> hobby and we were using the largest engines available, now I realize that
> with the conditions at the time a smaller engine would have resulted in an
> easier recovery (I think).
Engine size has two factors: thrust and total impulse. A B4 motor has
less average thrust than a B6, but both have the same total impulse. The
B14 motor is no longer manufactured. It had a good kick (high average
thrust). Again, the total impulse was the same as the B4 and B6 motors.
If one ignores drag, which increases as speed increases, all three
motors will push the same rocket to the same altitude. A B14 would get
it off the pad much faster than a B4, though. In reality, due to drag, a
rocket will probably reach a lower altitude with a B14 than a B4.
On a calm day a rocket may fly well with an A3 motor. On a windier day
you may want to use an A8. The rocket will reach about the same altitude
with each motor, but will move off the pad faster with an A8.
How far will your rocket drift? An approximate value can be calculated
if you know the rocket's approximate maximum altitude and descent rate
under parachute. If we assume a descent rate of 15 ft/sec and a wind
speed of 10 miles per hour, which happens to be about 15 ft/sec, a
rocket will move forward for every foot it drops. If we assume an
altitude of 800' the rocket will travel approximately 800' downwind. Now
consider what happens if a rocket deploys a parachute at 5,000', the
ground wind is 15 mph and the wind at 5,000' is 30 mph. Good luck
finding it. A descent rate of 15 ft/sec means the rocket will descend
for about 333 seconds (5.6 minutes). Assuming an average wind speed of
22.5 miles per hour (33 ft/sec) the rocket will drift for about 11,000'
- almost two miles.
I once saw an underpowered rocket launched in a brisk wind (an Estes
type rocket). The rocket kept the nose cone pointed up, but it moved
horizontally almost as much as it moved vertically while the motor
burned. It was quite funny.
dean_roth at yahoo dot com
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