Couple More Questions on my 4" LOC Goblin Build for L1

[Stargeezer]

I already epoxied the motor can into the body tube. Is it going to be hard to install my rail buttons now?

Also...is there a suggested shock cord protector for this particular model?

ALSO...is there a good video showing how to fold my recovery system with nomex blanket and tuck it into body tube?

 

[thzero]

Well loc sells shock chord protectors for those nylon shock chords.

Basically a burrito. Fold the parachute then place it in middle of protector and fold one side, then another over the top, then the two ends.

 

[waltr]

I like having a extra piece of wood glued on the rear CR to mount rail button.
The fins/CRs are 1/4" thick so one can drill into the rear CR then tap the hole (and harden with thin CA).

Here is a photo of how I prep the recovery system.
1st shows connections and the chute before rolled into Nomex.
2nd has the chute burrito rolled. Note the nylon cord braiding. This help dissipate energy and reduces shock forces and possible zippering. The 2nd Nomex is to protect the Nylon cord.
Note the nose attachment. Never trust the plastic nose loops. I
nstead drill holes in nose and tie a piece of Kevlar through.

 

[Tim51]

I already epoxied the motor can into the body tube. Is it going to be hard to install my rail buttons now?

With a bit of careful measuring and maybe a small pilot hole it should be possible to locate where the CRs are located inside the airframe. Failing that, use Acme conformal rail guides (which don't require any drilling) bonded with JB Weld.

 

[Scott_650]

Or just drill the body tube, use a dab of epoxy or gel-style CA and screw in the rail buttons. I have multiple flights on various rockets done that way. It’s not ideal and I always check the buttons before a launch but it works.

 

[Stargeezer]

I like having a extra piece of wood glued on the rear CR to mount rail button.
The fins/CRs are 1/4" thick so one can drill into the rear CR then tap the hole (and harden with thin CA).

Here is a photo of how I prep the recovery system.
1st shows connections and the chute before rolled into Nomex.
2nd has the chute burrito rolled. Note the nylon cord braiding. This help dissipate energy and reduces shock forces and possible zippering. The 2nd Nomex is to protect the Nylon cord.
Note the nose attachment. Never trust the plastic nose loops. I
nstead drill holes in nose and tie a piece of Kevlar through.

Oh wow, would you then suggest two blankets?

And you're saying I can just drill into the FWD and AFT ring and epoxy the buttons in there?

 

[David Schwantz]

The glue will harden the holes to give the threads a better bite.

 

[David Schwantz]

Kind of looks like he uses a 2nd blanket for just the cord. Nice thing about this hobby is no one is ever wrong, so many ways of doing the same thing.

 

[waltr]

Kind of looks like he uses a 2nd blanket for just the cord. Nice thing about this hobby is no one is ever wrong, so many ways of doing the same thing.

Yes, 2nd Nomex is just to protect the nylon cord. There is heavy Kevlar from the CR anchor to the swivel. A Nomex sleeve would also work. This is the configuration used when this Goblin flew for my L1 cert.

Another point: Be sure to use a full ejection charge of at least 1.4gram BP. More is ok and one could go to 1.8gram BP. A 4" tube and length has a pretty big volume so needs a good BP charge. It is worth while to empty the ejection charge from a DNS motor and ensure there is enough and add more if not.

 

[Stargeezer]

Yes, 2nd Nomex is just to protect the nylon cord. There is heavy Kevlar from the CR anchor to the swivel. A Nomex sleeve would also work. This is the configuration used when this Goblin flew for my L1 cert.

Another point: Be sure to use a full ejection charge of at least 1.4gram BP. More is ok and one could go to 1.8gram BP. A 4" tube and length has a pretty big volume so needs a good BP charge. It is worth while to empty the ejection charge from a DNS motor and ensure there is enough and add more if not.

This is probably a dumb question, but how do I set the ejection charge? And I'm still uncertain how I determine what delay I need? I'm trying to run OR and as mentioned the program glitches out on me and almost keeps duplicating pages and buttons disappearing...it's a mess. What was the name of the other SIM program everyone uses?

 

[waltr]

This is probably a dumb question, but how do I set the ejection charge?

On Reloads this is easy. Simply measure to BP that will be put into the charge well of the reload.
On DMS also easy. Pull the plug carefully out of the motor. Then carefully dump out the BP and measure how much is there. Add more if needed then put BP back into motor and insert plug.
This can also be done on most AT single use motors.

 

[Stargeezer]

On Reloads this is easy. Simply measure to BP that will be put into the charge well of the reload.
On DMS also easy. Pull the plug carefully out of the motor. Then carefully dump out the BP and measure how much is there. Add more if needed then put BP back into motor and insert plug.
This can also be done on most AT single use motors.

