What went wrong???

[Dradog]

So I launch my Wildman Jart on her maiden voyage on an Aerotech G77-7R and everything looks great until well before apogee, we see it come apart and the chute is fluttering away in the slight breeze. The nose and body fall within 5 meters of one another, 10 meters from the launch rail. On examination, the chute shroud lines were all broken and the plastic loop attachment on the Jart's nosecone was torn off. The first thing I think is that the ejection charge fired prematurely, but then I read in this forum that there is something called drag separation. I added a threaded engine retainer to the kit, which placed the motor about one and a half centimeters further aft than the plan so I added nose weight to compensate. The NC was very loose so I added a wrap of masking tape to it, but I could still hold it upside down and shake the nose off when I tried. So what do you think? was it a premature eject or the effect of a heavy, loose nose? What is the proper amount of friction for a nosecone and the best way get it??

 

[bill2654]

Sounds like the delay should have been a 10 instead of 7. You have the right idea when it comes to the tape. Just enough so that you can hold it up and shake it. NOT TOO MUCH!

 

[Dradog]

OK then. I'll shoot it again with no modification and report back. Thanks for the help bill2654.

 

[dpower]

It *could* have been drag separation. I've flown mine on a G77-7R, and it flew fine; The delay is a bit short, but not way short. The NC should be snug enough, so that the rocket can be held by the NC, pointy end up, and not fall off, just barely. The other thing required is to improve the NC shock cord mounting. For this plastic NC, I recommend drilling a lateral hole near the tip, sized just right for a dowel, wrap the kevlar around the dowel, then epoxy. This holds the nose weight in nicely too, since epoxy by itself can come loose inside these cones. Most plastic loops simply aren't strong enough.

 

[crossfire]

Mark
Not sure what chute brand you used for the flight. With all the shroud lines broke you had a very early deployment rocket must have under full power yet. What did you use to protect the chute. With nylon lines if they got burned or melted they will break. If it was a TFR chute we would like to see it.
Gary

 

[Dradog]

Mark
Not sure what chute brand you used for the flight. With all the shroud lines broke you had a very early deployment rocket must have under full power yet. What did you use to protect the chute. With nylon lines if they got burned or melted they will break. If it was a TFR chute we would like to see it.
Gary

Yes it is a Top Flight chute. 24 inch and as you can see from the pictures, the shrouds broke were I half hitched them to the 1/8 inch kevlar. The chute protection is a GLR and what I suddenly noticed is that there is no powder residue on anything. I'm very new to this so your assumption is probably correct. It must have come apart under full power, well before the ejection charge lit. It was still straight up when it happened. I'm going to try it again today. I have you 30 inch chute attached.

 

[Rex R]

gee, and to think that, I've been using a 15" chute for my Jart . seriously a 24" is bigger than you need, an 18" is as big as I would use.
Rex

 

[emckee]

I've got a 24" chute in mine, but haven't launched yet. If you're using a 18", how much does your Jart weigh in at?

 

[Dradog]

It *could* have been drag separation. I've flown mine on a G77-7R, and it flew fine; The delay is a bit short, but not way short. The NC should be snug enough, so that the rocket can be held by the NC, pointy end up, and not fall off, just barely. The other thing required is to improve the NC shock cord mounting. For this plastic NC, I recommend drilling a lateral hole near the tip, sized just right for a dowel, wrap the kevlar around the dowel, then epoxy. This holds the nose weight in nicely too, since epoxy by itself can come loose inside these cones. Most plastic loops simply aren't strong enough.

Todays flight on a G77R-M reload went ok. The nose stayed on, thanks to your tip. the delay went off, but way too soon. The M on the reload is for medium delay, so I am thinking I should delay at least 10 seconds or more. Before your excellent reply on how to properly attach the nose cone, I had already used the Canadian method of attaching it using the ring from an old swag lamp and a 1 inch washer to hold it in place. I'll definitely use your suggestion on my next build. Here's a vid of todays flight. https://www.youtube.com/watch?v=BeFLiO271Io

 

[Rex R]

mines a 'porker' at 23 oz.s (w/o motor)...doubt that it will win any drag races, but makes a nice sport flyer on F52-7s .
rex

 

[dpower]

A G77R-M should be 10s. A quick sim for my Jart (22 oz), says an 8 second coast time on a G77, I wonder why your delay was so short? Occasionally, AT reloads have the wrong delay in them, so that's one possibility. This can be verified by measuring the delay length, and comparing it to the charts from Aerotech's web site. The delay spacer is a clue also, they're color coded.

After watching the vid a few times, it seems like only about a 4-5 second delay. Did you do any delay adjustment? Any other assembly failure would likely have had NO delay, so that seems unlikely. Did anything appear amiss when disassembling the motor? If not, I'd chalk it up to a too-short delay in the package.

Anyhow, a better flight than the first time, so that's progress!

 

[3stoogesrocketry]

The delay was spot on . Look at the video time . There was at least a 9 second coast time . You where right at the top , it was arching over . It is far better to eject a second early , vs late . Very nice flight .
Eric

 

[Dradog]

A G77R-M should be 10s. A quick sim for my Jart (22 oz), says an 8 second coast time on a G77, I wonder why your delay was so short? Occasionally, AT reloads have the wrong delay in them, so that's one possibility. This can be verified by measuring the delay length, and comparing it to the charts from Aerotech's web site. The delay spacer is a clue also, they're color coded.

After watching the vid a few times, it seems like only about a 4-5 second delay. Did you do any delay adjustment? Any other assembly failure would likely have had NO delay, so that seems unlikely. Did anything appear amiss when disassembling the motor? If not, I'd chalk it up to a too-short delay in the package.

Anyhow, a better flight than the first time, so that's progress!

Everything looked good before and after. I've just ordered some delay kits so I'll experiment with the delay tool.