- This topic has 15 replies, 8 voices, and was last updated 15 years, 7 months ago by
edward.
edward.-
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greywolves
Hi everyone,
Seeing how i’m a curious guy, what size chute and what maker of chute have some of you used for the Little Dog DD kit. Rocket is not built yet, instructions say around 3lbs, sure i wont be much different, but for Now planning lets just say around 3.5lbs. Looking at all the different charts for each manufacture, i could use form a 32″ to a 44″ based on weight. Looks like i will have 10″ of packing space in a 54mm airframe.
What size drogue do you like? no drogue at all?
Thanks rockteers
Chad
Given that it is DD, you should plan slow it down plenty with the main, shoot for 15-20 fpm AT 5000′ altitude. RockSim will compute this for you, and you can figure it out using online descent rate calculators. If you can’t get it to automatically compute for altitude, then for 5000′ add 10% descent rate.
I prefer the hemispherical or eliptical chutes. Spherachutes are about the best value out there. I like my fruity chute too, but it was pricey. You should use a drag coefficient of 1.45 for the high end chutes, but only 0.75 for the flat chutes, using the stated skirt diameters. If you are short on space in your airframe, definitely go with a better hemispherical type chute. Wait till you finish the build and weigh in before you buy the chute. I’m guessing you can get by with a 32″ chute.
In a 54mm airframe with 10″ length, a 36″ fruity chute is VERY tight.
I haven’t had the best luck with drougues, so I’m not the guy to ask. I’d seriously consider a streamer though. 50-80 fps descent under drougue/streamer should be fine.
John A. Wilke
I use a 30″ CrossFire chute from Top Flight Recovery for most of my 54mm flights http://topflightrecoveryllc.homestead.com/page1.html Gary is one of the most reputable guys in the biz. I have used his stuff almost exclusively and I’ve never damaged my 54mm rockets.
The 30″ CrossFire is $24.95. You will have it in about 3 days and it will last forever. Also note that Jon Skuba of http://www.coolrocketstuff.com is a dealer and he flies with us.
I have several CrossFire chutes and would lend you my 30″ if you want to try it sometime. As noted above – it is a bit tight in 54mm but it WILL come out and it WILL bring you back safe and sound.
Tim Thomas
8) The Little Dog should be a very tough rocket. I would think that any chute from 24″ to 36″ would do fine. But I like Johns’ idea about the 30″ crossfire. A really sweet chute for 25.00. And a 30″ can be used in many different rockets.There is nothing better than having quality vendors in our club! 😆
Chad
One plug for Spherachutes- they are local out of Greeley. Like many vendors, they will do custom work for modest price. 30.57″ spherachute (equivalent to a 48″ flat) costs $39. These have vent holes at the top, so they seem to resist swaying.
Steve Jensen
I’m stuffing a Cessaroni 6 XGL motor (J-600) into my LDDD. I am also putting a DC-30 into a mini-payload bay below the NC with the antenna extending into the NC.
My build out weight with the DC-30, main chute deployment piston, and the large motor is approaching 5 pounds descent weight. I ordered a 48 inch Spherachute and think I can stuff it in there. I will keep you posted.
I wanted a DC-30 as it will approach 10,000 feet and I do not want to lose my little doggie!
Spherachute.com people were great. Ordered with custom colors and they shipped it out in less than 2 days. Pretty darn quick.
I’m a few months off, but hope to send it up at Mile High Mayhem.
edward
semi-ellipsoidal are very efficient but I think the packing depends a lot on the material. I have a 60″ rocket rage clone that holds 15 pounds at 15 fps. I can pack it into 8″ of 2.5″ airframe very comfortably. You’d have to go to between an 96″ spherachute to get the same descent rate.
Edward
Chad
A 96″ Spherachute measures 61″ across at the skirt, so they are about the same size. I’d agree that the ellipsoidal ones have about 0.1 cd better drag, and look cooler, but they seem to be a bit more expensive too.
It’s not just the canopy material that determines packing size, but the shroud lines too. Seems like a lot of shroud lines are overly conservative. Sometimes it seems like my parachute roll is 50% string.
It took me a while to decode parachute sizes and get the correct results in RockSim. Flat chutes are measured across the material- side to side (not corner to corner), and end up having a smaller skirt diameter when inflated during descent (about 65% of flat size). If you use the flat diameter in RockSim, you should put in a Cd of 0.70, or 1.65 if you use the inflated skirt diameter.
Similar goes for hemispherical or elliptical. The 96″ spherachute is the material semi-circumference of the canopy, measured along the material, while the inflated skirt diameter is 61″ (divided by Pie, times two). So if you use the flat/circumference measure, your drag coefficient should be about 0.60, if you use the skirt diameter, your drag coefficient should be about 1.50. For an elliptical design, I use a Cd of 0.70 for the material (bit less material then a hemispherical for a given skirt diameter) or 1.60 for the skirt diameter.
For quarter spheres or conics, I use a Cd based on skirt diameter of 1.3, but I haven’t verified these descent rates with a timer yet.
edward
The rocket rage clones I use I have a calculated Cd of 1.9, but I generally use 1.8 to be conservative.
Edward
John A. Wilke
I wanted a DC-30 as it will approach 10,000 feet and I do not want to lose my little doggie!
But if you DO lose it, I know someone who will sell you another 😀
I’m kidding, of course! I hope and know you will recover nicely. If the chute you chose is tighter than you like, please give my 30″ CrossFire a ride.
The “up” part is easy. Getting them back can be a challenge!
JW
greywolves
Chad
John A. Wilke
Tim Thomas
Steve Jensen
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