How Low Would You Go?

[n3tjm]

I'm looking at the specs to the the Adept Rocketry Adept22 Altimeter, and notice all the choices for main deployment. You got a choice of 300ft, 600ft, 900ft, 1200ft, 1800ft. I know that larger rockets, with larger recovery systems, require more room. I like the main deployment to be as low as safely possible. Just curious what altitude you guys use (or would use) for a 50lb rocket? If you don't have a Adept22, pick one that most closely matches the altitude you would use.

 

[gdiscenza]

I have the Adept22, and while I've yet to get a good DD flight out of it, the principle for selecting the altitude for main deployment remains:

Calculate the descent velocity of your rocket under drogue (or drogueless if you go that route), determine the maximum deployment time of your main chute, then add half that time or more to actually slow the rocket prior to touchdown. For example, if your rocket falls at 100fps, and your main chute takes 2.5 seconds to fully deploy, you do not want your main to come out at 300 feet, 600 feet would be the minimum safe deployment altitude, and depending on the winds, I might even consider 900 feet in order to reduce the stress on the rocket owner.

Having never built a 50lb rocket, I cannot tell you what altitude to use, but I'd be willing to be that if you are trying to minimize drift, 300 feet is out, and 600 feet would probably be marginal.

Good luck!

G.D.

 

[Yoehahn]

I would say 900... I use 700-800 in my 25lb EC4 and that isn't too bad... Talk to Rick Comshaw tho, he sometimes pops his main chute at 100' :y: thats how he wins first down in drag races...

 

[atxcple]

i set my main on Freedoms Price (65 LBS loaded, 48 LBS after motor burn) for 800ft with a backup at 700. this is still enough time to get the nose cone off, extend 30 ft of shock cord, and open the chute on a rocket that is already extended 30ft on the apogee shock cord. so thats a 12 ft rocket with 60 total feet of shock cord and a chute.

 

[n3tjm]

I have the Adept22, and while I've yet to get a good DD flight out of it, the principle for selecting the altitude for main deployment remains:

Calculate the descent velocity of your rocket under drogue (or drogueless if you go that route), determine the maximum deployment time of your main chute, then add half that time or more to actually slow the rocket prior to touchdown. For example, if your rocket falls at 100fps, and your main chute takes 2.5 seconds to fully deploy, you do not want your main to come out at 300 feet, 600 feet would be the minimum safe deployment altitude, and depending on the winds, I might even consider 900 feet in order to reduce the stress on the rocket owner.

Having never built a 50lb rocket, I cannot tell you what altitude to use, but I'd be willing to be that if you are trying to minimize drift, 300 feet is out, and 600 feet would probably be marginal.

Good luck!

G.D.

Good tips there. I know 300 is not going be enough. Any idea to determine how long it takes a chute to deploy? I'm going use a military surplus 15 footer that I never flown before so I don't have any "experience" to make a judgement call. Will most likely stick to 900 but would still be cool to show the math why I picked 900 in the L3 paperwork

 

[gdiscenza]

Good tips there. I know 300 is not going be enough. Any idea to determine how long it takes a chute to deploy? I'm going use a military surplus 15 footer that I never flown before so I don't have any "experience" to make a judgement call. Will most likely stick to 900 but would still be cool to show the math why I picked 900 in the L3 paperwork

Ground testing will show you how far the main chute and shock cord will deploy at the instant of ejection, and you want the deployment to not be instantaneous, so using a mil-surp chute you would probably have a bag of some sort that it came in. Stuff the chute and shroud lines into that bag, attach a 18" pilot chute to the top of the bag (which should be attached to the shock cord between the chute attachment and the NC) then tie it to a 10lb weight and chuck the whole thing (chute, bag, weight, and pilot chute - not the rocket itself) off of the roof of your house. Have a helper time the descent, and see whether the chute is fully open before the weight goes bang. I did this for my L1, and got some pretty accurate deployment times for my little 30" military flare cute, which deployed at apogee in about 2 seconds on average.

G.D.

