Dual deployment in a BT20 (18mm) min diameter rocket

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Adrian A

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Today I flew my first 18mm minimum diameter dual deployment rocket. I doubt I'm the first to have done this, but I don't know of any currently-available altimeters that could make this possible.

The rocket is scratch-built, made from Apogee parts, including the 18mm couplers and tubes. I had some 1/8" balsa laying around and I had some fun sculpting airfoils into them with my belt sander.
Here's the av-bay with charges connected. The charges are 1/4" launch lugs cut down to 1/2" long, with a hot-glued ematch at one end, about 0.1g black powder, capped again by hot glue

IMG_3194.jpg

Ground testing to verify charge sizing is always important. Below is slow-motion video of the apogee charge, which was captured by the phone app that also triggers the charge after a 5-count.


View attachment 1718456374885.mov

The camera man was startled by the report. It probably made the neighbors wonder what was going on, too.

Slow-mo video of the main chute charge:

View attachment 1718456581292.mov

I don't have video of the flight, but I do have some recorded data:
1718483612547.png

Part of the disagreement is due to the well-known under-reporting of baro-measured altitude in hot weather. On a hot day it can under-report by about 10%. It was pretty warm this morning here at the C.R.A.S.H. launch site in Ft Lupton, CO.

1718483630356.png
The future tilt is an estimate of what the tilt will be 3 seconds from now, based on the horizontal and vertical velocity. It's used for staging safety checking, though this isn't intended to be a staging altimeter.

When the apogee charge went off, the gyro max rate was exceeded, so the inertial navigation estimate of horizontal velocity is only good up to about that point.
1718483837142.png

The apogee and main charges fire when the -side of the charge is connected to ground through a MOSFET switch. There was some residue which makes a little bit of a conduction path after the 1-second firing is done.
1718483923833.png

This was a pretty fun way to do a dual-deployment flight, though honestly it would be easier with 24mm or larger tubes.
 
Fly it and see what happens. This is coming from someone who's blown out the sides of cardboard tubes with charges so please beware. Blow a side of a tube out with no deployment and an "off- nominal" flight will occur. Perhaps a lawn dart. Been there, done that. With a small diameter tube and charges the flier measures, would be "easy" to blow a rocket to pieces on recovery. Would be fun for a "laymen" crowd but not for the flier.
 
Now I can put my RMS 18/20 motor to good use! Maybe next January I'll order some 'seasonal' D2.3T loads to go in it :-D

So, you gonna offer a GPS tracker in a 18mm form factor too? 😉
The Featherweight GPS tracker is about as narrow as it can be and still use a good GPS ceramic patch antenna. It fits into a 24mm coupler.
 
Thanks!

Yes. I'll save some details for an announcement when it's closer to going on sale.
XWYycAu.jpeg
 
Dear sir, this is good news indeed! One of my biggest goals, if I ever can get even one tenth of the way into this as you have, is to have as many tools as possible for small-field fliers to get their rockets back safely, and to introduce these more advanced methods to a wider audience. Back East, here, the fields are small, the trees are plentiful, and in many fields, the athletes are plentiful as well! Houses, etc...

I've been watching your products and looking for an opportunity to jump in!
 
I am in the middle of a Quark in BT50 design for my local park. Since the park has a D-impulse limit, I'm designing it for the Aerotech 18/20 case and the Rocketarium screw-on retainer. But I could - and would - easily shift gears to friction fitting that case in minimum diameter . . .
 
You need one of those Mach 1 Rocketry 18mm fiberglass kits for playing with dual deployment.
O.M.G.

Not to mention, it's time to finally get off the pot and put my L2 to work and start researching 18mm EMK reloads !

Maybe even someday DIY like @beeblebrox and @Rocketjunkie do !

Not to mention that I could finally fly all my E27-4T motors in a rocket deserving of all those delicious 23 Ns :) :)

Can you tell how excited I am about the possibilities ?

Thanks for researching and sharing this, Adrian !

-- kjh

EDIT: p.s. what motor did you fly to 600 ft ?

And what does your axial acceleration look like ?
 
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I think there is a possibility of doing dual deploy with Adrel in a 13 mm body tube. Not easy though and strikes me as very finicky. I think the idea is to let the motor ejection do the first ejection, hopefully at apogee or high up. The main recovery device is then done electronically at a lower altitude.
 
I think there is a possibility of doing dual deploy with Adrel in a 13 mm body tube. Not easy though and strikes me as very finicky. I think the idea is to let the motor ejection do the first ejection, hopefully at apogee or high up. The main recovery device is then done electronically at a lower altitude.
Yes. Good suggestion. It can be used for dual deploy and it is mentioned in the DeployMax instructions. I do not see why it would not be easy, and that it would be finicky.

A true dual deploy is necessary for those of us that use a motor without an ejection charge. That, or two single deploy altimeters, or radio control.
 
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Yes. Good suggestion. It can be used for dual deploy and it is mentioned in the DeployMax instructions. I do not see why it would not be easy, and that it would be finicky.

