Clustering 3 BP and one Composite. Tips?

[ChrisLentz]

Hi everybody.

I have this build I am working on with 3 E12-0s and 1 F50-9. 158.4 Newtons of impulse. I don't have a L1 so under 160N it is.
I need to make sure that all the motors light simultaneously. I did buy a four motor whip.

What I know...
A. Its tricky.
B. Leave some slack and have a staked ignition cable.
C. Enough power to do the job. i.e. booster pack with 400A should do it.
D. Tape the ignitor wire to the motor so it doesn't get pulled out.

What I need clarification on...
A. Can I double up the ignitors to ensure lighting?
B. Should I add an extension to the composite motor ignitor for slack?
C. Any other experience/videos/help would be appreciated.

 

[Bat-mite]

Hi, Chris. There are some misunderstandings in your post about what qualifies as a high power rocket. According to NFPA 1127 and FAR 101.22:

• 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;
• Uses a motor with more than 80 Newtons average thrust (see rocket motor coding);
• Exceeds 125 grams of propellant;
• Uses a hybrid motor or a motor designed to emit sparks;
• Weighs more than 1,500 grams including motor(s); or
• Includes any airframe parts of ductile metal.

So, you are allowed up to 320 Newton-seconds of total impulse, since you are using multiple motors. You appear to be okay on bullets one, two, four and six. I don't know your rocket's loaded, final weight, so you would have to check it it weights less than 3.3 pounds on the pad.

However, bullet three has you in trouble. The propellant weight of those four motors comes out to 145 grams, which exceeds the 125. This is thus a high power rocket, requiring an FAA waiver.

Assuming you get a waiver, your next biggest problem is that composite motors take longer to ignite than BP. If you ignite them all at the same time, the BP motors will go first. Sounds like you are doing this on your own, and without a club, right? Do you have access to a second launch controller? If so, you could ignite the composite a second or so before the BP to try to get close to a simultaneous ignition.

 

[ThirstyBarbarian]

To keep under the propellant weight limit, maybe you could use D12-0 motors instead (I haven't actually looked up and added up the weights, but you could look into it).

I agree that there can be problems trying to light clusters of mixed types, because they light at different rates. I haven't built a rocket like this, but I have researched it a few times, and the feedback was that the best way to do it is to use electronics to airstart the outboards. You use a high-thrust motor in the central core that can get the rocket off the pad at a safe speed all by itself, and it looks like you have that in a F50. You light the central core using the launch controller, and hen the electronics detect the thrust of the launch and light the outboards when the rocket is already moving.

This is a more complicated setup, and that is the main reason I have never done it. But it solves a few problems. One problem is that if the outboards light, and the rocket leaves the pad without lighting the core, you have no deployment charge, and the rocket will lawn dart. The electronics ensure that the outboards won't light until the rocket is flying safely on the motor with the deployment charge.

Second problem is that if not all the outboards light on the pad, the rocket can take off at a weird angle, and you can get a cruise missile. The electronics make it so that the outboards won't light until the rocket is up to speed and moving downrange away from the pad. You have a better chance of getting them all to light, because the ignition circuit is flying along with the rocket, and you don't get leads pulled out at the pad if one lights a bit late. And even if one or two don't light, the rocket is already traveling quickly, so the fins are already stabilizing it, and it is less likely the rocket will go off at a really weird angle.

 

[Incongruent]

Use good igniters and preferably a 12v* launch system. For the BP motors, use quest Q2G2 igniters if you can find them (you might not be able to) or the older pyrogen covered Estes igniters. If you can't get the Q2G2s and don't have the older Estes ones, you can get the Estes ones from club members if you go to a club or in less commonly used motor packages at the hobby store. I was at my local Hobby Lobby a while ago and they had a few packs of C6-0s, all with older igniters. Not anymore. There are methods of making the igniters more reliable, but those involve dipping them into various compounds. Also be sure to prep well; hold (still gently though) the igniter so it touches the bottom of the hole while putting the plug in.

Composites need different igniters, and someone else will have to advise you on reliable and fast ones for that motor. Since they light slower, a little redundancy in the recovery system will come in handy if you can implement it, though unfortunately probably not. (at least not easily)

12V launch system: 12 volts will be able to provide more current to the igniters, which will light them off faster; however, the maximum current depends on the batteries used, so a 12v garage door opener battery will not fare as well as a 12v car battery, which is what most club launch systems use. You will find a lot of mixed opinions and advice here regarding what the bare minimum is, but the general consensus is, if you want it to light, to use a reasonably large 12v battery. (no connecting to the wall outlet... that's been done... just watch some YouTube videos on model rockets.)

EDIT: Sorry, I missed that part of your post somehow. Yea, that should do it, if the resistance isn't too high.

 

[qquake2k]

He did say he has a "booster pack with 400A", which I'm assuming is an automotive jump starter. In which case he has plenty of voltage and amperage, as long as the leads are thick enough.

 

[Incongruent]

Video on Quest Q2G2s
[YOUTUBE]4ZqpFCTS4P8[/YOUTUBE]

Here is a thread where someone wanted to do a similar launch, but they abandoned it for the difficulty in igniting composites and callous forum members reasons. I'm not saying to give up, but do understand that there are be timing issues that need to be overcome.

I think I read about ways to do it, but I can't recall right now or find the source. Sorry.

