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Re: Times and sec/ft
Posted: January 22nd, 2020, 9:17 am
by Airco2020
CookiePie1 wrote: ↑January 21st, 2020, 7:34 pm
Airco2020 wrote: ↑January 21st, 2020, 7:00 pm
builderguy135 wrote: ↑January 20th, 2020, 2:56 pm
lmao this was only a month ago. aren't people getting just under double that already?
Sorry, but how did you calculate this? and, theory tends to be quite different than practice in build events, especially one as complicated as parachutes.
For rocket team last spring we used the calculations from this site -
http://www.rocketmime.com/rockets/descent.html
If you scroll down on that page you can use the red calculation for velocity: v = sqrt( (8 m g) / (p r Cd D2) )
Where
D is the chute diameter in meters
m is the rocket mass in kilograms
g is the acceleration of gravity = 9.8 m/s2
p is 3.14159265359
r is the density of air = 1.22 kg/m3
Cd is the drag coefficient of the chute, which is 0.75 for a parasheet (flat sheet used for a parachute, like Estes rockets), or 1.5 for a parachute (true dome-shaped chute).
v is the speed we want at impact with the ground (3 m/s or less)
You just need to multiply the v which is in meters/sec by 3.281 to get Feet per second. If the claims are true you need .5 ft/sec in this calculation.
I know there are some people flying outside - and who knows what that means for times. And some of the gyms I've been in feel like a tornado - so maybe you can catch an updraft. It's also a bit hard to estimate height in the gym or exactly how high the rocket went on a launch, so there might be some error in reported numbers because of that. But to get .5 on this calculation you need to be around 2 meters and 5 grams unless you can build a super light dome shape (real) parachute and then you still need 1.5M.
Re: Times and sec/ft
Posted: January 22nd, 2020, 4:39 pm
by Paypog
Airco2020 wrote: ↑January 22nd, 2020, 9:17 am
CookiePie1 wrote: ↑January 21st, 2020, 7:34 pm
Sorry, but how did you calculate this? and, theory tends to be quite different than practice in build events, especially one as complicated as parachutes.
For rocket team last spring we used the calculations from this site -
http://www.rocketmime.com/rockets/descent.html
If you scroll down on that page you can use the red calculation for velocity: v = sqrt( (8 m g) / (p r Cd D2) )
Where
D is the chute diameter in meters
m is the rocket mass in kilograms
g is the acceleration of gravity = 9.8 m/s2
p is 3.14159265359
r is the density of air = 1.22 kg/m3
Cd is the drag coefficient of the chute, which is 0.75 for a parasheet (flat sheet used for a parachute, like Estes rockets), or 1.5 for a parachute (true dome-shaped chute).
v is the speed we want at impact with the ground (3 m/s or less)
You just need to multiply the v which is in meters/sec by 3.281 to get Feet per second. If the claims are true you need .5 ft/sec in this calculation.
I know there are some people flying outside - and who knows what that means for times. And some of the gyms I've been in feel like a tornado - so maybe you can catch an updraft. It's also a bit hard to estimate height in the gym or exactly how high the rocket went on a launch, so there might be some error in reported numbers because of that. But to get .5 on this calculation you need to be around 2 meters and 5 grams unless you can build a super light dome shape (real) parachute and then you still need 1.5M.
I'm not really into all the math that goes on but I can also confirm that 2sec/ft is possible and it may have something to do with the material that is being used because that would change the drag coefficient, as well as a plethora of other factors that go into the design of a parachute. Once again, I don't really know what I'm talking about but I wouldn't say that the numbers you're getting out of these calculations are finite. Like lavarball once said, if you want to succeed in this event, "find a way."
Re: Times and sec/ft
Posted: January 22nd, 2020, 5:06 pm
by rabbitman
Airco2020 wrote:
CookiePie1 wrote: ↑January 21st, 2020, 7:34 pm
Sorry, but how did you calculate this? and, theory tends to be quite different than practice in build events, especially one as complicated as parachutes.
For rocket team last spring we used the calculations from this site -
http://www.rocketmime.com/rockets/descent.html
If you scroll down on that page you can use the red calculation for velocity: v = sqrt( (8 m g) / (p r Cd D2) )
Where
D is the chute diameter in meters
m is the rocket mass in kilograms
g is the acceleration of gravity = 9.8 m/s2
p is 3.14159265359
r is the density of air = 1.22 kg/m3
Cd is the drag coefficient of the chute, which is 0.75 for a parasheet (flat sheet used for a parachute, like Estes rockets), or 1.5 for a parachute (true dome-shaped chute).
v is the speed we want at impact with the ground (3 m/s or less)
You just need to multiply the v which is in meters/sec by 3.281 to get Feet per second. If the claims are true you need .5 ft/sec in this calculation.
