In the second video, the combination of not seeing the rocket in the camera view, and then seeing the shadow of the rocket head off in a different direction just about turned my brain to mush. I do look forward to seeing how you mounted the camera.
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The idea was to have only the lens on the outside of the body with a way to turn on and off the camera from the outside. A small circular sled did the trick. The camera was just pressed against the body tube with cutouts for the on/off and run buttons along with a means to see the status light - so three cutouts altogether.
The lens was fed down to the cutout in the plastic transition and then pushed into the CA'd balsa mount to hold it in position. Somewhere along the way one side of the mount broke off. The arrangement with the sled was also cumbersome, so some re-engineering will take place before the next launch.
The view from the camera was a bit of a guess. Next time the body and fins will be visible to give some proper perspective.
The F15/D12 combination was marginal in the 10kt+ wind. So we will attempt using composite motors for the next flight. Maybe F25W/D13W.
Just a warning- AT motors, especially white, green, and maybe one other "flavor", are VERY hard to light. If you have a bit of cash to throw at this project and/or some way to get around HAZMAT (e.g. some clubs do group orders, CRMRC does it through Wildman) I'd highly recommend CTI. If not, Blue Thunder is marginally easier to light.
This is a really cool project BTW... Are you sure you're not me in an alternate universe? When you started this I was in the process of building both a Ventris and a rocket with drop-away boosters.
The Ventris has flown successfully, but the SRB style rocket hasn't- Both got a taste of my inner idiot: The booster rocket's core was lost on a solo flight while I managed to pop off a fin on the Ventris while trying to get a stubborn F26 out. Both have been repaired.
With a plethora of motors in the stockpile , there are a number of combinations I could try. A 24mm CTI G65 and two E31s could work. But cannibalizing an Aerotech D24 for some of those blue thunder pellets could be just the trick on "slow" starting Aerotech loads.
Can someone explain how to use a chunk of fast burning propellant to assure quick lighting?
I've only heard of people taping chunks of it to the igniter for Larger motors. Not sure itd work for the little ones (not to mention increased risk if overpressure).
Looking forward hearing from this who've tried it
I would say that if you have CTI you should use them. I would recommend against a G65 in the core though- it's a moonburner so it hits hard off the pad and might outrun your outboards.With a plethora of motors in the stockpile , there are a number of combinations I could try. A 24mm CTI G65 and two E31s could work. But cannibalizing an Aerotech D24 for some of those blue thunder pellets could be just the trick on "slow" starting Aerotech loads.
Can someone explain how to use a chunk of fast burning propellant to assure quick lighting?
All I know is that AT typically has a few seconds of "warm up" time while CTI lights right on cue because of the starter pellet. I don't have enough experience to know how consistent AT ignition times are but I'm guessing it's less reliable than CTI.First off great build, congrats on the flights. Hopefully you can mount the camera to see the boosters fall off?
Regarding the composite engines and tri-core:
The challenge isn't igniting the motors at all so much as igniting the motors at the same time. I've been planning a Falcon Heavy scale build and have been worried about this problem, and intend to address it by using a high amp 12V firing system on black powder motors.
With the design of fall away boosters, it can be pretty critical that the thrust curves of all the motors are as in synch as possible. This is all dependent on how punchy the motor is at lift off, and the thrust to weight ratios of your components. The Estes D12 & E9's I was planning to use all have a very big spike just past ignition before they level off. My concern was that if one motor is a little late to fully ignite to thrust one of two scenarios can happen: The Core comes up to thrust late and outruns the boosters, OR one booster is a little late and then pushes it and the core away from the second booster.
I created an excel model to simulate this, with D12's on 141 gram boosters and a E9 in the 259 gram core and found my acceptable variance was 0.4 and 0.2 seconds. Apogee put out a report on igniter firing times that lists measured deviation limits between igniters that is really helpful, and shows that that deviation limit is a lot more than the igniter itself, but doesn't tell me what the actual motor response is. I don't assume that the igniter firing actually means full thrust at that instance.
With a heavier core this model is a lot more forgiving, and the flatter the thrust curve of the motor particularly just past ignition the better.
Now I haven't yet had any experience firing composite motors, but from video's I've seen there appears to be a pretty big delay between when the all fire current hits the igniter and when the motor actually comes up to thrust. The randomness of that delay is something that may be an issue to you.
Anyone have any thoughts on the time delay on composite motors? I'm looking for this data myself to determine how I do some builds in the future.
Thanks for the input on motor selection. Here are a few factors that are being weighed:
- The Ventris is a lightweight cardboard rocket that is designed for up to one G80 (80 Ns total). The F15/D12 combo was 67 Ns.
- 2800' is maximum desired altitude.
- Higher booster initial thrust compared to main assures they stay on at launch.
- The objective is to have the boosters drop away at least a second before main engine burnout.
- LUNAR and TCC launch systems are strong and reliable. A three way clip whip provides equal energy to the igniters.
- The longest 10/10 rail is used to give the most time for all motors to come up to pressure.
Not many options on hand for CTI loads so AT will likely be the choice. Given that, what is the best way to assure a quick light. Black powder and compositor motors can be scavenged for material to add on top of the igniter. What is best, how much and how to attach it?
Third flight of the Ventris SRB, this time with the 808 camera taped to the booster tube, a G25W central motor with two E28T's in the boosters.
[video]https://youtu.be/kOFzvbrGleg[/video]
Post-flight analysis showed the G25 igniter never burned. Did the E28 Copperheads light faster than the G25 Firstfire? Wouldn't the Firstfire still have lit even if it was pulled out of the motor at liftoff?
Interesting that there was enough pressure to keep the boosters on even after the chutes came out. Saved the rocket from a terminal dive but broke a fin with the hard landing.
Steve, thanks for the lead on Boris Katan.
I like this. If at cluster ignition, a booster lights a bit late, does the rest of the rocket depart without it?Booster rail design included sections of Plaststruct 3/16 inch H column.
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Two pieces were epoxied to the booster with a gap wide enough to accommodate the third rail attached to the main rocket body.
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A small piece was glued on the end as a stop - at the top on the main rocket body and the bottom of the SRB as a back up if the top one failed.
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The booster then slid on the main rocket body until it hit the stop. With a bit of sanding on the inside of the rails, the boosters would just fall off when everything was upright.
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