Lightweight electronics

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brehos110

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I am building a rocket that I would like to fly as high as possible. Would it be lighter to build a sturdier airfare for a g80 or would it be lighter to build a regular airframe for a g12 and use an electronics bay?
 

rharshberger

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Lots of things come into play when building a rocket for altitude, lighter weight isn't necessarily one of them. There is whats known as optimum weight and on a cardboard airframe with plastic nosecone its likely that the optimum weight for altitude will require additional weight, whether it be electronics or noseweight. If you haven't already download Open Rocket (its free) design your rocket and pick a motor then play with adding and subtracting weight and see what effect it has on altitude.
 

dhbarr

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If you want to go high and cheap, try apogee aspire components and the AT 29/40-120 g76-g load.
 

heada

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Apogee Aspire on the F10 will break a mile high (just under 6000ft) You may not find it again though. Same kit on an H13 will go just over 2 miles (13500ft) but then you'd have to add electronics for deployment which could reduce that altitude by 1000ft or so.

G80 is a good motor but won't give you the best altitude. Standard paper tubes are up to the task for a G80, no need to go fiberglass.
 

Voyager1

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As Rich suggests, use OpenRocket to perform simulations of the various designs you're considering.

One thing to consider when you use a long burn low thrust motor such as the G12, is that you limit your max loaded rocket mass to about 100g to 200g depending on whether you use a 5:1 or 3:1 thrust-weight ratio. That loaded mass includes the rocket, motor, parachute and tether, plus a small altimeter if used.
 

BEC

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Taking into account Rich's comment that lighter isn't necessarily better once you reach a certain point, in general long, low thrust burns will get you more altitude than the same total impulse spent more quickly for the simple reason that drag increases with the SQUARE of velocity. So if you can get something that's moving quickly enough off the rail on a G12 that would be the way to go vs. G80.

Thrust to weight ratio is just one way to figure out if the thing is going fast enough at the end of the launch guidance. Again, OpenRocket will help you figure that out.

And of course there are peak reading altimeters that weigh only 3 or 4 grams (and one recording unit under 1g) so an altimeter isn't much of a constraint (not counting deployment electronics, of course, or tracking which might be needed for something like this....)
 
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Voyager1

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Taking into account Rich's comment that lighter isn't necessarily better once you reach a certain point, in general long, low thrust burns will get you more altitude than the same total impulse spent more quickly for the simple reason that drag increases with the SQUARE of velocity. So if you can get something that's moving quickly enough off the rail on a G12 that would be the way to go vs. G80.
Good point!
 

teepot

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If you want a heavier weight BT then the heavy walled BT's from BMS might be a better choice than an Estes weight tube.
 

OverTheTop

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Taking into account Rich's comment that lighter isn't necessarily better once you reach a certain point, in general long, low thrust burns will get you more altitude than the same total impulse spent more quickly for the simple reason that drag increases with the SQUARE of velocity. So if you can get something that's moving quickly enough off the rail on a G12 that would be the way to go vs. G80.

Thrust to weight ratio is just one way to figure out if the thing is going fast enough at the end of the launch guidance. Again, OpenRocket will help you figure that out.

And of course there are peak reading altimeters that weigh only 3 or 4 grams (and one recording unit under 1g) so an altimeter isn't much of a constraint (not counting deployment electronics, of course, or tracking which might be needed for something like this....)
That is one consideration, but not all to be accounted for. There is also the "gravity loss" for the flight which is the energy expended in lifting the fuel off the ground before it gets burned. To optimise for this it would be a very short burn, with maximum velocity down very low. So a balance needs to be found between this energy requirement and the drag losses during the flight. Simulations will provide insight as to where the optimum is.
 

BEC

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Interesting thought in the G impulse rocket context. The fuel fraction of the overall mass is not that significant here, I think. The range in propellant masses for Aerotech Gs is between ~55g and a little over 80g (for the G12). The G80’s propellant mass is 20g less than the G12. So we‘re talking about gravity loss for a delta of 20g over, what, maybe 8000 feet?

Agreed a simulation will likely sort this out readily, but I’d be skeptical, at least in the OPs case, that speed down low is better than a long, slow burn.
 

dhbarr

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Interesting thought in the G impulse rocket context. The fuel fraction of the overall mass is not that significant here, I think. The range in propellant masses for Aerotech Gs is between ~55g and a little over 80g (for the G12). The G80’s propellant mass is 20g less than the G12. So we‘re talking about gravity loss for a delta of 20g over, what, maybe 8000 feet?

Agreed a simulation will likely sort this out readily, but I’d be skeptical, at least in the OPs case, that speed down low is better than a long, slow burn.
Drag on a 32mm g12 is immense relative to one of the CTI 24mm 6H G's
EDIT: 32mm RC load vs 29mm ST, the cross sectional drag still stands.
 

BEC

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The recently released SU G12 is a 29mm DMS motor, but of course a model that would house that will have frontal drag than something built for 24mm. The OP asked about G12 and G80. Both are 29mm. The G12 does have the disadvantage also that it’s plugged, so electronic deployment is required, which adds mass and complexity (but only a little more skin friction drag to make room vs. the G80).
 

brehos110

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Thank you everyone for responding! I am working on an open rocket simulation for the rocket. Does anyone known what a good base weight number would be for electronic? I will probably just deploy the parachute with the electronics. I do not think that I will need a cable cutter/ chute release.
 
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