dual deploy question

So I understand . Take my mega Hi flyer and cut down the body then cut a 2" vent band make up a 9" coupler . Put the vent band back on the half way mark of the coupler . That would be my av bay and make the two bulk heads for the coupler and attach my charge cans and eye bolt top and bottom . Slid av bay in and the the tube I cut . Put shear pins in coupler for the nose cone . But with the J357 I only hit 1900ft with a J600 it would be 3600 ft . So go droguless and main at 1000ft ? Am I thinking this right . I would like to do duel at thunder struck

drogueless - yes please. I'm sure the debate will start behind this post, but I don't do drogues on rockets less then 6 inches.

The altitude you blow the mains depends on what you want to do and how big is your chute is. (does it have enough time to inflate?) After it inflates, any extra altitude is just longer walks.
I've been doing it a while and put them out pretty low. Not sure how many people fly lower as mine usually freak out the lco.
2.1 inch rockest, 200 feet (wildman recon drogue)
4 inch 400 feet (Wildman recon 60 inch chute)
6 inch+ 800 feet (B2 cert 3 XL chute)

Thanks , so I got the set up correct except the droge

I don't have too much experience with it, but I've always done drougueless with the main at 300'. First couple of times were at the sod farm here in Lafayette so ground was soft. Also done that at ash grove with frozen ground with no problems. Madcow SuperDX3 weighing about 4 lbs with a 36" parachute.

Rivet the payload to the coupler. Shear pin the nose.

Better to blow out than pull out.

I've flown DD for 7 year now. I never fly drogue-less any more. I've seen too many drogue-less flight with bad flight profiles. Most recover ok, but a few were very bad, like a 40 lb L3 fin can falling ballistic after the shock cord snapped like a thread.

Most add a lot of shock cord when flying drogue-less to prevent the two halve from contacting each other on the way down. Sooner or later, maybe on the 15th flight, the upper section is directly below the fin can when the main deploys. The main opens, stops, as the upper section falls to the end of it's shock cord. Then if the fin can hasn't landed on the main, it continues falling for a distance equal to both shock cords before it hits the end of its cord with tremendous force and shock. Most rockets are over built and can survive this if the fin can doesn't weigh too much, but when you hear of eye bolts opened and bad zippers, this is usually when it occurs. In larger rockets, this is where the recovery fails and the heavy fin can comes in ballistic.

When you had oversized ejection charges, "blow it up or blow it out", you add to the stress on the recovery systems.

A drogue can prevent all of this because it stabilizes the upper section above the fin can. A shorter shock cord can be used and when the main opens, it is above any potential fouling by the fin can. None of the parts are falling for long distances before reaching the end of the recovery harnesses so there is significantly less shock on the system.

I'm inexperienced with DD, so I'm not trying to step on any toes: correct me if I'm wrong. But when it comes to the standard methods for recovery, they are so overbuilt anyway, are they not? When you consider that he's asking about a Level 2 capable rocket, we're looking at weights in the neighborhood of what? Maybe 5 - 20 lbs?

A quarter inch eye bolt has a safe working load of about 100 lbs, which is FAR less than the actual failure strength. I use those and standard 550 paracord. The paracord has a safe working load of 150 lbs, but again the break strength is far greater at 550 lbs. Going drougueless and popping the main out at 300' is not going to come close to placing those kind of stresses on the recovery attachment points or the cord itself.

I agree that for much heavier rockets (your example of 40+ lbs) that may not be the safest or gentlest way to do it. But I don't think that on a rocket like we're talking about, with drogueless recovery and massive charges, we'll ever come close to destroying the recovery system. Zippers can happen, sure, but with a fiberglass rocket that is unlikely. Then again, this is all my opinion and I tend to try and think of a more minimalist approach.

Thanks everyone for the infomation .

jmight: stay away from the evil eyebolt, unless it is either forged (as one piece) or welded shut. The cold rolled ones eventually open. You'd be surprised at the dynamic load you put on it. You can also use the U bolt.

I'm still flying small to medium rockets drogueless. I find that fin cans are heavy enough to fall below the payload section. Occasionally they rotate, but that rotation prevents the main from fowling. I've yet to see the failure handeman describes, but I will stipulate that anything is possible (including having a drogue fowl the main. To drogue or not to drogue, that is the question that rocketeers will debate forever.
I generally size my shock cords to be able to pull the rocket out of a tree if the chute is in the top. the hickory trees at MARS surprised me ;>

A 300 ft. main might be good for smaller, lighter rockets.
Larger and heavier rockets require more air time to safely deploy the recover system.
I've seen rockets bounce on the ground just as the chute fully opens.

