Ideas on Fixing the Thud's Stats

[Nebbie]

Here's what's wrong with the Thud:

1. Its Isp is good for atmospheric, trash for vacuum (so it's an atmospheric engine)
2. It has higher drag than a radially-mounted hammer with an aerodynamic cap, so it causes a lot of drag in atmosphere
3. It's 0.9t...but you need at least 2, so it's more like 1.8t with double the thrust. That's as heavy as a Poodle, and much heavier than 1.25m engine options.
4. With the Making History DLC, it is massively outclassed by the Cub (especially for landers), an engine with 5x lower mass, but only 3x lower thrust, and +5/+5 Isp, with the only downside of only one axis of gimbal. While you effectively need 4x Cub minimum...that's still less mass than 1 Thud (of which you need 2).
5. Because of 1, and being radially-mounted, one of its niches is to be an early TWR booster...but the Spark outclasses it at this, and 2 means that it's probably better on drag to have radially-mounted tanks with caps and clustered Sparks on the bottom than to use Thuds.
6. It's obvious intended asthetics, and one niche where its radial mounting and gimbaling should make it great, is as a shuttle OMS. The terrible vacuum Isp holds it back, however, and this clashes with its other main use being atmospheric.

That drag needs to be fixed. Beyond that, I don't think it needs touching (and shouldn't be buffed much overall lest it become OP) for atmospheric use, since nobody really asked for that to begin with and not everyone even plays Career. The Cub also makes more asthetic/historical sense anyways.

As for vacuum, I think the obvious thing to fix would be the OMS use case, to make it actually do what it looks like it should do. The two problems here are its mass and vacuum Isp. I think both should be about in line with 2 Thuds being only a bit worse than a Terrier. It also should be slightly worse than the Skiff, as that engine's pretty good and there should be a slight penalty for radial-mounting. Thus, the stats change I recommend is: 0.9t, 275/305s Isp -> 0.6t, 270/325s Isp.

[KerikBalm]

If it gets good vacuum Isp, it shouldn't get as much of a TWR buff.

IMO, I'd mainly use it as a lander engine, up to places like Duna. So I would use it as a high TWR vacuum engine. Worse TWR than a poodle /terrier, better TWR. Your stats make it just plain better than the Swivel (another rather weak engine... IMO the swivel and the reliant are a bit underpowered.

The swivel has 320 vacuum Isp, you propose 325 for the Thud

The Swivel has a TWR of 14.62, the Thud currently has a TWR of 13.6, you propose increasing this to 20.4... Which is better than the Reliant (19.58), with better Isp in the atmosphere and in vacuum, and gimbal.

I'd propose a more moderate increase in stats: 315 vacuum Isp, and a mass of 0.7 tons.

Also, the Swivel needs a buff... or other parts need their stats brought down, the swivel (and to a lesser extend the reliant) suck pretty hard too. Its ok for career mode early tech, but then they are useless later.

Maybe a part upgrade through research (the laid the framework for upgrading stats through research), with the upgrade being active by default in sandbox? Then have similar upgrades for the thud?

[Nebbie]

8 hours ago, KerikBalm said:

If it gets good vacuum Isp, it shouldn't get as much of a TWR buff.

IMO, I'd mainly use it as a lander engine, up to places like Duna. So I would use it as a high TWR vacuum engine. Worse TWR than a poodle /terrier, better TWR. Your stats make it just plain better than the Swivel (another rather weak engine... IMO the swivel and the reliant are a bit underpowered.

The swivel has 320 vacuum Isp, you propose 325 for the Thud

The Swivel has a TWR of 14.62, the Thud currently has a TWR of 13.6, you propose increasing this to 20.4... Which is better than the Reliant (19.58), with better Isp in the atmosphere and in vacuum, and gimbal.

I'd propose a more moderate increase in stats: 315 vacuum Isp, and a mass of 0.7 tons.

Also, the Swivel needs a buff... or other parts need their stats brought down, the swivel (and to a lesser extend the reliant) suck pretty hard too. Its ok for career mode early tech, but then they are useless later.

Maybe a part upgrade through research (the laid the framework for upgrading stats through research), with the upgrade being active by default in sandbox? Then have similar upgrades for the thud?

I would not recommend balancing against the Swivel and Reliant because they're pretty much trash right now, and meant for atmospheric use (nobody really wants to use them for vacuum use despite their decent Isp in it because they weigh a [metric] ton and then some, and for upper stages, mass matters greatly). Also, the Spark utterly creams them in TWR and Isp right now. I do think they could use a buff like Reliant: 1.25t, 265/310s -> 1t, 275/305s and Swivel: 1.5t, 250/320s -> 1.25t, 260/315s.

The Thud should be primarily for vacuum use as OMS and should be balanced against the Spark, Terrier, Twitch, etc.; it needs at least 320s of vacuum Isp to be competitive due to the ultralight Spark (which has some gimbaling) having 320s.

Unfortunately, I think part upgrades are still off the table in Squad's current design philosophy. They would help a lot with alleviating the problems of balancing early Career vs Sandbox.

[Tyko]

Any engine balancing should take tech level into account too. It doesn't fix balance issues entirely, but it does help explain why Swivel and Reliant aren't competitive with later engines.

[Nebbie]

45 minutes ago, Tyko said:

Any engine balancing should take tech level into account too. It doesn't fix balance issues entirely, but it does help explain why Swivel and Reliant aren't competitive with later engines.

But there's no "high tech" radial-mounted engine for a shuttle OMS. You get the Thud, and only the Thud. Also, the Reliant would need a hell of a buff to compete with the Kodiak, and the Swivel a hell of a buff to compete with...well, anything really.

[OHara]

On 1/29/2019 at 11:47 PM, Nebbie said:

It has higher drag than a radially-mounted hammer with an aerodynamic cap

That is not true.

I just tried it.  Below the speed of sound the cap + Hammer-SRB has twice the drag of the Thud, as one would expect from the similar forward shapes and the SRB having twice the cross-sectional area. 

Above the speed of sound, the Thud has a little, 20%, more drag than the cap+SRB.    (This might be an effect of the attempt in version 1.2 to  make pointy things have less supersonic drag; the round cap has Cd=0.32 and the Thud has Cd=0.36, and KSP exaggerates that difference.)

Edited January 31, 2019 by OHara
clarify that the Thud has lower drag than the SRB

[Nebbie]

10 hours ago, OHara said:

That shouldn't be. 

I just tried it.  Below the speed of sound the cap + hammer-SRB has twice the drag, as one would expect from the similar forward shapes and the SRB having twice the cross-sectional area.   Above the speed of sound, the Thud has a little, 20%, more drag than the cap+SRB.    (This might be an effect of the attempt in version 1.2 to  make pointy things have less supersonic drag; the round cap has Cd=0.32 and the Thud has Cd=0.36, and KSP exaggerates that difference.)

Welcome to stock's utterly pants-on-head retarded drag modeling.