LV-909 Maximum Thrust on Launch Pad = 15.1 kN with TL set at 100% WTH?

[Landge]

KSP 1.02 LV-909 Bug or no?

As you can see I have thrust set to MAX and the TL is set to 100%, yet all I am able to get is a measly 15 kN.

It used to be that a craft this small has no problem launching using a LV-909.

This is perhaps my most used engine for powered and assisted landings so I didn't notice this until I was returning to Kerbin and smashed into the ground

(not this craft but a much bigger one).

Thinking the Thrust Limiter might have accidentally been changed I reverted to the VAB and replaced the engines. Same results. Got out the game, got back in, same results.

If this is the way the LV-909 engine in KSP 1.0 is supposed to operate then show me what I need to do to modify the cfg file and return it back to pre 1.0 settings.

I don't see why this would be an intentional change.

Edited May 3, 2015 by Landge

[Wanderfound]

The LV-909 is a high-efficiency small vacuum engine. It's not intended to be used at sea level.

[maccollo]

In 1.0 fuel flow is constant and thrust varies with ISP, as it should.

The 909 still gets it's 60 kN of thrust in vacuum.

[Kelderek]

There was a balance pass on all engines and any engine intended to be used as an upper stage engine now has poor performance at sea level. You actually need to pay attention to the "ASL" and "VAC" values for ISP when placing engines on your vessels now. They are trying to move away from a one-size-fits-all approach where you can just use one engine type for all sorts of things. Now you need to make a choice. It also seems to be more in line with the way engines really work IRL.

This was definitely intentional and you can find it in the 1.0 patch notes.

[Landge]

Did all the engines get nerfed this badly? This is a 75% reduction in power in atmosphere. I need to look at the other engines (it's late so I can't now) but I don't think they got it this bad.

These are fictional engines in a fictional game. There is no real life counter part that I'm aware of. Why change something that worked so well in previous releases prior to 1.0? I don't get it.

[Wanderfound]

Did all the engines get nerfed this badly? This is a 75% reduction in power in atmosphere. I need to look at the other engines (it's late so I can't now) but I don't think they got it this bad.

These are fictional engines in a fictional game. There is no real life counter part that I'm aware of. Why change something that worked so well in previous releases prior to 1.0? I don't get it.

The engines designed to be used in a first stage are still fine at sea level. LV-T30, LV-T45, Mainsail, Skipper, etc.

[Cerberus738]

you think 15kn is bad... try using it in the depths of Eve's atmosphere!

[Landge]

In game LV-909 description:

The 909 model was initially received with some skepticism by spacecraft engineers,

as it defied the long-standing convention that "More Power!" is always better. Despite this,

the 909 series has found its place in the spacecraft construction world, being particularly useful as

a final stage and landing engine.

I dug into the engine cfg files and here is what I discovered:

LV-909 Pre 1.0

-----------------

Max ASL = 300

Max VAC = 390

LV-909 Post 1.0

-------------------------

Max ASL = 85 a whopping -71.66% change!

Max VAC= 345 -11.53% change

Looking at equivalent engines that could serve the same role as a landing engine.

(I excluded the Ant and Ion engine because those are only suitable for use by ants. Not that I have anything against ants. I just don't want to get ants.)

48-7S Pre 1.0

-----------------------

Max ASL = 300

Max VAC = 350

48-7S Post 1.0

------------------------

Max ASL = 270 -1.0% change

Max VAC= 300 -14.29% change

Hardly any change at all but at 18 kN total thrust it's only good for small craft.

Aerospike Pre 1.0

----------------------------

Max ASL = 388

Max VAC = 390

Aerospike Post 1.0

----------------------------

Max ASL = 290 -25% change

Max VAC = 340 -12.82% change

The Areospike would definitely be the more powerfully suitable equivalent to the LV-909.

Same diameter and height. The only difference is it being toroidal with a total 180 kN.

I don't have it unlocked at the moment since it's quite a bit farther down the tech tree.

Poodle Pre 1.0

-----------------------

Max ASL = 270

Max VAC = 390

Poodle Post 1.0

-------------------------

Max ASL = 85 -68.52% Ouch! This one two!

Max VAC = 350 -10.26% change

The Poodle is for the larger 2.25 diameter tanks but I wanted to show that it too has been nerfed just as much as the LV-909.

It has the same 85 ASL! Could it be that somebody just forgot to add a digit? Maybe it was supposed to be 185 ASL perhaps? A copy paste error.

A 185 ASL would have made it a -31.48%, still sucks IMO, but keeping it more inline with the other changes that were made and be able to stomach.

