How to use 5m parts?

[HeronRocketry]

I’m just wondering. Has anyone found a practical application for or how to use 5m parts in making history?

[Gaarst]

Have you tried making big rockets out of them?

[Zeiss Ikon]

They'd be just the thing for launching a heavy, heavy upper stacks.  The original Saturn V booster stage lifted the  SII second stage, SIV-B third (transfer) stage, LEM with fairing, and CSM high enough to require vacuum nozzles on the second stage, and fast enough to make that worthwhile.  I don't have the figures in front of me for the stack mass remaining when the SV staged off, but the third stage stack was something like 60 T.

If you see a rocket that requires six or eight Reliant-based boosters with a Mammoth core, it would probably lift with 5 E1 engines mounted on a thrust plate under 5 m tanks.

[Starman4308]

I suspect what the OP means is "are there any mission profiles, ones that aren't just about sending more to a place, that would make the 5m parts practical?".

To that, I answer: Eve ascent. Even if the EAV (Eve Ascent Vehicle) itself doesn't use 5m parts, the stack to get it up into LKO might practically use 5m parts.

Also, if you're playing with an upscaled system, even with Real Fuels or SMURFF, 5 meter parts are very welcome, as are even bigger parts.

[Foxster]

27 minutes ago, Starman4308 said:

Eve ascent. Even if the EAV (Eve Ascent Vehicle) itself doesn't use 5m parts, the stack to get it up into LKO might practically use 5m parts.

 

The drag of 5m parts on Eve is very high. The craft would balloon in mass to overcome this. Much better to keep the stack(s) skinny for Eve. 

[HeronRocketry]

Okay, let me clarify. Could I get some photos of practical 5m craft? The new 1.85s are super useful, but the 5ms seem frivolous.

[Starman4308]

1 hour ago, Foxster said:

The drag of 5m parts on Eve is very high. The craft would balloon in mass to overcome this. Much better to keep the stack(s) skinny for Eve. 

Are you sure? Under a realistic aero model, they should be quite effective due to a low surface area/mass ratio. I haven't played with the stock aero model in a long time: do 5 meter parts just have absurdly large drag cubes out-of-proportion to their actual size or something?

[Atkara]

37 minutes ago, HeronRocketry said:

Okay, let me clarify. Could I get some photos of practical 5m craft? The new 1.85s are super useful, but the 5ms seem frivolous.

Define "practical"  

Anyway, I can't provide any photos, as I don't have MH yet and even if I had it, I wouldn't have seriously dived in it from day one. I suppose 5m parts can simplify the launch of heavy -and fully fueled- payloads, as opposed to launching them empty and fueling them up in orbit, to get a similar result. Same goes for making larger fuel tankers/drones/depots.

But this comes from someone who puts "the business" above all else. I'm sure others will come up (if not already) with unique and creative uses 

[invision]

5m only good if you plan on lifting an entire house in one go

[Foxster]

7 hours ago, Starman4308 said:

Are you sure? Under a realistic aero model, they should be quite effective due to a low surface area/mass ratio. I haven't played with the stock aero model in a long time: do 5 meter parts just have absurdly large drag cubes out-of-proportion to their actual size or something?

Yup, I'm sure. The drag of stock parts increases dramatically with part size. Anything above size 1 on Eve leads to large losses that need bigger engines and more fuel to overcome, rinse+repeat.

[magnemoe]

9 hours ago, HeronRocketry said:

Okay, let me clarify. Could I get some photos of practical 5m craft? The new 1.85s are super useful, but the 5ms seem frivolous.

Has managed to lift everything I have needed with 3.5 meter tanks, could use the larger fairing for a few launches. 
However I always refuel large ship in orbit, so my payloads are huge but light. 


This used some SRB to help it, 

[KerikBalm]

 

10 hours ago, HeronRocketry said:

Okay, let me clarify. Could I get some photos of practical 5m craft? The new 1.85s are super useful, but the 5ms seem frivolous.

Well, I play on a 3x rescale, so I'm quite looking forward to them. Otherwise for stock, I imagine that they are useful for single launch vessels to destinations with high dV requirements when you have a large payload mass. (Like a surface science base, a biom hopper to collect science, a surface miner, etc).

11 hours ago, Foxster said:

The drag of 5m parts on Eve is very high. The craft would balloon in mass to overcome this. Much better to keep the stack(s) skinny for Eve. 

Are you sure... for these reasons:

9 hours ago, Starman4308 said:

... they should be quite effective due to a low surface area/mass ratio. I haven't played with the stock aero model in a long time: do 5 meter parts just have absurdly large drag cubes out-of-proportion to their actual size or something?

I would expect 2.5m parts of the same length (and capped at each end with a 2.5m diameter nose cone) to have ~4x the drag of a 1.25m part, and 4x the fuel under a simplified aero model (where all that matters is the area of the cross section).

Of course, this would be like 4x 1.25m stacks, which is bad... but you can still have rather tall rockets with 2.5m or 5m parts... past a certain point, it will be the reduced Isp and the gravity drag that matters more than aero drag.

