Intake Differences?

[ZentroCatson]

What's the difference between using a shock cone, stack ramp intake or one of these diverter less intakes? There's not much info on the info panel. I've been using shock cones for SSTOs up to now since they look really cool! But are there benefits of using a ramp intake or diverter less intake? A possible benefit of a diverter less intake is that you can put a more heat-resistant part in front.

So, I want to hear what you guys have to say! 

[Flamingo]

Im only saying what I have heard, so it might not be true, but the shockcone has a high heat resistans, which makes it great for SSTOs and supersonic planes. The ramp has a higher intake capacity, this means that it can be used at higher altitudes because it takes more air and oxygen in, but when you close it, it has a lot of drag. I have not even used the diverterless intake once, so i have no idea about what its pros and cons are.

[JadeOfMaar]

The main difference between intake parts are their speed ratings. Some will only work at low speeds, some work very well at very high speeds. The large stock Engine Nacelle with (I think) 5 IntakeAir and more LF than the Precooler, won't feed Whiplashes at over 1km/s at 10km alt...But it may sustain Rapiers and some mod engines all the way. Their static suction value also matters as that shows how well they can feed air engines that show themselves to be gluttonous at very low speed/at launch. This is the most important for VTOLs about to touchdown.

The 0.625m and radial intakes are only for subsonic or very small craft, but you're very well covered for spaceplanes and SSTOs with nearly any 1.25m intake, especially the Precooler with 5 IntakeAir and 40 LF. Also, you can read "subsonic" or "supersonic" in the part descriptions.

@Flamingo The Mk1 Divert-less Intake is just fine as a supersonic intake and in the OP's list is the only intake with added tankage, but it has a fairly low heat tolerance forcing my craft that used it to keep a very shallow reentry.

Edited December 26, 2016 by JadeOfMaar

[Guest]

Here ya go!

Shock cone doesn't experience a performance drop and has the same max temp as nosecones at 2400K as well as practically the best performance at all speeds. The only reason not to use it would be if you need frontal space for something else (like nose cargo ramp because rear space for engines takes precedence, maybe).

The circular intake is the least draggy frontal intake, but not by much, still it might be better for subsonic planes.

 

Also closing intakes is actually bad, it seems!

 

Edited December 27, 2016 by Guest

[sardia]

25 minutes ago, String Witch said:

Here ya go!

Shock cone doesn't experience a performance drop and has the same max temp as nosecones at 2400K. The only reason not to use it would be if you need frontal space for something else (like nose cargo ramp because rear space for engines takes precedence, maybe).

The circular intake is the least draggy frontal intake, but not by much, still it might be better for subsonic planes.

 

Also closing intakes is actually bad, it seems!

 

You saying the Ramp intake Ramjetthingy loses performance when using the whiplash jet engine?

[Guest]

1 minute ago, sardia said:

You saying the Ramp intake Ramjetthingy loses performance when using the whiplash jet engine?

I'm not aware of any correlation between certain engines working a particular way with certain intakes, so I think that is a reasonable hypothesis, yes.

[sardia]

Ok, that explains why my SSTO rapidly shuts down once it gets past 1500 m/s. I had just thought I was too high up.

[mystik]

8 hours ago, String Witch said:

Here ya go!

Shock cone doesn't experience a performance drop and has the same max temp as nosecones at 2400K as well as practically the best performance at all speeds. The only reason not to use it would be if you need frontal space for something else (like nose cargo ramp because rear space for engines takes precedence, maybe).

The circular intake is the least draggy frontal intake, but not by much, still it might be better for subsonic planes.

This graph helps in my quest for a universal miner and rover carrying SSTO that can reach other planets. I was using the Engine pre-cooler with the shock cone in front of it. Does this affect the performance of the engine? Should I use only one intake? Does the pre-cooler reduce performance when paired with another intake?

[Guest]

14 minutes ago, mystik said:

This graph helps in my quest for a universal miner and rover carrying SSTO that can reach other planets. I was using the Engine pre-cooler with the shock cone in front of it. Does this affect the performance of the engine? Should I use only one intake? Does the pre-cooler reduce performance when paired with another intake?

