Lvl 1 cert on an Aerotech G-force - Stock shock cord good enough?

[overklock]

Hopefully not driving too many people crazy here with how many questions I have, but was curious if anyone here has certified on an Aerotech G-force, and if the stock shock cord setup is good enough.

Primary concern would be the ejection charge being too strong and burning the elastic shock cord up. Although this has never been an issue on any of my other Aerotech models with the cooling mesh, I’ve never launched with an H motor either.

Here’s the setup:

- Elastic shock cord
- Aerotech’s cooling mesh
- parachute mounted on shock cord 1 foot down from nose cone

I plan on using a Cesaroni H90, cutting the delay down to 7 seconds. My understanding here is that the 29mm cesaroni has a 1.3g charge.

I know in the long run that a nomex blanket + nylon cord will be better, but for my cert I want to keep it as simple and stock as possible.

Has anyone here certified on the G-force? Any words of advice?

Edited with rocksim file for those who need it in the future.

 

[KenECoyote]

For what it's worth, I certed using a stock Aerotech Sumo on an H and it was fine; however, the construction is different and it uses a piston system. Still, I think you'll be good.

 

[tsmith1315]

Although this has never been an issue on any of my other Aerotech models with the cooling mesh, I’ve never launched with an H motor either.

Do you have a specific concern?

 

[FlyBy01]

Just curious on why the G-force? There are cheaper and more capable kits made by LOC Precision that only require epoxy and paint to safely and easily get your level 1 Certification. The G-force is $150 bucks ish; a LOC IV is $102 bucks ish.

Tim from Apogee has the information on his website that yes you could cert on that setup: https://www.apogeerockets.com/Rocket-Kits/Skill-Level-3-Model-Rocket-Kits/G-Force

 

[Steve Shannon]

Hopefully not driving too many people crazy here with how many questions I have, but was curious if anyone here has certified on an Aerotech G-force, and if the stock shock cord setup is good enough.

Primary concern would be the ejection charge being too strong and burning the elastic shock cord up. Although this has never been an issue on any of my other Aerotech models with the cooling mesh, I’ve never launched with an H motor either.

Here’s the setup:

- Elastic shock cord
- Aerotech’s cooling mesh
- parachute mounted on shock cord 1 foot down from nose cone

I plan on using a Cesaroni H90, cutting the delay down to 7 seconds. My understanding here is that the 29mm cesaroni has a 1.3g charge.

I know in the long run that a nomex blanket + nylon cord will be better, but for my cert I want to keep it as simple and stock as possible.

Has anyone here certified on the G-force? Any words of advice?

That’ll work fine. As you gain experience and fly higher performance rockets you will probably decide you want to tweak some things, but what you have is good enough to certify. The time to start making significant changes from what you are familiar with is either before or after you certify, not while certifying.

 

[overklock]

That’ll work fine. As you gain experience and fly higher performance rockets you will probably decide you want to tweak some things, but what you have is good enough to certify. The time to start making significant changes from what you are familiar with is either before or after you certify, not while certifying.

Thanks!

 

[overklock]

Just curious on why the G-force? There are cheaper and more capable kits made by LOC Precision that only require epoxy and paint to safely and easily get your level 1 Certification. The G-force is $150 bucks ish; a LOC IV is $102 bucks ish.

Tim from Apogee has the information on his website that yes you could cert on that setup: https://www.apogeerockets.com/Rocket-Kits/Skill-Level-3-Model-Rocket-Kits/G-Force

Primary reason is altitude. I want to keep the rocket low and slow.

Any kit from LOC in specific? I think I may have screwed up the center of gravity on my G-force by adding epoxy filets...

 

[FlyBy01]

Primary reason is altitude. I want to keep the rocket low and slow.

Any kit from LOC in specific? I think I may have screwed up the center of gravity on my G-force by adding epoxy filets...

