SpaceX Falcon Heavy Build 4.0 (1:65 Scale, BT-70 tubes) - a work in progress...

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I just posted my most recent SpaceX Falcon Heavy (3.0) build at 1:90 scale on this forum. That rocket is ready to fly!

And I'm working on repairs to my SpaceX Falcon Heavy (2.0), and Falcon 9 Crew Dragon Build 2.0 (1:65 Scale BT-70). I'm hoping to fly these all at the next SARG club launch on April 23rd 2022.

In this post, I'm going to work on a SpaceX Falcon Heavy with the goal of consolidating everything I've learned from those projects into my dream build...

A SpaceX Falcon Heavy at 1:65 scale.

Photo note: On Feb 6, 2018 SpaceX conducted their first Falcon Heavy test flight. They used Elan Musk’s red Tesla Roadster as the payload. You can view the actual launch here.


My SpaceX Falcon Heavy 1:65 scale design goals:

• 27 core, 2 stage rocket (Just like the real Falcon Heavy!)
  • 9 cores in center core: 1:E12-0 + 8:A10-0T
  • 9 cores in each booster: 1: D 12-0 + 8:A10-0T
  • 1 A8-3T in the 2nd stage
  • BT-70 body tubes for core and booster rockets. est. 108 cm (42") tall
• Booster separation at booster engine cutoff (BECO)
• Second stage ignition at main engine cutoff (MECO)
• Recovery of boosters and core using rear ejection of the rocket motor tubes
• Magnetic shear pins for booster attachment/separation
• Replaceable parts: minimal use of glue
• Parts designed using FreeCAD software and printed using a Prusa i3 MK3s 3D printer.
• Hidden “flip out” fins for the second stage* based on Tim's design at Apogee Rockets
• Magnetic shear pins for landing leg retention and release
• Articulating landing legs that extend during landing.
• Retracting thrust struts on the core after booster separation
• Movable grid fins*
• Magnetic shear pins for motor retention
• Pneumatic/magnetic booster separation from the core at BECO
• Upright core and booster recovery
• Use of self adhesive paper “skins”* adapted from AXM Paper Scale Models.
• Use of snap-in parts**
• Minimal paint***. On Build 2, a significant amount of effort was spent on painting and wet sanding and I never figured out how to apply SpaceX graphics over the 3D printed parts.
• Hybrid BT-50/BT-20 core motor tube. The BT-20 tube extends from directly above the part that houses the motor to the 2nd stage, which permits more room for the recovery chute. This also allows for more powerful (D and E) motors which Build 2.0 did not.
• Magnetic booster attachment of the upper booster mount with magnetic-puenatic separation (basically I learned in the 2.0 build that puenatic separation alone does not work).
• 3D printed parts using two colors (black and white) in the same part
• Magnetic lower booster attachments.
• Improved reverse recovery mechanisms
• Improved techniques for using tape to secure motor parts.
• Payload: Red Tesla Roadster with Starman
• 

*These were first developed on my Space X Falcon 9 Crew Dragon BT-60
**This was introduced on my Falcon 9 Crew Dragon Build 2.0
*** I still plan to paint on the nose cones but everything else is White PET plastic or self adhesive paper printed on a color printer.

Also, I'm pretty sure I'm going to need to build a custom launch pad for this project. I'd love to model the strong back and gantry tower, one day...

As I mentioned, the next SARG club launch is April 23rd 2022, so I've only got a couple of weeks to get this baby built. I figured with a deadline of April 23rd fast approaching, it would be more fun (and motivating) to post my progress up to that date rather than wait until I find time to write up this build which might take months.

_______________________________________________________________________________________________________________________________________________________________________________

What I have so far is:
1: A reasonably well working 1:65 scale Falcon 9. The last two launches demonstrated successful ignition of all 9 cores on each launch with successful 2nd stage ignition as well. Issues with flip out fin design and recovery have been remediated in the current build.
2: Designs for the 9 cluster motor mounts for the core an boosters are done and printing complete.
3: The design for the Falcon Heavy at 1:90 scale in FreeCAD, and a method for up-scaling the 1:90 FreeCAD designs to 1:90 is also complete.

