Staging question

[hedgie6]

Is it possible to use 2 booster engines to a single sustainer? I am thinking about building a Titan II. I want to have it 2 stage with a 2 engine cluster for the booster to a single engine for the sustainer. It would need to be gap staged and if Estes re-releases the A10-0T I would like to use them as the boosters and another mini as the sustainer. If it is about 1:100 scale it should be about 8 inches for the gap between the stages. Does any of this sound possible?

Thanks
James

 

[Micromeister]

yes: its very possible.
Does require a little more prep work and original setup. Sometimes a directing funnel and exhaust port(s) are needed to direct the burn through gasses etc depending of the distance between boosters and upper stage.

 

[tbzep]

The 8" gap should be no problem, just make sure it's vented like Micro said or it will probably pop apart before the sustainer ignites. The real Titan II has open panels in the interstage so venting could easily be done there.

 

[hedgie6]

yes: its very possible.
Does require a little more prep work and original setup. Sometimes a directing funnel and exhaust port(s) are needed to direct the burn through gasses etc depending of the distance between boosters and upper stage.

Do you think it would be better to cant the first stage engines or use a funnel for directing the gasses?

 

[adrian]

I'd definitely use a funnel anyway. The nozzle of the upper stage motor is a pretty small target for the particles of burning fuel which shoot out of the booster motor when it burns through, and a funnel will make sure they hit that target.

Canting the motors has another benefit, though. If one of them doesn't light, the unbalanced thrust from the one which did could make the rocket turn and fly off to the side; I've seen this happen and it is not a pretty sight. If the motors are canted slightly to point them somewhere nearer the CG, the unbalanced thrust will have less of a turning effect.

 

[hedgie6]

Thanks for the tips. I was trying to build this in the demo version of RockSim but I'm running in to several problems. 1. Is it possible to do the canted engine mounts. 2. Where is a good place to download the motors and other Estes parts that are not in the database?

Thanks
James

 

[tbzep]

Unless you just want to cant the motors, it's not necessary to do so. It won't really give you any significant advantage in ignition of the upper stage as long as you keep the two motors together. The only significant advantage to canting them would be if one motor doesn't ignite. Check continuity of both igniters before you install them and use a 12v launch system. If you do this, and are careful when installing the igniters and twisting the leads together, you will get a very high reliability rate of ignition.

For the staging to a 13 mm motor, use a piece of BT-5 tube the length of the stage gap. It will keep the burning particles concentrated and on track to the nozzle of the sustainer. Don't forget to vent the BT-5 all the way to the outside of the airframe. If you only vent the BT-5 and the gases can't get completely out of the airframe, you may still have a problem with expanding gases popping the stages apart before the second stage has a chance to ignite. To vent the BT-5, you can cut some holes, or you can just leave a small gap between the tube and the upper stage motor. To get the gases all the way out of the airframe, you can punch holes in the centering rings all the way out the back end of the booster, or you can vent out the side at the interstage area scaled with retangular holes like the real Titan.

On a side note, I don't have much experience gap staging to a mini-motor. I've staged plenty with no gap and short gaps and have never had any problems. The A3-4T has a fairly small nozzle. The A10-3T has a larger nozzle. Generally you get more consistent staging with motors that have a larger nozzle opening. I don't know if the A10's cored profile will affect ignition reliability or not as I've never gap staged any significant distance with a cored motor for the sustainer. I wouldn't hesitate to stage to either motor with a short gap, but it wouldn't hurt to do a little research on gap staging reliability of mini motors before you put a lot of time into a scale model. I'm sure that there are several scale competitors that have gap staged mini motors at the 8" distance and would be able to help you. You could also consider an 18mm upper stage. The A8-5 has a nice large nozzle and would give you good reliability of ignition and plenty of delay time.

 

[luke strawwalker]

Do you think it would be better to cant the first stage engines or use a funnel for directing the gasses?

I'd go with the funnel... canting the motors will DEFINITELY cause problems if one or the other doesn't light. Also canting won't ensure the particles get up there in the upper nozzle where they need to be.

