the "right" assent profile for new aero?

[Brainlord Mesomorph]

I thought I could figure as the new aerodynamics by myself, it turns out, not so much.

I think my vehicle has plenty of thrust and fuel. Maybe I just need help with my flight profile:

It used to be: 500m/s at 15km would be the right set up for 1km/s at 20km, from there, it was a matter of air hogging and for as long as you could, and switching to LFO engines was as late as possible.

It used to be: if you were burning atmosphere on the way up you’re doing something wrong.

Now it seems that I am burning atmosphere at 800 m/s at 23 km. What’s up?

Does the plane have too much drag?

Edited August 25, 2015 by Brainlord Mesomorph

[Vegetal]

You WILL see burning effects, but as long as nothing is in fact melting, you are good. Try to ride the hypersonic boost as long as you can before 20km, make a very shallow climb (usually no more than 10 deg pitch). I reach 1500 m/s orbital most of the time on air breathing mode before engaging the rockets.

[Brainlord Mesomorph]

Try to ride the hypersonic boost as long as you can before 20km,

The white effect?

That's a boost? I thought it represented some kind of buffeting to be avoided. I was trying to slow down and climb when that happened.

[Vegetal]

The effect is just your craft breaking the sound barrier (and then flaming like a meteorite), the boost comes from the engine thrust curves. The Turboram and Rapier work better at super and hypersonic speeds, so above 10km you have to be accelerating almost flat in the atmosphere to gain the most speed possible from this property.

If you reach 20km and still are going 800m/s you lost the opportunity to accelerate.

TL;DR: 10 to 20km is the prime acceleration zone. Let your aircraft melt, but gain the most speed there. Then rockets...

[eddiew]

Definitely not a thing to avoid! Airflow, thrust and speed are synonymous in nuKSP. The more speed you have at a given altitude, the more air is crammed into your intakes, the more thrust your engines produce. The white effect seems to be a a general encouragement meaning 'you're doing well!'. If you don't see it, that's when to level off and speed up, exactly the opposite of what you've been doing (which should explain a lot)

Intake hogging is also a thing of the past; engines WILL fade at around 16-18km and cut out by 22-26, regardless of speed or airflow. One shock or ram intake per engine is thus good enough, while more is just adding drag without making the situation better.

As Vegetal says, super shallow is the way forward. Mostly you can get to 9-10km however you like, then get the nose right down and let your speed build. Most engines hit max thrust at 15-17km or so, so that is where you have to be doing your acceleration. My rules of thumb;

Turbojets; if you're not doing mach 3.5 (1050m/s) at 17km, you've left it too late.

Rapiers; if you're not doing mach 4.5-5 (1400m/s) at 19km, you've left it too late.

White effects; mean your engines are getting lots of oxygen!

Flames; everything is normal!

Yellow overheat bars; everything is normal!

Red overheat bars; you flew too low too long and should stop trying to exceed mach 5 on air

And in general, lowering drag has more effect than increasing thrust. You're better with two engines in a sleek, streamlined 35 tonner than four engines in a lumpy box of the same weight. Check out the SSTO showcase thread for recent examples and the sort of shapes that work in the 1.0.4 world

Edit;

tends to come out well. Triple rapiers, smooth expansion of cross section, and a slight taper at the back. Inverted nosecones on the back of rapiers is a bit of a cheat, but there's clearly some code in KSP that adds drag to unattached nodes, and these little beasties will clear that for you and reduce engine drag.

Edited August 25, 2015 by eddiew

[ajburges]

air hogging

That tells me you are using a plane SSTO and still thinking like it's .90

Limit your search to posts since July (version 1.03)

In summary:

> You only need 1 shock cone of air per engine.

> You fly jets to the edge of their envelope (Mach 3-4 and higher than angels 18) how you get there varies depending on jet engine array.

> As you reach that pull up and light rockets to switch from aerodynamic to ballistic flight.

> Once you're in ballistic flight, you are a rocket that had a shallow gravity turn. Plan for 16 km/s on rockets.

[Brainlord Mesomorph]

oh, ok!

As soon as I saw fire, I thought I was too fast too low and was trying to slow down and climb.

That explains it.

- - - Updated - - -

That tells me you are using a plane SSTO and still thinking like it's .90

I'm not thinking that. I'm trying to learn the differences.

(oddly the new seems more intuitive to me so far, scary flame effects notwithstanding)

[ajburges]

Mach effects:

Below 7 km these are bad for Whiplash engines. ISP is fixed so more thrust kills your fuel economy if it's just to fight drag on a climb.

RAPIER engines have a different thrust curve that makes it hard to go supersonic, but easy to stay there. They often are better just going supersonic ASAP and climbing fast. It helps that they often have less drag because of reduced radial stacks.

[OldLost]

Plan for 16 km/s on rockets.

