Question about extendable parts breaking in the atmosphere

[KerikBalm]

So based on a thread about eve ascent vehicles, and questions about electric charge consumption, I did a quick spreadsheet to determine part count and mass needed ...

Spoiler

to supply 108k EC at 300 EC/second, for a large eve plane running  6x heavy rotors at full power.

I figured I needed either:

27x 2.5 meter batteries, massing 5.4 tons,

56-108 Ox-stat panels at 2.24-4.32 tons (depending on if i use kerbin EC values, or Eve EC values, knowing that there is atmospheric attenuation and suboptimal alighnment except when flying equatorial at certain times of day). This option is attractive in terms of mass, but not part count

7-13 Gigantors at 2.1-3.9 tons(same conditions as above). This option is very attractive in terms of part count and mass.

17 Fuel cells, plus 1.35 tons of fuel, for 5.43 tons

... lets not even talk about RTGs

In the end, the mass concerns are minimal, and what I am really seeking are part count reductions: thus the best options are gigantors, followed by fuel cells

Gigantors were by far the best option, but they can break off due to atmospheric pressure, unlike Ox-stat arrays. Ox-stat arrays require really high part counts though.

Has anyone made a plane flying on Gigantor power? I was thinking that if I had them parallel to the direction of travel, they probably shouldn't break. My fear is that as soon as they have the slightest AoA, they will break off. Has anyone tried this with any success?

I was hoping to be able to make a craft with these attached so that they extend along the length of the plane, to put some incidence into the plane's wings, and have the plane do a gentle climb at nearly 0 AoA thanks to wing incidence, my hope is that the panels won't break off like this.

Once max altitude is reached, I'll retract the panels and engage rockets. 

Is this a viable option? has anyone built a plane that flies in the atmosphere of kerbin or eve with breakable parts extended?

[jimmymcgoochie]

If you’re going for a heavier than air craft that uses wings for lift, the extra weight of batteries is less of an issue and you can always set them up to drop once you engage the rocket engines, assuming this is a single use thing. Much like staging an empty booster, getting rid of the batteries once they’re spent will reduce weight and allow the remaining craft to perform better.

A combination of batteries, solar panels and a few fuel cells might be the best way forward, saving weight on batteries without adding too many parts. Charge the batteries up with solar power then use the fuel cells during the ascent to extend your battery life, don’t worry about maintaining power for the rocket stage unless your engine doesn’t generate power with an alternator (e.g. Terrier).

[KerikBalm]

It is not single use.

Using batteries results in higher part count, but nearly identical mass. Batteries have the advantage of being rechargeable after landing, to return to the launch site where it can refuel. Fuel cells would require putting away even more fuel to fly back.

Anyway, I am really just interested in knowing if there is a practical way to fly with gigantors extended

[herbal space program]

Perhaps you could mount them to small nosecones embedded in the trailing edges of your wings so that they extend backwards?  If they're mounted vertically, then pitching up probably wouldn't snap them off, although turning most likely would. I'm kind of curious about it now, so I might try fooling around with that type of design myself in the sandbox later. One thing I can tell you, although you probably already know it, is that the aero forces low in Eve's atmo are just brutal. I've often snapped off wings that were strutted out the wazoo by turning just a little bit too aggressively.

 

(edit)... And it actually seems to work! I tried mounting a pair of Gigantors to my existing Eve plane, first facing outwards. In that configuration, they caused massive drag and snapped off right at 100m/s:

 

If OTOH I mounted them to the backs of my rotors facing backwards, they caused a lot less drag, and I couldn't get them to snap off even at >140m/s:

Teleporting the test to Eve didn't seem to change anything either:

So I'm gonna say, yes, you could actually  do it that way!

Edited July 22, 2021 by herbal space program

[KerikBalm]

11 hours ago, herbal space program said:

Perhaps you could mount them to small nosecones embedded in the trailing edges of your wings so that they extend backwards? 

Well, extending them backwards is what I had in mind when I said "I was thinking that if I had them parallel to the direction of travel, they probably shouldn't break. "

I didn't plan on using small nose cones, just surface attachment and the rotate and offset tools, since their base is fairly thick anyway. I am trying to keep partcount down though (the craft I want to use them on has a ridiculously high part count (>300) and I am looking to reduce it. To put on 8 gigantors that way makes the part count go to 16... which makes it similar to the part count for fuel cells arrays...

11 hours ago, herbal space program said:

it actually seems to work! I tried mounting a pair of Gigantors to my existing Eve plane, first facing outwards. In that configuration, they caused massive drag and snapped off right at 100m/s:

[snip]

If OTOH I mounted them to the backs of my rotors facing backwards, they caused a lot less drag, and I couldn't get them to snap off even at >140m/s:

Teleporting the test to Eve didn't seem to change anything either:

[snip]

So I'm gonna say, yes, you could actually  do it that way!

