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John Ross

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New member John Ross here with my first post.

I was born in 1957 and started building model rockets in 1963, initially using Estes kits and components, and eventually, by the end of the decade, rockets with larger E and F motors from Flight Systems.

My dad had started teaching me woodworking skills when I was four years old, and model rocketry was a wonderful hobby to share with him until his death. In addition to being an amateur cabinetmaker, dad was also an experienced photographer, and with his help I took many photos with my Camroc, eventually some in color.

Dad got me a Cineroc when they first came out, and marveled at the footage we got. I still have it, and all the original packaging.

Dad also loved fireworks, and had displays on our hundred acre summer property on the Mississippi River 25 miles south of St. Louis. July 4 was my favorite holiday, even better than Christmas.

In August 1963, after I had been building and launching model rockets for several months, I was helping Dad set up a fireworks display for my cousin Katie's engagement party that evening, and I noticed him putting out some of the buzz bombs upside down. When I mentioned this, he considered for a moment, then said "By God, you're right. That's why some of them always just spin around on the ground. I never looked carefully enough." Then he held out the Bernz-O-Matic torch, and said "Make sure we've got everything set out right, then you light this show. I'll sit with the rest of the audience and watch."

I was thrilled.

After Dad died of pancreatic cancer in October of 1970, I pretty much stopped doing anything with model rocketry, but I kept shooting fireworks displays 1 to 3 times every year. I've now been doing that for over half a century.

In 2013 I sold my investment business to concentrate on writing as my profession, and spend more time on my other passions. I acquired the appropriate state and federal explosives licenses, dusted off my thermodynamics textbooks, and joined several fireworking forums. My main goal was to build rockets. Virtually no professional operators in this country use rockets in their public displays, so really good rockets are the one type of firework that is pretty much unavailable to buy in this country, regardless of what licenses you hold.

Before joining this forum, I pored through the rules, and could find no prohibition against talking about firework rockets. If I somehow missed such a rule, please delete this post, and I'll terminate my membership.

The reason I am making my first post to the forum in the Rocketry Electronics and Software section is that I own an Acme test stand, which records thrust and time data on the rocket motors I make, and will show predicted altitude data based on the total weight of the rocket. Thus, you can easily figure out what size ball or cylinder shell can be lifted to the desired height, and how many seconds of delay comp to use in the motor for the shell to explode at the rocket's apogee.

This brings me to the question I am posing today. Yesterday I downloaded the open source software OpenRocket. Unlike most rocket builders, I prefer to use fins instead of sticks, and launch my rockets out of large HDPE tubes. I felt that OpenRocket would be a much better tool than trial and error for determining stability levels of different fin dimensions for my rockets with various headings.

Getting OpenRocket to actually run on my computer took over an hour, and I still wish I had someone familiar with the program looking over my shoulder telling me how to do what I want. I have not been able to find a comprehensive "user's manual" to answer the two main questions that I have:

There is a large database of commercially available model rocket motors. Is there any way to create a database of homemade rocket motors, either using data acquired by my Acme test stand, or more crude methods that people have used, such as using video of kitchen scales to get an idea of duration and peak thrust?

If the moderators feel this post, and other discussions of homemade motors is not within the scope of this discussion forum, please delete it and accept my apologies for joining.

JR
 
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John Ross

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Here's a thrust curve for one of my most energetic small motors. This is what we call a "4 oz" skyrocket motor: 1/2" ID, 3/4" OD (19mm) and 5" (127mm) long. A weak "E" Class motor, but with enough thrust to put a 5" ball shell to a nice display height:
 

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neil_w

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Getting OpenRocket to actually run on my computer took over an hour
It sounds like you've gotten it to work. Did you try this? https://www.rocketryforum.com/threa...d-mac-to-solve-all-your-java-problems.143540/

I still wish I had someone familiar with the program looking over my shoulder telling me how to do what I want.
<raises hand>

First, there is a large database of commercially available model rocket motors. Is there any way to create a database of homemade rocket motors, either using data acquired by my Acme test stand, or more crude methods that people have used, such as using video of kitchen scales to get an idea of duration and peak thrust?
Adding your own motors is easy, provided you have the data in the form of an RSE or ENG file. The file formats are documented... somewhere. :) Examples can be found on thrustcurve.org. Basically, they give the key statistics of the motor along with a thrust curve.

