How do I get a higher cruising attitude?

[Andrew1233]

I made this commercial jet that I want it to go to at least 10000 meters high, but  my max is only 7000, do you guys know how to improve it?

Image:

https://imgur.com/a/zeCGxoh

also don't mind the decoupler that's for a test, you know, for science >:)

Edited April 22 by Andrew1233

[Aelfhe1m]

How high a plane can get essentially depends on its lift to drag ratio. To go higher you need more lift or less drag.

You get more lift from more speed or more wing area (angle of incidence/attack also matters for lift).

Drag reduces speed (and hence lift), so adjusting wing incidence so that the plane body is as close to horizontal when cruising will improve your lift/drag ratio. The long body surface of a passenger plane can generate a lot of drag if it's not facing directly into the airflow.

Also check your engines are getting enough air. Might need larger/extra intakes to fly at high altitude. Thrust will decrease if engines are starved of air, which will slow the speed and hence reduce lift.

[Andrew1233]

1 hour ago, Aelfhe1m said:

How high a plane can get essentially depends on its lift to drag ratio. To go higher you need more lift or less drag.

You get more lift from more speed or more wing area (angle of incidence/attack also matters for lift).

Drag reduces speed (and hence lift), so adjusting wing incidence so that the plane body is as close to horizontal when cruising will improve your lift/drag ratio. The long body surface of a passenger plane can generate a lot of drag if it's not facing directly into the airflow.

Also check your engines are getting enough air. Might need larger/extra intakes to fly at high altitude. Thrust will decrease if engines are starved of air, which will slow the speed and hence reduce lift.

How should I see the life-drag ratio? Can I see it in game with KER? Also Im gonna use better intakes

1 hour ago, Aelfhe1m said:

How high a plane can get essentially depends on its lift to drag ratio. To go higher you need more lift or less drag.

You get more lift from more speed or more wing area (angle of incidence/attack also matters for lift).

Drag reduces speed (and hence lift), so adjusting wing incidence so that the plane body is as close to horizontal when cruising will improve your lift/drag ratio. The long body surface of a passenger plane can generate a lot of drag if it's not facing directly into the airflow.

Also check your engines are getting enough air. Might need larger/extra intakes to fly at high altitude. Thrust will decrease if engines are starved of air, which will slow the speed and hence reduce lift.

tho I wasn't sure about the max thrust height for the Goliath engine 

[Aelfhe1m]

For in depth video tutorials about KSP stock aerodynamics check out Kerbal University by Lt_Duckweed.

The various aerodynamic information can be enabled through the Mod+F12 "cheat" menu (mod = Alt on Windows), Physics => Aero.

Edit: 

For a more visual representation of how much drag (red arrows) or lift (blue/yellow arrows) each part is generating press F12.

Edited April 23 by Aelfhe1m
Added info about F12

[Andrew1233]

31 minutes ago, Aelfhe1m said:

For in depth video tutorials about KSP stock aerodynamics check out Kerbal University by Lt_Duckweed.

The various aerodynamic information can be enabled through the Mod+F12 "cheat" menu (mod = Alt on Windows), Physics => Aero.

Edit: 

For a more visual representation of how much drag (red arrows) or lift (blue/yellow arrows) each part is generating press F12.

alr thx!

 

[DeadJohn]

I think you already have enough intake air considering that your still flying at a modest altitude. What engines & how many are on that plane? Do I see 1 Panther at the tail, 2 Junos on wingtips, 2 Goliaths under wings?

If that's the engine config consider redoing it to be only Panthers. They perform better at high altitude than those other engines do.

The Whiplash engine is even "better" but arguably too good and too expensive for your desired 10km altitude.

[KerikBalm]

You are going way too slow to be flying in air that thin.

I don't really play much with the high bypass turbofans. I do a lot of air launch to orbit, but those are with hypersonic spaceplanes.

When I do play around with subsonic aircraft, it's mostly using electric rotors, for operation on Duna, Eve etc.

[Andrew1233]

6 hours ago, KerikBalm said:

You are going way too slow to be flying in air that thin.

I don't really play much with the high bypass turbofans. I do a lot of air launch to orbit, but those are with hypersonic spaceplanes.

When I do play around with subsonic aircraft, it's mostly using electric rotors, for operation on Duna, Eve etc.

yeah i  shouldn't use the real life scale of 35000 feet(about 10000 m) to ksp, I should make a supersonic airliner to do far range high attitude high speed

8 hours ago, DeadJohn said:

I think you already have enough intake air considering that your still flying at a modest altitude. What engines & how many are on that plane? Do I see 1 Panther at the tail, 2 Junos on wingtips, 2 Goliaths under wings?

If that's the engine config consider redoing it to be only Panthers. They perform better at high altitude than those other engines do.

The Whiplash engine is even "better" but arguably too good and too expensive for your desired 10km altitude.

yeah i  shouldn't use the real life scale of 35000 feet(about 10000 m) to ksp, I should make a supersonic airliner to do far range high attitude high speed, you know, concorde

6 hours ago, KerikBalm said:

You are going way too slow to be flying in air that thin.

I don't really play much with the high bypass turbofans. I do a lot of air launch to orbit, but those are with hypersonic spaceplanes.

When I do play around with subsonic aircraft, it's mostly using electric rotors, for operation on Duna, Eve etc.

wait u can reach almost sonic speed using rotors?

 

6 hours ago, KerikBalm said:

You are going way too slow to be flying in air that thin.

I don't really play much with the high bypass turbofans. I do a lot of air launch to orbit, but those are with hypersonic spaceplanes.

When I do play around with subsonic aircraft, it's mostly using electric rotors, for operation on Duna, Eve etc.

or is it only duna or eve, not kerbin

 

[KerikBalm]

@Andrew1233

I didn't say you have to go supersonic like the concord: just that you go too slow. Airlinerd cruise at 250-270 m/s at those altitudes, you're going about 100 m/s - that is way too slow.

My comments about hypersonics only meant to imply that I can't give you any rules of thumb off the top of my head for wingloading or TWR for those sort of planes.

As for the altitude: kerbin's atmosphere is about 80% to scale. 8500m on kerbin has the same pressure as about 35'000 feet on Earth. 

Regarding rotors, I said subsonic, not transonic, but yes, you can almost go supersonic with rotors:

And that was a tilt-rotor VTOL carrying a 36 ton rockonax 64 fuel tank as payload 

[Aelfhe1m]

Here's a very quick (and horridly handling) aircraft I slapped together.

Spoiler

As you can see four Goliaths are enough to push that plane body to over 10km (even with 80+ kerbals on board) but it could do with more wing incidence as it needed to hold nose up to get enough lift and the wings are frankly about half the size I'd want for that size of craft.

Spoiler

 

[KerikBalm]

10 hours ago, Aelfhe1m said:

Here's a very quick (and horridly handling) aircraft I slapped together.

Add some wing incidence to decrease how much you need to pitch up, and you'll save a lot of drag from the fuselage

Also, I can't help but feel that the wings are too small for that fuselage: