Sizing pilot/drogue chutes for Deployment bags

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mrwalsh85

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Hi everyone:

I'm flying a large bird next weekend, using a Skyangle Cer3 XL chute and it's corresponding deployment bag. I have practiced packing the chute time and time again, and everything makes sense. I conned the kid next door into riding down the street with the deployment bag, a 40" Spherachute and trying out the deployment bag. I would estimate he was moving at a speedy 15mph when he tossed the d-bag. The chute moved out of the bag, but it still didn't budge.

How can I size my pilot chute? I will be freebagging this setup, so the nosecone will be going off on it's own.

I do have a Skyangle 60" ClassicII chute I could use for this application. The nose cone is currently only 3-4# and the rocket will need some nose weight anyway... So I think a 60 might work better for the nose cone anyway. I'll have two trackers (one for the cone, one for the body) so I'm not entirely worried about this setup.

Thoughts? Info-central has not been updated in a long time. Once I've done some toying around with this, I hope to see if I can't submit some information for Info-central if things work well for me.

Thanks!

Mike
 
One reasonably rational way is to get one of those hanging scales - something like:

https://dx.com/p/1-4-lcd-portable-electronic-handheld-hanging-digital-scale-2-x-aa-40kg-158324

... and then determine how much force it would take to fully deploy the canopy (pulling everything out to full line stretch) and then backing out the design of a pilot chute to create that much force (at 'x' FPS). Obviously, as the fall rate increases, the force the pilot chute can generate increases as well. I'd pick some number (say, 40-50 FPS) and target that as your design descent rate (to deploy -- or, to be conservative, maybe even half that - such that you are absolutely sure the vehicle can fall at that rate at some point in the recovery). Once you know how much force it takes to deploy your canopy, then you know you *must* generate that much force and can better select a pilot chute to give that much force to you.

-- john.



mrwalsh85 said:
Hi everyone:

I'm flying a large bird next weekend, using a Skyangle Cer3 XL chute and it's corresponding deployment bag. I have practiced packing the chute time and time again, and everything makes sense. I conned the kid next door into riding down the street with the deployment bag, a 40" Spherachute and trying out the deployment bag. I would estimate he was moving at a speedy 15mph when he tossed the d-bag. The chute moved out of the bag, but it still didn't budge.

How can I size my pilot chute? I will be freebagging this setup, so the nosecone will be going off on it's own.

I do have a Skyangle 60" ClassicII chute I could use for this application. The nose cone is currently only 3-4# and the rocket will need some nose weight anyway... So I think a 60 might work better for the nose cone anyway. I'll have two trackers (one for the cone, one for the body) so I'm not entirely worried about this setup.

Thoughts? Info-central has not been updated in a long time. Once I've done some toying around with this, I hope to see if I can't submit some information for Info-central if things work well for me.

Thanks!

Mike
Click to expand...
 
If it takes any appreciable force to deploy from the bag, then likely something is wrong in the packing arrangement. Do you have pictures to show what you have done so we can check it out?

Gerald
 
I fly a variety of rockets from 3 to 120 pounds. They fall under drouge between 50 to 100 fps (35-70 MPH). I think the 15 MPH bike test was way too slow to be realistic.
 
I agree: bike test was too slow--but fun for the kid nonetheless. I'm assuming this is a freebag setup, where the drogue deploys at apogee, tethered to the bag and at main deployment the tether is released, the NC and drogue fall away under their own 'chute, and the main is released from the bag --correct?

I'd size the drogue based upon the NC weight, targeting 17-20 FPS, perhaps a bit quicker, depending upon NC material and finish. Once that's determined, size the main for whatever you use as a target landing speed for the remaining weight --Minus NC that floats away. Determine drogue fall rate for the entire rocket, including burned-out motor, and then convert to MPH. Find an empty road or private area and test at this speed. May need a car, truck, four wheeler, hovercraft, speeder bike or something with a bit more top-end than the local kid's legs. But he'd probably want to see/participate in the test anyways....

Later!

--Coop
 
Hi guys!

Sorry for the delay. I have been getting ready for my trip to NYPower, so my mind has been elsewhere.

I kind of figured that the kid was going too slow, but I figured if it could deploy at that slow a velocity, it should deploy at a higher velocity.

I will try to see if I can't deploy this next week by deploying behind a vehicle or something of the sort.

Thanks all, for the advice!

Mike
 
Mike, I think bike is too slow as most others do. Try deploying out of a car- at least that would be my thought.
 

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