I think a lot of my problem is all the acronyms everyone keeps using lol.

 

[David Schwantz]

waltr, I think he is asking how do I "guess" what length of delay I need.

 

[David Schwantz]

I use Rocksim from Apogee Components. But you have to buy it. I have not used OR, so maybe someone else can help there.

 

[David Schwantz]

BP = black powder
DMS = disposable motor system
AT = Aerotech
MMT = motor mount
CR = centering ring
NC = nose cone
CA = super glue

 

[Stargeezer]

I am a she lol, and no I'm not asking how you "guess"...I know there's a way to know for sure and I'd like to learn how to determine that.

 

[thzero]

This is probably a dumb question, but how do I set the ejection charge? And I'm still uncertain how I determine what delay I need? I'm trying to run OR and as mentioned the program glitches out on me and almost keeps duplicating pages and buttons disappearing...it's a mess. What was the name of the other SIM program everyone uses?

OR will predict an Optimum Delay on the flight simulations. Assuming your weight in and CG in OR are correct and match your actual rocket, and you've tweaked the start altitude, etc. then it should get a reasonable estimation.



These are excellent things to be practicing with a MPR build/rocket launches - i.e. being able to judge the delay, being able to adjust delay on an RMS or DMS motor, etc.

Should also ask for help from the club/mentor you are planning to fly at. There should be experienced folks who can help show you how to adjust delay and even probably have tools to help with it.

OR isn't a mess, sounds like its an environment/hardware issue. Go to the https://www.rocketryforum.com/forums/rocketry-electronics-software.36/ thread and ask if you haven't already, also OR has a Discord server that many folks are on and are willing to help with issues.

 

[thzero]

https://www.rocketryworks.com/content/PDF/DMS Delay Adjustment Instructions.pdfhttps://aerotech-rocketry.com/products/product_d208be9f-32da-778d-77e9-093c84bb0508 (tools)
https://aerotech-rocketry.com/products/product_dc42d26a-c119-36bd-7642-85cb913cc1d5 (tools)
https://www.rocketryworks.com/content/PDF/RMS-29 - 60-180 Motor Instructions.pdf
Some quick references I found googling "dms adjust ejection charge aerotech". usually this should be in instructions in your motor package.

 

[Stargeezer]

OR will predict an Optimum Delay on the flight simulations. Assuming your weight in and CG in OR are correct and match your actual rocket, and you've tweaked the start altitude, etc. then it should get a reasonable estimation.

View attachment 626954

These are excellent things to be practicing with a MPR build/rocket launches - i.e. being able to judge the delay, being able to adjust delay on an RMS or DMS motor, etc.

Should also ask for help from the club/mentor you are planning to fly at. There should be experienced folks who can help show you how to adjust delay and even probably have tools to help with it.

OR isn't a mess, sounds like its an environment/hardware issue. Go to the https://www.rocketryforum.com/forums/rocketry-electronics-software.36/ thread and ask if you haven't already, also OR has a Discord server that many folks are on and are willing to help with issues.

Another noob question...is there any harm in NOT drilling and setting perfect delay and ejection charge etc.? Say if I were to just use the H115DM-14A and just fly it as is would the rocket do its thing?

And let's say my SIM is stating an optimum delay of 5.89 seconds.....I need to drill down from 14 seconds all the way down to the 5.89 suggested?

 

[thzero]

Another noob question...Is there any harm in NOT drilling and setting perfect delay and ejection charge etc.? Say if I were to just use the H115DM-14A and just fly it as is would the rocket do its thing?

Well that is a 14 second delay. So if your flight is relatively short then that could cause the flight to terminate with a ground impact, or if cause the parachute to come out at a high rate of speed causing a crash or a zipper (i.e. shock chord tearing the rocket body). All of which would cause a level flight to fail

 

[Stargeezer]

Well that is a 14 second delay. So if your flight is relatively short then that could cause the flight to terminate with a ground impact, or if cause the parachute to come out at a high rate of speed causing a crash or a zipper (i.e. shock chord tearing the rocket body). All of which would cause a level flight to fail

Will there be people at the launch to help me learn how to properly drill my motor and set the delay etc.? Or do they just expect you to be able to do that before going?

 

[tsmith1315]

And let's say my SIM is stating an optimum delay of 5.89 seconds.....I need to drill down from 14 seconds all the way down to the 5.89 suggested?

Drill 1/32” per second needed to shorten the delay. To shorten from 14 to 10 seconds, remove 4 seconds. That is, drill 4/32” (aka 1/8”) into the delay element.

There is an AeroTech tool to guide you in doing this, available from your dealer. I use a 1/4” drill bit at times, as well.

