Using Mk1 vs Mk2 fuselage

[Jestersage]

I was trying to convert the Stock Learstar and Stock Slim Shuttle into SSTO for Kerbin-Station transfer, and I found that it's easier to get the Mk1 design into orbit compared to the Mk2 design, and requiring less engines (2 instead of 4)! Is there an explaination for why it's easier to use a Mk1 to make orbit?

EDIT: Related question: Is it better to go without a size converter or not in terms of drag? Namely, from mk2 to 1.25?

EDIT 2: Never mind: just saw AeroGav's mk2 tutorial (https://forum.kerbalspaceprogram.com/index.php?/topic/165435-basic-mk2-spaceplane-guide/. Thanks.

Edited November 12, 2017 by Jestersage

[DrLicor]

Mk1 parts are much lighter and can therefor get a lesser amount of resources into orbit, however, the mk2 parts have relative much more drag compared to the other parts, so that's also a factor to keep in mind. 

Edited October 16, 2017 by DrLicor

[Blaarkies]

MK2 parts have excessive amounts of drag. Don't pick them for any prolonged use in atmospheres (rovers might be the exception here). They hold the same amount of fuel per unit of length compared to MK1, supply some extra lift, but at the cost of a disproportionate amount of extra drag.

If you have the technology, i find MK3 parts easy, practical and useful due to the huge cargo payload bay.

[AeroGav]

All of these parts hold 800 units of LF/Oxidizer

Compare the drag values however - 

Mark One FT800 tank - 1.40kn
Mk1 to Mk2 Adapter (long) - 1.93kn
Mk2 Rocket Fuel Fusealge (long) - 2.36kn
2.5M to Mk2 Adapter - 2.44kn
2.5M Rockomax X200-8 Tank   -  0.47kn
 

[Jestersage]

Thanks. I ended up replacing as much of the Mk2 Fuel tanks with the standard 1.25m, and it can actually fly on two RAPIERs.

Now I have to debate which one look closer to Concord, Mk1 or Mk2 fuselage.

[DrLicor]

@JestersageMk1 for sure, the cabins of the concorde where very small (not as small as the MK1), they where also round. 

[Jestersage]

Related question: Is it better to go without a size converter or not in terms of drag? namely, from mk2 to 1.25?

Edited October 17, 2017 by Jestersage

[Palaceviking]

21 minutes ago, Jestersage said:

Related question: Is it better to go without a size converter or not in terms of drag? namely, from mk2 to 1.25?

Always. 

[AeroGav]

1 hour ago, Jestersage said:

Related question: Is it better to go without a size converter or not in terms of drag? namely, from mk2 to 1.25?

Always use size converters.  You can easily test these things for yourself - press ALT F12 in flight, go to the physics tab, tick the "enable aero data in action menus" checkbox and right click on parts of your aircraft to get drag numbers.

[AeroGav]

I tried a quick and dirty conversion of the Learstar, was going to put two panthers on decouplers for a 90% re-usable vehicle with decently quick time to orbit.

Just look at the drag from those short cargo bays though - 180kn each ! and it has three of them.   The wings are making 12kn drag.  We can't get supersonic in a dive, with all 5 engines going..

Lift to drag ratio 0.5 to 1.....   real supersonic aircraft do 20x better at this speed.

For comparison, look at my latest craft on KerbalX, which carries 11 to orbit and uses less than half its fuel to do so

https://kerbalx.com/AeroGav/MK1-Griffon-Deep-Space-Crew-Shuttle

[AeroGav]

29 minutes ago, AeroGav said:

I tried a quick and dirty conversion of the Learstar, 

Just look at the drag from those short cargo bays though - 180kn each ! and it has three of them. 

 

After rage quitting,  I decided to take another look at the vehicle.    180kn drag is ridiculous even for a mk2,  i discovered that the cargo bays don't seem attached to each other properly.

If you try to remove the front cargo bay, you'll see that it's actually radially attached to the sections in front as opposed to end attached, and in fact it is impossible to re-attach the piece.

