Not Enough Thrust from BP?

[sr205347d]

Recent posts about the Aerotech B14 lament the demise of the Estes B14-0, as it would provide extra oomph off the rod for multi-stage rockets.

I have experienced excessive weathercocking from my Star Orbiter using Estes E12, (because I loaded it down with additional stuff like: a bulkhead and screw eye to make a payload section; a nomex chute protector and a quick link to attach it; a JLCR; an altimeter; and, a GPS tracker).

So, as someone said recently, clustering is your friend!

Here is my thrust solution for my SO. The "strap-on" motors could be plugged, ejected, or the pods could be vented to release the ejection charge gas. This could also be done on a booster for a multi-stage rocket. A pair of mini A10s would be cheap and relatively light, while providing a good kick off the pad.



I haven't flown this yet, but I did fly this. I put a D12-3 in the center and B6-4s in the sides:



Just leave out the aft centering ring to let the ejection charge gas from the side motors vent out the back. I have lots of wire left over from a garage door installation that I use to connect the ignitors. So, no clip whips are required.



I just built a Great Goblin, and plan to mount A10 motors inside, similar to the above photo. The mini motor mount tubes will be small enough to leave room for the supplied retainer for the center motor if they are glued to the inside of the body tube rather than the center motor mount tube.

 

[Alan15578]

Yes, especially using A10 and MMX motors. And if you are too cheap to by motors, or too lazy to cluster, you could use a piston launcher.

 

[Rocketjunkie]

Aerotech allows the removal of ejection charges (BP only).

 

[teepot]

Recent posts about the Aerotech B14 lament the demise of the Estes B14-0, as it would provide extra oomph off the rod for multi-stage rockets.

I have experienced excessive weathercocking from my Star Orbiter using Estes E12, (because I loaded it down with additional stuff like: a bulkhead and screw eye to make a payload section; a nomex chute protector and a quick link to attach it; a JLCR; an altimeter; and, a GPS tracker).

So, as someone said recently, clustering is your friend!

Here is my thrust solution for my SO. The "strap-on" motors could be plugged, ejected, or the pods could be vented to release the ejection charge gas. This could also be done on a booster for a multi-stage rocket. A pair of mini A10s would be cheap and relatively light, while providing a good kick off the pad.

View attachment 626939

I haven't flown this yet, but I did fly this. I put a D12-3 in the center and B6-4s in the sides:

View attachment 626942

Just leave out the aft centering ring to let the ejection charge gas from the side motors vent out the back. I have lots of wire left over from a garage door installation that I use to connect the ignitors. So, no clip whips are required.

View attachment 626943

I just built a Great Goblin, and plan to mount A10 motors inside, similar to the above photo. The mini motor mount tubes will be small enough to leave room for the supplied retainer for the center motor if they are glued to the inside of the body tube rather than the center motor mount tube.

Apogee sells hooks that hold SRB's to the main BT. I have several rockets that use them. When the ejection charge goes off on the SRB motors they detach from the core and come down on their own chutes.

 

[sr205347d]

My Great Goblin is now set up to cluster either 18mm or 13mm side boosters. (Or both!?)



I didn't have any BT-5 on hand, so I rolled my own 13mm motor mount tubes using the Apogee method. I just glued some scrap wood in the ends as thrust blocks.

If using 18mm side boosters, there is no room for the screw-on retainer, so the center motor would need to be a good friction fit. But I think a pair of A10s, almost doubling the initial thrust of the Estes E or F motors, would be good enough to get it off the rod with good speed.

The GG may not even need the extra boost, but the cluster would be cool anyway!

 

[bad_idea]

Here is my thrust solution for my SO. The "strap-on" motors could be plugged, ejected, or the pods could be vented to release the ejection charge gas. This could also be done on a booster for a multi-stage rocket. A pair of mini A10s would be cheap and relatively light, while providing a good kick off the pad.

I've clustered this way, and it works, but if you're relying on motor ejection, you have to be 100% sure the main motor lights, or you have a lawn dart, at least if the side motors have enough oomph to get the rocket going without the main motor. I use MJG black powder starters for my black powder clusters and trust them a lot further than I trust the stock Estes starters. Still in most cases instead of relying on venting side motors in a mixed cluster, I'd be happier to fly a conventional cluster of motors that all eject at once, electronic deployment, or simply a thrustier composite.

The GG may not even need the extra boost

It certainly does, IMO, at least with the Estes 29mm motors it was supposedly made for. GG's thrust-to-weight on those motors is comically low.

Question though: the ID of the Estes 3" tubing is around 74.4mm, the OD of BT20 is around 18.7mm, and the OD of the caps of the Estes 29mm retainers is around 43.5mm. Aren't you going to torch the retainer cap with those 18mm motors?

 

[SolarYellow]

My Great Goblin is now set up to cluster either 18mm or 13mm side boosters. (Or both!?)

View attachment 627248

I didn't have any BT-5 on hand, so I rolled my own 13mm motor mount tubes using the Apogee method. I just glued some scrap wood in the ends as thrust blocks.