Keep in mind that precision in the pyrotechnic delay is limited to +/- a couple of seconds. No need for decimals. From ThrustCurve:



Hang loose and let the OR experts help you get it running, then you can feel confident in your estimation.

 

[thzero]

Will there be people at the launch to help me learn how to properly drill my motor and set the delay etc.? Or do they just expect you to be able to do that before going?

No idea - you'd have to reach out to the club that is running the launch. And/or attend club meetings (not all clubs have them). Talk to the RSO and the person that is going to be signing off on the flight.

 

[Rondaview]

This has mostly already been answered but I'll chime in anyway as I used the same kit for my level 1 a few years ago.

An H motor is on the small side for this rocket and leaving the delay at 14 seconds will make for an overly "exciting" flight. If it doesn't hit the ground before the delay charge fires it will be darn close and it will likely damage the rocket.

If you can't get OR to work you can almost always find a simulation on a website that helps with these types of things. Thrustcurve,org has tons of motor information and for a LOC kit it will almost certainly have someone else who has sim'd it and can give you a good approximation for the delay. I know for certain that the 4" goblin is in there. Even if you can't find an exact match for your rocket you can almost always find something close using a diameter and weight approximation that will get you in the right ballpark for a good delay. As was also noted, the delay for a short flight like this doesn't have to be particularly accurate as your rocket will spend a few seconds at or near apogee and as long as you don't have a fragile rocket (aka build it right and pack the chute correctly) it should be able to fall quite a distance before you get a zipper. Especially with a relatively short fat rocket like your Goblin it takes a while in freefall to get to terminal velocity and even at max ballistic speed it isn't going that fast. To be clear , it's fast enough to be dangerous and you don't want it coming in ballistic but it's not going to act like a minimum diameter lawn dart. I try to go a little longer than optimal for the delay so my rocket doesn't get "cheated" out of some of the flight but that's just my preference.

While most public/club launches will have people who will be willing to help you work through the details of building a motor and figuring out typical delay and charge configuration in real time, most of them are there to fly their own rockets so helping you with the basics that you should be able to handle with some on-line research is probably not their highest priority. You should do everything you can to research what information is out there before you show up at the field. The Level 1 certification flight is supposed to be your opportunity to demonstrate that you understand the basics and can be trusted to do it without help once you have your certification so take that as a challenge and be prepared to demonstrate those skills.

There is also a lot to be said for spending time with smaller rockets until you have the basics. While flying that Goblin is cool you can get a lot of good experience flying D through F motors on something that doesn't have the downside consequences if you make a rookie mistake. There is a reason why the Estes Der Big Red Max or similar mid-power rockets are so popular. They are cheaper to build and fly and if you know what you are doing you can modify that kit to go a lot of different directions in the hobby. LOC makes great rockets and I love my Goblin but I also have been flying mostly mid power stuff since my certification several years ago and I am still learning a ton about the physics and process of flying rockets.

Good luck.

 

[mcderek]

Will there be people at the launch to help me learn how to properly drill my motor and set the delay etc.? Or do they just expect you to be able to do that before going?

The expectation for a Level 1 cert flight is that you can demonstrate how to do it if asked. Since you plan on using a single use motor I would expect to be asked how you set the delay and the rational for that decision. An answer like "the sim predicts x altitude and a delay of x seconds. I drilled the delay to this setting" should be fine.
And yes you should drill the delay from 14 seconds to whatever is predicted. A long delay increases the chance of a zipper which if bad enough would fail the cert flight.

 

[Stargeezer]

The expectation for a Level 1 cert flight is that you can demonstrate how to do it if asked. Since you plan on using a single use motor I would expect to be asked how you set the delay and the rational for that decision. An answer like "the sim predicts x altitude and a delay of x seconds. I drilled the delay to this setting" should be fine.
And yes you should drill the delay from 14 seconds to whatever is predicted. A long delay increases the chance of a zipper which if bad enough would fail the cert flight.

Derek I guess my main question is...in OR if I use the H195T it states the optimum delay should be 6.79 seconds. Does that mean I need to drill the motor down to around 7 seconds?

OR says an altitude of around 1300 feet with an optimum delay of 6.79 seconds if I'm doing it right.

 

[mcderek]

Derek I guess my main question is...in OR if I use the H195T it states the optimum delay should be 6.79 seconds. Does that mean I need to drill the motor down to around 8 seconds?

OR says an altitude of around 1300 feet with an optimum delay of 6.79 seconds if I'm doing it right.

You drill it to the closest set value you can. If it is 8 seconds then that's it. Once you are familiar with the tool you can get a bit closer by using the next deeper setting but only going a half turn or so. Then it's slightly shorter than 8 seconds. I wouldn't worry about that at first though. Within a second should be fine.