Mk2 Balance

[Jarin]

I was going to put this in suggestions, but realized I really didn't have a strong enough grasp of the situation to suggest intelligently, so I'll start a discussion instead. 

But basically my issue is something I've seen brought up a number of times, but never directly addressed (I'm sure it has been discussed somewhere before, but my search only found pre-1.0 discussions). In the context of supersonic aircraft, it seems like Mk1 parts are superior to Mk2 in almost every respect. Whta do you get for using Mk2?

-No extra fuel
-Some extra impact durability, but no joint strengthening (same chance of midair unplanned disassembly)
-Extra mass
-Extra lift that is notably more draggy than just a bit of extra wing with incidence
-A cargo bay
-Spiffy appearance

Those last two points are literally the only reason I have continued to design anything with Mk2 parts. I know I have to be missing something here, but I don't know what. Is this just a weird imbalance? Am making some incorrect assumptions? I really want to like these parts, but it's just so difficult.

Edited November 11, 2016 by Jarin

[Streetwind]

You also get significantly uprated heat tolerance. Mk1 parts are not really meant to go to space and reenter; you can make it work in a pinch, but it's less than ideal and you don't have complete design freedom. Mk2 parts however are easily able to take the heat load of reentry. They are designed to be spaceplane parts from the ground up.

[Kertech]

They look cool

[AeroGav]

3 hours ago, Jarin said:

I was going to put this in suggestions, but realized I really didn't have a strong enough grasp of the situation to suggest intelligently, so I'll start a discussion instead. 

But basically my issue is something I've seen brought up a number of times, but never directly addressed (I'm sure it has been discussed somewhere before, but my search only found pre-1.0 discussions). In the context of supersonic aircraft, it seems like Mk1 parts are superior to Mk2 in almost every respect. Whta do you get for using Mk2?

-No extra fuel
-Some extra impact durability, but no joint strengthening (same chance of midair unplanned disassembly)
-Extra mass
-Extra lift that is notably more draggy than just a bit of extra wing with incidence
-A cargo bay
-Spiffy appearance

Those last two points are literally the only reason I have continued to design anything with Mk2 parts. I know I have to be missing something here, but I don't know what. Is this just a weird imbalance? Am making some incorrect assumptions? I really want to like these parts, but it's just so difficult.

That pic shows why a LF fuselage short has no more fuel capacity than a mk1 LF tank , which is the same length.  In the middle is a mk1 tank, it's just got chines stuck on the side.   Notwithstanding the fact that in real aircraft, chines often hold fuel,  why then does it have three or more times the drag of a mk1 part?   It has less than twice the frontal area and same length.  Even assuming that those chines are a total failed concept and don't reduce drag at all, when in practice  wing /body blending does reduce drag.

[magnemoe]

1 hour ago, Streetwind said:

You also get significantly uprated heat tolerance. Mk1 parts are not really meant to go to space and reenter; you can make it work in a pinch, but it's less than ideal and you don't have complete design freedom. Mk2 parts however are easily able to take the heat load of reentry. They are designed to be spaceplane parts from the ground up.

Add that they also have significant lift. I made an SSTO with MK3 parts and control surfaces 

[Streetwind]

32 minutes ago, magnemoe said:

Add that they also have significant lift. I made an SSTO with MK3 parts and control surfaces

Yeah, he already wrote that in the OP. I just added something he missed

[Jarin]

8 hours ago, Streetwind said:

You also get significantly uprated heat tolerance. Mk1 parts are not really meant to go to space and reenter; you can make it work in a pinch, but it's less than ideal and you don't have complete design freedom. Mk2 parts however are easily able to take the heat load of reentry. They are designed to be spaceplane parts from the ground up.

