How do I properly setup my staging timer

[mrgabb]

Hello All,
I am getting into staging and CPR at the same time. I am purchasing a PML Terrier Booster and Mini BBX CPR3K for my first project. A couple of questions have crossed my mind that I wanted to ask about.
1) I have seen altimeters that are barometric and some that are both barometric and use an accelerometer. Is this a form of redundancy in the firing circuit It occurs to me that if a rocket lays over in flight the air pressure will no longer change and could precipitate an early ejection. Is this the reson for the accel?
2) What are your recommendations for electronics as far as different brands and types.
3) I have a good idea how to setup the altimeter but how do I determine the proper staging delay without being to liberal and still having peak performance.
4) I tend to beef up my rockets to fly more powerful motors (hee hee) are there any concerns I should have about my choice for a 2 stage CPR project?

Any help you guys can give me is greatly appreciated.

 

[MaverickLV]

Hi,
I also got into CPR and staging recently with the finish of my PML Thunder N' Lightning kit, which looks great but hasn't flown yet. Based on my research, which seemed like an awful lot of research, I have answered your questions below. These are just my ideas and opinions based upon my research, don't just rely on them, other people may have more experience on the topic.

1. First, what do you mean "lay over in flight." Personally, I'd rather use an altimeter that just used barometric sensors for parachute deployment because accelerometers can be tricky to use and have been known to cause premature deployment due to vibrations, I've been told.

2. Because you are using CPR and the interstage system, your choices for your electronics are limited by size but some possibilities for the altimeter are obviously the Co-Pilot, by PML, Missile works RRC2, Transolve P3000, and two altimeters from perfectflite. I believe all these will work with probably a little bit of modification to the mounts of the altimeter or the battery location. I chose the co-pilot because it meant there would be no modifications. For the staging timer I am having some difficulties. PML will soon be releasing their Accu-Fire timer which is what I'll be purchasing but transolve and missile works also make staging timers that will probably work.

3. For the staging delay, you want to be safe. If your in doubt as to whether the delay is too long or not, then shorten it. Shorter is better. You would rather have a flight thats 100 feet shorter than a flight that has the rocket pointed downward when the 2nd stage lights. The best way to find safe, but perfomance inducing delays is to get Rocksim 5.0 and run simulations to find out. Even using the free version off their website is better than guessing.

4. Your choice for getting into CPR and staging is good. Personally I got the Thunder N' Lightning because it offers room to increase motor diameter to 54mm if I really wanted to and by itself it can fly on twin J350's making a high flying lvl 2 bird. I find the Terrier and Mini BBX to be a little small. The sustainer is limited to 29mm motors and the booster can only take up to a I284. However, for a person with a smaller budget and smaller flying fields it is a very good rocket.

By the way, how much did you pay for your rocket. If you bought direct from PML then you overpayed a little. For instance, the Thunder N' Lightning costs over $200 from PML but from Discount Hobby Center it only costs $150. They carry everything cheaper. I'm just sharing a little advice, but from DHC.

Dave

 

[mrgabb]

Thanks Dave,
This info you gave me is helpful. I have decided to settle on a basic barometric type of altimeter. What I meant by "laying over" is if the rocket doesn't have enough velocity to be stable as it leaves the launch rod it will "lay over" and fly sideways. Since it no longer will be gaining altitude the altimeter will deploy the drogue. However after more consideration, I would rather that happen and the rocket be destroyed than to cause somebody property or physical damage.
The thunder and Lightning was my first choice but I am very limited in places to launch. So I reluctantly settled for The Mini BBX CPR3K and Terrier Booster.
The timer I am considering is the Transolve ST2B available through Magnum. Any comments.
I am probably going to use Transolve P5 for the Sustainer.
I have not made a purchase yet, I am pretty anal about thoroughly analyzing every aspect of a project before I get into it. Thank you for the tip about Discount Hobby Center. I will definately take a look!
One of the things That I discovered in my research is that a staging timer gives you 2 channels to fire and set delays. The first channel fires the sustainer motor while the second fires the booster's recovery system (unless you use the motor delay charge for recovery.) The Terrier booster does not give me the option for electronic recovery so I would only need to set a delay for sustainer ignition. In this senario If I chose an H97-7 for the booster I am guessing that I would set the delay for 7-8 seconds so that the booster is not trying to fly off on it's own. Is this the correct way or is their a better way such as a "rule of Thumb" for setting sustainer delays.
I am using Rsim 5 that I purchased but hven't been able to use it to accurately predict optimum second stage delays. Any input?

 

[MaverickLV]

First of all, your correct in that the design of the terrier doesn't allow you to use electronic chute deployment. I'm not sure what your asking when you talk about setting the delay for 7-8 seconds but I think I have answered your question below.

1. First, say your using a H97 as your booster. Design the rocket on rocsim. Be very detailed in your design and be sure to get the weight right on and the CG the same place as it is on the completed rocket (you may have to add a mass object to add weight and/or change the CG).

2. Then run rocksim with the H97 in the booster but nothing in the sustainer. The delay that shows up as the best delay for this simulation is the delay that you should use for your booster motor. For instance (only an example) if the simulation from the H97 in the booster shows that the whole rocket as one, took 5 seconds to reach apogee after motor burnout, then you want to use a 5 second delay for the booster motor. The booster isn't as aerodynamic as the sustainer but it will still travel quite a bit.

3. Then, once you have your delay time, example 5 seconds, you can choose your delay between boster burnout and sustainer ignition. Now, you have to understand that it will take a second or two for the motor to ignite so you have to account that into your decision. 5 seconds isn't very long, so the rocket won't be traveling very fast. Subtract 1 to 2 seconds from that depending on the motor choice and how safe you want to be. If your using, blue thunder or redline, it lights up prettey quick so one second is probably enough. White lightning takes a little longer so maybe 1.5 seconds. Black jack takes even longer and less kick to it so 2 seconds or more is probably good. Lets say your using an H128 in the sustainer. 5-1.5=3.5 Now from 3.5 you have to subtract the time that the rocket was starting to arc over because most rockets don't travel straight up and go into tail slides, although some do. And besides, you want your rocket traveling at a good amount of speed so the fins can stabilize it. This has to be an estimated guess. Experience usually helps here, and rocsim (be sure to add about 5 mp/h of wind in the simulation). Personally, I think the rocket will probably be vertical for about 1.5 to 2 seconds. Here, to be safe (remember the rocket motor might take really long to come up to power, it does happen occasionally) I would use a delay of .5 seconds to 1 second.

I hope this answers your question, if not, then let me know.

Dave

 

[MaverickLV]

I forgot to mention something about your selection of your staging timer/altimeter!

The P5 is a good choice and its reasonably priced.
You could get the ST2B from magnum but PML is going to realease their new Accu-Fire timer is a couple of weeks, and if I were you I'd wait and at least check out the differences between the two and the prices.

Dave

 

[mrgabb]

Hi Dave,
You confirmed what I kind of figured. I have to say though that I completely messed up my senario with the H97. Rather than waitng longer than the delay time I meant to say wait about one second longer than the burn time so that the booster is not under thrust but the rockets velocity is conducive to stable flight. What I was concerned about was not waiting too long for sustainer ignition but also getting maximum performance out of both stages. I forgot about the slight delay in motor ignition though. If I set my timer to ignite the sustainer at booster motor burnout, there should be a slight delay between booster burnout and sustainer ignition. I might try that until I get the "feel" for setting it up. Also thanks for telling me how to setup Rsim for the booster optimum deployment delay. I am going to try that now.

Cya!!