CG and CP which where how to figure on a Saturn V estes Rocket

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jrap330

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OK OK I mis-spoke I know CG is above CP.. I got it. I've been busy with life but let me answer a few questions. I figured out the CP with the cardboard cut out I have not ventured into the rocksim but now I know I will have to. So if I have a proper CP and it is below the CG and I put in the engines Estes said should work and the sale of the rocket is based on it it will fly. I did not overweight mine I did not slop paint on it I did not attach heavy metal objects to it but it would not fly until I experimented with larger engines then Estes called for...That's my point..... I balanced the rocket to acquire the CG with everything loaded on the rocket like it was going to fly. I was not using heavier motors then suggested and yet it was underpowered.

I understand about the F24 Aerotech motor and you load it I got that and have one but not to that stage yet. I don't want to get into it but someone mentioned about cg being in front of cp by one body diameter tube size if you do that on a Saturn V you have to add a lot of weight into the nose to make it stable and now how is that to have been flown out of the box with the suggested engines. Kits other then Estes provide a cg if built as shown, Estes gives no advice or any info on cg or stability???? I'm on some other thread about my two versions of Saturn V and the amount of weight you need to make it stable by the information you have provided, rocksim or no rocksim now its so heavy trying to get off the pad and reaching 250 feet and this is on an Aerotech engine. Ok one area I need more understanding cause trying to read about the aerotech engines the different blue,white,black.. and all the numbers given and how one article talks about power to get a heavy rocket off the pad but it does not have p-ower to accelerate, or this color will accelerate or for heavy weight, so ok what numbers are you using to get a more powerful engine(one that will liftoff the rocket and accelerate to a safe altitude with ample room for the delay to happen and then the chute to come out and not make a hail Mary landing????? They have numbers in 8 different categories and weight of max liftoff??? so how do you look at all the numbers and say this has enough total power to launch this rocket. I used a E30-4T and it got the Saturn V to 250feet, but I wanted more room and so I tried a F44-4W and a F32-4T but these did not increase the altitude what so ever so I might as well use a E30 Aerotech so what did I read wrong and how do you pull out the real number of these engines other then by experimenting...I'll take any advice. Ok enough for now
Sterk03
Understand your concern...but you know 250 is not bad. Issue is will all 3 chutes deployed and I for one always consider changing out the 2 chutes on the body for just 1 chute.....either the 24 incher or a larger one. BobbyG23 did a built thread last year and after crashing on an E12 ..he tried a E30 and like the result. Check out his build thread.....search Saturn V build thread.
 

Sterk03

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Just to update things yes I get if it is built light and little weight is added it might fly on a D12-3 but if you build it light and accordting to the plans it’s as light as you can make it but then when you measure cog and add nose weight to make it stable you have to add too much weight to get it in the stable range that there is no way to fly it with a D12-3 that is all I’m saying. SoI have had successful flights with the AeroTech E30-4T but these are barely 200 feet with using a lot more power then a D and I.m trying to get it higher then that just for a little more safety margin for chutes. So I did see theF24 rocket video very impressive I.m not sure I want it that high I. The limited launch area but I used a F44 thinking this will make it go higher plus fit I the old Saturn that can only take a (D) size motor and it maybe went not as high as the E30.
yes I am not used to theAerotech and I,m trying to learn how to read the numbers given with the engines and which numbers are most important in motor selection but felt a F should be more thena E or D motor and it was not, So engine letter is not enough soI need to find the out of all the numbers listed which ones I need to use for engine selection, I was taking notice of liftoff weight also and though this should be helpful but not sure it was. Also the AeroTech article about flame color which is not only about tracking the rocket but also liftoff power and acceleration etc.

I need a more accurate graph f the possible AeroTech motors and definitions on all the columns of numbers and use them and test fly some larger motors.
Again thanks for all the help.
At least I have accomplished several successful flights thanks to the E30-4T AeroTech.

Sterk 03
 

bobbyg23

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Understand your concern...but you know 250 is not bad. Issue is will all 3 chutes deployed and I for one always consider changing out the 2 chutes on the body for just 1 chute.....either the 24 incher or a larger one. BobbyG23 did a built thread last year and after crashing on an E12 ..he tried a E30 and like the result. Check out his build thread.....search Saturn V build thread.
I did. I learned a lot from that build. that rocket is my avatar pic
 
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bobbyg23

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For motors, you really need to look at its thrust curve. The E30 has an initial thrust of 11lbs. That gives it its pop off the pad to get enough airspeed so the fins can take over the stability. You can't just go by the letter. That is the total impulse range. To over simplify it, if I have an E motor, a 12 would have lower initial thrust but a longer burn time. A 30 would have higher initial thrust with a shorter burn time. Don't be concerned with the propellent color, look at the thrust curve to figure out what you need. A thrust to weight ratio of 5:1 or higher is preferable in my opinion.