I would reach out to one of your club members to take a look at it before scraping the kit. The LOC IV is the old reliable of Level 1 Certs. The Goblin is a few bucks more but would allow the use of 29mm, 38mm, and 54mm motors with out having to purchase anything extra.
https://www.rocketryforum.com/threads/cert-1-and-2-jolly-logic-challenge.158100/
LOC IV Kit
LOC Goblin Kit

 

[overklock]

I would reach out to one of your club members to take a look at it before scraping the kit. The LOC IV is the old reliable of Level 1 Certs. The Goblin is a few bucks more but would allow the use of 29mm, 38mm, and 54mm motors with out having to purchase anything extra.
https://www.rocketryforum.com/threads/cert-1-and-2-jolly-logic-challenge.158100/
LOC IV Kit
LOC Goblin Kit

I'll check it out, thanks.

 

[ThirstyBarbarian]

A G-Force is a fine kit for a level 1 cert flight. No worries there. I had one for several years. I would fly it on G motors at non-HPR launches to around 700 feet, and fly it on H motors at HPR launches to around 1,500 feet. That’s a perfect L1 cert flight. My cert flight was on a different rocket, but the G-Force is a fine pick.

I think the stock setup should be fine. Eventually you might want a nylon shock cord and a blanket for the chute, but the stock setup should be fine for a few flights. I did not install the cooling mesh in mine, because I had the other protection for the chute from the beginning, and I wanted to be sure I could fit longer motors in the tube. If you installed the mesh, be sure you can fit your motor case in there before you go to the launch.

Also, did you make the rocket center break style like in the instructions? If so, then the stock ejection charge will be fine, because the chute bay is not very big. If you made it traditional nose cone style, then the extended body tube is much bigger than the chute bay, and the standard charge is kind of under-powered.

 

[overklock]

A G-Force is a fine kit for a level 1 cert flight. No worries there. I had one for several years. I would fly it on G motors at non-HPR launches to around 700 feet, and fly it on H motors at HPR launches to around 1,500 feet. That’s a perfect L1 cert flight. My cert flight was on a different rocket, but the G-Force is a fine pick.

I think the stock setup should be fine. Eventually you might want a nylon shock cord and a blanket for the chute, but the stock setup should be fine for a few flights. I did not install the cooling mesh in mine, because I had the other protection for the chute from the beginning, and I wanted to be sure I could fit longer motors in the tube. If you installed the mesh, be sure you can fit your motor case in there before you go to the launch.

Also, did you make the rocket center break style like in the instructions? If so, then the stock ejection charge will be fine, because the chute bay is not very big. If you made it traditional nose cone style, then the extended body tube is much bigger than the chute bay, and the standard charge is kind of under-powered.

Hi Barbarian, thanks for your reply.

I did the standard mid-body break per the instructions.

I've been seeing your posts left and right as I do research for my level 1 on the gforce, I had a quick question if you have the time.

After adding rocketpoxy fin fillets to my build, I'm a bit worried about stability (due to added weight). I've yet to find an accurate rocksim file for the build, and right now, my CTI motor adds substantial aft end weight.

After loading my motor, it brings the center of gravity from 37.5 inches, all the way to 40.5 from the tip of the nosecone. With a "projected" center of pressure being around 46 (again, rocksim file doesn't seem accurate). Obviously, this does not add a lot of wiggle room for stability.

Have you ever had any issues with this? Did you add epoxy fin fillets to any of your g-force builds? Could you tell me where your center of gravity is when you have an H motor loaded?

Sorry for the laundry list of questions here, I can tell you're very well versed in this rocket is all.

 

[ThirstyBarbarian]

Hi Barbarian, thanks for your reply.

I did the standard mid-body break per the instructions.

I've been seeing your posts left and right as I do research for my level 1 on the gforce, I had a quick question if you have the time.

After adding rocketpoxy fin fillets to my build, I'm a bit worried about stability (due to added weight). I've yet to find an accurate rocksim file for the build, and right now, my CTI motor adds substantial aft end weight.

After loading my motor, it brings the center of gravity from 37.5 inches, all the way to 40.5 from the tip of the nosecone. With a "projected" center of pressure being around 46 (again, rocksim file doesn't seem accurate). Obviously, this does not add a lot of wiggle room for stability.

Have you ever had any issues with this? Did you add epoxy fin fillets to any of your g-force builds? Could you tell me where your center of gravity is when you have an H motor loaded?

Sorry for the laundry list of questions here, I can tell you're very well versed in this rocket is all.

No worries! I’m happy to answer questions.

I did not add epoxy fillets to mine, but I can’t imagine it would throw things off enough to worry about. It’s a pretty stable rocket. Unfortunately, mine was destroyed in a motor cato, so I can’t measure the CG on it anymore, but tomorrow I can check my old sims to see if I saved any mass and CG overrides for the completed rocket. Typically, I do, so there should be a record.

 

[overklock]

No worries! I’m happy to answer questions.

I did not add epoxy fillets to mine, but I can’t imagine it would throw things off enough to worry about. It’s a pretty stable rocket. Unfortunately, mine was destroyed in a motor cato, so I can’t measure the CG on it anymore, but tomorrow I can check my old sims to see if I saved any mass and CG overrides for the completed rocket. Typically, I do, so there should be a record.

Thank you! That would be very helpful.

Does the G-force need added weight to the nosecone? A bit late now since it's all sealed up.

Something odd that is totally throwing me off. My G-force comes in a bit lighter than rocksim's model. Rocksim estimates a 1300 gram load without motor with the CG landing at about 36 inches from nose cone. My fully built model comes in at just 1014 grams with the CG at 37.5, split up like the following:

Forward end (nose cone + tube + coupler) = 375 grams
Aft end (Fins+motor mount etc) = 546 grams

Putting this into rocksim, it says my center of gravity should be WAY more forward than it currently is. Something seems off there.

Adjusting for the CG, and loading the motor puts it at a 1.01 margin... Doesn't seem right.

 

[ThirstyBarbarian]

Thank you! That would be very helpful.

Does the G-force need added weight to the nosecone? A bit late now since it's all sealed up.

Something odd that is totally throwing me off. My G-force comes in a bit lighter than rocksim's model. Rocksim estimates a 1300 gram load without motor with the CG landing at about 36 inches from nose cone. My fully built model comes in at just 1014 grams with the CG at 37.5, split up like the following:

Forward end (nose cone + tube + coupler) = 375 grams
Aft end (Fins+motor mount etc) = 546 grams

Putting this into rocksim, it says my center of gravity should be WAY more forward than it currently is. Something seems off there.

Adjusting for the CG, and loading the motor puts it at a 1.01 margin... Doesn't seem right.

View attachment 550679

I don’t think you should need any nose weight.

I’m not sure what’s going on with the file, and it could have to do with the history of the file and how the 1300 grams was arrived at.

Sim programs can use the weights and CG for each individual component to calculate the estimated mass and CG of the entire rocket. But typically that is not going to match the exact mass and CG of your own built rocket. Usually the built weight is higher than the calculated one, because it doesn’t consider the mass of glue, filler, primer, paint, etc.

So a very important step for getting accurate sims is to do what you have done and weigh your actual built rocket and balance it to find the actual CG. Make sure you put EVERYTHING in the rocket that will be on the flight, except the motor and motor hardware, when you take your measurements. Put all the recovery gear in the chute bay and put the motor retainer on. Then you should put in the actual measured weight and CG in the sim program as global overrides for the entire rocket. I use Open Rocket, so I’m not sure how you enter your global overrides in Rocksim, but there is a way to do it. I wasn’t sure if you have done that, but if not, you’ll need to in order to get accurate flight sims with correct speed off the launch guide, maximum altitude, optimal delay time, etc.

