Recommended L1 and L2 Cert Motors for Madcow Cowabunga

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lowga

A.K.A. 'Mr. HoJo'
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I would like to attempt both my L1 and L2 certification flights on an "over-built" 4" Madcow Cowabunga rocket. My demanding work schedule makes it nearly impossible to attend rocket launches regularly, which is why I'd like to attempt both my L1 and L2 certification flights on the same weekend if possible. I've overbuilt the rocket with upgraded components, and fiberglass reinforcements to ensure that it survives the higher power motor required for Level 2. It's also equipped with both GPS and RF tracking to help be sure that I get it back.

Adhering to the Keep It Simple Stupid principle, I plan to fly with one-time use motors such as the Aerotech 38mm H100W-14A for Level 1, and possibly the J270W-14A for Level 2 certification. Wondering if anyone has experience flying this bird on these motors? Also, if someone has a recommendation for a different Level 2 motor, I'm open to those suggestions.

"Low and Slow" is my preference.

Thanks in advance for all the helpful advice and expertise on this forum.
 
I love the Cowabunga!
But how overbuilt is it? As in how heavy is it? The J425 would probably keep the rocket lower than the J270 but certainly not slower, sims put mine up around 1070 ft/s. Your looking at over 4000 ft on your J. The H100 will work fine if the rocket isn't too heavy, around 2000 ft.
No, I don't have experience with either just putting the motors in my Cowabunga sim.
 
For a low and slow L1 on a Madcow Cowabunga, you're looking at something in the H100 ranges. I like the CTI H100 IM motor. But you'll need to drill the delay down from it's stock 14s. OpenRocket says you'll hit an apogee of around 1,800' with an optimal delay of 7s. But if you've overbuilt it, your results might be different.

It's tough to get low and slow on a Cowabunga with something in a J or K. You have a stubby rocket. A 38mm motor in a J or K gets long really fast. I don't know how you've built it and where your laundry is. You're likely limited to a motor with a length of 15" max. That limits your selection among CTI or Aerotech to about 19 motor choices. Among those, you can either go low, or you can go (somewhat) slow; not really both.

A CTI J94 will launch moderately slowly, but with its long burn of 7s, you'll hit an altitude of 3700'. You need electronic deployment. Not sure if you have that built in yet.

An Aerotech J420 will rip off the launch rod like a bullet, but at least you'll hit an apogee of 2,700'.

You should get a copy of the free OpenRocket and get familiar with it. It will open your world to all the motor selections you can consider and how your flights would go.
 
Mikey,

Thank you for the recommendations. I'm flying the 30" Nylon Chute but will be using a Jolly Logic Chute Release to try and limit the drift. I have a copy of RockSim software, and have downloaded the model for the Cowabunga from MadCow. Played around with some simulations, however, my rocket has been modified with the addition of an external camera shroud. Also upgraded the nosecone to add a birchwood altimeter bay which added some weight up front. I'm not confident in my ability to properly modify the RockSim file which is why I wanted to ask for advice about motors.

Staying away from electronic deployment for now. My plan was to overbuild the rocket, fly single-use motors, and get L1 and L2 certifications complete. That will allow me to purchase motors and keep reloads handy so that I'm prepared for the odd weekends when our club has a launch scheduled, and my time off from work align. Plan to build a DD rocket for my next project, and tackle that challenge next.

Thank you again for the advice.
 
This is an easy way to get what you need with Rocksim.

Weight the rocket without the motor.
Measure the CG from the tip of the nose cone.

When you go to do a sim go to MASS OVERRIDE.

On the screen that comes up, left side, enter the weight under MEASURED MASS DATA.....SUSTAINER.

Enter the CG in the MEASURED CG DATA section on the right side.

Do not worry about the camera shroud. BTW...how heavy is it?

Remember....you are not "attempting" your cert flights. You are getting your cert after the flights. Clearly a different state of mind.
 
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Can't say I agree with your hurried approach, but it's a free country.

I am confused by your request. You said KISS, but you are plowing ahead through L motor capability in one day, upgrading components, adding fiberglass, GPS, RDF, cameras, and av-bays. However, you don't seem to know how to select a motor to safely launch and recover this rocket over two flight regimes. That should be first priority. Maybe I am missing your tone/intent over the interwebs. Are you looking for validation of your motor choices, or are you really unsure how to fly this thing?

We don't know how you built the rocket or how much it weighs, so we can't predict the performance for you. Since the rocket is already built, there is no need to mess around in Rocksim or OpenRocket. To quickly look at motor choices (KISS) use thrustcurve.org motor guide.
 
Perhaps I should explain.