Considering that in the previous 4 year this engine worked as advertised, in any real world equivalent this engine would be an obvious manufacturing defect, pulled from the shelves, and subject to an immediate global recall. Any accidents caused by using this engine would lead to a public outcry plus a number of class action lawsuits against the company. To make matters worse the company was complacent and willfully decided not to share publicly this information and just bury this change in the "fine print".

Name me one Kerbal who reads the fine print?

TL/DR: The LV-909 and Poodle (and possibly other engines) have wrong ASL values and need to be fixed.

Edited May 3, 2015 by Landge

[JWag]

The 909 and Poodle are fine landing engines on worlds without atmospheres.

[Wanderfound]

By "landing engine" they mean the Mun. To land a rocket in atmosphere, use parachutes.

Apart from the aerospike, any rocket with good vacuum efficiency is going to have relatively lousy atmospheric thrust. That's just a consequence of how rockets work. This is a part of the game that was broken pre-1.0; now it's fixed.

[Landge]

And they were fine before as landing assist engines to be used along with parachutes on worlds with atmospheres and didn't want parachute spam.

My point is that it is a suspicious coincidence that both engines have the same 85 ASL and I am questioning why there is such a drastic change.

Edit: Can we expect the 48-7S to be nerfed next because it's values didn't change as drastically as the others.

Edited May 3, 2015 by Landge

[Bill Phil]

This is for a balancing reason. We don't want those people using upper stage engines on the first stage!

But it's great in vacuum.

[Landge]

The same could be said for the 48-7S but it's ASL value only changed by -1% where the others were from -65% to -75% It's not an aerospike either. That's pretty inconsistent.

I hereby reject your reality and substitute my own. I modified the cfg files to be more inline with my reality not yours.

Edited May 3, 2015 by Landge

[Deutherius]

The same could be said for the 48-7S but it's ASL value only changed by -1% where the others were from -65% to -75% It's not an aerospike either. That's pretty inconsistent.

Your results are skewed, because you are not taking into account changes in maximum thrust (thrust is now tied with Isp, so it is relevant). Yes, the LV-909 atmo Isp got nerfed, but its maximum thrust got a boost (from 50 kN to 60 kN if my memory serves well).

Meanwhile, the 48-7S got a whopping 40 % maximum thrust reduction independent on Isp, it only makes sense that its Isp didn't need to be nerfed that much.

[Landge]

Excerpt from my previous post:

48-7S Pre 1.0

-----------------------

Max ASL = 300

Max VAC = 350

48-7S Post 1.0

------------------------

Max ASL = 270 -1.0% change

Max VAC= 300 -14.29% change

Edit: Nevermind you were talking thrust not iSP. Apologies.

What we were expecting:

What we got:

Edited May 3, 2015 by Landge

[Jouni]

Let's look at all LF/O engines at the same time:

There are two general trends that can be seen. Big engines are more efficient than small ones, and you can gain vacuum Isp by trading away sea level Isp. The Aerospike is an outlier, with an almost-optimal performance both at sea level and in vacuum.

[Bekiekutmoar]

I had a similar discovery with the Skipper Engine on Eve. In the VAB, info regarding the Skipper says maximum thrust in atmosphere is somwhere in the 500's, but at 400 meters above sea-level on Eve I only got around 155-160 Kn of thrust. It seems there's a huge difference in engine outputs between 1 ATM and 4-5 ATM.

[Landge]

Look at the difference between the inline and radial versions. Inline iSP is 85 while the radial counterpart is 185. Look at the LV-N it's iSP in ASL is also 185! See the similarities.

This is why I believe someone forgot to add 100 to the ASL number in these cases. A simple keypress that didn't register when they meant to enter 185 and instead they got 85. Somewhere there is a keyboard with a broken 1 key.

Here is what I changed in each of the engine cfg files that use 85 as the ASL:

		atmosphereCurve
		{
			key = 0 345 // LV-909 default VAC 1.0
			// key = 1 85 // LV-909 default "broken" ASL 1.0
			key = 1 185 [B]// modified ASL[/B]
			key = 3 0.001 // Location in Tech Tree
		}

The performance of the LV-909 at sea level is now a more tolerable 32 kN instead of the horrible 15 we were given.

WARNING: Please make a backup of the cfg files before you attempt to edit them. I take no responsibility if you screw it up. However I claim full responsibility for restoring any fun you may have after using this fix.

Edited May 3, 2015 by Landge

[Jouni]

Look at the difference between the inline and radial versions. Inline iSP is 85 while the radial counterpart is 185. Look at the LV-N it's iSP in ASL is also 185! See the similarities.

Which engine are you referring to? The LV-N is the only engine with sea level Isp 185 s. The Poodle, the Ant, and the LV-909 all have 85 s, while the Rhino has 170 s.

[Landge]

Which engine are you referring to? The LV-N is the only engine with sea level Isp 185 s. The Poodle, the Ant, and the LV-909 all have 85 s, while the Rhino has 170 s.