Once you have a motor file in one of those formats, go into OpenRocket and open up Edit -> Preferences. In the General tab you'll see a way to specify the location of custom motor files:
1595170277569.png


Dump your motor files into that directory and you're good to go.

Second, building firework rockets is a simpler procedure than building a model rocket that is designed to be reused. Is there some way to set the program defaults where the fins are directly attached to the motor, and the "nose cone" is a cylinder or ball shell of known dimensions, weight, and CG, glued to the front end? Motor dimensions and CG would also be known.
Not exactly, but you can certainly create a minimal rocket that'll approximate what you're doing. That is, just a single body tube the size of the motor, with the ball in front. Set the wall thickness of the body tube to be zero, and it'll have zero mass. Attach the fins to that body tube.

Yes, if you swap in different motors with different dimensions, you'll need to change the dimensions of that body tube accordingly, and possibly the ball as well.

As for that ball, create it with two elements: First, an ellipsoid nose cone with length equal to half the diameter, followed by an ellipsoid transition, again with length equal to 1/2 diameter. This won't get you a perfect sphere, but should be close enough.

Attached is a sample file. Be sure to override mass of each component to match your measurements, or set the material and dimensions of the fins so it'll calculate correctly.

If the moderators feel this post, and other discussions of homemade motors is not within the scope of this discussion forum, please delete it and accept my apologies for joining.
Although we don't generally discuss fireworks here, I don't think there's anything wrong with discussing OpenRocket in this way.
 

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NateB

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Welcome to this forum too. I haven't been able to build those types of rockets in a while, but I'm glad you're getting them in the air.
 

John Ross

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Boy howdy, this looks like exactly what I was asking for!

I haven't opened the sample file yet, but will do so shortly.

Since you volunteered to be the guy standing over my shoulder at the computer, is the information in the screenshot of the thrust curve of my 4oz firework IBP (Insane Black Powder) motor sufficient to create a motor profile?

And how about this specific simulation:

I'm always looking to make impressive firework effects that can be made both quickly and cheaply, and that can be fired in quantity from existing equipment. I have literally hundreds of HDPE mortar tubes for consumer fireworks aerial shells that are 1.92" ID and 12" long, mounted on boards in groups of 16.

I have thousands of convolute Kraft tubes, 1" ID and 1.25" OD, 4" long, that I use to press up rocket motors (as well as other effects, like flying spinners.)

Here is what I want to do: Affix a 1.25" diameter hemi as a nose cone, and use three tongue depressors glued flat as fins, so the rocket can be launched out of the 1.92" ID mortar tubes.

Tongue depressors are 6" long, .7" wide, .070" thick birch. I want to use the program to help me decide how much of the TD to glue to the tube, and how much I should have extending at the back. This would change depending on if I put a heading on the rocket instead of just the 1.25" hemi.

Can OpenRocket manage "fins" like this?

JR
 
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neil_w

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Since you volunteered to be the guy standing over my shoulder at the computer, is the information in the screenshot of the thrust curve of my 4oz firework IBP (Insane Black Powder) motor sufficient to create a motor profile?
I would say probably yes, but I can't offer you advice on how to actually generate the new motor files, if that software won't already do it. However, given how many folks make their own motors and generate files, I'm sure that info is readily available. You can try asking on the Propulsion forum and I'll bet you'll get your answer.

Here is what I want to do: Affix a 1.25" diameter hemi as a nose cone, and use three tongue depressors glued flat as fins, so the rocket can be launched out of the 1.92" ID mortar tubes.

Tongue depressors are 6" long, .7" wide, .070" thick birch. I want to use the program to help me decide how much of the TD to glue to the tube, and how much I should have extending at the back. This would change depending on if I put a heading on the rocket instead of just the 1.25" hemi.

Can OpenRocket manage "fins" like this?
I'm not 100% sure what you mean by "glued flat". The fins need to mounted perpendicular to the body to be effective. If you really mean flat like I suspect you do, then they won't behave as fins, and no OR won't really help you.

In any case, when you have an oversized ball in the front (rather than just a hemi) then there are also issues with that ball shielding the fins from the airflow and reducing their effectiveness; normally in our rocket designs we would try to make sure that the fins extend out beyond the fat nose. I don't know to what extent OR takes that sort of thing into account.

