Normal plane behavior?

[took]

I find that climbing with my plane gains speed relative to well...anything, and loses speed when falling. Is that how normal planes work? I was under the impression it was the opposite, namely trading speed for height and vice versa. I could be misunderstanding the indicators, I suppose.

Edited April 13, 2014 by took

[cpt_nosh]

Higher up = less air and hand in hand with that less drag from your airplane. Vice versa at lower altitudes.

[White Owl]

You may have discovered the infini-glide bug in stock KSP aerodynamics. Planes won't actually stall, just keep producing magical amounts of lift and keep climbing even without engine thrust. Perpetual motion as long as you have atmosphere. It's extremely unrealistic and the most annoying bug in this otherwise excellent physics sandbox game, IMO.

[Zephram Kerman]

Cpt_nosh is correct, air density greatly affects your speed when traveling fast. But your original understanding is correct too; trading altitude for speed is the normal situation when flying slowly and efficiently. These two effects are always at work, but you will notice one or the other depending on airspeed.

[took]

Cpt_nosh is correct, air density greatly affects your speed when traveling fast. But your original understanding is correct too; trading altitude for speed is the normal situation when flying slowly and efficiently. These two effects are always at work, but you will notice one or the other depending on airspeed.

I think air density is a fair point, however I'm not sure about the extremes I'm seeing. I'll try to compare it to something but even with that explanation, falling and not gaining speed doesn't make sense.

Edit: I suppose my drag could be such that the higher air density at lower atmosphere is causing more force than gravity pulling me down - which would account for slowing. But uh, I didn't design a brick and I'm pretty sure normal planes with jet engines can "swoop down" level out, and increase their overall speed by trading altitude. I'm still not sure what's different here.

Edited April 12, 2014 by took

[vetrox]

Anthing under 10km will cause extreme drag/brick effect due to kerbins unique atmosphere. Add to that the wierd and wonderfull way that ksp currently calculates lift and drag, you really cant compare it to IRL aircraft

You can always give FAR a try but I find it a bit extreme without a joystick I really wish there was a FAR lite

[took]

Does anyone know how common it is for a plane with just 2 basic jet engines to reach 36km?

[took]

Anthing under 10km will cause extreme drag/brick effect due to kerbins unique atmosphere. Add to that the wierd and wonderfull way that ksp currently calculates lift and drag, you really cant compare it to IRL aircraft

You can always give FAR a try but I find it a bit extreme without a joystick I really wish there was a FAR lite

Fair enough, if it's a feature of the atmosphere to be extremely dense at 10km - do we see other effects from that? If it's just a way of saying "that's how it works get over it." I get that too

[vetrox]

Fair enough, if it's a feature of the atmosphere to be extremely dense at 10km - do we see other effects from that? If it's just a way of saying "that's how it works get over it." I get that too

I think its definatley a case of the "thats how it works get over it" 's. Like I said, FAR fixes the atmosphere to be completley linear as well as calculating lift and drag correctly Heres a link to the FAR thread

As an experiment, make a big flat square with wings and an engine. I guarantee you it will fly in stock ksp

[CoolBeer]

Does anyone know how common it is for a plane with just 2 basic jet engines to reach 36km?

While Kerbins atmosphere is certainly strange, the jet engines are as well, this forum post/mod tries to explain/fix the issues.

-

Kolbjorn

[took]

I think its definatley a case of the "thats how it works get over it" 's. Like I said, FAR fixes the atmosphere to be completley linear as well as calculating lift and drag correctly Heres a link to the FAR thread

As an experiment, make a big flat square with wings and an engine. I guarantee you it will fly in stock ksp

I took a quick look, but I'm heading to sleep. Thanks for the replies. Does FAR mess with space much? I don't have much trouble with the space maneuvers (yet). So I wouldn't mind just making the atmospheric stuff a little more challenging, but by the sounds of it it makes it frustratingly difficult (to some).

[Claw]

I beg to differ. I don't think it's just a "that's how it works so get over it." It might be a bug, or stock game limitation, it might not.