The mystery of the 1300 grams could be that it was calculated from component weights, and some of those weights were incorrect. Or it could be that whoever made the file entered the 1300 grams as an override. That seems likely to me, because typically the caculated weight is less than the built weight, but this is more. And if it’s exactly 1300 grams, then that’s definitely an override. Also, I don’t have my records in front of me, but 1300 just seems high to me, because it’s so close to the 1500 gram limit for a fully loaded class 1 rocket, and I don’t think the G-Force cuts it that close.

After you enter your weight and CG overrides, double-check your stability margins for each of your motors. I think it’s going to be ok. Also recheck your optimal delay times and max altitude. And if that screenshot you included was calculated based on a 1300 gram rocket, I think you are going to find that more G motors are going to work after you fix that. The G-Force was designed by Aerotech to use Aerotech single-use G motors, and you should get nice flights on G77, G78, G79, and G80. The G40 and G38 will still be risky, but the others should have safe speed off the guide, and in the screenshot, it looks like the G80 is just barely making it.

 

[overklock]

I don’t think you should need any nose weight.

I’m not sure what’s going on with the file, and it could have to do with the history of the file and how the 1300 grams was arrived at.

Sim programs can use the weights and CG for each individual component to calculate the estimated mass and CG of the entire rocket. But typically that is not going to match the exact mass and CG of your own built rocket. Usually the built weight is higher than the calculated one, because it doesn’t consider the mass of glue, filler, primer, paint, etc.

So a very important step for getting accurate sims is to do what you have done and weigh your actual built rocket and balance it to find the actual CG. Make sure you put EVERYTHING in the rocket that will be on the flight, except the motor and motor hardware, when you take your measurements. Put all the recovery gear in the chute bay and put the motor retainer on. Then you should put in the actual measured weight and CG in the sim program as global overrides for the entire rocket. I use Open Rocket, so I’m not sure how you enter your global overrides in Rocksim, but there is a way to do it. I wasn’t sure if you have done that, but if not, you’ll need to in order to get accurate flight sims with correct speed off the launch guide, maximum altitude, optimal delay time, etc.

The mystery of the 1300 grams could be that it was calculated from component weights, and some of those weights were incorrect. Or it could be that whoever made the file entered the 1300 grams as an override. That seems likely to me, because typically the caculated weight is less than the built weight, but this is more. And if it’s exactly 1300 grams, then that’s definitely an override. Also, I don’t have my records in front of me, but 1300 just seems high to me, because it’s so close to the 1500 gram limit for a fully loaded class 1 rocket, and I don’t think the G-Force cuts it that close.

After you enter your weight and CG overrides, double-check your stability margins for each of your motors. I think it’s going to be ok. Also recheck your optimal delay times and max altitude. And if that screenshot you included was calculated based on a 1300 gram rocket, I think you are going to find that more G motors are going to work after you fix that. The G-Force was designed by Aerotech to use Aerotech single-use G motors, and you should get nice flights on G77, G78, G79, and G80. The G40 and G38 will still be risky, but the others should have safe speed off the guide, and in the screenshot, it looks like the G80 is just barely making it.

I think one of the main issues is just the beginning accuracy of the Rocksim file. It's the one provided by apogee (also available on rocket reviews) and it's just not accurate. Fins are in the wrong position, the weight of each component is incorrect, it's setup for dual deploy etc. I DID make some modifications to it to bring it more in line with the actual rocket, but as mentioned, the weight is still off. Unfortunately, I can't weigh each component individually as I have everything glued together.

The weight on the prepped file comes out to 1298.510g. So not exactly 1300, but still quite close. Screenshots below, center of gravity is clearly off on both of them.

I'm going to have to learn how to override the center of gravity in RockSim. I'm not seeing any immediate way to do so.

Here's the Apogee provided file. If I remove the DD stuff, then the center of gravity is almost spot on, but the center of pressure is clearly not because the fins are in the wrong position.




