Building a Stable Spaceplane SSTO

[I likeOxidizerrfuel]

Hello, I am having problems with keeping my Space plane inline with the prograde marker at around 6-7 thousand meters. 

However, it is still stable and able to fly once it get's unalighned with the prograde marker. The prograde marker dips below 0° and I start losing vs. 

Edited February 11, 2020 by I likeOxidizerrfuel

[XLjedi]

Without a link to the actual plane, or even maybe a picture... 

About all I could say is, the problem is most likely related to "something" on your plane.

[I likeOxidizerrfuel]

Idk how to lol.

[Meecrob]

Sounds like you need more lift (more wing area, or higher velocity with same wing area), or less drag (zoom climb to thinner air). Sorry, I'm not an SSTO guy, but I'm pretty sure in KSP, you want to ascend to 10,000-13,000-ish before accelerating past 250-300-ish m/s.

[I likeOxidizerrfuel]

I usually like to accelerate above 250 below 10,000 m. I also use Air tunnels, a mod that makes it easier to build planes and changes the CoL a little bit.

[sturmhauke]

14 minutes ago, I likeOxidizerrfuel said:

Idk how to lol.

1. take screenshot
2. upload to imgur or another image host of your choice
3. post link here

[I likeOxidizerrfuel]

Here's the craft: https://postimg.cc/kRX2WJH1

 

[DunaManiac]

1 hour ago, I likeOxidizerrfuel said:

Hello, I am having problems with keeping my Space plane inline with the prograde marker at around 6-7 thousand meters. 

However, it is still stable and able to fly once it get's unalighned with the prograde marker. The prograde marker dips below 0° and I start losing vs. 

Usually, you almost always need canards to keep it up in the air. There is a reason why high-speed military jets have them. Also, you should also add some more wing area, more lift would definitely help.

Edited February 11, 2020 by DunaManiac

[sturmhauke]

Just now, I likeOxidizerrfuel said:

Here's the craft: https://postimg.cc/kRX2WJH1

 

I'm guessing that your CoM moves too far back as you burn fuel. You could try moving the side tanks forward a bit, closer to the overall geometric center, and then adjusting the wings. I also tend to go for fewer and taller vertical stabilizers, and as far back as you can put them. Yaw stability is often overlooked on spaceplanes. The Mk3 space shuttle-looking rudder will probably fit the bill, or you can make one out of wing segments.

[Warmachine]

Just now, sturmhauke said:

I'm guessing that your CoM moves too far back as you burn fuel. You could try moving the side tanks forward a bit, closer to the overall geometric center, and then adjusting the wings. I also tend to go for fewer and taller vertical stabilizers, and as far back as you can put them. Yaw stability is often overlooked on spaceplanes. The Mk3 space shuttle-looking rudder will probably fit the bill, or you can make one out of wing segments.

I tend to agree with the CoM assessment, but disagree with the yaw control. He could drop the inward vertical stabilizers and make them into elevators. Might give him better control when the CoM moves.

That said his description almost sounds like a not enough power scenario. I'd recommend more wing personally, so that he has more lifting surface in the thinner atmosphere.

[XLjedi]

Based on the pic...  work on your wings. 

When the wings look proportional to the fuselage, it will probably fly fine.

Edited February 11, 2020 by XLjedi

[swjr-swis]

1 hour ago, I likeOxidizerrfuel said:

Here's the craft: https://postimg.cc/kRX2WJH1

Your wings, size aside, are not generating any lift when flying exactly prograde. Give them a bit of angle and you'll notice a world of difference.

[I likeOxidizerrfuel]

I got it into orbit woohoo! But how do I get back down again... *vsause music plays*

[sturmhauke]

40 minutes ago, swjr-swis said:

Your wings, size aside, are not generating any lift when flying exactly prograde. Give them a bit of angle and you'll notice a world of difference.

Right, yeah I usually do 2 degrees for SSTOs and 3-5 degrees for subsonic aircraft. It helps generate a bit more lift while also keeping the nose pointed into the airstream, reducing form drag.

[sturmhauke]

Just now, I likeOxidizerrfuel said:

I got it into orbit woohoo! But how do I get back down again... *vsause music plays*

Congrats! To get down you simply reverse the procedure. 

Oh, you probably want more details. Rotate your plane until you are facing retrograde (that is, backwards in your orbit). If you don't care where you land, start burning until your apoapsis drops to 20km - atmospheric braking will slow you down the rest of the way. If you want to land at a specific place (say, back at the KSC), wait until the target area is about 60 degrees ahead of your current position and then make the deorbit burn.

Before you hit the edge of the atmosphere, pitch your nose up a few degrees. A higher angle will slow you down and drop you to lower altitude faster, so you can use that to control your rate of descent. You can also try S-turns, which is where you also bank left and then right. This can help bleed off horizontal speed in a shorter distance.

[Vanamonde]

This question about how to play the game has been moved to Gameplay Questions.