I was looking for a description for the parachute harness, container and method of deploying the the pilot chute or ballute so your bird doesn't end-up with a tangled mess? Have you considered enlisting the help of a certified rigger who has experience packing for high-speed HALO or BASE openings? -peter
at the moment there is no more than the parachute and the parachute bay. I’m still brainstorming about the ejection mechanism. Because of the very small plane there is only very little space available, so I think it should be a pyro-based ejection system (small and powerful). Maybe an air-bag-like device that is placed under the parachute or a pneumatic cylinder with a pyro-charge inside can do the task (this kind of deviceI tested already for the balloon separation).
Parachute systems can be quite complex. But in this case it’s simply not possibly because of the small size. There is a lot of experience available from the rocketry guys. For small devices it seems to be common to use no pilot chute or any anti-tangling arrangements.
I think you are on the right track with the ejection system: A VERY small amount of FFF-G (gun powered) in an "air bag" will eject a properly packed and stowed parachute. The question is this: how fast will your craft be traveling when the chute is deployed?
When you say "rocketry guys," I assume you mean a group like the Tripoli Rocketry Association. The High Powered (model) Rocketry members of Tripoli do have a lot of experience with high-speed, parachute opening. However, they keep using parachute recovery methods that are meant for slow, model rocket-type openings.
If you attend a Tripoli launch and watch the really experience guys launch and recover their scale models, you will notice that most time, their round parachutes will blow a panel, or shred, or the Nylon or Kevlar "riser" connecting the chute to the rocket will cut through the rocket body like a "hot knife through butter."
Case in point: See Steve Eve's (link) launch (link 2) of his 1/10 scale model of the Saturn 5 (link 3). Notice how the riser, or shock cord, cut through the rocket body. (see 4 minute mark for close-up - link 4) Steve's rocket opened at apogee, the SLOWEST part of the flight, and yet the riser still cut-through a very solid rocket body. The "anti-tangling" device can help slow the opening and prevent the aircraft from being ripped apart from the open shock.
Can I suggest visiting a couple of the larger skydiving centers and consult several certified riggers, with a B or C license? In your case, the parachute deployment MUST be made gradual, or in stages, or the risers will rip the mooring from the aircraft, if the aircraft is traveling more than 200 mph when the ejection charge goes-off. A pilot chute, or sleeve, or bag is used by skydivers to delay or soften the open shock of their parachutes: something that is essential for any craft (or human) traveling more than 150 mph when the chute is deployed. Conversely, if the craft is traveling less than 50 mph when the chute is deployed, a staged deployment is NOT desirable.
Have you tested your balloon-launched aircraft recovery system at lower altitudes, like 5000 feet or less, where you can observe your design in action, and are more likely to recover most of the parts. It will cost more, but, if you can capture the opening with a min-cam or GoPro, you'll learn more about what works, or doesn't work.
That's an interesting idea, Monroe....using a "ring" on a round parachute that performs the EXACT same function of a "slider" on a square parachute. Murphy's Law say that unless you have some way vent and inflate a round parachute, the "ring" might prevent the parachute "skirt" from swallowing enough air to inflate the parachute. And you'll have what parachutist-over-50 call a "streamer." AGAIN, test this "ring" idea under the same conditions of aircraft flight when its parachute is deployed. The rocket guys use "sleeves" on their round parachutes, the same as was used by skydivers of the 1970's.
Instead of using masking tape as Monroe suggests, I would stow the cord using very light rubber bands. Masking tape...even gaffer tape....can roll-up-and-bind into a "rope," making it impossible to break. If you do use masking tape, DO NOT wrap it around the lines. Instead, find a way to use the tape to gently tack-down the lines. Better still, find a rigger over 50-or-60 who can remember and demonstrate how to pack-and-stow the lines of round parachutes using rubber bands, as was done with parachutes like the Para-Commander ;-)
I'm showing my age :-(
Fair enough, Monroe. And you are right. I probably need to see photo's of your masking tape method to understand and appreciate it. My experience is based observations of folks who test methods and material by making 500 lb bomb drops from small aircraft, and time spent skydiving, and learning from riggers, and time spent in High Powered Rocketry hobby. In fact, I think I admitted that I am brand new (and excited) by this H.A.B. activity; especially with the prospect of being able to "fly" my payload back to its launch site.
Please keep in mind the small size of the plane (look at the pencil on the photo), the target mass is below 500 g. Packing of the parachute for rockets of that mass seems to be easy compared to large chutes.
The speed of the plane for a planned chute ejection is very low to compared to rockets. If we assume 30 m/s the maximum force for a non elastic non damped instantly deploying chute (diameter 0.8 m) would be around 400 N. That’s a little bit too high for the palne, but there are only 200 J that has to be absorbed. With a setup for the shock cord like Monroe proposed that should be easily handled I assume.
If the over-all mass of the "foamy" is low-enough, a parachute may not be necessary....just design-or-allow the "foamy" to absorb the impact...that means sacrificing the aircraft in a way that saves your instruments....or shift the center of gravity so the foamy become unstable and floats to earth for the last 100 feet-or-so. Also, I wonder if a steamer could be used here?
The parachute is designed for a decent speed of 3.3 m/s. As I know that is a common design goal for the decent speed of rockets. A higher speed will lead to a significant damage on impact.
A streamer is much simpler for sure, but for the same (required) drag its size would be much bigger and heavier than a chute.
What we have here is a collision of design philosophies :-)
Good-natured, well-meaning and constructive, I hope.
Foamy's are cheap and expendable...in my opinion. If they are big-in-size and low-in-density, they should be able to absorb any shock that could damage instruments. This is common practise with the "rocket guys." The best HPR-type rockets only fly a few times. Frangibility (I think that is the right term) is built into the design to save instruments and lives and video cameras. Data and cool pictures rule!!! Even with parachutes, HPR-type rockets are so damaged by super-sonic flight, they can only be re-built and re-flown a couple of times. The main reason for a parachute is to prevent the rocket from breaking stuff and killing people when it lands.