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Thud engines (the radial LFEs) appear to be fairly draggy, making them once again not-so-great.


Frostiken
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So for almost all of KSP's life, the radial LFEs have been just god-awful terrible. Bad ISP, heavy, an extremely obsolete and lackluster model, on top of being somewhat niche to begin with.

A couple versions ago, they FINALLY got a much-needed improvement in isp and I think their gimbal range was improved. They're still pretty inefficient engines and not-so-great, but they were no longer the worst thing in the game.

Now I'm not so sure about that. With the new aerodynamic model, radial attachments of parts makes much less sense than it used to. I don't know how to determine the exact drag characteristics of a part, but when I turn on the aerodynamic arrows, I get MASSIVE red spikes off of my Thud engines. I'm guessing they are imparting a LOT of drag.

So it's my super-professional analysis that these engines are now terrible again, and need to be greatly improved to justify the drag losses you're going to incur by using them.

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I kinda think of them as engines for use in space. Their IsP may not suggest this (I don't know what it is) but when I make space tugs and such, I always make the engines radial but attaching the shortest fuel tank to the side of the main one and put the engine there, with a fuel line to the smaller tanks.

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I think that, similar to the 909, the radial engines are better suited to a vacuum. That's where I've found the most use for them, especially in base construction on the Mun and Minmus. Even though the drag is high, they're still useful. I think a buff would be unnecessary for what use there already is for them.

Edit: welp the ninjas have found me.

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Radial engines are less than ideal in general. You always need at least 2 to keep CoT balanced, but it's always more efficient to use fewer engines.

The Thud is only good for when you need a TWR boost and can spare the delta v, or for odd designs like shuttle OMS'.

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Radial engines are less than ideal in general. You always need at least 2 to keep CoT balanced, but it's always more efficient to use fewer engines.

The Thud is only good for when you need a TWR boost and can spare the delta v, or for odd designs like shuttle OMS'.

Or if you have a really tall lander and need to angle the landing gear way out, therefor limiting the space under the lander for engines. Then radial engines begin to make sense.

Or if you have a space tug that you want to be able to pull and push. Makes sense there too.

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I'm not disputing they have their uses, I'm merely pointing out that the engine - while of use but still coming at a cost before - now has more downsides against it with nothing to compensate. Regardless if you want to use it in a vacuum, it does still come with the drag penalty getting it INTO space, or mandates the use of an aeroshell which is extra mass, cost, etc. No matter which way you cut it, the engine is objectively worse than it was prior to 1.0. Therefore, it deserves a little buff to compensate.

Either buff the engine's isp slightly to make it a wee bit better and to 'balance' the extra drag, or reduce the drag it's causing and leave the engine otherwise alone. I would lean towards the latter, since the drag arrows are so damn big it looks like it's treating it as any other unaerodynamic radially-attached part.

And give it a new model and attachement properties already, sheesh. You *have* to use the offset tool to make it not look awful.

EDIT: I decided to do a little test. The drag they produce isn't nearly as much as a radially-attached uncovered 'flat top' 1.25m tank, but it IS more draggy than a covered nosecone'd 1.25m tank. Considering its much smaller size and seemingly more aerodynamic profile (not to mention hugging the side of the rocket, which I have no reason to assume helps, but I assume it does), it should be LESS draggy.

Edited by Frostiken
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In 1.0+ they're clearly modeled as verniers, to be used on lower stages to increase control authority, and in particular when you have only one main engine on the stage and want some roll authority (ignoring magicTorque from pods/cores/etc). The 1B as vernier for the .625 and 1.25m engines, the 24-77 as vernier for the 1.25 and 2.5, and the Mk55 as vernier for 2.5 and 3.75 engines. Though even 8 degrees of gimbal is not as much as real verniers have, it's rather a lot in KSP terms.

If you want the equivalent in vacuum, you're probably better off with some RCS ports and a bit of monoprop for roll....

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They probably should have a little less drag if they're beat by a 1.25m nosecone stack but they're still pretty useful.

In career, I got to a point where I wanted to lift a good sized load (some 40T thing). I had 2.5m tanks but didn't yet have the Skipper.

I improvised a high thrust engine using a T-30 and a bunch of MK55's placed/offset/rotated such that they were below the fuel tank, in a circle around the T-30. I THINK they were protected from forward drag this way (Does occlusion work for radial parts now or just inline ones?). I'm not sure if it was more efficient than making additional 1.25m stacks to attach engines to, but it worked pretty well.

It seems to be an oddball part that doesn't really fill a specific niche, but is very easy to integrate into designs since it can attach anywhere.

-Need more thrust but don't want another 2 stacks alongside your central one? MK55s

-Need some gimbal without changing your existing stack engine? MK55s

-Need vacuum engines but don't have stack space (double-ended tug, small spaceplane)? MK55s

If you're looking for the most fuel efficient designs, you might never use it, but if you're lax on the efficiency requirement, I bet it can be used to simplify designs at the expense of some additional weight/fuel.

