Hard landing - possible Chute Release issue - top of booster hit ground first - how?

[billdz]

Today I launched my LOC Expediter with an AT I-180 motor and a JL Chute Release. I had some trouble with my Chute Release when I first got it, although lately I felt I had gotten the hang of it. I've used it successfully with this rocket several times before. Today, after a nice flight to 1650', the chute deployed right at apogee, but something went wrong on descent. I couldn't see it, but witnesses said the chute stayed balled up and never opened.

What's really strange to me is how the rocket landed. Judging by the dirt, it appears that the top of the booster stage of the rocket hit first and made a dent and small tear at the top of the airframe, as the attached photo shows. Since the bottom of the booster has the motor casing and the fins, it is much heavier and one would think it would hit first. The payload section hit nose cone first, fortunately no damage except some dirt on the nose cone.

On the ground, the Chute Release was open and the chute and shock cord lay freely on the ground, no sign of anything twisted or hung up. A witness said that the Chute Release must have opened when the rocket hit the ground, because the chute stayed bundled all the way down. Yes, before launch I did the usual tests and did remember to turn it on.

Any thoughts on what might have gone wrong? And can I just pop the dented airframe back into shape and apply some CA, or is more elaborate action required?
Thanks,
Bill

 

[MikeyDSlagle]

I'm no expert but I would be inclined to say your two pieces collided in the air causing your damage; and the dirt is from being drug, but your chute wasn't open to drag it. Probably just landed tail first and flopped over to pick up the dirt.

I've had a rocket take damage similar because the chute deployed early. It was a fiberglass rocket so the damage was a crack and chip not a dent.

Don't know but that is my analysis. I have been in the sun all day though.

Mikey D

 

[billdz]

Thanks for the reply, I had also thought perhaps it landed tail first and flipped, but there's no sign of any dirt on the fins or elsewhere. Here's a pic of how this rocket looks on a normal descent.

 

[billdz]

Anyone else have any thoughts? I'm wondering if perhaps something got hung up on a fin and turned the booster section so the top hit first.

 

[Q-Aero]

If you look at your pic , the booster is at 45' when pull by the chute , ( the fins try to make the bottom go up ) without chute it may be normal if the bottom of the booster section is on top , even heavier the bottom section of the booster have more surface with the fins

 

[REK]

I have no experience with this unit, but I have read the manual several times and one thing bugs me. Being baro sensor based I pressume a pressure port is necessary. Maybe John can chime in on this. I think I remember asking this and he stated that it isnt required.

Next up if your unit can still be powered on, check to see if the reading of ground level was detected. In the user manual it states that if all the lights flash after attempting to acquire ground level. It failed to pick up ground level. If it does this everytime you power it on. The baro sensor could be damaged.


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[dhbarr]

Pressure Port is unnecessary because the CR is hanging in the free air on the way down.

 

[Q-Aero]

é. Being baro sensor based I pressume a pressure port is necessary. .

A pressure port is usually in the altimeter bay and the CR goes in the booster section. For good practice you drill a vent hole in the booster section. The CR doesn’t depend on it, goods think because the pressure of the ejection charge will trigger false reading. This also happen when the altimeter bay is no seal from the booster section resulting in the opening of the main.

I pretty sure they have something about vent hole in the book of High Power rocketry

 

[REK]

Dhbarr and Q-Aero I thought that might have been the case. My only assumption is that the baro did not pick up ground level on start up.


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[MikeyDSlagle]

Anyone else have any thoughts? I'm wondering if perhaps something got hung up on a fin and turned the booster section so the top hit first.

Lots of folks at NSL this weekend, or at the lake or what not. You may get more responses after the weekend.

If you look at your pic , the booster is at 45' when pull by the chute , ( the fins try to make the bottom go up ) without chute it may be normal if the bottom of the booster section is on top , even heavier the bottom section of the booster have more surface with the fins

I've thought of this as well. I've seen plenty fall horizontally after the apogee event. The chute bundle is usually enough to keep the fin can horizontal or with fins coming in first. But it still may be possible I suppose.