The numbers back this up, but in practice, I've had no more trouble with Mk1 spaceplane re-entry than Mk2. It's never the hull parts that are in danger, just control. Tons of body heat tolerance doesn't help much if everything else burns off. I do a fairly sharp deorbit starting at the edge of the western continent and ending right on KSC, and it drops me just east of the mountains for an easy flight home. Maybe because I always radiate my heat, so I'm not carrying any ascent heat on my return? 

Edited November 11, 2016 by Jarin

[DrunkenKerbalnaut]

8 hours ago, Streetwind said:

You also get significantly uprated heat tolerance. Mk1 parts are not really meant to go to space and reenter; you can make it work in a pinch, but it's less than ideal and you don't have complete design freedom. Mk2 parts however are easily able to take the heat load of reentry. They are designed to be spaceplane parts from the ground up.

I play on normal re-entry heating levels, but the shrouded docking port and a pair of airbrakes  usually solves this, as long as you enter easy.  Worst case, just slip a service bay with a radiator in the mix. Cold as ice. And if you feel particularly game-ey, an antenna on the nose somehow disrupts the plasma in front of the craft. Or at least that's what I tell myself when I resort to such BS  .

We need Mk1 cargo bays. 

[GluttonyReaper]

4 hours ago, Jarin said:

The numbers back this up, but in practice, I've had no more trouble with Mk1 spaceplane re-entry than Mk2. It's never the hull parts that are in danger, just control. Tons of body heat tolerance doesn't help much if everything else burns off. I do a fairly sharp deorbit starting at the edge of the western continent and ending right on KSC, and it drops me just east of the mountains for an easy flight home. Maybe because I always radiate my heat, so I'm not carrying any ascent heat on my return? 

I've personally found that Mk1 parts are usable for LKO reentries, but Munar reentries and further aren't very survivable without multiple passes. Mk2 planes get pretty dicey from the Munar reentries, but the extra tolerance means you tend to survive more often than not.

[Sharpy]

4 hours ago, DrunkenKerbalnaut said:

I play on normal re-entry heating levels, but the shrouded docking port and a pair of airbrakes  usually solves this, as long as you enter easy. 

Are you playing 1.2.x? Because airbrakes got a MASSIVE heat tolerance nerf, and they are very quick to go on reentry if you're not careful. They are fine to bring you down from 1200 to drogue speeds, but in the hottest part of reentry - 1900-1200m/s at 3500-2000m, airbrakes are useless.

[Jarin]

45 minutes ago, GluttonyReaper said:

I've personally found that Mk1 parts are usable for LKO reentries, but Munar reentries and further aren't very survivable without multiple passes. Mk2 planes get pretty dicey from the Munar reentries, but the extra tolerance means you tend to survive more often than not.

Haven't managed a munar Mk2 return myself. Not a direct one, anyway. The cockpit always goes. Besides, airbraking back down to LKO means I can properly aim my descent for KSC.

 

16 minutes ago, Sharpy said:

Are you playing 1.2.x? Because airbrakes got a MASSIVE heat tolerance nerf, and they are very quick to go on reentry if you're not careful. They are fine to bring you down from 1200 to drogue speeds, but in the hottest part of reentry - 1900-1200m/s at 3500-2000m, airbrakes are useless.

They got nerfed, but I wouldn't call them useless at high speeds. They just have to be used a bit differently. They still add a fair bit of drag even if obscured from the re-entry plasma by the body of your craft, i.e. dorsal airbrakes on a spaceplane pitched up at least a few degrees. You may need to pulse them a bit, but they don't explode instantly like some parts. You have plenty of warning to let off the brakes before the temp gauges top out. With proper balance (CoP/CoL near CoM) so I can keep a moderate pitch on re-entry, I regularly have the brakes out all the way down, and they make a reasonable difference, getting out of the "burn zone" earlier.

Edited November 11, 2016 by Jarin

[DrunkenKerbalnaut]

2 hours ago, Sharpy said:

Are you playing 1.2.x? Because airbrakes got a MASSIVE heat tolerance nerf, and they are very quick to go on reentry if you're not careful. They are fine to bring you down from 1200 to drogue speeds, but in the hottest part of reentry - 1900-1200m/s at 3500-2000m, airbrakes are useless.

