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AHeroReborn

pointless engine?

Question

the twitch is better than the spider in every way, why would anyone use it?

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Because the spider is tiny, and weighs less, so it could be a better fit for a tiny ship where mass is the ultimate price.

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I very rarely use either.   But it's similar to the Ant vs the Spark.  The larger version has generally better stats, but very low mass can make the smaller version worthwhile in tiny spacecraft 

Also, when setting your satellite orbits precisely (such as for CommNet), sometimes you want very low thrust so you can fine tune better. 

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Because one is inline and one is radial?

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1 minute ago, klesh said:

Because one is inline and one is radial?

No, they're both radial. Twitch is the orange one, spider the small black one.

You might be thinking of the Ant, which is also small and black, but inline.

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Posted (edited)

Its funny, I bothered to learn all their names before they were given animal /casual counterparts, yet, I can't seem to remember those.  

I was thinking of the 48-7S, or what these whipper snappers are calling the Spark these days.   :wink:

Edited by klesh
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3 minutes ago, Aegolius13 said:

Also, when setting your satellite orbits precisely (such as for CommNet), sometimes you want very low thrust so you can fine tune better. 

This, too. When the smallest engine available early game is the Terrier, I'll dial the thrust limiter way down on my Mun science landers, for example, until Spark is unlocked.

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14 minutes ago, monstah said:

Because the spider is tiny, and weighs less, so it could be a better fit for a tiny ship where mass is the ultimate price.

to exemplify lets consider a small craft, intended to do a "put in orbit" contract with a thermometer for the eventual "collect science" contract:

Probodobodyne Okto, communotron 16, 2xOX-STAT photovoltaic panels, 2Hot Thermometer, Oscar-B Fuel Tank, 2xengine of choice.

Spider version: 430kg and 1779m/s for 2060Funds

Twitch version: 550kg and 1285m/s for 2620Funds

Around 25% extra deltaV in a 20%  light and cheaper package. Sound like a great deal to me.

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Exactly. Ships should be built for what they need to achieve. If all you have is a small payload, and all you need is to achieve orbit, there's no reason to beef up TWR

In fact, in @Spricigo's example, not only the probe has more DV, but since it is lighter the lifter itself will have more DV, so that it can go even farther (or just need a cheaper lifter). 

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4 hours ago, klesh said:

Its funny, I bothered to learn all their names before they were given animal /casual counterparts, yet, I can't seem to remember those.  

I was thinking of the 48-7S, or what these whipper snappers are calling the Spark these days.   :wink:

You mean the good old 48-7OP?

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Posted (edited)

The Spark used to be really OP (like, more dV on both tiny and medium sized ships), got nerfed to where you really were better off scaling up to a Terrier/909, then got a mild buff in 1.2. Now its low mass and moderate ISP means it has a slight dV advantage on tiny ships, and still loses to the 909 on medium ships. I'd call that balanced, personally. 

Edited by fourfa

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5 hours ago, Red Iron Crown said:

You mean the good old 48-7OP?

I use MechJeb for everything (except docking), and I think using the old 48-7S is cheating.

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For me, most engines have regular use, some not so often but still get used. The only engine  I have problems finding a use for is the Mk-55 "Thud".

Its not even the fact I don’t use, its that I don't find a situation where I may say "the /thud should be good there".

 

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24 minutes ago, Spricigo said:

The only engine  I have problems finding a use for is the Mk-55 "Thud".

Need more fuel on your small-ish ascent stage, but the single Swivel can't lift anything else? Throw a couple Thuds in, replace the Swivel for a Reliant now that you have the Thud's vectoring.

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6 minutes ago, monstah said:

Need more fuel on your small-ish ascent stage, but the single Swivel can't lift anything else? Throw a couple Thuds in, replace the Swivel for a Reliant now that you have the Thud's vectoring.

