Nifty Plane 9000 doesn't go even past Mach 1

[BenKerman]

Hi,

I made a spaceplane based exactly on the Nifty Plane 9000 as described in the Kerbal Player's Guide.  I flew it successfully a couple of years ago (one year?), and I'm pretty sure I could get it past Mach 3 in air-breathing mode.  I tried again today after that long hiatus and couldn't even break Mach 1.  Have the game mechanics changed at all?  I know early on they changed the way atmospheres worked.

 

Thanks,

Ben

[camacju]

What does the nifty plane 9000 look like? I'm guessing you're using subsonic jet engines (Wheesley, Goliath), and/or your craft is not drag optimized.

[Guest]

I don’t know exactly but they’ve definitely changed something in recent versions because I used to need FAR to get anything  to work/be half flyable but now not so much.

[Guest]

12 hours ago, camacju said:

What does the nifty plane 9000 look like? I'm guessing you're using subsonic jet engines (Wheesley, Goliath), and/or your craft is not drag optimized.

Maybe this one? The one peculiarity I can see that could cause this are the air intakes -- circular intakes don't work well at high altitudes and speeds and I don't know if the pre-coolers are enough to make up for it. If that's the problem you'll see premature flame-outs just when you should start to be going really fast.

I'd just replace the pre-coolers with Lf fuselages and the circular intakes with shock cones, I expect it'll make orbit easily with lots of dV to spare. Also at least in this pic the main landing gear is splayed out which is going to cause problems taxiing straight.

https://www.oreilly.com/library/view/the-kerbal-players/9781491913475/ch04.html

Edited May 1, 2021 by Guest

[camacju]

The plane as-is should easily be able to get up to 1400-1500 m/s. Are you accelerating to Mach 1 at sea level or at altitude?

[Wizard Kerbal]

I’m thinking it’s really draggy and heavier than it has to be.

The It has really big, THICC wings, and it has quite a lot of intakes. It only needs the 2 at the front for good performance, or 2 pre-coolers and no other intakes for more than enough air. 
(And the shock cones are less draggy)
And the fuel tanks on it contain oxidiser as well. Replacing them with liquid fuel only would be better, even if you drain some of it.

Edited May 1, 2021 by Wizard Kerbal

[OHara]

Aerodynamics has not changed for a few years.  I agree that @BenKerman could make a better spaceplane than the Nifty Plane in that book, but even the Nifty Plane can get to Mach 5 easily.

If there is something inside that cargo bay, it is easy to accidentally connect the rear portion of the plane to those contents, rather than to the back wall of the cargo bay.  One unfortunate aspect of KSP is that it figures drag based on what is connected to what, ignoring how parts are offset relative to one another, so connecting to the cargo will make KSP think the front plate of the Mk2 fuel tank is facing the wind.  That could preventing breaking the sound barrier.

You can check that things are connected as they appear to be, by selecting the offset tool, marked 'Tool: move', offsetting all contents of the cargo bay including docking ports, and checking that the remainder of the plane stays put.

[Reactordrone]

On 5/1/2021 at 7:11 AM, BenKerman said:

Hi,

I made a spaceplane based exactly on the Nifty Plane 9000 as described in the Kerbal Player's Guide.  I flew it successfully a couple of years ago (one year?), and I'm pretty sure I could get it past Mach 3 in air-breathing mode.  I tried again today after that long hiatus and couldn't even break Mach 1.  Have the game mechanics changed at all?  I know early on they changed the way atmospheres worked.

 

Thanks,

Ben

In order to get maximum thrust from the rapiers you need to be going fast. Try leveling off or even going into a shallow dive at about 5000m to pick up speed. Once over mach 1 the engine thrust will start to rise and you can pull the nose back up a bit to climb out. Air breathing thrust will die at just over 20km so pick up most of your speed at 10-15 km.