Well, I had some time to test yesterday. I mounted some on my quad tilt rotor cargo craft, which is normally capable of about 320 m/s, and I think I got to about 160 m/s before they snapped off.

I am surprised that yours didn't snap off in that pic above where your craft orientation deviated by several degrees from your velocity vector.

I have a few hypotheses:

1) Even going backwards, they have non-zero drag, when drag exceeds a certain value, they snap. pointing them backwards reduces, but does not eliminate drag. Gigantors will have a speed limit for various atmospheric pressures.

I think at higher altitudes, this wont be a problem

Spoiler

but I'd probably need to limit the speed at lower altitudes, where shockwaves start to be visible:

2) The exposed node in my setup creates more drag, which results in it snapping sooner than on your plane.

3) My craft's wings have some incidence (5 degrees), at high speeds, the velocity vector points above where the nose points, this results in negative AoA, and this non-zero AoA may be what breaks the solar panels.

I think it may be workable to have gigantors deployed on Eve, and then retract them just before lighting the rockets.

I'm also thinking of adding a free-floating hinge, with a starting 5 degree tilt (to match the 5 degree incidence ofthe wings), with solar panels and some wings attached to it with. I'll try giving the wings some ever so slightincidence (not the 5 degree snap rotation, but maybe 1 or 2 pixels of non-snap rotation). The point of the wings would be to lift the hinge ensure that the angle of attack of the hinge and the solar panels very close to zero.

Before lighting rockets, retract the panels, then light rockets, go suborbital, and then I think I will power up the hinge, and lock it in place for the descent, it could help with stability on reentry too...

I think further part count reductions can be made via replacing 8 vectors with 2 mammoths...

I also note that nearing its previous max altitude (it was "max" because it started to run out of power), the rotors were not strong enough to maintain 460 RPM (that screenshot shows 346 RPM). I'm counting 12 sets of 8 turbine blades... that's 96 parts for prop blades alone. If I reduce them to sets of 6 instead of 8, I save 24 parts.

Perhaps with more EC generation, I can get to a higher altitude, and I won't need as much fuel for the suborbital 1st stage, and I can get a virtuous cycle going.

As you see here, despite tons of batteries, it is my power consumption that was limiting my altitude:

Climb rate was still a decent 9.67 m/s...

AoA was still quite modest, so maybe the free-floating hinge idea is not needed

[herbal space program]

9 hours ago, KerikBalm said:

Well, extending them backwards is what I had in mind when I said "I was thinking that if I had them parallel to the direction of travel, they probably shouldn't break. "

Sorry, I did figure out that's what you meant, but not until after I had replied.

9 hours ago, KerikBalm said:

I didn't plan on using small nose cones, just surface attachment and the rotate and offset tools, since their base is fairly thick anyway. I am trying to keep partcount down though (the craft I want to use them on has a ridiculously high part count (>300) and I am looking to reduce it. To put on 8 gigantors that way makes the part count go to 16... which makes it similar to the part count for fuel cells arrays...

True, but it also means you can ditch all that extra fuel you needed to power the fuel cells, probably in turn significantly reducing the number of rotors/blades you'll need, not to mention all those batteries! In general, it also looks like your plane has more torque than it needs. When I'm flying the one above, my 10 small rotors don't get near their max RPM until I am approaching the top of my envelope, which is around 20km for that plane. It's able to do that using just the power from the  OX-Stat panels you see, although the sun angle does need to be fairly high for that. It also carries only ~6K in electric charge. Of course it is nothing like the behemoth that yours is, but at 82 tons it's no paper airplane either!  And although I  understand your issue about part count, the small rotors have 20 times less torque than the big ones, but weigh almost 40 times less.  I never actually found a situation where the bigger rotors performed better.

9 hours ago, KerikBalm said:

Well, I had some time to test yesterday. I mounted some on my quad tilt rotor cargo craft, which is normally capable of about 320 m/s, and I think I got to about 160 m/s before they snapped off.

I am surprised that yours didn't snap off in that pic above where your craft orientation deviated by several degrees from your velocity vector.

I have a few hypotheses:

1) Even going backwards, they have non-zero drag, when drag exceeds a certain value, they snap. pointing them backwards reduces, but does not eliminate drag. Gigantors will have a speed limit for various atmospheric pressures.

I think at higher altitudes, this wont be a problem

2) The exposed node in my setup creates more drag, which results in it snapping sooner than on your plane.

3) My craft's wings have some incidence (5 degrees), at high speeds, the velocity vector points above where the nose points, this results in negative AoA, and this non-zero AoA may be what breaks the solar panels.

I'm pretty sure hypothesis 2 is correct. When I had the panels mounted backwards behind the nose cones, I was not actually able to do anything that snapped them off, although I didn't push it all that hard.  I imagine a large yaw excursion could be problematic, but OTOH maybe having that nosecone in front just reduces the panels' drag beyond all reason due to how the aero model works. I will see how far I can push it later today. I'll also mention that you don't really need to go all that fast to use props to lift you out of the soup on Eve.  I unfortunately didn't take a snap, but I don't think I was flying at even 200m/s  when I was at 20 km in that plane.

