Perseus II

[flying_silverad]

I am currently building a model from Launch pad called the Perseus II. They recommend a pair "D" motors for launch. I was wondering if I could get away with some Estes 24mm C motors for the first launch. Any thoughts?

 

Hello all,
I myself am a Launch Pad fan. I dont know that I would risk all that building time, effort, and $$$ to two or three 24mm motors.
I dont think that the C's motors will have the thrust for a safe lift off also. Rocketry Online has a good section with excellent emplanation on propulsion and wieght ratio's at:

https://www.info-central.org/index.cgi?propulsion
Check it out its very good.


James Pierson Manager
Rocketry Preservation Society
https://groups.msn.com/ROCKETRYPRESERVATIONSOCIETY/_whatsnew.msnw?pgmarket=en-us

 

[flying_silverad]

The engine mount is set up for 2 D12's. If I put in 2 C11's won't that give me enough for at least a test launch? I don't have a sim program yet but is there too much weight for this combo?

 

[airforce]

Airforce to Silverad...RPS might be correct with his under power estimation. Let me share this with you and then you can decide.
I have the Estes Executioner, it calls for the D engines also. I have a few launches with the D's with great success. I had some of the big C motors, hey what the heck, they look as big as the D's. I loaded her up with one and WOW, you talk about an exciting launch. The excitement came from everyone looking at this rather large rocket coming at us after only about a 50 foot launch. The ejection happened just in time to save it from a harder landing then it took. If you can find some big C's with a 2 second delay you might go ahead and give it a try. A more logical thought, buy the D's that it calls for, however, if your completed rocket is only, say, twice the weight of an executioner???!!! its your rocket.
Airforce to Silverad, over and out.

 

[trogdor]

I don't know how much this rocket weighs, but I just did a couple runs in wrasp (free sim at wrasp.com) and if it weighs in the 8-10oz range (I use lots of epoxy!) with 2 c11's and their quick burn you're looking at around 300 feet.... not too high but about what an optima (roughly same size and probably weighs a bit more) would do on one D12.. use the short 3 second delay and you should be ok although if one doesn't light I think you're in big trouble and not just for the stability factor. However, BP clusters shouldn't be a problem with a suitable launch controller. The C11's are kinda like D12s for the first half second or so and seem to kick it off the pad at very nearly the same speed as the D12s would. I'd suggest getting wrasp, weighing your model and seeing how comfortable you are with the educated guess it provides... FWIW, I would probably do it myself...

 

[trogdor]

Yikes... in regard to airforce's reply.... ya I'd guess ONE C11 WOULD be an eventful flight!

 

[flying_silverad]

I am going to stick with two D's for now. If a C11 only gives me around three hundred feet, it doesn't leave much for error (no wind). I would guess maybe 900' with the two D's. Not using a lot of epoxy here. Soaked the fins with CA...pretty hard. One thing I would like input on......DUAL PARACHUTES! The kit only supplies one 18". Would 2 18" or one 24" be better?

 

As far as C-11 verses D-12 look at the motor thrust curve chart that comes in the motor package. That important piece of paper we all throw away without thought. In particular look at the graph showing (thrust in newtons) and (time in seconds). The D-12 initial thrust phase has about 28 newtons of thrust in about 1.5 seconds. I have not seen a thrust chart for the C-11's to compare how fast the thrust is given ( for lift off speed).

As far as dual parachute I personally would go with the 24" chute on a windless day. On a day with some wind I would go with the 18" chute to help prevent wind drift out of the launch area. Dual parachutes tend to tangle and only work well in seperate deployment tubes( like the Estes Genini D.C.). However I have always wanted to try an experiment with dual chutes with one shock cord 12"-16" longer than the other which may or may not help to prevent tangling. Just another idea.

These links may help you out as well:
https://www.performancehobbies.com/timtrsz.htm

https://www.performancehobbies.com/timtrisp.htm



James Pierson Manager
Rocketry Preservation Society
https://groups.msn.com/ROCKETRYPRESERVATIONSOCIETY/_whatsnew.msnw?pgmarket=en-us

 

[Stymye]

the C-11 has nearly the same "initial" thrust but, the thrust duration is only 0.9 sec.(mini stump- puller)
I see people make the mistake with the E-9 thinking
just because its an E motor It will go twice as high as a D
but a few rockets that fly well on the D-12 are marginally safe
on the E-9 ( like my over-built Big Daddy)
has anyone tried the C-11 in a Maniac or mabey a Black Brant II?

stymye