Rocksim Software Question: calling all experts,

Using Version 9.14. In the past, I have tried to take my actual altimeter altitude and change something in Rocksim to match the projected altitude with actual. Like taking the finish and changing it to matte. I have done that and still of by 300 feet. rocksim always seems to over estimate. what else can I change on my rocket attributes to give it lower numbers for altitude.

Change the drag (cd) until it matches the altitude. I've done this with my optima and the new predictions on other motors turned out very close.

Before the Cd change I would check the following.
1) weight of rocket
2) finish quality
3) launch rod/rail angle
4) wind, temperature

Rarely does anyone actually fly pure vertical. This would likely require measuring the angle with a smart phone or some type of gauge.

You already touched on finish quality.

Weight is obvious

Wind can mess with you a bunch. You almost need an anemometer to measure wind velocity.

If you can get within 5-6% I would stop worrying about it and just fly.

Plus the winds at altitude can be significantly different than on the ground....

les said:

Plus the winds at altitude can be significantly different than on the ground....

Click to expand...

Absolutely the truth. I got to use Rocksim Pro for a while, and that was one of the cool features- you could have many layers of air complete with direction and velocity. Needed to do a 6 DOF sim and splash patterns.

and then there's also variability from motor to motor and possible differences between your motor and the ONE(?) used for creating the motor file used in the simulation. You could always launch three times and take an average before you start tweaking.

NikeMikey

A couple other things I would consider are:

1) One won't get in trouble if their flight doesn't go as high as simulated. But if you are anywhere close to max waiver height, you would be in violation should you go over. I know clubs normally leave some buffer. I just don't want attention for getting too close.

2) If you do nothing except plot the simulation and actual there is a good chance that you would find a fairly constant percentage difference. So then you would be able to know that actual performance would fall say between 85 and 90 percent of simulation.

Kirk