What I really want is a picture of your craft. Preferrably in the SPH and in flight showing the problem.

My guess is actually that your craft is flying plenty fine. You are climbing up and accelerating. When you descend, you are going back into more dense air. An airplane's engines can only push it so fast, based on it's drag. If you make the air more dense, there is more drag. If there is more drag, then the engines won't be able to maintain speed and you will, in fact, slow down. This will happen in either FAR or stock (and real life for that matter).

Alternatively, your navball might be in orbit mode. In which case your speed won't make much sense at all. I think that is unlikely, but possible.

In either case, I see the topic of air density came up before, but you don't mention what the extremes are that you are seeing. As a baseline, it's pretty easy to get a plane up to 1600+ m/s at 30km. If that plane starts to descend, it's speed will almost certainly go down, and quite a lot. The atmosphere starts to thicken up around 25km (where it will probably slow to 700 m/s or less) and even more around 12km (300 m/s ish).

KSP actually lets you accelerate to a craft's high end of drag pretty easily. So you end up finding yourself going at the fast end of the drag curve most of the time, even if you don't intend to.

Edited April 12, 2014 by Claw

[Zephram Kerman]

A simpler way to describe the two effects is the journey of a skydiver. Guy jumps out of a perfectly good airplane. He falls through the air faster and faster, until achieving "terminal velocity". At that particular speed, the force of gravity equals the resistant force of aerodynamic drag. As air density increases, drag becomes greater, so terminal velocity decreases. So at first, the skydiver accelerates, but later slows down. (Hopefully completely, using a parachute.)

[took]

The extremes I'm seeing is two basic jet engines taking a plane to about 700 m/s+ relative to the surface - straight up at 0 degrees inclination - propelling the plane straight out of the atmosphere and into the orbit. Then I'll turn around and dive nose first and go from 700 m/s to ~100 m/s free-falling straight back down. I don't think there is anything right about that, and if you have the .craft or a link to a vehicle that is very well designed for aerodynamics, I'd love to load it up and see if the issue changes due to better drag coefficients.

[MarvinKitFox]

....that is very well designed for aerodynamics....

Sorry, KSP doesn't DO aerodynamics.

Consider the following:

* An E-class asteroid, about as big as the VAB building, falls straight down. It enters atmosphere at 8 km per second.... And slows down to gently waft to the ground at 115 m/s.

* The following two rockets have ***EXACTLY*** the same drag and flying characteristics.

KSP simply does not do aerodynamics. It doesn't even fake it very well. It just does *stuff*, and calls that drag.

[took]

Sorry, KSP doesn't DO aerodynamics.

Consider the following:

* An E-class asteroid, about as big as the VAB building, falls straight down. It enters atmosphere at 8 km per second.... And slows down to gently waft to the ground at 115 m/s.

* The following two rockets have ***EXACTLY*** the same drag and flying characteristics.

http://i.imgur.com/xHlcZ6D.pnghttp://i.imgur.com/5zuTSXr.png

KSP simply does not do aerodynamics. It doesn't even fake it very well. It just does *stuff*, and calls that drag.

I figured this was the case, but there seems to be some argumentation on the side of it not being a game limitation, when I've played other flight simulators that attempt some aerodynamics...so I guess that kind of settles it, it's not normal plane behavior. But it's fun, and it's a game so /forgive and /mod.

Also for those curious what plane I'm flying:

My first actually "flying" plane. Mind you it needs SAS and RCS to do it.

Edited April 12, 2014 by took

[Zephram Kerman]

Hey that's pretty cool. Kinda unstable without any tail surfaces, but it looks like maybe that's intentional. Very maneuverable that way, and could come in handy if you want to land vertically.

By the way, Sam Hall made a mod to replace the inline cockpit internals, so that you can see out the window. Looks much better during IVA.

http://forum.kerbalspaceprogram.com/threads/44012-Mk2-Cockpit-Internals

[O-Doc]

Your thrust to weight ratio is about 10:1 so, yeah, that'll go into space no prob. There's nothing unusual going on besides that plane not actually having jacks!