Agreed. I learned from another member here when their L3 project suffered airframe damage from a hefty charge that blew a pvc charge holder out the side of the airframe. He can add more, or correct me, if I misunderstood the underlying issue.
L3 Post Mortem - Flight of the Terminator
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Agreed. I learned from another member here when their L3 project suffered airframe damage from a hefty charge that blew a pvc charge holder out the side of the airframe. He can add more, or correct me, if I misunderstood the underlying issue.
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Bill-late to the party as usual, but condolences on your bird. Kudos for your unflagging forensics and good nature during this loss. Sorry we didn't hook up at LDRS, but if you ever need anything-ask me first, brother. I promise somewhere next year we'll get some facetime! Straight smoke and good chutes! (and no- I wasn't being sarcastic.)
cherokeej
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You're right, I didn't reread the entire thread. But I've got to disagree with you. He may have run some ground tests, but apparently something went amiss. Cuz I watched the project slam into the Fresno clay.
It was a 5" bird. I fly both a Comp4 and a Comp5. Similar. In the C4, I use two #2-56 nylon shear pins in my drogue. 2 grams of 4F in a micro-centrifuge vial opens it up every time. In the C5, I use 3 grams in a similar vial, same shear pins. Many, many flights, and still flyin'.
Looks like Bill ran 2 grams with his 4-40's in a 5". Not gonna be enough.
And I can't help but notice you edited out the most important part of my post. "Blow it out or blow it up, but don't leave the laundry in the tube."
If you want to quote me, then quote me. But please don't edit me.
One thing to keep in mind is how loose the motor fits in the motor tube. I've noticed on the FWFG motor tubes, the fit can sometimes be a bit loose, and this can allow some of the ejection gasses to escape out the back.
dshmel
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I wrap masking tape around the top of the motor case for a tighter fit. I also wrap the coupler tubes on the e-bays and the nose cone shoulders. This also reduces the likelihood of the tubes binding during separation.
Blow out the side of a rocket? Wow! I've done this twice in cardboard rockets with unrestrained microcentrifuge canisters on ematches. If a fellow blew up a PVC charge holder in a " 'glass" rocket that would be one heck of a charge.
I'd say they probably sealed the end of the canister too tightly.
I experimented one time with a canister with a screw on lid and put powder in a open canister, cardboard endcap, dog barf and two layers of duct tape. Blew nicely and noisily outside of a rocket.
Did the same test where I did an endcap, dogbarf and screwed on a lid where I drilled a 1/4" "restrictor" hole (before screwing it on of course) Pushed the button, it exploded and the canister "shrapnellized" in a striking fashion with a much louder
bang.
Wellll, I scrapped the "restrictor" hole in the lid deal right then and there.
Here's my scoop with the powder mixing in with the dog barf on top. If one's charge is on the edge of being "borderline", probably not a good thing to have happen as perhaps the efficiency of "all" the powder burning at once might be inhibited to some degree. Get around it by using a calipers to measure the diameter and use a cardboard disk pressed in place against the powder charge. That will prevent the bulk of the dog barf mixing with the powder that's on top.
Of course, if one tosses in extra powder, shouldn't be an issue mixing or otherwise. I've done charges with disks and no disks and have been burned either way if the charge is too small. I think after this discussion, I'll be cutting disks for all my charges!
Kurt
rharshberger
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+1 Kurt, I like the idea of the paper over powder separator disc, I don't believe there is really much mixing of the powder and dog barf but there probably is a very small amount.
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I've had a few Dog House PVC charge wells get blown up by a little too much powder, but they did deploy...
edited for brevity:
"For every action there is an equal but opposite reaction"
Any charge holder that has appreciable mass should have the closed side restrained against a bulkead. (The exception being something like fingertips or latex tubing.) Otherwise physics says the charge canister is going to go in the opposite direction of the charge with a lot of energy that has to be dumped somewhere, hopefully not the side of your rocket but rather a bulkhead that's up to the task. My big charge holders are screwed to a piece of wood which is then screwed to the bulkhead to spread the impact load across a large area. The heavier the holder the more damage it can do do otherwise.
Shooters have been killed by nothing more than a piece of cartridge brass that was unrestrained by a chamber. Our pressures are nowhere near that but we are still generating a lot of force with all that powder.