Without getting into the whole argument some folks tend to have as to whether the hot gases or the burning BP particles ignite the upperstage motor (or the intense heat coming off the particles) a funnel wouldn't be particularly hard to make and would be much more likely to ensure upper stage ignition--

What I'd do is using either a pair of balsa strips and a couple triangular shaped balsa pieces, is make a squared-off 'funnel' going from the upper ends of the motor tubes in the booster to a stuffer tube glued into the top end of the funnel. Or, you COULD just make the thing go up at a shallow angle to the nozzle of the upperstage motor-- have a little bit of clearance so it will slip over the upperstage motor nozzle end, and a couple vent ports on either side in the tips of the triangles to vent the gas so it doesn't blow the stage apart prematurely. Another way you could do it is make a 'cone' out of cereal box cardboard (easy to do) flatten it slightly so it goes over the booster motor tube top ends, and extends up to the upperstage motor nozzle end, and use a holepunch to put a couple vent holes 180 degrees apart on the upper end. I think I'd harden it with CA and maybe give it a good thick smear of yellow glue inside to help it resist the booster engine blow-throughs through...

The "cereal box funnel" would be the quickest and easiest to do, and the lightest... the balsa box funnel would probably be a little more durable, but heavier and harder to make. Good luck and post pics of whatever you do! OL JR

 

[hedgie6]

Here is my basic RockSim file for this. I did end up putting an 18mm mount in the 2nd stage. I couldn't figure out how to create a funnel in RockSim but it will be right above the booster motor mounts. I'm using lexan fins and trying to figure out a way to make them removable for display. I'm also considering paper engine bells for the booster. Please take a look and give me your :2:

Thanks
James

View attachment Titan 2.rkt

 

[luke strawwalker]

Here is my basic RockSim file for this. I did end up putting an 18mm mount in the 2nd stage. I couldn't figure out how to create a funnel in RockSim but it will be right above the booster motor mounts. I'm using lexan fins and trying to figure out a way to make them removable for display. I'm also considering paper engine bells for the booster. Please take a look and give me your :2:

Thanks
James

Looks pretty good... you can't do a funnel in rocksim... the only real way to 'account for it' is to do a "mass object" equal to it's weight and placement in the rocket, to get the weight distribution right.

What booster motors are you looking at for this??

I've made a rocket with lexan fins that basically just slides into the back of the rocket body, sorta like a removable motor mount. The fins are glued to it and the engine mount is inside it. Problem is, this sticks out the bottom of the rocket, which messes up the location of your 'motor mounts' and especially if you want to make them look like real engine bells (ALA Dr. Zooch) and have them mounted over the motor tubes.

One possibility is, you COULD make the 'bottom section' of the rocket removeable-- use a coupler and build TWO bottoms for the rocket of the proper length-- one just long enough to hold the two motor mounts and the Lexan fins, with the bottom end decorated up with the Titan II rocket nozzles and thrust structure tubes, and another bottom section strictly for display-- a coupler and piece of body tube with a simple cardboard disk in the bottom of it, with another set of nozzles and structure tubing glued to it, strictly for display-- no centering rings or motor tubes. Have the 'funnel' in the upper part of the lower stage, and friction fit the two together before launch. This is sort of what I'm thinking of doing with my Dr. Zooch Ares I since I don't want the "flame fins" stuck to the bottom of the rocket at all times... cut the tube above the fins/motor mount, use a coupler, and friction fit the main body tube to the coupler before launch, yet still be able to remove the motor mount and flame fin unit and display the model as it really would look.

It's a lot of work, but if you REALLY want a nice display model that flies, sans the lexan fins when she's sitting all pretty on the display shelf, it's about the only way I can think of on this rocket... At least your modelling skills would get a good workout! OL JR

PS... try to hide the 'seperation line' at the top edge of the roll pattern or something like that...

 

[hedgie6]

I had a couple of ideas for the fins. For the booster, one idea is to have slits in the tube that the 4 fins would slide in and notch into the centering rings. Another idea was 2 fins that notch as above and the other 2 would be a single piece of lexan that would slide through the entire booster (between the motor tubes) and extend out either side. Wonder if there is any way to do a lexan ring fin/display stand... For the upper stage I was just loking at the notch method.

For the booster motors I am hoping that Estes will rerelease the A10-0T, or I will by a few of the old production and retire it when I am out. The upper stage will be an A or 1/2A and I'm also thinking of how to build it to fly single or double stage.

I have no building supplies right now so everything is just in the idea stage.

Thanks for the ideas!