Instead, i had to get rid of the internal docking port, then detached and reattached the cargo bays one at a time.

It now goes to orbit, quickly and easily.

BTW I cannot fly the stock learstar or slim shuttle at all.     They just start tumbling on launch,  so at least I can safely say my creation is an improvement on the original

https://www.dropbox.com/s/iy44a82dwnxe84h/Learstar A2.craft?dl=0

[linuxgurugamer]

Can someone explain why the mk2 parts have so much more drag?

And please don't say it's because of what's in the cfg file

[bewing]

42 minutes ago, linuxgurugamer said:

Can someone explain why the mk2 parts have so much more drag?

And please don't say it's because of what's in the cfg file

Note that there are some bugs with cargo bay aero drag right now. But besides that, you get to choose the answer to your question:

A) Because god made it that way.

B) There is no good reason. The next time the full set of parts goes through a "balance pass", it'll all get changed to be more rational.

C) It is a test to make sure you are paying attention. Building aerospace gadgets always involves noting the quirks and funkyness of the parts you have available, using the least quirky, and designing around the funkyness.

 

[linuxgurugamer]

23 minutes ago, bewing said:

Note that there are some bugs with cargo bay aero drag right now. But besides that, you get to choose the answer to your question:

A) Because god made it that way.

B) There is no good reason. The next time the full set of parts goes through a "balance pass", it'll all get changed to be more rational.

C) It is a test to make sure you are paying attention. Building aerospace gadgets always involves noting the quirks and funkyness of the parts you have available, using the least quirky, and designing around the funkyness.

 

It does make sense if you were going at right angles to the part, I suppose, but how often does someone fly a fuselage horizontally?

Thanks, I just needed to be sure it wasn’t me.

[bewing]

1 hour ago, linuxgurugamer said:

It does make sense if you were going at right angles to the part, I suppose, but how often does someone fly a fuselage horizontally?

Thanks, I just needed to be sure it wasn’t me.

Heh. Well, an airplane is almost always a bit off prograde. And spaceplane pilots who are really smart always reenter horizontally.

 

[linuxgurugamer]

Just now, bewing said:

Heh. Well, an airplane is almost always a bit off prograde. And spaceplane pilots who are really smart always reenter horizontally.

 

What is really needed is a drag value for all three axises.

That being said, I guess that when a Mach 2 spaceplane is reentering it gets more drag then a Mark 1 space plane, and therefore can slow down faster.

[bewing]

7 minutes ago, linuxgurugamer said:

What is really needed is a drag value for all three axises.

That being said, I guess that when a Mach 2 spaceplane is reentering it gets more drag then a Mark 1 space plane, and therefore can slow down faster.

That's what AeroGav's scientific-type experimentation is for. Everyone should do it. Pick a part, mount it all 3 ways, launch it with a big fat rocket, and look at the drag values.

 

[linuxgurugamer]

Just now, bewing said:

That's what AeroGav's scientific-type experimentation is for. Everyone should do it. Pick a part, mount it all 3 ways, launch it with a big fat rocket, and look at the drag values.

 

Can you post a link, please?

[bewing]

Just now, linuxgurugamer said:

Can you post a link, please?

Don't have one. I just know that for MK1 it's nice, and for MK2 right now it's ugly.

 

[luizopiloto]

MK2 parts are more heat resistant, have wing Lift, less drag, but are heavier...

[Gordon Fecyk]

*looks at Tanbro* Gav! You monster! Sending Tanbro on a one-way trip when a probe core would've sufficed... 

Seriously though, for the sake of completeness I reproduced your test craft, using a probe core and nose cone! ... with the current Ferram Aerospace. All of the fuel tanks displayed similar drag.

At maximum dynamic pressure, all of these parts displayed identical drag numbers. (Not identical drag force though.) We know this is not stock aero though, but I think it demonstrates why I like FAR so much.

 

Edited October 18, 2017 by Gordon Fecyk

[Jestersage]

8 hours ago, AeroGav said:

Always use size converters.  You can easily test these things for yourself - press ALT F12 in flight, go to the physics tab, tick the "enable aero data in action menus" checkbox and right click on parts of your aircraft to get drag numbers.

