1.0.2 - Any hope left for SSTOs?

[EladDv]

I think one issue with aircraft is that it seems thrust is proportional to altitude.

In real life, higher altitude = less drag. Less drag = faster speed. Faster speed = more air to the engines. Aircraft at high altitudes fly faster and farther than aircraft at low altitudes.

In KSP, higher altitudes seem to make your engines produce less thrust, and I have no idea why. With just two normal jet engines and one air scoop, I can't break 300m/s at 7-8k, and I actually start losing thrust. I seem to be exactly as limited in airspeed at 400m as I am at 4000m. I can't even break 300m/s if I nose down at high altitude and apply maximum thrust.

well different engines have different curves for both thrust vs. atmo and thrust vs. speed the regular jet stop working at about mach 1.5 and 10-13k while turbo-ramjet engine peaks at mach 3 and an altitude of about 15-17k while rapiers max at mach 3.8-3.9 and at altitudes of 15-20k.

[regex]

In KSP, higher altitudes seem to make your engines produce less thrust, and I have no idea why. With just two normal jet engines and one air scoop, I can't break 300m/s at 7-8k, and I actually start losing thrust. I seem to be exactly as limited in airspeed at 400m as I am at 4000m. I can't even break 300m/s if I nose down at high altitude and apply maximum thrust.

One problem is transonic drag. As you approach 300m/s at altitude drag increases dramatically. If you climb to 10~10.5km while making sure you're still going at least 275m/s or so, you can enter a shallow dive to @7.5~8km which should help you punch through the sound barrier. This should build up speed to about 450~475m/s, where drag is reduced to be closer to subsonic speeds, at which point you can level out and climb again with you newfound speed. This is how I've managed even Mk3 planes to space.

You do need thrust, however. A TWR around 1.0 is pretty good.

[Alias72]

I think one issue with aircraft is that it seems thrust is proportional to altitude.

In real life, higher altitude = less drag. Less drag = faster speed. Faster speed = more air to the engines. Aircraft at high altitudes fly faster and farther than aircraft at low altitudes.

In KSP, higher altitudes seem to make your engines produce less thrust, and I have no idea why. With just two normal jet engines and one air scoop, I can't break 300m/s at 7-8k, and I actually start losing thrust. I seem to be exactly as limited in airspeed at 400m as I am at 4000m. I can't even break 300m/s if I nose down at high altitude and apply maximum thrust.

Notice how increasing altitude decreases thrust faster than increasing speed. That means that flying higher will generally produce less thrust. You can go faster to counteract that but you will eventually run out of air to shove through your engine. What you are actually banking on is the loss in drag resulting from lower airpressure. Unfortunately the same thing that decreases drag decreases engine thrust.

the normal jet engine is rated neither for high speeds or altitudes. On the other hand the ram air intake is rated for VERY high speeds. The result is that you are losing thrust from an inefficient inlet, and then you are losing more thrust from the wrong engine. Not all engines are made equal. Engines are optimized for a specific altitude and speed regime. deviating from that decreases performance. Your engine is good for mach 1.2 @ 6-8km IF it has adequate airflow. You have half the inlets and they are the wrong type. try 2 of the simple circular intakes instead and you should go much faster.

[Frostiken]

Well before 1.0.2, my simple little guy here could hit 350-ish, and break 500-550 if I dropped from high altitude.

Now it's basically trapped at 300 no matter what I do.

And no, there is NO issue with the single air scoop whatsoever. Adding a second scoop literally does nothing except adds more drag and weight.

- - - Updated - - -

One problem is transonic drag. As you approach 300m/s at altitude drag increases dramatically. If you climb to 10~10.5km while making sure you're still going at least 275m/s or so, you can enter a shallow dive to @7.5~8km which should help you punch through the sound barrier. This should build up speed to about 450~475m/s, where drag is reduced to be closer to subsonic speeds, at which point you can level out and climb again with you newfound speed. This is how I've managed even Mk3 planes to space.

You do need thrust, however. A TWR around 1.0 is pretty good.

Except the issue is that with 1.0.2, I can no longer add ANY appreciable velocity by diving. In 1.0 I could do exactly what you said - climb to higher altitude, enter a shallow dive, and gain speed gradually, usually getting to around 500m/s or so.

That no longer happens.

Edited May 2, 2015 by Frostiken

[NathanKell]

Yes the transonic drag spike seems a bit high, and it's combined with drag being a bit high at low (<5km) altitude...but only for sharply-tapered parts. Blunt parts, the drag looks spot on to me.

