Pilot chute sizing.

[Bat-mite]

Okay, hopefully this is my last question before LDRS.

My Formula 200 ... burnout weight is about 60#. Main chute is a 15' military silk. Shroud lines are also about 15', paracord. Lots of them.

D-bag is a Fruity 10" for 5.5" - 6" tubes. 8" bag would have been too big for my chute.

Planning to pull the bag off with a pilot chute. I happen to have an Estes 30" not in use at the moment. It has a few small burn holes in it.

Here is my deployment strategy.


So, the question is: how big of a pilot chute do I need? Also, how big is too big? Can I use the 30" slightly holey Estes, or should I get something bigger?

Thanks, gurus.

 

[mpitfield]

Have you considered the "free" bag method?

 

[NateLowrie]

John,

You don't need an extra chute. Use your drogue chute. Giant Leap has the best image for the 2 types of setups you can do. See https://giantleaprocketry.com/images/products/comp/tacbag2_lg.jpg and let me know what you think. I am freebagging mine.

 

[Bat-mite]

Have you considered the "free" bag method?

Yes, but I wanted to keep things as inexpensive and simple as possible. Traditional dual deployment, single main.

 

[Bat-mite]

John,

You don't need an extra chute. Use your drogue chute. Giant Leap has the best image for the 2 types of setups you can do. See https://giantleaprocketry.com/images/products/comp/tacbag2_lg.jpg and let me know what you think. I am freebagging mine.

I'm using the integrated method, but the GLR picture doesn't show the apogee event. My drogue will already be out between the booster and the AV bay.



Sorry for the lousy MS Paint drawing.

 

[NateLowrie]

I'm using the integrated method, but the GLR picture doesn't show the apogee event. My drogue will already be out between the booster and the AV bay.

View attachment 314007

Sorry for the lousy MS Paint drawing.

Ok, so the deployment back should be packed tight to the point where the bottom spills out easily. If you pick it up by the top and give it a shake or two the chute should spill out. That said, you don't need much to pull the bag off. I would still think you could use the drogue without an extra chute. Just do something like this:



Your nosecone failing free until the shock cord is stretched out should pull the chute out of the DBag. Your drogue still provides the pull upward on the other end of the DBag.

 

[rharshberger]

Okay, hopefully this is my last question before LDRS.

My Formula 200 ... burnout weight is about 60#. Main chute is a 15' military silk. Shroud lines are also about 15', paracord. Lots of them.

D-bag is a Fruity 10" for 5.5" - 6" tubes. 8" bag would have been too big for my chute.

Planning to pull the bag off with a pilot chute. I happen to have an Estes 30" not in use at the moment. It has a few small burn holes in it.

Here is my deployment strategy.
View attachment 313997 View attachment 313996

So, the question is: how big of a pilot chute do I need? Also, how big is too big? Can I use the 30" slightly holey Estes, or should I get something bigger?

Thanks, gurus.

I use the method you describe here, the pilot for my setup is 24 inches, and the distance between the d-bag attachment and the chute attachment points need to be futher apart than the length of the shroud lines. My d-bag and pilot are attached to the nose cone, the main to a 3rd loop that just clears the payload bay.

 

[mpitfield]

Yes, but I wanted to keep things as inexpensive and simple as possible. Traditional dual deployment, single main.

If the D-bag is packed correctly you really don't need a big pilot. I have not deployed a chute this big but I use the same setup on my 3" Darkstar with a 15" drogue @ apogee and a 12" pilot to pull my d-bag from my 48" main @ 700AGL.

If this is an LDRS flight I am happy to lend you what you need from my Fruity collection. I have quite a few chutes to chose from, just let me know and I will pack what you need.

 

[Bat-mite]

If this is an LDRS flight I am happy to lend you what you need from my Fruity collection. I have quite a few chutes to chose from, just let me know and I will pack what you need.

That is very kind of you, but I really want to see this work with what I have.

I think my 30" will work. I was thinking that someone out there probably has some numbers on what size pilot to use. It's very funny to me -- there are guys on here that pull equations out for just about everything, but there are these little pockets where the general answer is ... "that looks about right."

 

[Handeman]

I have a 9' chute as my main that drops the rocket at 15 - 17 ft/sec. My 60" pilot chute is attached to the nose cone and d-bag. It drops the nose cone at 10 - 13 ft/sec. There is 100 ft piece of 150 lb dacron connected to the inside of the d-bag and the top of the main chute.

When the main deploys, the pilot pulls the nose cone up and the d-bag with chute out of the payload tube. The main shroud lines are zig-zagged through elastic loops on the d-bag so they pull out first and stretch out as the rocket stretches out below it. Once the shroud lines are out the d-bag is pulled off the main and it opens quickly with little shock to the whole system. The 100 ft of dacron keeps the nose cone and pilot attached to the main and since the pilot has a slightly lower decent rate, it stays above the main.

