Scratching my two-stage itch

[Dotini]

Yesterday I launched my two stage rocket - but only after testing it first in single stage mode. The first test was with a B6-4, the 2nd with a B6-0 and 1/2A3-2T.


Note spin tabs on the fin tips.

My next plan is to make a new model, even lighter so that I can launch on an A8-0. And I will make a much nicer-looking booster, too.

 

[Fattbank64]

I like the paint scheme.

Airbrush or rattle can?

 

[Dotini]

I like the paint scheme.

Airbrush or rattle can?

Upper stage is Rustoleum 2X, fluorescent yellow, fluorescent orange, and Spa blue. It still needs finishing - the front launch lug was a late add-on.That poor little booster isn't even painted, just dolled up with Sharpies and tape. I'll do better next time.

 

[BABAR]

I hope to launch some two LONG GAP stage HSR rockets at NARAM this weekend. I think HSR will be a perfect recovery scheme for long gap boosters.

 

[Dotini]

I hope to launch some two LONG GAP stage HSR rockets at NARAM this weekend. I think HSR will be a perfect recovery scheme for long gap boosters.

Yes, and their long length should also make them suitable for CHAD boosting, don't you think?

 

[Hobie1dog]

I only own 1 staged rocket that was given to me, and have never launched it yet.

 

[Dotini]

I only own 1 staged rocket that was given to me, and have never launched it yet.

In the distant past I've launched, recovered and launched again a 4 stage model rocket. But I got lucky. Since then, I've come to appreciate the major increase in both performance and risk, especially at the small parks I prefer. So my latest new model focuses on very low power and low altitude. Below is the new part that should enable me to drop down to an A8-0 boost motor.


This transition from the fin can section to the payload section will enable me to switch more than half the model from BT-55 tube to BT-20 tube, with a significant savings in weight.

Note 1/4" diameter drilled passage to transmit the ejection charge through to the payload section.

 

[Joekeyo]

Two of my favorites are two stage rockets. I load them up and have them ready for almost every launch. I have a long thin scratch built that flies high on a C6-0/A8-5 combo. The other is a Super Chief II. It use pass port gap staging. Stages D12-0/B6-4. The JLCR helps prevent real long walks on this one.

Usually I find the booster within 50' of the launch pad. If I dont find it on the initial sustainer recovery walk, someone finds them and brings it to the LCO

Credit: Mark Kirschner

 

[BABAR]

Sure would be nice if Estes would put out a C5-0!

 

[BABAR]

In the distant past I've launched, recovered and launched again a 4 stage model rocket. But I got lucky. Since then, I've come to appreciate the major increase in both performance and risk, especially at the small parks I prefer. So my latest new model focuses on very low power and low altitude. Below is the new part that should enable me to drop down to an A8-0 boost motor.


This transition from the fin can section to the payload section will enable me to switch more than half the model from BT-55 tube to BT-20 tube, with a significant savings in weight.
View attachment 594595
Note 1/4" diameter drilled passage to transmit the ejection charge through to the payload section.

You are probably all over this, but just in case, keep track that the max recommended lift off weight for A8-0 is 85 grams. Add to that the fact that you need a lot more fin surface total for a two stage rocket, AND the fact that you REALLY don’t want to push the limits with a draggy two stage bird. Unless you build reeeeeaaallly light, I would hesitate to go under a B. YMMV.

 

[Dotini]

You are probably all over this, but just in case, keep track that the max recommended lift off weight for A8-0 is 85 grams. Add to that the fact that you need a lot more fin surface total for a two stage rocket, AND the fact that you REALLY don’t want to push the limits with a draggy two stage bird. Unless you build reeeeeaaallly light, I would hesitate to go under a B. YMMV.

I'm partially motivated by a substantial inventory of A8-0 motors left over from a previous era of my rocketry. And I'd like to find the smallest park that I can reliably launch and recover my two-stage model.

Below is the new unfinished airframe that nets me a full 2/3 of an ounce.

 

[jqavins]

You are probably all over this, but just in case, keep track that the max recommended lift off weight for A8-0 is 85 grams. Add to that the fact that you need a lot more fin surface total for a two stage rocket, AND the fact that you REALLY don’t want to push the limits with a draggy two stage bird. Unless you build reeeeeaaallly light, I would hesitate to go under a B. YMMV.

I'm partially motivated by a substantial inventory of A8-0 motors left over from a previous era of my rocketry. And I'd like to find the smallest park that I can reliably launch and recover my two-stage model.

Below is the new unfinished airframe that nets me a full 2/3 of an ounce.

View attachment 594779

What's your weight with the reducer and BT-20 fin can? Are there any other weight saving opportunities? As BABAR said, you're probably all over this, yet it does look concerning. My guess is that the A8-0 must be meant for really tiny rockets, and this is, well, not really tiny.

Here's a thrust curve overlay of the A8 and the B6. The B6's greater total impulse (almost twice) is bad for you goal of low altitude, we get that. But the greater thrust and impulse in the first 0.2 seconds would make the rod exit speed a lot more comfortable.


