Clustering Q-Jets

[Antares JS]

I have a Boyce Gemini-Titan that I'm planning to fly on a pair of D16's per the manufacturer's recommendation. While I have plenty of experience at this point clustering BP, I've never clustered composite before. Would quickdip on the stock igniters help? I use it a lot on my BP motors. I've also heard that D16's have a tendency to chuff, which makes me really nervous. I don't know where Black Max falls on the easy/hard to start scale.

Are there any tips out there from someone who has clustered Q-jets before?

 

[jnmiller]

I clustered 6 D16's and an E, all composite, in a Clusterduck last year at MDRA. There was no chuffing on any of the motors and they all lit. The D10's were notorius for chuffing. They've been discontinued. I haven't heard of a problem with the D16's.

 

[Antares JS]

I clustered 6 D16's and an E, all composite, in a Clusterduck last year at MDRA. There was no chuffing on any of the motors and they all lit. The D10's were notorius for chuffing. They've been discontinued. I haven't heard of a problem with the D16's.

Maybe it was D10's I was thinking of...

When lighting that cluster, did you use the stock igniters and/or did you augment them in any way?

Also, *MDRA fistbump* I hope we can fly again soon with Maryland starting to open up.

 

[neil_w]

I haven't clustered Q-Jets yet myself yet, but what I think I know is:
1) The Black Max is an easy-to-light propellant, and the stock igniters are fin as-is.
2) There have been other reports on TRF of folks successfully clustering them. I can't find any links quickly though.
3) I do recall hearing that the Q-Jets do sometimes like to chuff once before lighting, but I have *not* heard of it causing problems with clusters.
4) My own Q-jet launches (admittedly not a large number) have all ignited on the first try, and I haven't noticed any significant delay due to chuffing.

 

[mbeels]

4) My own Q-jet launches (admittedly not a large number) have all ignited on the first try, and I haven't noticed any significant delay due to chuffing.

Same experience here, very little time from hitting the button to lift-off with the Q-jets. I think that the D16s should be the easiest of the lineup to ignite, because there is no empty space or large internal voids like the smaller Q-jets (A3, etc....).

Maybe it was D10's I was thinking of...

I've only launched one D10, but it took a surprisingly loooong time to come up to pressure and get the rocket off the pad.

 

[Antares JS]

I think that the D16s should be the easiest of the lineup to ignite, because there is no empty space or large internal voids like the smaller Q-jets (A3, etc....).

Side question, just out of curiosity, does anyone have any idea how the propellant grains of the different Q-Jets are shaped? Are the smaller ones shorter but still placed at the forward end, or are the core bores bigger?

 

[jnmiller]

Maybe it was D10's I was thinking of...

When lighting that cluster, did you use the stock igniters and/or did you augment them in any way?

Also, *MDRA fistbump* I hope we can fly again soon with Maryland starting to open up.

I used stock igniters with no augmentation.

Here's the video. The up part was good, the down part not so much (forgot to attach the parachute quick link!).

 

[mbeels]

Side question, just out of curiosity, does anyone have any idea how the propellant grains of the different Q-Jets are shaped? Are the smaller ones shorter but still placed at the forward end, or are the core bores bigger?

That's a good question, I'd like to know as well. Actually, I assumed that the smaller motors had empty space inside, but maybe it is filled with something.

 

[Nytrunner]

All same c-slot cores. The grain is shorter for the lower impulse classes. Grain towards front of motor. (and annoying to fish the igniter into for A and B motors without bending or crushing the tip)

(Hobbyline loads have the shorter grains towards the aft, but you put a piece of tape over the slit as an igniter stop when building them. Not an option for Q-jets, so they put the grain forward)

 

[BEC]

Side question, just out of curiosity, does anyone have any idea how the propellant grains of the different Q-Jets are shaped? Are the smaller ones shorter but still placed at the forward end, or are the core bores bigger?

Yes, that's it exactly - they are shorter and at the forward end...which requires a bit of care installing "initiators" in the As an Bs, in particular.

I am one who has reported a single "chuff" with C12s and D16s. It is a very short interval—a fraction of a second—between the "chuff" and the subsequent quick liftoff. To me it seems to happen maybe 1/3rd of the time.

Adding pyrogen won't help. As noted above, Fast Jack is really easy to light, and will even light with just bare nichrome—no pyrogen at all—as sometimes is seen on the supplied initiators (which are kind of fragile). I flew a C12-6 lit with a bare wire initiator on Sunday....and it didn't "chuff".

