Coop
Well-Known Member
- Joined
- Dec 15, 2011
- Messages
- 1,768
- Reaction score
- 8
I would believe the recorded data. I've been doing a lot of this kind of work lately.
To accurately profile an unknown Cd, you need to know what the chute is recovering--that means weighing the complete assembly as it is recovered--that is, nosecone, shock cords, chute, rocket, left over dog barf, case, and spent motor--even that grasshopper that was a stowaway, if you want to get 5-decimal place nutty with it.
Is the 12.6 oz the weight of the SPENT motor, or the motor itself? I suspect it is the latter, as more people are using that figure for thrust:weight ratios for liftoff than they are for profiling their recovery systems...
I don't think the 0.4 Cd you determined is accurate. Cds in the 0.4-0.6 range are the realm of disk-gap-band parachutes, and I'm pretty extra-special sure TFR doesn't offer one of those. I suspect your determined Cd is so low because your assumed weight was incorrectly high.
Later!
--Coop
To accurately profile an unknown Cd, you need to know what the chute is recovering--that means weighing the complete assembly as it is recovered--that is, nosecone, shock cords, chute, rocket, left over dog barf, case, and spent motor--even that grasshopper that was a stowaway, if you want to get 5-decimal place nutty with it.
Is the 12.6 oz the weight of the SPENT motor, or the motor itself? I suspect it is the latter, as more people are using that figure for thrust:weight ratios for liftoff than they are for profiling their recovery systems...
I don't think the 0.4 Cd you determined is accurate. Cds in the 0.4-0.6 range are the realm of disk-gap-band parachutes, and I'm pretty extra-special sure TFR doesn't offer one of those. I suspect your determined Cd is so low because your assumed weight was incorrectly high.
Later!
--Coop