Aerotech DMS J270W

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crossfire

crossfire

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I purchased one of the AT DMS J-270s and was just wondering how flyers who have used the motor feel about it. And that rocket flyers have used to fly the motor. Will it fly ok with in a 8lb rocket?
 
Gary,

That's the motor we flew in the Super Jart. I would recommend adding a bit of glue to the factory installed thrust ring. Mine pulled off and the motor pushed up into the rocket, melting off my Aeropack. Otherwise, great flight. I'm sure it will be fin in an 8 pounder.....won't go very high.
 
crossfire said:
I purchased one of the AT DMS J-270s and was just wondering how flyers who have used the motor feel about it. And that rocket flyers have used to fly the motor. Will it fly ok with in a 8lb rocket?
Click to expand...

I flew one in a 7 pound rocket at LDRS. It was ultra draggy, so it only went around 2k feet.
 
Why did you buy one if you weren't sure?
Are you even L1?
A L2 flyer should know enough to; figure out how to calculate if it is safe or not.....

JD


crossfire said:
I purchased one of the AT DMS J-270s and was just wondering how flyers who have used the motor feel about it. And that rocket flyers have used to fly the motor. Will it fly ok with in a 8lb rocket?
Click to expand...
 
GRIFFIN said:
Gary,

That's the motor we flew in the Super Jart. I would recommend adding a bit of glue to the factory installed thrust ring. Mine pulled off and the motor pushed up into the rocket, melting off my Aeropack. Otherwise, great flight. I'm sure it will be fin in an 8 pounder.....won't go very high.
Click to expand...
Use masking tape for a thrust ring. I've seen the glued on ones fail by separation within the layers of paper. 1/2" wide tape will withstand an average thrust of 700N.
 
Rocketjunkie said:
Use masking tape for a thrust ring. I've seen the glued on ones fail by separation within the layers of paper. 1/2" wide tape will withstand an average thrust of 700N.
Click to expand...

The one I flew had a pre-glued-on short FWFG section for a thrust ring.
 
I saw CarVac's flight; it was pretty nice. It seemed like it would make a great motor for a 38mm MD, but I know not everyone is performance-centered like I am. It was slow and loud and bright and wonderful. (sorry it's dark-the auto-prossing script I used didn't do a great job and I haven't taken the time to fix it yet.)
9868767006_1879f9062d_b.jpg
 
T-Rex said:
I'm considering using one for my L2 in a 7lb draggy rocket....
Click to expand...

Heh, that's a pretty accurate description of my rocket in the above photo. It only went 1750 feet on that flight. (I just looked up the data file from the Raven)
 
Last edited:
JDcluster said:
Why did you buy one if you weren't sure?
Are you even L1?
A L2 flyer should know enough to; figure out how to calculate if it is safe or not.....

JD
Click to expand...

We sure can be a rough group sometimes....
 
CarVac said:
Heh, that's a pretty accurate description of my rocket in the above photo. It only went 1750 feet on that flight. (I just looked up the data file from the Raven)
Click to expand...
The only J270 in the OR data base says a Warlock should reach 2000ft. My original thought was in the 3" Starship Vega, but it violates our 2500ft waiver.
 
T-Rex said:
The only J270 in the OR data base says a Warlock should reach 2000ft. My original thought was in the 3" Starship Vega, but it violates our 2500ft waiver.
Click to expand...

Then you need more drag. Upward Propensity is only 4 inch diameter and 3.5 feet long.
 
I’m getting about 5,300 ft in a Wildman Sandhawk sim. Mach 0.89. I’ll L-2 after I graduate college. Just shopping motor sales right now. Thanks.
 
It's a single use version of the J350 reload, probably the most popular L2 cert motor. After you graduate, you can build a bigger rocket (with 54mm mount so you can fly bigger motors. I consider L2 the sweet spot and it also allows research motor making with Tripoli.
 
crossfire said:
I purchased one of the AT DMS J-270s and was just wondering how flyers who have used the motor feel about it. And that rocket flyers have used to fly the motor. Will it fly ok with in a 8lb rocket?
Click to expand...
I have used the DMS J-270 on at least three occasions. The flights were great with this motor. Unfortunately, the last flight ended up as a ballistic return because the ejection cap failed to pop out, resulting in the ejection gases being expelled back through the motor and out the nozzle. A deployment event was observed at apogee. However, on examining the remains after recovery, the ejection cap was still welded into the top of the charge well. I suspect that the issue here might be the fact that the recommended installation of the ejection cap is to install it dome end first, as shown in the image from the AT instructions. I believe that installing it this way, rather than dome end out, might cause it to jam.

upload_2018-9-3_13-10-29.png
 
Interesting theory, I’ve only flown one H219T-14A DMS so far, and the cap was installed dome side down. Mine also had a washer installed and worked as advertised.
 
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4256.png
I just got my L2 cert. Saturday on the J270. It was an awesome flight to 2700' in a 4" diameter, 7' tall, 7.5# rocket.
 
Since then I have odopted the practice of not using the supplied caps, but using dog barf and masking tape to secure the charge instead. I have never had a failure that way.
 
Voyager1 said:
I have used the DMS J-270 on at least three occasions. The flights were great with this motor. Unfortunately, the last flight ended up as a ballistic return because the ejection cap failed to pop out, resulting in the ejection gases being expelled back through the motor and out the nozzle. A deployment event was observed at apogee. However, on examining the remains after recovery, the ejection cap was still welded into the top of the charge well. I suspect that the issue here might be the fact that the recommended installation of the ejection cap is to install it dome end first, as shown in the image from the AT instructions. I believe that installing it this way, rather than dome end out, might cause it to jam.

View attachment 360808
Click to expand...

Did you happen to forget to use the metal washer in the ejection well. I flew a older K535 this year that had no metal washer with the motor. I was told by WM that the powder gets sucked out the nozzle end. I was using electronics was all worked out ok but was very surprised when taking motor out of the rocket and the red cap was still in the motor. The powder was gone. I was put dome side down first the ejection well.
 
I note in the general DMS instruction sheet from AT that these washers are mentioned, but they haven't been included in the DMS J-270 kits I've used. The PDFs below show the instructions in the supplied kits. You will note that there is no mention of a charge baffle washer in the "Package Contents" list, or in the instructions. I also have an unused K535 DMS which does not have a washer included, or mentioned in the instructions.
 

Attachments

  • DMS-1.pdf
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  • DMS-2.pdf
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How old are your motors? I was told by Wildman that all DMS motors now a have washer. I think AT even put out a post on the washer. I will not fly my last older K353 without a washer. Also I always push thr red plug in flush with yellow plastic part.
 
I have also seen ejection charges fail to blow out the cap when the metal washer is not used. That washer functions to keep powder and ejection charge pressure on the ejection well side of the motor.
Please turn in a MESS Report each time a motor fails, whether it’s a CATO, or a failure to eject, even if you think it’s your fault, because it can help the certification organizations understand when instructions have problems.
The current DMS instructions specifically instruct to add the washer and include a photograph showing the washer:
https://www.aerotech-rocketry.com/u...2_29-54mm DMS Instructions 12-29-15 Small.pdf
 
crossfire said:
How old are your motors? I was told by Wildman that all DMS motors now a have washer. I think AT even put out a post on the washer. I will not fly my last older K353 without a washer. Also I always push thr red plug in flush with yellow plastic part.
Click to expand...
The batch number on the K535 I have is 102215 which I believe is the date of manufacture, that is, 22 Oct 2015. Unfortunately, I don’t have the batch numbers for the J270s I have used.
 

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