16,000 meters per second? That I'd like to see...

[Vegetal]

About the scary flaming effects not being so intuitive, remember: One of the X-15 planes was almost completely coated in ablator material to withstand the heat from hypersonic flight. So it makes sense that your plane in KSP is on flames when trying to get to orbit.

[almagnus1]

Does it matter which intake you're using?

[KerikBalm]

FYI

Assent is like agreement

Ascent is the word you are looking for.

Do not use radial intakes.

Your engines will cut out at a fixed altitude(different for each engine type) no matter what, as long as you can feed air up to that point, additional intakes are just drag and dead weight.

Shock one intakes are best, the inline intakes are also pretty good as a low drag solution

Ram intakes were favorable 1.0-1.02 because they had a higher maximum heat tolerance than the shock cones, but that is no longer the case.

The flame effects don't mean that you are going to fast, but it does mean that you are heating up.

Contrary to what some people said, do not fly flat at 10km picking up speed. With a high enough TWR, if your ascent profile is too flat, you will burn up.

I find keeping a 20 degree attitude/pitch to be pretty safe for most SSTOs, that should put you up high enough into the atmosphere that you don't overheat, but it should still let you get well on the way to orbital velocity (>1200 surface velocity)

[almagnus1]

What's the recommended way to mount engines on the wings, rather than have them inline?

I am using an 8 whiplash engine configuration (with two rocket engines on a bicoupler on the SSTO core), with four whiplash engines to either side of the main fuselage, and the whiplash engines paired above and below the wing. I've also got enough TWR to go at max throttle from takeoff, hold to a 45 degree angle of attack, and put my apoapsis in space without using the rockets. It's just going from suborbital to orbital that's the current problem.

Edited August 25, 2015 by almagnus1

[Vegetal]

Well, in short: Accelerate as most as possible without melting under 20km.

Above this altitude, drag gets really low, so you should be more concerned about your orbital speed rather than escaping the atmosphere quickly.

EDIT: To almagnus: Your ascent is really inefficient. If your TWR is that high, you have too many engines, and that ascent profile doesn't take advantage of the hypersonic boost of the engines. Just for you to have an idea, my latest cargo spaceplane takes more than 42 tons to LKO, and only has 6 Rapiers.

Edited August 25, 2015 by Vegetal
To almagnus

[Nothalogh]

I thought I could figure as the new aerodynamics by myself, it turns out, not so much.

I think my vehicle has plenty of thrust and fuel. Maybe I just need help with my flight profile:

It used to be: 500m/s at 15km would be the right set up for 1km/s at 20km, from there, it was a matter of air hogging and for as long as you could, and switching to LFO engines was as late as possible.

It used to be: if you were burning atmosphere on the way up you’re doing something wrong.

Now it seems that I am burning atmosphere at 800 m/s at 23 km. What’s up?

Does the plane have too much drag?

Climb at about 30deg to 9km or so in a supersonic climb

Pitch down to 15deg and ride that to ~20km and (1250m/s with a Whiplash) and (1500m/s with a RAPIER)

Switch on the rockets and close all intakes

Pitch up to about 20 to 25 degrees and push apoapsis to about 72km

Align to prograde and coast clear of the atmosphere

Either circularize there or execute transfer to desired orbit

[ajburges]

16,000 meters per second? That I'd like to see...

Derp! Lost a decimal. Can't fix it without deleting the post though. Mobile interface is broken.

[Hagen von Tronje]

Red mach effects and even heat bars mean little. Spaceplane parts default at 2000K heat tolerance, and heat bars show up at 40% of that, so you can keep going for quite some time after. Red mach effects without bars means nothing other than that you're going fast.

Heat buildup will also be almost entirely in the skin and will be shed pretty much soon as you get to space.

[Alshain]

oh, ok!

As soon as I saw fire, I thought I was too fast too low and was trying to slow down and climb.

That explains it.

Shock heat is not as harsh as you might think, your plane can handle a little heat. It's significant heat over long duration that kills it (and you can tell when it's significant heat by the amount of flames, raging inferno = don't stay too long). The key thing is to watch for parts that might start to overheat, try to relocate those to other areas. The cockpit, cargo bays, tanks and fuselage pieces are going to be the most heat resistant.

- - - Updated - - -

Does it matter which intake you're using?

No, but some intakes are better than others. in general, those with wider openings will take in more air, but also take up more space and create more drag.

- - - Updated - - -

What's the recommended way to mount engines on the wings, rather than have them inline?

I am using an 8 whiplash engine configuration (with two rocket engines on a bicoupler on the SSTO core), with four whiplash engines to either side of the main fuselage, and the whiplash engines paired above and below the wing. I've also got enough TWR to go at max throttle from takeoff, hold to a 45 degree angle of attack, and put my apoapsis in space without using the rockets. It's just going from suborbital to orbital that's the current problem.