Should I test them all in one test? I am trying to figure out which is lower drag, 1 Long Mk2-1.25 adapter, or a Standard mk2-1.25 adapter+  ft400. And does orientation matter? Are they additive?

Edited October 18, 2017 by Jestersage

[Spricigo]

30 minutes ago, Gordon Fecyk said:

but I think it demonstrates why I like FAR so much.

Not sure if I followed you. May you give a bit longer explanation why the fantastic mod is fantastic?

[Gordon Fecyk]

28 minutes ago, Spricigo said:

May you give a bit longer explanation why the fantastic mod is fantastic?

Ferram Aerospace Research uses a different aerodynamics model that takes the whole craft's shape into account, rather than the individual parts' drag characteristics. The Mk2 parts are as sleek as they look with this installed.

Here's a simple example: If you try attaching anything to the inside walls of a cargo bay, stock aerodynamics treats the parts as though they were attached to the outside, drag and all. With FAR installed, parts attached to the outside walls add drag, but parts attached to the inside walls do not. Things enclosed in fairings, cargo bays, service bays, heck even a container made out of structural panels with a pointy end, won't contribute to drag.

A FAR craft might feel like it's flying in thinner air, but it's just calculating drag differently.

The big disadvantage is you'll need to think more like an aircraft designer. You'll want more wing area to get the same lift that you'd get in stock aero. For instance, Mark Thrimm's LTS Kestrel craft has plenty of lift in stock aero, but hardly any lift in FAR. I had to triple the wing surface area and add tail planes to get the same lift and stability that it had in stock aero. FAR craft also tend to kill kerbals on landing because of very high stall speeds.

But if you can overcome the new challenges, you can build more efficient craft. That Kestrel-FC can carry four times the cargo up to low Kerbin orbit.

[AeroGav]

2 hours ago, Jestersage said:

Should I test them all in one test? I am trying to figure out which is lower drag, 1 Long Mk2-1.25 adapter, or a Standard mk2-1.25 adapter+  ft400. And does orientation matter? Are they additive

An adapter with the pointy end facing the back of the airplane has the same drag as one with the pointy end facing forwards.       Prograde and Retrograde are minimum drag orientations - but the more degrees it points away from prograde or retrograde the more drag  you get.

It does not matter where a part is in the stack for drag - if an FT800 adapter is the second, or second last piece in the fuselage stack, it will have the same drag.   However, if it does not have  a piece attached to its front or rear nodes then its drag is greatly increased as you are exposing a flat face to the airflow  - it's just as bad doing that at the front as it is at the back. .     Obviously you want something pointy at the front and ends of each stack. 

As for doing them all in one test,  for maximum accuracy the parts being compared should be on the same vessel at the same time, by pinning multiple right click menus open then taking screenshots.   That way you can guarantee that all the parts are being compared on a level playing field - same speed, altitude, and angle relative to airflow.     Running separate tests you can get a rough idea if you can think of a way to  even out those differences.

For example, I did some tests by launching a rocket straight up with SAS set to radial out (same angle of attack) , taking screenshot as soon as our speed hit 200m/s (same speed, with some error from my reaction time)  .    I adjusted the fuel load on the rocket so all versions being tested had the same TWR, so would hit that speed at the same altitude (more or less)

3 hours ago, Gordon Fecyk said:

*looks at Tanbro* Gav! You monster! Sending Tanbro on a one-way trip when a probe core would've sufficed... 

I've now got 11 assorted rockets and prototype spaceplanes in LKO, Tanboro is among them.  None of them have parachutes, heat shields or decouplers.   The Learstar is up there as well, with only one seat occupied.    I could send it to rendezvous with the rockets and EVA the crew over.    Then again I don't actually know if it can re-enter, because i've never tried.   Actually I've never even landed it before,  but i've no reason to think it can't.       Or I'll just leave them floating up there for eternity and start a new save.