Next, it's worth recalling that those Basic Jet Engines are...basically F100s in mil thrust. You're not going to go supersonic easily with a low bypass turbofan in non-afterburner.

Finally, the plane in your pic has a fair amount of frontal drag because essentially you have three nosecones (recall that the only drag occlusion is from stack mounting, not surface-attaching, so you get the full frontal area of both tailconnectors in addition to your cockpit, and in addition to the sharp spike of drag from that flat-backed tank.

If you want something that handles clipping, get nuFAR, it's the only game in town.

[Robotengineer]

Not a hotdog.

[Aanker]

Looks pretty much like every other entry - six or eight wing parts, long Mk2 fuselage section... Yawn, I've seen this already.

Now this is creativity bounded by realism!

[Robotengineer]

Looks pretty much like every other entry - six or eight wing parts, long Mk2 fuselage section... Yawn, I've seen this already.

Now this is creativity bounded by realism!

http://i.imgur.com/TiA2PB5.png

Ah, but the hotdog is outside the bun.

[PotatoOverdose]

Won't claim any particular creativity, but this gets 1365 dV in LKO with a 3 ton payload in the cargohold, and the nerva can run for 15 minutes+ without exploding anything. Will probably take it to laythe once i have an ISRU refueling craft out there.

Edited May 3, 2015 by PotatoOverdose

[WOODY01]

Looks pretty much like every other entry - six or eight wing parts, long Mk2 fuselage section... Yawn, I've seen this already.

Now this is creativity bounded by realism!

http://i.imgur.com/TiA2PB5.png

Nice recreation.

I see where you are coming from having more restrictions placed to build more realistic vehicles can take the fun away for some people.

It is really hard to balnce simulator type games for different types of players. I like the new update simply because I can now design a plane or SSTO and understand how it will behave a slow and fast speeds and when it will likely have control issues. Since the release of 1.0 I am finding it more intuitive for me because it follows more realistic rules but I am also finding it more restrictive when it comes to asthetics. I have one plane I would really like to move the wings back on a little, just so it would look better to me. I probally can with some tweaking of the fuel in the tanks but decided to put plane/SSTO designs on hold until I am sure Squad will make no adjustments to the aero model.

As for your design options to be honest I have not seen much variation simply because this is not a game focusing on fantasy based designs. If everything you design can work it takes away one of the challenges of the game. If I can get a jet engine to put me on a suborbital trajectory you took away a lot of the challenge, if they model the aero to be more forgiving and allow designs like that x-wing to work you take away the challenge simply because it would allow everything to fly.

I think you can adjust most of what you are complaining about by hitting f-12 and adjusting some sliders, I am sure I saw a slider to adjust drag and some other things not sure if it all adjusted something with the aero or not.

[Aanker]

if they model the aero to be more forgiving and allow designs like that x-wing to work you take away the challenge simply because it would allow everything to fly.

Well, that's the thing. The x-wing flies perfectly in 1.0.2, but many of my more realistically designed craft do not. And I don't see why, if realism isn't the issue anyway, they shouldn't be able to.

[WOODY01]

Well, that's the thing. The x-wing flies perfectly in 1.0.2, but many of my more realistically designed craft do not. And I don't see why, if realism isn't the issue anyway, they shouldn't be able to.

My guess there is some part clipping involved with that design and maybe taking advantage of stacked SAS? Not saying you can not make things work, I have seen a pic of a flying box somewhere on the forums today. Most games you can figure out how to exploit the mechanics.

As for me I just find it more intuitive. High aspect wing ratios do not perform as well as low aspect ratio wings at high speeds, jet engines perform how somewhat as I would expect them to losing thrust and having max operating ceilings regardless of how many intakes you put on, more advanced intakes increase the max altitudes, more advanced engines increase operating altitude, planes that look like they should fly will fly relatively well in alot of cases unless the balnce of COL, COM, COT is too far off, COL closer behind COM more nimble aircraft further away less nimble, put it ahead and you have a plane prone to flip out of control. I am just finding it a lot easier to trouble shoot designs now since the rules are more realistic.

Also just to make it clear I am not saying the aerodynamics are realistic, I would not want them to be anyway, just closer to being realsitic.

[Aanker]

My guess there is some part clipping involved with that design and maybe taking advantage of stacked SAS? Not saying you can not make things work, I have seen a pic of a flying box somewhere on the forums today. Most games you can figure out how to exploit the mechanics.

