Duna Electric Rotocraft

[Shadowmage]

Hi all;

Curious if anyone has designed electric rotocraft capable of flying on Duna?  Helo, coax, quad, tilt-rotor, std fixed-wing, whatever.  Would love to see images.

 

Trying to get an idea of what is needed for allowing for aero flight on Duna.  I built an excellent little tilt-rotor that flies great on Kerbin; ascends stably at ~1.5 degree of prop pitch in vertical mode, and can do ~150m/s in airplane mode.  Sadly, when testing on Duna the best I could get is a semi-controlled 30m/s vertical descent.  The props didn't seem to produce much/any lift at any sort of RPM or blade pitch; craft dropped at 30m/s regardless of 0-degree, 40-degree, or 80-degree of prop pitch.

I only tested the one iteration on Duna though.  It used 2x the smallest airplane prop per rotor (4 rotors total).  My next test will be a 4-bladed variant; possibly just needed more actual lift?  I also experimented with using helicopter blades for the tilt-rotor blades.  Worked really well in helicopter mode/vertical ascent (in Kerbin testing at least), but the max speed in airplane mode was abysmal at something like ~35m/s.

 

Anyone have any luck at Duna rotorcraft they would like to share/show-off?

 

[OHara]

Brikoleur made a few,  before stock prop-blades, on kerbalx

Snark made a hybrid, on the general-purpose thread

[Shadowmage]

5 hours ago, OHara said:

Brikoleur made a few,  before stock prop-blades, on kerbalx

Snark made a hybrid, on the general-purpose thread

Thanks for the links.  Certainly more information than I had before

Looks to be the trick is providing separate lift and thrust mechanisms.  I'll post up some pics of my little beastie, and try and document whatever I find for a working solution.  From the examples you've linked -- I might have been trying to go 'too small'

[Shadowmage]

Few pics of the first attempt, that worked so well on Kerbin, but failed to produce sufficient lift/thrust on Duna.  All are mostly the same craft at various iterations:

~1.2t, ~48 parts.  Infinite flight time in sunlight.

Streamlined probe version at max speed:

Jeb practicing VTOL

Max speed of the crewed version:

Which also folds up:

 

And.... props are some kind of magic in regards to drag/max speed.  This is a full-speed dive on the craft in helo mode with powered props at hover pitch; it caps out at ~70m/s, gravity be darned.  Drops like a rock if I turn off the props though

 

I'll be playing around with making a Duna capable version, and post any successful results.

[Shadowmage]

The updated fifth revision seems to fly acceptably on Duna.  Main change was to increase the # of blades per rotor, from two to four.  Blade pitch acts very strange compared to Kerbin; some difference was expected, but this is just odd.

 

 

Don't mind the odd planet colors.  Just landing in an Ike-eclipse of the sun...

 

[BigFatStupidHead]

I made a little quad-copter drone that flies very well on Kerbin, but fails to produce any lift on Duna. Used the smallest propellers also; maybe they're too small to produce lift on Duna?  Modified the rotors to a coaxial setup using Propeller B, it can get into the air but doesn't have much speed.

[Shadowmage]

11 hours ago, BigFatStupidHead said:

I made a little quad-copter drone that flies very well on Kerbin, but fails to produce any lift on Duna. Used the smallest propellers also; maybe they're too small to produce lift on Duna?  Modified the rotors to a coaxial setup using Propeller B, it can get into the air but doesn't have much speed.

Your rotor is the same basic setup as mine above; smallest props on the smallest rotor.

Try increasing it to four blades per rotor.  And then try using a deployed pitch in the range of ~15-20 for hovering (maybe less depending on mass).

When I switched from two to four blades-per rotor on the craft, it went from 'unable to hover' to 'capable of controlled and sustained flight'.

[BigFatStupidHead]

3 hours ago, Shadowmage said:

Your rotor is the same basic setup as mine above; smallest props on the smallest rotor.

Try increasing it to four blades per rotor.  And then try using a deployed pitch in the range of ~15-20 for hovering (maybe less depending on mass).

When I switched from two to four blades-per rotor on the craft, it went from 'unable to hover' to 'capable of controlled and sustained flight'.

Oh, this IS the modified copter. It uses four of the mid-sized props and is capable of slow flight, but couldn't seem to get any lift during fast decent. It benefits greatly from four props per blade.

Still can't save itself from a fast decent in that thin Duna air.

[Guest]

Yep I made a few, including a tilt-rotor I'm operating there in career mode. It's 1.7.2 though so uses rotors made with elevons rather than the official rotor blades. It works extremely well -- flight on Duna is different than on Kerbin and it took me a while to become properly comfortable with it but once I did it's lovely, easily the most fun craft to operate there I've made. It cruises at over 100 m/s and is remarkably easy to hover, land, and take off. It's 100% solar-powered. 

https://kerbalx.com/Brikoleur/BAK-6000D-Ikarus

Like most Duna craft, she needs rather more wing/rotor than a comparable craft for Kerbin or Eve.

