Initiator mystery needs solution

[Atlasboy]

Mentioned in another thread a weird flight I had several days ago. Essentially, had quite a bit of curvature instead of straight shot. Wind not an issue. After examination, looked like problem caused by igniter going along for ride.

But, fixed that by using suggestion from another post to only insert cap a little bit. Clean ejection this time. But still some curvature. Not as much but definitely not straight.

My only explanation is the following guess. I removed the motor clip with a dremel. Pushed out the internal motor ring with a dowel. BUT I did not dremel out the little part of the motor clip in the tube b/c I could not get to it. So, my guess is that the RMS casing is tight against the clip and I'm getting thrust directly on that piece of metal which is causing the curvature. What do you think?

In the meantime, I used another suggestion from the forum and got a flexible dremel attachment and took out that little piece of the hook. So, I'll try a launch in the next few days to see. But in the meantime, I'm open to suggestions as to what the heck I'm doing that suddenly caused my straight as an arrow rocket to decide to be a curvy little devil.

Thanks for all the great suggestions on my other posts. Incredibly helpful.

[shreadvector]

Need photos as I'm not getting your verbal description.

Check nozzle. If there are any grooves in the used nozzle, then there was most likely a bad batch of plastic that eroded during the motor firing. If not, then check for anything else that is off center:
Nose weight shifted?
Parachute or something else internal shifted to one side?
Useing a Mantis pad (they do the "Mantis Dance" and the rocket flies in random directions which can look like something deflected the rocket)?
Fins bent?
Anything else internal that could be an off center mass (such as a pool of epoxy on one side, etc.)?

[Atlasboy]

Thanks. I'll get some photos tonight. Fins look good. The Aeropack is a good install. Inside of motor tube looks good except for the piece of metal from the old hook that was in there (I now removed it). So what I was trying to describe was the ejection cap on the RMS was hitting the clip inside the mount.

I've never heard of the Mantis dance. Can you see it? I did find that the aluminum rod was shot so I bought a stainless 1/4 yesterday that I will try. Maybe that was an issue.

My first three flights (pre aero pack install) were straight shots and beautiful. So my obvious guess is that it was something I did when I did the install. Thanks again.

[shreadvector]

Mantis Dance is when the rocket takes off and the Mantis pad and rod flexes and the legs can lift off the ground. The rocket moves up the rod, but depending upon the wind and exactly where the rod/pad/rocket are pointing as it leaves the rod and any rotational velocity imparted to the rocket as it leaves the rod, it might fly in a strange direction.

I suggest always using a 6 foot long steel rod with a Mantis and put weights on all 4 legs to minimize dancing.

[Atlasboy]

Thanks. The steel rod I've got is a few inches under 6. I'll use some rocks or weights on the legs on the next launch as well.

[chadrog]

Thanks. The steel rod I've got is a few inches under 6. I'll use some rocks or weights on the legs on the next launch as well.

If your launch site allows, tent stakes work nicely on the Mantis. Drill a small hole through the end of each leg and stake it down. Beats carrying a bucket of rocks around.

[Atlasboy]

Great idea. Thanks.

[Nerull]

Thanks. I'll get some photos tonight. Fins look good. The Aeropack is a good install. Inside of motor tube looks good except for the piece of metal from the old hook that was in there (I now removed it). So what I was trying to describe was the ejection cap on the RMS was hitting the clip inside the mount.

I've never heard of the Mantis dance. Can you see it? I did find that the aluminum rod was shot so I bought a stainless 1/4 yesterday that I will try. Maybe that was an issue.

My first three flights (pre aero pack install) were straight shots and beautiful. So my obvious guess is that it was something I did when I did the install. Thanks again.

h

[Atlasboy]

Wow. Okay, the kind of curvature I had was nothing like that. That shot looks only about fifteen feet above the pad. I didn't see much curvature for at least a couple hundred feet. So I don't think I experienced Mantis dance. I am anxious to do a test launch now that I got the internal piece of motor clip out of the inside of the mount. I still think the casing thrusting against that could have done it. Or, maybe I'm totally barking up the wrong tree.

[shreadvector]

Unless the casing was mounted at an angle, then the motor clip and the motor thrusting against the motor clip could NOT have anything to do with what you describe.

Was it windy?

Was it windier up at altitude?

What motor were you using? Thrust to weight ratio is important. if the motor had low thrust compared to the weight of the rocket, it would not fly very fast and it would be rotated by any cross wind. This is like a weathervane turns and so it is called "weathercocking".

Wow. Okay, the kind of curvature I had was nothing like that. That shot looks only about fifteen feet above the pad. I didn't see much curvature for at least a couple hundred feet. So I don't think I experienced Mantis dance. I am anxious to do a test launch now that I got the internal piece of motor clip out of the inside of the mount. I still think the casing thrusting against that could have done it. Or, maybe I'm totally barking up the wrong tree.

[CPUTommy]

From my expereinces, there are a few rockets out there that just dont Fly straight.. Im not sure if its the kit itself, or the assembly.. Im leaning towards the kit itself. From ONE distributor (who will not be mentioned) every rocket built by this company, Has arched itself out of the field. I think out of 10 rockets my buddy has 2 that alwalys fly straight. Alwalys... One that was from this mfg.. Count on it being lost or destroyed... Here are some videos for ya to look at.. As you will see...
100 feet..ok....
500 feet.. NOT ok...

http://www.youtube.com/watch?v=S7pLq...4&feature=plcp

http://www.youtube.com/watch?v=zuN7o...3&feature=plcp

hope that helps..
Tom

[Atlasboy]

I had a G54. Wind maybe six mph ground. Same reload that I used for straight flights before I installed the Aeropack retainer.