So I would say you are kind of skating on the edge here. :)
 

John Ross

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Okay, I'll have to try it, but I'm pretty sure 5" X .7" of TD behind a 4" long 1.25" diameter motor weighing 4oz would put the CG well ahead of the CP. And no, I will not be putting anything on the front bigger than a tube-diameter hemi...

Here's another thought, getting into actual Model Rocketry:

As a kid, the single model rocket I flew the most was the Estes Streak. Minimal prep, and no possibility of the wind drifting a parachute into the trees. I flew my Streak nearly 100 times. The worst part was finding the damn thing after flying it with C6-7 motors, which once took almost an hour.

How about an enlarged Streak using a 1.75" OD motor 6" long that weighs (motor alone) 10 ounces? I can roll my own body tube and nose cone. It should be easy to design a rocket with 1/8" thick birch plywood fins that tumbles once the motor blows out. Should be a lot easier to find...

JR
 

neil_w

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As a kid, the single model rocket I flew the most was the Estes Streak. Minimal prep, and no possibility of the wind drifting a parachute into the trees. I flew my Streak nearly 100 times. The worst part was finding the damn thing after flying it with C6-7 motors, which once took almost an hour.
You actually flew and recovered the same Streak that many times? And flying it with C6s? That's incredible.

How about an enlarged Streak using a 1.75" OD motor 6" long that weighs (motor alone) 10 ounces? I can roll my own body tube and nose cone. It should be easy to design a rocket with 1/8" thick birch plywood fins that tumbles once the motor blows out. Should be a lot easier to find...
That is pretty heavy for tumble recovery. For rockets of that size you should have some sort of recovery mechanism to enable a safe landing.
 

tsmith1315

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How about an enlarged Streak using a 1.75" OD motor 6" long that weighs (motor alone) 10 ounces? I can roll my own body tube and nose cone. It should be easy to design a rocket with 1/8" thick birch plywood fins that tumbles once the motor blows out. Should be a lot easier to find...
We call those enlarged models "upscale", you'll find a lot of upscaled classics. Some are absurdly large, like this 16" diameter Mosquito pictured below. Upscale thread here



Please note:
A decade or two ago, our national clubs (NAR & TRA) spent years and big money in litigation with the ATF to successfully isolate hobby rocketry from explosives regulations, I would kindly suggest leaving the aspect of propelling explosives with a rocket motor out of this discussion.

Aerial fireworks displays and amateur rockets are different animals by definition, and IMHO, it's important that we retain that distinction.


Look around, you may find high-power rockets exciting.
 

John Ross

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Well understood. I'll make no further mention of headings, ever.

JR
 

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Do you still have the cineroc footage? I marveled at them in the catalogs, but they were expensive!
 

John Ross

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You actually flew and recovered the same Streak that many times? And flying it with C6s? That's incredible.
It was actually two of them; the first had the nose cone let go after a while. I only used C motors on a few flights because they always went out of sight. Most flights were with A motors and 1/2A.

As to a big Streak being too heavy for tumble recovery, by my calculations, a 1.75" diameter Streak with a 6" body tube and three fins each 1" X 12" made of 1/8" marine plywood would have a total rocket weight of about 3 ounces without motor.

What is considered the upper weight limit for tumble recovery?

JR
 

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It was actually two of them; the first had the nose cone let go after a while. I only used C motors on a few flights because they always went out of sight. Most flights were with A motors and 1/2A.

As to a big Streak being too heavy for tumble recovery, by my calculations, a 1.75" diameter Streak with a 6" body tube and three fins each 1" X 12" made of 1/8" marine plywood would have a total rocket weight of about 3 ounces without motor.

What is considered the upper weight limit for tumble recovery?
I don't know a number, but for a 3 oz rocket IMHO there should definitely be some form of recovery. My guess is that if you really want to pursue this you should start a new thread (perhaps in the Recovery subforum) to discuss; not many folks will see it here.

A lot of times rockets that are designed to tumble don't exactly do that, and end up coming in ballistic. Not so bad when it's a fraction of an ounce, not good for a 3 oz rocket.
 

John Ross

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Okay, back to OpenRocket. I am doing something wrong.

When the program opens and I start to design a rocket, I click on the "Nose Cone" button and choose the type, dimensions, material, etc. in the pop-up box, then hit "close."

