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Newbie ... question on launch rod for Aerotech G-Force

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Underdog

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Another new guy here. Never personally seen a rocket launch but now there's one spread across the dining room table.
I wish I had found this web site before choosing a first rocket ....but here I am.
Question: does this rocket need a rod or launch rails?
Yesterday I found this comment on the Apogee Components https://www.apogeerockets.com/Rocket_Kits/Skill_Level_3_Kits/G-Force web site:
"A Note About the G-Force - This kit pushes the limits of "mid-power" rocketry. Aerotech says it will fly on the Mantis Launch Pad, but based on simulations, even the G80 will be underpowered leaving the rod. We recommend either purchasing a longer rod from a hardware store, or modifying the kit to fly off a launch rail (this would require adding rail buttons).
If you add rail buttons and launch it off an 8ft rail instead, you can use a wider selection of G motors to safely fly it."


I don't completely understand this comment. I realize that upon launch the rocket needs to reach a certain velocity before the fins can be expected to provide stability in the direction of flight, however why is the seller saying a G80 (powerful) motor is not enough?
When I looked at the rocket in http://www.rocketreviews.com/aerotech-aerospace-g-force--by-dan-schneider.html almost everyone was happy with a G40-4 for a first flight. I ordered a Aerotech RMS Motor Case 29mm with a G-53- motor reload kit to avoid hazmat mailing fees (no hobby shops in my area). I have a bicycle repair stand that is pretty sturdy (can support 100 lbs) that I was planning on adapting to a launch pad by finding a long rod at the hardware store. My hips are old so I wanted the rocket up off the ground to avoid crawling around in the wet dew covered grass to hook up the igniter. I picked G-force because I have trouble seeing small parts and pieces and need glasses. Thank you.
workstand.JPG
 
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EXPjawa

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Apogee's own simulation testing had less than satisfactory results. Keep in mind that Apogee also developed and sells one of the popular rocket design software packages, so simulations are their thing. Also, a rocket that might be borderline in terms of weight by design can be pushed way over by building heavy, so that's a factor as well. The listed mass is 32 oz, but you can easily add a bit to that if you over do it. Throw in some conservative thinking (for liability purposes?), and you have what they've published. But it is a largish, fairly heavy rocket. They are correct that it pushes the limit of mid-versus-high power rocketry; my Level-1 rocket is roughly the same size and weight, and I wouldn't fly it on anything less than a big G. It mostly flies on small H's.

Just keep in mind that with lower initial thrust, the initial acceleration is also lower. So you will need more distance to reach that stable speed before leaving the guide if you try that. I personally wouldn't try to fly anything that heavy off of a 1/4" rod unless it was calm. People do, but I'd prefer the extra rigidity and possible length of a launch rail instead. You aren't likely to find a 1/4" rod at your local hardware store longer than 4'. That's pretty short unless the motor has relatively high initial thrust.
 

EXPjawa

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Also, FWIW, I downloaded Apogee's simulation file for the G-Force. On the G80 motor, according to their file (I did nothing to adjust it or check it for correctness), it needs a little more than 4.5 feet to reach stable speed. You won't get that from a 48" rod. And the G40, it needed 7.5 feet (91 inches) to get there. So, that's why they've made the recommendations that they did. If you do fly from a 1/4" rod, get at least 5' of it (since you'll probably loose a some length in mounting it), and stick to the G80, at least until you certify for something larger. Based on that alone, I'd only fly the G40 off of an 8' rail, which you're likely to find at a local club launch. Just my $0.02...
 

shreadvector

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G motors have different thrust levels and "total impulse". The thrust varies over time, so you need to look at the thrust-time curve to see how much thrust is being generated - ESPECIALLY at the beginning when it is trying to gain speed on the launch rod (or rail). Also, if the thrust drops off in flight, a slow moving rocket can start to 'fall out of the sky'.

