Motor ejection timing

[Lt72884]

Ok, the LOC IV file from loc precision, using the exact motor i have purchased for my level 1(DMS-H550ST-14A), open rocket states optimum delay time is 10.9 seconds. The motor can only do 2 second intervals, so should i do 10 seconds or 12?

with this particular instance, is it better to be later or earlier (way to many jokes, and im trying to keep this place professional )
i have no real numbers to work off of for total apogee time, or i would have a better guess. My team members who launched their LOC iv's 2 weeks ago, some siad it took 10 seconds to apoge, some said 8 seconds, while another thought it was closer to 7.

thanks

 

[John_461]

H550T for your cert flight eh? Go big or go home I guess

Either 10 or 12 seconds will be fine. There is a 3-4 second window at apogee where your rocket is going slow enough to safely deploy the parachute.

Did your friends use H550s for their flights? An H550 (0.6 sec burn time) will require a longer delay than an H100 (2.3 sec burn time).

 

[T-Rex]

When my numbers come up like that, I will usually sim both and see which gives the slowest deployment. Since you are so close to the middle, in your case, as @John_461 stated, either, it probably won't matter much.

 

[tsmith1315]

Keep tolerance in mind when evaluating your simulations.

From the motor certification page at Thrustcurve.org:

• The total impulse must not have a standard deviation greater than 6.7%.
• The ejection delay must not vary more than 1.5 second or 20% (whichever is greater, up to 3s) from average.

 

[bobbyg23]

Ok, the LOC IV file from loc precision, using the exact motor i have purchased for my level 1(DMS-H550ST-14A), open rocket states optimum delay time is 10.9 seconds. The motor can only do 2 second intervals, so should i do 10 seconds or 12?

with this particular instance, is it better to be later or earlier (way to many jokes, and im trying to keep this place professional )
i have no real numbers to work off of for total apogee time, or i would have a better guess. My team members who launched their LOC iv's 2 weeks ago, some siad it took 10 seconds to apoge, some said 8 seconds, while another thought it was closer to 7.

thanks

12. A little late is better than early from my experience.

 

[Lt72884]

H550T for your cert flight eh? Go big or go home I guess

Either 10 or 12 seconds will be fine. There is a 3-4 second window at apogee where your rocket is going slow enough to safely deploy the parachute.

Did your friends use H550s for their flights? An H550 (0.6 sec burn time) will require a longer delay than an H100 (2.3 sec burn time).

yes, they used the exact same rocket kit and motors. One rocket zippered though when using 14 sec delay. about 8 inch zipper.

ill probably use 12 seconds

 

[Lt72884]

12. A little late is better than early from my experience.

ok, good to know. One teammate used 14 seconds and zippered the rocket about 8 inches

 

[bobbyg23]

ok, good to know. One teammate used 14 seconds and zippered the rocket about 8 inches

I remember the thread

 

[bobbyg23]

ok, good to know. One teammate used 14 seconds and zippered the rocket about 8 inches

Just a heads up, mine still sims at 9.6 seconds. I would go down to 10 to be safe.

 

[sriegel]

Watch the weather and wind, too. If the rockets are weathercocking strongly, you'll want to go with the shorter delay. Otherwise, you'll come over apogee sooner and have a longer downward coast picking up speed on the longer delay.

 

[Lt72884]

I remember the thread

meee tooo! haha. I learned alot from that thread.

 

[David Schwantz]

With your delay tool you can flip the washer over, remove washer, add another washer, add a thicker washer to get delays that are 1 second apart.

 

[mbeels]

With your delay tool you can flip the washer over, remove washer, add another washer, add a thicker washer to get delays that are 1 second apart.

Do I remember right? Is it 1/32" per second?

 

[John_461]

With your delay tool you can flip the washer over, remove washer, add another washer, add a thicker washer to get delays that are 1 second apart.

I've never even considered this. Definitely worth some experimenting.

 

[Steve Shannon]

Do I remember right? Is it 1/32" per second?

Yes, approximately.

 

[teepot]

I was going to say the same thing as David.

 

[Lt72884]

With your delay tool you can flip the washer over, remove washer, add another washer, add a thicker washer to get delays that are 1 second apart.

ok, so kinda like what i did for sugar rockets last year. 1/32 of an inch is a bout a second of time or something similar to that.

 

[Tractionengines]

My opinion is: A little early is better than late. Early means your rocket is decelerating and since you are before apogee the nose is still "up" (maybe arching, but still above horizontal). When the charge goes off "equal and opposite force" comes into play. The charge pushes the nose up and off; but also pushed the body down and away. Not likely to tangle or zipper. (Unless your WAY early, but that's a different story.)

