Mark:
On first inspection I would say there must be something wrong with the
second chart: it does not make sense that Cd is increasing over the entire
coast period of that flight.
Assuming the vehicle was supersonic at burnout, Cd should increase as
velocity drops to about Mach 1.1 and then decrease as it goes subsonic and
drops to a minimum near peak. I would expect Cd to then increase as the
vehicle falls, peaking again around Mach 1.1 and then declining until
impact.
Does the second chart include a parachute deployment? A Cd of 1.4 is a
parachute kind of number....
Bill
On Sun, Dec 13, 2020 at 12:36 AM <mark.spiegl@xxxxxxxxx> wrote:
Question about the calculation of CD numbers in RASAero. Im using Derek
Deville's QU8K as a test case because tons of information exists on the
Internet.
RASAero CD vs Mach chart shows a predictable pattern
CD is 0.6 subsonic
CD spikes at 0.75 around Mach 1
CD gradually decreases from 0.75 spike at Mach 1 and beyond
QU8K RASAero flight simulation
Totally different pattern
Powered flight basically follows above
Coasting phase shows gradual increase in CD all the way to
1.3
Nowhere do the CD vs Mach chart show CD's anywhere near 1.3
What is missing from my interpretation??? (figs attached) Thanks.
*
Background: Im trying to incorporate better CD models into OpenRocket.
The code is written. It works, but the answers don't make sense due to the
problem I identified above. (actually I think found a ugly bug in OR but I
will assume it's my error until proven otherwise)
--MCS
.