To make an analogy... please no comments on the politics of guns... these were just examples that I could think of that demonstrated shapes and sizes roughly

On the left is a 50 BMG. The bullet diameter is half an inch, on the right are .22 caliber bullets, bullet diameter is 0.22 inches. The bullet on the left has a higher ballistic coefficient. Its a wider bullet, but its also taller. It would have an even better ballistic coefficient if it was more like a sabot round/flechette/dart... long and skinny. If it was 4x longer and half the diameter, it would have the same mass with 1/4 the cross section area... but such a long and skinny thing is not practical.

One thing in KSP to consider, is thrust to cross sectional area. Until the vector, 2.5m engines were better than 1.25m engines, and 3.75m engine were even better. 2.5m stacks could be made taller before the stack TWR was insufficient, and side stacks had to be made. The vector changed this....

Essentially, if KSP only models cross section area, you want the tallest stack you can while still managing a high enough TWR. Jumbo-64 tanks are easier to achieve tall stacks with than FL-800s, simply because they are twice as long. For two stacks of tanks of equal length, the jumbo stack will be less bendy because it has half as many joints.

I imagine the 5 meter parts will be like this.

So... lets not look at bullets, but imagine the whole cartridge is a rocket.

(a 300 winchester magnum, and a 300 winchester short magnum)

They both contain the same amount of "fuel" (gunpowder in this case). The one on the right would obviously perform better aerodynamically.

Using a 5 meter part to make your rocket less tall is not going to improve its aerodynamics.

It will improve part count, which is important for many people when playing KSP though.

Edited March 15, 2018 by KerikBalm

[HeronRocketry]

One last question: what engines should be used on the engine plates of 5m parts? I’ve tried putting 24 kodiaks on and they barely move it but don’t take up much fuel. Any suggestions for engines?

[evileye.x]

 

14 hours ago, HeronRocketry said:

I’m just wondering. Has anyone found a practical application for or how to use 5m parts in making history?

Two digits: 6.4x

Edited March 15, 2018 by evileye.x

[Starman4308]

5 hours ago, Foxster said:

Yup, I'm sure. The drag of stock parts increases dramatically with part size. Anything above size 1 on Eve leads to large losses that need bigger engines and more fuel to overcome, rinse+repeat.

The proper comparison is not 1 1.25m part to 1 5m part. The proper comparison is a 5m part to enough 1.25m parts to contain the same amount of propellant.

My gut instinct is that unless you're trying a 5 meter pancake, it should help. If you replaced a 5m stack with a quartet of 2.5m stacks of identical height, your cross section is the same... but you have more wetted surface area.

If you replaced a 5m stack with a 2.5m stack that is 4x taller, it depends. At supersonic velocities in particular, cross section becomes more important than total wetted surface area, so the reduced surface area of a 5m stack (so long as it's not a pancake) might be less important than its increased cross section. 

All of this, of course, is subject to the whims of the stock aero model that I don't fully understand. 

[Foxster]

3 hours ago, Starman4308 said:

The proper comparison is not 1 1.25m part to 1 5m part. The proper comparison is a 5m part to enough 1.25m parts to contain the same amount of propellant.

My gut instinct is that unless you're trying a 5 meter pancake, it should help. If you replaced a 5m stack with a quartet of 2.5m stacks of identical height, your cross section is the same... but you have more wetted surface area.

If you replaced a 5m stack with a 2.5m stack that is 4x taller, it depends. At supersonic velocities in particular, cross section becomes more important than total wetted surface area, so the reduced surface area of a 5m stack (so long as it's not a pancake) might be less important than its increased cross section. 

All of this, of course, is subject to the whims of the stock aero model that I don't fully understand. 

Seems like there are a lot of guesses going on here from a couple of folks. I've built a lot of Eve return craft (my record for the lightest manned still stands I believe @ ~19t) and I can tell you from much experience that getting craft up from the surface of Eve is about taking stuff away, not adding to it or making it bigger. 

Edited March 15, 2018 by Foxster

[Starman4308]

7 minutes ago, Foxster said:

Seems like there are a lot of guesses going on here from a couple of folks. I've built a lot of Eve return craft (my record for the lightest still stands I believe @ ~19t) and I can tell you from much experience that getting craft up from the surface of Eve is about taking stuff away, not adding to it or making it bigger. 

We're arguing past each other here. You're arguing "a 5 meter stack is unnecessary for an EAV", I'm arguing "that argument about drag makes no sense for something big enough to need a 5m stack", and that it might not be the EAV itself: it might be the booster to get that EAV off Kerbin 

[KerikBalm]

1 hour ago, Foxster said:

I can tell you from much experience that getting craft up from the surface of Eve is about taking stuff away, not adding to it or making it bigger. 

Umm, this applies to anything that has a high dV requirement.

Curious about your 19 ton EAV. Was it from sea level, was it for a Kerbal, or just a probe core? I had my best results for a sea level 3 kerbal ascent vehicle with 1.25m parts, but I used Vectors... which are really way out of whack with the other 1.25m engines, they get that thrust:cross section ratio waaayyyy up there, enabling very tall stacks, adn thus a high BC.

