Blue Ninja - post mortem

[plummet]

Hi

My Estes Blue Ninja died on the weekend…and before I buy my next rocket I’d appreciate your help figuring out where I went wrong.

I used a recovery upgrade kit – a nylon chute with Kevlar shock cord and a nomex protector. I didn’t use any additional wadding. I’ve shown in the photo attached how I connected the whole thing up – basically the shock cord threaded through a small hole in the nomex, which I’d shove down the tube before inserted the parachute. I’d try to keep as little shock cord as possible below the nomex (see rig.jpg)

I also used some masking tape on the launch rod to hold the rocket high, rather than have it fly the whole length of the rod (see rod.jpg)

All went well for the first 4 flights (mixture of C11-3 and D12-3), but on the 5th I noticed a few minor burn marks on the parachute. I also remember that the motor was quite a tight fit, hadn’t had that problem before.

Then it all came apart on the 6th (with a crowd of about 30 people watching!). The engine just wouldn’t fit, and because I was keen to launch the rocket I hammered it home by banging it against my car tyre. Yep…I guess this wasn’t the wisest thing to do… I also found I couldn’t fit the engine retaining ring as it was too tight.

I assume that either the engine was in at an angle, or I’d bucked the tube a bit, as the rocket left the pad but then at about 30 feet just spun in circles for a while. The nose cone came off at ejection but the parachute didn’t come out in time. The parachute was badly burnt (see toast.jpg)

So…here’s my questions:

1. Is it a good idea to have the rocket high on the launch rod, or should I have let it fly the whole length? I can’t remember where I read to have it high.
2. Would people recommend using some wadding as well as the nomex? Or maybe did I rig / insert the nomex incorrectly? I’ve read lots of conflicting suggestions on this.
3. Is it possible I had the nose cone too tight? I used a small amount of masking tape to make it snug – tight enough that I could hold it by the nose cone without the tube dropping off, but with a reasonable shake it would drop off. What’s the best rule of thumb on nose cone fit?
4. Do you think the parachute didn’t deploy on the last flight because there wasn’t sufficient speed/time for the nose cone to pull it away?
5. How many flights should I expect to get from a model like this? I’m guessing way more than 5?
6. Any ideas what might have caused the tight engine fit? I’m wondering if either the engine tube or the engines themselves might have swollen - they were kept in a garage for about 9 months, so through a range of temperature and humidity, but shouldn’t have become wet. I can’t see any obvious distortion in the engine tube. Is there a good way of coping with this, like some kind of lubricant, or trimming of the engine?

Finally, I’m torn between getting another Blue Ninja or going for a Big Daddy. I don’t fly the rocket very often (generally at parties or camping trips), so something reasonably flexible with launch site is good, but I do like the ‘wow’ you get from a D-engine so I’m thinking an E might be fun (unless it’s so much more powerful it will scare the children!)

Appreciate it’s a big list of questions, grateful for any help you can offer.

Tony

 

[hardinlw]

1. Is it a good idea to have the rocket high on the launch rod, or should I have let it fly the whole length? I can’t remember where I read to have it high.

You want it to run the full length of the launch rod. I'm guessing that what you are remembering is that you may need a spacer so the igniter does not sit right on the blast deflector.

2. Would people recommend using some wadding as well as the nomex? Or maybe did I rig / insert the nomex incorrectly? I’ve read lots of conflicting suggestions on this.

I mentored a TARC team and they used a nomex protector with no wadding. There was never any damage to the parachute. The way I had them pack the chute was to roll it up following the directions on the FruityChutes web site. The shock cords were also folded around fingers and held bundled with tiny strips of masking tape so they would not tangle until the chute pulled them straight. The chute and shock cords were laid on the top half of the nomex protector and the bottom half folded up over it, then the two sides were folded over and the package was dropped into the rocket. The chute was completely enclosed in nomex with the top open so it would pop out when the payload section was blown free.