Then I click on "Body Tube" and do the same. The program has drawn these two items. I don't want a "transition," but that is the only button left that will create a pop-up box. The "Fins" buttons (and the others) are more pale than the three previous ones, and don't work.

HELP!

JR
 

tsmith1315

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Highlight the body tube in the tree on the left. The fins should then be available.
 

John Ross

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Then I put the fins on, then I add an "inner tube" that I designate as a motor mount, then I'm stuck again.

How do I put a motor in it?

JR
 

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Go to the Motors & Configuration tab and create a new configuration. You will see the select motor button there.

The Streak, I am pretty sure, does not tumble but comes in ballistically. At 1/8 of an ounce that is safe enough. It was called "featherweight recovery". At three ounces, you're gonna need at least some kind of big streamer if not a 'chute as that is far from featherweight.
 

K'Tesh

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Being in China, and working weekends, I wasn't able to reply to your questions before someone was able to help you. Looks like you got some good advice already. One caution... It's always possible for someone to make the body tube (outer) a motor tube, and forget about it when they add an inner tube that is the real one. It's good to make sure that the correct motor tube is selected and all others are not.

You know... It might be a good idea to transfer your Cineroc footage to digital (then share it with us). Film doesn't last forever, nor does video tape (if already transferred to VHS).

If you're interested in making an exact clone of your old Omega for the Cineroc, I've got a sim for you. If you don't want to clone it, but buy a kit, eRockets.biz has a Retro-Reproduction that is very much in the same vein as the Omega.

1595215106367.png
 

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Here's one way to take data from your test stand (well, an image like the one you posted) and turn it into a file that OpenRocket can then understand: http://www.thrustcurve.org/tctracer.shtml
Thanks! I loaded the program and it appeared to let me save a file, as the data points it listed very closely matched the actual results. I think I may have done something wrong when trying to put it somewhere OpenRocket could access. I've attached the file:
 

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John Ross

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Being in China, and working weekends, I wasn't able to reply to your questions before someone was able to help you. Looks like you got some good advice already. One caution... It's always possible for someone to make the body tube (outer) a motor tube, and forget about it when they add an inner tube that is the real one. It's good to make sure that the correct motor tube is selected and all others are not.

You know... It might be a good idea to transfer your Cineroc footage to digital (then share it with us). Film doesn't last forever, nor does video tape (if already transferred to VHS).

If you're interested in making an exact clone of your old Omega for the Cineroc, I've got a sim for you. If you don't want to clone it, but buy a kit, eRockets.biz has a Retro-Reproduction that is very much in the same vein as the Omega.

View attachment 425241
As I said in an earlier post, all the original footage was burned up in a house fire over 30 years ago.
However, I still have this:

Cineroc1970.jpg


JR
 

neil_w

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Thanks! I loaded the program and it appeared to let me save a file, as the data points it listed very closely matched the actual results. I think I may have done something wrong when trying to put it somewhere OpenRocket could access. I've attached the file:
I was able to load that motor up in OR just fine:
1595256019402.png

That's quite a thrust curve, yielded 132G off the pad in a 5 oz rocket. :shocked:
 

John Ross

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What's my motor do with a minimum-drag rocket that weighs 32oz at launch? The motor is .750" OD and 5" long.

And BTW, thanks again for making that sample "template" file, or whatever you want to call it. I just change the dimensions, override the calculated weight settings with actual values, hit "save as" with a descriptive file name, and Bob's your uncle. Easy peasy Japanesey!

JR
 
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John Ross

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MANY THANKS FOR ALL THE HELP! Annnnnd.....

I've managed to get OR to look in the right place for my motor files!

Now I'm really going to be dangerous...

Happy Dance!

JR
 

K'Tesh

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As I said in an earlier post, all the original footage was burned up in a house fire over 30 years ago.
However, I still have this:

View attachment 425270

JR
Didn't catch that about the fire... Sorry to hear about that.

Dang, you looked a lot like Sean Astin (Goonies, Lord Of The Rings), or I should say, he looked a lot like you.
 

John Ross

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RUDY...? I'll take that. Here's what I looked like 6 years later. For any "gun guys" frequenting this Forum, yes, I am that John Ross...

JR76Crop.jpg




JR
 
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