[Foxster]

With a Kerbal in a can from sea level and, yes, a Vector as the 1st stage. 

 

Edited March 15, 2018 by Foxster

[Snark]

22 hours ago, HeronRocketry said:

Has anyone found a practical application for or how to use 5m parts in making history?

They're handy for large booster stages to loft really big ships off the pad in one piece.  Can also be useful for orbital tankers, or large mining vessels.

For example, here's a big fuel tanker, 812 tons on the pad, lofts 184 tons into LKO.

Lifts off the pad on 13 Mastodons (two 4-engine asparagus stages around a 5-engine core).  Sitting on top of the main central booster is the upper stage, powered by three Wolfhounds.

Fairly quick to build, performs nicely without having to have a top-end machine (low part count), simple to launch and fly.

[HeronRocketry]

Awesome, @Snark! Thanks for giving me a practical ship. I’m thinking about using a small 5m tank and using it as fuel storage for my min base after that.

[Snark]

(Oh, also, moving to Making History Discussion.  Forgot to do that.) 

[TeslaPenguin1]

On 3/15/2018 at 1:02 PM, Snark said:

They're handy for large booster stages to loft really big ships off the pad in one piece.  Can also be useful for orbital tankers, or large mining vessels.

For example, here's a big fuel tanker, 812 tons on the pad, lofts 184 tons into LKO.

I also use them for my Heavy-lift to LKO. I haven't found an upper limit for payload mass, just payload diameter (if it gets to big it has too much drag). It uses asparagus staging with a 9-mastodon core, and mammoths with fuel tanks around the outside (w/ 8way symmetry) staged with asparagus. The first stage alone is enough to reach space, and the second is barely used, just for circularization. I use it to launch huge space station modules, and as far as I know, I could get a small-ish lander to the moon. If I wanted.

Edited May 14, 2018 by TeslaPenguin1

[xRDK]

I know this is an old thread, found it via searching for what 5m to 3.75m adapters there are, however I've got a practical example - I have a mission to test (via staging sequence) a mammoth engine in orbit of Ike and you can't attach anything to the bottom of the Mammoth...

 

(To give an idea of my skill level (or, more appropriately, lack of); I only reached Duna for the first time yesterday and I used a Matt Lowne design to do it...)

 

The only options I can see here are, keeping in mind the previous "lack of skill level" info;

 

A. Put the mammoth at the top of the rocket, facing the wrong way, within a fairing.

B. Have it at the bottom of a long central shaft with radially attached stages to get it to it's destination

C. Put it in some 5m parts...

 

I went with C, as I have a Duna satellite mission also - the rocket isn't finished yet but so far I have;

 

At the top; a small satellite using 1.25m/1.875m parts/engines with the 100g relay antenna, encased in a 5m fairing for aero reasons

Under this; a mammoth engine within a 5m structural tube

Finally; Various 5m fuel tanks/engine plates to get it to Ike orbit (not finished yet)

 

Probably an irrelevant reply now, but thought I'd chime in anyway, in case newer peeps have the same question.

[HeronRocketry]

5 hours ago, xRDK said:

I know this is an old thread, found it via searching for what 5m to 3.75m adapters there are, however I've got a practical example - I have a mission to test (via staging sequence) a mammoth engine in orbit of Ike and you can't attach anything to the bottom of the Mammoth...

 

(To give an idea of my skill level (or, more appropriately, lack of); I only reached Duna for the first time yesterday and I used a Matt Lowne design to do it...)

 

The only options I can see here are, keeping in mind the previous "lack of skill level" info;

 

A. Put the mammoth at the top of the rocket, facing the wrong way, within a fairing.

B. Have it at the bottom of a long central shaft with radially attached stages to get it to it's destination

C. Put it in some 5m parts...

 

I went with C, as I have a Duna satellite mission also - the rocket isn't finished yet but so far I have;

 

At the top; a small satellite using 1.25m/1.875m parts/engines with the 100g relay antenna, encased in a 5m fairing for aero reasons

Under this; a mammoth engine within a 5m structural tube

Finally; Various 5m fuel tanks/engine plates to get it to Ike orbit (not finished yet)

 

Probably an irrelevant reply now, but thought I'd chime in anyway, in case newer peeps have the same question.

Wow, pretty impressive idea! What if you inverted the mammoth and had it have its own fuel tanks, so you have an upside down rocket, and then you use 5m parts to get that into orbit? I should try that.

 

As with the old thread quote, don’t worry- I’m still following it so I saw your message, but beware necroposting. This wasn’t too bad because it was only 3 months, but don’t post on threads that haven’t had posts in 6-9 months. 

 

Also, welcome to the forums! It’s a great place to learn about ksp. Before I joined I hadn’t landed on Minmus, but now I’ve landed on every Jool moon but Tylo! (Seriously, Tylo is a kerbal killer. RIP Patsen, Bill, Bob, Lolo and Val, from 3 separate Tylo missions.) Maybe 5m parts can help with my fatality rates...