Main chute fouled by nosecone ?

[JW562]

Had a successful maiden launch of my first dual deploy this weekend, a Wildman Jr on a CTI i212. Rocket left the rail good under boost with a nice coast to apogee. The rrc2+ kicked the Rocketman 12” drogue just after apogee and the rocket fell a little slow for my liking but the inverted v seemed on point. Got down to 500’ and thats when things went south. The main charge fired, the nosecone separated from the payload tube and seemed to get wrapped up in the main chute preventing inflation. The rocket landed on the lakebed with no damage. What went wrong and how can I prevent this on the next launch? The chute was attached directly to the nc, perhaps I should move it down the line?

 

[Voyager1]

Typically the main chute is attached about 1/3 of the way down the cord from the NC. This would allow the NC to fly clear of the chute if packed appropriately.

 

[teepot]

I'm down about 3' from the nose cone. Exposed shock cord about 12' to 15'.

 

[waltr]

I also attach Main chute down a bit from the nose even with motor ejection.

It looks like you have just the chute inside the tube. picture looks like the Chute was blown into the nose at ejection.
I use a Nomex blanket with the chute wrapped inside as a burrito. The Burrito wrapped chute then is not a tight fit inside the tube and ejection gases can get past the chute bundle and push off the nose which then pulls out the chute. This keeps the chute bundled away from the nose and with a couple of feet of cord between the nose and chute it can not tangle.

 

[sriegel]

Concur with a bit tighter pack on the chute bundle. Let the shock cord get fully extended before the chute starts to really come out of the burrito. Your pack should let the suspension lines reach full stretch before the canopy starts to inflate.

 

[JW562]

Moved the main roughly 1/3 down the line as suggested and ready for my next club launch, weather permitting. Just dawned on my, should I be worried about my RRC2+? I wouldnt call the impact from the fouled shoot too too hard, but I know electronics can be sensitive. The altimeter was reporting 3,362' which is a full 1k over the sim altitude (2213'). Maybe that is an indicator of possible damage?

 

[waltr]

Hard to tell if altimeter is working properly.
Do you have another altimeter?

If so then put both into a vacuum chamber, draw a vacuum to simulate launch and altitude. Then compare what they report.

 

[Voyager1]

I agree. If you do have a second altimeter, then use it as a reference to test out your RRC2+. You can create a vacuum chamber quite easily with a sealable container and small DC vacuum pump, or a large syringe, or just a vacuum cleaner with a suitable leaky coupling. Don’t allow the vacuum to build up too quickly, though. Take it slowly.

At the very least, you should check the RRC2+ carefully for any physical damage to the board and component solder joints. You could also check its function with a straw test with its outputs wired to small low voltage bulbs to indicate drogue and main deployment.

Did you had the appropriate vent holes in your payload/avbay section?

 

[JW562]

Unfortunately it’s my only altimeter for now so a comparative test is out And yes The Avbay was properly vented

I suppose a vacuum test with igniters to confirm both channels fire is the best I can do ?

 

[Steve Shannon]

Unfortunately it’s my only altimeter for now so a comparative test is out And yes The Avbay was properly vented

I suppose a vacuum test with igniters to confirm both channels fire is the best I can do ?

I would just use LEDs.

 

[waltr]

Unfortunately it’s my only altimeter for now so a comparative test is out And yes The Avbay was properly vented

I suppose a vacuum test with igniters to confirm both channels fire is the best I can do ?

Just use low Voltage Xmas tree lights.

 

[JW562]

Made a makeshift vacuum chamber using a mason jar with hose barb epoxied into the lid. Wired up some Christmas bulbs and pulled on it slowly with a slow, gradual release. Happy to report both bulbs “fired” in the correct sequence. Altimeter reported 3,746, with nothing to compare it to (for now) I guess I can call it safe to launch unless anyone else has any other recommendations ?

 

[waltr]

That is what I do to test altimeters.
I typically get in the 3000ft range with full vacuum.
I would consider this good to go even if apogee is not correct.

 

[rokit]

The altimeter was reporting 3,362' which is a full 1k over the sim altitude (2213').

How accurately does the sim match the actual conditions of the flight? Things that can cause that much difference include Cd and launch site elevation (Lucerne Dry Lake is something like 2800'). Other factors like weight, launch angle, crosswinds, etc. can also make a difference.

 

[Banzai88]

The thing about sims is.......they're good for planning, but they are 100% theory UNTIL the first flight. THEN, take the empirical performance and adjust things in the sim (such as finish quality, etc) until the sim matches the "real world". Most folks either forget that or don't know that.

Make sure that the conditions of the sim launch match where you're launching, too! That accounts for as much variance as any other factors.

I use OR. After the first flight adjustments, my sims are ALWAYS within 5%, usually within 1%.

 

[DAllen]

If your nose cone is pointed down during drogue descent then IMHO your drogue is too big. I've seen it before where the nose is pointed down and the main gets fouled because everything else behind the main on the recovery train just falls right on top of it thus not allowing the main to inflate. Doesn't happen every time. In my mind, I think the ideal scenario is to have the main and nose cone pointed horizontally when the main charge goes off.

 

[Voyager1]

^^ Yes! A sim is only as good as the input data for the rocket and launch conditions. I’m inclined to think that your altimeter is closer to the mark than your sim.

 

[Onebadhawk]

The main chute should be attached directly to the hard point in the nose cone..
The 2 legs of the inverted V should be far apart..
The smaller the drogue the more the nose / payload section is pointed out and away from everything else..
The larger the drogue the more the legs of the inverted V are closed, the nose / payload section is pointed down..

You need pics of a flight with a set up you're questioning.

I know a 16" Ultra X Form is perfect on a heavy 4" rocket, bout, say, between 38 lbs and 48 lbs on the pad according to the motor..
All same on a gusty day a 20" gives more control..

I believe the drogue you quoted has a higher drag coefficient than one of my Ultra X Form drogues..
That must also be taken into account..

Your drogue was substantially too big enough to cause the main to foul.

Nothing is 100% fool proof..

You have to go with statistics and percentages..
There is just no benefit to allowing another section of harness between the nose and the main
so the nose can spin around the harness below the main chute..

Teddy

Pics or video will answer all of your question..

 

[DAllen]

If Teddy agrees with me I'm right.

 

[Onebadhawk]

If Teddy agrees with me I'm right.

Ha,, lol..

Teddy

 

[BABAR]

Just a Humble L-0 here, but I've seen X-chutes foul because of spin, and I am guessing an incompletely unfurled standard chute or undeployed chute under drogue might also spin a bit before it gets enough velocity to fully open. Spinning tends to wrap up the cords. So a good swivel might be helpful, I got great service and a good product from @Onebadhawk . The experts posting above may be able to tell you best place to PUT the swivel in the system.

 

[Handeman]

Moved the main roughly 1/3 down the line as suggested and ready for my next club launch, weather permitting. Just dawned on my, should I be worried about my RRC2+? I wouldnt call the impact from the fouled shoot too too hard, but I know electronics can be sensitive. The altimeter was reporting 3,362' which is a full 1k over the sim altitude (2213'). Maybe that is an indicator of possible damage?

I'm still using an altimeter that was in a rocket that lawn darted at 300 mph. They are amazingly resilient.
The battery was poured out of the remains of the av-bay so I would replace that anytime you have a non-nominal landing.