 

[Q-Aero]

I used the word "may" with my explainaition why the heaviest part may bnot touch the ground first. I don't get the part where the op said de chute deploy at Apoogee, he probably means ejection, but how come someone see the apooge ejection at 1600 feet and don't see the rocket fall ? A free fall rocket don't drift too much

 

[John Beans]

Sounds like the Chute Release let go of the pin, but the band was pinched by the chute and still partially wrapped around it. I have personally witnessed an open Chute Release (pin hanging free) but the band still stretched around the chute, pinched by it, still bundled, at the landing site. You gently kick it with your foot, and the chute falls open.

The issue seems to be bundles that are not firm. You'll notice in the video that I made on the Jolly Logic site that I mention that you want a nice firm bundle. The firmer and smoother your bundle, the less chance the band has of getting caught after release.

The perfect bundle (something to shoot for) is one that is very firm, where when you ground test and the band flies off and away from it, and the chute bundle just falls apart. With this as the goal, you want to avoid a pillow-y bundle, or winding the shroud lines around the outside of the chute (since it won't flop open if you do that). The way to judge a good bundle: it won't stay together at all without the Chute Release, but WITH the Chute Release it is a tight bundle that survives a good shake test.

I think sometimes people have a tendency (I know I personally did at first) to take their tried-and-true (from lots of trial and error) parachute folding technique and then just simply add Chute Release on top of that. But I have come to the conclusion that you'll end up with a different folding technique once you commit to a Chute-Release-dependent bundle. I did a lot of experimentation using AltimeterThree to measure exactly how long it took to inflate, since just eyeballing it can be very deceptive. And I kept experimenting until I could pretty reliably inflate within about 50 feet of planned release. In other words, I'd set it for 300 feet, and the rocket was slowed to landing speed by about 250 feet above ground level. My first attempts took as much as 200 feet of altitude to inflate, but back then I was still rolling the chute up tight with shrouds on the outside.

If you ever find the pin still in (no release) on the ground, AND YOU ARE CERTAIN YOU TURNED IT BACK ON AFTER GROUND TESTING IT (sorry for yelling there, but it needs to be said), then maybe you've got a stuck Chute Release. If you then immediately ground test it right there and it pops open, though, I'd still suspect (even if it was me) that it wasn't turned on before. Remember, a Chute Release that is charged up and turned on will run for days unless it is triggered or turned off. So if it just fails to "work properly" it will still be turned on when you find it.

I hope that is all helpful. I guess it helps to think of release and inflation as separate events, and the time/distance between them has to do with how your bundle is constructed.

 

[John Beans]

Also, with regards to venting: venting is NOT required for Chute Release. With the help of the beta testers we tweaked the release algorithm so that it wasn't needed.

Personally, I'd still add vents for altimeters (which require them). But by figuring out how to NOT require venting we made Chute Release just a little easier to use.

 

[rstaff3]

Parachute bundles are weird animals at times. I have had several rockes over the years fall under bundled chutes and, when I picked up the rocket, it unfurled nicely with no tangles.

 

[billdz]

Thanks for the replies. I did mean eject at apogee. Several people did see the rocket fall but I didn't ask them about the configuration of the rocket. On past occasions where there was a Chute Release issue, the components came down in the usual configuration, with the unbundled chute on top, the payload section nose down, and the booster section fins down. Apparently that was not the case this time, although the unbundled chute evidently furnished enough drag so that the rocket landed with only minor damage.

Yes, as dhbarr stated, Chute Release does not require vent holes because it releases the chute outside the airframe. There were no flashing lights and the CR was away from the chute on the ground.

John, thanks for your thoughts, hard to envision a chute "pinching" the band but perhaps that is what happened.

I was able to pop the dented body tube back into circular shape and I applied plenty of CA to the small tear, am I good to launch again?

