LPR/MPR Simple Drift Cast and Chute Chooser in Excel

[MarsLander]

Hey!

As you know, I'm a BABABAR. I have a 1500'x1500' field. First time back in 10 years (last year), first rocket I built last year was a Cherokee E. Went out and let'r rip on an E12...1700' with the stock parachute (18"). Winds were 10mph or so...She Gone.

As a result I built the following spreadsheet (attached).

Rocket Data Sheet

1. Weigh your model with parachute, without wadding or motor. Enter the grams in the g column.
2. Enter the expended motor weight in grams in the Case Colum. I use 10g for the motor case weight for A/B/C motors, 15 for D motors and 20 for E motors (you might weigh your own, but good enough for our purposes.
3. Enter the altitudes you expect with the appropriate motors.
4. Total oz and kg will calculate out.

Descent Rate Sheet

1. This will show you descent rates for the weight of the model and the size of the parachute.
2. For LPR/MPR and my field (hay), I accept anything up to 23 FPS as safe.
3. Use this sheet to choose your parachute size. Using the Cherokee E, that I lost from above, we are at .09kg...so 9" parachute should be fine, with descent rate of 23 FPS.
4. Note: The descent rate on the 18" chute is 11 FPS...

Drift Distance Sheet

1. It all comes together. Assume that we are going to use a E12 and a 9" parachute. We know the altitude is 1700', and a descent rate of 23 FPS.
2. Reading the drift table, it will likely drift about 1084' on a 9" parachute...well within the field, even at 10MPH.
3. Read the drift table for the 11FPS 18" chute....2,267' drift (Yep, that is where it ended up...see terrain map below, right where it ended up).
4. If your winds are 5pm, you can divide the drift by 2. If your winds are 15mph, you can multiple by 1.5 to get the drift.

1. You can print out all three sheets and take them with you to the field, if you don't prep rockets the night before. We laminated them and take a three ring binder with all the sheets for game time calls.
2. You can also you windy.com to get forecasted winds the night before and prep all the rockets with appropriate chutes for the field and the winds.
3. You can also use google maps, like I did below, use the windy data and drift data to draw a measured distance on your map with the right click of your mouse from your launch location to get a sense of where they will likely land.

I hope this helps you to retain more of your rockets, and sacrifice less of them to the tree gods.