[Shadowmage]

15 hours ago, BigFatStupidHead said:

It uses four of the mid-sized props and is capable of slow flight, but couldn't seem to get any lift during fast decent. It benefits greatly from four props per blade.

After retrying mine yesterday/last night, I found that it is extremely sensitive to... just about any sort of modification.  Added ~0.05t to it, and now it barely can hover under full power.  Sad times.

Even more strange, it seems to get an increase in lift if I decrease prop RPM from 460 to ~400.

Really wanted some sort of micro-aerocraft for Duna, but it looks like I'm going to have to go bigger if I want it to work.  Trying to use props for lift (trying to stay small) is apparently not going to be sufficient, and might have to switch over to using a dedicated set of helicopter blades for lift.

 

19 minutes ago, Brikoleur said:

Like most Duna craft, she needs rather more wing/rotor than a comparable craft for Kerbin or Eve.

Yeah, been awhile since I've done anything aero on Duna (since before 1.x aero update), and I'm learning that quickly.  Always knew to pack extra chutes, but the changes to thrust/drag in flying machines is... odd... to get used to.

[BigFatStupidHead]

3 hours ago, Brikoleur said:

Yep I made a few, including a tilt-rotor I'm operating there in career mode. It's 1.7.2 though so uses rotors made with elevons rather than the official rotor blades. It works extremely well -- flight on Duna is different than on Kerbin and it took me a while to become properly comfortable with it but once I did it's lovely, easily the most fun craft to operate there I've made. It cruises at over 100 m/s and is remarkably easy to hover, land, and take off. It's 100% solar-powered. 

https://kerbalx.com/Brikoleur/BAK-6000D-Ikarus

Like most Duna craft, she needs rather more wing/rotor than a comparable craft for Kerbin or Eve.

She's a pretty one!

3 hours ago, Shadowmage said:

After retrying mine yesterday/last night, I found that it is extremely sensitive to... just about any sort of modification.  Added ~0.05t to it, and now it barely can hover under full power.  Sad times.

Even more strange, it seems to get an increase in lift if I decrease prop RPM from 460 to ~400.

Really wanted some sort of micro-aerocraft for Duna, but it looks like I'm going to have to go bigger if I want it to work.  Trying to use props for lift (trying to stay small) is apparently not going to be sufficient, and might have to switch over to using a dedicated set of helicopter blades for lift.

 

Yeah, been awhile since I've done anything aero on Duna (since before 1.x aero update), and I'm learning that quickly.  Always knew to pack extra chutes, but the changes to thrust/drag in flying machines is... odd... to get used to.

Ditto on the sensitivity to modification. And very interesting on the lift increase from decreased RPM. I wonder what is going on there... shouldn't be any sort of mach effects with a thinner atmosphere, but this is KSP after all. It will require more research.

[Shadowmage]

1 minute ago, BigFatStupidHead said:

And very interesting on the lift increase from decreased RPM.

Yeah, made zero sense to me, but was consistent and repeatable on that craft.  Thrust decreased below ~400 RPM, and decreased above it as well.

I'll be experimenting more with Duna rotorcraft through the week, until I have at least a couple usable designs, and will post up any other information or interesting findings I come across.

[Guest]

2 hours ago, Shadowmage said:

Yeah, made zero sense to me, but was consistent and repeatable on that craft.  Thrust decreased below ~400 RPM, and decreased above it as well.

With constant pitch, or varying pitch to find maximum thrust?

If constant pitch it makes sense as thrust is a function of pitch, radial velocity, and forward velocity.

[Shadowmage]

9 minutes ago, Brikoleur said:

varying pitch to find maximum thrust?

Toying with pitch the whole time to find maximum thrust.

Going to do more experimentation this evening to see if I can find the why behind it.  Likely some contributing factor that I'm overlooking that caused what was seen as a side-effect.

[BigFatStupidHead]

Here's my Duna SCIENCE-copter on a test-flight.

Makes a good clip, pretty maneuverable, and can fly forever in the sun. I haven't tested its full capabilities yet, but I'm pretty pleased with it.

I didn't notice any difference between 400 and 460 RPM, but hey, it saves me some power.

[Shadowmage]

Well, my recent testings have not gone well at all.

Pretty sure the reason my craft above failed on its second attempts were simply the duna terrain level I was at.  Huge difference in air pressure between 3km and 500m ASL on duna.  However that just means I have a craft that an only fly in the lowlands.  No good.

All of my other attempts at micro-scale Duna rotorcraft have had very similar outcomes.  Tear-themselves-apart-from lift on Kerbin, but can't seem to do anything on Duna.