What I need to do is:
1: Perform the actual scaling up and printing of the 1:65 scale parts. This requires considerable test printing.
2: Cut the BT-70 (core and booster rocket) and BT-80 (payload faring)
3: Scale AXM paper model rocket skins
4: Design launch system for 27 cluster launch (12 clips?)
5: everything I haven't thought of yet.

Core 9 cluster motor assembly (locked and loaded)


Core and booster lower sections designed and printed:

 

[Switch]

One thing I've learned on these projects is to lay out all of the parts prior to assembly to see if anything is missing.
Here, missing are:
1: BT-70 couplers (because the core body tubes need to be longer than 18")
2: Black Grid Fins
3: Landing legs with slots for fins
4: Centering ring for core motor mount
5: Tips for landing legs
6: some telescoping landing leg parts.
7: All of the magnets
8: Motors
9: Parachutes
10: more stuff that I didn't notice tonight.


I'm working on the missing parts. Also, I wish I took a before photo of these parts. They all had flanges or brims to aid the printing process. Tonight, the entire evening was spent removing plastic for the finished part. Here is the flip out fin before and after excess plastic was trimmed off.





Fuel lines before trimming (two on the right are mostly trimmed). The thrust struts (top) are also shown trimmed, but they had similar brims that needed removal.

 

[Switch]

Here's my update on this build. I've got everything ready for assembly (I think):


Firs step is to test fit everything. Starting with the magnets for the lower booster attachments:



When I did the test fit for the BT-70 couplers, I realized I forgot to included a sleeve at the mid point to hold the coupler in place. Recall that one goal of this project was to minimize the use of glue & use the adhesive paper skins to hold the body tube parts together. So I need to reprint these couplers with a BT-70 tube OD ring to old them in place.

meanwhile the engine assembly starts with taking the two top magnet centering rings and gluing them together:

The magnet mount bore runs all the way through to aid adjustment and ejection of magnets & tune the number of magnets required.


Here, the two parts are glued together with superglue to form one part holding magnets with opposite polarity in place for upper booster attachment and separation:

 

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Test fit of motor tube:



Once I get the Bt-70 couplers redesigned, I can lengthen the 1st stage body to the scale length. Here, I also realized I am missing couplers for the BT-20 engine tubes. Hopefully this will all come together tomorrow. But I'm starting to doubt if I will get this build complete tomorrow evening and be able to test this on Saturday. There are just so many variables that take time to tune...

{Edit] S note about the BT-70 and 3" tubes: they arrive "painted" but their is a noticeable stripe in the coil of the tube (seen above in the the interstage section above the center core). This shows through the adhesive paper skins applied later so requires the extra step of painting the tubes. The extra layer of paint also really helps the removal of the adhesive paper skin & prevents the skin from peeling away the underlying cardboard.

So I neglected to mention the need to paint all of the tubes even though paper skins are applied after that.

 

[SmurfTacoSupreme]

Lookin good. Following...

 

[Switch]

Starting to work on the skins that hold the tube parts together. The first part takes the most time because the booster mounts and landing leg mounts are not snap in parts. So the skins need to be cut to fit.

Here's the first skin:

That goes around the bottom.

The next skin needs to be centered on a line drawn down the BT-70 tube.


You can see how the skin needs slits to fit over the landing leg tube mount. The key is to apply the skin very slowly and evenly from the center of the skin to the ends. If I make a mistake and need to peel the skin back, I use a heat gun to slowly warm the skin and peel it back so it does not delaminate paint from the tube or tear. Then reapply more carefully.

That's all I got done today. Plus the design and printing of the couplers I realized I needed yesterday.

 

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Putting the engines together while I wait to reprint the BT-70 couplers that were not quite right.

Here is the motor clip for the E12-0 motor.


It doesn't fit through the printed part unless I heat the end to bend it straight and then bend it back.


