Dual deployment for beginners

[Tamir Friedman]

Hello!

We are currently designing our first rocket to use dual deployment recovery system. We are trying to assess what parachutes we should get for each deployment and we were wondering if there is a rule of thumb to the velocity we are trying to achieve by the first deployment and also at what altitude would you usually suggest to deploy the second parachute?

Thank you!

 

[Zeta]

Tamir,
how much does your rocket weight, and what diameter and length is it?

 

[Tamir Friedman]

Tamir,
how much does your rocket weight, and what diameter and length is it?

Our current simulation estimate it will weight 1.3kg and it's length will be around 1.5m (we are still debating some of the materials)

 

[Tamir Friedman]

Our current simulation estimate it will weight 1.3kg and it's length will be around 1.5m (we are still debating some of the materials)

(the added weight is becase we have a payload that we are still unsure of it's weight, but it shouldn't be big)

 

[Tamir Friedman]

(the added weight is becase we have a payload that we are still unsure of it's weight, but it shouldn't be big)

oops I am sorry, didn't notice the simulation removed the motor. With the empty motor it should weight at about 2kg

 

[manixFan]

Very good question, but one without a definite answer. However the most common rule of thumb I've run into seems to be about 15.2-21.3 m/sec (50-70 ft/sec). Basically you want to control the descent and keep the payload bay above the fin can. That way when the main deploys there is less chance of it fouling with the lower section.

In practice it does not take a very big chute to slow the descent rate because of the loss of stability when the parts separate. My guess is depending on design a 300mm or 450mm drouge (12" or 18") will be plenty big enough, but it will be good to hear what others recommend.


Tony

 

[David Schwantz]

A lot of chutes makers list descent rates per chute on their sites. Top Flight Recovery for one. For the drogue you want enough drag to form an inverted "V" in your shock cord. That way when the main blows, it is away from the rocket booster. But not so much that she will drift away under drogue. I have gone to 30' and 60' streamers on some of my rockets. When you have an all up weight after burnout you can go to the descent rate chart and figure the size of chute you will need for the weight at your desired descent rate.

 

[Zeta]

David, my daughter and I carried her last rocket into the UPS store to get an accurate weight on it. You should have seen the looks we got. People that have never seen an HPR think all kinds of crazy things when they see one! So anyway what I am trying to say to Tamir is you can always wait until the rocket is built to figure out the chute sizes.

 

[Jmhepworth]

For something that small, I either go drogue-less or a really small chute—6-9”.

 

[David Schwantz]

Zeta, wish I could've seen that one
Kind of what I meant when I said all up weight minus propellant. Wait till she is all built, then add motor hdw to total. Believe it or not, even paint can add a lot of weight.

 

[OverTheTop]

I normally target around 80fps on drogue, perhaps up to 100fps on occasions.

Most of my flying works with around 22fps for landing.

 

[teepot]

Landing speed is also dependent on what your landing on. Nice soft grass or a dry lake bed. I try to land at 12 FPS because the lake bed is like concrete. If I was landing on grass I would come down faster.

 

[Voyager1]

Our current simulation estimate it will weight 1.3kg and it's length will be around 1.5m (we are still debating some of the materials)

I occasionally fly a Madcow Formula54 in a dual deploy configuration that has a launch mass of about 1.6kg and a length of 1.5m. Typically I would use a 40-45 cm (~15"-20") drogue and an 80cm (32") main with deployment and landing velocities of 15-20 m/s and 6-7m/s, respectively. I will adjust these chute sizes depending on the current wind conditions. I generally deploy the main at between 500'-700'.

 

[Zeus-cat]

Just to let you know, fps is feet per second

 

[Rex R]

There is another to consider for when to deploy the main chute, which is, how long will it take to unfold every thing ànd slow down. My descent rates of about 60 fps under drogue it takes about 100' to deploy the main and slow for landing, so I figure 400' to be safe.