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They're working fine for me; just the thing for boosting a basic jet aircraft into the upper altitudes.

http://i.imgur.com/YrMvrCU.jpg

I'd considered making a design like this (in fact, my very first successful spaceplane back in the day was like that, only with 24-77s), but my question is:

Is that more, less, or equal to the drag of a "hot dog" design?

If it's less drag, then the Mk55 is definitely filling a niche.

This might be why such designs are uncommon in real life?

Probably. Plus the radial attachment would involve a fair deal of extra mass for the support structure that can withstand the thrust.

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So for almost all of KSP's life, the radial LFEs have been just god-awful terrible. Bad ISP, heavy, an extremely obsolete and lackluster model, on top of being somewhat niche to begin with.

A couple versions ago, they FINALLY got a much-needed improvement in isp and I think their gimbal range was improved. They're still pretty inefficient engines and not-so-great, but they were no longer the worst thing in the game.

Now I'm not so sure about that. With the new aerodynamic model, radial attachments of parts makes much less sense than it used to. I don't know how to determine the exact drag characteristics of a part, but when I turn on the aerodynamic arrows, I get MASSIVE red spikes off of my Thud engines. I'm guessing they are imparting a LOT of drag.

So it's my super-professional analysis that these engines are now terrible again, and need to be greatly improved to justify the drag losses you're going to incur by using them.

First off, props for such a well written analysis! I've been a fan of these engines for a while aesthetically, and I completely agree with your statements.

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I used them once for a Minmus lander (way pre 0.90) and it didn't have enough TWR to stop so I ditched them and made a different design. Not even sure it's worth it to try a new design with them really.

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I agree they could use a buff. In previous versions they needed to be a little weak to make up for the fact that they are really convenient to just slap anywhere. In 1.0+ the added drag of radial-anything makes them a sub-optimal choice most of the time.

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I'd considered making a design like this (in fact, my very first successful spaceplane back in the day was like that, only with 24-77s), but my question is:

Is that more, less, or equal to the drag of a "hot dog" design?

If it's less drag, then the Mk55 is definitely filling a niche.

Is it possible to build a "hot dog" that small? I've got a similar design about to fly, and the purpose as I see it is that it's a small, not very high tech craft that can hit high-altitude objectives for missions.

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I recently used them early on in a career game for a rocket that needed more thrust early on. SRBs would have put it over the weight limit, and decreasing the weight of the rocket to make them work would have decreased total dV. So I put 2 thuds on decouplers and blew them off when I no longer needed them and when the isp of the main engine was significantly better.

Edited by The Yellow Dart
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Is it possible to build a "hot dog" that small? I've got a similar design about to fly, and the purpose as I see it is that it's a small, not very high tech craft that can hit high-altitude objectives for missions.

I have a one-seat/probe-augmented "hot dog".. uh let me see if I can dig it up..

Here it is, close to orbit:

100-HotDoggin.jpg

I forget the proper launch profile for it, so couldn't quite get it to orbit this time (it did fly up to orbit before when it was built). It was a variant of my two-man "hot dog", didn't use it much.

It's a bit heavier/wingier than the original but is roughly the same length (plus an extra bay where the probe core lives)

I recently used them early on in a career game for a rocket that needed more thrust early on. SRBs would have put it over the weight limit, and decreasing the weight of the rocket to make them work would have decreased total dV. So I put 2 thuds on decouplers and blew them off when I no longer needed them and when the isp of the main engine was significantly better.

That's pretty much how the Mercury-Atlas system worked :)

Edited by Renegrade
put in rest of url~
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I'm a KSP newbie so this probably seems stupid, but I use them for turning simple planes into low-tech VTOLs. They're great for daisy-chaining surface surveillance missions in the early career game, where conventional take-offs on the local terrain would be hazardous. The drag is a real issue though; they won't fly faster than about 240 m/s (they're super fuel inefficient) but seriously, Jeb will never die in one of those things.

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They probably should have a little less drag if they're beat by a 1.25m nosecone stack but they're still pretty useful.

In career, I got to a point where I wanted to lift a good sized load (some 40T thing). I had 2.5m tanks but didn't yet have the Skipper.

I improvised a high thrust engine using a T-30 and a bunch of MK55's placed/offset/rotated such that they were below the fuel tank, in a circle around the T-30. I THINK they were protected from forward drag this way (Does occlusion work for radial parts now or just inline ones?). I'm not sure if it was more efficient than making additional 1.25m stacks to attach engines to, but it worked pretty well.

It seems to be an oddball part that doesn't really fill a specific niche, but is very easy to integrate into designs since it can attach anywhere.

-Need more thrust but don't want another 2 stacks alongside your central one? MK55s

-Need some gimbal without changing your existing stack engine? MK55s

-Need vacuum engines but don't have stack space (double-ended tug, small spaceplane)? MK55s

If you're looking for the most fuel efficient designs, you might never use it, but if you're lax on the efficiency requirement, I bet it can be used to simplify designs at the expense of some additional weight/fuel.

One thing I like to do with the engines is stack fuel tanks beneath them with decouplers and fuel lines. It's like... linear asparagus. As I burn tanks, I drop them behind me.

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