This is a situation that I Solve with a 1 or 2 SRBs. The rocket is tilted In the VAB (up to 5°), fine tunning the thrust and fuel amount allow for an automatic gravity turn (hit spacebar and let the rocket fly itself most of the way). You need to be sure that the rocket its designed well enough to not flip due drag, which is not difficult.

I didn’t calculated it but, given that 2 Thuds costs almost as much as 2 Thumpers, seems that SRBs will be cheaper. The convenience of gimbals and thrust up/down its  not enough to convince me.

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Posted (edited)

 

6 hours ago, Spricigo said:

This is a situation that I Solve with a 1 or 2 SRBs. The rocket is tilted In the VAB (up to 5°), fine tunning the thrust and fuel amount allow for an automatic gravity turn (hit spacebar and let the rocket fly itself most of the way). You need to be sure that the rocket its designed well enough to not flip due drag, which is not difficult.

I didn’t calculated it but, given that 2 Thuds costs almost as much as 2 Thumpers, seems that SRBs will be cheaper. The convenience of gimbals and thrust up/down its  not enough to convince me.

You'll need radial decoupler which costs 600 each with Thumper. Or live with 3t dry mass and nosecone(240)... Also it has lower ISP, which means the LF tank cost needed for Thud to achieve the same dv can be lower than the cost. Thumper could be waste in this case, also considering the thrust.

I think Thumper is only good as standalone. Kickback standalone gets way better thanLF engines with 2 Thumpers on the side.

EDIT: Just realized that the setup given above is more expensive than single kickback. So no, unless you are planning to recover it, It's just useless.

Edited by Abastro

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On 10/03/2017 at 8:43 PM, Abastro said:

 

You'll need radial decoupler which costs 600 each with Thumper. Or live with 3t dry mass and nosecone(240)... Also it has lower ISP, which means the LF tank cost needed for Thud to achieve the same dv can be lower than the cost. Thumper could be waste in this case, also considering the thrust.

I think Thumper is only good as standalone. Kickback standalone gets way better thanLF engines with 2 Thumpers on the side.

EDIT: Just realized that the setup given above is more expensive than single kickback. So no, unless you are planning to recover it, It's just useless.

No, decoupler or nosecones are not necessary. Just direct attach the SRBs and live with the drag. It's not meant to be the most effective way, just to set a parameter to look at the performance of the Thuds. 

 

 

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4 hours ago, Spricigo said:

No, decoupler or nosecones are not necessary. Just direct attach the SRBs and live with the drag. It's not meant to be the most effective way, just to set a parameter to look at the performance of the Thuds. 

Though drag matters a lot for small crafts like that. In my experience, something like that gets 100~150kN of drag on transonic region, which is big enough to shave dv of at least 200m/s.

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Posted (edited)

On 3/9/2017 at 3:32 PM, monstah said:

Exactly. Ships should be built for what they need to achieve. If all you have is a small payload, and all you need is to achieve orbit, there's no reason to beef up TWR

monstah,

 Likewise, there's no need to beef up DV. Having more DV than you need isn't actually an advantage. It's just more mass and fuel that you'll never use. Not an attack against the Twitch or Spider (I rarely find a use for either). Just pointing out that saying "You don't need all that t/w and this one has more DV" is every bit as misguided as saying "you don't need all that DV and this one has better t/w". The *proper* design philosophy is to have adequate t/w and DV in the lightest and cheapest package possible.

 Best,
-Slashy

Edited by GoSlash27
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Then again, extra delta-v in a satellite can let you grab those "adjust your orbit" contracts a a later date, or deorbit, or whatever's needed at a later date.  Not that that's a reason to go overboard, of course...

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1 hour ago, GoSlash27 said:

monstah,

 Likewise, there's no need to beef up DV. Having more DV than you need isn't actually an advantage. It's just more mass and fuel that you'll never use. Not an attack against the Twitch or Spider (I rarely find a use for either). Just pointing out that saying "You don't need all that t/w and this one has more DV" is every bit as misguided as saying "you don't need all that DV and this one has better t/w". The *proper* design philosophy is to have adequate t/w and DV in the lightest and cheapest package possible.