It helps to have a motor inserted for stability for this and everything that follows. Here on the left I use a soldering iron to melt the BT-20 coupler to the top of the motor mount. On the right, the parts have just been assembled.



Next I need to put a plug on the ends of the Estes 13mm A10-0T . I haven't found a cheap source for these that don't have the ejection charge, so I need to stop up the end to keep that from burning the recovery parachute.

It helps to use the motor mount assembly to hold the motors (inserted upside down for this purpose)



Next I use these:


First I put a drop of glue in each A10 motor:


Then stuff a 1/8 piece of toilet paper into the end:


Followed by another drop of glue


Then tamp down the tissue:


Then top off with another drop of glue (being sure the meniscus touches the edge all the way around):


Then add all of the remaining motor retaining clips:


And use a 3D pen to secure in place:


Note the tape used on one motor due to the retainer clip being broken at the end. I did that before I figured out how to use a blow torch to bend them straight then back again (per note above).


My plan on the next build is to complete redesign the motor assembly to significantly simplify these steps.

 

[Switch]

Next I worked on the 2nd stage motor and flip-out-fin assembly. This consist of 6 printed parts, plus a motor retainer clip and dental rubber bands to provide the spring action on the fins.

Here are the 3D printed parts which consist of a top and bottom that fit together plus the 4 fins that fit between them:



And this is why this project takes so much time to assemble. Every part needs additional sanding or trimming to fit properly. Holes need to be machined to the proper size etc.


After some sanding to bore out the top mount, the pieces fit together:





I used a handheld 3D pen to weld the top and bottom flip out fin assembly together:


and then flex the fins to get them into place:


I'll add the dental rubber bands just before launch. For now it is easier to complete the build with the fins folded back.

 

[Switch]

Early this morning I tried to get everything together for the SARG club launch today. But I misaligned the core booster mounts to the boosters and had to use a heat gun to remove all of the skins and start over. Lessoned learned, use a little scotch tape to hold everything together so nothing rotates out of alignment.

Here's everything test fitted. I made sure everything was aligned by laying the rocket flat on a table & connecting the upper and lower booster mounts. Then I drew two lines all the way down each rocket on each side to use as guides for the application of the adhesive skins. As mentioned above, I also taped everything together.


The 2nd stage tube is press fitted over the flip out fin assembly. Not shown is a ring of electrical tape around the top of the assembly tube to make it fit snug. It is so tight that I cannot easily pull it apart.


Here's the part of the 2nd stage that joins the BT-70 tube to the 3" payload faring. You can see the electrical tape in this photo.


Here's is the entire rocket with all of the skins applied:


Next step is to cut the holes in the skins where parts like the grid fin mounts snap-in. I discovered the upper booster mounts were just a bit too small, causing the boosters lean inward noticeably from the bottom upward. So while the new upper booster mounts are printing, I'm working on the landing legs and final assembly of the motors.

 

[bad_idea]

Amazing build. Would love to see it launch. What are you using for ignition?

I'm told that stuffing the forward cavity of the booster with wadding and taping it will suffice and will give RSOs fewer qualms about whether or not a motor has been modified. Also, there is a plugged version of the A10 directly from Estes (A10-PT), though it only seems to be available in infrequent batches. I stocked up on them when AC Supply last had them in stock, for a similar cluster (though overall a far less ambitions project than yours!).

It looks to me like you'll be about 50g over the 125g propellant limit, so this is technically a high power rocket. If you're not L1 or higher, I'd bet you can find someone in your club who'd be happy to be involved as the flyer of record on such a cool project. Had a friend with an L3 offer to help me fly my 7x18 cluster rocket legally if I don't cert L1 by the time I finally get around to building a matching 7x18 booster stage.

 

[Switch]

Now for the landing legs. A few days ago. I realized I printed 12 regular landing legs, but I needed 4 with slots for the tail fins on the core to stabilize flight after booster separation. I kept having problems with the slotted landing legs prints. The three on the left all have horizontal lines. Then I noticed something snagging the feed of the PET to the printer.


A 4x6mm magnet is press fitted into the end of each landing leg.