Design configuration is what KSP is all about. How you place the engines is not something we should tell you, it's something you should experiment with. I have at least 100 planes I've built throughout the versions. I'm always thinking up new ways to build stuff. If you really want some ideas, try looking at real planes.

Edited August 26, 2015 by Alshain

[ajburges]

Design configuration is what KSP is all about. How you place the engines is not something we should tell you, it's something you should experiment with. I have at least 100 planes I've built throughout the versions. I'm always thinking up new ways to build stuff. If you really want some ideas, try looking at real planes.

This is a biggie. Some like to ruthlessly cut anything they can from a design, others are not happy until some aspect is over engineered, and others just build by formula.

I have a 2 RAPIER VIP shuttle. the payload is literally just the cockpit and the docking clamp. Its TWR is so crazy it could do a vertical launch on RAPIERs! Its ascent profile is to set slope to 30 degrees and go. Any higher and it overshoots Ap, any lower and it incinerates. Most my normal SSTO designs follow the TWR and dV numbers I have developed through trial and error.

[almagnus1]

Design configuration is what KSP is all about. How you place the engines is not something we should tell you, it's something you should experiment with. I have at least 100 planes I've built throughout the versions. I'm always thinking up new ways to build stuff. If you really want some ideas, try looking at real planes.

As I have, but most of my experience with planes (sans FAR and DRE on the stock aero model in 1.0.x) has been purely atmospheric, and I've gotten that down.

The problem I think I'm facing is either building a lawn dart (yay), or building a SSTO that works great in atmosphere, but can't make it to orbit - which I suspect to be too much drag combined with a bad ascent profile.

I probably need to examine the design (again), then spin this off into another thread.

[ajburges]

Pitch up to about 20 to 25 degrees and push apoapsis to about 72km

Finally got fed up and did the math.

Assumptions:

> Pe of -400 km (fairly typical in the early part of the gravity turn)

> Can model circularization as the second burn of a Hohmann transfer (instant prograde burn)

> Initial speed (@ 50 km) takes roughly proportionate dV to reach

> drag past 50 km is trivial and can be ignored (less than 12 m/s for a half period)

Circularization at 50 km takes 38 m/s less acceleration. This savings comes from the required speed at 50 km

50 km circularization + Hohmann: 1599.00+731.92+21.89+21.68=2374.49

75 km circularization:

1671.60+740.82=2412.42

[Nothalogh]

Finally got fed up and did the math.

Assumptions:

> Pe of -400 km (fairly typical in the early part of the gravity turn)

> Can model circularization as the second burn of a Hohmann transfer (instant prograde burn)

> Initial speed (@ 50 km) takes roughly proportionate dV to reach

> drag past 50 km is trivial and can be ignored (less than 12 m/s for a half period)

Circularization at 50 km takes 38 m/s less acceleration. This savings comes from the required speed at 50 km

50 km circularization + Hohmann: 1599.00+731.92+21.89+21.68=2374.49

75 km circularization:

1671.60+740.82=2412.42

I do that one as well sometimes, but nobody else seems to use it, so I went with the more common option

[ajburges]

I do that one as well sometimes, but nobody else seems to use it, so I went with the more common option

It's the classic efficiency vs time problem. For a small penalty you get to orbit and faster warp windows in a smaller fraction of a period.

I like it because the smaller your final burn, the easier it is to have good accuracy.

Fun fact, after fudging some numbers to explore the problem a bi-elliptical launch only saves dV for final orbits past Keosynchronus. I kinda want to plan a HKO satilite that uses a Minmus gravity assist for bi-elliptic circularization now. The launch planning will probably suck though.

[Nothalogh]

It's the classic efficiency vs time problem. For a small penalty you get to orbit and faster warp windows in a smaller fraction of a period.

I like it because the smaller your final burn, the easier it is to have good accuracy.

Fun fact, after fudging some numbers to explore the problem a bi-elliptical launch only saves dV for final orbits past Keosynchronus. I kinda want to plan a HKO satilite that uses a Minmus gravity assist for bi-elliptic circularization now. The launch planning will probably suck though.

So you're gonna gain all the oberth effect you can by burning for a Minmus encounter while at 50km and grav brake into a Kerbin orbit?

[ajburges]

So you're gonna gain all the oberth effect you can by burning for a Minmus encounter while at 50km and grav brake into a Kerbin orbit?

More like establish a radial trajectory with a high Ap then raise Pe to desired orbit (higher than Keosynchronus) and circularize at Pe. Minmus gravity assist would just be a further fuel optimization. Pe is negative until you reach Minmus.

A very silly mission. It's optimal, not practical!

OTOH it does sound like a kickass early Minmus flyby + satilite mission.