Lifelong amateur radio operator, N1LF--so adding telemetry, tracking, and the camera are easy enough for me. BAR with lots of mid-power experience too. Again, fiberglass fin reinforcement, and the nose cone modifications are simple enough. My thought was that single-use engines would be more reliable than reloads for certification flights. Also avoiding dual deployment removes several points of failure from the flights.

My logic may be flawed, but that's how it tracked for me.

My priority was ensuring a robust reliable recovery system. After that, I do want to focus on proper motor selection. I'm trying to modify the RockSim file to account for the modifications now--but wanted to seek some advice from others too.

Hopefully that makes more sense.
 
Yep, I think you are rushing this. Let's start with basic questions.

Today, without motor, but fully prepped what is the mass of the rocket, and the center of gravity measured from the tip of the nose.

I believe you need to do some flying before you go to L2. I think folks rush this a lot. There is a lot to learn and this really can only be achieved by doing.

I also think your assumption that single use motors are more reliable than reloads is questionable. I have been flying high power for twenty years- I have had a few single use motors fail, but only one reload. I have flown mostly reloads to boot.


Sent from my iPhone using Rocketry Forum
 
Why rush? You’ll be a better rocketeer and enjoy it more if you build a simple Level 1 rocket, fly it successfully, and then fly that same rocket on two or three additional H and I motors of different thrust profiles. Spend some time mastering that level. I guarantee you’ll enjoy it more.
If you are unable to fly very often what’s the motivation to get to L2?


Steve Shannon
 
I do want to focus on proper motor selection.

You can generate an Open Rocket file yourself by measuring each component dimensions in metric lengths, then record the masses of each part and adjust the horizontal positions of the internal hardware you add to the kit later to get a good approximate CG location. You want your stability caliber in a region of 1.5-2.0 or its not going to fly right for a subsonic below Mach 1 project. If it sims over Mach 1 you might want RAS Aero 2 which is also free. Too high of stability it will point into wind on a windy launch day and too low it will go unstable and crash. You could ask the manufacturer of Cowbunga kit for the masses of components since you already assembled your kit. (You may have errors only slightly).

Then you can go into motor configuration and there is an entire database of motors to select based on motor mount diameter. You can sim your rocket for a specific launch site at a specific elevation. Try to match apogee altitude vs time to a motor delay fuse time as close as possible to reduce velocity and forces on a parachute as you don't want it ripping off. Anyways when you email an RSO your rocket sim file it helps the cert process a lot, because you understood what you did. I've built and designed two scratch build L-1 multistage for university project and I had a lot of fun along the way. You may fail the L-1 cert if the shock cord snaps or a problem happens, so don't expect a perfect flight on either cert attempt. What you don't have is the experience of doing it which worries a lot of people. The RSO/LCO will make some criticisms if they see your build quality or fashion wasn't adequate. Prepare to listen and learn for a bit.

J-350W is also a popular L-2 cert motor by Aerotech. You are a smart guy with electronics, you will make it happen, but try to make certain rocket is stable.
 
You can generate an Open Rocket file yourself by measuring each component dimensions in metric lengths, then record the masses of each part and adjust the horizontal positions of the internal hardware you add to the kit later to get a good approximate CG location. You want your stability caliber in a region of 1.5-2.0 or its not going to fly right for a subsonic below Mach 1 project. If it sims over Mach 1 you might want RAS Aero 2 which is also free. Too high of stability it will point into wind on a windy launch day and too low it will go unstable and crash. You could ask the manufacturer of Cowbunga kit for the masses of components since you already assembled your kit. (You may have errors only slightly).

Then you can go into motor configuration and there is an entire database of motors to select based on motor mount diameter. You can sim your rocket for a specific launch site at a specific elevation. Try to match apogee altitude vs time to a motor delay fuse time as close as possible to reduce velocity and forces on a parachute as you don't want it ripping off. Anyways when you email an RSO your rocket sim file it helps the cert process a lot, because you understood what you did. I've built and designed two scratch build L-1 multistage for university project and I had a lot of fun along the way. You may fail the L-1 cert if the shock cord snaps or a problem happens, so don't expect a perfect flight on either cert attempt. What you don't have is the experience of doing it which worries a lot of people. The RSO/LCO will make some criticisms if they see your build quality or fashion wasn't adequate. Prepare to listen and learn for a bit.

J-350W is also a popular L-2 cert motor by Aerotech. You are a smart guy with electronics, you will make it happen, but try to make certain rocket is stable.