No, still on 1.something.

 @Jarins experiences are pretty much in line with what I encounter, though. However, it's not often I make a direct landing upon arrival.  I suck at aiming for KSC, so my planes are designed for hairy landings. This affords me the ability to do as shallow an entry as I like. I'm getting pretty used to unpowered landings on rolling foothills at >100 m/s.

I should stick to rockets haha. 

Anyways, Mk1 crew cabins are the lightest way to move a kerbal, outside of ladders, space boots, or external command seats. You can make pretty light LKO buses, just gotta have a plan to deal with their low heat resistance. In my experience, Mk1 spaceplanes seem to behave a little better in atmo, too. I guess because you have a bit finer control over COL. 

[RocketBlam]

On 11/11/2016 at 0:55 PM, Sharpy said:

Are you playing 1.2.x? Because airbrakes got a MASSIVE heat tolerance nerf, and they are very quick to go on reentry if you're not careful. They are fine to bring you down from 1200 to drogue speeds, but in the hottest part of reentry - 1900-1200m/s at 3500-2000m, airbrakes are useless.

I'm never going that fast, that low. I usually drop below 1200 m/S at about 18000 meters.

[Sharpy]

51 minutes ago, RocketBlam said:

I'm never going that fast, that low. I usually drop below 1200 m/S at about 18000 meters.

oops, missed a zero. 35000-20000m.

[RocketBlam]

15 hours ago, Sharpy said:

oops, missed a zero. 35000-20000m.

Ah, that makes more sense. I think my whole ship would explode going that fast, that low.

One thing to do is to put your craft in a very un-aerodynamic attitude when you re-enter. That is, flying with the "flat part forward." That increases drag. The problem of course is that it's hard to keep it like that when the atmosphere gets very thick. 

[DrunkenKerbalnaut]

7 hours ago, RocketBlam said:

One thing to do is to put your craft in a very un-aerodynamic attitude when you re-enter. That is, flying with the "flat part forward." 

I steal moves from the Space Shuttle, "S Turns". If you have a good RCS setup, it'll get you through the Danger Zone. (I promise the link isn't Kenny Loggins)

http://www.planetary.org/blogs/guest-blogs/jason-davis/3106.html

[Leafbaron]

On 11/11/2016 at 9:40 AM, DrunkenKerbalnaut said:

I play on normal re-entry heating levels, but the shrouded docking port and a pair of airbrakes  usually solves this, as long as you enter easy.  Worst case, just slip a service bay with a radiator in the mix. Cold as ice. And if you feel particularly game-ey, an antenna on the nose somehow disrupts the plasma in front of the craft. Or at least that's what I tell myself when I resort to such BS  .

We need Mk1 cargo bays. 

Check out Modular Rocket Systems mod. They have Mk1 service bays that make for perfect Spaceplanes for small .625m satellites/probes.

15 hours ago, RocketBlam said:

Ah, that makes more sense. I think my whole ship would explode going that fast, that low.

One thing to do is to put your craft in a very un-aerodynamic attitude when you re-enter. That is, flying with the "flat part forward." That increases drag. The problem of course is that it's hard to keep it like that when the atmosphere gets very thick. 

Got to be careful doing that as well. I was practicing some Re-entry maneuvers with a spaceplane and i actually stalled at like around 30,000 meters because my verical velocity was greater than my horizontal velocity. Almost put me in a flat spin. it was tough regaining control but in the end Jeb got it and managed to get back on the tarmac safe and sound. 

[DrunkenKerbalnaut]

5 hours ago, Leafbaron said:

Check out Modular Rocket Systems mod. They have Mk1 service bays that make for perfect Spaceplanes for small .625m satellites/probes.

Oh I prefer the B9 ones. But I meant in stock. 