170 - 185 there is not a big difference there. 85 - 185 HUGE DIFFERENCE!

Look at the 48-7S and compare it to it's counterpart the 24-77. Look at the LV-1 and compare it to it's counterpart the LV-1R. Inline is 85. Radial counterpart 185. Why is there a difference of 100 where they should operate very similar to each other? Give or take a few kN.

The LV-N was only to show that it also is 185 since it also sucks while operating in the atmosphere.

I believe somebody was copy/paste happy and screwed up these cfg files. That's all.

Edited May 3, 2015 by Landge

[xrayfishx]

in any real world equivalent this engine would be an obvious manufacturing defect, pulled from the shelves, and subject to an immediate global recall.

TL/DR: The LV-909 and Poodle (and possibly other engines) have wrong ASL values and need to be fixed.

As an RO player I can tell you that you're wrong. Two of the first examples that come to mind are the J-2 and RL10. The J-2 engine used on Saturn V second and third stages has an atmospheric ISP of about 200 while its vacuum ISP is, iirc, a little less than 450. The RL10 engine used on, for example, the Delta IV upper stage simply doesn't work in atmosphere (I imagine actually it does, for a moment) and if it did, then its ISP would likely be similar to that of the Poodle and Terrier.

I was very happy to see their ISP turned so low. But then I'm just a realism nut, maybe they really should have made them at least slightly useful in atmo. Who am I to tell what's best for the average player? But their ISPs sure as hell aren't a mistake.

Edited May 3, 2015 by xrayfishx

[Woopert]

This is done for realism. Upper stage engines have larger bells and are different shapes for vacuum operation where the expansion ratios are different. As mentioned above upper stage engines don't work ASL and have different performance, or lack thereof.

In old KSP the thrust was constant and mass flow rate varied with atmosphere. This doesn't happen in real life - the only time something similar would happen would be throttling, but then Isp, thrust, and mass flow rate would all change. You can look at the stat changes and notice trends for it all but it's a matter of physics. Mass flow rate doesn't magically change to keep the same thrust, and engines designed for vacuum won't work ASL and vice versa.

Cheers

Here is a basic equation for Isp

thrust = Isp * mass flow rate * 9.81

As you can see, thrust is a result of constant acceleration to gravity, constant mass flow rate, and varying Isp. This means thrust will also vary as a result.

Edited May 3, 2015 by Woopert

[Jouni]

Look at the 48-7S and compare it to it's counterpart the 24-77. Look at the LV-1 and compare it to it's counterpart the LV-1R. Inline is 85. Radial counterpart 185. Why is there a difference of 100 where they should operate very similar to each other? Give or take a few kN.

The LV-1 and the LV-1R are completely different engines. The LV-1 is a vacuum engine with Isp 85/315 s, while the LV-1R is a small, not very efficient general-purpose engine with Isp 260/290 s.

[Kelderek]

I believe somebody was copy/paste happy and screwed up these cfg files. That's all.

Just because the numbers changed by a large margin does not necessarily mean that it was a mistake. As everyone else here has pointed out, this was intentional and it's not a typo and no digits are missing. It was a balance change and it makes sense that you shouldn't be able to use some engines in an atmosphere or at least not efficiently. You're only mad because you became accustomed to different behavior in the past and it no longer works the same way. I don't think any new players will have trouble enjoying the way these engines work if they just bought the game with 1.0.

[arkie87]

As an RO player I can tell you that you're wrong. Two of the first examples that come to mind are the J-2 and RL10. The J-2 engine used on Saturn V second and third stages has an atmospheric ISP of about 200 while its vacuum ISP is, iirc, a little less than 450. The RL10 engine used on, for example, the Delta IV upper stage simply doesn't work in atmosphere (I imagine actually it does, for a moment) and if it did, then its ISP would likely be similar to that of the Poodle and Terrier.

I was very happy to see their ISP turned so low. But then I'm just a realism nut, maybe they really should have made them at least slightly useful in atmo. Who am I to tell what's best for the average player? But their ISPs sure as hell aren't a mistake.

I'm not a realism nut, but i like what they did. It's educational and creates "aha" moments when you dont factor that part into the equation...

Case in point, i had a a space station that i decided to de-orbit. Since it was a space station, i never put parachutes on it. However, i had like 1600 m/s deltaV on it, so i figured i could slam it into the atmosphere, slow it down to 200-300 m/s, and then use the engine for a powered landing. I had like TWR = 3 in vaccuum, so i figured it would be easy. I entered the atmosphere, slowed down to 200 m/s, and then fired up the engines, not realizing thrust would be reduced, and my TWR actually dropped to 0.8, so needless to say, i had to launch a quicksave