1632154039092.png
 

Antares JS

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The limited launch area but I used a F44 thinking this will make it go higher plus fit I the old Saturn that can only take a (D) size motor and it maybe went not as high as the E30.
The F44 is a baby F that doesn't have much more total impulse than an E. It has higher thrust (44 N average vs. 30 N in the E30) but that's not always a good thing, especially on a draggy rocket like a Saturn V. More thrust gets the rocket going faster, but drag also increases with speed. These two reasons, that the F44 does not have much more impulse than the E30 and the higher speed causing higher drag, are probably the reasons why the Saturn V didn't go higher on the F44 than the E30.
 

bobbyg23

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For instance, here is the thrustcurve chart for my saturn v. Everything else was too slow off the rod resulting in a less than desirable flight.
1632157131852.png
 

Blast it Tom!

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You know, this one has me wondering... obviously the peak thrust and total implulse are key; you have to get the rocket moving fast enough to get off the rail and then keep burning until you get far enough from the ground. @bobbyg23 shows this nicely.

But as to the title... when I look at the Barrowman method for CP and other stability parameters, and think of how it would be applied to this rocket, I see a "nose cone" element, two transition elements 'way up front, and itsy-bitsy fairings/fins back at the back end. Now I am just learning the original method, so maybe there are updates/changes/improvements, but as I understand it, straight cylindrical sections of body tube aren't counted. Yet for this beauty, they make up a HUGE part of the area. So how does that work?

And isn't it amazing that in real life they can balance 6.2 million pounds of mass 363ft tall, on a pillar of flaming gas, like balancing a broomstick on the palm of your hand? I dorn't know if I'll ever loose my sense of marvel over that. Actually, I hope I don't.
 

Antares JS

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they make up a HUGE part of the area. So how does that work?
My understanding is that the reason body tubes are left out of barrowman equations is because the surface of the body tube is parallel to the airflow, and so theoretically isn't bending/affecting it like your forward surfaces (nose/transitions) and fins are.
 

smstachwick

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You know, this one has me wondering... obviously the peak thrust and total implulse are key; you have to get the rocket moving fast enough to get off the rail and then keep burning until you get far enough from the ground. @bobbyg23 shows this nicely.

But as to the title... when I look at the Barrowman method for CP and other stability parameters, and think of how it would be applied to this rocket, I see a "nose cone" element, two transition elements 'way up front, and itsy-bitsy fairings/fins back at the back end. Now I am just learning the original method, so maybe there are updates/changes/improvements, but as I understand it, straight cylindrical sections of body tube aren't counted. Yet for this beauty, they make up a HUGE part of the area. So how does that work?

And isn't it amazing that in real life they can balance 6.2 million pounds of mass 363ft tall, on a pillar of flaming gas, like balancing a broomstick on the palm of your hand? I dorn't know if I'll ever loose my sense of marvel over that. Actually, I hope I don't.
I’ve been looking at some of the principles behind the simplified Barrowman equation everyone’s familiar with, and there are some idiosyncrasies to watch out for. If you have a wide BT on the aft end and a teeny tiny nose, it’s entirely possible for the calculations to think that the fins are going to be more effective than they actually are because they stick so far out into the airstream and give you a CP much further to the rear than in reality. Apogee had a great article on this regarding RockSim’s stability calculations and its incorporation of elements of the full Barrowman calculations (i.e. accounting for a specific nose shape, unusual fin configurations, etc., all of which were taken into account in Barrowman’s original work) into the program.

But considering that this is a kit build that has already demonstrated successful flight, I don’t think this will be an issue. As long as the components aren’t damaged and @Sterk03 didn’t go crazy with adhesives and packs the parachute as close to the nose as possible, the CG and CP should be pretty close to the rocket’s design.

As far as flight safety, I can say that I’ve had some successful sub-100ft flights with underpowered rockets on a 2-second delay. In my case it was an Estes Firestreak deploying a streamer on a 1/4A3-2T, which is a smaller motor than is recommended. I’ve also flown an Estes Phantom (basically an Alpha III with transparent plastic components) to about 65 ft on an 18mm 1/2A6-2 and got it back without damage despite the parachute not opening completely.

A 100ft flight on a D12-3 in this bird (per the Estes specifications) should be plenty safe.

Even if it’s too long of a delay, you’re not likely to suffer major structural damage or create an unreasonable hazard from a late deployment or ground impact when you’re dealing with an apogee that low. Seeing performance figures for this thing and comparing it to my own experience with similar flights (albeit at a smaller scale) leads me to conclude that perhaps our friend Sterk is overthinking things here. A build to specification and with the recommended motors should get this thing in the air and back on the ground in flyable condition or needing only minor repairs.
 

Blast it Tom!

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Well, I'll admit that my thoughts were toward an eventual Saturn V of my own someday, perhaps not a kit, but a "build of a lifetime" model. I'd agree with you and Sterk that a retail kit should fly as advertised if built according to their instructions - as an engineer I'd be embarrased if a product of mine was found to underperform, you'd think I'd have tested it quite exhaustively.
 
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