A Super-roc PD

[PunkRocketScience]

I had a thought for trying to deploy a bigger chute for superroc. Has anyone tried splitting the body tube length-wise so that at deploy the tube opens into two parts, allowing for a higher chance of a really big chute making it out of a bt-5 tube? Would the split tube have sufficient strength to survive the boost?

 

[George Gassaway]

RocketmanTM wrote:
>>>>
I had a thought for trying to deploy a bigger chute for superroc. Has anyone tried splitting the body tube length-wise so that at deploy the tube opens into two parts, allowing for a higher chance of a really big chute making it out of a bt-5 tube? Would the split tube have sufficient strength to survive the boost?
<<<<

The old CMR “Breakaway” PD kit from the early 1970’s. Sorta nice in theory, not so great in practice. A round body tube is relatively stiff because it is a tube. Cut it into two long halves and it is weak. Try to stuff a chute inside that produced any significant amount of pushing against the tube wall, and the tube halves bulge out, with gaps in the joints.

So, it’s better to just learn how to pack a chute that can go into a long length of tube, and eject out. For PD chutes in long skinny tubes, I like to “spike” a chute, then fold in half once, so its folded length is 25% of its diameter (so an 18” chute would be 9” when spiked, then 4.5” when folded in half). Then compress the chute together to make it fit inside the tube. Using a good bit of wadding to help make sure the chute got pushed out by the ejection charge, and didn't' get burned or melted.

Note the above didn't even matter regarding superroc, it was about parachute duration models in general. Doing a “Breakaway” type approach with a superroc would be even worse, as superrocs are generally weak overall and do not need much to be “off” to help them buckle on boost, or bend and fly off on a curved flight path.

- George Gassaway

 

[urbanek]

I had good success with a muli-break Super-roc once. I had a tiny Adept timer that fired two charges. The motor ejection deployed one chute out of the bottome section. The timer was in a coupler between two body tube sections, so it deployed one chute out of each section.

Adept doesn't make the timer I used anymore, but I think there are even smaller timers on the market now, so this is very doable. It's just more complex and in contest flying, complex is a disadvantage. I'm not sure if the advantage compensates for the disadvantage.

At the time, I was new to electronics. I accidentally pulled the pull pin on the pad, so it deployed and damaged the rocket. The fixes I made added more weight, but I still got a very good time.

Unfortunately, the nose cone came off (again, I was new). The weight was negligible, but it was a SEP and a DQ. I didn't have two more e-matches, so I didn't make another flight. The one flight I did do would have been a new record.

The easiest way to improve your super-roc times is to use a bigger launch pad. I've had good success using 13mm tubing for launch lugs and flying off a 6' long stainless steel 1/2" rod. Straight boost helps heaps.

urbanek

 

[PunkRocketScience]

Thanks for the advice George. Got any recommendations on how big a chute to try to get into a BT-5?

Urbanek, again thanks...but the body tube I'm going to be using will only be 13mm at the largest...13mm lugs might be overkill...

 

[George Gassaway]

Todd Mullin wrote:

>>>>>
Thanks for the advice George. Got any recommendations on how big a chute to try to get into a BT-5?
<<<<<

18” can be done reliably if you use 1/4 mil dropcloth plastic. 20” is possible but sort of pushing it. If you can’t get 1/4 mil dropcloth,, then the chute would need to be smaller. There is 1/4 mil mylar of course, but I personally never liked it for a PD material as I could not get it to deploy as reliably as 1/4 mil dropcloth (but it works for others).

Like I said, “spike” the chute, then fold in half once. That’s it. Compress the chute to make it fit inside the BT-5. Twisting the whole thing helps with the compression to get it into the tube. Load in the shroud lines afterwards, do not wrap them around the chute as you might for packing chutes for regular models. Use sufficient talcum powder to keep the chute from sticking.

BTW, while I don’t have anything on Superroc or PD there, you might want to check out the tips I put together for NARAM-46’s events. Sometime in the next few months I’ll update it for NARAM-47’s events.

https://members.aol.com/GCGassaway/event_tips_1.html

- George Gassaway

 

[Zack Lau]

Thanks George for the great info.

Has anyone tried the obvious solution of using a piston that splits in half? The parachute is held inside a piston that fits inside the body tube--the doubled wall of the body tube/piston should be pretty rigid--especially with the parachute stuffed inside.

During flight, the piston should stiffen the body tube, improving the chances of a straight flight. At ejection, the piston will help move the chute(s) out of the body tube. Tangling might be a problem--but maybe not, as you do need a return under present rules. At our small fields--less than perfect flights can be quite useful for winning an event. Two bad flights can beat two flights that flew away.