On 3-4"diameter rockets ( depending on weight) I pop the main at 500 to 800ft.
Rockets will free fall between 50 to 85 fps, sometimes even faster.
That's as long as you have an apogee event occur.


JD

jmight said:

I don't have too much experience with it, but I've always done drougueless with the main at 300'. First couple of times were at the sod farm here in Lafayette so ground was soft. Also done that at ash grove with frozen ground with no problems. Madcow SuperDX3 weighing about 4 lbs with a 36" parachute.

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cbrarick said:

jmight: stay away from the evil eyebolt, unless it is either forged (as one piece) or welded shut. The cold rolled ones eventually open. You'd be surprised at the dynamic load you put on it. You can also use the U bolt.

I'm still flying small to medium rockets drogueless. I find that fin cans are heavy enough to fall below the payload section. Occasionally they rotate, but that rotation prevents the main from fowling. I've yet to see the failure handeman describes, but I will stipulate that anything is possible (including having a drogue fowl the main. To drogue or not to drogue, that is the question that rocketeers will debate forever.
I generally size my shock cords to be able to pull the rocket out of a tree if the chute is in the top. the hickory trees at MARS surprised me ;>

Click to expand...

To be fair, weight has nothing to do with descent rate, it's drag/density related (old Hammer vs. feather on the moon experiment). I'm new to DD as well, but it stands to reason that the fin can will have much higher drag than the nose, and will therefore tend to be above the nose for the descent?
Wondering also if you could quantify "small to medium" for us newbies? I have a Frenzy on my bench that I plan to use for L2, and then will fly DD. Published kit weight is 76oz. I'm planning on fiberglassing it for practice and strength, and estimate that the final weight will be ~96oz. To hit a descent rate of 75-80fps, my sim shows a drogue of 1 foot. This seems reasonable to me, and also pretty close to "drogue-less", or am I being a fool? Even though it's falling fast, the added drag should further keep the av bay north of the fin can.

Lastly, aside from cost perhaps, is there a reason drogue-less is something to fly?

I use a streamer at apogee (homemade 15 foot nylon streamer) for visibility, and then I deploy my main chute at 800 feet.

jmight said:

I'm inexperienced with DD, so I'm not trying to step on any toes: correct me if I'm wrong. But when it comes to the standard methods for recovery, they are so overbuilt anyway, are they not? When you consider that he's asking about a Level 2 capable rocket, we're looking at weights in the neighborhood of what? Maybe 5 - 20 lbs?

A quarter inch eye bolt has a safe working load of about 100 lbs, which is FAR less than the actual failure strength. I use those and standard 550 paracord. The paracord has a safe working load of 150 lbs, but again the break strength is far greater at 550 lbs. Going drougueless and popping the main out at 300' is not going to come close to placing those kind of stresses on the recovery attachment points or the cord itself.

I agree that for much heavier rockets (your example of 40+ lbs) that may not be the safest or gentlest way to do it. But I don't think that on a rocket like we're talking about, with drogueless recovery and massive charges, we'll ever come close to destroying the recovery system. Zippers can happen, sure, but with a fiberglass rocket that is unlikely. Then again, this is all my opinion and I tend to try and think of a more minimalist approach.

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What breaks the recovery components is the jerk, or dynamic load, not a static load.

Cheap bent eyebolts don't break, they bend open, and bending is a much lower energy process than breaking. This is why experienced folks use welded or forged eyebolts or u-bolts with backers.

You have to be very careful when specifying a working load for cord. I'm not sure I have ever seen a "working load" for paracord, but a static load of 150 pounds versus a 550 pound breaking strength is reasonable based on an elastic limit argument. That being said, a 4 g shock load applied to a 150 pound static load is 600 pounds and that will break a 550 paracord every time........