Actual real motor performance data is on the NAR website:

http://www.nar.org/SandT/pdf/Aerotech/G53FJ.pdf

http://www.nar.org/SandT/pdf/Aerotech/G80-20071207.pdf

The G80 has MUCH more total impulse than a G53 and a nice high thrust level that stays high. The G53 has less thrust at the beginning and then it drops off RAPIDLY. it will be a horrible and possibly dangerous choice for your massive and huge rocket. Your rocket weighs a lot and needs a LOT of thrust to get up to speed and should use a LONG launch rod. Buy a 6 foot steel rod at a hardware store, like Home Depot or Lowes and mount it to a secure and stable launch pad.

Your bicycle stand can support weight, but it is not designed to hold a massive rocket suspended from a launch rod with any wind blowing (let alone the 'kick' from motor ignition). It can work if you add MASSIVE weights on each of the legs to attempt to prevent it from tipping over in the wind or at ignition.

Most good rocket launch pads have a very low center of gravity - they get this by not suspending the rocket too high up and they use very heavy legs at the bottom. And many people add sand bags or small boulders to the legs to stabilize them.

Another new guy here. Never personally seen a rocket launch but now there's one spread across the dining room table.
I wish I had found this web site before choosing a first rocket ....but here I am.
Question: does this rocket need a rod or launch rails?
Yesterday I found this comment on the Apogee Components https://www.apogeerockets.com/Rocket_Kits/Skill_Level_3_Kits/G-Force web site:
"A Note About the G-Force - This kit pushes the limits of "mid-power" rocketry. Aerotech says it will fly on the Mantis Launch Pad, but based on simulations, even the G80 will be underpowered leaving the rod. We recommend either purchasing a longer rod from a hardware store, or modifying the kit to fly off a launch rail (this would require adding rail buttons).
If you add rail buttons and launch it off an 8ft rail instead, you can use a wider selection of G motors to safely fly it."


I don't completely understand this comment. I realize that upon launch the rocket needs to reach a certain velocity before the fins can be expected to provide stability in the direction of flight, however why is the seller saying a G80 (powerful) motor is not enough?
When I looked at the rocket in http://www.rocketreviews.com/aerotech-aerospace-g-force--by-dan-schneider.html almost everyone was happy with a G40-4 for a first flight. I ordered a Aerotech RMS Motor Case 29mm with a G-53- motor reload kit to avoid hazmat mailing fees (no hobby shops in my area). I have a bicycle repair stand that is pretty sturdy (can support 100 lbs) that I was planning on adapting to a launch pad by finding a long rod at the hardware store. My hips are old so I wanted the rocket up off the ground to avoid crawling around in the wet dew covered grass to hook up the igniter. I picked G-force because I have trouble seeing small parts and pieces and need glasses. Thank you.
View attachment 296139
 

Zeus-cat

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Hi Underdog,

Are there any clubs near you? My club bends over backwards to help a newbie (if they want help). Let us know where you are at or look up on the NAR website if there is a club near you. Clubs usually have a good assortment of rods and rails and tons of free advice. I held off joining my local club for a long time - big mistake. A great group of guys and I learned a lot from them and got access to nice fields and good equipment.
 

Bat-mite

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The problem with launch rods is that they are hard to keep straight up. They bend, they wag in the wind. A G-Force requires a 1/4" rod, but this is not optimal, especially if it is windy. The longer the rod, the more stable the flight will be. You have a few options:

  • Launch with a Mantis pad or an Estes Pro Series pad in calm days.
  • Build your own launch pad with PVC and a stainless steel 1/4" rod.
  • Buy rail buttons, and then either fly with a club, or build a rail pad, but now you are talking a lot more money. But you can build one with a Rockwell Jawstand and a six-foot piece of rail, and a little hardware.
 

shreadvector

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A 1/4" rod is not a complete answer.

The Mantis pad loses about 9 inches of the rod inside the pad and deflector. Also, the rod is only about 5 feet log and is Aluminum. it is good aluminum, but it is not as stiff as Steel.

For any pad, for this size rocket, you want a 6 foot long steel 1/4" diameter rod. Even if you use a Mantis pad, (which you are not) and you lose 9 inches inside the par, you will still have at least 5 feet or rod to guide the rocket.

The steel rods are about $6 at Home Depot or Lowes. Probably $7 at Ace Hardware.
 