 

[atxcple]

I can tell you from experience with the 15ft round military chute you will need extra room for it to sort out and fully inflate. 900 ft is marginal 1000 ft is just okay. i have had one not deploy fully at 1000 ft becouse not enough air was moving into it at 67fps. really have to calcutate your drouge speed and make super sure all your shoud lines are straight no twists or tangles

 

[n3tjm]

Good advice. I usually go drogue-less. I'm thinking the 1200 would be best then. The chute did not come with the bag, so I am planning to use a large nomex bag.

 

[G_T]

I flew Sprite at Red Glare with main at 600ft. Descent was around 100fps on drogue. Main deployment - tether, dbag - took about 1.5 seconds. Main begins slowing rocket at 450ft. By 250-300ft it is floating in. There is not much margin for problems there. I'm increasing it to 700ft next time, to add a second. The rocket weighed approximately 60#.

I use a relatively small main - an IRIS Ultra. A bigger main may well take an extra half second to open.

Gerald

 

[troj]

There are numerous factors that affect the time required for a recovery system to begin to do its thing.

How the parachute is packed will have a huge impact on inflation time. The length of the recovery harness will also play into it -- the longer it is, the more time you need to provide.

For a 50lb rocket, I doubt I'd go under 1,000 feet. Why? Because if there's a problem that causes the canopy to take a bit of time to "shake itself out," I'd rather give it the time to do so.

Better I have to walk farther than have someone (or something) at risk, because the rocket came in ballistic.

-Kevin

 

[Rocketjunkie]

I use 700 feet for the 15 foot surplus chute. Otherwise, it depends on the size of the rocket and chute, 300 feet for most rockets 4" and smaller. If the chute is over 5', I'll up the deployment altitude to 500 feet.

 

[JDcluster]

Older Adept devices use to be 250fta with no other options.
One of Earl Cagles BALLS videos had a rocket hit the playa just as the main fully opened.

JD

 

[Salvage-1]

I voted 600 as the bare minimum, but 900 would be better. A small flat square pilot chute with only 4 suspension lines may be useful to pull the main out and away from the body FAST.

 

[Tetrahedron]

Older Adept devices use to be 250fta with no other options.
One of Earl Cagles BALLS videos had a rocket hit the playa just as the main fully opened.

JD

Yes, my ALTS2 (2002 version) and even the ALTS2 (90s versions) have 250ft but it seems more like 100ft when then main comes out.:y:

 

[5x7]

Good advice. I usually go drogue-less. I'm thinking the 1200 would be best then. The chute did not come with the bag, so I am planning to use a large nomex bag.

I agree (I fly 40, 50 and 130 pounders)

 

[Eat, sleep, and Fly]

I would definetley go to 1200, If you are investing time and money into a project, you want it to have as good a chance as possible of recovering safely, so whay not give the chute some extra time to inflate.
Just my:2:

 

[atxcple]

Good advice. I usually go drogue-less. I'm thinking the 1200 would be best then. The chute did not come with the bag, so I am planning to use a large nomex bag.

the data i told you was drougless believe it or not.

 

[JDcluster]

On the opposite side of the spectrum; I used my 90's era Adept ALTS25 for my L3 rocket twice and seems to like deploying at 1,600 ft ( set at 1,200 ft) according to recorded data from another altimeter.


JD

 

[JDcluster]

My Intimidator 5.0" was set to deploy at 1,000 ft. and 950 ft. as backup; The free bag never pulled free until it was below the tree tops.
I was starting to cringe as I didn't think it was going to open in time.
The data showed that it was falling around 85 feet per second.
It weighed 41 lbs. on a 2 grain 98 mm.

JD

I'm looking at the specs to the the Adept Rocketry Adept22 Altimeter, and notice all the choices for main deployment. You got a choice of 300ft, 600ft, 900ft, 1200ft, 1800ft. I know that larger rockets, with larger recovery systems, require more room. I like the main deployment to be as low as safely possible. Just curious what altitude you guys use (or would use) for a 50lb rocket? If you don't have a Adept22, pick one that most closely matches the altitude you would use.