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Is it just me, or does Poodle have effectively better delta-V?


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Agree with @5thHorseman.  Delta-v is not a constant property of a given engine, like ISP or TWR.  It's the output of a multi-variable equation, so one engine may not always generate better or worse delta-v than another.  In the case, the Wolfhound has better ISP and more thrust than the Poodle, but higher mass.  So even if the Wolfhound has better TWR than the Poodle (think this used to be true but maybe not after the 1.6 rebalance), that doesn't tell the whole story.  On a small ship, the extra dry mass of the Wolfhound brings your delta-v down more than the extra ISP, brings it up.  After all, this is why you wouldn't put a Rhino on a tiny space probe, even if it has pretty good ISP.  Conversely, when you have a really big ship, the dry mass of the engine is a drop in the bucket, so the extra ISP of the Wolfhound will likely result in more delta-v.

 

 

 

 

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4 hours ago, Aegolius13 said:

Agree with @5thHorseman.  Delta-v is not a constant property of a given engine, like ISP or TWR.  It's the output of a multi-variable equation, so one engine may not always generate better or worse delta-v than another.  In the case, the Wolfhound has better ISP and more thrust than the Poodle, but higher mass.  So even if the Wolfhound has better TWR than the Poodle (think this used to be true but maybe not after the 1.6 rebalance), that doesn't tell the whole story.  On a small ship, the extra dry mass of the Wolfhound brings your delta-v down more than the extra ISP, brings it up.  After all, this is why you wouldn't put a Rhino on a tiny space probe, even if it has pretty good ISP.  Conversely, when you have a really big ship, the dry mass of the engine is a drop in the bucket, so the extra ISP of the Wolfhound will likely result in more delta-v.

 

Yeah, been experimenting as a test. Guess I have not hit the limit yet -- been testing up to S3-7200.

How big is your hypotheorical outbound transfer stage is?

Edited by Jestersage
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13 hours ago, Jestersage said:

I am still trying to compare between Wolfhound and Poodle, and so far, it seems that Poodle have better Delta V, while Wolfhound have better TWR.

Yup. While the WH is efficient, it's also heavy. Simply put, it needs to push heavy loads and/or run for a long time in order to become effective.

If you only have a small payload or limited dV requirements, a lightweight engine may perform better even though it has a worse ISP. You can observe similar effects between LV-909 and 48-7s.

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9 hours ago, Jestersage said:

How big is your hypotheorical outbound transfer stage is?

None big. I never hypothesized any ships, just that maybe the engine had a breakpoint somewhere.

It's also fully okay for an engine's main positive to be high TWR. Sometimes you WANT high TWR. If you didn't, then every ship would have a single ion engine and we'd all be sleeping through our burns.

Edited by 5thHorseman
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The Wolfhound will beat the Poodle on "big" ships; the Poodle will beat the Wolfhound on "small" ones.

Exactly where the break-even point is, though, is not a simple answer but rather a line on a graph, since it depends on both the wet and dry masses of the craft, and those are independent of each other.

About the only way to answer the "which is better" question, for a particular craft, is to try it both ways.  Solve the rocket equation (or look at a dV tool) with a Wolfhound in place, and then do the same thing with a Poodle substituted, and whichever one wins is "better" for that rocket. 

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2 hours ago, Snark said:

About the only way to answer the "which is better" question, for a particular craft, is to try it both ways.  Solve the rocket equation (or look at a dV tool) with a Wolfhound in place, and then do the same thing with a Poodle substituted, and whichever one wins is "better" for that rocket. 

Of course, even if a toss-up on delta-v, there are other differences to keep in mind.    The extra thrust for the Wolfhound usually counts in its favor.  On the other hand, a Wolfhound stage would have more total mass, which would decrease the delta-v obtained from earlier stages (though the difference here is quite minor).  

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Okay, hate to answer my own question, but a quick seat-of-the-pant test indicate where it is going to start favoring 1xWolfhound: at 46t, created through a combination of the KV-3 capsule and S3-7200. Ofocurse the TWR is less than 1, but still much better than Poodle.

Over all, the Wolfhound will have better TWR consistently, but worse Delta-V -- until that point, in which the the Wolfhound is only 10m/s less. Switching out to S3-14400 and Wolfhound actually jumped ahead.

Edited by Jestersage
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On 2/21/2019 at 3:31 AM, Jestersage said:

but a quick seat-of-the-pant test indicate where it is going to start favoring 1xWolfhound: at 46t, created through a combination of the KV-3 capsule and S3-7200.

That's a lot of fuel to burn for such a small engine...

Keep in mind that the WH also benefits if you have a heavier load to push. Using a 2.5m ore tank for ballast, you'll find that the WH wins at nearly any amount of fuel. Compared to the heavy payload, the extra mass hardly matters, while the better ISP still works in your favor.

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