths, diameters, etc. in OR. You will notice that there is a balance between performance and stability when you try to push it.

The Tomach is a great bird for your first MD and you will have a lot of fun with it. If the MD concept bites you then expand into other areas of it with the next build, and there are a lot of areas where you can expand your knowledge and challenge your abilities.
 

rc dude

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I would classify the tomach as high performance. An l935 sent mine over 24k ft. Another quite capable 54mm md is the Wildman blackhawk. But if you want ultimate performance you are probably going to have to scratch build.
 

DavidMcCann

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I built one... haven't flown it. I think you'd be fine adding a band. Pretty sure you need another bulkhead or two. I dislike the stock design.
 

dhkaiser

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I built one... haven't flown it. I think you'd be fine adding a band. Pretty sure you need another bulkhead or two. I dislike the stock design.
What do you dislike? I am about to start on mine. BTW mine came with a switch band.
 

jkovac

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"Where do you fly?"

Black Rock and the Tripoli Central CA site, which is Maddox Dairy farm outside of Fresno. I think the standing waiver is 16,000 ft., but we get a significantly higher one for the big multi-day launches in May and October.

"easing into it may be a more enjoyable way to go"

Yes, I agree. That is what I have been doing. So far my best is 12,562 ft on the 2.6" Tomach with an external camera shroud. Now going to see what will happen with the 2.2" version and camera inside the AV bay.
 

jkovac

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What do you dislike? I am about to start on mine. BTW mine came with a switch band.
Do you have the 2.2" version? I built and flew the 2.6" version and that came with a switch band. The 2.2" kit I received did not, and it's not an accidental omission - the instructions, which are dated 2016, show it is not part of the design. I think this is a new version of the 2.2" kit - it has a composite nose cone tip and is thin-wall fiberglass.
 

watermelonman

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Do you know of any other 54mm MD rockets in kit form that are higher performance, or are we talking custom-built? I am new to this and still trying to learn the secrets of minimum diameter.
I do not keep track of minimum diameter kits, I bought a Tomach because I love the look and my friends were also happy with them. I have no problem with these kits, but most people interested in minimum diameter are looking for performance. Frequently performance is improved by minimizing and simplifying, which takes away from the value of a kit!

I am no aerodynamics PhD, but every few weeks I have lunch with one! I will ask him for a rundown of the Tomach profile in more detail next time I see him. But right off the bat I can tell you that it is way too long and the fin shape is suboptimal. Ironically those are the attributes that make it look so good to me, so obviously there are tradeoffs.

Are you going to be at Black Rock tomorrow? I would be happy to blab about rocket design over a playa beer.
 

DavidMcCann

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I prefer two stepped bulkheads and to be able to remove the payload from the av bay. I also like making the nose a bay as well

The way I read the 2.2" MD instructions, that's not how they say to build it.
 

jkovac

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Are you going to be at Black Rock tomorrow? I would be happy to blab about rocket design over a playa beer.
Unfortunately not. Next flight for me will be at TCC October Skies. Hope you have some great flights this weekend!
 

dhkaiser

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Do you have the 2.2" version? I built and flew the 2.6" version and that came with a switch band. The 2.2" kit I received did not, and it's not an accidental omission - the instructions, which are dated 2016, show it is not part of the design. I think this is a new version of the 2.2" kit - it has a composite nose cone tip and is thin-wall fiberglass.
Mine is the 2.6 TWFG. It does have the switch band, however I'm unsure that I will fly it DD. I really like the Chute Release and it's simplicty.
 

OverTheTop

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I have built a Tomach and flown it successully. A switch band (15-20mm wide) was made by cutting a slight amount off the airframe and gluing it onto the standard coupler. Switching was done with an RBF pin through one of the vent holes. That is my preferred method. See picture on the thread. Build was a bit non-standard, but I have not done a complete build thread for it yet.

Here is the link to my build:
http://www.ausrocketry.com/forum/viewtopic.php?f=6&t=4758&hilit=orange+revolution

First Flight
Motor: L640DT
Altitude: 21512'
Max Velocity: Mach 1.8
Max Accel: 47G

Flew with two Ravens and a TeleMega for electronics.

Currently lost after its second flight. Flew really well. :) Hope I get it back :(
 

jkovac

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I have built a Tomach and flown it successully. A switch band (15-20mm wide) was made by cutting a slight amount off the airframe and gluing it onto the standard coupler. Switching was done with an RBF pin through one of the vent holes. That is my preferred method. See picture on the thread. Build was a bit non-standard, but I have not done a complete build thread for it yet.

Here is the link to my build:
http://www.ausrocketry.com/forum/viewtopic.php?f=6&t=4758&hilit=orange+revolution

First Flight
Motor: L640DT
Altitude: 21512'
Max Velocity: Mach 1.8
Max Accel: 47G

Flew with two Ravens and a TeleMega for electronics.

Currently lost after its second flight. Flew really well. :) Hope I get it back :(
Wow, beautiful rocket and great numbers on the flight.
 
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