Duel deployment options

[north boy]

Hi everyone, I've a 3.5 lb rocket which Ill be putting up on a 32mm 4 grain reload and its going duel deploy on an RRC2. The rocket will part come apart in the middle deploying the drogue and then the nose cone will come off at 1000ft to deploy the main. Is there any way to do this without the nose cone being held on with sheer pins or is this the only way ???

If the nose cone was of a tight fit and ground tested to ensure the event was successful would that be sufficient or am I just going to get seperation at 3,500 ft of both ???

Thanks for advice

[blackbrandt]

According to several sources, shear pins typically are used if you have a loose nose cone or separation joint. Ground testing would be your best option. Please correct me if I am wrong.

[cwbullet]

Hi everyone, I've a 3.5 lb rocket which Ill be putting up on a 32mm 4 grain reload and its going duel deploy on an RRC2. The rocket will part come apart in the middle deploying the drogue and then the nose cone will come off at 1000ft to deploy the main. Is there any way to do this without the nose cone being held on with sheer pins or is this the only way ???

If the nose cone was of a tight fit and ground tested to ensure the event was successful would that be sufficient or am I just going to get seperation at 3,500 ft of both ???

Thanks for advice

I used shear pins, but there are many who do not on small rockets. If you are confortable that the rocket will no drag separate, you should be fine.

What motor is 32mm?

[north boy]

I used shear pins, but there are many who do not on small rockets. If you are confortable that the rocket will no drag separate, you should be fine.

What motor is 32mm?

TYPO error sorry Pro 38mm ......

[north boy]

I used shear pins, but there are many who do not on small rockets. If you are confortable that the rocket will no drag separate, you should be fine.

What motor is 32mm?

Cw, the rocket is 5 ft long and 3.5 lbs in weight. Its a 3" dia tube and will be propelled by a 300 n 4 grain burn hitting .5 mach. I dont have the experience to know if it will drag separate or not. I suppose the fact that the main is in the nose and the charge theoretically has to eject the main chute out if the nose cone comes of through drag separation its no big deal. I'd rather avoid sheer pins just now.

[bill2654]

I use masking tape instead of shear pins. I hate poking holes in my rockets. If you can pick it up (with motor loaded) and it doesn't separate then your good. If it separates then add more tape. Hold it up buy the nose cone and test it.

[llickteig1]

Hi everyone, I've a 3.5 lb rocket which Ill be putting up on a 32mm 4 grain reload and its going duel deploy on an RRC2. The rocket will part come apart in the middle deploying the drogue and then the nose cone will come off at 1000ft to deploy the main. Is there any way to do this without the nose cone being held on with sheer pins or is this the only way ???

If the nose cone was of a tight fit and ground tested to ensure the event was successful would that be sufficient or am I just going to get seperation at 3,500 ft of both ???

Thanks for advice

Shear pins are the most sure way to keep the nosecone on, but it can be done without them.

The nosecone should be really tight and the ejection charge ample. Just being able to hold the rocket by the nosecone is not sufficient - it has to be tighter than that to stay on during the apogee event. Use masking tape for a tight fit and don't let the tape roll so that you get any of the sticky side out. You will also need a pressure relief hole in the airframe so that the inside and outside pressure can equalize more readily as the rocket ascends. Probably a 3-4mm (about 1/8") hole would suffice. Do your ground test with a really tight nosecone and make sure the charge will blow it off and push out the parachute.

It is difficult to replicate the forces during the flight when the apogee charge fires, so you have to rely a little on luck and/or experience. Getting the main out too early is the best type of "failure".

Good luck,

--Lance.

[KevinDunn]

Last weekend a customer had a drag separation on his WildmanJr on an I800 Vmax. The rocket was DD with shear pins on the NC but not the booster, and had several good flights previously without them. The booster was tight enough that the rocket could be picked up by the payload without separation. But it seems the I800 had high enough acceleration to separate the booster on motor burnout. It completely shredded the main chute and actually broke the shock cord (750 lb breaking strength). There was a half-inch zipper in the fiberglass booster, otherwise no damage. I had not previously taken drag separation seriously, but I am going to be adding shear pins to all my rockets at all joints from now on. The cost is small, the effort minimal, and the reduced uncertainty is well worth it. It was just one flight, but a memorable one.

[JDcluster]

Did that customer have vent holes in the main air frame?
The main reason for drag separation is lack of venting. I had it happen to my I5 at LDRS and it had 2 sheer pins holding the NC on.
I had no trouble on the first flight on a 98mm L. The M 2450 hit quite a bit harder.

I have used tape successfully many times to secure the NC.
The real problem with tape is: how much is too much?


