The Thud - an underrated launcher engine?

[moogoob]

Recently I've been playing around with some of my light (size 1) launchers, and have been turned on to using a cluster of three or four Thuds on my first stage. I mount the thuds around an inverted Advanced Nose cone and clip the engines down and into the cone to make a discrete cluster, as such:

There are a few advantages to using Thud clusters on payloads that are getting too heavy for a single LVT-45 without SRBs:

-High TWR lets you keep a single stack (less complicated than triple LVT-45 stacks, which are my usual "size up" option)

-Slightly lower efficiency isn't too much of an issue because it only has to lift its own fuel - which is cheap to take extra. Greater length of resulting rocket can only help aerodynamic stability.

-Gimbal range needs to be capped to keep rockets under control.

Anyone else use Thuds for launch engines?

[Alshain]

Depends on what you are targeting, I always target lowest cost to orbit.  They can be used in lieu of SRB's at some stages where you need just a little more power as a replacement for the Swivel.  The problem is, that really is only useful in the 2-3 ton payload range. 2 thuds probably won't lift more than that and it's less powerful and more expensive than even 2 flea boosters, which at that range is often all you need to get your Swivel engine high enough for a manageable TWR.

However, they have less than half the power of Thumpers for more then half the cost.  Furthermore, in 1.1, fuel consumption on SRB's scales with thrust limiter (previously fuel consumption would be the same regardless of the thrust limiter setting), and on top of that you can throw away the SRB's to lose weight when you wouldn't need the extra power anyway (I suppose technically you can throw away the thuds, but then you have to factor in decoupler costs and that would definitely be too expensive). For that reason I wouldn't use them as boosters to a Swivel.

2 Thumper + Decouplers = 2900 Funds for 500Kn

2 Thud = 1700 Funds for 216Kn.

2 Thud + Decouplers = 2840 Funds for 216Kn.

As for your "triple LVT-45" setup, I would always recommend against that for cost efficiency.   LFO engines are expensive and it isn't necessary to have more than 2, one upper stage, one lower.  I have lifters for up to 120 ton payloads in increments and none of them have more than 1 LFO on the lower stage.

Edited May 8, 2016 by Alshain

[AbacusWizard]

I sometimes add two or three to a launch stage if the current TWR is just a *little* less than 1 and I don't want to go all the way up to the next engine size.

[bewing]

I only use them on early contracts where they want me to stage an SRB or engine at a very particular altitude and speed. (If I even take the contract, because those contracts are among the most annoying to fulfill.)

[moogoob]

7 hours ago, Alshain said:

Depends on what you are targeting, I always target lowest cost to orbit.  They can be used in lieu of SRB's at some stages where you need just a little more power as a replacement for the Swivel.  The problem is, that really is only useful in the 2-3 ton payload range. 2 thuds probably won't lift more than that and it's less powerful and more expensive than even 2 flea boosters, which at that range is often all you need to get your Swivel engine high enough for a manageable TWR.

However, they have less than half the power of Thumpers for more then half the cost.  Furthermore, in 1.1, fuel consumption on SRB's scales with thrust limiter (previously fuel consumption would be the same regardless of the thrust limiter setting), and on top of that you can throw away the SRB's to lose weight when you wouldn't need the extra power anyway (I suppose technically you can throw away the thuds, but then you have to factor in decoupler costs and that would definitely be too expensive). For that reason I wouldn't use them as boosters to a Swivel.

2 Thumper + Decouplers = 2900 Funds for 500Kn

2 Thud = 1700 Funds for 216Kn.

2 Thud + Decouplers = 2840 Funds for 216Kn.

As for your "triple LVT-45" setup, I would always recommend against that for cost efficiency.   LFO engines are expensive and it isn't necessary to have more than 2, one upper stage, one lower.  I have lifters for up to 120 ton payloads in increments and none of them have more than 1 LFO on the lower stage.

Are they more expensive/less effective than SRBs? Yup. You have a point.