DavidMcCann

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Regarding motor choice, did you purchase a 29/40-120 case like the one pictured here:


If yes, then I would recommend using a G76 Mojave Green reload with a 4 second delay. It has much more initial thrust, requires no haz mat, and fits in that case.

G76G-


G53-


G80T-



I've launched my 3.3 pound Mini Magg off 4 foot of rail with a G76G-
 
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EXPjawa

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Regarding the simulations that Apogee ran that are sort of the basis of this whole discussion, well, as eluded to, sims are only as good as the input. Despite that being their forte, I took another look at the rocksim file that they have on their site. The empty mass is 45.7 oz, a substantial amount more than the 32 oz figure that Aerotech claims. Now, as I said, YMMV, and its more than possible to add extra mass in the build process. But that's a near 50% increase, so its pretty significant. By overriding the mass numbers in the sim, based on the manufacturer's claim, you get much better performance (as you would imagine). The G80 now reaches stability speed at 44.6", and the G40 shortens that distance by 20", down to 71". That's still a lot, and requires a long rail. But the bottom line is that mass is not to be ignored. If you want to be able to fly on those motors, you'll need to keep the build relatively light.
 

Underdog

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Hi Underdog,

Are there any clubs near you? My club bends over backwards to help a newbie (if they want help). Let us know where you are at or look up on the NAR website if there is a club near you. Clubs usually have a good assortment of rods and rails and tons of free advice. I held off joining my local club for a long time - big mistake. A great group of guys and I learned a lot from them and got access to nice fields and good equipment.
No clubs near me. The NAR sight does have lots of helpful information. There is a site near my brother's house in New Jersey. I could give him the rocket is all else fails.
 

Underdog

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Yes, I purchased a RMS29/40-120 motor case. I would prefer to launch it the field next to my house. The field is big but not huge. The field measures 800 feet wide and 1600 feet long. I was hoping that a lower altitude climb would increase the odds of the rockets staying nearby and in the vicinity of the launch pad. That is why I thought that a G-40 size might be a good fit for the field (and my legs). I am working on how to read the thrust curves (thank you) however I am still at a loss. How high up in the air is the G-Force rocket going to travel based on the thrust curves?
Regarding motor choice, did you purchase a 29/40-120 case like the one pictured here:


If yes, then I would recommend using a G76 Mojave Green reload with a 4 second delay. It has much more initial thrust, requires no haz mat, and fits in that case.


G53-


G80T-



I've launched my 3.3 pound Mini Magg off 4 foot of rail with a G76G-
 
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Underdog

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I have seen the jawhorse on craigslist locally for about $30. That is not too bad. But these rails (1010) seem to be one of those proprietary items that are expensive and expensive to ship.

a few options:

  • Launch with a Mantis pad or an Estes Pro Series pad in calm days.
  • Build your own launch pad with PVC and a stainless steel 1/4" rod.
  • Buy rail buttons, and then either fly with a club, or build a rail pad, but now you are talking a lot more money. But you can build one with a Rockwell Jawstand and a six-foot piece of rail, and a little hardware.
 

EXPjawa

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The rails themselves aren't that expensive, but shipping can be - especially for longer ones. However, the price doesn't change much when you add multiples; the shipping rate is probably by dimensional weight rather than real weight. So, you could buy several and spread the shipping out. Not that you would need several, but that's why folks sometimes team up to buy them. It's perfect if you were to, say, start a local club. But less so for a single flyer. You might also check buying the rails from McMaster Carr. Though its tough to determine their ship costs before the purchase, they have a pretty good rate negotiated with shippers due to their volumes. They probably ship that reasonably too, though I'll let others chime in on that.
 

samb

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So did you already buy the Mantis and the G40 motor ? The Aerotech product catalog says 600 feet projected altitude for that motor. Accurate ? It depends. :) How close is your model to Aerotech's 32oz weight (mass reduces altitude) ? How smooth is the surface finish (drag reduces altitude) ? How windy is it on launch day ? Larger diameter rockets will tend to fly a curved trajectory into the wind with lower impulse motors (lower thrust reduces altitude).
The Mantis pad has been known to jump (the Mantis dance) when the ignition exhaust hits the blast deflector. Please follow the advice to weigh or stake down those legs. I would do that for your bicycle repair stand as well if you go that route. And by all means, go find a 6 foot 1/4inch rod. The Mantis anchor and deflector set-up eats up 9 inches of the launch rod and you definitely want to make up that lost guidance for the bigger Aerotech models.
Hope this helps.