JD

Last weekend a customer had a drag separation on his WildmanJr on an I800 Vmax. The rocket was DD with shear pins on the NC but not the booster, and had several good flights previously without them. The booster was tight enough that the rocket could be picked up by the payload without separation. But it seems the I800 had high enough acceleration to separate the booster on motor burnout. It completely shredded the main chute and actually broke the shock cord (750 lb breaking strength). There was a half-inch zipper in the fiberglass booster, otherwise no damage. I had not previously taken drag separation seriously, but I am going to be adding shear pins to all my rockets at all joints from now on. The cost is small, the effort minimal, and the reduced uncertainty is well worth it. It was just one flight, but a memorable one.

[DM1975]

I had a rocket drag separate on me with vent holes and no shear pins. The fit was tight and could be picked up and shaken but I think it was inconsistent of a fit and was just tight enough around a certain area as the coupler had been painted and I removed paint to get it to fit. I thought the fit was good but I figure that I managed to have tapered the fit just enough to matter.

[llickteig1]

Did that customer have vent holes in the main air frame?
The main reason for drag separation is lack of venting. I had it happen to my I5 at LDRS and it had 2 sheer pins holding the NC on.
I had no trouble on the first flight on a 98mm L. The M 2450 hit quite a bit harder.

I have used tape successfully many times to secure the NC.
The real problem with tape is: how much is too much?

JD

+1 on JD's comment on early separation due to venting problems. It is surprising how many flyers are unaware of the need for vents.

We have a KloudBuster kit rocket that is made from 8"X34" Sonotube. I usually fly mine on something like a J275 or J415. I flew it last year on a J1299 and the nosecone pushed out just after burnout. I had made a repair and forgotten to re-drill the vent. It isn't technically drag separation, but looks the same. The very first flight of the prototype kit the Sonotube split lengthwise in several places after the nosecone pushed off way too early.

There is a lot of pressure differential trapped in those tubes, especially in the big ones.

--Lance.

[Sully]

The real issue with the nose cone coming off at apogee isn't drag separation, but more likely shock from the payload section reaching the end of the shock cord. If the shock cord is too short, the nose cone may have enough momentum to loosen itself and separate at apogee when it reaches the end of the cord during deployment. This is especially true if you have any significant nose weight or if you use excessive ejection charge. I had this happen on my first few DD flights due to nose weight and loose fit of the nose cone. The nose didn't feel "loose" by any means, and wasn't that easy to separate on the ground, but consistently came out at apogee. There were no real negative consequences to main deployment at apogee, just a longer walk for recovery.

After adding shear pins, the problem has been solved, deployment has gone as planned. Shear pins are cheap and easy to work with, and I recommend them. But don't forget to have a long-enough shock cord (3 times rocket length is the rule of thumb I have read here, others go longer) and ground test, ground test, ground test!

[cwbullet]

The real issue with the nose cone coming off at apogee isn't drag separation, but more likely shock from the payload section reaching the end of the shock cord.

This is what I worry about, especially if I use a kevlar shock cord.

[north boy]

Thanks for all the replys. I am going to vent the avionics bay with a 1/8 th hole. With the ground testing of the RRC2 how do you actually get the charge to fire???? Do you try to fool the RRC2 into thinking its agogee or what ? It mentioned about putting a pipe to the vent hole and blowing in it to change pressure . Is this a way to do it or am I just being silly LoL

[dixontj93060]

For ground testing assemble your recovery as in flight and have your specified/calculated charges prep'd and in place, but instead of having the electronics in the av-bay simply extend the charge wires out a vent hole and back to a battery 15+ feet away. Then when you are ready to test each charge, touch the lead ends to the battery terminals.

Thanks for all the replys. I am going to vent the avionics bay with a 1/8 th hole. With the ground testing of the RRC2 how do you actually get the charge to fire???? Do you try to fool the RRC2 into thinking its agogee or what ? It mentioned about putting a pipe to the vent hole and blowing in it to change pressure . Is this a way to do it or am I just being silly LoL

[DM1975]

For ground testing assemble your recovery as in flight and have your specified/calculated charges prep'd and in place, but instead of having the electronics in the av-bay simply extend the charge wires out a vent hole and back to a battery 15+ feet away. Then when you are ready to test each charge, touch the lead ends to the battery terminals.

This is what I do but I use a cheap Estes launch controller to fire the charge. I have a few of them laying around and if it can fire the charges then the altimeter surely can.

[north boy]

Thanks everyone, Ill make the N.C as tight a fit where I can pick up the rocket by the cone and ground test a charge to see what happens. Ive never done this before so kinda excited always relied on Motor ejection and single deployment.

[north boy]

Ok I masking taped out the N.C on the rocket and its very....very tight almost to tight I thought...........I can pick the thing up by the N.C and shake it all day long and it doesnt move. I loaded a 3 gram load of Pyrodex and ground tested the charge and big pop and a poof of smoke walaaaa.....It seperates ....With force so much the N.C goes about 9 feet at least. I think this is a total success so thanks for the advice and hopefully a test flight coming soon