And here is my modified file. Center of gravity gets shifted even higher, along with the center of pressure. Center of gravity being incorrect here again.




Here are my fillets, which are not crazy at all. I did use epoxy inside as well but nothing over the top.

 

[overklock]

Ok, update, I was able to override the mass and center of gravity to bring it more in line with what it actually is. Presuming I did this right, we should have a stable rocket... Barely. Stability Margin of 1.06

 

[Handeman]

That should be fine at 1.06. If you use the base drag hack on there, you will find your margin is actually more than that 1.06.

 

[FlyBy01]

I think you are fine with those fillets; they do not seem excessive to me. I would argue the weight impact would be negligible.

As a tip for your next build weigh every components prior to bonding then weigh the components to find out how much weight was added; this is overkill but I want to know in an effort to keep my sim as accurate as possible.

 

[overklock]

That should be fine at 1.06. If you use the base drag hack on there, you will find your margin is actually more than that 1.06.

I actually messed up the CG, it's 38.5, not 38. This brings it to .96. Is that ok still? Sim seems to launch alright.

 

[FlyBy01]

I actually messed up the CG, it's 38.5, not 38. This brings it to .96. Is that ok still? Sim seems to launch alright.

your good

 

[overklock]

your good

Cheers, fingers crossed for my level 1.

 

[ThirstyBarbarian]

Those fillets look good to me and will not throw your CG off enough to be any kind of problem. One thing you can reassure yourself about is that the G-Force is a well-known kit with a long history, and as long as you built it according to the instructions, it’s going to fly great, with no odd problems, especially stability. The design is good, and the rocket as designed is stable.

I agree, that original Rocksim file looks screwy. That’s kind of surprising, coming from Apogee.

Rocksim and OpenRocket have a few different purposes, and the purpose of the component by component weights and CGs is mostly for designing rockets, and getting an idea of what they will weigh and how they will balance BEFORE building it. But once it is built, the component weights don’t really matter anymore. At that point, you shift from design to flight simulations, and it’s the overall weight, balance, and shape of the rocket as a whole that matters.

I’m not familiar with Rocksim, but how do you set the mass and CG of an individual component? Double-click the component in the component list to bring up the parameters? Try double-clicking the “Sustainer” in the components list, and see if there is a way of setting the mass and CG of the entire sustainer. I also see a tab labeled “Mass override”. What’s that?

The most important next step is overriding the mass for the entire rocket as a whole. That will give your sims more accurate speed, max altitude, and optimal delay.

Next, overriding the CG of the rocket as a whole will give you more accurate stability calculations, so you want to figure out how to do that. But honestly, as long as the rocket actually is stable, and the sims don’t show it as unstable, the CG is not as important as the mass for flight sims.

And the final thing is CP. The program calculates CP based on the size, shape, and position of the components that touch the wind. So in this case, that’s the nosecone, the two body tube sections, and the fins. None of the internal components matter. I see in the original, the fins were at the wrong position. As long as you have fixed the position of the fins and verified the shape and size are accurate, that’s all you need to do with those. Then just verify that the body tubes are the correct diameter and length, and the nosecone length and diameter are correct, and you should be good to go for an accurate CP calculation.

I have an appointment this morning, so later this afternoon I will check my sim files for my G-Force mass, CP, and CG info.

 

[ThirstyBarbarian]

Ok, update, I was able to override the mass and center of gravity to bring it more in line with what it actually is. Presuming I did this right, we should have a stable rocket... Barely. Stability Margin of 1.06

View attachment 550728

Lol. You figured it out while I was typing my reply. It looks good to go to me. That stability margin is fine.

How do the flight sims look now? Altitude, speed, delay? And how does that G80 look now?

 

[overklock]

Lol. You figured it out while I was typing my reply. It looks good to go to me. That stability margin is fine.