Perhaps my enthusiasm comes from trying to reduce the complexity in my rockets, at least when launching smaller payloads. I feel bad for some reason needing boosters just to space a Mun lander probe, when a cluster of Thuds, while slightly more expensive, has no parts being shed and is in my opinion easier to fly.

To sum up, I only use this in that intermediate payload class when a single Swivel is too weak, a Skipper is too powerful and I'm not in the mood to strap tubes filled with explosive to the sides of my rocket.

On days when I AM, well... (Your launcher array is awesome, BTW!)

[Alshain]

2 hours ago, moogoob said:

Are they more expensive/less effective than SRBs? Yup. You have a point.

Perhaps my enthusiasm comes from trying to reduce the complexity in my rockets, at least when launching smaller payloads. I feel bad for some reason needing boosters just to space a Mun lander probe, when a cluster of Thuds, while slightly more expensive, has no parts being shed and is in my opinion easier to fly.

To sum up, I only use this in that intermediate payload class when a single Swivel is too weak, a Skipper is too powerful and I'm not in the mood to strap tubes filled with explosive to the sides of my rocket.

Well that is perfectly fine, I build for cost but not everyone needs to.  The most important thing is you have fun.

2 hours ago, moogoob said:

On days when I AM, well... (Your launcher array is awesome, BTW!)

Thanks!  It's grown over the years.  Though the size of the collection now makes it a bit hard to maintain when Squad changes something .

[monophonic]

4 hours ago, Alshain said:

Well that is perfectly fine, I build for cost but not everyone needs to.  The most important thing is you have fun.

We need more of this attitude on this forum. Kudos to you!

On the topic, I have used them as second stage engines when I need to shave just a meter off the top to fit in the earlier pads' limits. Also when I lack a suitable 2.5m engine to use inline on a stack of that size.

[Belerafon]

I use quad F9 boosters if you know about SLS. Much simpler, plus they're severely overpowered.

[Dispatcher]

I've used Thuds on small SSTOs.  Recall that the iSP remains the same, but the thrust is multiplied by the number of units {radially attached in this case).  I think they perform better since 1.1 than previously.

Edit:  since their being remodeled, they look cool too.

Edited May 10, 2016 by Dispatcher

[wumpus]

Typically I find that they are just too big and too expensive for the job at hand (and the smaller copies are often too high in the tech tree when needed).

On place they come in handy is if your NERVA stage needs more thrust.  Presumably terrier/poodle engines are "supposed" to be used in those situations, but Thuds are far easier and won't have all the aero issues getting there.

[Brian444444]

I use them early on so I can land on the Mun and Minmus on my fuel tank(s) instead of the feeble early landing gear.

[HoloYolo]

I use Thuds for landing base parts that aren't vertical. They work great and the gimbal is great for such a small engine.

[suicidejunkie]

I use a triple-T30 stack as the first stage sustainer (after the bag-o-hammers to get it up to mach 1) of my munar tourister.

Just one parachute each gets them recovered for an over 90% refund making cost a non-issue.

 

I suppose I should look into using a set of thuds on my Minmus base for hopping thanks to the vectoring.  Right now I'm living with puffs and a gyro.

[mk1980]

they are somewhat useful to fill the gap between the ~200kN swivel and the 650kN skipper and also to fill the gap between the skipper and the mainsail. that being said, the same problem can usually also be solved with radial boosters (SRB or LFO, wahtever you prefer), so they don't see much use in my games.

oh and i also used them as the rocket engines on some early SSTO planes, but i'm not sure they are a good choice for that task. the swivel engine seems to be better suited (better vacuum Isp), and for mk3 planes, the skipper is definitely superior to a combo of skippers and thuds.

i consider them pretty much obsolete later in the game. 

[sal_vager]

Oh I dunno, they are good for shuttles as well when you don't have the Vector.