Don’t bother trying to compile all the individual masses. You should be able to just override the mass and override the Cg of the assembled rocket.
Also, it doesn’t matter whether you use metric; Open Rocket is capable of using either.
As long as your dimensions are correct in Open Rocket your Cp will be close enough. Everything else can be gotten by weighing and balancing. There’s no point in making it difficult.


Steve Shannon
 
My priority was ensuring a robust reliable recovery system.

Use a quality Kevlar or Nylon shock cord from OneBadHawk harnesses or another name brand. I failed an L-1 cert with a shock cord snapping after driving 7 hours to a launch site. Yeah. I would have gladly paid more money for a excellent shock cord up front had I known better. Get a nomex patch to roll parachute in and another patch for wadding. The RSO may want up to 15 ft of shock cord or more, so have extra and some epoxy to swap cord lengths if needed. Take some basic tools if in doubt. Worst case you can fix rocket on site. The airframe itself can also cut a lesser quality shock cord or zipper so make sure to read up on those behaviors. Apogee usually publishes articles.
 
I always compiled the masses then used override feature on OR for the compiled mass data. Seemed accurate enough.
 
IMO there's a lot to be learned between L1 & L2 certifications. To my point, going through the decision process on motor selection based on a set of objectives.

I've discussed with the NAR the idea of establishing some reasonable time period between certification levels based on the need to develop various skills and experience between HPR levels.

The NAR Safety Committee Chairman stated that this notion has been discussed multiple times but they are reluctant to set a firm wait time. Instead, NAR relies on the certification personnel to conduct a readiness assessment that covers ..."knowledge of safety procedures, good building practices (e.g. appropriate use of adhesives), and basic rocket science..."

Certainly there are some that could gain those skills faster than others, and my comment here is not a criticism of the topic's author or his capabilities. Rather, it is an expression of my growing concern that I have witnessed this year where individuals coming to my club are trying to fast-track HPR certifications having no, or little, practical model rocketry experience or understanding of building practices or rocket science.
 
I always compiled the masses then used override feature on OR for the compiled mass data. Seemed accurate enough.

There’s nothing wrong with using individual mass data. In fact it’s a great way to go when the rocket is still in kit form. It’s just not needed to gather that data once the rocket is assembled.
 
There’s nothing wrong with using individual mass data. In fact it’s a great way to go when the rocket is still in kit form. It’s just not needed to gather that data once the rocket is assembled.

I would agree. The best way is to start with the components, weighing and measuring them all, and entering them into the sim. This includes mechanical fasteners, epoxy etc. the thing with sims is that they are only as good as the data you enter into them- the closer to reality the better.


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I usually just build then weigh the final product. Weighing each individual screw, rivet, drop of epoxy...that's crazy. Build the thing, weigh it, measure the CG and go forth. Only issue is when trying to add nose weight to the nose cone. But I actually get the mass and CG of the nosecone and the rocket minus nosecone separately. That way I can add mass to the nose cone to get more accurate sims. I mostly worry about stability and speed off the rail because 10,000 feet is way above anything I am flying and on some rockets I miss the altitude be a few hundred, some hits within a few feet...on the same rocket.

Measurements do no have to be metric.

The AT J350W is not a single use motor.

Do you know the zero mass tailcone trick for short stubbies?

You do not want to put nose cone weight in the Cowabunga to bring it up to 1.5 cal stability and especially 2 cal. You would be looking at around 12 to 20 ounces in the tip. Mine has some weight in the nose via an electronics sled; and it did have 2 oz of fishing weights on the sled. But I got rid of all that, streamlined my sled and poured 5 oz of sand/epoxy around the bulkhead in have in the shoulder. It has about .9 cal stability empty, .4 cal with an "I" in it. Flies straight up, even in moderate winds. It should be able to fly a 38mm baby J like that. But I don't know how much weight you added to the tail end portion via your fiberglass and what not.

The standard nylon recovery harness that comes with that kit will suffice. Did you order the chute and chute protector with it? If so then you have everything you need and it is probably a thin mil chute that can pack pretty small. You are still gonna be tight on space cramming a J in there. It can be done of course, just practice the technique. Or you can order a payload kit from Madcow and stretch it a foot or two for the level 2 flight, just to be sure you have plenty of room.

Depending on how much weight you added, a 30" chute may bring it in pretty fast.

I agree there is a lot to learn and I really don't see why you would want to hurry along the level 2 just for the sake of doing it, especially if you rarely fly. Get your level 1. And between launches build you a level 2 bird. It will keep you engaged and you will have another bird to fly. Then after level 2, stick a J in your Cowabunga and let er rip. But it is you doing it so you do it how you want to.

