Quantcast

Dual Deployment Parachute

The Rocketry Forum

Help Support The Rocketry Forum:

Ganji

Member
Joined
Oct 29, 2020
Messages
10
Reaction score
0
Hi,
I'm making recovery system using two parachutes, the main one and the drogue one. here is my concept :
zoobrazowanie.jpg

zoobrazowanie 2.jpg

drogue chute(the one in the middle of rocket) will be deployed using nitrocellulose wich will push the piston out deploying the chute and splitting the rocket in two( body tubes are connected by connector) and thats easy to do, the problem is to connect the nosecone the way that it wont fall out during drogue chute deployment but it will fall out when the main chute will be deployed( main chute is being deployed the same way as a drogue chute using nitrocellulose)

I thought abaut using 3 ring deployment system but im not sure abaut that, its going to be a little bit too complicated to pull the cotter.
3 ring.jpg

Any ideas how make this dual deployment system ?
 

Attachments

Nytrunner

Pop lugs, not drugs
Joined
Oct 15, 2016
Messages
7,187
Reaction score
2,667
Location
Huntsville AL
he problem is to connect the nosecone the way that it wont fall out during drogue chute deployment but it will fall out when the main chute will be deployed( main chute is being deployed the same way as a drogue chute using nitrocellulose)
A common method is to use nylon shear pins (#2-56 or M2 screws) or styrene rod of a similar diameter that run through airframe and nosecone shoulder.

#2-56 screws can have an expected breaking force of 25-30 lbs in shear (~111-133 Newtons), so you'll install enough of them to restrain the nosecone's mass during an ejection event.
For heavier cones you may want to use #4-40 or M3 nylon screws that have a stronger breaking force of 45-50 lbs (~200-225 Newtons)

In a bad event, a rocket could get near 50G's of shock, so many fliers will use that as a basis for how many pins they'll need for the mass of their cone.

Then you must calculate your ejection charge so that it creates enough pressure in the bay to apply a large enough separating force to the nose bulkhead to shear the pins
 

Ganji

Member
Joined
Oct 29, 2020
Messages
10
Reaction score
0
Im not sure abaut that solution, the pins will stick out of the airframe effecting the air flow and slowing down the rocket.
 

Nytrunner

Pop lugs, not drugs
Joined
Oct 15, 2016
Messages
7,187
Reaction score
2,667
Location
Huntsville AL
the pins will stick out of the airframe effecting the air flow and slowing down the rocket.
It is a tried and true method. Any disturbance from the head of the pin will make a negligible difference to your achieved altitude. The surface finish of our rocket and the motor performance variation will have more of an impact than the heads of a few shear pins. (Plus if you're that worried about it, you can snip the heads of the pins once they're installed)
 

Ganji

Member
Joined
Oct 29, 2020
Messages
10
Reaction score
0
It is a tried and true method. Any disturbance from the head of the pin will make a negligible difference to your achieved altitude. The surface finish of our rocket and the motor performance variation will have more of an impact than the heads of a few shear pins. (Plus if you're that worried about it, you can snip the heads of the pins once they're installed)
how big should the shear pins be if my airframe is carbon pipe with a 2.5 mm wall thickness
 

ether

Well-Known Member
TRF Supporter
Joined
Oct 22, 2019
Messages
229
Reaction score
108
What motor are you going to use? 2.5mm thickness is very thick for a carbon tube.

As to the size - this is great guidance that was posted

"#2-56 screws can have an expected breaking force of 25-30 lbs in shear (~111-133 Newtons), so you'll install enough of them to restrain the nosecone's mass during an ejection event.
For heavier cones you may want to use #4-40 or M3 nylon screws that have a stronger breaking force of 45-50 lbs (~200-225 Newtons)"

If you share more details on the rocket components and motor selection, people can give you more guidance
 

Ganji

Member
Joined
Oct 29, 2020
Messages
10
Reaction score
0
What motor are you going to use? 2.5mm thickness is very thick for a carbon tube.