This magnet pairs with a magnet in the motor tube to hold the landing leg upright. When the motor ejects during reverse recovery using rear ejection, the landing legs are released.

A small eyelet screw is used for the landing leg attachment to the body of the rocket:


The landing legs have telescoping tubes; extended:

note the eyelet is at 30 degrees. this allows the tube to lie flush to the rocket body (imagine the rocket body on the left of the tube shown above.
Compressed"


The end that attaches to the landing leg uses the same eyelet screws as used elsewhere.


On the end of the telescoping tube that attaches to the rocket, I made a small plug that fits the inner diameter of the largest tube and has a hole for the eyelet screw at 30 degrees so that the tube fits inside the landing leg properly.



Each of those plus needs to be sanded to remove the brim required for printing:


Then I take all of the parts and put them together:


The smallest tube has a larger part that prevents is from coming completely out of the middle tube.


It needs to be sanded slightly so that is slides freely inside the middle tube.


Here, all of the smaller tubes have been sanded an fit into the middle tubes:


The middle tubes are then fitted into the largest tubes:




And the plug with the eyelet added at the end:


Then I add the eyelets at the end of the smallest tube by slightly heating some needle nose plyers and pinching the tube over the eyelet screw:

I use 120 and 220 sandpaper to clean up the tubes; squaring the ends and reducing the diameter so they slide freely.


Also helpful is my LED magnifying headset for dealing with all of the tiny screws.



Finished telescoping tubes with eyelets at both ends:

 

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As I mentioned above, the motor tube has magnets that hold the landing legs upright. It's important to keep the polarity of the magnets correct, so I always double check. Here I stacked several magnets directly on a landing leg so I know I have the polarity correct and then insert the magnets one at a time into each of the 4 positions on each motor.

Later I will adjust the height of the magnet ring


A note about magnets, they are easy to press fit into PET plastic but unless you plan ahead, a real devil to get out again:


The landing legs are secured using small screws


The lower booster attachment magnet obstructs access to secure the landing leg, but can be removed to allow access for this purpose.



First all of the landing legs are screwed into place:

Then the telescoping tubes are added:





Landing legs installed:

Next steps:
1: Finish motor tubes for booster attachment, release, and recovery.
2: Fins for the core that use the slotted landing legs...
3: Upper thrust struts
4: LH2 and LOX lines
5: Launch lugs and cluster ignition configuration.
6: Whatever I forgot.

 

[Switch]

Amazing build. Would love to see it launch. What are you using for ignition?

I'm told that stuffing the forward cavity of the booster with wadding and taping it will suffice and will give RSOs fewer qualms about whether or not a motor has been modified. Also, there is a plugged version of the A10 directly from Estes (A10-PT), though it only seems to be available in infrequent batches. I stocked up on them when AC Supply last had them in stock, for a similar cluster (though overall a far less ambitions project than yours!).

It looks to me like you'll be about 50g over the 125g propellant limit, so this is technically a high power rocket. If you're not L1 or higher, I'd bet you can find someone in your club who'd be happy to be involved as the flyer of record on such a cool project. Had a friend with an L3 offer to help me fly my 7x18 cluster rocket legally if I don't cert L1 by the time I finally get around to building a matching 7x18 booster stage.

My plans for ignition are to do some kind off crazy clip whip from hell. I've had luck with my Falcon 9 version of this rocket - I just need to multiply by three



Plugging the A10's is a chore I'd avoid if I could source A10-PT engines. Apogee doesn't stock them...

I hadn't done the math on the power of this thing so thanks for that! Sadly, I missed the SARG launch today, but they only do up to mid-power rockets.

I need to find a place to fly this thing!

 

[BrendanH69]

My SpaceX Falcon Heavy 1:65 scale design goals:

• Hidden “flip out” fins for the second stage* based on Tim's design at Apogee Rockets

Thanks for the reference to the flip out fins article in Apogee's POF issue 313. This gives me some ideas for flip-out-fins for the Thales Starstreak project.

Enjoying the build thread and lots of little inspirational techniques.

