trajectory?

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rocketsonly

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Does anyone know any simple principles of trajectory?

I do know you aren't allowed to tilt the launch rod more than 30 degrees from perpendicular.

One of my previous science teachers asked if my TARC team could launch some rockets on Veterans day (November 11). We were thinking of using some G's and tiliting the rail so that the rocket would go over to this gigantic piece of land consisting of a football field, a 400m track (and field), and a soccer field side by side.

Is this a good idea? Bad idea? Comments?

Thanks.
 

Justin Horne

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If it's angled enough to have the effect you want, you are going to (or very likely with g's and f's) sipper your tube, shred a chute, or cause a separation... Personally, I wouldn't do it... Straight up, or as close to that for wind, for me. Just MY opinion though, so keep that in mind.:)
HOWEVER, using Cs or Bs, you could probably get away with it.
EDIT: Don't know where I got Gs and Fs... Anyhoo, same answer..:)
 

Stymye

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that doesn't sound like a good idea
the rocket may go further than you anticipate,why not launch from the actual field(if it's big enough)?
 

teflonrocketry1

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You need some flight simulation software to give you an idea of how much tilt to put on the launch rod. You can download a Demo version of RockSim to get some idea of how to do this, visit:

https://www.apogeerockets.com/rocksim_demo.asp

You need to view the 2D flight profile and change the launch rod angle to see how it affects the range when the simulation reaches the end.
This also depends on the rocket; larger wider rockets won't go as high and may not require as much angle on the launch rod.
I have given public demonstrations where 2 hours of simulation work before the flight allowed me to land the rocket back on the launch pad or into my hands!

I wrote an article on this a while ago when the software was much less sophisticated, visit:

https://www.apogeerockets.com/education/newsletter24.asp

If you build a typical parachute recovered model rocket you should launch it so it comes down safely within the suggested launch area.

Bruce S. Levison, NAR #69055
 

rocketsonly

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Originally posted by Justin Horne
If it's angled enough to have the effect you want, you are going to (or very likely with g's and f's) sipper your tube, shred a chute, or cause a separation... Personally, I wouldn't do it... Straight up, or as close to that for wind, for me. Just MY opinion though, so keep that in mind.:)
HOWEVER, using Cs or Bs, you could probably get away with it.
EDIT: Don't know where I got Gs and Fs... Anyhoo, same answer..:)
I said in the first post we were thinking of using G's :D
Don't worry, you arn't hearing things.
 

rocketsonly

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Originally posted by stymye
that doesn't sound like a good idea
the rocket may go further than you anticipate,why not launch from the actual field(if it's big enough)?
The teacher wanted us to launch it from the Quad at lunch because most people hang around there and it's pretty much in the center of our campus. He worried that nobody would come out to the fields to see a rocket launch; but heck, if it was a G I WOULD definetly come out!
 

brianc

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Originally posted by rocketsonly
We were thinking of using some G's and tiliting the rail so that the rocket would go over to this gigantic piece of land consisting of a football field, a 400m track (and field), and a soccer field side by side.
Do a search for 'St. Louis Arch' or 'Gateway arch' launch. This sounds like something
you might want to learn from....

GOOD LUCK!
 

DynaSoar

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Originally posted by rocketsonly
Does anyone know any simple principles of trajectory?

I do know you aren't allowed to tilt the launch rod more than 30 degrees from perpendicular.

One of my previous science teachers asked if my TARC team could launch some rockets on Veterans day (November 11). We were thinking of using some G's and tiliting the rail so that the rocket would go over to this gigantic piece of land consisting of a football field, a 400m track (and field), and a soccer field side by side.

Is this a good idea? Bad idea? Comments?

Thanks.
Lookout, Rocketguts is going Hollywood!

Sure, you can do it. Any scientific calculator has the right buttons. Which ones to push comes from trigonometry.

This is going to a be perfect-world, Newtonian, Galilean, physics class description. We'll deal with reality later.

A rocket, having no lift, follows a ballistic trajectory. In the simplest case, a falling object accelerates at 16 feet per second squared -- it just falls. If that object also had speed relative to a point on the ground -- forward speed -- that would continue. Gravity doesn't care if something's dropped or moving forwards. A bullet does this. Once fired, it may be going forwards real fast, but it drops to the ground at the same time it would have if you'd dropped it from your hand at the same height.

If the object has upward speed, gravity still acts exactly the same way. The object "falls" as long as it's not being pushed up. If it's travelling upwards but not under power, this means that the acceleration due to gravity is simply a subtraction in its upwards speed, at the same rate: 16 ft/sec^2. Until that becomes zero, of course, then it's adding and down.

A rocket gets pushed up by thrust. As long as the thrust pushes, the above doesn't apply. When the thrust stops, though, gravity takes over. The best way to see this is to use Rocsim, SpaceCad or even just the rocket simulators on EMRR and get a point by point prediction for any old rocket. Thrust accelerates it, when that stops the upward acceleration switches to gravity powered decelleration, it peaks and starts to fall. If you fire a rocket straight up, it follows its boost phase and then "falls", even if it's while it's still rising.

