Mach 1 - Omicron BT60 Build

[halek]

Hi,
In progress on my first minimum diameter build, Mach 1 Omicron BT60. Completed the payload section AV bay and nose cone bay components. I have a question about the booster section motor mount. The two choices I selected are the Bandit motor retainer or Slimline retainer. Each has advantages/disadvantage.
Bandit retainer - threaded mount, fixed motor length, requires threaded forward closure, blocks optional use of motor ejection
Slimline retainer - adds bulk to aft end, variable motor length, standard motor components, use of ACME hard point anchor to allow optional motor ejection

The plan is to use Aerotech 29mm 120/40 (29mm-38mm Aeropak adapter) and 38mm 120 cases with propellants in the sub 3000' altitude.

Any suggestions or experiences with this type of build?

Thanks.

 

[laizalott]

Hey there! I actually just finished building the Mach 1 Daedalus in early June, easily my favorite mid-power rocket now. These Mach 1 kits are fantastic.

In my case, mine was not a minimum diameter build, so I just went with the Bandit Slim Line retainer they suggested, and I will be limited to 29mm motors.

To actually use 38/120 case in yours, you would have a minimum diameter rocket, which would mean you'd want the bandit minimum diameter retainer you have pictured in order to get the aerodynamic benefit of such a config, but yeah, you are limited to a single casing length.

Using both 38/120 and 29/40-120 like you said, that will really complicate things. You'll need either a standard 38mm or slimline 38mm closure, using the aeropack or some other adapter to use the 29/40-120 like you mentioned. You cannot really adapt a 29/40-120 to a rocket with a 38mm minimum-diameter retainer, unless there is a product for this I am unaware of or you have the skill to machine something yourself. You would also have to plug the 29/40-120 with some dog-barf or something to avoid fouling the space between it and the minimum-adapter.

Personally, for something like the Omicron, I would rather make it a proper minimum diameter 38mm rocket for the 38/360 casing length, then get the "AEROTECH 38MM RELOAD ADAPTER SYSTEM" which allows you to turn the 38/360 into a 38/240 or 28/120. Quick chart from Apogee's website for the adapters:



Of course, you would not be able to keep this rocket below 3000' on a 38/360 reload, and it stops you from using the cheaper 29/40-120 E/F/G reloads, but it provides the most customizability while still allowing you to load G loads in a 38/120 configuration.

If you've already decided and built the rocket, put up a picture and let me see what you did!

 

[SolarYellow]

You can use different lengths of motor, just use threaded rod to connect your plugged/threaded forward closure to the bulkhead. You don't need to spend a lot of money on fancy hardware, either. A plywood bulkhead with a hole in the middle and a piece of threaded rod with some nuts will work perfectly. Use a tee-nut if you want to be fancy.

Or, since your airframe is fiberglass, you can use one of these https://www.homedepot.com/p/Oatey-Gripper-1-1-2-in-Plastic-Mechanical-Test-Plug-33400D/100342630 and have a moveable bulkhead. Only tighten it enough to hold, no need to swell/crack the fiberglass.

 

[laizalott]

You can use different lengths of motor, just use threaded rod to connect your plugged/threaded forward closure to the bulkhead.

I was honestly today-years-old when someone pointed this out to me...so simple I could not even imagine it until someone else said it, lol

 

[SolarYellow]

You can even get aluminum threaded rod from zoro.com in 1/4-20 and 5/16-18 if you want it to be lighter.

 

[halek]

Hey there! I actually just finished building the Mach 1 Daedalus in early June, easily my favorite mid-power rocket now. These Mach 1 kits are fantastic.

In my case, mine was not a minimum diameter build, so I just went with the Bandit Slim Line retainer they suggested, and I will be limited to 29mm motors.

To actually use 38/120 case in yours, you would have a minimum diameter rocket, which would mean you'd want the bandit minimum diameter retainer you have pictured in order to get the aerodynamic benefit of such a config, but yeah, you are limited to a single casing length.

Using both 38/120 and 29/40-120 like you said, that will really complicate things. You'll need either a standard 38mm or slimline 38mm closure, using the aeropack or some other adapter to use the 29/40-120 like you mentioned. You cannot really adapt a 29/40-120 to a rocket with a 38mm minimum-diameter retainer, unless there is a product for this I am unaware of or you have the skill to machine something yourself. You would also have to plug the 29/40-120 with some dog-barf or something to avoid fouling the space between it and the minimum-adapter.

Personally, for something like the Omicron, I would rather make it a proper minimum diameter 38mm rocket for the 38/360 casing length, then get the "AEROTECH 38MM RELOAD ADAPTER SYSTEM" which allows you to turn the 38/360 into a 38/240 or 28/120. Quick chart from Apogee's website for the adapters:

View attachment 661318

Of course, you would not be able to keep this rocket below 3000' on a 38/360 reload, and it stops you from using the cheaper 29/40-120 E/F/G reloads, but it provides the most customizability while still allowing you to load G loads in a 38/120 configuration.

If you've already decided and built the rocket, put up a picture and let me see what you did!

 

[halek]

Thanks for the ideas! The threaded rod and expansion plug suggestion is a great one. Simple and easy. I had moved on with the build during the time after posting. Proceeded with Option 1 - Slimline motor retainer and Hardpoint anchor point from Giant Leap. The Hardpoint is mounted via (3) 4-40 screws threaded into aluminum casting to allow future adjustment and positioned to fit 29mm 120/40, 180, and 38mm 240 case lengths. The 120 and 240 cases are roughly the same length. The longer 29/180 case is necessary to use 29mm H motors. Also, the Hardpoint is open for optional ejection charge. It all fits up very well. The attached pic shows completed Omicron assembly with 29mm 120 and 180 cases / 38mm Aeropack adapter and 38mm 240 case with one grain spacer. Another pic with 38mm motor parts.
For the 3000' max altitude requirement here's the sim data.
38mm G67R 1 grain 1720'
38mm G61W 1 grain 1725'
29mm G64W 2027'
29mm H128W 2679'
29mm H238T 2875'
38mm H73J 2 grain 2876'