9 hours ago, KerikBalm said:

I think it may be workable to have gigantors deployed on Eve, and then retract them just before lighting the rockets.

Absolutely!

9 hours ago, KerikBalm said:

I think further part count reductions can be made via replacing 8 vectors with 2 mammoths...

Indeed. You might also consider replacing 2 Vectors  and their tank(s) with a Twin Boar if you don't want to move up to 3.75M fuselages, although you'll take a bit of a hit on ISP

9 hours ago, KerikBalm said:

I also note that nearing its previous max altitude (it was "max" because it started to run out of power), the rotors were not strong enough to maintain 460 RPM (that screenshot shows 346 RPM). I'm counting 12 sets of 8 turbine blades... that's 96 parts for prop blades alone. If I reduce them to sets of 6 instead of 8, I save 24 parts.

See my above comments about the rotors.   When  was making my first prop-driven Kerbin SSTO, I found that 6 large turbine blades on a small rotor gave me the best performance overall, with max RPM happening only near my operational ceiling.  Based on that, you should have something like 120 blades on those big rotors!  FWIW,  I also found that offsetting my blades outwards a bit gave them more  lift per blade at the expense of requiring more torque, with the caution that you'll need a bigger nose cone because exposing the blade bases to the wind creates terrible drag.

9 hours ago, KerikBalm said:

Perhaps with more EC generation, I can get to a higher altitude, and I won't need as much fuel for the suborbital 1st stage, and I can get a virtuous cycle going.

Absolutely!

[KerikBalm]

33 minutes ago, herbal space program said:

I'm pretty sure hypothesis 2 is correct. When I had the panels mounted backwards behind the nose cones, I was not actually able to do anything that snapped them off, although I didn't push it all that hard.  I imagine a large yaw excursion could be problematic, but OTOH maybe having that nosecone in front just reduces the panels' drag beyond all reason due to how the aero model works.

I thought I used to be able to node-attach gigantors, but I'm trying it out now, and they all seem to be radial attachments... even when put on nose cones.

Consistent breaking at 180 m/s... I even removed all rescale mods to see if that had anything to do with it

 

[fourfa]

I have an idea for shenanigans... mount the base of the gigantor inside a closed service bay (or cargo bay, or closed fairing), and extend the panel - is it able to be shielded from drag and still collect EC?

[KerikBalm]

4 minutes ago, fourfa said:

I have an idea for shenanigans... mount the base of the gigantor inside a closed service bay (or cargo bay, or closed fairing), and extend the panel - is it able to be shielded from drag and still collect EC?

I tried that, starting extended, with the base inside a fairing, it gets drags and breaks. Starting retracted, it gets no drag, but gives a message that it can't deploy

[fourfa]

I wonder if there's a way to trick it, using a service bay and changing the open/closed state of the bay during the deploy animation, and catch it out.

Or with advanced tweakables on, is there a 'deploy while shielded' option?  sorry, I can't get in the game right now to check myself...

[Lt_Duckweed]

Panels cannot produce ec while shielded.  Even if extended and shielded they will display a message that they are blocked by aero shielding.

 

As for blades, I have found that offsetting blades inwards rather than outwards significantly increases performance.  Due to the way ksp handles prop blades, the reduction in torque needed is a lot larger than the decrease in blade speed.  Normally the reduction in blade speed is a downside and means less thrust. But this isn't really a problem on Eve because the lower speed of sound means you want a lower blade speed so you don't exceed the fan blade's efficient region.

The end result is the number of blades you need to power the craft stays about the same, but the ec and rotor counts are reduced by a large amount.

Edited July 23, 2021 by Lt_Duckweed

[Lt_Duckweed]

Just tested, regardless if orientation, gigantors break when dynamic pressure exceeds 16kPa

[herbal space program]

 

2 hours ago, Lt_Duckweed said:

Just tested, regardless if orientation, gigantors break when dynamic pressure exceeds 16kPa

Well  on the upside,  I think that with the panels facing backwards you could still probably manage to keep it below that hard limit for the entire propeller phase of the Eve flight.  I'm pretty sure my plane was only going 160 m/s or so at 20km on Eve, although OP's craft looks like it has relatively less wing area than mine does. I might give it a try later just to see...

Edited July 23, 2021 by herbal space program

[KerikBalm]

22 hours ago, Lt_Duckweed said:

Just tested, regardless if orientation, gigantors break when dynamic pressure exceeds 16kPa

Hmm, in my "high altitude" pics above, between 10,200 and 10,900, and nearly 140 m/s, dynamic pressure was exceeding 26 kPa.

Looks like I will need a lower wingloading, or to see how it handles at a higher AoA.

(I think I can drop some fuel and an engine pair if I have the power to climb higher)

Angle to the relative wind seems to matter too though, so I wonder how much AoA they can take before breaking