 

[John Beans]

Parachute bundles are weird animals at times. I have had several rockes over the years fall under bundled chutes and, when I picked up the rocket, it unfurled nicely with no tangles.

Yeah, this exactly. I wouldn't have believed it if I didn't see it happen a couple of times. It's like the released chute bundle and the jet stream arrive at a stable equilibrium, and it just never gets ripped open.

 

[T-Rex]

Good info Mr Beans! Thanks for sharing! I haven't used my Chute Release yet, but I figure the more information I get vicariously, the better my first time will be.

 

[crossfire]

I used my JLCR Sat. In my WM 3" Punisher all went great. I think as with all new devices there is a learning curve to it. I have heard many different ways of folding the chute. I do mine the same all the time. Only problem I had so far on one flight out of 7 was a rubber band breaking. And I blame myself for not checking it out before the flight.

 

[Buckeye]

The problem is that you appear to be launching a can of tennis balls.....

 

[EXPjawa]

I'll second what John's stated. I've used mine for a year and half now, and the only times I've had issues with the chute not opening were similar to what you've described and could also be attributed to the release occurring, but the pin not popping out. More often than not I found (in ground testing) that the pin can get hung up in loose flaps of chute gore that near the CR's pin hole. I've seen several times that the servo releases, but the pip only moves slightly due to the drag of those flaps, or the band simply wasn't taught enough. Any time I find that in ground test, I refold, reorient the CR on the chute until I'm satisfied with the release.

 

[billdz]

CR is an amazing piece of technology, only problem is that the result of the flight can be really bad if something goes wrong and the chute doesn't open, whether from operator error, tangling, or the pin getting "hung up in loose flaps of chute gore". That's why I read with interest the thread about using CR to"reef" a chute so the chute would act more like a drogue during descent, see https://www.rocketryforum.com/showthread.php?140583-Using-Chute-Release-to-reef-a-parachute&highlight=chute+release.

Interestingly, one of the posters in that thread commented that with CR his unreleased chute had "enough drag from the chute and nose cone that the booster comes down fins first and pretty vertical." Obviously that did not happen in my case, unfortunately.

 

[REK]

Sounds like the Chute Release let go of the pin, but the band was pinched by the chute and still partially wrapped around it. I have personally witnessed an open Chute Release (pin hanging free) but the band still stretched around the chute, pinched by it, still bundled, at the landing site. You gently kick it with your foot, and the chute falls open.

The issue seems to be bundles that are not firm. You'll notice in the video that I made on the Jolly Logic site that I mention that you want a nice firm bundle. The firmer and smoother your bundle, the less chance the band has of getting caught after release.

The perfect bundle (something to shoot for) is one that is very firm, where when you ground test and the band flies off and away from it, and the chute bundle just falls apart. With this as the goal, you want to avoid a pillow-y bundle, or winding the shroud lines around the outside of the chute (since it won't flop open if you do that). The way to judge a good bundle: it won't stay together at all without the Chute Release, but WITH the Chute Release it is a tight bundle that survives a good shake test.

I think sometimes people have a tendency (I know I personally did at first) to take their tried-and-true (from lots of trial and error) parachute folding technique and then just simply add Chute Release on top of that. But I have come to the conclusion that you'll end up with a different folding technique once you commit to a Chute-Release-dependent bundle. I did a lot of experimentation using AltimeterThree to measure exactly how long it took to inflate, since just eyeballing it can be very deceptive. And I kept experimenting until I could pretty reliably inflate within about 50 feet of planned release. In other words, I'd set it for 300 feet, and the rocket was slowed to landing speed by about 250 feet above ground level. My first attempts took as much as 200 feet of altitude to inflate, but back then I was still rolling the chute up tight with shrouds on the outside.