If you fire at an angle, the amount of speed it gets remains the same as if you'd fired it straight up. Hopwever, the amount of speed that goes to "up" and the amount that goes to "forwards" will depend on the angle. The flight path is the hypotenuse of a right triangle. You have that length from the alitude prediction, and you have the adjacent angle. Now it's time to get out the trig book and calculate the length of the other two sides. Their length, divided by the boost time, gives you the speed.

Ignore the forwards part for now. Take the upwards part and start subtracting speed until it reaches zero, then start adding downwards speed. Keep track of how much "up" is left, until that amount is zero. The Eagle has landed. Hard.

The forwards speed, well you know how much it gets. Just assume it keeps all that. Now you can calculate the forwards speed just like the upwards and add up how much you get if it travels forwards until the zero altitude time you just calculated. Multiply speed times time and you've got downrange distance.

We haven't figured in airflow drag. The simulators do. Trust them.

So, you come up with flight path described by a diagonal line at an angle to the ground which is your launch angle. Starting from there, your trajectory becomes a parabola. That continues until it hits the ground, or something.

Or Something: We don't want to hit the ground yet. We have a delay and ejection. So, follow the path only as far as the boost time plus delay. At that time, the chute comes out, and it comes down in a completely unscientific and realistic manner. Descent can be calculated by the descent calculators on EMRR (love that "tools" section). Now you've got a diagonal line, mostly up, some forwards, then a parabola, don't worry about the up, still forwards, until a certain point X amount downrange and Y amount altitude. The path after that depends upon the wind speed, chute efficiency, weight, the attractive field of Rocket Eating Trees, etc.

If you want to spot land these, calculate the trajectory as above (for different launch angles and/or distances from the landing area. With a little trig and the data from a flight predictor, you can draw it out.

My recommendation is to do this all the way to the ground, adjust your angle so that a lawn dart would land dead center of the landing area, and use as long a delay as possible as long as it's not after your altitude prediction says zero. And use real tough recovery gear. The higher the ejection, the more your landing will be at the whim of the Rocket Ghods. I say dead center because if the chute works, it'll land closer which is a good thing, and if it lawn darts, you've got maximum safety zone, a major consideration for public displays. T

To be on the safe side, do the calculations with zero, 5 10 and 15 MPH additions to the forwards speed, and what angle you have to use to hit dead center. On the day of launch, check the wind speed and direction and adjust your launch angle accordingly, including even a left/right component if necessary.

And since you're doing this in public and want it to look professional, after calculating everything, go practice. Because it's scientific, and engineeringistical, and hey, you've got an excuse to launch more rockets.

Veteran's Day? Plenty of time. I know a amateur mad rocket scientist verteran who could help out. He's got a caulculator. As you can probably tell from a few vague points above, he doesn't have a trig book. I bet the school does though.
 

MetMan

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Originally posted by DynaSoar
A rocket, having no lift, follows a ballistic trajectory. In the simplest case, a falling object accelerates at 16 feet per second squared -- it just falls.
I believe that's 32 ft/sec/sec, or 9.8 m/sec/sec. But what he said--do the physics on it. Then for laughs run it through Rocsim...

MetMan
 

rocketsonly

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Veteran's Day? Plenty of time. I know a amateur mad rocket scientist verteran who could help out. He's got a caulculator. As you can probably tell from a few vague points above, he doesn't have a trig book. I bet the school does though.
Haha, so are you the amatuer mad rocket scientist? Thanks for all that explaining, must have taken you a while to type the whole thing up.

I learned a little about trig, such as vectors, towards the end of last year in my geometry class. For example who calculated how far an airplane will diverge if some wind was blowing at X angle and Y speed. I'm sure it wasn't accurate or anything.

I'll look for a trig book next week, and I've got a calculator that should do that task.

Thanks again!
 

BlueNinja

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General rules to follow:

Tartaglia's laws of gunnery, adapted for model rocketry.


1. A rocket that will go 1000 feet up will go 2000 feet if launched at an angle of 45 degrees.

2. When launched at an angle of 45 degrees, a rocket that would do 1000 feet up will only achieve 500 feet.

3. The path followed by a model rocket when launched at any angle except the vertical is described as a parabola.


From the Handbook of Model Rocketry


Blue
 

JStarStar

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adding on to Blue Ninja,

-- the effects of air drag effectively guarantee that a rocket will always land short of where its parabolic path would indicate.

-- In actual flight, a rocket generally will follow the parabolic path most accurately while under powered boost, and once the engine thrust cuts out, the parabolic path will be flattened and shortened by the effects of drag.

--Weathercocking into any prevailing winds will also affect the parabolic path of the rocket.


There are more and more accurate ways of estimating range, etc., like RockSim, but you still definitely want to make several test flights before doing the actual demo. ;)
 
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