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Airbrakes, is they less efficient in 1.2?


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I copied my design for an Mun and Minmus LV-N passanger craft. 
Seen here docked to miner.
QFor2Yhh.png
Inflatable heat shield, reaction wheels, MK2 landing can cockpit, MK3 passenger cabin, cargo bay for science, life support and light cargo, Fuel tank, with radial LV-N, this version miss the airbrakes but the follow up has 6, landing legs on wings to get it wider. 

In 1.13 I could aerobrake this at 40 km then comming back after an dip outside Kerbin SOI, it would put AP around 200 km. 
in 1.2, going below 45 km makes it tumble even with rcs and vernier running returning from Minmus so speed would be lower. 

My heavy tanker has much of the same issue
tqK2Wpfh.png
yes its a bit too large for the heat shield so legs and rcs has problems but that should just make it more stable?
 

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Aerodynamics were changed in 1.2, to make pointy objects have a bit less drag (planes fly faster lower down) but blunt objects have a bit more drag (pods slow down better on reentry).

This means that the large heat shield generates more drag in the same aerobraking profile, pulling the center of aerodynamic pressure further forward. This can cause a previously stable craft to become unstable, because the center of mass is no longer far enough forward.

Admittedly the airbrakes should serve to pull the center of pressure well backwards... still, on average, it will be a bit further forward now, simply from the heatshield alone.

Edited by Streetwind
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I'm pretty sure the aero model is also different for super/hypersonic and subsonic flight. I've had spaceplane designs which tumble out of control on re-entry, but can be re-stabilised into stable flight once they're below 10k altitude and 300 m/s velocity.

Or, put another way: making sure the centre of lift is behind the centre of mass is no longer sufficient to ensure that a craft is stable. It also has to be pointy.

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