3. Is it possible I had the nose cone too tight? I used a small amount of masking tape to make it snug – tight enough that I could hold it by the nose cone without the tube dropping off, but with a reasonable shake it would drop off. What’s the best rule of thumb on nose cone fit?

That sounds reasonable

4. Do you think the parachute didn’t deploy on the last flight because there wasn’t sufficient speed/time for the nose cone to pull it away?

Did the parachute actually come out of the rocket and just not open? That's often a problem with how it was packed. If it never came out, it could be a stuck NC. We had a couple of failures with the TARC rocket deployment early on that resulted from the shock cord getting wrapped over the parachute as it was inserted into the rocket and then holding the parachute in when the ejection charge went off.

5. How many flights should I expect to get from a model like this? I’m guessing way more than 5?

Last summer at NYPOWER a kid I took with me got 22 flights on an Apogee Texas Twister before the accumulated residue from the ejection charges made it impossible to get another engine into it. I ended up replacing the motor mount because it was charred. One TARC rocket lawn-darted because the ejection charge had burned through the engine mount tube and managed to vent the ejection charge out the rear without deploying the parachute. That rocket had 15 flights on it. They subsequently doubled the engine mount tube to prevent a repeat performance.

6. Any ideas what might have caused the tight engine fit?

The engine could have been swollen. With only 5 flights, I would not expect ejection residue buildup to be an issue, but cleaning the motor mount with some rolled up sandpaper is good preventative maintenance. Just don't use really coarse paper of you'll cut into the tube and weaken it. If you find an engine that tight, don't use it.

 

[plummet]

Thanks Larry - some good advice. I particularly like the idea of the whole parachute being wrapped in nomex. My sheet was nowhere near big enough for that (less than double the diameter of the tube). I think I'll go for 9" square if I do go for the Big Daddy

If I remember correctly the nose came off but the parachute was still in the tube. That's why I was wondering if the chute is normally blown straight out of the tube by the ejection charge, or whether the rocket needs to be travelling at speed so that the drag of the nose cone can pull it free. I'm guessing that because the rocket was at a low speed the chute wasn't dragged free so got nicely cooked instead.

Tony

 

[TheAviator]

Thanks Larry - some good advice. I particularly like the idea of the whole parachute being wrapped in nomex. My sheet was nowhere near big enough for that (less than double the diameter of the tube).

Tony

Your Nomex protector should always be 3x the diameter of the rocket. This allows plenty of extra to move around. If you look at LOC/Precision's protectors, you will see that they are rated this way.

 

[powderburner]

Plummet,

If you have just joined in here (welcome to TRF!, by the way) you may not have seen enough of the old threads to learn these tidbits, but there are some other ways you can add ejection wadding to protect the recovery system.

You can use a handful of cellulose insulation with the wadding or with the Nomex sheet. This is the stuff sold as attic insulation for your house, and it is treated with a fire retardant chemical. You can find it at places like Home Depot or Lowes. It comes in a lumpy, loose condition (after you break it out of the package and fluff it up a bit) that seems to remind some people of......dog barf. Try it, it works. A bale of that stuff lasts forever!

Some people have used party streamer crepe material. If you try this I recommend the white streamers because the color from just about any other will rub off on your hands. This stuff is also treated to be flame resistant. You can usually find a big roll or 50 cents or a buck at places like Wmart.

Some people have even used a handful of lettuce leaves. Hey, it's definitely bio-degradable!

 

[plummet]

Thanks all - I'll definitely get a bigger nomex next time and I'll try the insulation as well - I had read a few threads about dog barf but I hadn't figured out that it was attic insulation!

I fancy making my own parachutes this time as it seems to be one of the most expensive components. I'll let you know how it works out!

 

[hardinlw]

If I remember correctly the nose came off but the parachute was still in the tube. That's why I was wondering if the chute is normally blown straight out of the tube by the ejection charge, or whether the rocket needs to be travelling at speed so that the drag of the nose cone can pull it free. I'm guessing that because the rocket was at a low speed the chute wasn't dragged free so got nicely cooked instead.