But I am not one to talk about restraint. I rarely fly and I just recently got my level 2, but I enjoyed my down time between launches by building the bird for my next cert flight. The second (or was it third) motor I assembled was for my level 1 flight. My level 1 flight had electronic deployment and my level 2, which was barely less than a year and maybe 3 flights later, had dual altimeters and GPS tracking. Every flight above an F has had electronics for deployment. And soon even my Big Daddy will have an altimeter.

The main thing that will get you is the recovery. Learning to pack you chute and harnesses, and that only comes with practice. You can fold and pack on the ground until you are blue in the face but when pieces get to spinning and flopping around on descent, things get tangled, broke, dented, things just happen.

Get it flight ready minus motor. Weigh it and balance it to get your CG. Post those numbers here. And also if your fins are rounded, airfoil or square. That will go along way to getting help from the good folks here. Get a good handle on the OpenRocket program as well and that will help tremendously.

Mikey D
 
I also recommend enjoying your weekend with some more L1 motors before rushing into L2. There is a lot to learn, like assembling motors and getting the timing right for your rocket. Also just overall experience. I also think building a second rocket for the L2 can be a fun way to use things you learned about how you setup this rocket.

That being said with all the electronics I would recommend making a checklist for yourself. Good luck with your cert flight(s).
 
I would like to attempt both my L1 and L2 certification flights on an "over-built" 4" Madcow Cowabunga rocket. My demanding work schedule makes it nearly impossible to attend rocket launches regularly, which is why I'd like to attempt both my L1 and L2 certification flights on the same weekend if possible. I've overbuilt the rocket with upgraded components, and fiberglass reinforcements to ensure that it survives the higher power motor required for Level 2. It's also equipped with both GPS and RF tracking to help be sure that I get it back.

Adhering to the Keep It Simple Stupid principle, I plan to fly with one-time use motors such as the Aerotech 38mm H100W-14A for Level 1, and possibly the J270W-14A for Level 2 certification. Wondering if anyone has experience flying this bird on these motors? Also, if someone has a recommendation for a different Level 2 motor, I'm open to those suggestions.

"Low and Slow" is my preference.

Thanks in advance for all the helpful advice and expertise on this forum.

For L1, I would consider the H219T instead of the H100W just because of the higher thrust off the pad. I'm sure the H100W will work for your 30+ oz rocket, but I flew a BD Thug for a number of years and a little more average thrust on the low end always seemed to work better.
For L2, the J270W is about the smallest SU J motor you'll get so I would use that. There is no way to get "low and slow" on the L1 designed 4" Cowabunga when using a L2 motor.

My personal recommendation is to fly the range of L1 motors while building a rocket designed for L2 motor use, 54mm or even 75mm MMT. That way when you cert L2, you can actually fly large J, K or even L motors. There are a lot of folks that get their L1 with a 29mm MMT rocket and L2 with a 38mm MMT rocket, but don't understand until they build a bigger rocket and they actually move up into the full range of their cert what the true power of the motors are and how that changes the way they pick motors and fly their fields. You can run sims all you want, but until you actually fly, it's not the same. Flying the field is a skill you acquire in your cert range, especially on the smaller fields east if the Mississippi. What you learn flying L1 is a great help when you move up to L2.
 
I've decided to heed the collective wisdom of the group, and take my certifications at a slower pace. Plan now is to fly in January (fingers crossed that work won't interfere) and fly a SU motor for L1 Cert. Then later the same day, fly a reloadable H motor for fun, and experience. If all goes well, I'll try a J motor (reloadable) for L2 Cert in February or March.

Thanks for sharing the wisdom and sage advice. Happy Holidays to all Rocketeers.
 
The greatest skill, all new fliers getting ready to cert, need is........finding/tracking the rocket! LOL:wink:
 
Regarding using individual masses for components or a mass overrride for the entire rocket in the simulators (RS or OR), if you are looking for anything relating to the dynamic stability figures (rotational moment of inertia etc) then the individual masses must be done. If you are just looking for altitude and other basic sim data then the single mass override will give you those numbers (assuming the dynamic stability etc is good :)). I usually just go with the individual override in the end, but if stability were marginal I would go back to individual parts.

I suspect this is really important for 6DoF sims, but less so for the run-of-the-mill rockets.
 
The greatest skill, all new fliers getting ready to cert, need is........finding/tracking the rocket! LOL:wink:
Got that with a TeleGPS. FCC license and a yagi with a laptop not hard at all. It spits you info within 10ft.
The issue I have is avoiding the components coming down without the recovery system attached. Anyways. I've snagged a H219T for my next L-1 Cert. Handeman was right it leaves the rail 15 m/s faster than h100w on 3.5 lb rocket.
 
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