OK, enough of that. Where do you plan to put the aft launch lug?

 

[Dotini]

What's your weight with the reducer and BT-20 fin can? Are there any other weight saving opportunities? As BABAR said, you're probably all over this, yet it does look concerning. My guess is that the A8-0 must be meant for really tiny rockets, and this is, well, not really tiny.

Here's a thrust curve overlay of the A8 and the B6. The B6's greater total impulse (almost twice) is bad for you goal of low altitude, we get that. But the greater thrust and impulse in the first 0.2 seconds would make the rod exit speed a lot more comfortable.
View attachment 595644

OK, enough of that. Where do you plan to put the aft launch lug?

You guys are probably right that I need to make a smaller model. And I will, no doubt! The current model is 1.29 oz less motor, payload and booster. I do run a 42" launch rod, one piece cold rolled steel, well polished. With 3/16"lugs, it's a loose running fit.


The fat and heavy payload section is BT-55, and it doesn't really need to be any bigger than BT-50 to carry my thin mil 10" X-form parachute (or streamer) and optional altimeter. I'll get there one way or another.

Thanks for your input!

 

[jqavins]

Yeah, weight without engine is especially inapplicable for the booster engine, since it has to lift the sustainer including that engine. At 37 g (1.29 oz) without motor, plus 16 for an A8, you'd be at 53 grams, well within the 85 g max liftoff weight, if running single stage. But then add another 16 g for the booster engine and you're at 69 g plus the booster structure... Hmm, maybe it's OK after all. It'd leave you 16 g for the booster structure to come in right on the line (if you use no payload). Hmm. Dicey, says my mind sim, but if the wind is very light...

Of course, if you get out to a bigger field it'd be fun to let that bad boy go on a C6-0 to C6-something; just make sure that your parachute or streamer is brightly colored.

Oh, and it's looking good. Questions of weight and staging aside, I like that rocket!

 

[BABAR]

Yeah, weight without engine is especially inapplicable for the booster engine, since it has to lift the sustainer including that engine. At 37 g (1.29 oz) without motor, plus 16 for an A8, you'd be at 53 grams, well within the 85 g max liftoff weight, if running single stage. But then add another 16 g for the booster engine and you're at 69 g plus the booster structure... Hmm, maybe it's OK after all. It'd leave you 16 g for the booster structure to come in right on the line (if you use no payload). Hmm. Dicey, says my mind sim, but if the wind is very light...

Of course, if you get out to a bigger field it'd be fun to let that bad boy go on a C6-0 to C6-something; just make sure that your parachute or streamer is brightly colored.

Oh, and it's looking good. Questions of weight and staging aside, I like that rocket!

An option to reduce weight on sustainer is to down size to a 13 mm motor.



First, especially with small fields, but also because I like seeing the whole flight , I always start with a very low impulse motor in the sustainer at least for first flight.

I haven’t built for A8-0, interestingly they don’t even include it in the motor chart.

The 13 mm motors weigh half what the 18 mm motors do. If you are starting minimum diameter BT-20 for the A8-0, you will either need to add the weight of a BT-5 motor mount or an 18-13 mm motor adapter, but can shave a few grams off sustainer, which given you are limited to 85 grams MAX, even 5 grams helps for both stability and getting good velocity off the rod.

 

[Dotini]

An option to reduce weight on sustainer is to down size to a 13 mm motor.



First, especially with small fields, but also because I like seeing the whole flight , I always start with a very low impulse motor in the sustainer at least for first flight.

I haven’t built for A8-0, interestingly they don’t even include it in the motor chart.

The 13 mm motors weigh half what the 18 mm motors do. If you are starting minimum diameter BT-20 for the A8-0, you will either need to add the weight of a BT-5 motor mount or an 18-13 mm motor adapter, but can shave a few grams off sustainer, which given you are limited to 85 grams MAX, even 5 grams helps for both stability and getting good velocity off the rod.

Regarding 13mm motors, I have some possibly false impressions they are more likely to Cato than 18mm motors, the nozzles are smaller and may be less likely to ignite from a booster motor, and the ejection charge is weaker and may be less able to eject the nosecone and chute on a slightly larger model. Am I misinformed?

 

[GlenP]

I have been able to get 4 13mm motors to ignite from a single gap-staged 18mm booster, this is a kit bash variation of the Seattle Rocket Works MIRV Gryphon. I replaced their 13mm cluster booster with a single 18mm booster.



sorry for the poor video quality, you can't really see the sustainers land on the far side of the field by the tree line. Booster landed not too far from the pad.

 

[BABAR]

Regarding 13mm motors, I have some possibly false impressions they are more likely to Cato than 18mm motors, the nozzles are smaller and may be less likely to ignite from a booster motor, and the ejection charge is weaker and may be less able to eject the nosecone and chute on a slightly larger model. Am I misinformed?

I personally haven’t had a rocket CATO (knock wood), although I was present at a spectacular series of A10-0 CATOs while visiting @ronzrocket.