Tony

If the parachute is really loose in the tube, the ejection gasses my blow past it, particularly if it snags on something. In that case, you are counting on the momentum of the nose cone being blown off to yank it out. The older Estes kits had the shock cord mounted to the inside of the body tube near the top. If the Blue Ninja uses that approach, it is a potential point for the chute to snag. I've started putting a kevlar shock cord anchor onto the engine mount so there is no obstruction between the parachute and the great outdoors at ejection time.

One option the kids tried on their TARC rocket was to use a leader that was much heavier than what they needed to carry the loads of the parachute opening. This leader stuck out of the body tube by about three inches. Because of the large diameter (about 1/8" on a BT-80 rocket), there is little tendency to zipper (cut through the body tube) on early or late ejections. They connected the main shock cord (also Kevlar, but much smaller) to a loop in the end of the leader with a heavy snap swivel. This allowed them to disconnect everything for storage/transportation and to easily replace the shock cord if it got frayed.

 

[Mikus]

One option the kids tried on their TARC rocket was to use a leader that was much heavier than what they needed to carry the loads of the parachute opening. This leader stuck out of the body tube by about three inches. Because of the large diameter (about 1/8" on a BT-80 rocket), there is little tendency to zipper (cut through the body tube) on early or late ejections.

That will still zipper the body tube. The leader needs to go no further than the top of the body tube or that kevlar will just laugh as it cuts through the tube. But that setup is still workable - put a piece of masking tape around the leader where it extends out of the body tube to spread out the force from the leader hitting the tube. That should help protect against all but the harshest deployment.

Oh yeah, Blue Ninjas are great for CHAD staging a D to an E motor. :y:

And until you get parachute protection concepts down, I'd stay away from Big Daddys. Due to the freaking huge nose cone shoulder, there is little room for the recovery system in the bird. In fact, I'm thinking a Nomex protector will be a must for the next one I build. :2:

 

[hardinlw]

That will still zipper the body tube. :2:

At the TARC finals, the chute deployed 4 seconds into the flight (as evidenced by the abrupt deceleration in the altimeter data) and it did not zipper the body tube. The leader used is a good 1/8" diameter, much bigger than you would get by wrapping the skinny shock cord with masking tape. It is also braided and hence soft. When you pull it against the edge of body tube, it flattens to maybe 1/4" wide.

 

[shreadvector]

Your rocket flew unstable. This design rocket is quite stable and since you added more nose weight with the recovery system retrofit, it was even more stable. The motor can get it off the rod at a pretty good speed, even if you made the usable rod length pretty short. Longer is better.

So, why did it fly in loops? You probably damaged the nozzle when you hammered the motor. If the clay is damaged, you can get asymmetric thrust and if the nozzle throat erodes larger you will have a tremendous loss of thrust.

Hammering a motor is how you tell it "Please destroy my rocket and while you're at it, feel free to set fire to my launch site and/or injure someone nearby (including me)".

 

[Mikus]

At the TARC finals, the chute deployed 4 seconds into the flight (as evidenced by the abrupt deceleration in the altimeter data) and it did not zipper the body tube. The leader used is a good 1/8" diameter, much bigger than you would get by wrapping the skinny shock cord with masking tape. It is also braided and hence soft. When you pull it against the edge of body tube, it flattens to maybe 1/4" wide.

Accomplishing the same thing as the tape. Yeah that should work.

Got any pics?

 

[fxrs]

my son and I fly our ninja off of a home made launch pad
with a 3/16" stainless steel rod 5 feet long. The blue ninja
is a fun and easy rocket to fly. We launch it everytime
we go out flying. Here is a video below. If you watch
the video you will see the launch pad at the begining and
end of video.


https://www.youtube.com/watch?v=MQLwn-bWHHU