[hardinlw]

You mentioned the igniter going along for the ride. Does that mean the red cap was stuck on the engine? If so, it would have vectored the thrust and caused the arc. Cramming it on too far or cutting too big a notch can cause it not to pop off like it's supposed to.

[Atlasboy]

Right. That DID happen two flights back. Got VT for sure. So I thought that was it. But last flight clean eject but still curvature (although less). I took a careful look a few minutes ago. Fins straight etc. I took some pics I will post tonight. Maybe I am just missing something really obvious

[Rex R]

did you happen to notice which way it curved? like did it curve toward the launch lug or away from them?
rex

[kjohnson]

So when you say the flight had a curve, was it like one of these?

[Atlasboy]

Yes. Both times towards the lugs.

[Atlasboy]

I'd say two.

[CPUTommy]

I would think that an easy fix is to double the lugs on the other side of the bird..

Interesting to say the least..

Tom

[shreadvector]

Or, it could simply be the wind at higher altitude making it weathercock as the thrust level drops way off. Look at the thrust-time curve for the motor he listed.

Trajectory curve number 2 is NOT arcing way over. it is a slight angle at altitude. Not tipping off the pad.

I would think that an easy fix is to double the lugs on the other side of the bird..

Interesting to say the least..

Tom

[Rex R]

since it only just started, and it appears at speed/altitude, then either it is a higher wind at altitude, or a burr causing off axis drag on that side.

[Atlasboy]

I suppose it is possible I'm just reacting b/c of lack of experience and that I was just lucky on my first three having dead wind and straight shots. For example, the first three I recovered within about 30-40 yards of pad. These last two were between 100 and 150 yards or so. The only other thing I noticed was on this last launch when I put the rocket in the car the top lug looked off. I touched it and it fell off. Obviously, I've now fixed it. Also, as I mentioned my old aluminum screw in rod seized so I replaced that.

Without having a video (which I will do on the next launch) the only other description about the curve is that it was enough that it did not reach sufficient altitude so that ejection happened as rocket was plummeting down. On the first three the deployment came at a point where I could barely see it but pretty sure higher.

[kjohnson]

Probabaly. When you picked trajectroy 2, that's what I would expect any rocket to do when flown in a pretty low wind. The fins of the rocket get pushed "down wind" while the nose points into the wind. You'll find that you don't want to point the model into the breeze, as that makes things worse. A vertical rod/rail, and an angle slightly downwind will get your flights looking more straight up.

kj

[CPUTommy]

Again, Someone proves to me, just how stupid I really am.. That totally makes sense now and would explain a few launches we had that left everyone scratching there heads..

:-)

Tom

[Atlasboy]

Well you guys are amazing. Thanks so much. So here is the plan. I will videotape for sure. I'll use the new steel rod, use only a sleeve of the cap or tape to hold the ignitor, use rocks, weights or tent spikes on the Mantis and let her rip. I'll hold onto the nozzle and take pictures just in case it is the "bad batch of plastic" scenario. With that data, I suppose the answer will be certain. I'm just hoping you guys don't see me do something stupid in the video --- that would sure be embarrassing after all the help you've offered.

Can't thank you enough. What a great resource for a newcomer.

I did not end up flying late afternoon/evening. About 15 mph so I didn't want that to be a factor. I'll update when I get a good time to go. Thanks.

[rifleshooter]

Mantis Dance is when the rocket takes off and the Mantis pad and rod flexes and the legs can lift off the ground. The rocket moves up the rod, but depending upon the wind and exactly where the rod/pad/rocket are pointing as it leaves the rod and any rotational velocity imparted to the rocket as it leaves the rod, it might fly in a strange direction.

I suggest always using a 6 foot long steel rod with a Mantis and put weights on all 4 legs to minimize dancing.

Isn't this simply called "rod whip," which is a problem with wind?

[Nerull]

Isn't this simply called "rod whip," which is a problem with wind?

Yes, and no. What he described is rod whip. The Mantis Dance is what happens when you get rod whip on a mantis pad that isn't staked/weighted down - one side of the pad actually lifts off the ground, and the pad 'dances'.

Rod whip isn't really wind related, though. Thrust from the rocket motor combined with drag from the launch lug creates a torque force on the rod, flexing it. If the rod rebounds back at just the wrong moment, it 'throws' the end of the rocket, sending it wildly off course.

[Atlasboy]

Looked like a good flight to me. Sorry the video isn't that great. But not much curvature. Had to take a hike to get it but looked pretty good. How does the nozzle look?

[Rex R]

can't watch the video, I don't do facebook.
rex

[Atlasboy]

ah okay. I'll post it on youtube in a sec. Probably won't help --- I was way too close. But it looked pretty good to my novice eye.

Here it is Rex: http://www.youtube.com/watch?v=DZ_Ls...ature=youtu.be

Nozzle looks fine, right? I don't see any weird grooves, etc.