Chute protection and minimum diameter

[rocketcharlie]

Hello Recovery Forum,

I have been flying a 54 mm minimum diameter, dual deploy rocket the last couple of years. The flight have mostly gone well with one exception. I keep burning holes in expensive parachutes.

I have tried several approaches to chute protection, dog barf, nomex blankets, the flame proof toilet paper and most recently all three. Still there has been minor holes burned in my chutes, both drogue and main.

I dont feel there is enough room in this airframe to get a large enough nomex blanket wrapped around a parachute to do the job.

What are you folks doing? I suspect some will say " a piston". I believe there sometimes is problems with this ejection method. Do you still recommend?

Thanks in advance-

 

[Rocketman19]

I use a baffle in Saturn I. In my other one I use dog barf and it works fine. I hate pistons though because little pieces of crap always get stuck and the piston seizes up. I hope this helps!

 

[dhbarr]

What size BP are you using, and how are you constraining it? Have you considered something like the dino chutes petal protector ?

 

[rocketcharlie]

dhbarr-

If you are asking how much black powder, I am doing ground testing to figure out what is enough but not over kill. The BP is in a charge well, a 44 caliber spent casing.

Thank you for informing me about petal chutes, I didn't know about them. Have you used them? It looks like the smallest size is for 2.6 inch though.

 

[rocketcharlie]

Cellulose insulation seems to be called "dog barf" by everyone. I think this is interesting. Anyone know where the term came from? Who started it and when?

 

[crossfire]

Cellulose insulation seems to be called "dog barf" by everyone. I think this is interesting. Anyone know where the term came from? Who started it and when?

Just look at a pile of it laying on the ground. If it is wet you got barf.

 

[PieroAcme]

Maybe a baffle like this could help. It is becaming more and more popular here in Europe. I newer been a fan of the baffles. The one I testedin the past were not so good. But I have to say that this configuration is very effective. I saw a lot of launches without chute wadding or blankets and no one single hole burned was found in the parachute after.

 

[dhbarr]

If you are asking how much black powder, I am doing ground testing to figure out what is enough but not over kill. The BP is in a charge well, a 44 caliber spent casing.

Thank you for informing me about petal chutes, I didn't know about them. Have you used them? It looks like the smallest size is for 2.6 inch though.

I meant which grade of black powder, and whether or not you are using a substitute. FFFFg BP burns out much faster than, for instance, FFg Pyrodex.

I have used the petal protector and I like it better than a nomex burrito, functions about like a shotgun wad. I'll bet they'd make you a 54mm if you a$ked nicely :-D

 

[rocketcharlie]

I meant which grade of black powder, and whether or not you are using a substitute. FFFFg BP burns out much faster than, for instance, FFg Pyrodex.

I have used the petal protector and I like it better than a nomex burrito, functions about like a shotgun wad. I'll bet they'd make you a 54mm if you a$ked nicely :-D

I have been using 4F black powder. Yes, if you a$k nicely enough it often does the trick-

Also I like the baffle in the above very well done illustration. I dont think there is enough room for that in the rocket I have built, but I will file that away for future reference.

 

[manixFan]

I was having the same issue as the OP. I've tried the following:

• use a longer shock cord and move the chute close to the nosecone so hopefully it inflates away from the body tube
• contain the black powder better - I also use cartridge cases. Longer cases allow more of the powder to burn in the case or in a directed flame front
• place a number of squares of Quest wadding over the end of the chute burrito facing the charge well
• put the e-match on top of the BP to lessen the chance of powder being blown out by the ignition of the e-match
• use a chute protector that completely encases both the top and bottom of the chute, as well as the sides - I was actually getting some burns on the top of the chute as the flame went past the protector and over the top
• ground test to make sure you are not using too much powder
• burned chutes are a badge of honor showing that you have been able to fly your rockets

Good luck,


Tony

 

[PieroAcme]

Hi Charlie here an interesting sequence that illustrate a way how the ejection gases could push out the parachute and how this could negatively affect the parachute protection made with nomex blanket.
Here below the pictures. The tube is transparent. The parachute is wrapped into a blue blanket.



Here above the ejection charge release the hot gases. The gasses bypass the parachute and push the nose cone. Here below you see the nose cone that flies away (white) and the blanket, that pulled by the shock cord, leaves the parachute unprotected.

Here above you see that some sparks are inside the tube and quite close to the parachute.


Here after some 1/100 of seconds nose, blanket and parachute are flying away.
So this video shows that the acceleration that the nose cone gets when it is pushed out by the gasses could have as consequence that the blanket is not capable to keep inside the parachute because of the intertia of that one. The parachute slips out unprotected when still some burning sparks are in the body tube.
Dhbarr proposed the petal protector, I think this system should be free of this "failure mode" that could affect blankets.