Tony
Let's not forget about one of those laws of physics:
"For every action there is an equal but opposite reaction"
Any charge holder that has appreciable mass should have the closed side restrained against a bulkead. (The exception being something like fingertips or latex tubing.) Otherwise physics says the charge canister is going to go in the opposite direction of the charge with a lot of energy that has to be dumped somewhere, hopefully not the side of your rocket but rather a bulkhead that's up to the task. My big charge holders are screwed to a piece of wood which is then screwed to the bulkhead to spread the impact load across a large area. The heavier the holder the more damage it can do do otherwise.
Shooters have been killed by nothing more than a piece of cartridge brass that was unrestrained by a chamber. Our pressures are nowhere near that but we are still generating a lot of force with all that powder.
Tony
Nick@JET
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I'll second that with the doghouse 2 gram - they are thinner than their larger one, although mine blew out the air frame so it didn't deploy. My fault though, I stuffed the dog barf in extremely tight so the primary wouldn't blow the backup - but I won't make that mistake again.
EeebeeE
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I used this same rocket for my L3 and it was successful. I think you did not use enough charge. I ended up doing 8 total ground tests and determined that I needed 4 grams of FFFF to separate a strongly friction fit booster from the payload bay and 4.5 grams to separate the nose cone from the payload bay. Back up charges were 4.5g and 4.75g respectively. I used copper plumbing caps screwed to my bulkheads for charge cups. The NC was held in place with 3 #40 shearpins.
Also curious why you did not go with the more traditional configuration of drogue aft of the e-bay and main forward. I have been leery of putting a chute that far forward into the NC. After two failed L3 attempts with something a little more complex, I opted for straight simplicity. I used nomex cloth instead of deployment bags and went with a configuration that I had used often. I did not want to do anything new. The only exception was that I added a removable 5-lb. ballast inside the AV Bay so that I made sure not to bust the waiver. According to your altitude, that turned out to be a good decision.
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This was my configuration and launch photo. Hopefully most of the rocket survived so you can try again. It really is a great bird and it has a lot of versatility, being able to fly on strong K's as well as full M's.
Also curious why you did not go with the more traditional configuration of drogue aft of the e-bay and main forward. I have been leery of putting a chute that far forward into the NC. After two failed L3 attempts with something a little more complex, I opted for straight simplicity. I used nomex cloth instead of deployment bags and went with a configuration that I had used often. I did not want to do anything new. The only exception was that I added a removable 5-lb. ballast inside the AV Bay so that I made sure not to bust the waiver. According to your altitude, that turned out to be a good decision.
. This was my configuration and launch photo. Hopefully most of the rocket survived so you can try again. It really is a great bird and it has a lot of versatility, being able to fly on strong K's as well as full M's.
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Congrats on your successful flight. It is a nice looking rocket.
Also curious why you did not go with the more traditional configuration of drogue aft of the e-bay and main forward. I have been leery of putting a chute that far forward into the NC. After two failed L3 attempts with something a little more complex, I opted for straight simplicity. I used nomex cloth instead of deployment bags and went with a configuration that I had used often. I did not want to do anything new. The only exception was that I added a removable 5-lb. ballast inside the AV Bay so that I made sure not to bust the waiver. According to your altitude, that turned out to be a good decision.
I went with a slightly unconventional layout for a couple of reasons that really amount to personal preference. First, since it's a 75mm motor mount, I wanted the the design to handle the longest 75mm motor, without worrying about having space for drogue, harness, etc. So, I went with the drogue forward of the AV bay, and the main in the voluminous nose cone. Another advantage of this approach is carrying the weight of the entire recovery system well forward of the CG, lending even more stability without adding ballast.
Perhaps a somewhat more complex design with some fancy electronics, but nothing in the design contributed to the failure. It was my mistake to be too conservative with BP, and not doing more boundary testing to understand how much more or less I could safely use. As I said in an earlier post, a single ground test was insufficient. I now know to run and document several tests to understand how much is not enough, and perhaps how much is too much.
It’s most likely that more BP would have made for a successful flight. I tried to be too precise, and erred on the side of not enough BP rather than more than enough. Lesson learned. More complete ground testing would have demonstrated this.
All this being said, I want draw attention to everything that worked right – credit where credit is due.
Marsa Systems. The dual Marsa54L’s, using the MrfBridge and MrfPyro for remote ematch ignition of the main worked exactly as intended. They endured a very hard landing, and were still functional. (Only one had a damaged LCD display that can be replaced). John Derimiggio provides excllent customer service. Thanks John!
And yes, my Schurter switches and Featherweight magnetic switches worked great.
Real Flight Systems: James Dougherty's GPS-1 is first class tracking hardware. Flying at over 1300 fps to 12k feet, the GPS never lost contact. The data available post flight is priceless.
OneBadHawk Kevlar harnesses. These harnesses took a beating due to my mistake, but didn’t fail. Notice how the stitching held up. I’ve heard you should not tie loops in Kevlar, now I see why. This is the only damage to the harness, and it's my fault. Thanks Teddy!
Fruity Chutes: Gene's Compact Ultra Iris is an amazing chute. I chose it because I wanted something that would fit easily in the nose cone for a 30+ lb rocket. Deploying at 550 fps, I did not expect it to survive, but the failure mode is interesting. The swivel was completely gone, and the fabric disintegrated, not the stitching of the lines at the point of attachment. I will be ordering the exact replacement as soon as my new airframe arrives.
CORRECTION: This chute uses a 1/4 inch Kevlar bridle, not a swivel. That's what I could not find.
All this being said, I want draw attention to everything that worked right – credit where credit is due.
Marsa Systems. The dual Marsa54L’s, using the MrfBridge and MrfPyro for remote ematch ignition of the main worked exactly as intended. They endured a very hard landing, and were still functional. (Only one had a damaged LCD display that can be replaced). John Derimiggio provides excllent customer service. Thanks John!
And yes, my Schurter switches and Featherweight magnetic switches worked great.
Real Flight Systems: James Dougherty's GPS-1 is first class tracking hardware. Flying at over 1300 fps to 12k feet, the GPS never lost contact. The data available post flight is priceless.
OneBadHawk Kevlar harnesses. These harnesses took a beating due to my mistake, but didn’t fail. Notice how the stitching held up. I’ve heard you should not tie loops in Kevlar, now I see why. This is the only damage to the harness, and it's my fault. Thanks Teddy!
Fruity Chutes: Gene's Compact Ultra Iris is an amazing chute. I chose it because I wanted something that would fit easily in the nose cone for a 30+ lb rocket. Deploying at 550 fps, I did not expect it to survive, but the failure mode is interesting. The swivel was completely gone, and the fabric disintegrated, not the stitching of the lines at the point of attachment. I will be ordering the exact replacement as soon as my new airframe arrives.
CORRECTION: This chute uses a 1/4 inch Kevlar bridle, not a swivel. That's what I could not find.
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ChrisAttebery
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Talk to Gene and see if it can be repaired.
I'm not throwing it away. It's perfect for ground testing. I won't mind a few burn holes in a chute that is otherwise 'well vented'.
I'm not throwing it away. It's perfect for ground testing. I won't mind a few burn holes in a chute that is otherwise 'well vented'.
Holee molee! Teddy had posted a pic of one of his harnesses still attached to an eyelet that sheared off of the base of a forged eyebolt. He makes mucho strong harnesses.
Also, one gets what they pay for. That picture of the Fruity Chute shows it's worth the price premium and would likely have long life if used in more nominal situations.
I was wondering about your configuration too Bill and I see your reasoning clearly now. You planned for longer motors. Nothing wrong with that. Also, your sequence of events worked perfectly except the amount of apogee charge issue.
I had previously posted about the complexity and took me hour to realize I was wrong. Your events occurred as planned except for the charge size. I say build another so you can use your current documentation and have another go at it.
I've been guilty lately of under dosing charges and have a flat spot on my forehead from all the times I keep hitting myself in the head! I keep telling myself I have yet to "overcharge" and break a harness from too rigorous a deployment
so I've resolved to go on a kick to add a bit more. Also I "restrain" charges in cardboard rockets. It's as easy as a long screw through the bulkhead I can ziptie the microcentrifuge charge holder to.
I highly recommed this to all with cardboard rockets. Kurt Savegnago
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Bill,,
I'm not really understanding what I'm lookin at..
I see a sewn eye that looks fine..
where the other quick link is , if that's a sewn eye why don't I see any sewing ??
If that's a sewn eye, it's the worst damaged sewn eye of mine that I've ever seen...