 

[PieroAcme]

Hi Switch, Nice building , I really want to see the flight

I think there is no issue for propellant weight and L1 cert.

NAR rules are:

• High Power Certification is required if a person wishes to:
  1. Launch rockets containing multiple motors with a total installed impulse of 320.01 Newton-seconds or more, or
  2. Launch rockets containing a single motor with a total installed impulse of 160.01 Newton-seconds or more, or
  3. Launch rockets that weigh more than 53 ounces (1500 grams), or
  4. Launch rockets powered by motors not classified as model rocket motors per NFPA 1122, e.g.:
     1. Average thrust in excess of 80.0 Newtons
     2. Contains in excess of 125 grams of propellant
     3. Hybrid rocket motors

You are in the case 1. I think you are far from 320Ns. The 125g limit is for not classified motors (Point 4).

I just notice one thing in your ignitors cabling. The A are partially in series. You have 1 group of 3 and another of 4 . Then the central one is in parallel with the other 2 groups. This means that you will have different current flow in each of the 3 groups of ignitors. This could led to partial ignition.
My suggestion is to place the central in series with the group of 3 A. In this case you'll have 2 series groups of 4 in parallel.

 

[neil_w]

This is a very impressive project and a great build thread.

I'm intrigued by use of a 3D pen as a gluing implement (don't know what else to call it)... does it really create a strong bond, or are you just using it in spots where you don't need something too strong.

 

[Switch]

This is a very impressive project and a great build thread.

I'm intrigued by use of a 3D pen as a gluing implement (don't know what else to call it)... does it really create a strong bond, or are you just using it in spots where you don't need something too strong.

Thanks. This is a great question! The answer is it is pretty damned strong. After my first failed attempt with a 9-cluster, the motor mount was destroyed and it was a real b*tch to get the retainer clip out to reuse.

But your question made me want to do a test. Here's two 10x40 mm pieces of PET that I welded together.


& here is another test ~25x50mm


I can't break these using my hands.

BTW I forgot to mention this above: I'm using a SCRIB3D Advanced 3D Printing Pen with Display.

 

[bad_idea]

My plans for ignition are to do some kind off crazy clip whip from hell. I've had luck with my Falcon 9 version of this rocket - I just need to multiply by three

However you wire it (see PieroAcme's comment), I'd recommend doing a full ignition test on a complete set of igniters prior to stacking the loaded rocket, and doing so every time you use different launch equipment. My relay launcher struggles with more than six igniters (MJG blackpowder starters) in parallel, but fortunately the launchers of both my local clubs can handle at least seven with aplomb. I've not tried series wiring yet, but if I do, I'll test igniters in advance then too.

Plugging the A10's is a chore I'd avoid if I could source A10-PT engines. Apogee doesn't stock them...

When I needed A10-PTs, I refreshed this page from AC Supply every few days until I saw they were back in stock: https://www.acsupplyco.com/estes-mo...mini-engines/estes-a10-pt-model-rocket-engine

I'm not sure how often Estes produce these or how often AC Supply have them in stock. I'm guessing not very often, since they appeal to rocket glider pilots who like very small gliders and people like you and me building clusters with different motor types, and unfortunately neither is a large pool of fliers.

I think there is no issue for propellant weight and L1 cert.

NAR rules are:

• High Power Certification is required if a person wishes to:
  1. Launch rockets containing multiple motors with a total installed impulse of 320.01 Newton-seconds or more, or
  2. Launch rockets containing a single motor with a total installed impulse of 160.01 Newton-seconds or more, or
  3. Launch rockets that weigh more than 53 ounces (1500 grams), or
  4. Launch rockets powered by motors not classified as model rocket motors per NFPA 1122, e.g.:
     1. Average thrust in excess of 80.0 Newtons
     2. Contains in excess of 125 grams of propellant
     3. Hybrid rocket motors

You are in the case 1. I think you are far from 320Ns. The 125g limit is for not classified motors (Point 4).