[DChurchill]

On 5/8/2016 at 2:32 AM, AbacusWizard said:

I sometimes add two or three to a launch stage if the current TWR is just a *little* less than 1 and I don't want to go all the way up to the next engine size.

This. But I only use them on the pad if I think the overall dV is a shade low, or the TWR is not enough over 1. It doesn't need to leap off the pad, but just hovering there trying to build up enough speed is inefficient.

Edited May 9, 2016 by DChurchill

[AbacusWizard]

I do occasionally find them useful for landers and skycranes. Sometimes a design just doesn't have room for an engine at the bottom of the stack (maybe I need a docking clamp there, or maybe it just barely fits into a cargo bay) and radial attachment is the only spot available. Sure, the low I_sp means I don't get quite as much ∆v as I could, but for a tanker that's just repeatedly hauling a huge load of fuel from a Minmus mining outpost up to low orbit, ∆v isn't all that much of a concern.

[samstarman5]

One Skipper and four Thuds give you a launch platform that may or may not be better than one Mainsail(I have yet to test the comparison, and I am not going to just blankly assume it is.).  I've enjoyed some excellent launches with the Skipper/Thud combo, which I can get going early on in a career.  Thuds do offer excellent assistance to control, as well, as long as they are balanced.

[sgt_flyer]

the Thuds allow for very pretty engine clusters, that can neatly fit within a 1.25m package

 

[Mastikator]

Thud
TWR: 12.26/13.6
Isp: 270s/305s

Swivel
TWR: 11.48/13.6
Isp: 270s/320s

Reliant
TWR: 17/18.28
Isp: 280s/300s

The thud is worse than the reliant at sea level and worse than the swivel in space. I don't think it's underrated.

[Jovus]

19 minutes ago, Mastikator said:

The thud is worse than the reliant at sea level and worse than the swivel in space. I don't think it's underrated.

Which is why you bind them to an action group so you can turn them off at 10-15km (depending on the needs of your launcher) and push the rest of the way to space on your LV-T45.

 

Complete side note: I miss the days when all we had for engines was their designations.

[Norcalplanner]

They're handy for skycranes and in situations where you want an unobstructed end of the craft (such as having a large docking port).  Other than that, not much use for Mr. Thud.

[Belerafon]

On 5/9/2016 at 1:43 PM, sal_vager said:

Oh I dunno, they are good for shuttles as well when you don't have the Vector.

True. Plus you should seriously fix the vectoring overpoweredness of the vector. Jeez. It shook my launch system to bits. 

16 hours ago, sgt_flyer said:

the Thuds allow for very pretty engine clusters, that can neatly fit within a 1.25m package

 

Noice.

[sgt_flyer]

28 minutes ago, Belerafon said:

True. Plus you should seriously fix the vectoring overpoweredness of the vector. Jeez. It shook my launch system to bits. 

you can reduce the gimbal range with the slider if you need  

but i'd prefer they keep their current maximum gimbal range  very useful for assymetric rockets like shuttles  

still, yes, too much control authority (either from SAS or gimbal range) can be dangerous with the current PID controllers  on my soyuz cluster pic, the thud's gimbals are disabled, only the 24-77s are providing thrust vectoring

, 

Edited May 10, 2016 by sgt_flyer

[Alshain]

So I decided to try a little empricial testing on what I believed the numbers were telling me from my earlier posts and in the end I believe I was correct, I could not build a Rocket capable of orbit using the Thud cheaper than an equivalent payload rocket using a Swivel and SRB's (specifically Hammers).  I did come really really close however, within a few hundred funds. Now I am not perfect by any means, so here is a picture of my rocket including cost and if anyone can build a cheaper rocket using Thuds I would be very curious to see it. This is a 2 ton (2.040 precisely) payload lifter aimed at 100km orbit and I wanted to keep it around 1.5 TWR on the launchpad, I used ore and parachutes to simulate payload.  Of course none of this matters if cost is not your concern, but it's still something to consider.

Edited May 10, 2016 by Alshain