How do the flight sims look now? Altitude, speed, delay? And how does that G80 look now?

Thanks as always for your input. Much appreciated and thank god for this forum.

With the stability margin at .96, I'm looking at the following:

Motor: Aerotech RMS G80-7T
Motor loaded weight: 1118 grams
Projected Altitude: 1054ft
Max velocity: 191MPH
Deployment velocity: 14.05mph

Motor: CTI H90-7
Motor loaded weight: 1204 grams
Projected altitude: 1565ft
Max velocity: 248 MPH
Deployment velocity: 21.30MPH

 

[overklock]

To anyone searching in the future, I've attached my custom made rocksim file on the original post. The CG and CP match perfectly to what is measured IRL. Hopefully it'll help someone somewhere.

 

[ThirstyBarbarian]

Thanks as always for your input. Much appreciated and thank god for this forum.

With the stability margin at .96, I'm looking at the following:

Motor: Aerotech RMS G80-7T
Motor loaded weight: 1118 grams
Projected Altitude: 1054ft
Max velocity: 191MPH
Deployment velocity: 14.05mph

Motor: CTI H90-7
Motor loaded weight: 1204 grams
Projected altitude: 1565ft
Max velocity: 248 MPH
Deployment velocity: 21.30MPH

View attachment 550738

Great! That looks more like what I would expect for a G-Force. An altitude around 1500’ is great for an L1 cert flight. The G80 flight is actually a bit higher than I would expect. My G-Force generally kept under 1000‘ on G motors. But mine was painted, had the decal on it, plus a lot of other “bling” on it that would add weight and drag. If you paint your rocket, fill spirals, use the decal, etc., be sure to weigh it again, check the balance, and update your overrides.

You have good speed off the launch guide in all of those sims — anything over 30 miles per hour (45 feet per second) is good, and you are well above that.

I think you are set for a good flight. You might want to print out the screenshot of your sims and bring it to your cert flight. Also, you might want to run some sims of motors your on-site vendor might have in stock, including some single-use Aerotech motors, like H115, H135, H182, etc. If you want to take a victory lap or stock up for later, you’ll have the info on your options.

One final tip for the G-Force. You might want to drill a 1/8” vent hole into the parachute bay. Drill it through the side of the body tube in the upper section, so it’s not blocked by the coupler. The coupler can be almost airtight, and when you put a motor in the retainer and try to insert the coupler into the lower section to seal up the chute bay, or you try to open it again, the coupler can feel extremely tight. It’s because of the air pressure in the chute bay compartment, and it can be very confusing why the coupler is suddenly so tight with a motor in the tube. A vent hole will prevent that. Also, it’s just a good idea to have vent holes in rockets to prevent pressure from separating the rocket during high or fast flights. Just a small hole 1/16” to 1/8” will be enough.

 

[overklock]

Great! That looks more like what I would expect for a G-Force. An altitude around 1500’ is great for an L1 cert flight. The G80 flight is actually a bit higher than I would expect. My G-Force generally kept under 1000‘ on G motors. But mine was painted, had the decal on it, plus a lot of other “bling” on it that would add weight and drag. If you paint your rocket, fill spirals, use the decal, etc., be sure to weigh it again, check the balance, and update your overrides.

You have good speed off the launch guide in all of those sims — anything over 30 miles per hour (45 feet per second) is good, and you are well above that.

I think you are set for a good flight. You might want to print out the screenshot of your sims and bring it to your cert flight. Also, you might want to run some sims of motors your on-site vendor might have in stock, including some single-use Aerotech motors, like H115, H135, H182, etc. If you want to take a victory lap or stock up for later, you’ll have the info on your options.