I believe that is incorrect. The NAR Model Rocket Safety Code says:

7. Size My model rocket will not weigh more than 1,500 grams (53 ounces) at liftoff and will not contain more than 125 grams (4.4 ounces) of propellant or 320 N-sec (71.9 pound-seconds) of total impulse.​

The NAR High Power Rocketry page states:

A rocket exceeds the definition of a Model Rocket under NFPA 1122 and becomes a High Power Rocket under NFPA 1127 if it:​

• Uses a motor with more than 160 Newton-seconds of total impulse (an “H” motor or larger) or multiple motors that all together exceed 320 Newton-seconds; or
  • Uses a motor with more than 80 Newtons average thrust (see rocket motor coding); or
  • Exceeds 125 grams (4.4 ounces) of propellant; or
  • Weighs more than 1,500 grams (53 ounces) including motor(s); or
  • Uses a hybrid motor or a motor designed to emit sparks; or
  • Includes any airframe parts of ductile metal.

NFPA 1122 (Code for Model Rocketry) states:

4.4.2 A model rocket shall use no more than 125 g (4.4 oz) of​

rocket propellant.​

NFPA 1127 (Code for High Power Rocketry) defines model and high power rockets as follows:

3.3.13.2 Model Rocket. A rocket that (1) weighs no more​

than 1500 g (53 oz) with motors installed; and (2) is pro-​

pelled by one or more model rocket motors having an in-​

stalled total impulse of no more than 320 N-sec (71.9 lb-​

sec); and (3) contains no more than a total of 125 g (4.4 oz)​

of propellant weight. [1122, 2013]​

​

3.3.13.1 High Power Rocket. A rocket vehicle that (1) is pro-​

pelled by one or more high power rocket motors; or (2) is​

propelled by a combination of model rocket motors having​

an installed total impulse of more than 320 N-sec (71.9 lb-​

sec); or (3) is propelled by a combination of model rocket​

motors having more than a total of 125 g (4.4 oz) of propel-​

lant weight; or (4) weighs more than 1500 g (53 oz) with mo-​

tor(s) installed.​

It will also be an FAA Class 2 rocket so will an FAA waiver if operated in controlled airspace (the altitude of which varies, but is usually low enough to be troublesome to HPR), though any high power club launch should have one already. From FAA Part 101, section 22:

§ 101.22 Definitions.​

​

The following definitions apply to this subpart:​

​

(a) Class 1 - Model Rocket means an amateur rocket that:​

(1) Uses no more than 125 grams (4.4 ounces) of propellant;​

(2) Uses a slow-burning propellant;​

(3) Is made of paper, wood, or breakable plastic;​

(4) Contains no substantial metal parts; and​

(5) Weighs no more than 1,500 grams (53 ounces), including the propellant.​

​

(b) Class 2 - High-Power Rocket means an amateur rocket other than a model rocket that is propelled by a motor or motors having a combined total impulse of 40,960 Newton-seconds (9,208 pound-seconds) or less.​

(I won't quote the operating limitations because they get quite long-winded, but they're on the same page.)

Like I said though, I don't think it would be a problem to get a high-power flyer involved in flying what will be the coolest rocket within 500 miles. (I'd talk with the club in advance though.)

 

[Switch]

Here is how the upper booster mount works:


The upper booster mount is printed separately from the core body section:




The top of the 1st stage core is 3D printed with holes for the booster and grid fin mounts and other parts.


The booster mount part has tabs that fit into the holes on the core:

The printed part needs to be sanded to remove the brim:

Note the pin hole to remove the magnet from the booster mount if needed.

Then the magnet hole is machined for a 4x6mm magnet. Note I don't use a drill for that. The hole is almost perfect. I just attach the drill bit to a vice and hand turn the booster mount on it. I then do some light sanding to clean up the burs and PET filaments.


Meanwhile the upper motor tube centering ring has holes for two magnets.


Here's the booster motor core without the booster body tube attached to the booster mount:


The lower booster motor magnet attracts the magnet of the core booster mount. Meanwhile, the polarity of the upper booster magnet is reversed so that when the booster motor assembly ejects during rear ejection recovery, the upper booster magnet repulses the core booster magnet to facilitate booster separation.

