Strange incident with Estes D12-3 driven rocket

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OZ1SEJ

OZ1SEJ

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I built a model rocket, weight 250 grams, 54 mm in outer diameter and roughly 500 mm in length, with 3D-printed nosecone and motor mount, 2 mm ABS plastic. I've launched this rocket four or five times before, and it always flew straight up. This day, it was absolutely quiet - there was no wind. You can see the flight here:

[video=youtube;L5RiG9K0sik]https://www.youtube.com/watch?v=L5RiG9K0sik[/video]

(For scale, the distance to the yellow building in the background is roughly 100 meters.)

To me, it looks like a considerable torque is working on the rocket approximately from the time it leaves the launch rod. Thank goodness it took to the lake and not the opposite way :shock:

I've launched this rocket four or five times before, and on this day, there was no visible damage or wear to the motor mount.

Unfortunately, the rocket ended up in the lake, so I've had no opportunity to perform a postflight analysis.

The only positive thing about this flight was that the parachute deployed nicely four meters above the water.

Has anyone ever seen anything like this before? To me, it looks like an asymmetric thrust issue, but I would like to hear your comments.

Best regards,
Steen
 
It's an Estes Porta Pad, so the launch rod is 1/8 in. or 3.2 mm in diameter.
 
Is the all-up weight 250g or is that the weight without a motor? If it’s 295-ish grams loaded you’re already over the total launch weight for a D-12 so a slow burning motor plus rod whip could give you an erratic flight. One way to check would be if you still have a D-12 from the same pack and a heavier/longer launch rod so you could try another launch.
 
at 250g you should be using a rod at least 4.76mm in diameter. to answer your original question, yes I have seen that sort of behavior before associated with rod whip. heavy rocket (with perhaps a smidge of lug bind) goes up the rod, under load the rod bends, as the lugs clear the rod it straightens out giving the rocket a kick in the nether regions and it goes in an odd direction. to combat this you need a stiffer launch guide.
Rex
 
Check the burn pattern on the nozzle.

I’ve had similar odd results with a regularly stable flyer and the burn pattern looked like the nozzle/motor provided a canted thrust - the scorch pattern was a line across one side of the nozzle.

That might have been your issue?


Sent from my iPhone using Rocketry Forum
 
>250g rocket on a D12 with a ~1 meter long 3mm rod is certainly a recipe for rod whip and unpredictable launch angles. Estes would typically recommend using at least a 3/16" rod for D engines and above, and *especially* with a rocket that heavy.

You need a heavier and preferably longer launch rod.
 
For those of you asking him to check various things about the rocket or motor, it is in a lake. No can do.

Steen, welcome to the forums. Look like you have your answer.
 
Very nice to hear from the European rocketeers on this forum. This one is quite a puzzle: 4 or 5 straight flights then this one on a windless day and the evidence ending up at the bottom of the lake. What motor(s) was used on the previous flights ? Was the same launch pad used ? Where was the flight-ready cg (balance point) of the model ? What was the fin span (distance from root to tip) ?

I want to say it was a little nose-heavy but I can't account for the previous successful flights. We may need another prototype to get to the bottom of this.
 
I just want to follow up on my own note. There's no way to know *exactly* what happened on that flight. The motor could have had asymmetric thrust, who knows. Rod whip might not have caused it. But either way it would simply be better and safer practice to use a heavier rod for launching a rocket like that.
 
It sounds, judging from the posts by others more experienced than I, like rod whip is the most likely culprit. That could be caused by a little schmutz on the rod or inside the lug that wasn't there on the previous flights.

But, if you'd like to flog this dead horse a bit more, do you have a RockSim, OpenRocket, or other design file for the rocket? If so, has it been tweaked with actual weight and CG from before the final, fatal flight? Is the lake shallow and clear enough to attempt recovery of the rocket come summer? (The nozzle burn pattern might still be visible, and in any case the plastic parts could be reused.)

