Mk1 ablator too aerodynamic?

[GoSlash27]

All,
My "rescue1" career craft is very nearly killing Kerbals because it's not bleeding off airspeed sufficiently at subsonic speeds. I'm barely getting the 'chute out and deployed by 300m.
I suspect the heat shield.
To test this, I ran 2 identical reentries at 72km x 45km. Here's the safe chute deployment altitude with the ablator:
[IMG]http://i52.photobucket.com/albums/g13/GoSlash27/Chuteshield1_zpsdvfnrzjy.jpg[/IMG]
And here it is without:
[IMG]http://i52.photobucket.com/albums/g13/GoSlash27/Chutebare1_zpsvhlhzwte.jpg[/IMG]

As you can see, the bare capsule decelerates to 250m/sec over 2km higher than the capsule with heat shield. A clean reentry capsule ends up deploying just barely in the nick of time at sea level.

I'd recommend increasing the drag coefficient for the ablator to match the capsule. In the meantime, it can be worked around by using a decoupler to detach the heat shield after reentry heating subsides.

All of this was done with a stock Windows install and no mods.

Best,
-Slashy Edited November 16, 2015 by GoSlash27

[Claw]

Hmm, interesting. I know the heat shield adds a little weight, but...yeah...

[Jouni]

That looks about right. If you have 30% more mass for the same cross-sectional area, you need 30% more drag to decelerate at the same rate. In Kerbin's lower atmosphere, that means going about 2 km lower.

The real issue here is that the Mk1 pod is quite heavy for its size.

[GoSlash27]

Jouni,
This should only be a problem in early career play, where players are going to design something similar to this and have a limited selection of parts. I'll run another test with the ablator turned down.

Best,
-Slashy

[sal_vager]

I think all drag is via the drag cubes now, and parts don't have separate drag coefficients, some parts such as the bays have to have override cubes though.

[spoiler=Maybe someone can check these values]PART
{
url = Squad/Parts/Aero/HeatShield/HeatShield1/HeatShield1
DRAG_CUBE
{
cube = Fairing, 0.3803446,0.7544904,0.7807983, 0.3803446,0.7544887,0.7807983, 1.435374,0.9637347,0.182152, 1.435374,0.9648821,0.3016892, 0.3803446,0.7545046,0.7746984, 0.3803446,0.7544985,0.7807984, 0,-0.05125761,0, 1.355496,0.2838411,1.355497
cube = Clean, 0.1841511,0.4700066,0.740204, 0.1841511,0.469997,0.7344211, 1.270047,0.9548434,0.1829091, 1.270047,0.9467862,0.217749, 0.1841511,0.4685453,0.7402042, 0.1841511,0.4714554,0.7402042, 0,0.005576342,-1.994255E-09, 1.274625,0.1701732,1.274625
}
}

PART
{
url = Squad/Parts/Command/mk1pod/mk1Pod/mk1pod
DRAG_CUBE
{
cube = Default, 1.015811,0.6676595,0.7373285, 1.015811,0.6767812,0.7315681, 1.250829,0.4803877,1.097382, 1.250829,0.9479992,0.3448916, 1.013055,0.6637006,0.7325699, 1.013055,0.6617755,0.7441065, 0,0.104412,-0.001005709, 1.268897,1.132536,1.270908
}
}[/spoiler] to see how adding the heatshield effects the shape of the base of the Mk1 pod.

Though I think this will come down to the added mass, rather than drag.

[GoSlash27]

sal_vager,
I agree; I think it has more to do with the mass than drag box figures, but I suspect the fix isn't going to lie in reducing the heat shield's mass. Folks are beginning to report similar experiences on the forum. [url]http://forum.kerbalspaceprogram.com/threads/139957-Were-the-heat-shields-intended-to-act-this-way[/url]
My recommended work- around of decoupling the heat shield after reentry seems to be working well in the meantime.
Hope you get this sorted out!
-Slashy

[sal_vager]

I'm not sure I'd even call this a bug to be honest, it's definitely a change from 1.0.4, but not unrealistic.

[quote name='sal_vager']Reality may have to be sacrificed for gameplay to "fix" this, as the pod with heatshield seems to be working correctly compared to a pod without.

The greater mass means there's more inertia for the aerodynamic drag to overcome.

Reducing the pod and heatshield mass will have negative effects in other areas unfortunately, such as moving the rockets center of mass downward, reducing stability.

And accounting for occlusion from parts in collision would eliminate the double drag, causing you to fall faster, and that may end up being a bad thing depending on your angle.

Plus the occlusion checks are computationally expensive, additional checks for collided parts are better avoided.

Artificially increasing the size of the heatshield drag cubes might work, drag cubes can already be overridden and this is done for the cargobays and fairings (cue bug reports that heatshields are unrealistically draggy).

I don't mind the extra decoupler to drop the heatshield on a Mk1 pod, the separator on the Mk1-2 doesn't look bad either and I can use the next size down and the offset tool to hide them later in career.

So there is a workaround, and we can adapt, we can't expect nothing to change with each update to KSP.

Maybe heatshields do need built-in decouplers though as that'd encourage players to drop them, and the double drag may actually come in handy to save your Kerbals on occasion if you're lucky enough to have your heatshield stay pressed against your pod by aero forces during descent.[/QUOTE]

I think people need to adapt, a lot of info on playing KSP is out of date anyway.

[U][URL="http://forum.kerbalspaceprogram.com/threads/138802-Kerbal-Space-Program-1-0-5-New-Issues-Repository#heatshield_drag"]I'll add this to the known issues thread[/URL][/U] with your heatshield onna decoupler workaround. Edited November 20, 2015 by sal_vager

[GoSlash27]

sal_vager,
Thanks for the update. I've passed it on.
FWIW, 5thHorseman has come up with a .cfg change to the heat shields to give them a built-in decoupler. This would seem to be the smart way to handle it IMO for the reasons you outlined above. Altering the drag figures could upset the aerodynamic stability of our capsules during reentry, and we *really* don't want that.
Best,
-Slashy