As for me I just find it more intuitive. High aspect wing ratios do not perform as well as low aspect ratio wings at high speeds, jet engines perform how somewhat as I would expect them to losing thrust and having max operating ceilings regardless of how many intakes you put on, more advanced intakes increase the max altitudes, more advanced engines increase operating altitude, planes that look like they should fly will fly relatively well in alot of cases unless the balnce of COL, COM, COT is too far off, COL closer behind COM more nimble aircraft further away less nimble, put it ahead and you have a plane prone to flip out of control. I am just finding it a lot easier to trouble shoot designs now since the rules are more realistic.

Also just to make it clear I am not saying the aerodynamics are realistic, I would not want them to be anyway, just closer to being realsitic.

Yeah sure, you make good points, but I just think that wing parts right now are subject to way too high drag (I did a comparison in another thread: 16 small wing parts which were basically out of the airflow's way caused more than a 550 m/s decrease in top speed at SL). Your idea of more intuitive craft design and my want for less wing unfriendlyness are not incompatible. In fact, if you want to build a large wing for a large spaceplane right now, the system is very unintuitive - somehow, building a large wing (out of smaller parts) results in unexpected and massive drag.

[EnDSchultz]

I suppose I'm just bad with this. Need to trim down my planes or something. My second SSTO spaceplane is a ~65 tonne monstrosity which, while it does have a payload bay, I'm not convinced would be able to take anything of significant weight. Granted, I'm trying to do it with turbojets and aerospikes, but I'm running Career and haven't unlocked the RAIPERs yet.

[KerikBalm]

>33% payload fractions

Tolerant of very large payload sizes.

Not sure if the SSTO is a hotdog, or the bun, and the cargo is the hotdog:

http://forum.kerbalspaceprogram.com/threads/116729-Stock-Payload-Fraction-Challenge-1-0-2-Edition?p=1896106&viewfull=1#post1896106

I could easily cram a lot more LF in there, and surely get that thing to laythe and back....

Setting that thing down on laythe would be another issue entirely (maybe I could slap on enough parachutes, evenly distributed, and just drop it down?)

[Aanker]

It's a French hotdog, going by the way the external stuff wraps around the cargo.

[KerikBalm]

Without the cargo though... its not anything like a hotdog... and it will SSTO without cargo just fine.

And the cargo, obviously can be made wider (though that will negatively affect the maximum payload fraction), I left plenty of room for less "sausage" shaped payload

[Kuu Lightwing]

Umm, I just made this Skylon-ish SSTO plane. 21 ton on the runway, puts ~2.2ton scan sat into orbit. 10% payload fraction. Oh, forgot to mention... into POLAR orbit.

[GoSlash27]

Looks pretty much like every other entry - six or eight wing parts, long Mk2 fuselage section... Yawn, I've seen this already.

Well... people are going with that for a reason

The "hot dog in a bun" approach makes for mass-efficient SSTO spaceplanes. For many of us, this is the entire point of building them.

Best,

-Slashy

[EladDv]

Well... people are going with that for a reason

The "hot dog in a bun" approach makes for mass-efficient SSTO spaceplanes. For many of us, this is the entire point of building them.

Best,

-Slashy

have you been able to test the Titan i sent you? BTW after applying your recommendations on a new large Mk.3 Plane (mammoth) i concluded it could get 45 mT into orbit with total weight of 260 mT 20 engines and big (rectangular yes rectangular) Mk.3 wings.

[raygundan]

I just wish they would make up their minds. I was finally getting a handle on 1.0 and made 2 test SSTO's and this update hits and it killed them. It also made my normal difficulty career mode a bit harder. Now I'm going to have to redesign everything all over again. >.<

Yeah... I'm honestly sorta indifferent to whether we end up with realism or soupodynamics or something totally new and different. I just want it to stop changing so I can settle in and play.

[GoSlash27]

EladDv,

Sorry, I never got it. Did you put it in my PM in- box?

Check this out:

The wet wings allow me to build it aerodynamically cleaner, so I get more mass moving hypersonic with the same thrust and ultimately more payload.

This represents approx. 20% payload fraction.

Best,

-Slashy

[Kuu Lightwing]

Is it just two SABREs?

[GoSlash27]

Is it just two SABREs?

Aye. 33 1/2 tonnes of spaceplane with 2 sabres.

Best,

-Slashy

[Wheffle]

I just saw this thread and was about to post a quick spaceplane I put together (haven't really played too much yet, waiting for mods to update, but I got on to check out what the aero complaining was about). Granted I've been playing with FAR for ages; it feels a bit different, but spaceplanes are definitely not "dead".

To my pleasant surprise there are already a ton of working designs posted. Awesome!