 

[bad_idea]

This is an amazing build!

 

[Switch]

Here's the detail on the grid fins.

The core and boosters have sections that are 3D printed with square holes into which the grid fin mounts snap in. This allows application of adhesive paper skins that hold these sections to the BT-70 tubes. The paper skin does not require any cutting for the parts until after it is applied which is much easier than if the grid fin mounts were printed as part of the core tube & I had to cut the skins before hand.


and round holes hidden behind the grid fin (explained below).

The grid fin mounts are printed separately (each one is only about 10mm on a side):

The grid fin mounts snap in the holes and the grid fins snap onto the grid fin mounts:

Here you can also see the hole for the booster mount and the receiving magnet on the motor tube centering ring.

The grid fins can pivot on the mounts:

here you can see a small exhaust hole to allow cold gas to escape the booster during rear ejection. The idea was that this is enough pressure to extend the grid fins for landing but that doesn't actually work. I think the holes still keep the pressure of the recovery ejection charge from blowing up the rocket but on the center core they are critical for 2nd stage ignition. They allow cold gases to escape & keep the 2nd stage from popping off like a Champaign cork & allow the hot gases of the ejection charge to ignite the 2nd stage motor.

 

[Switch]

The lower booster mounts work much like the upper booster mounts but needed considerable redesign compared to my 1:95 scale version which had only a single Estes motor in each core. Because the A10 motors take up so much space, in the boosters, I had to use 12x6x3mm magnets aligned flat against the body tube (see below) instead of the cylindrical magnets that were also in the upper centering ring.

The lower booster mount on the core has a 4x6mm magnet that fits into a hole on the booster and side mounts also have magnets for additional lateral stability.




The booster motor mount has a magnet that attracts the magnet of the core:


When the booster motor ejects during rear ejection, a second magnet with the opposite polarity passes past the core magnet applying a repulsive force to facilitate ejection of the booster from the core.

 

[Switch]

I made this poster to explain how the booster attachment/separation and recovery works with rear ejection of the 1st stage motors on my 1st Falcon Heavy, the current build works almost the same.

The rear ejection of the motor tubes minimizes the stress on the recovery parachutes since the rocket is not at apogee when the ejection charge ignites on the boosters or the core.

 

[Switch]

However you wire it (see PieroAcme's comment), I'd recommend doing a full ignition test on a complete set of igniters prior to stacking the loaded rocket, and doing so every time you use different launch equipment. My relay launcher struggles with more than six igniters (MJG blackpowder starters) in parallel, but fortunately the launchers of both my local clubs can handle at least seven with aplomb. I've not tried series wiring yet, but if I do, I'll test igniters in advance then too.

When I needed A10-PTs, I refreshed this page from AC Supply every few days until I saw they were back in stock: https://www.acsupplyco.com/estes-mo...mini-engines/estes-a10-pt-model-rocket-engine

I'm not sure how often Estes produce these or how often AC Supply have them in stock. I'm guessing not very often, since they appeal to rocket glider pilots who like very small gliders and people like you and me building clusters with different motor types, and unfortunately neither is a large pool of fliers.

I believe that is incorrect. The NAR Model Rocket Safety Code says:

7. Size My model rocket will not weigh more than 1,500 grams (53 ounces) at liftoff and will not contain more than 125 grams (4.4 ounces) of propellant or 320 N-sec (71.9 pound-seconds) of total impulse.​

The NAR High Power Rocketry page states:

A rocket exceeds the definition of a Model Rocket under NFPA 1122 and becomes a High Power Rocket under NFPA 1127 if it:​

• Uses a motor with more than 160 Newton-seconds of total impulse (an “H” motor or larger) or multiple motors that all together exceed 320 Newton-seconds; or
  • Uses a motor with more than 80 Newtons average thrust (see rocket motor coding); or
  • Exceeds 125 grams (4.4 ounces) of propellant; or
  • Weighs more than 1,500 grams (53 ounces) including motor(s); or
  • Uses a hybrid motor or a motor designed to emit sparks; or
  • Includes any airframe parts of ductile metal.

