1.05 Intakes - Lets figure them out

[Right]

What is the new "effective base speed" metric in the part description? I seems like lower is better for higher speeds ops?

Its a suction speed. In ensures that you have some air while stationary. It adds to your current velocity, so its benefit falls off extremely fast once your moving.

[NathanKell]

Yep, it's always better to have more...but it's a tradeoff, the ones with better suction have worse supersonic performance.

322997am: that limit is far, far above where your engines cut out, and is therefore not worth worrying about.

[GoSlash27]

So how do you guys even know how much drag a particular part has? I.e. how can you tell if a shock cone or nose cone will be more draggy.

A-Name,

All that info is in the PartDatabase.Cfg file. Each part has a "drag cube" in there that defines its cross section area, drag coefficient, and side flow drag for every axis. For example:

PART

{

url = Squad/Parts/Aero/circularIntake/intakeShockCone/shockConeIntake

DRAG_CUBE

{

Default = Default, 0.7486105,0.6887614,0.7221569, 0.7486105,0.6887677,0.7221569, 1.213026,0.3,1.183155, 1.213026,1,0.100694, 0.7486105,0.6903304,0.7221569, 0.7486105,0.6871722,0.7221569, 0,-0.08307549,0, 1.25,1.083849,1.25

}

}

This would be interpreted as

Shock cone intake

Area /Cd /laminar drag

X+0.7486105,0.6887614,0.7221569,

X-0.7486105,0.6887677,0.7221569,

Y+1.213026,0.3,1.183155,

Y-1.213026,1,0.100694,

Z+0.7486105,0.6903304,0.7221569,

Z-0.7486105,0.6871722,0.7221569,

Occlusion centers

x/y/z

0,-0.08307549,0,

Occlusion range

x/y/z

1.25,1.083849,1.25

When the intake is aligned into the airflow we look at the Y+ values.

Y+1.213026,0.3,1.183155,

1.213 is exactly the frontal area of Mk1 parts so the stuff behind it will be nicely occluded and 0.3 is an excellent drag coefficient. We don't worry about the laminar drag numbers above Mach 1, since their effect is so minor. But they are a bigger deal at subsonic speeds.

As good as the shock cone is, there are other parts that exhibit even lower drag at supersonic speeds. The tailcone A is the best by a wide margin, but it's increased laminar drag makes it draggier at subsonic speeds and it's mass is a penalty for closed cycle ops.

HTHs,

-Slashy

- - - Updated - - -

So how do I analyze the number of intakes I need? Let's say I'm cruising at 20k alt on 2 rapiers. By what metrics do I determine how many and what kind of intakes I need? Do I use the "intake air" resource, and verify I need some minimum amount? Do I look at the "flow rate" of the intakes themselves? Just wonder what the actual "workflow" to better engineer my vehicles would be?

Thanks!!!

g00bd0g,

For the moment, I'm looking at the "effective intake area" at the top end Mach of my engine. It seems to be right around .001m^2 per engine in 1.05. It was about .007m^2 in 1.04.

So for example looking at a "radial variable ramp", the velocity multiplier looks like this:

area = 0.001

Mach/multiplier/ slope in/slope out

key = 0 0.85 0 0

key = 1 1 0 0

key = 2 0.95 -0.08751557 -0.08751557

key = 4 0.5 -0.4034287 -0.4034287

key = 8 0.01 0 0

A single intake will have about half the required effective area at Mach 4, but 2 would be sufficient and empirical testing bears this out.

All of these curves are presented in Right's graph on page 1.

Best,

-Slashy

Edited November 12, 2015 by GoSlash27

[percyPrune]

Question for the Wise Ones:

Please can you tell me in simple words: Are there any lines in the cfg I can alter to skew the intake air toward low speed, stationary & reverse?

This 'fairly realistic' VTOL works all the way through to 1.0.4 but the new 'effective speed' means that the lift engines flame out at hover:

I haven't found a stock solution to the problem (even intake spamming) so I will have to fall back on a modded cfg. Can't live without my VTOL!

From its proportions, I thought that the simple intake would allow enough airflow, even when stationary, for a Weesley to run without flameout, even if not at full thrust?

Thanks,

percy

[NathanKell]

Quick note, for the triplets in a DRAG_CUBE, first is area (yep), second is unmodified Cd (yep), third is depth.

I.e. looking from that angle, taking the bit of the part nearest you as 0m depth, what is the depth of the widest bit of the part?

For a cone, looked at from the tip's side, depth is (height of the cone). Looked at from the base's side, height is 0. Looked at from a side, depth is (radius). Make sense now?