Stalling at 30k? That bird must have had serious pitch authority. 

[AeroGav]

On 11/11/2016 at 11:30 PM, DrunkenKerbalnaut said:

No, still on 1.something.

 @Jarins experiences are pretty much in line with what I encounter, though. However, it's not often I make a direct landing upon arrival.  I suck at aiming for KSC, so my planes are designed for hairy landings. This affords me the ability to do as shallow an entry as I like. I'm getting pretty used to unpowered landings on rolling foothills at >100 m/s.

 

Your landing speed is 100m/s empty?   This is an example with a really oversized wing, this is it parking landing .

Having larger wings makes re-entry safer too, because you stay up higher down to lower speeds, and can aerobrake better.  Also , wings make very good radiators - attach them direct to the cockpit, then adjust them backwards to where needed, and the cockpit can shed heat through them.  Pitching up to max lift,  we're able to turn a steep descent into a steep climb at 40km up 

As for hitting KSC, when coming back from a sane orbit,  I aim for the big desert on the continent west of KSC.  The far western end if i have a high PE,  if i retro burn to a low one, i aim the eastern shore.

Once we encounter the atmosphere I control my glide distance by manipulating angle of attack -

If you pitch to about 7 degrees above prograde, you'll see the point at which the blue line hits ground level in the map screen move steadily east.  You can stretch the glide a long way by doing this.     When you're starting to overshoot , pitch up, where the lift drag ratio is worse, and the line starts to go the other way.  Pitching up has the added benefit of bringing you into thinner air, so the heating rate decreases.

[DrunkenKerbalnaut]

5 minutes ago, AeroGav said:

-snip-

Thanks for the detailed primer. I'll have to take a spin in my ORCA (Orbital Resupply, Cargo, and Airliner - yay acronyms  ) to confirm that speed, but yeah. Pretty much. I think it stems from my desire to build spaceplanes, especially SSTOs, with higher TWR than necessary. So I end up sacrificing in the lift category. Pretty much all of my winged SSTO could carry more weight if I just put more lifting surfaces on, but I'm no pro at spaceplane ascent paths. So I just juice it and muscle through. For instance, 2 Rapiers is 20-25 ton SSTO territory for me, whereas those who really rock out can manage 30+ tons on 2 Rapiers. I just end up landing like a flaming stork in the boonies somewhere. Drogue chutes help . And the inherent light-ness of the mk1 parts bin.

[AeroGav]

16 minutes ago, DrunkenKerbalnaut said:

Thanks for the detailed primer. I'll have to take a spin in my ORCA (Orbital Resupply, Cargo, and Airliner - yay acronyms  ) to confirm that speed, but yeah. Pretty much. I think it stems from my desire to build spaceplanes, especially SSTOs, with higher TWR than necessary. So I end up sacrificing in the lift category. Pretty much all of my winged SSTO could carry more weight if I just put more lifting surfaces on, but I'm no pro at spaceplane ascent paths. So I just juice it and muscle through. For instance, 2 Rapiers is 20-25 ton SSTO territory for me, whereas those who really rock out can manage 30+ tons on 2 Rapiers. I just end up landing like a flaming stork in the boonies somewhere. Drogue chutes help . And the inherent light-ness of the mk1 parts bin.

Yeah i think for spaceplane ascent, you want to have your wings at 5 degrees to the airflow most of the time, where lift/drag is best.  The exception being when penetrating the sound barrier, where you just want raw speed and are pushing the nose down a bit,  and when you've reached 20km+ in air breathing mode and are trying to get as much speed out of jet mode as possible before switching to rocket/exploding form overheating - then you will also be pushing the nose down.

I'd say one rapier per 30 tons is fine.    If you watch the beginning of that video i posted, you see my craft start its journey to duna.   16 tons being pushed by one nuke - 60kn, a single rapier makes three times that power in closed cycle, though in air breathing mode it's probably only got 45kn above 20km.  No fancy flying involved i just hold the nose 5 degrees above prograde and wait...