Run a sim and see what the deployment g load is before you determine if your recovery system is good enough...... A 5 pound rocket experiencing a 30 g deployment shock puts a 150 pound load on the paracord. Exceed this and you will weaken the cord. Several 40-50 g deployment shocks will probably cause the cord to part on the next deployment......

soopirV said:

To be fair, weight has nothing to do with descent rate, it's drag/density related (old Hammer vs. feather on the moon experiment). I'm new to DD as well, but it stands to reason that the fin can will have much higher drag than the nose, and will therefore tend to be above the nose for the descent?
Wondering also if you could quantify "small to medium" for us newbies? I have a Frenzy on my bench that I plan to use for L2, and then will fly DD. Published kit weight is 76oz. I'm planning on fiberglassing it for practice and strength, and estimate that the final weight will be ~96oz. To hit a descent rate of 75-80fps, my sim shows a drogue of 1 foot. This seems reasonable to me, and also pretty close to "drogue-less", or am I being a fool? Even though it's falling fast, the added drag should further keep the av bay north of the fin can.

Lastly, aside from cost perhaps, is there a reason drogue-less is something to fly?

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Actually weight has a lot to do with the descent rate due to atmospheric drag.

Drag (force) = 0.5 x Cd x air density x drag area x velocity squared = rocket weight (force)

Velocity = square root [(2/Cd)x (weignt/area)/air density] where the weight/area is known as the sectional density.

Without a chute, the area is the cross-sectional area of the rocket, and orientation is very important. The minimum area is the circular cross-sectional and the maximum area is the longitudinal cross-section. In a drogueless recovery, you want 2 equal weight rocket sections with similar aerodynamic sectional densities attached by the shock cord. If the sectional densities or weights are widely different, then you need a drogue to insure a stable high velocity descent...

Bob

soopirV said:

To be fair, weight has nothing to do with descent rate, it's drag/density related (old Hammer vs. feather on the moon experiment). I'm new to DD as well, but it stands to reason that the fin can will have much higher drag than the nose, and will therefore tend to be above the nose for the descent?
Wondering also if you could quantify "small to medium" for us newbies? I have a Frenzy on my bench that I plan to use for L2, and then will fly DD. Published kit weight is 76oz. I'm planning on fiberglassing it for practice and strength, and estimate that the final weight will be ~96oz. To hit a descent rate of 75-80fps, my sim shows a drogue of 1 foot. This seems reasonable to me, and also pretty close to "drogue-less", or am I being a fool? Even though it's falling fast, the added drag should further keep the av bay north of the fin can.

Lastly, aside from cost perhaps, is there a reason drogue-less is something to fly?

Click to expand...

Not in my opinion. I will never fly drogueless. You have no control over the way things fall if you don't use a drogue chute. I've seen the fin can leading the upper section, but the fin can goes flat and actually flies the rocket off in some random direction. That's OK if it's into the wind and toward you, makes for a longer walk if it's with the wind and away from you. The biggest issue is when the payload leads the fincan down. It can actually get ballistic, just not as fast as if the apogee didn't work, but when the main opens, the fincan can foul the main and everything continues down at the 100 ft/sec rate.

Watch drogueless flights at the next launch and really pay attention to how they fall, fincan and payload, where they are and how they act. Watch closely what happens when the main opens. How close does the fin can get to it. Do the lines tangle? Does the fin can hit the end of the cord hard?

A drogue will prevent most issues you will see.

IF designed properly; the rocket will float horizontally.
When you add nose weight or a short and stubby rocket, it throws things out of whack.
Another problem is this so called Zipperless design. It too throws off the balance of the rocket.

I have over 300+ DD flights (dating back to 1996) and have only used a drogue a hand full of times.


JD

Handeman said:

Not in my opinion. I will never fly drogueless. You have no control over the way things fall if you don't use a drogue chute. I've seen the fin can leading the upper section, but the fin can goes flat and actually flies the rocket off in some random direction. That's OK if it's into the wind and toward you, makes for a longer walk if it's with the wind and away from you. The biggest issue is when the payload leads the fincan down. It can actually get ballistic, just not as fast as if the apogee didn't work, but when the main opens, the fincan can foul the main and everything continues down at the 100 ft/sec rate.

Watch drogueless flights at the next launch and really pay attention to how they fall, fincan and payload, where they are and how they act. Watch closely what happens when the main opens. How close does the fin can get to it. Do the lines tangle? Does the fin can hit the end of the cord hard?

A drogue will prevent most issues you will see.

Click to expand...

The only dual deploy rocket I have is my Nuke Pro. I fly it drogueless. The rocket tends to come down in a flat spin. Not exactly sure how I managed that but the nose and booster section are about the same length and weight roughly the same.