Delta v anomaly/human error

[thatoneguy423]

I'm pretty new to all this rocket science, so my goal with all this was basically to practice applying the rocket equation with a simple scenario.

I built as simple a rocket as I could. It consisted of just the following components:

1. Command Pod Mk1

2. Mk16 Parachute

3. TR-18A Stack Decoupler

4. FL-T200 Fuel Tank

5. LV-T30 Liquid Fuel Engine

Obviously with this set up I'm not even trying to get into orbit. I just wanted to predict what the velocity of the rocket would be at the exact instant that the burn ended.

I used this formula,

vf = (Thrust/m')*ln((mtotal)/(mtotal-m'(tf)))-g0*tf

I calculated a tf of 14.6 seconds which is roughly consistent with when the burn ended during the actual launch. Using the above formula I calculated a vf of 963.76 meters per second, whereas my rocket's actual velocity peaked at about 363 meters per second.

So was the discrepancy caused by drag, an error in my calculations, or something else?

[purpletarget]

Yes....you'll loose most of it to drag.

~15 sec at 9.8ms-2 will see about 150m/s lost to gravity alone. With a high TWR of your ship (don't have numbers on me) but you could be easily losing 2-4x as much on air drag as well after you hit terminal velocity.

[TechnicalK3rbal]

It was caused by drag. Try it in a vacuum, it'll work perfectly.

[Tank Buddy]

You lost a boat load to air resistance and gravity drag. If you use Mr. Manley's video:

You can edit your ship right into orbit (stock); there you will have negligible losses. I did something like this, testing the Rocket equation, and my calculation was only off by 1 m/s.