 

[Cabernut]

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View attachment 310835
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That does not look stable. Those fins are way too small for all the weight in the bottom end. You could go with 3xE12 and 1xE16, stay all BP, and be just under the 150g propellant limit. Increasing stability would be step 1. Larger fins, then go from there.

 

[The_Lone_Beagle]

Here's a video where the fellow faced a similar situation:

[video=youtube;UWEFZmvVPII]https://www.youtube.com/watch?v=UWEFZmvVPII[/video]

 

[BABAR]

That does not look stable. Those fins are way too small for all the weight in the bottom end. You could go with 3xE12 and 1xE16, stay all BP, and be just under the 150g propellant limit. Increasing stability would be step 1. Larger fins, then go from there.

Concur with above, not nearly enough fin area just on basic look, but wait wait waaaaaiiiiiiiiiit a minute.

What is the goal? You are not going to set any altitude records with this, so why do you neeeeeeeeed so much engine power?

If you are clustering for sake of clustering, that is cool and challenging and a lot of fun. I like clusters.
But unless that tubing is really heavy or you have one heck of a payload (your rocket looks like it was built for cool factor, and I like design even if I do suggest more finnage! But doesn't look like a payloader) weigh the thing and see if you can get by with all 4 black powder motors, like maybe even a D12 central and D12 or even C6 outboards. Yes you will need to put in adaptors, but from the look of your rocket I have no doubt you have skills to make them.

Mixing black powder and composites is probably do-able, but sort of looks like here complexity just for the sake of complexity, which runs counter to safety.

 

[ChrisLentz]

Hi, Chris. There are some misunderstandings in your post about what qualifies as a high power rocket. According to NFPA 1127 and FAR 101.22:

• 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;
• Uses a motor with more than 80 Newtons average thrust (see rocket motor coding);
• Exceeds 125 grams of propellant;
• Uses a hybrid motor or a motor designed to emit sparks;
• Weighs more than 1,500 grams including motor(s); or
• Includes any airframe parts of ductile metal.

So, you are allowed up to 320 Newton-seconds of total impulse, since you are using multiple motors. You appear to be okay on bullets one, two, four and six. I don't know your rocket's loaded, final weight, so you would have to check it it weights less than 3.3 pounds on the pad.

However, bullet three has you in trouble. The propellant weight of those four motors comes out to 145 grams, which exceeds the 125. This is thus a high power rocket, requiring an FAA waiver.

Assuming you get a waiver, your next biggest problem is that composite motors take longer to ignite than BP. If you ignite them all at the same time, the BP motors will go first. Sounds like you are doing this on your own, and without a club, right? Do you have access to a second launch controller? If so, you could ignite the composite a second or so before the BP to try to get close to a simultaneous ignition.

I am in Canada. According to Transport Canada...
High Power Rocket
: A launch vehicle:
(a) equipped with one or more
rocket engines/motors contributing to an installed total impulse greater than 160 newton seconds but less than or equal to 40,960 newton-seconds,
(b) that weighs more than 1.5 kg (3.3 pounds),
(c) equipped with a parachute or other device capable of retarding its descent, and
(d) whose primary uses are for purposes of education and/or recreation.

https://www.canadianrocketry.org/files/tc_hpr_reqs_jan00.pdf full pdf

That being said, it is under 3.3 pounds even with all the noseweight.. I am pretty sure I am good with all the requirements.

 

[ChrisLentz]

That does not look stable. Those fins are way too small for all the weight in the bottom end. You could go with 3xE12 and 1xE16, stay all BP, and be just under the 150g propellant limit. Increasing stability would be step 1. Larger fins, then go from there.

Rocksim claims it is stable. Of course I will redo everything again Rocksim wise to ensure safety. I think the outer pods act like fins so the little fins I added are adequate. According to Rocksim.

 

[ChrisLentz]

Concur with above, not nearly enough fin area just on basic look, but wait wait waaaaaiiiiiiiiiit a minute.

What is the goal? You are not going to set any altitude records with this, so why do you neeeeeeeeed so much engine power?

If you are clustering for sake of clustering, that is cool and challenging and a lot of fun. I like clusters.
But unless that tubing is really heavy or you have one heck of a payload (your rocket looks like it was built for cool factor, and I like design even if I do suggest more finnage! But doesn't look like a payloader) weigh the thing and see if you can get by with all 4 black powder motors, like maybe even a D12 central and D12 or even C6 outboards. Yes you will need to put in adaptors, but from the look of your rocket I have no doubt you have skills to make them.

Mixing black powder and composites is probably do-able, but sort of looks like here complexity just for the sake of complexity, which runs counter to safety.

The goal is the complexity of the ignition. The closeness to the threshold limit of 160 for Canada. In the smallest possible package. I plan on launching this on a frozen lake with massive recovery area and an ice shack for a bunker. Should be safe enough if they all light. And what a show for the video and stills.

 

[KennB]

Check out this site.
Boris flies lots of BP/APCP clusters and has had nearly 100% success rate of lighting all the motors "simultaneously".

 

[ChrisLentz]

Here's a video where the fellow faced a similar situation:

[video=youtube;UWEFZmvVPII]https://www.youtube.com/watch?v=UWEFZmvVPII[/video]

Awesome video, exactly along the lines I was looking. Thank you for the tip.