I think the parts work independently; I don't see why they wouldn't, but I know airhogging (clipping an assload of intakes together onto a plane to feed it until the very end of the atmosphere) was fixed long ago and I can imagine an aggregated airflow mechanic being implemented as the fix. I really don't know though. Having the precooler gives you more intakeair resource as mentioned by JadeOfMaar (not sure this matters though), but it's possible the extra mass and drag negate that. I'm not someone who has put much time into planes overall, let alone SSTOs, but I think I know of someone whom has: @GoSlash27

Bear in mind I didn't make the graph.

[GoSlash27]

 All,

 We had worked out this relationship for intake performance back in 1.02 (I think). Those charts are good, but what is important to remember is that a single engine only needs so much airflow to operate at it's full potential. Any more than that is wasted and just adds drag.

The idea is to give an engine "enough" air to keep it humming up to it's limit while incurring the minimal drag. The ideal intake is actually the precooler because it adds zero drag in the transsonic region, yet supplies adequate air to keep an engine fed to it's velocity limit.

I haven't revisited this since 1.2 and there may be changes... but my designs based on the earlier findings still work as expected.

HTHs,
-Slashy

 

 

[Just Jim]

11 minutes ago, GoSlash27 said:

 All,

 We had worked out this relationship for intake performance back in 1.02 (I think). Those charts are good, but what is important to remember is that a single engine only needs so much airflow to operate at it's full potential. Any more than that is wasted and just adds drag.

One question... how does one know when an engine has reached it's full potential? Is there a formula, or maybe right clicking an engine?

JJ

[GoSlash27]

4 minutes ago, Just Jim said:

One question... how does one know when an engine has reached it's full potential? Is there a formula, or maybe right clicking an engine?

JJ

Just Jim,

 If the engine runs out of thrust and stops accelerating at the top end, then it is adequately fed. If it is still accelerating and suddenly flames out, it's not.

Best,
-Slashy

[Just Jim]

1 minute ago, GoSlash27 said:

Just Jim,

 If the engine runs out of thrust and stops accelerating at the top end, then it is adequately fed. If it is still accelerating and suddenly flames out, it's not.

Best,
-Slashy

Gotcha... thanks!  

[mystik]

38 minutes ago, GoSlash27 said:

 All,

 We had worked out this relationship for intake performance back in 1.02 (I think). Those charts are good, but what is important to remember is that a single engine only needs so much airflow to operate at it's full potential. Any more than that is wasted and just adds drag.

The idea is to give an engine "enough" air to keep it humming up to it's limit while incurring the minimal drag. The ideal intake is actually the precooler because it adds zero drag in the transsonic region, yet supplies adequate air to keep an engine fed to it's velocity limit.

I haven't revisited this since 1.2 and there may be changes... but my designs based on the earlier findings still work as expected.

HTHs,
-Slashy

 

 

Hi,

 

Thanks for getting back to the thread to clear some of the points. I almost always stick a precooler for my engines, but I do find them that they are bulky and I often wonder if all this is really needed. I know that they have better intake based on the description, but it does make the whole ship building harder.

 

Do you know if one intake is enough for 3+ engines, based on your previous tests? I know that for 2 engines one will work, but I am not certain if adding 3 or more is pushing the limit. The issue is that the game always displays "requirements 100% met" but that tells me nothing in real terms. I wish it told me how much over the 100% requirements I am meeting so that I can better plan things.

 

I am only asking since I understood that when it comes to planes you know a lot. Does adding the cone to the top of it affect its performance or just adds to it? What about sticking these things behind the plane in order to hide them from drag? I know in real life that would be dumb, but KSP isn't entirely realistic, so I'm curious about performance. I'm not very familiar with drag and I've recently looked more into the supersonic drag issues. I'm looking to build an advanced SSTO and it's kinda been a... drag. *BA-DUM-TSSSS*

 

Thanks,

M

Edited December 27, 2016 by mystik

[GoSlash27]

Mystik,

 Remember that intakes (no matter which you use or in what combination) have the sole purpose of keeping your engine lit up to the point where it can't accelerate any more. Adding intakes doesn't add thrust, it just extends the condition where the engine stays lit. The speed at which an engine stops producing thrust is completely dependent upon the engine itself.

 When we look at how much intake is needed to feed an engine, we look at the effective intake area at speed. That is, we note the engine's max speed, then interpolate the intake's flow multiplier at that speed and multiply it by the intake area. In a practical sense, you can think of it as the intake area opening or constricting with speed. So long as you have about .0012 m2 of effective intake area per engine at speed, you should be good to go. If memory serves, the Whiplash needs a little more, like .0015 or so.
 