Edited November 15, 2016 by AeroGav

[Leafbaron]

15 hours ago, DrunkenKerbalnaut said:

Oh I prefer the B9 ones. But I meant in stock. 

Stalling at 30k? That bird must have had serious pitch authority. 

it sure did thanks to my RCS  thrusters and well balanced design when wet and dry. I was coming in at probably 60-75 degrees. perpendicular to my prograde velocity. Just wanted to see what happened for excrementss and gigs. 

B9 isn't updated for 1.2 yet

[Jarin]

... okay, from test flights today, I can say that the extra impact durability can be worthwhile. It's a heck of a lot easier to drop an out-of-control aircraft below 50m/s impact speed than it is to drop below 20.

[AeroGav]

On 11/11/2016 at 5:44 AM, Jarin said:

I was going to put this in suggestions, but realized I really didn't have a strong enough grasp of the situation to suggest intelligently, so I'll start a discussion instead. 

But basically my issue is something I've seen brought up a number of times, but never directly addressed (I'm sure it has been discussed somewhere before, but my search only found pre-1.0 discussions). In the context of supersonic aircraft, it seems like Mk1 parts are superior to Mk2 in almost every respect. Whta do you get for using Mk2?

-No extra fuel
-Some extra impact durability, but no joint strengthening (same chance of midair unplanned disassembly)
-Extra mass
-Extra lift that is notably more draggy than just a bit of extra wing with incidence
-A cargo bay
-Spiffy appearance

Those last two points are literally the only reason I have continued to design anything with Mk2 parts. I know I have to be missing something here, but I don't know what. Is this just a weird imbalance? Am making some incorrect assumptions? I really want to like these parts, but it's just so difficult.

Time to put this to the test.     I calculated the fuel capacity (units of oxidizer and liquid fuel stored by each part) divided by the drag value in kn for every part of the above rocket.    What makes the comparison easier is that the mk1 , mk2 and 2.5m parts all hold 800 exactly.  The mk3 tank and 2.5m to mk3 adapters are the odds ones out, both holding 2500 units.

But anyway, here's the numbers crunched -

Part			Fuel capacity per kn drag
Mk 0 LF Fuselage			294.1176
FT800 Tank			533.3333
Mk2 to 1.25m Adapter Long			347.8261
Mk2 Rocket Fuel Fuselage			271.1864
2.5M to Mk2 Adapter			289.8551
Rockomax X200-8 Fuel Tank			1818.182
Mk3 to 2.5m Adapter			615.7635
Mk3 Rocket Fuel Fuselage			642.6735

 

So there you go.    MK2 parts are twice as draggy as mk1 parts of the same fuel capacity.   Mk3 parts are 20% more drag efficient than mk1, but the real stars of the show are the 2.5m items. They have 2.4 times less drag per unit of fuel carried than mk1,  and 6.7 times less drag than a mk2 fuselage of same capacity.

That last statement made me check my maths.

But look at the picture for confirmation :

Rockomax X200-8 Fuel Tank

Drag       0.44

Mk2 Rocket Fuel Fuselage

Drag       2.95

Both parts have exactly the same fuel capacity, 800 units.

 

 

 

[Jarin]

4 minutes ago, AeroGav said:

Part			Fuel capacity per kn drag
Mk 0 LF Fuselage			294.1176
FT800 Tank			533.3333
Mk2 to 1.25m Adapter Long			347.8261
Mk2 Rocket Fuel Fuselage			271.1864
2.5M to Mk2 Adapter			289.8551
Rockomax X200-8 Fuel Tank			1818.182
Mk3 to 2.5m Adapter			615.7635
Mk3 Rocket Fuel Fuselage			642.6735

Wow, so the Mk2 really is the worst of all possible options. That's... even more disappointing than I thought. I think it's time to seriously start talking rebalance here.