 

[HHaase]

Fantastic photos, really making me re-think a few things. I haven't re-flown my Painkiller 3 because the Fruity Chute I have in it got scorched, despite being burrito wrapped. The photos make me wonder if I shouldn't re-evaluate pistons and other systems.

-Hans

 

[Handeman]

I usually use my chute protectors as burritos, but lately I've been just stuffing them into the tube to act more as a piston instead of wrapping the chute.
I don't have enough data to say which works better, but maybe some of you do.

 

[caveduck]

I've been using oversize blankets for a while on the mains, with pretty good results- that seems to give more of a piston effect. However my DD drogues seem to have a short life. I'm building a 54MD for AirFest, tempted to go drogueless and trust a Fruity main to survive the deployment. Also considering using a foam plug with the shock line in a slot. In LPR comp that will protect a Mylar chute from even the teeniest burn. I've got some 2" thick 60# wing core foam that should make a fantastic plug. Getting that stuff was a PITA though, had to chase (genuine) Styrofoam distributors. You have to use *extruded* foam, not the much more common expanded foam, which disintegrates back into beads when an ejection charge hits it.

 

[tfish]

I've played around with placing stainless steel scrubbing pads from the 'dollar store' onto the shock cord. It works great. But ground test before you fly it. I tried this with an old 54mm min dia rocket that I had without ground testing. The SS scrubbing pads suck the heat of of the ejection charges (hence how they work) but sucking the heat out of the charges also takes away some of the gas generated. You'll have to use slightly bigger ejection charges.

Tony

 

[manixFan]

Great job on those still frames. As I mentioned in my list, I make sure the chute protector goes over the top of the chute as well as the bottom. So it is like a burrito with both ends folded over towards the middle. The ends can't come come open until the burrito slides out of the body tube. I also try and not have a lot of open space around the chute, I'll use dog barf to fill it if necessary.


Tony

 

[o1d_dude]

Great job on those still frames. As I mentioned in my list, I make sure the chute protector goes over the top of the chute as well as the bottom. So it is like a burrito with both ends folded over towards the middle. The ends can't come come open until the burrito slides out of the body tube. I also try and not have a lot of open space around the chute, I'll use dog barf to fill it if necessary.


Tony

This is what I do as well.

Thus far it has worked well and my Fruity Chutes have survived well.

Fruity Chutes make a FRB device they call a “Chute Slipper”. Similar to the Petal Protector, think of it as a bucket that has an overlapping wall section. I have them in 3”, 4”, and 5” sizes.

 

[dhbarr]

https://shop.fruitychutes.com/search?q=slipper"slipper" did not match any results.

 

[Joshua F Thomas]

Maybe he means the deployment bags?

https://shop.fruitychutes.com/collections/deployment-bags

 

[Joshua F Thomas]

Or perhaps these parachute liners: https://shop.fruitychutes.com/collections/parachute-liners

 

[o1d_dude]

https://shop.fruitychutes.com/search?q=slipper"slipper" did not match any results.

Mea culpa.

Gene now refers to these a “liners”.

 

[Buckeye]

Here after some 1/100 of seconds nose, blanket and parachute are flying away.
So this video shows that the acceleration that the nose cone gets when it is pushed out by the gasses could have as consequence that the blanket is not capable to keep inside the parachute because of the intertia of that one. The parachute slips out unprotected when still some burning sparks are in the body tube.

Nice images, indeed.

If the blanket rips off the parachute while the parachute is still in the airframe, then the packing method must be the culprit. Is the blanket fixed to the harness very close to the nosecone? This would be a bad idea, I think. I always attach the blanket to the harness below the parachute. I don't constrain the blanket, either. I just thread the harness cord through the little slot in the corner, no knots.

 

[Handeman]

I always attach the blanket to the harness below the parachute. I don't constrain the blanket, either. I just thread the harness cord through the little slot in the corner, no knots.

I did that once. The blanket slid up the cord as the chute pulled away and stayed wrapped around the chute which never opened. I fixed the damage to the rocket and attached the blanket to the cord about 1 ft. further from the anchor point of the chute than the length of the chute when stretched from anchor to tip.

 

[rocketcharlie]

OP here. I love it when these threads catch fire! Thank you everyone, there has been some very good info here.