 Best,
-Slashy

Of course, which is why my last sentence there was "or just need a cheaper lifter" :wink: 

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On 10/03/2017 at 11:43 PM, Abastro said:

 

You'll need radial decoupler which costs 600 each with Thumper. Or live with 3t dry mass and nosecone(240)... Also it has lower ISP, which means the LF tank cost needed for Thud to achieve the same dv can be lower than the cost. Thumper could be waste in this case, also considering the thrust.

I think Thumper is only good as standalone. Kickback standalone gets way better thanLF engines with 2 Thumpers on the side.

EDIT: Just realized that the setup given above is more expensive than single kickback. So no, unless you are planning to recover it, It's just useless.

Small Hardpoint costs only 60 Funds  and is a better way of attaching your Thuds.  That way you can lose their mass when surplus to requirements. But , it's a Tier 6 tech (Advanced Aerodynamics, 160 Science) so may not be available.

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On 3/10/2017 at 0:18 PM, Spricigo said:

 

For me, most engines have regular use, some not so often but still get used. The only engine  I have problems finding a use for is the Mk-55 "Thud".

Its not even the fact I don’t use, its that I don't find a situation where I may say "the /thud should be good there".

 

I used it once (and probably will again), although with a design that would be useless in the stock game.

I'm running Automated Science Sampler, when it's turned on even a very short excursion into a biome lets you grab the science in it.

Now, rovers can get all the ground science but what about flying low?  AFIAK there's no good autopilot for flying a plane around everywhere, especially not one that can run in the background.

Solution:  I built a rover with thuds on it.  Something like a half-second burn causes the rover to hop--now it's flying low.  The burn must be very short as it wasn't perfectly balanced and it has no descent system, it would break on a hard landing.

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13 hours ago, GoSlash27 said:

Likewise, there's no need to beef up DV. Having more DV than you need isn't actually an advantage.

It is when it allows you to toss some fuel away before launch. Which actually then raises your TWR even more.

Of course you can (and I have in the past) add fuel launch to "overcome" the "problem" of a too-high TWR, but it's a bit more economical to solve your "I'm just too darn good at what I need to do" by removing things than adding them.

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5 hours ago, AeroGav said:

Small Hardpoint costs only 60 Funds  and is a better way of attaching your Thuds.  That way you can lose their mass when surplus to requirements. But , it's a Tier 6 tech (Advanced Aerodynamics, 160 Science) so may not be available.

Wow, that's impressive! Only 60 funds for a decoupler? I totally forgot about those aerodynamic(?) decouplers.

(It's in aerodynamics tab, right?)

Then thud seems to be reasonably good. (As it won't be holding Thumpers safely) I think one can use it to augment Kickbacks on top tier tech. (I think Reliant is too overkill for small adjustments & there's the aerodynamic loss)

Also it can be attached to the second stage, to give initial boost.

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funny how my disregard for the Thuds caused the discussion to veer toward decouplers...

Small hardpoint cost 60 funds and requires Advanced Aerodynamics (160science)

Strutural Pylon cost 125 funds and requires High Altitude Flight (300science)

At this tech level I’m usually launching larger rockets with larger payloads, engine choice goes toward skipper, mainsail and twin-boar. I can't say if at this point Thuds are interesting for "just a bit more power" since I never needed "just a bit" was either "had more than enough" or "needs a couple kickbacks"

But notice, there is a lot of my preferences(and maybe prejudices) about not using the thuds. I don't design my vessels to be the most efficient cost wise, I'd rather pump the TWR a bit, so it reach orbit a bit faster . Launching feel like the major expenditure of timetoplay and I prefer to waste some funds than waste some timetoplay. Likewise I don’t give much consideration for a choice that just save some funds (game gives plenty) if there is an option that use less timetoplay (scare because real life)

And in the limited cases where I would consider Thuds they never looks like a good idea to me.

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