NFPA 1122 (Code for Model Rocketry) states:

4.4.2 A model rocket shall use no more than 125 g (4.4 oz) of​

rocket propellant.​

NFPA 1127 (Code for High Power Rocketry) defines model and high power rockets as follows:

3.3.13.2 Model Rocket. A rocket that (1) weighs no more​

than 1500 g (53 oz) with motors installed; and (2) is pro-​

pelled by one or more model rocket motors having an in-​

stalled total impulse of no more than 320 N-sec (71.9 lb-​

sec); and (3) contains no more than a total of 125 g (4.4 oz)​

of propellant weight. [1122, 2013]​

​

3.3.13.1 High Power Rocket. A rocket vehicle that (1) is pro-​

pelled by one or more high power rocket motors; or (2) is​

propelled by a combination of model rocket motors having​

an installed total impulse of more than 320 N-sec (71.9 lb-​

sec); or (3) is propelled by a combination of model rocket​

motors having more than a total of 125 g (4.4 oz) of propel-​

lant weight; or (4) weighs more than 1500 g (53 oz) with mo-​

tor(s) installed.​

It will also be an FAA Class 2 rocket so will an FAA waiver if operated in controlled airspace (the altitude of which varies, but is usually low enough to be troublesome to HPR), though any high power club launch should have one already. From FAA Part 101, section 22:

§ 101.22 Definitions.​

​

The following definitions apply to this subpart:​

​

(a) Class 1 - Model Rocket means an amateur rocket that:​

(1) Uses no more than 125 grams (4.4 ounces) of propellant;​

(2) Uses a slow-burning propellant;​

(3) Is made of paper, wood, or breakable plastic;​

(4) Contains no substantial metal parts; and​

(5) Weighs no more than 1,500 grams (53 ounces), including the propellant.​

​

(b) Class 2 - High-Power Rocket means an amateur rocket other than a model rocket that is propelled by a motor or motors having a combined total impulse of 40,960 Newton-seconds (9,208 pound-seconds) or less.​

(I won't quote the operating limitations because they get quite long-winded, but they're on the same page.)

Like I said though, I don't think it would be a problem to get a high-power flyer involved in flying what will be the coolest rocket within 500 miles. (I'd talk with the club in advance though.)

Thanks for all of this information! And I posted this in the mid power forum...

 

[Switch]

OK, so I reached out to a club in Nevada (ROCKONN). They told me I'd need to apply for a NAR Level 1 certification & bring the paper work with me. So I joined NAR & got the Level 1 application ready. Looks like I'm heading to Artesia Lake, Nevada for ROCKONN's May 21st launch event!

Directions

 

[bad_idea]

OK, so I reached out to a club in Nevada (ROCKONN). They told me I'd need to apply for a NAR Level 1 certification & bring the paper work with me. So I joined NAR & got the Level 1 application ready. Looks like I'm heading to Artesia Lake, Nevada for ROCKONN's May 21st launch event!

Good luck! If you don't already have an L1-capable rocket to cert with, you certainly have the skills to build one between now and then, scratch or kit.

 

[Switch]

Next step is the thrust strut arms:




Like many other parts a slight machining is needed.

Here is a video of the thrust struts retraction mechanism.:

 

[jmasterj]

Good luck! If you don't already have an L1-capable rocket to cert with, you certainly have the skills to build one between now and then, scratch or kit.

Right, you have to cert with an H or I motor before you launch this beast.

 

[boatgeek]

Right, you have to cert with an H or I motor before you launch this beast.

You could also fly with just the three center E motors as a shakedown flight if you have enough thrust off the pad if you can't get your cert in time.

 

[Switch]

Right, you have to cert with an H or I motor before you launch this beast.

So it appears I have a high power rocket that I cannot use for a Level 1 certification and cannot fly without the Level 1. Or, I can scale back the number of motors until I'm below the 125g limit. Or build another rocket for the Level 1 cert & then fly the Falcon Heavy after that...