If you ever find the pin still in (no release) on the ground, AND YOU ARE CERTAIN YOU TURNED IT BACK ON AFTER GROUND TESTING IT (sorry for yelling there, but it needs to be said), then maybe you've got a stuck Chute Release. If you then immediately ground test it right there and it pops open, though, I'd still suspect (even if it was me) that it wasn't turned on before. Remember, a Chute Release that is charged up and turned on will run for days unless it is triggered or turned off. So if it just fails to "work properly" it will still be turned on when you find it.

I hope that is all helpful. I guess it helps to think of release and inflation as separate events, and the time/distance between them has to do with how your bundle is constructed.

Basically you need the rubber band to be tight (not too tight of course) or else what happens is that it doesnt pull away from the chute and thus causing the chute not to inflate, is this correct?


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[REK]

Also, with regards to venting: venting is NOT required for Chute Release. With the help of the beta testers we tweaked the release algorithm so that it wasn't needed.

Personally, I'd still add vents for altimeters (which require them). But by figuring out how to NOT require venting we made Chute Release just a little easier to use.

That is what makes your chute release even more awesome.


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[Flyfalcons]

Plus the chute release only gives a small window of time to release the pin before returning to the locked position and turning off. Perhaps JLCR v2.0 can leave the pin unlocked after release, and returning the servo to the lock position when powered back on.

 

[Flyfalcons]

That is what makes your chute release even more awesome.


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Venting might not be required but we were able to get a Chute Release to pop while on the ground with a rocket that had a tight-fitting nose cone. I drill a vent hole on all my stuff.

 

[noffie79]

There really is no reason for a failure using JLCR. John has some pretty specific instructions on how to fold a chute using this device. Fold tight, with shroud lines wrapped inside the chute. Test before flight. If these directions are followed, there won't be any failures and there won't be a need for threads like this.
Here are some screenshots from a video of mine showing CR in action. It just so happens that this rocket is a LOC Expediter, the same as the rocket in question in the OP. Notice that the chute is tight and there are no folds of the chute keeping the band from letting go of the chute. Once the pin releases, the chute can be seen unrolling and opening within a split second. It took the chute about 75 feet to fully open and slow the rocket to landing speed on this flight.

 

[EXPjawa]

At the end of the day, the CR is a piece of equipment that requires the user to follow some protocol, like most of the equipment used in rocketry. There is a learning curve, and without proper setup, it shouldn't be expected to preform miracles or be fool proof. But with those lessons learned and protocol followed, it is highly reliable, and has the bonus of being very portable. As much as I hate to be that guy that blames the victim, what I see here falls squarely on the user for making sure that procedure is followed. John has explained what to do and what checks to perform many times, and through my own unintended experimentation, I've found that he knows what he's talking about!

 

[John Beans]

Plus the chute release only gives a small window of time to release the pin before returning to the locked position and turning off. Perhaps JLCR v2.0 can leave the pin unlocked after release, and returning the servo to the lock position when powered back on.

This is true when you ground test, but in an actual flight Chute Release rapidly cycles TWICE to be doubly sure.

You can test this yourself pretty easily. Turn on Chute Release and cup it in your hands (or in a glass or jar if you can't quite make an airtight little container with your hands), then suck the air out, hold it for three or four seconds, then slowly let air back in. With a little practice you can "simulate" a flight and you'll hear Chute Release cycle twice like it would in flight. A quick way to test that your pressure sensor is still working.

 

[noffie79]

I've posted this video before, but I'll post it again. This is the flight of my LOC Expediter using CR. Please disregard the completely inaccurate CTI ejection delay. This is a 50" chute and I'm using the larger band supplied with the CR.
https://youtu.be/lT2RknQJ6xQ

 

[billdz]

@noffie, @Rick,

While I'm far from perfect, how can you be so sure the blame for the incident is on me? The unit was ground tested, it was turned on, and the chute was folded the same as it had been for several previous successful flights, in accordance with John's video to the best of my ability.

A video of a ground test is at https://goo.gl/photos/Ed3ozSQAVm5KWDi38, let me know if anything can be improved.