But that's probably overthinking it. A lot.
 
jqavins said:
It sounds, judging from the posts by others more experienced than I, like rod whip is the most likely culprit. That could be caused by a little schmutz on the rod or inside the lug that wasn't there on the previous flights.
.
Click to expand...

I agree - I've had the same kind of rod whip on the same rocket on the same day after 3-4 launches. Crud (don't really know what shcmutz is?) from the engine burns get on the rod and causes stickyness. I wipe my (launch) rod w a dry cloth most every launch, if I can remember.

I also put oversized lugs on most rockets - I can use just 1 launch pad that way.

I think you should take up scuba diving! LOL

Pat
 
Presuming that the rocket has some buoyancy, I'd go and check around the edges of the lake and see if it blew into shore. If someone has already found it, I hope it has ID for you to be contacted to get reunited with it.

Oh, and Welcome to the Goldfish Club!
 
Our club keeps steel wool at the pads for rod cleaning. Also I keep waxed paper in my range box to give the rod a final slicking up (tip originally from Hornet Driver I believe)
 
OZ1SEJ said:
I built a model rocket, weight 250 grams, 54 mm in outer diameter and roughly 500 mm in length, with 3D-printed nosecone and motor mount, 2 mm ABS plastic. I've launched this rocket four or five times before, and it always flew straight up. This day, it was absolutely quiet - there was no wind. You can see the flight here:

[video=youtube;L5RiG9K0sik]https://www.youtube.com/watch?v=L5RiG9K0sik[/video]

(For scale, the distance to the yellow building in the background is roughly 100 meters.)

To me, it looks like a considerable torque is working on the rocket approximately from the time it leaves the launch rod. Thank goodness it took to the lake and not the opposite way :shock:

I've launched this rocket four or five times before, and on this day, there was no visible damage or wear to the motor mount.

Unfortunately, the rocket ended up in the lake, so I've had no opportunity to perform a postflight analysis.

The only positive thing about this flight was that the parachute deployed nicely four meters above the water.

Has anyone ever seen anything like this before? To me, it looks like an asymmetric thrust issue, but I would like to hear your comments.

Best regards,
Steen
Click to expand...

frame by frame shows some definite thrust vectoring (maybe a whole degree), though what it was caused by is anyone's guess. And the fins were just a bit small to mitigate it. Probably not rod-whip this time, however it should have a thicker rod, but mainly a longer one. Manufacturing variations can cause the initial thrust spike to vary a significant amount, so you may have flown it on a motor with a weak spike that didn't get it up to speed as fast as the previous flights. The mass and diameter of the rocket put it near-but not over the edge for the D12.
 
I guess we will never really know what happened. Because I once saw a rocket (a friend's beautiful Estes Maxi-Brute V-2, incredible camouflage paint pattern) fly almost horizontally because of rod-whip, I always launch everything size A-C on minimum 3/16" rod (so, that would be about 4.8mm), and would use a 1/4" rod (about 6.3mm) rod on D engines and up, with a rail once I get to F and above.

It looks like it started arcing toward the lake immediately...not sure if it got hung up on the rail, or there was something wrong with the engine. This is another reason why I don't launch straight up, I always try to aim it a couple degrees down range, so if something goes wrong with the parachute deployment, I have a pretty good chance it will land in a safe area. No guarantees, but I try to make sure risk is minimized.

Sorry you lost the rocket!
 
snrkl said:
Check the burn pattern on the nozzle.

I’ve had similar odd results with a regularly stable flyer and the burn pattern looked like the nozzle/motor provided a canted thrust - the scorch pattern was a line across one side of the nozzle.

That might have been your issue?


Sent from my iPhone using Rocketry Forum
Click to expand...

Of course, I couldn't be sure, but I'd bet something like this is the culprit. No way to check if the motor is lost. But I've had a number of Quest BP motors that flew really oddly, and the nozzle was oddly burned, as though the thrust came out at an angle.

Not sure why that would be, but it seemed to be a whole set of B motors (of which I only had two - a friend gave them to me to try. He flew a bunch of them and they all behaved oddly like that).
 

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