[Right]

Are there any lines in the cfg I can alter to skew the intake air toward low speed, stationary & reverse?

That an interesting problem. Try going into the cfg file of the circular intake and dialing up the intakeSpeed from 15 to maybe 50.

Hey Slashy, is occlusion range and centers new?

Edited November 13, 2015 by Right

[GoSlash27]

Right,

No Sir. They've always been there.

They don't have any effect on how I estimate drag, so I ignore them.

Best,

-Slashy

Quick note, for the triplets in a DRAG_CUBE, first is area (yep), second is unmodified Cd (yep), third is depth.

I.e. looking from that angle, taking the bit of the part nearest you as 0m depth, what is the depth of the widest bit of the part?

For a cone, looked at from the tip's side, depth is (height of the cone). Looked at from the base's side, height is 0. Looked at from a side, depth is (radius). Make sense now?

NathanKell,

Ah. Yes it does. Thanks!

-Slashy

[percyPrune]

Originally Posted by percyPrune

Are there any lines in the cfg I can alter to skew the intake air toward low speed, stationary & reverse?

That an interesting problem. Try going into the cfg file of the circular intake and dialing up the intakeSpeed from 15 to maybe 50.

Hi Right,

Thanks for the suggestion but I sorted it by altering the 'Area' from 0.006 to 0.06 (was going to post later). It makes a massive difference to the static air but doesn't seem to make much difference to the drag at normal airspeed so I will stick with it.

What units is 'Area' in? I would have thought m2 but 0.006m2 is only 87mm diameter! 0.06m2 is 276mm dia which, if the fuselage is 1250mm dia, still seems a bit small for the proportions of the model.

[GoSlash27]

Right,

After fiddling with the numbers and empirical testing, I have come up with a recommended list of engine/ intake combos for minimum drag.

Tech level 6: Panther, 1 Nacelle per, and Tailcone A as required.

Tech level 7: Panther, 2 variable ramp inlet (radial mount) per

Tech level 8: Whiplash, 1 Precooler, and Tailcone A as required.

Tech level 9: RAPIER, 1 Precooler, and Tailcone A (better heat dissipation and lower drag) as required *or* 1 Shock cone inlet (better heat tolerance and lighter weight).

Best,

-Slashy

[Starhawk]

Tech level 6: Panther, 1 Nacelle per, and Tailcone A as required.

Tech level 7: Panther, 2 variable ramp inlet (radial mount) per

Tech level 8: Whiplash, 1 Precooler, and Tailcone A as required.

Tech level 9: RAPIER, 1 Precooler, and Tailcone A (better heat dissipation and lower drag) as required *or* 1 Shock cone inlet (better heat tolerance and lighter weight).

Thank you so much for doing the research and sharing the results.

This is extremely valuable data.

Happy landings!

[Johould]

How are you comparing drag? Turning on drag numbers in the right click menu shows more drag from the tailcone under any conditions, and a lot more if it's not pointed exactly prograde.

[GoSlash27]

How are you comparing drag? Turning on drag numbers in the right click menu shows more drag from the tailcone under any conditions, and a lot more if it's not pointed exactly prograde.

Johould,

The tailcone has more drag at subsonic speeds but much lower drag at Mach 1 and above. This is the critical part in spaceplanes.

Best,

-Slashy

[Johould]

Ok, but you should mention that you have to fly exactly prograde for the tailcone to save drag.

Flying more carefully, I can get half as much drag from the tailcone, but its drag increases much more quickly with angle - it's even with the shock cone you are pointed 1/2 of the way from the center to the circle of the prograde marker, and gets hugely worse after that.

Thanks for the table. The shock cone intake has reasonable drag over a lot wider range of angles, but it's good to know the tailcone can give lower drag if used carefully.

[Dispatcher]

Of course a design consists of several components. Not really discussed earlier are lift and control surfaces, the cockpit, monopropellant tank, cargo/ personnel compartments, energy collection/ generation/ storage, command/ control equipment, radiators, fuel tanks, fuel/ oxy tanks, perhaps ladders and landing gear (and most of these things are treated as if they have mass and drag). So design is a major factor.

I just made and flew an SSTO using Slashy's ideas and those of the OP. For this thread, I'll mention that I used one Rapier and two Whiplashes, with one shock cone and one pre cooler per engine. Even with my poor piloting skills, I attained a pretty decent orbit and enough dV to get back down. The design was quick and dirty and didn't look too bad; I'm sure it could have been optimized and tweaked.