I gap stage up to 53”. With appropriate vent placement (just aft of nozzle of sustainer) I have only had 3 failures, two were at 72”, and one was at NARAM where I put the sustainer motor in backwards .

Since it is the radiant heat from the flame of booster burn through and not particles, nozzle size isn’t critical.

 

[jqavins]

View attachment 595678

I thought I understood the max lift weight, but this looks really weird. It's supposed to take into account not only rod exit speed, but also sufficient altitude for safe recovery deployment. In upper stage motors, rod exit speed is not a factor, but safe altitude is. With both some initial altitude and a good initial speed from a booster, a given engine should be able to handle greater weight as a sustainer than as a booster, right? But the ½A3 is shown with a 2.0 oz max lift weight in a single stage, and only 1.0 oz as a sustainer. What gives?

 

[BABAR]

? But the ½A3 is shown with a 2.0 oz max lift weight in a single stage, and only 1.0 oz as a sustainer. What gives?

I think you are comparing the
1/2A3-2T to the 1/2A3-4T. (Edited)

The longer delay suggests the rocket may hit apogee and pass it and start down the dreaded “St Louis Arch” before deployment. All the upper stage motors have more conservative (lower) Max Lift Off weights than their shorter delay corresponding first letter/number counterparts.

you make an interesting point, however, as when used as a SUSTAINER motor, the purple motors at ignition do not need to waste/expend energy to overcome inertia, the rocket is already up to speed (or at least it better be!). I would think this would more than make up for the longer delay. What does Open Rocket say?

I suspect the chart’s Max Lift Off weights for the “purple” upper stage motors are calculated presumed the motor is actually used as a SINGLE stage motor. Which kind of makes sense, as the term “Max Lift Off weight” implies “Lift Off” from a standing start. So these would be altitude seekers for very light single stage rockets, justifying the long delays.

 

[86mustang408w]

Thats awesome man, I've got that itch too!!

 

[jqavins]

I think you are comparing the
1/2A3-2T to the A4-4T.

I don't think so. Look again (I just did). Items 1503 and 1504.

 

[BABAR]

I don't think so. Look again (I just did). Items 1503 and 1504.

My bad. Typo.

As I read it

1/2A3-2T Max Lift Off Weight 2 oz.

1/2A3-4T Max Lift Off Weight 1 oz.

Confirmed on website

1/2A3-2T​

https://estesrockets.com/products/1-2a3-2t-engines?_pos=1&_sid=2fe61e46f&_ss=r

• Max Lift Weight

2.0 oz (57 g)

1/2A3-4T​

https://estesrockets.com/products/1-2a3-4t-engines?_pos=2&_sid=c020c04c1&_ss=r
The Estes 1/2A3-2T engine is single stage engine designed for model rocket flight. This engine is a mini engine designed for flights in lightweight rockets.

• Max Lift Weight

1.0 oz (28 g)

“The Estes 1/2A3-4T engine is single stage engine designed for model rocket flight. This engine is a mini engine designed for flights in lightweight rockets”

Did I get it right and does my conjecture make sense?

Interesting that this is a”purple labeled” motor but the description doesn’t mention staging, although on the motor page above the two stage CheckMate (a rocket @BEC really likes) recommends.

Just based on listed weights for rocket and motors for the two stage CheckMate, the pad weight (WITH A10-0T and 1/2A3-4T motors) at a minimum come in at 1.57 oz. So I think the motor chart “Maximum Lift Off” weights apply for single stage OR booster usage (both of which are true”Lift Offs” from motionless to stable flight after 3 feet of rod. So they have to overcome a lot of inertia.). For SUSTAINERS, IMO you can downsize as much as you want, so long as you have an appropriate delay.

 

[jqavins]

What you're saying, if I'm following it correctly, makes sense for real application, but doesn't seem to match up with the chart. What I think you're saying is that a ½A3 employed as a sustainer engine should be able to handle more weight than one employed as a single stage engine, because it doesn't have to handled the initial rapid acceleration. Perhaps I've misunderstood you. And what I think you're you're saying is the same what I believe to make sense, but is the opposite of what the table says. Which is weird.

 

[BEC]

Just for reference, my Checkmates come in at just over an ounce for the stack sans motors. I add a small amount of weight in the process of turning the top 1.5 inches into a payload section (a coupler and a fiber bulkhead). I can‘t give a more precise value at the moment as my current Checkmate is well down in my traveling model box and I don’t want to dig it out. (I’m currently in Santa Fe at my Dad’s house — we start home Monday).

The Beta is a little lighter and is becoming a new favorite, even though I have to clone it. It pushes 1000 feet flown A to A and goes as high A to 1/2A as the Checkmate does A to A.

Also….there’s something funky in that usage chart especially with respect to the recently added A3-2T and A3-6T though I guess we were been flying lots of A3-6Ts single stage in the recently concluded NARAM.

 

[BABAR]

. And what I think you're you're saying is the same what I believe to make sense, but is the opposite of what the table says. Which is weird.

I think the table NUMBERS assume single stage for calculating Max Lift Off weight.