What I found back when I ran this study was that intakes were ridiculously overpowered, and almost any intake is adequate. The focus then becomes "how do I supply adequate air with a minimum of additional drag?"

For this part of the job, you look at the drag of the part in the PartDatabase.Cfg and see how much "flat plate area" it adds to your design. The analysis must include how the intake is installed; at the front of a stack, radially, or within a stack because they add drag differently.

So to get to your questions...

1) I have found that a single precooler is adequate *by itself* to feed a single engine. This is ideal because it is the only intake that adds no frontal area.

2) Some intakes are adequate to feed a ridiculous number of engines, especially the shock cone. Others may require several intakes to feed a single engine. It all comes down to how much effective intake area it has at speed.

3) Remember that the work that I'm going on is dated now. Squad may have changed some things...

HTHs,
-Slashy

Edited December 27, 2016 by GoSlash27

[mystik]

I'll experiment a bit with several configurations to see if things are still up to date, will probably try flying one engine at a time with little wings attached at ridiculous speeds and altitudes to see the limits and come back if I find anything worth adding to this.

 

Thanks,

M

[GoSlash27]

mystic,

 Sounds good. The altitude limit really only applies to the engine itself, so I'd recommend focusing on speed at 20km altitude (so long as you don't fry it). This is how we confirmed a lot of our older findings.

Best,
-Slashy

 

[GoSlash27]

I found a link to the old discussion:

 

 I'm still operating on this info and it still works fine in 1.2.2, but that doesn't mean that Squad hasn't changed some things since then.

Best,
-Slashy

[sardia]

If the pre Cooler is the best, what's the best way to get a pair of precooler attached to a pair of engines? Cap them both radially with advanced nose cones? 

[GoSlash27]

Sardia,

 Attach them serially in front of the engines. That way you add intake area without adding any cross section area.

They are only the lowest drag option when you can do that. You don't want to add a radial stack to your plane if you don't have to, certainly not just to have somewhere to put an intake.

Best,
-Slashy

 

[Jarin]

2 hours ago, GoSlash27 said:

I found a link to the old discussion:

I'm still operating on this info and it still works fine in 1.2.2, but that doesn't mean that Squad hasn't changed some things since then.

I think most of what's changed is in the drag model, and that's just how the engine deals with pointy bits. Honestly, going through all the conversations and testing in the past month, I think the differences just boil down to "don't bother closing intakes anymore".

[GoSlash27]

4 minutes ago, Jarin said:

I think most of what's changed is in the drag model, and that's just how the engine deals with pointy bits. Honestly, going through all the conversations and testing in the past month, I think the differences just boil down to "don't bother closing intakes anymore".

Jarin,
 We had come to that conclusion back in 1.04. There is definitely a change in how the game engine handles drag; it now gives you "brownie points" for an overall clean shape, whereas previously it just computed it from how the parts were assembled.

 I can't say for certain that there has been no change in the behavior of the intakes, as I haven't researched it since 1.05.

Best,
-Slashy

[Jarin]

4 hours ago, GoSlash27 said:

 We had come to that conclusion back in 1.04.

Huh, I was still seeing a lot of "close the intakes for better drag" then. Hadn't heard anything about it actually taking the whole design into account now; just the pointyness of the part at the top of any given stack. Need to figure out some proper testing...

[GoSlash27]

1 hour ago, Jarin said:

Huh, I was still seeing a lot of "close the intakes for better drag" then. Hadn't heard anything about it actually taking the whole design into account now; just the pointyness of the part at the top of any given stack. Need to figure out some proper testing...

Jarin,

 I'd recommend balance beaming 2 intakes on a booster and closing one of them. That's how we confirmed it.
 I think that not everyone had gotten the word, so "close your intakes" was vestigal advice from previous versions.

Best,
-Slashy

[Jarin]

41 minutes ago, GoSlash27 said:

 I'd recommend balance beaming 2 intakes on a booster and closing one of them. That's how we confirmed it.
 I think that not everyone had gotten the word, so "close your intakes" was vestigal advice from previous versions.

Oh I know about that. I mean testing drag for the "brownie points" you mentioned from shape. Need to find that variable-weight mod so I have ballast to offset aerodynamic parts for consistent drag testing.