newbie

i jsut started builind rockets, i want to peice together my own rocket and double stage it, possibly with a dual d setup or a c booster then a d upper stage? any thoughts or advice, ps appolo 13 is my fav movie!!!

Welcome!

If you've just started, I'd suggest buying a relatively simple 2-stage rocket kit and see how it goes together and how staging woks. Then you can strike out on your own with a scratch build.

I second that. Staging is a bit tricky... I think starting with a proven design first, and getting flying experience, is the only way to go.

Or, you could download the instructions for an out of production 2 stage kit from Estes or Centuri and clone that - it's almost like scratch building without having to design the rocket first - a great intermediate step!

You can find plans at Ye Olde Rocket Shoppe:

https://www.rocketshoppe.com/

or Jimz:

https://www.dars.org/jimz/rp00.htm

Have fun!

lfried said:

i jsut started builind rockets, i want to peice together my own rocket and double stage it, possibly with a dual d setup or a c booster then a d upper stage? any thoughts or advice, ps appolo 13 is my fav movie!!!

Click to expand...

My first piece of advice if you're planning on designing your own rocket of any sort is to get VCP:

https://myweb.cableone.net/cjcrowell/VCPMAIN.htm

This free program is easy to use and calculates the rocket's centre of pressure (CP). Load the rocket up as if you were about to launch it and find where it balances; this is its centre of gravity (CG). The CG should generally be between one and two times the body diameter ahead of the CP for the rocket to be stable.

My second piece of advice is about staging. The first stage motor has to be more powerful as it has to lift a greater load, so that's where you want the D. The upper stage can be a C. But first, try building one with a C in each stage to get some experience.

oh ok right on, thanks. yeah i was thinking it would look cool to have it lift off slowly accelerating and then stage to a higher output engine like the D to accelerate faster. it would just kind of look like a missle being launched out of a submarine, then ignites and picks up speed? any thoughts or am i asking for weather-cocking and ill be dodging a killer D?

Weathercocking: Not likely, but sometimes things happen... Think about this: You should be able to fly the upper stage of any 2-stage rocket by itself (as a single stage, just like regular rockets). The only way it would be problematic is if something bad happened during the staging process (bad/no stage separation, late/delayed/no ignition of the sustainer, etc.), and at that point you're not really in control of it anyway, right?

To answer the original question, it's relatively rare to stage from a smaller to a larger engine because you need the additional power of the first stage engine to initially lift the whole stack. The sustainer (get used to that term - it's the upper stage) has a good running start and doesn't have to push as much mass as the booster (another term - it's the first or bottom-most stage, the one you light).

A D12-0 booster motor has 20Nsec of total impulse and a max lift weight of 14 ounces. In comparison, the C6-0 has only 10Nsec of total impulse and only 4 ounces of max lift weight. So you really want the D to start the whole thing moving. (Those two motors, BTW, are the only booster motors currently in production for low-power rockets. Quest has only a C6-0; Estes makes both the C6-0 and D12-0.)

DaveCombs said:

A D12-0 booster motor has 20Nsec of total impulse and a max lift weight of 14 ounces. In comparison, the C6-0 has only 10Nsec of total impulse and only 4 ounces of max lift weight.

Click to expand...

The Estes C6-0 is reported to have only 9 Newton-seconds:
https://www.nar.org/SandT/pdf/Estes/C6.pdf
The Estes D12-0 was tested and found to have only 17:
https://www.nar.org/SandT/pdf/Estes/D12.pdf

This gives you even **less** lifting power if you use a C in the booster.

The advice already given above (to try some existing designs first, and work your way toward a new design after you collect some experience) is good advice. And slow lift-offs are kind of dangerous in their own way; it is much better to leave the end of the launch rod with a substantial velocity so the fins will be effective. You can use the TRF search tool to find gobs of info on these subjects already posted.

For slow lift-offs:
https://www.fliskits.com/products/rocketkits/kit_detail/praetor.htm

Here's how you two-stage it:
https://www.fliskits.com/products/rocketkits/kit_detail/praetor-2.htm

powderburner said:

The Estes C6-0 is reported to have only 9 Newton-seconds:
https://www.nar.org/SandT/pdf/Estes/C6.pdf
The Estes D12-0 was tested and found to have only 17:
https://www.nar.org/SandT/pdf/Estes/D12.pdf

Click to expand...

Completely fair; I was quoting the Estes catalog. But your point is absolutely spot-on.

i bought a new rocket, d single engine, ill dual it and post results!!!

If you want the slow liftoff and fast boost after seperation, I got a rocket that does exactly that. It's a build of the OOP Astron Avenger. The last flight was a C6-0 to C6-7. The liftoff was slow and it staged at about 250 ft. Once the booster lit, it screamed! I was surprised at how much faster the upper stage flew.

One thing about the Avenger, it is a low wind or long launch rod rocket. The large booster fins and slow liftoff speed can make it weathercock pretty bad if the wind is up a little and you don't use at least a 4 foot rod.

I think you will find that any 2 stage that has a slow liftoff and screaming second stage will probably do the same thing.

Good luck

lfried said:

i bought a new rocket, d single engine, ill dual it and post results!!!

Click to expand...

I would suggest you post your ideas for mods here and gather some valuable advice Build threads are a great way to get good suggestions. What sort of rocket did you purchase if you dont mind my asking
Cheers
Fred

DaveCombs said:

(Those two motors, BTW, are the only booster motors currently in production for low-power rockets. Quest has only a C6-0; Estes makes both the C6-0 and D12-0.)