This deployment has worked so well and consistent the first 4 times I've lowered the main deploy altitude from 1000 to 700 ft. I plan two flights at LDRS, if I get a second motor mixed in time.

 

[Bat-mite]

I have a 9' chute as my main that drops the rocket at 15 - 17 ft/sec. My 60" pilot chute is attached to the nose cone and d-bag. It drops the nose cone at 10 - 13 ft/sec. There is 100 ft piece of 150 lb dacron connected to the inside of the d-bag and the top of the main chute.

When the main deploys, the pilot pulls the nose cone up and the d-bag with chute out of the payload tube. The main shroud lines are zig-zagged through elastic loops on the d-bag so they pull out first and stretch out as the rocket stretches out below it. Once the shroud lines are out the d-bag is pulled off the main and it opens quickly with little shock to the whole system. The 100 ft of dacron keeps the nose cone and pilot attached to the main and since the pilot has a slightly lower decent rate, it stays above the main.

This deployment has worked so well and consistent the first 4 times I've lowered the main deploy altitude from 1000 to 700 ft. I plan two flights at LDRS, if I get a second motor mixed in time.

I'd love too see your set-up. I'll PM you.

 

[iowadan]

T Knake in his book Parachute Recovery Design Manual recommends that the pilot parachute produce, for reliable deployment, four times as much force as the weight of the parachute it will be deploying. As the force the parachute is dependent on velocity at deployment he has recommendations for the ratio of area of pilot chute to main based on velocity. For speeds less than 150 knots, which your's should be, the pilot parachute should have and area of 3% of the main parachute. For your parachute that works to a diameter of 2.7 feet, 32 inches. Based on this I would say your damaged 30 inch ESTES chute is not a good idea. Something new and larger would be a safer bet.

 

[Bat-mite]

T Knake in his book Parachute Recovery Design Manual recommends that the pilot parachute produce, for reliable deployment, four times as much force as the weight of the parachute it will be deploying. As the force the parachute is dependent on velocity at deployment he has recommendations for the ratio of area of pilot chute to main based on velocity. For speeds less than 150 knots, which your's should be, the pilot parachute should have and area of 3% of the main parachute. For your parachute that works to a diameter of 2.7 feet, 32 inches. Based on this I would say your damaged 30 inch ESTES chute is not a good idea. Something new and larger would be a safer bet.

Thanks. That's the kind of thing I was looking for. However, it raises a question. In the book, is the pilot chute attached to the main chute and responsible for pulling the main chute open? If so, that is a far cry different from pulling a bag off. Know what I mean?

 

[iowadan]

In the examples he gives in the book he use the same rules to size the pilot parachute whether it is attached to a deployment bag or directly to the main parachute. He does say that if the pilot parachute attaches directly to the main parachute the pilot parachute should never exceed 6% of the area of the main parachute. In that case the force from the pilot parachute may prevent the main from opening fully.

 

[Bat-mite]

In the examples he gives in the book he use the same rules to size the pilot parachute whether it is attached to a deployment bag or directly to the main parachute. He does say that if the pilot parachute attaches directly to the main parachute the pilot parachute should never exceed 6% of the area of the main parachute. In that case the force from the pilot parachute may prevent the main from opening fully.

Okay, thanks. Look like I'll pick up another PAR-36.

 

[Handeman]

In the examples he gives in the book he use the same rules to size the pilot parachute whether it is attached to a deployment bag or directly to the main parachute. He does say that if the pilot parachute attaches directly to the main parachute the pilot parachute should never exceed 6% of the area of the main parachute. In that case the force from the pilot parachute may prevent the main from opening fully.

I ended up making my pilot chute 30% of the main, by area. There were several reasons, the first was because the pilot was also lifting the nose cone, the second was because I wanted it to lower the nose cone at a slower rate then the main lowered the rest of the rocket. Calculation of chute size based on the decent rates of the nose cone and the rest of the rocket is what determined the size of the main and pilot for me. It just so happened the pilot has an area 30% of the main. 5' ft diameter vs. 9 ft diameter.

 

[Coop]

I recover the nose separately and size the pilot according to the weight it will be recovering --trying to keep it near the same descent rate as the rest of the rocket under the main chute so this way they land close to each other. On Hellraiser, that was a 48", which brought my nose and deployment bag down about the same rate as the rest. It was recovered within 30 yards of the main.

 

[NateLowrie]

I recover the nose separately and size the pilot according to the weight it will be recovering --trying to keep it near the same descent rate as the rest of the rocket under the main chute so this way they land close to each other. On Hellraiser, that was a 48", which brought my nose and deployment bag down about the same rate as the rest. It was recovered within 30 yards of the main.

This is what I do. The drogue chute ends up pulling the bag off and since they are not attached to each other the size of the drogue relative to the main chute isn't critical. I just size my drogue to a compromise between the desired descent rate and the weight of the portion it's recovery and it's fine.