My point is, KSP stock parts in 1.0.5 should allow anyone with a halfway decent design to get an SSTO to orbit and back. In earlier versions, it was more challenging for me to do so. Have fun with [I]your[/I] SSTOs!

[spiritplumber]

THe problem is that I get a "resource not present" above roughly 36Km on Kerbin, even if I make the intakes have unrealistic areas, they get nothing - this was not the case in 1.0.4

[problemecium]

Aha! This graph explains how my newest spaceplane designs are managing to get to orbit with fewer intakes than I'd expected. Before, the basic recipe was a minimum of one "real" intake (e.g. shock cone) or 2 radial intakes per engine, but now I'm getting by with significantly fewer (although I haven't run tests to see just how few I can manage).

[NathanKell]

And as I said before, engines flame out long before that, so it doesn't matter, and at 36km the resource _is_ indeed effectively not present (36km Kerbin -> 45km Earth -> 150,000ft). You can of course tweak the minimum threshold, in the module, if it will make you feel better to have intakes producing a trickle of a resource no one can use. :)

[royying]

Is intake spamming still useful now?

[Geschosskopf]

Somewhat of a sidetrack here, but related. On my game, IntakeAir no longer shows up in the resource tab. Is that for everybody or just me (although I don't have any mods that modify the resource display that I know of). And why would this be removed? I found it rather useful to know when the air was going away.

[Right]

[quote name='royying']Is intake spamming still useful now?[/QUOTE]

Not generally.

[quote name='Geschosskopf']Somewhat of a sidetrack here, but related. On my game, IntakeAir no longer shows up in the resource tab. Is that for everybody or just me (although I don't have any mods that modify the resource display that I know of). And why would this be removed? I found it rather useful to know when the air was going away.[/QUOTE]

Mine is gone too. It was useful when you understood it, but with the changes they made (engines need far less air, and they produce less thrust at very high altitudes/speeds regardless of air availability) its not a very relevant stat anymore. If you have mechjeb, add "Intake Air" and "Intake Air Needed" from Vessel stats - you'll probably find you won't run out of air unless you use the wrong intake for the job. You can even run 3 rapiers on a single engine precooler, and probably like 5-7 on a shock cone (once you get moving)

[Starhawk]

[quote name='Geschosskopf']Somewhat of a sidetrack here, but related. On my game, IntakeAir no longer shows up in the resource tab. Is that for everybody or just me (although I don't have any mods that modify the resource display that I know of). And why would this be removed? I found it rather useful to know when the air was going away.[/QUOTE]

SQUAD indicated that the old intake air display was confusing and have implemented a display on the engine's right-click menu.

Happy landings!

[Geschosskopf]

[quote name='Starhawk']SQUAD indicated that the old intake air display was confusing and have implemented a display on the engine's right-click menu![/QUOTE]

I disagree with this. I liked the old display because I could note it at a glance just by having resources open. Right-click menus, especially for jet engines, are just too cluttered up with stuff I don't care about to be useful at all, plus get in the way of enjoying wathcih my plane fly.

The need for less air has been around since 1.0, although not as marked as it is now. So what the IntakeAir display showed was whether or not you'd flame out before your thrust fell off the table. It was a nice check on everything else, simple, quick, intuitive, and out of the way. I wish they'd bring it back.

[Dispatcher]

Yes, intake air is no longer displayed in the resources menu at upper right of HUD. Since I use KER, I'm hoping that this mod will display this resource when air intakes are attached to the craft.

[NathanKell]

just remove isVisible = False from the IntakeAir entry in GameData/Squad/ResourcesGeneric.cfg if you don't like it.

That said, that display showing 0 is *not* indicative of you being likely to flame out from insufficient intakes. In fact, the only case it will not be 0 is if you have [I]more[/I] intakes than you need. (Not a bad position to be in, true, but the bar being at 0 isn't necessarily a worry anymore).

The reason the change was made in 1.0.5 was because I quite totally rewrote the intake module, so the info displays for it *do* make sense now, including flow rate.

[GoSlash27]

[quote name='royying']Is intake spamming still useful now?[/QUOTE]

No, it's not. Intake spamming is counterproductive from 1.0 on. All it does is add drag in exchange for air that you can't use. If engines are fed beyond their useful speed and altitude, they will produce nothing but noise, heat, and *negative* thrust at the expense of fuel.

The goal now is to have just enough intakes to keep the engines lit while they are still useful while adding as little drag as possible. Precoolers are the new hotness in 1.05.

Best,
-Slashy