A true dual deploy is necessary for those of us that use a motor without an ejection charge. That, or two single deploy altimeters, or radio control.
Although, not a true dual deployment device, a deploy of a recovery device at low altitude for 13 mm BT's could be valuable in NAR Competition events.
 
OK then ... I am ready to place an order from Mach 1:
View attachment 651536

Next, I guess I will need is an AT B14T and a new Featherweight flight computer :)

-- kjh

p.s. just showing off ... no pressure, Adrian :) :)
Well, that kinda interests me in these 18mm EMK reloads you mentioned. Although the specific E that you referred to is only 3 Ns more than a top-end D, I wonder if whatever else you were referring to goes higher. Are the cases longer, etc. I can design, but it helps to know what's available! Plus, we must be ready to send Adrian our money! 😁
 
Well, that kinda interests me in these 18mm EMK reloads you mentioned. Although the specific E that you referred to is only 3 Ns more than a top-end D, I wonder if whatever else you were referring to goes higher. Are the cases longer, etc. I can design, but it helps to know what's available! Plus, we must be ready to send Adrian our money! 😁
@Blast it Tom! --

Yes, the E27-4T motors I have are going on 30-years old and they're 23 Ns baby E-motors.

I believe they're out of production now.

If you have a L2 cert, you can apply for access and then browse the TRF [Restricted] Research sub-forum.

A couple TRF members have been making their own propellant grains for 18mm D, E and F motors ( ? and maybe G motors ? ) and there is a long ongoing thread about 18mm Experimental Motors ( ! whee ! ).

Some of their motors have OOO 6-inches of propellant in them :)

I am not ready to mix and cast my own propellant but RCS does sell 18mm EMK kits ( Experimental Motor Kits ) and Blue Thunder and White Lightning propellant grains where you can play with your RMS 18/20 motor casing with AT reloads.

RCS > Store > Experimental Motor Kits (EMKs) > 18mm Model Rocket RMS EMKs

I've not spec'd out the parts for the two 18mm EMKs ( one White Lightning, one Blue Thunder ) but I imagine the you end up with something like a D13W or a D24T, respectively ( need to check the nozzle throats to see for myself ).

So you're not going to end up with more powerful motors but I thought it might be fun to try ...

Is this what you're asking about ?

-- kjh

EDIT: I just realized that the AT RMS 18/20 E27T is not available on ThrustCurve.org.

Attached and here is a plot:
e27.png
 

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@Blast it Tom! --

Yes, the E27-4T motors I have are going on 30-years old and they're 23 Ns baby E-motors.

I believe they're out of production now.

If you have a L2 cert, you can apply for access and then browse the TRF [Restricted] Research sub-forum.

A couple TRF members have been making their own propellant grains for 18mm D, E and F motors ( ? and maybe G motors ? ) and there is a long ongoing thread about 18mm Experimental Motors ( ! whee ! ).

Some of their motors have OOO 6-inches of propellant in them :)

I am not ready to mix and cast my own propellant but RCS does sell 18mm EMK kits ( Experimental Motor Kits ) and Blue Thunder and White Lightning propellant grains where you can play with your RMS 18/20 motor casing with AT reloads.

RCS > Store > Experimental Motor Kits (EMKs) > 18mm Model Rocket RMS EMKs

I've not spec'd out the parts for the two 18mm EMKs ( one White Lightning, one Blue Thunder ) but I imagine the you end up with something like a D13W or a D24T, respectively ( need to check the nozzle throats to see for myself ).

So you're not going to end up with more powerful motors but I thought it might be fun to try ...

Is this what you're asking about ?

-- kjh

EDIT: I just realized that the AT RMS 18/20 E27T is not available on ThrustCurve.org.

Attached and here is a plot:
View attachment 651598
Yes, it is. I thought Aerotech was doing something to get D impulse into the 18/20 case. And thanks for the EMK decode. But alas! Me, a lowly L0, cannot get into the research forum. It's sure a thread I'd like to read, though! I need to review my thermodynamics first...
 
Yes, it is. I thought Aerotech was doing something to get D impulse into the 18/20 case. And thanks for the EMK decode. But alas! Me, a lowly L0, cannot get into the research forum. It's sure a thread I'd like to read, though! I need to review my thermodynamics first...
I don't see why I can't share a YouTube link: YouTube > TomB0667 ... look for the chain link fence and there are some 18mm F-motor launches.

-- kjh
 
Yes, it is. I thought Aerotech was doing something to get D impulse into the 18/20 case. And thanks for the EMK decode. But alas! Me, a lowly L0, cannot get into the research forum. It's sure a thread I'd like to read, though! I need to review my thermodynamics first...
My feelings too, Tom. I'm a lowly L0 that made the longest burning "M"oonburner of 54 seconds. That's me next to it in my profile picture. The paper is on the RCS site. In 1978 at NARAM 20, I gave Vern two 18x70mm composite motors. Vern was interested in a higher performance 18x70mm motor. His jaw hit the floor, not only that they were "F" motors, but the propellant had an Isp of 239. These 18x70 & 80mm motors were a real kick if you had a fiberglass rocket that could go supersonic within 50ft off the launch rod. Model rocketry was not ready for an 18mm "F" motor in 1978.
 

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