One final tip for the G-Force. You might want to drill a 1/8” vent hole into the parachute bay. Drill it through the side of the body tube in the upper section, so it’s not blocked by the coupler. The coupler can be almost airtight, and when you put a motor in the retainer and try to insert the coupler into the lower section to seal up the chute bay, or you try to open it again, the coupler can feel extremely tight. It’s because of the air pressure in the chute bay compartment, and it can be very confusing why the coupler is suddenly so tight with a motor in the tube. A vent hole will prevent that. Also, it’s just a good idea to have vent holes in rockets to prevent pressure from separating the rocket during high or fast flights. Just a small hole 1/16” to 1/8” will be enough.

Thanks! I'm definitely going to want to stock up. I'm assuming by single use, you mean Aerotech's DMS series? I haven't seen single use other than that. I'll look into drilling a vent hole.

One odd thing I did notice, (Sorry bombarding you with more questions) is that Rocksim and OpenRocket have completely different centers of pressure. Enough to change it from a successful flight, to an unsuccessful one.

In fact, even with the wonky rocksim file downloaded from apogee, rocksim shows a CP at 46 inches, while openrocket shows a CP at 42.8 inches.

Oddly enough, it does the same thing for my Mega Der Red Max simulation file. Putting the center of pressure an entire inch higher in OpenRocket.

Do these pieces of software calculate the CP differently? Which is more accurate?

EDIT: Looks like the difference is in the calculation equation. Rocksim equation vs Barrowman. Not sure which one to trust here.

 

[Steve Shannon]

Thanks! I'm definitely going to want to stock up. I'm assuming by single use, you mean Aerotech's DMS series? I haven't seen single use other than that. I'll look into drilling a vent hole.

One odd thing I did notice, (Sorry bombarding you with more questions) is that Rocksim and OpenRocket have completely different centers of pressure. Enough to change it from a successful flight, to an unsuccessful one.

In fact, even with the wonky rocksim file downloaded from apogee, rocksim shows a CP at 46 inches, while openrocket shows a CP at 42.8 inches.

Oddly enough, it does the same thing for my Mega Der Red Max simulation file. Putting the center of pressure an entire inch higher in OpenRocket.

Do these pieces of software calculate the CP differently? Which is more accurate?

RockSim allows the user to choose between two or three different algorithms for calculating CP. The default is one that Apogee considers an improvement over the one that OpenRocket uses. Try switching to the different algorithms in RockSim to see how the location of the CP changes.

 

[overklock]

RockSim allows the user to choose between two or three different algorithms for calculating CP. The default is one that Apogee considers an improvement over the one that OpenRocket uses. Try switching to the different algorithms in RockSim to see how the location of the CP changes.

Yep, switched to the barrowman method just to test in RockSim. It puts it in line with Open Rocket. However if the Barrowman method is accurate, holy **** this rocket is inherently unstable. Loading a G engine into the file downloaded from Apogee puts the CG and CP just 1.5 inches away from each other (.43 margin). Loading a 3 grain H puts that at .23

They do both fly successfully in the sim, but that seems sketch, no?

 

[ThirstyBarbarian]

Thanks! I'm definitely going to want to stock up. I'm assuming by single use, you mean Aerotech's DMS series? I haven't seen single use other than that. I'll look into drilling a vent hole.

One odd thing I did notice, (Sorry bombarding you with more questions) is that Rocksim and OpenRocket have completely different centers of pressure. Enough to change it from a successful flight, to an unsuccessful one.

In fact, even with the wonky rocksim file downloaded from apogee, rocksim shows a CP at 46 inches, while openrocket shows a CP at 42.8 inches.

Oddly enough, it does the same thing for my Mega Der Red Max simulation file. Putting the center of pressure an entire inch higher in OpenRocket.

Do these pieces of software calculate the CP differently? Which is more accurate?

EDIT: Looks like the difference is in the calculation equation. Rocksim equation vs Barrowman. Not sure which one to trust here.

Yep. I meant DMS. Those are good for second flights when you don’t want to clean hardware or build motors at the launch. If you are stocking up, then reloads are obviously an option too. I find it helpful to have sims of the motors with me when shopping.