Just How High, How Far Is This Thing Gonna Go?
Altitude
Let's assume you've bought a starter set that has a rocket of about 16"
length and 1" diameter. It likely weighs about 2oz on-the-pad (motor
and all). Your mileage may vary, but assuming that your rocket goes
straight up, computer altitude estimates for
that rocket are as follows:
- A8:
- Motor burnout at 0.45 sec, 32 ft high at 75 mph. Maximum altitude of 185
ft reached 3.1 seconds later.
- B6:
- Motor burnout at 0.75 sec, 92 ft high at 140 mph. Maximum altitude of 500
ft reached 4.8 seconds later.
- C6:
- Motor burnout at 1.45 sec, 290 ft high at 230 mph. Maximum altitude of 1050
ft reached 6.1 seconds later.
Drift
A 10 mph breeze will push your rocket approximately 15 ft per second. I get
this from 5280 ft/mile * 10mph / 3600 sec/hr = 14.7 ft/sec. I also use a
rule of thumb for this rocket of 5 seconds descent time per 100' of altitude.
- A8:
- 180/100*3 = 5.4 sec * 20 ft/sec = 108 ft downrange.
- B6:
- 500/100*3 = 15 sec * 20 ft/sec = 300 ft downrange.
- C6:
- 1050/100*3 = 31.5 sec * 20 ft/sec = 630 ft downrange.
Keep in mind that several things will change this calculation.
- More wind - more drift, less wind - less drift.
- Having part of the rocket (motor casing/bodytube) separate from the
rest will cause a slower descent rate and more drift.
- A faster descent rate will give the wind less time to push your rocket.
That is why experienced rocketeers advise cutting a 2" hole in the middle
of your parachute, or using a streamer or x-form parachute on windy days.
These let the rocket drop faster and drift less, but there is a danger in
dropping it too fast and damaging your rocket. If you want to experiment
with this, try to find a launch site with nice soft ground, not hard pavement.