I want to restate though that I am talking about a 54 mm Minimmum diameter rocket. Nomex blankets are thick and bulky and I dont seem to be able to get a big enough blanket in with the parachute to encapsulate the chute. Even when making the section of airframe longer that houses the parachute I still dont seem to be able to get the blanket wrapped well enough around the chute to completely protect it. Maybe the answer is some of the non- blanket suggestions like SS scouring pads, foam plugs or liners.

 

[manixFan]

OP here. I love it when these threads catch fire! Thank you everyone, there has been some very good info here.

I want to restate though that I am talking about a 54 mm Minimmum diameter rocket. Nomex blankets are thick and bulky and I dont seem to be able to get a big enough blanket in with the parachute to encapsulate the chute. Even when making the section of airframe longer that houses the parachute I still dont seem to be able to get the blanket wrapped well enough around the chute to completely protect it. Maybe the answer is some of the non- blanket suggestions like SS scouring pads, foam plugs or liners.

I fly a lot of MD 38mm and 54mm rockets, so I feel your pain. Over the years I've found several blankets that were much thinner than typical Nomex, so I've set those aside for my MD rockets. I wish I could tell you where I bought them or what brand, but all I can say is that they are orange in color. Using those has helped a lot. But the real answer is the chute itself. I use the FruityChute 36" Iris Ultra light version. It's far smaller than the other versions of that chute


(the strength of the bridle for the light version is not listed on their website)

You can see from the chart I made that compares the various 36" chutes, the light version takes up the smallest amount of room, far less than the standard version. The reason is only 6 gores vs 8, and all spectra risers and bridle. Each gore has seams that adds to the volume so using fewer gores makes a big difference. It's also the lightest. Through lots of careful practice, I was able to consistently pack the chute so it would be a nearly perfect fit inside the 54mm body tube. I find that you have to really compress the material while rolling it in the chute protector to get the right result. I've had many flights on CTI L265 and L935 motors with zero recovery issues. The CF Mongoose will easily exceed Mach 2 on the L935.

Good luck,


Tony

PS: one of the biggest challenges to packing the Iris style of chute is the big 'wad' caused by the spill hole in the center of the chute, its seams, and the riser attachments. Learning how to minimize that wad though careful arrangement of the chute also helps reduce the maximum diameter needed to pack the chute.

 

[tim cubbedge]

I wish I could tell you where I bought them or what brand, but all I can say is that they are orange in color. Using those has helped a lot.

I get the orange ones from either Chris Short or Madcow.

 

[g.pitts]

Or perhaps these parachute liners: https://shop.fruitychutes.com/collections/parachute-liners

I use these AND a suitably-sized Nomex blanket from Fruity Chutes such that the opening of the liner opposes that of the Nomex blanket. Think of a capsule of medication and you’ll get a sense of what I’m going for. So far, the only parachute damage I’ve sustained has been small tears from landing in the sagebrush of eastern Oregon. I don’t fly min diameter rockets, and acknowledge that my method will not work for everyone.

 

[Dan Griffing]

I've played around with placing stainless steel scrubbing pads from the 'dollar store' onto the shock cord. It works great. But ground test before you fly it. I tried this with an old 54mm min dia rocket that I had without ground testing. The SS scrubbing pads suck the heat of of the ejection charges (hence how they work) but sucking the heat out of the charges also takes away some of the gas generated. You'll have to use slightly bigger ejection charges.

Tony

I experimented with using a SS scrubbing pad Kevelar-tied into a section of 1.6' tube to protect the parachute and Nomex from burn-through's from a the 2g FFFFG BP ejection charge from long 38mm motor that jutted into the parachute space of my DD-configured Zephyr.

Most of the time the SS containing 1.6' tube blew off of the end of the motor so I made a slow motion video of a spent J270W motor with an e-match simulating the motor ignition of the 2g FFFFG BP. When the 1.6" SS flash inhibitor was somewhat loose it just blew off with a big flash of burning BP. But when I wrapped masking tape around the fore-end of the motor to force the burning BP through the SS scrubber, not only did it stop the flame from getting through, there was only a small amount of the volume of gas as well. I have slow motion videos that can be posted as evidence.

This might also happen when the heat from BP combustion gets absorbed by other materials like large amounts of Kevlar shock cord.

It would be instructive to repeat the transparent parachute compartment experiment but with a baffle of SS scrubber that the burning BP has to go through before ejecting the chute. My bet it that there would be a significant number of ejection failures because the SS absorbs so much heat that the BP combustion and gas generated aren't sufficient for a reliable deployment.

But OTOH, the parachute recovered from the "lawn dart" will probably be undamaged and without any holes burned in it.

 

[rocketcharlie]

Was this a motor based ejection? This sounds like you made a sort of piston ejection system. Is this correct? It sounds like you are not a fan in any case.