I know there are some people flying outside - and who knows what that means for times. And some of the gyms I've been in feel like a tornado - so maybe you can catch an updraft. It's also a bit hard to estimate height in the gym or exactly how high the rocket went on a launch, so there might be some error in reported numbers because of that. But to get .5 on this calculation you need to be around 2 meters and 5 grams unless you can build a super light dome shape (real) parachute and then you still need 1.5M.
bro check ur numbers you can get 0.5 ft/s with like .9m diameter and 15 grams... idk how realistic these numbers are because i dont do the event, but someone else can check
also I dont think there is a point in doing calculations (especially given that the formulas you are using are approximations) for something like this... experimenting is better imo
Re: Times and sec/ft
Posted: January 22nd, 2020, 7:13 pm
by newflight
@Xiangyu, @ lavarball , did you actually already get about 30 seconds in a 25ft gym? that is so amazing.
xiangyu wrote: ↑January 22nd, 2020, 8:59 am
newflight wrote: ↑January 22nd, 2020, 8:20 am
Does that mean you can get 37.5 second in a 25ft high gym?
37.5 second seems to be unbelievable good
xiangyu wrote: ↑January 21st, 2020, 8:18 pm
Nice. I think I´m pretty close to achieving 1.5 soon as well (hopefully). Got a nice design and some prototypes in testing, just gotta make them a little more consistent and fix a couple of small issues.
Probably possible, but most likely a little less IMO since the parachute will likely drop a few feet before it fully opens.
Re: Times and sec/ft
Posted: January 22nd, 2020, 7:58 pm
by xiangyu
newflight wrote: ↑January 22nd, 2020, 7:13 pm
@Xiangyu, @ lavarball , did you actually already get about 30 seconds in a 25ft gym? that is so amazing.
xiangyu wrote: ↑January 22nd, 2020, 8:59 am
newflight wrote: ↑January 22nd, 2020, 8:20 am
Does that mean you can get 37.5 second in a 25ft high gym?
37.5 second seems to be unbelievable good
Probably possible, but most likely a little less IMO since the parachute will likely drop a few feet before it fully opens.
TBH not yet, but I have a descend time of ~6 s in 4 feet drop space, consistency a little low at around 60% success rate which is what I'm tuning rn. Ofc, once I have that tuned the deployment will also be a pain in the neck and cause me a little trouble and experiments.
What's your highest time?
Xiangyu
Re: Times and sec/ft
Posted: January 22nd, 2020, 8:16 pm
by newflight
I only get around 14 seconds @25 ft gym
xiangyu wrote: ↑January 22nd, 2020, 7:58 pm
newflight wrote: ↑January 22nd, 2020, 7:13 pm
@Xiangyu, @ lavarball , did you actually already get about 30 seconds in a 25ft gym? that is so amazing.
xiangyu wrote: ↑January 22nd, 2020, 8:59 am
Probably possible, but most likely a little less IMO since the parachute will likely drop a few feet before it fully opens.
TBH not yet, but I have a descend time of ~6 s in 4 feet drop space, consistency a little low at around 60% success rate which is what I'm tuning rn. Ofc, once I have that tuned the deployment will also be a pain in the neck and cause me a little trouble and experiments.
What's your highest time?
Xiangyu
Re: Times and sec/ft
Posted: January 22nd, 2020, 9:16 pm
by Airco2020
newflight wrote: ↑January 22nd, 2020, 8:16 pm
I only get around 14 seconds @25 ft gym
xiangyu wrote: ↑January 22nd, 2020, 7:58 pm
newflight wrote: ↑January 22nd, 2020, 7:13 pm
@Xiangyu, @ lavarball , did you actually already get about 30 seconds in a 25ft gym? that is so amazing.
TBH not yet, but I have a descend time of ~6 s in 4 feet drop space, consistency a little low at around 60% success rate which is what I'm tuning rn. Ofc, once I have that tuned the deployment will also be a pain in the neck and cause me a little trouble and experiments.
What's your highest time?
Xiangyu
That would have placed 1st and 2nd at the two invitationals I've been to.
Re: Times and sec/ft
Posted: January 22nd, 2020, 10:07 pm
by Sc1olygod
Airco2020 wrote: ↑January 22nd, 2020, 9:16 pm
newflight wrote: ↑January 22nd, 2020, 8:16 pm
I only get around 14 seconds @25 ft gym
xiangyu wrote: ↑January 22nd, 2020, 7:58 pm
TBH not yet, but I have a descend time of ~6 s in 4 feet drop space, consistency a little low at around 60% success rate which is what I'm tuning rn. Ofc, once I have that tuned the deployment will also be a pain in the neck and cause me a little trouble and experiments.
What's your highest time?
Xiangyu
That would have placed 1st and 2nd at the two invitationals I've been to.
What type of invitationals are these?
Re: Times and sec/ft
Posted: January 23rd, 2020, 5:29 am
by Hartman
I placed first in an invitational with a 6 second parachute. First time I was surprised to get a medal.
So it seems like everyone’s doing a bit better than me so far...
Re: Times and sec/ft
Posted: February 3rd, 2020, 4:06 pm
by donutsandcupcakes
In my invitationals the 1st place winner had time of around 20 secs. I was surprised at the time. But the top 5 scores were 15-20 with like i said around 20 secs as the 1st place winner.