If using 18mm side boosters, there is no room for the screw-on retainer, so the center motor would need to be a good friction fit. But I think a pair of A10s, almost doubling the initial thrust of the Estes E or F motors, would be good enough to get it off the rod with good speed.

The GG may not even need the extra boost, but the cluster would be cool anyway!

Since you have those open cavities in the back, just epoxy a chunk of threaded rod along one of the fin roots and use a flange nut to hold the central motor in. You can make it a nylock if that makes you feel better.

 

[mh9162013]

Do the A3 13mm engines have the same CATO risk as the A10s? If A3s are less likely to CATO, maybe the performance/boost decrease is worth the more reliable launch?

 

[lakeroadster]

Sure, I get using BP for clusters on certain rockets, like the Saturn V or tractor motors, etc.

But for the rockets in this thread, why not simply ditch the BP and pick a single composite motor with the thrust in excess of the other motors combined?

 

[sr205347d]

I use MJG black powder starters for my black powder clusters and trust them a lot further than I trust the stock Estes starters.

I ordered a bunch of those two days ago. Besides reliability, they would be more convenient to connect together with 12 inch leads.

 

[SDramstad]

Because a single motor doesnt look like this on liftoff.




Flash Daddy on 30 c6-5 motors lit with a flash pan.

 

[sr205347d]

Aren't you going to torch the retainer cap with those 18mm motors?

The retainer cap won’t fit with 18mm motors installed. I would need an alternate means to retain the center motor.

 

[sr205347d]

But for the rockets in this thread, why not simply ditch the BP and pick a single composite motor with the thrust in excess of the other motors combined?

Yes, of course I could do that, easily.

The challenge is flying MPR with cheap motors I can get locally at Hobby Lobby.

 

[bad_idea]

The retainer cap won’t fit with 18mm motors installed. I would need an alternate means to retain the center motor.

Ah, that makes sense. Nothing wrong with tape retention, either friction fit or external, or both.

 

[lakeroadster]

Yes, of course I could do that, easily.

The challenge is flying MPR with cheap motors I can get locally at Hobby Lobby.

Sure, local availability.​

Cheap, as in inexpensive, motors though... add the price together of the motors you are using... composites start to make sense.​

 

[sr205347d]

Do the A3 13mm engines have the same CATO risk as the A10s? If A3s are less likely to CATO, maybe the performance/boost decrease is worth the more reliable launch?

Don’t fly if you can’t tolerate the risk of a CATO!

Besides, Estes will replace the kit. An E12 blew up my first Star Orbiter, and I got another build project.

 

[sr205347d]

Sure, local availability.​

Cheap, as in inexpensive, motors though... add the price together of the motors you are using... composites start to make sense.​

One E12 -- six bucks; two A10s -- four bucks. That is $10 plus tax, at HL. One E20 from Wildman is $13, plus shipping. Sure, I can afford it, but where is the excitement, wondering if all three will ignite?

 

[sr205347d]

Do the A3 13mm engines have the same CATO risk as the A10s? If A3s are less likely to CATO, maybe the performance/boost decrease is worth the more reliable launch?

I am looking for the extra thrust the A10s provide to help get the rocket off the pad at a safe speed.

 

[Back_at_it]

WOW, I totally forgot about this. Many many years ago I came to the same solution with a clone build. I wasn't into composites yet but I had done some clustering so I had an idea.

I had built a clone of the Colossus with a 24mm mount. Flights on the D12 were not exciting and the E12 wasn't much better. My biggest concern was getting it off the pad. At time I was still using the 3/16 maxi rod so I didn't have a lot of length to get it up to speed. My solution was to drill two holes in the lower centering ring and glue two BT5 body tubes to the 24mm motor mount. Both tubes were plugged.

It worked perfectly without any issues. With the A10 and the main motor it had plenty of punch. Sadly I gave that rocket away when I left the hobby years ago. I feel like I might need to do another one.

 

[sr205347d]

Here are some videos of the maiden launch of the Great Goblin. Looks like good speed off the rod. I can see a drop in acceleration as the thrust of the A10s pass their peak.

 

[sr205347d]

Here is my scratch built Trident, on an E12-6 and two plugged C6-0s.

 

[sr205347d]

Star Orbiter

 

[sr205347d]

See this post about clustering three E12s in a Phantom 4000.

https://www.rocketryforum.com/threads/ncr-motor-retainer.184636/post-2564437

In this case, the rocket had one 28mm motor mount tube, so my options were limited. I couldn't put in a large enough composite motor.

 

[sr205347d]

See this post about clustering three E12s in a Phantom 4000.

https://www.rocketryforum.com/threads/ncr-motor-retainer.184636/post-2564437

In this case, the rocket had one 28mm motor mount tube, so my options were limited. I couldn't put in a large enough composite motor.

I just realized that an Estes F15 will fit in the 28 mm motor tube. So, if I clustered an F15 with two E12s, that would give it over 125 grams of propellant weight, making it high powered. (Requiring an FAA waiver and Level 1 certification.) Be careful out there.