A little late means you've arched over. The rocket is accelerating so every little bit of time means more wind force pushing the nose onto the body. Your charge need to push the nose out hard enough that is not only separates, but does so with enough force to pull the chute out. The other issue is your rocket pointing down. If you do push out the cordage and laundry: Your body tube is falling thru it as the parachute inflates, increasing the chance of entanglement.

I will try to find a video I have of a low-n-slow flight with a late deployment. The nose pops but that was it. (Nose blow type rocket, so not much inertia to pull anything out.) When I walked up and picked up the rocket, I tipped it nose down everything was loose enough it just slid out by gravity. The wind resistance was enough to keep it inside the body.

Mike

 

[strider07928]

After I zippered my rocket from too long a delay, a more experienced rocketeer suggested I create a ball of tape on the cord just inside the tube to keep the line from hitting the edge thus preventing a zipper. Thought it was a great idea. Been doing dual deploy on fiberglass rockets since then so haven’t had the need, but next time I launch with motor ejection I’ll definitely try it.

 

[Lt72884]

thanks guys. Todays launch for level 1 and 2 was sucessfull. The mentor on site had us do 12 seconds instead of 10. It felt a little late, but it worked. Next time i will try 10. I hit apogee way faster than open rocket suggested. But we were still successful for lvl 1 and 2.

 

[Lt72884]

After I zippered my rocket from too long a delay, a more experienced rocketeer suggested I create a ball of tape on the cord just inside the tube to keep the line from hitting the edge thus preventing a zipper. Thought it was a great idea. Been doing dual deploy on fiberglass rockets since then so haven’t had the need, but next time I launch with motor ejection I’ll definitely try it.

tape on the shock cord or paracord? i was going to put tape on the shock cord to make it wider and less chances of zippering but i did not do tht today.

 

[jimzcatz]

Do I remember right? Is it 1/32" per second?

Yes, you don't even need the delay tool. I never use them.

 

[Lord Rory Gin]

Ok, the LOC IV file from loc precision, using the exact motor i have purchased for my level 1(DMS-H550ST-14A), open rocket states optimum delay time is 10.9 seconds. The motor can only do 2 second intervals, so should i do 10 seconds or 12?

with this particular instance, is it better to be later or earlier (way to many jokes, and im trying to keep this place professional )
i have no real numbers to work off of for total apogee time, or i would have a better guess. My team members who launched their LOC iv's 2 weeks ago, some siad it took 10 seconds to apoge, some said 8 seconds, while another thought it was closer to 7.

thanks

Just me but I would set it for 10 sec. Slightly early is better than too late as the rocket will be decelerating. When I select delays I go with the delay closest to 1 second early or 0.2 seconds late in my tolerance. But like I said, that's just me. I once asked TvM if using a washer to get a more exact timing and he didn't think that it was necessary due to the variability with the delay burn itself. He said, try it, if it works for me then go for it. Also, when I looked beyond 29-38mm CTI motors and into the 54mm CTI motors, I found out that the user can select in 1 sec increments instead of 2 sec.

 

[waltr]

The AT delay adjustment tool comes with a 1/16 inch spacer which is 2 seconds. I made a 1/32" spacer from a piece of G10 so I can adjust within 1 second increments.
There is still the tolerance of the delay but feel better to adjust to closer to expected and have the tolerance go from there.

 

[rharshberger]

The AT delay adjustment tool comes with a 1/16 inch spacer which is 2 seconds. I made a 1/32" spacer from a piece of G10 so I can adjust within 1 second increments.
There is still the tolerance of the delay but feel better to adjust to closer to expected and have the tolerance go from there.

Adjusting as close as possible is my method as well, and I rarely have issues with delay times. Since I almost never seen a stop watch being run during flights most fliers dont have an accurate method of determining short or long delays.

 

[strider07928]

tape on the shock cord or paracord? i was going to put tape on the shock cord to make it wider and less chances of zippering but i did not do tht today.

Tape on the shock cord- make a ball at the mouth of the tube so the cord cannot zipper the frame.

 

[strider07928]

Yes, you don't even need the delay tool. I never use them.

Lol, I have two destroyed rockets that say otherwise

 

[jimzcatz]

You measured wrong.

 

[John Taylor]

yes, they used the exact same rocket kit and motors. One rocket zippered though when using 14 sec delay. about 8 inch zipper.

ill probably use 12 seconds

Have you used a simulation program?
If not try Thrustcurve.org
Free, fun, accurate, easy, and quick.

 

[Lt72884]

Have you used a simulation program?
If not try Thrustcurve.org
Free, fun, accurate, easy, and quick.

we did. We used thrustcurve and OR. But that team no longer exists. I am doing my L3 solo now. I have most of my stuff, just need time now haha