Oddball parachute sizes

[Bill S]

I've got a scratchbuilt rocket I launched for the first time yesterday. It weighs 5.25 oz empty, and I put a 24" thin-mil parachute from Top Flight on it. Because I wanted to get the rocket back, I only launched it on the smallest motor feasible (C11-3), and it only went about 250 feet. Winds were less than 5mph, but on a 24" parachute, it drifted quite a ways, nearly ending up in a pond.

Rocksim says this rocket on a 24" parachute should descend at 11.9 fps. I played around with different parachute diameters, with an 22" descending at about 12.9fps, an 20" descending at about 14.2fps, and an 18" at about 15.8fps.

I was under the impression that a spill hole would do more to minimize wind drift vs a smaller parachute, but being as the parachutes I have are thin-mil nylon, I don't see a good way to put in a spill hole and not have the hole edges get all raggedy, etc.

A complicating factor is that the rocket uses 4 small fins made out of 1/16" lexan, that are expoxied on, so I don't want them to get broken as they'd be a serious hassle to repair.

Does anyone have thoughts on what I could do to minimize wind drift in this situation, so I can break out larger motors on this rocket. I'd like to at least be able to use a D12-5 and have the rocket fly to 600 feet or so, max.

 

[pnobile]

Bill

I sent you a PM.

Preston

I've got a scratchbuilt rocket I launched for the first time yesterday. It weighs 5.25 oz empty, and I put a 24" thin-mil parachute from Top Flight on it. Because I wanted to get the rocket back, I only launched it on the smallest motor feasible (C11-3), and it only went about 250 feet. Winds were less than 5mph, but on a 24" parachute, it drifted quite a ways, nearly ending up in a pond.

Rocksim says this rocket on a 24" parachute should descend at 11.9 fps. I played around with different parachute diameters, with an 22" descending at about 12.9fps, an 20" descending at about 14.2fps, and an 18" at about 15.8fps.

I was under the impression that a spill hole would do more to minimize wind drift vs a smaller parachute, but being as the parachutes I have are thin-mil nylon, I don't see a good way to put in a spill hole and not have the hole edges get all raggedy, etc.

A complicating factor is that the rocket uses 4 small fins made out of 1/16" lexan, that are expoxied on, so I don't want them to get broken as they'd be a serious hassle to repair.

Does anyone have thoughts on what I could do to minimize wind drift in this situation, so I can break out larger motors on this rocket. I'd like to at least be able to use a D12-5 and have the rocket fly to 600 feet or so, max.

 

[neil_w]

For what it's worth: 24" is a *very* large parachute for a ~5 oz rocket. I'd use 18" or maybe even 15" if I think the rocket is not vulnerable to landing impact damage (disclaimer: I normally land on soft grass). I understand you want to protect those fins but that's gonna drift no matter what you do.

Spill holes do not reduce drift so much as they increase stability of the descent. I put them in all my plastic parachutes, but don't have the nerve to mess with my nylon chutes.

 

[Bill S]

Neil,
I've generally had good luck with 18" parachutes, except for my Estes Interceptor. That thing seems to break fins frequently, though at least half the time its due to the parachute lines getting caught up on the wing pods or the fin tip spikes.

Most of the areas I fly in have grassy areas to land in; yesterday was an exception in that while the area was grassy, it was cut short and due to lack of rain, it was crinkly and the ground was hard. I even had something drive itself through a rocket fin, and out the other side - not sure if it was a thick dry grass stem or what, as someone "helped" me by picking up my rocket and bringing it to me since he was nearby. I then couldn't fly it the rest of the session because it would need to be disinfected, and hand sanitizer (alcohol) isn't good to use on rocket paintjobs.

I'm talking to Preston about what would be a good option for this rocket.