Is 1.0.5 shock cone drag independant of being open / close

[Ridiculous Richard]

As part of some nose cone testing (put nose cone on a Hammer SRB with minimal control surfaces and ballast to even out weight differences and see how high they go) I noticed that a shock cone appears to have the same drag regardless of being open or closed (the test vehicle reaches the same height).

Has anyone else observed this or is there something screwy with my test?

 

Thanks,

Richard

[ElWanderer]

I've not tried it, but everyone who has reports that the drag doesn't seem to change on closing/opening any intakes.

[Starhawk]

You are correct.  None of the air intakes have drag changes based on whether they are open or closed atm.

Happy landings!

[Ridiculous Richard]

Thanks,

I had gathered that there was a significance difference based on youtube videos.  It's nice to kill a myth.

 

Richard

[fourfa]

It's vestigial from previous versions - probably was the case when those videos were made

[swjr-swis]

I was curious, so I set up a quick experiment.

Two identical rockets with the shock cone on top. Built side by side from a central truss, by making use of symmetry, to avoid any differences. I angled them to make them take a longer route through the atmosphere. Fired ten times, alternating between no change at all, and closing one of the cones. I switched to map view, set whichever the other rocket was as target so I could see both paths, and checked the apoapsis at one minute something into the flight. Revert flight, ~10 seconds wait to let everything settle, close a cone on alternating flights, launch, rinse and repeat.

None of the flights were completely identical. On an apoapsis of around 84km, the variance was about 500m up or down. But the same variance appeared whether one of the cones was closed or both were left open. Sometimes it was the left rocket on top, sometimes the other, again no connection to close or open of the cone.

I got bored after 10 times seeing how the random variation when both were open seemed to seemed to be just as much as with one cone closed, but if anyone feels compelled to redo this to get more data points, I'll upload the test craft setup.

Looks like no effect to me.

[Ridiculous Richard]

I was firing them up to 100.7km with I think less than 100m variation between repetitions.

If you are interested im my results from this I have typed them in below

 

The test vehicle used:

Nose assembly

RC-001S

FL-R25 ballast tank to approximately even out the weight between nose cones (ballast figure is amount of RCS fuel loaded)

HammerSRB

2xElevon 1 for stability control

 

Modus operandi:

Throttle full, SAS on (+ open/close intakes), launch, no time acceleration in the atmosphere, get peak hight from F3 once vehicle starting to descend

 

Results for 4.2t 1.25m tests

Nose assembly	Ballast Added	Peak altitude with 40% thrust limit	Peak altitude with no thrust limit except for survivability
Fairing 2 section	0	122km	69.5% thrust => 145km
Fairing 1 section	25	116km	N/C
Fairing shortest possible	50	55km	N/C
FL-A10 NC	50	98km	100% => 102km
Aero NC	75	79km	100% => 79km
Shielded clamp-o-tron	50	66km	100% => 59km
Heat shield	0	52km	100% => 42km
Advanced NC	50	105km	71.5% => 121km
Closed shock cone	50	101km	93% => 117km
Open shock cone	50	101km	93% => 117km
Tail cone A	25	108km	71% => 128km

The accuracy of this comparison is limited by the VAB mass readout in steps of 0.1t. Adding ~0.1t to the Fairing 2 section reduced the 40% altitude from 122km to 105km so it is hard to measure the difference between the following with confidence

* Fairing 1 or 2 sections

* Advanced Nose cone

* Tail cone A

If you want to be more accurate then you need to control the test vehicle mass more closely. Or do something like the suggestions in http://forum.kerbalspaceprogram.com/index.php?/topic/129655-what-options-are-there-in-ksp-for-quantitatively-determining-the-drag-produced-by-parts/

From the above experiment I have gone with a 1 section fairing over a shielded clamp-o-tron for it's much lower drag and higher temperature limit.

 

Regards,

Richard

Edited January 12, 2016 by Ridiculous Richard