 

[boatgeek]

Yes, that's it exactly - they are shorter and at the forward end...which requires a bit of care installing "initiators" in the As an Bs, in particular.

I am one who has reported a single "chuff" with C12s and D16s. It is a very short interval—a fraction of a second—between the "chuff" and the subsequent quick liftoff. To me it seems to happen maybe 1/3rd of the time.

Adding pyrogen won't help. As noted above, Fast Jack is really easy to light, and will even light with just bare nichrome—no pyrogen at all—as sometimes is seen on the supplied initiators (which are kind of fragile). I flew a C12-6 lit with a bare wire initiator on Sunday....and it didn't "chuff".

Have you clustered Q-Jets? If so, what battery did you use? I tried a cluster that was a bit too big for the 2s LiPo I had, so it didn't light. I'm not easily finding an all-fire current on the interwebs.

 

[Rocket86]

Just to play Devil's Advocate, I had only one of three clustered D16's light with the stock initiators. There were a few chuffs before it limped off the pad. I tried it again with the old school drop of Duco and dip in BP done to the initiators and it screamed off the pad. I plan on doing that regularly.

 

[Antares JS]

Just to play Devil's Advocate, I had only one of three clustered D16's light with the stock initiators. There were a few chuffs before it limped off the pad. I tried it again with the old school drop of Duco and dip in BP done to the initiators and it screamed off the pad. I plan on doing that regularly.

What is Duco? I have never heard of it.

 

[dhbarr]

A type of "cement" that's mostly acetone and cellulose nitrate

 

[Rocket86]

Correct, Duco Cement. It's a general purpose glue that works pretty well, and is very flammable even when cured due to the nitro-cellulose base.

 

[BEC]

Have you clustered Q-Jets? If so, what battery did you use? I tried a cluster that was a bit too big for the 2s LiPo I had, so it didn't light. I'm not easily finding an all-fire current on the interwebs.

No, I haven’t. Since the little Estes Astron II launch controller (the little orange 9V battery one) will fire them, the all-fire current can’t be to terribly high, but you’re right, I’ve not seen the number either.

Just to play Devil's Advocate, I had only one of three clustered D16's light with the stock initiators. There were a few chuffs before it limped off the pad. I tried it again with the old school drop of Duco and dip in BP done to the initiators and it screamed off the pad. I plan on doing that regularly.

Sorry to hear about that, John. But I can see where a cellulose glue/BP dip would certainly encourage one to light even more quickly. So maybe the suggestion above to use QuickDip might be a thing to do for clustering them after all....as long as one can get the igniter in the motor after dipping.

As I say I have seen a number of cases where a C12 or a D16 would chuff once then quickly take off. I think I’ve probably had ~2 outright failures of a Q-Jet to light in, by now, probably close to 100 flights.

 

[5x7]

All same c-slot cores. The grain is shorter for the lower impulse classes. Grain towards front of motor. (and annoying to fish the igniter into for A and B motors without bending or crushing the tip)

The Qjet diagram and the C and D progressive trust curves indicate single grain core burner configuration, not a c slot like the hobbyline reloads.

 

[Rocketjunkie]

I've flown my standard size Deuce on Quest B4-4's. I used the starters that came with the motors. They were a tight fit through the nozzle and I did break one starter. The club launch controller uses a sealed lead acid bettery at the pad and has plenty of current capability.

 

[NateB]

I haven't built it yet, but I have a Trivecta 318 kit that I intend to fly on a cluster of 3 C and D Q-Jets. The Cobra system I use as a controller has 14.8v internal and can take a 24v external power source too. It should be able to fire the cluster with ease.

 

[Nytrunner]

The Qjet diagram and the C and D progressive trust curves indicate single grain core burner configuration, not a c slot like the hobbyline reloads.

Dunno for sure. The igniters were real fiddly to get in there, just like a c-slot. Bet the AT folks over on their thread could clear the matter up

 

[Initiator001]

The A3 and B4 Q-Jets are C-slot grains.

The C12 and D16 motors are core burners.

 

[Nytrunner]

Guess I'm wrong. Hiw small are those cores? The igniters are still finicky to get in there

 

[5x7]

The A3 and B4 Q-Jets are C-slot grains.

The C12 and D16 motors are core burners.

Thanks, that's great info. I didn't want to say anything about the A and B because the Curves were so different. Now that you IDed the C slot, they fit typical cslot curves pretty well.