As to the size - this is great guidance that was posted

"#2-56 screws can have an expected breaking force of 25-30 lbs in shear (~111-133 Newtons), so you'll install enough of them to restrain the nosecone's mass during an ejection event.
For heavier cones you may want to use #4-40 or M3 nylon screws that have a stronger breaking force of 45-50 lbs (~200-225 Newtons)"

If you share more details on the rocket components and motor selection, people can give you more guidance
i guess if i will but the 2-56 mm shear pins into 2,5 mm aireframe only 0,06 will get throught so its too short ? do i understand corectly ?
the motor is being made on my university it will be hybrid motor with 1500 Ns total impulse.
the airframe will be 3 carbon pipes 75cm-85mm-80mm and the nose cone is still being tested abaut the best material so i cant tell what is it going to be made from. but the point is to use dual deployment cuz of expecting 2-3 km attitude, and thats why we wanna use dual deployment system.
 

Ganji

Member
Joined
Oct 29, 2020
Messages
10
Reaction score
0
i guess if i will but the 2-56 mm shear pins into 2,5 mm aireframe only 0,06 will get throught so its too short ? do i understand corectly ?
the motor is being made on my university it will be hybrid motor with 1500 Ns total impulse.
the airframe will be 3 carbon pipes 75cm-85mm-80mm and the nose cone is still being tested abaut the best material so i cant tell what is it going to be made from. but the point is to use dual deployment cuz of expecting 2-3 km attitude, and thats why we wanna use dual deployment system.
ok, now i see 2-56 does not mean the lenght.
i found ones 2-56 and lenght of 6mm guess they will be ok ?
 

JoePfeiffer

Well-Known Member
Joined
Jun 15, 2013
Messages
107
Reaction score
70
Something I noticed in your post is that you are planning to use nitrocellulose as your ejection charge. Be aware that it is much more difficult to use that than black powder, and you'll need to make sure you can keep it in a confined charge well to build pressure to get a fast burn.
On the other hand, the same characteristics that make it harder to use also make it safer, so it's easier to get.
 

Zeus-cat

Well-Known Member
Joined
Mar 14, 2009
Messages
4,480
Reaction score
679
You will want to test your ejection system on the ground before flying. Calculate your ejection charges, install them so you can fire them with a battery.

Lay your rocket on the ground with the nose slightly elevated. You need something behind the rocket to keep it from moving when the charge goes off. Now fire the charge. You want to test if your ejection charge will break the shear pins and push the nose off and the parachute out. Do the test in a location that will not damage the rocket, nose or any people. Repeat the test until you are sure the system works. The nose and parachute need to come out forcefully, not just fall off.

You can search this forum for Pyrodex. It is a black powder substitute that some people use for ejection charges. It must be contained to build up enough pressure to use as an ejection charge just like your nitrocellulose.
 

Nytrunner

Pop lugs, not drugs
Joined
Oct 15, 2016
Messages
7,187
Reaction score
2,667
Location
Huntsville AL
My theory is that this is a non-US competition and they don't have access to the same materials we might. Thus using NC
 

Ganji

Member
Joined
Oct 29, 2020
Messages
10
Reaction score
0
My theory is that this is a non-US competition and they don't have access to the same materials we might. Thus using NC
thats true, here in poland its hard to get those 2-56 mm nylon shear pins so im forced to use something different.
and black powder is illegal without special permisions.
 

Ganji

Member
Joined
Oct 29, 2020
Messages
10
Reaction score
0
A common method is to use nylon shear pins (#2-56 or M2 screws) or styrene rod of a similar diameter that run through airframe and nosecone shoulder.

#2-56 screws can have an expected breaking force of 25-30 lbs in shear (~111-133 Newtons), so you'll install enough of them to restrain the nosecone's mass during an ejection event.
For heavier cones you may want to use #4-40 or M3 nylon screws that have a stronger breaking force of 45-50 lbs (~200-225 Newtons)

In a bad event, a rocket could get near 50G's of shock, so many fliers will use that as a basis for how many pins they'll need for the mass of their cone.

Then you must calculate your ejection charge so that it creates enough pressure in the bay to apply a large enough separating force to the nose bulkhead to shear the pins
how do i calculate all this things ?
 
Top