g-force.jpg
 
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DavidMcCann

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Yes, I purchased a RMS29/40-120 motor case. I would prefer to launch it the field next to my house. The field is big but not huge. The field measures 800 feet wide and 1600 feet long. I was hoping that a lower altitude climb would increase the odds of the rockets staying nearby and in the vicinity of the launch pad. That is why I thought that a G-40 size might be a good fit for the field (and my legs). I am working on how to read the thrust curves (thank you) however I am still at a loss. How high up in the air is the G-Force rocket going to travel based on the thrust curves?

Thrust curves alone won't tell you how high you'll go.... for that I'd go here and run some sims- http://www.thrustcurve.org/guidepage.jsp

The benefit of the G76 is that the initial thrust is 150N, where the G53 is around 85. The G76 will take off faster, and go up straight. the G53 may go off at an angle depending on wind, etc. leading to landing further away.

Note that the G40 may only have a 40 average, but it's still 113.7 N of total impulse, so it's going to go slower, but just as high (or further) than a G76 that has 118N (the G53 has 90N )


I wouldn't be discouraged. I flew my Optima on a G53 to around 450 feet. It's around 43 oz. Just make sure there's not a lot of wind. (I was also off a 6 foot rail)
Watch the wind, and realize the rocket will tend to fly into the wind, and obvious drift with it under chute. Once you get used to it, you can nearly land back on the pad.
 
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Underdog

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So did you already buy the Mantis and the G40 motor ? The Aerotech product catalog says 600 feet projected altitude for that motor. Accurate ? It depends. :) How close is your model to Aerotech's 32oz weight (mass reduces altitude) ? How smooth is the surface finish (drag reduces altitude) ? How windy is it on launch day ? Larger diameter rockets will tend to fly a curved trajectory into the wind with lower impulse motors (lower thrust reduces altitude).
The Mantis pad has been known to jump (the Mantis dance) when the ignition exhaust hits the blast deflector. Please follow the advice to weigh or stake down those legs. I would do that for your bicycle repair stand as well if you go that route. And by all means, go find a 6 foot 1/4inch rod. The Mantis anchor and deflector set-up eats up 9 inches of the launch rod and you definitely want to make up that lost guidance for the bigger Aerotech models.
Hope this helps.
I have not purchased mantis or other launch as of yet. Would this 80/20 rod work for a launch rail with this rocket? The price is certainly attractive (but safety first). I would be happy with 600 ft on a G-40. That sounds manageable. I would be nervous about anything higher and frankly would be fine with 300 feet. I called and cancelled the G-53 until I can figure out how to read a thrust curve. I was under the impression that a "slow" launch would be more interesting to observe (at least for me).
t slot rocket rail.JPG
 
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DavidMcCann

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Those 80/20 1010 rails are exactly what I use.

the G64 isn't a bad option for you.... I'd fly that or the G76. But if you hit the same weight Aerotech did, they do recommend the G38- which has a max thrust of around 55N. That opens up the possibility of flying on an F52 or F50 motor, which has a max thrust of 79N. It'd be a 300 foot flight, and F's are all sadly hazmat.... but if it worked it'd be a nice pop. (again I've flown F50's and F52's in my 43 oz optima). They punch hard enough off the pad to work just enough with no wind.

 
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Underdog

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Those 80/20 1010 rails are exactly what I use.

the G64 isn't a bad option for you.... I'd fly that or the G76. But if you hit the same weight Aerotech did, they do recommend the G38- which has a max thrust of around 55N. That opens up the possibility of flying on an F52 or F50 motor, which has a max thrust of 79N. It'd be a 300 foot flight, and F's are all sadly hazmat.... but if it worked it'd be a nice pop. (again I've flown F50's and F52's in my 43 oz optima). They punch hard enough off the pad to work just enough with no wind.
Great, that's easy! Is 97" long enough? What button guides do you J-B Weld to your rocket tubes (if I may ask?)?
 