Please send that back to me,,
I'd like to see it...
Do you have my shipping address ??
Teddy
I'm not really understanding what I'm lookin at..
I see a sewn eye that looks fine..
where the other quick link is , if that's a sewn eye why don't I see any sewing ??
If that's a sewn eye, it's the worst damaged sewn eye of mine that I've ever seen...
Please send that back to me,,
I'd like to see it...
Do you have my shipping address ??
Teddy
Yeah, not so much. I can tell the damage is not repairable. It would be like trying to repair a popped balloon.
Yeah, not so much. I can tell the damage is not repairable. It would be like trying to repair a popped balloon.
Why not? Just use plenty of rubber cement on the balloon!:lol:
Teddy, yes I will send the harness so you can check it out firsthand.
The harness and your sewn loops worked perfectly with no serious damage, just some minor fraying. In fact, your sewn loops were stronger than the Kevlar material itself. The photo below is where I simply tied a loop for a quick link, just for attaching the Nomex blanket.
From the looks of the loop, bad idea. I should have listened when others (perhaps even you) said, "don't tie loops in Kevlar." Now I can at least be used as a bad example for others not to imitate.
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So what's the best practice for the kevlar harness when you need to connect something like the chute in the middle? Use 2 shorter harnesses with a quick link connecting them to the chute? I've done exactly what is pictured before, and while it's never caused a problem, I'd prefer to adjust my practices before it does.
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ooohhhhhhhh,,,
it's a knot,,,,,
I didn't realize it was a knot,,
It looked like one of my loops that frayed in the pic....
That explains a lot Bill,,,,
I've never seen a loop of mine do that,,
it was a knot you tied in the material...
ok,,ok,, I get it...
Send it back to me anywhoosie Bill,,
I'll fix it up for you....
Teddy
it's a knot,,,,,
I didn't realize it was a knot,,
It looked like one of my loops that frayed in the pic....
That explains a lot Bill,,,,
I've never seen a loop of mine do that,,
it was a knot you tied in the material...
ok,,ok,, I get it...
Send it back to me anywhoosie Bill,,
I'll fix it up for you....
Teddy
Perhaps someone can tell me if I'm interpreting the Raven 3 data correctly.
Trying to tell how many G's when the main deployed, the inset shows -81.9 Axial G's. With a 30 lb rocket (after motor burnout), that comes in at about 2,450 lbs when the chute fully deployed.
Is that right?
Trying to tell how many G's when the main deployed, the inset shows -81.9 Axial G's. With a 30 lb rocket (after motor burnout), that comes in at about 2,450 lbs when the chute fully deployed.
Is that right?
Yeah, the conversation went something like this:
Teddy: "What is that? One of my sewn loops? "
Bill: "No, Frayed knot"
Sorry, couldn't resist.......
dixontj93060
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Perhaps someone can tell me if I'm interpreting the Raven 3 data correctly.
Trying to tell how many G's when the main deployed, the inset shows -81.9 Axial G's. With a 30 lb rocket (after motor burnout), that comes in at about 2,450 lbs when the chute fully deployed.
Is that right?
Yes, quite a shock!
mikec
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The axial accelerometer on a Raven is only rated to 70G so the -81.9 isn't reliable, but it was definitely quite a shock.
BTW, on this whole discussion of charge holders, I have always used tie-wrapped glove fingers instead of any kind of charge well. YMMV.
Did the GPS-1 survive or did you lose it?
Teddy sells a 3 loop harness, and if you tell him the config you want when you order it, he will do what you ask, unless he sees a problem then he will tell you.
Yep - The GPS-1 came through it great. It's going to fly again. It's a high quality product - I'm very pleased.
The Google Earth data in my original post came off the on-board memory card. It was still transmitting when I walked up to the rocket. It never lost contact throughout the flight, or when it impacted the ground.
You are correct - and I have purchased 2-loop and 3-loop harnesses from him. I didn't see any harm in tying a knot "just for the Nomex". I learned my lesson. It didn't cause a failure, but I can now see the damage that Kevlar can do to itself under the stress of a high load.
It's really important that I stress that the Kevlar and his stitching worked flawlessly. Teddy's work is top notch, and the harness did even better than I would have expected under that kind of shock load.
He even does custom harnesses. The harnesses for my L2 bird were great!