Click to expand...

I beg to differ. Quest makes a B6-0. Here it is:

Quest B6-0

Estes also makes a B6-0. The only catch is you have to buy it in a bulk pack with 12 B6-0's and 12 B6-6's. Here it is:


Estes B6-0/B6-6 Engine Educator Pack

Booster motor selection, upper stage motor selection, launch rod length, rocket weight, rocket drag, wind speed...yes, these are all important in determining how a rocket will perform.

lfried,
have you done any dabbling with fin size and rocket stability? You can get the Barrowman equations online for free. Here is one site that presents the eqns in an easy-to-follow form:
https://my.execpc.com/~culp/rockets/Barrowman.html
and there are lots of places with extra help explaining stability, like
https://www.apogeerockets.com/Education/rocket_stability.asp
and there are sites with info on improving the Barrowman eqns
https://www.argoshpr.ch/PDF/sentinel39-galejs.pdf

But let me just say that the basic eqns are enough to get you started. If you have your own questions on how to use them, PM me or throw a post up here.

There are other ways to check for stability too, like the old-fashioned (and probably slightly conservative) cardboard cut-out technique. You can do a search on the old TRF posts for an explanation of that one.

Your rocket needs to be stable as a two-stage design, and after dropping the booster, as a one-stage design. If you make it too stable (in either configuration) it will tend to be affected more by cross-winds, resulting in the dreaded weathercocking. You can avoid (or at least reduce) this by keeping your stability margins lower.

Good luck with your designs! (Be sure to come back and tell us how they worked!)

STRMan said:

I beg to differ. Quest makes a B6-0. Here it is:

Quest B6-0

Click to expand...

I stand corrected. But that motor isn't in either of their current catalogs. And I absolutely haven't seen any of them in any hobby shop I've been to.

Judo said:

For slow lift-offs:
https://www.fliskits.com/products/rocketkits/kit_detail/praetor.htm

Here's how you two-stage it:
https://www.fliskits.com/products/rocketkits/kit_detail/praetor-2.htm

Click to expand...

And a beautiful combination it is too

DaveCombs said:

I stand corrected. But that motor isn't in either of their current catalogs. And I absolutely haven't seen any of them in any hobby shop I've been to.

Click to expand...

I haven't either. I have 2 local hobby shops. Even though they both sell Quest igniters and rockets, neither sells Quest engines. One is not interested, and the other is looking into getting them in. Also, while both stores sell the Estes Blast Off Flight Pack, neither sells the educator packs with the booster motors.

One of my hobby shops doesn't have any booster engines at all. The other one regularly has C6-0's and D12-0's in stock.

Luckily, there are many places you can pick these items up at online. In fact, I just bought a 3 pack of Estes B6-0 boosters. Even though they are not sold this way any more, there are places that still have them in stock.

DaveCombs said:

I stand corrected. But that motor isn't in either of their current catalogs. And I absolutely haven't seen any of them in any hobby shop I've been to.

Click to expand...

Quest doesn't make B6-0's anymore... they don't make ANY engines anymore. After their plant burned, they started buying engines from a German manufacturer, who apparently does not make boosters.

Reportedly, Quest will soon sell Chinese-made motors in a variety of unusual sizes. I hope they continue to sell the German motors as well.

lfried said:

i bought a new rocket, d single engine, ill dual it and post results!!!

Click to expand...

Which rocket did you buy?

The kit is probably stable if built according to the instructions, but if you add a booster onto the back, this will move the CG back and may make it unstable. You'll need to put fins on the booster. Use VCP to check the CP and make sure the rocket it stable fully loaded with the booster attached.

You probably thought all this advice was free. It's not - the price is pictures of the rocket.

Do get a bit of experience with single-stage rockets before moving up. An over-powered rocket is all very well but you may never see it again.
This little rocket, for example (thanks Adrian for the photograph) flew vey high on an A motor but it went so fast I never saw it under boost. I even painted it orange but it didn't help. I eventually lost it on Guy Fawke's Night.

Another way to stage is CHAD staging. CHAD stands for CHeap And Dirty.

A good rocket for this is a Estes Maniac, if you can still find one. Use a motor mount reducer to put a 18mm motor in the Maniac. The motor needs to hang out the back, oh, 3/8ths of an inch or so. Not the motor tube, the motor. A C6-7 is good for this, I used up the last of my B14-7 on this. Worked great. Now, take a D12-0 booster motor and twist it onto the smaller motor, it fits tight and rather well. Tape a short piece of crepe' paper(12" or so) to the D12 wrapping it around the motor so that it lies flat. Add a small piece of tape to the upper part so that when the upper motor ignites it blows the booster off and the the streamer unfurls and it comes in under recovery. Thus meeting the rule of recovery.

Pretty easy way of staging, actually

Oh, do not let the motor sit flat on the blast plate, an effect called Bernolli will lock it in place. Use a standoff or angled plate to prevent this.

lfried said:

oh ok right on, thanks. yeah i was thinking it would look cool to have it lift off slowly accelerating and then stage to a higher output engine like the D to accelerate faster. it would just kind of look like a missle being launched out of a submarine, then ignites and picks up speed? any thoughts or am i asking for weather-cocking and ill be dodging a killer D?

Click to expand...

Hehehe... yeah, like THIS?? https://www.rocketryforum.com/showthread.php?t=44262

And it was D12-0 to D12-7...

Hope your luck is better than mine OL JR