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Underdog

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You can screw these in with a little CA or epoxy on the screw.
I called AMWPRO-X and spoke with Robert DeHate. He said he could drop a package of two in mail for me today. Is two enough?
buttons.JPG
 
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dhbarr

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Two is exactly right, unless you need spares.
 

Underdog

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Regarding motor choice, did you purchase a 29/40-120 case like the one pictured here:


If yes, then I would recommend using a G76 Mojave Green reload with a 4 second delay. It has much more initial thrust, requires no haz mat, and fits in that case.
I've launched my 3.3 pound Mini Magg off 4 foot of rail with a G76G-
When reading this thrust curve is the "average" the value of significance. Now I'm curious to know what the completed Rocket will finally end up weighing. Maybe I can skip the epoxy and use something lighter.
thrust.JPG
 
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Underdog

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So now I think I understand that the forces on that the launch needs to support are not just the rocket's downward thrust but the force created when a breeze blows against the rocket up 6-8 feet high on the launch rail, and any side to side force as the fins get up to speed. With a launch rail this tall I imagine there could be some mechanical leverage involved. How wide of a stance does the base need to be? Is there a formula for this? Is "light and portable" mutually exclusive of "safe and secure" for a rocket/rail combination of this size?
fulcrime.JPG
 

dhbarr

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Leg extensions, tent pegs, and / or weights.
 

DavidMcCann

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It would have to be a pretty hard wind to compromise the rail itself. The idea is to keep the light rocket stable from wind yes, but those forces don't translate to much stress on the pad. Sandbags/tent pegs will be enough.


The average value in a thrust curve is the number after the letter in a motor's name. a G80-4T has 80N average thrust, a 4 second after burnout delay before ejection, and the T stands for Blue Thunder propellant. What's not in the name is the total impulse. In this motor's case, it is 137N.

You can have motors with very different properties. some burn fast with a hard thrust for a short duration that drops off quick....or a nice even burn across a couple seconds, or one that starts slow and builds up more thrust as it burns. All part of the fun.
 
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Underdog

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Why does Aerotech list a G-38 and a G-40 in the SU motor but not a G-53 or G-60 in the RMS motors? Is there that big of a difference in these re-loadable (RMS) motors vs the SU motors?
aerotech.JPG
 
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AfterBurners

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It's a big rocket don't be intimidated by it. Like all Aerotech kits they go together rather easy and their fin lock systems guarantees your fins get on straight. I probably would have started with one of their smaller kits but you'll be fine.
 

Steve Shannon

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Why does Aerotech list a G-38 and a G-40 in the SU motor but not a G-53 or G-60 in the RMS motors? Is there that big of a difference in these re-loadable (RMS) motors vs the SU motors?
View attachment 296216
The G53 and G60 RMS motors may not have been out when the package art was designed. I wouldn't worry about it.


[emoji1010] Steve Shannon [emoji1010]
 

samb

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Why does Aerotech list a G-38 and a G-40 in the SU motor but not a G-53 or G-60 in the RMS motors? Is there that big of a difference in these re-loadable (RMS) motors vs the SU motors?
View attachment 296216
It's not so much RMS vs. SU as it is how the thrust is delivered over time (the thrust curve :)) for a specific motor. IDK but my guess is that the G53 wasn't available when Aerotech came up with their list. Aerotech doesn't make a G60 that I know of. We have digital tools like ThrustCurve and Openrocket that are very useful aids in picking motors (after a short learning curve). I still find value in using the manufactures recommendations as a starting point for motor selection, keeping in mind the fact that your models weight compared to the catalog weight is a critical factor. I've also found an old school tool I picked up from the defunct Info-Central site to be a useful addition to the motor selection tool box.

View attachment 296225View attachment 296226

http://www.thrustcurve.org/guidepage.jsp

http://openrocket.sourceforge.net/index.html


A nice video tutorial on choosing motors: http://www.jcrocket.com/choosing-motors.shtml
 
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