 

Haven't tried sending anything larger to Duna yet for testing, because that is simply not what I was trying to accomplish here.  I was looking to design a small (<2t) functional, crewed, science-capable craft, which does not seem to be possible.  Just the blades and engines to get it flying on Duna are > 2t, and huge.

 

@Brikoleur  As a sanity check, I did design a tilt-rotor similar to yours posted above, but using stock helicopter blades.  Apparently those things are garbage compared to ailerons for use as rotors, as the most it could manage under full blade-pitch was ~60m/s (150% authority limiter).  And that was on Kerbin; doubt it would pull half that on Duna.  Those helicopter blades seem to have some really odd properties though, where I couldn't even force it to go faster in a nose-first vertical dive.

Flew great at 60m/s on Kerbin though.  Wouldn't be any faster than a rover on Duna unfortunately.

 

*sigh*

Back to rovers it is.

[Guest]

I think the top speed of mine on Kerbin is somewhere around 60-75 m/s as well. They're a lot faster on Duna.

I still haven't used the new prop/rotor blades so I can't comment on that. However I do know that with the elevons you need very steep blade pitch to go fast, on the order of 75 degrees. If the stock blades don't go that far using deploy/authority limiter then that could be the problem right there; the workaround would be to mount them on servos that allow unlimited rotation.

I also don't know how the props and rotor blades behave differently, but it might be worth experimenting to see if prop blades work better. 

Edited July 26, 2019 by Guest

[Snark]

On 7/22/2019 at 3:04 PM, Shadowmage said:

Looks to be the trick is providing separate lift and thrust mechanisms.

Well, not necessarily.  My own craft does do that,

...but it doesn't actually need to.  It can fly just fine on the helicopter blades alone, i.e. flying somewhat nose-down in order to generate forward motion.  It's perfectly happy to do that, can do a vertical takeoff and landing, can cruise on the level at around 35-40 m/s on heli blades alone.

The forward-thrust props are just for putting on extra speed.  When I'm running those, I can get up to around 60-80 m/s horizontal cruise speed, depending on altitude (Duna air pressure is pretty altitude-sensitive).

 

[Shadowmage]

Thanks for the responses and feedback guys, much appreciated

I have managed to create a semi-micro VTOL that flies very well on Duna.  I'm sure it could be refined a bit more with some further knowledge and testing. but the design was holding up my mission planning, so I went with what worked.  Barely managed to sneak in under my 2t goal, though it was a bit wider than I had desired.  Indeed the trick seems to be to simply give more lifting surface than you might think necessary, by about 3-4x what you need on Kerbin.

Stuck with a minimalist design, only the bits needed to make it function.  Wings are mostly decorative / to give a place to mount stuff.  They are angled such that on Kerbin they provide decent lift, but in the thin Duna air... its nothing compared to the rotors.  Has sufficient lift from the rotors to fly up to at least ~6km and remain very controllable, haven't tested beyond that.  Sustained top speed of ~45m/s in level flight at 6k, or ~65m/s closer to sea level.  With limiting of the rotors' motor torque it is capable of indefinite flight under solar power, but has very limited battery capacity otherwise.

Extremely controllable at all attitudes and altitudes, it is about as COM and COP neutral as a flying machine can get, in every angle of attack.  Wings are directly on the vertical COM and COP, so even in vertical flight they do not effect stability.  Even with SAS off it simply flies wherever you point it, at whatever attitude you left it (aside from from very slight weathervane effect from the tiny tail-fin). 

It has a bit lower top-speed than I really wanted, but given the very gentle nature of the craft and its well rounded flight capabilities, I'll call it a win.  Jeb got a fun little rockhopper, and I got to learn a few things about KSPs newest physics toys

[KerrMü]

@Shadowmage

Hi, 400 RPM seems to be the sweetspot. Thank you very much for that info.  

This was very helpful for my little project. From earlier Duna planes I kinda knew that surface is key, but for testing this craft started out with 2 motors with 4 blades each... I could have just left them at home. Now I ended up with 4 motors and 48 blades and it flies really nicely.

[Flying dutchman]

In my experience flying on duna isn't the problem. The landing is as stall speeds are very high and the terrain is rough.

[KerikBalm]

Well, I'm working on a small helo that can deploy from a mk3 cargobay using the new helo blades. I have 4 of the medium sized helo blades, they aren't at 90 degrees to each other, more like 15, 165, 15, 165, so that they can fit in the mk3 bay without adding additional parts for a folding mechanism. 2 of the tiny rotors are used, with their max torque turned down (un necessary, but saves power consumption and weight). 1 Rtg powers it, and it can break 50 m/s with a full science kit (including large scanner arm, and experiment storage container), it was getting close to 60 m/s. With its weak rotors, it took a while to spin up to 460 rpm, but it was able to keep the rotors at that speed in the thin air.

I was testing it in my scaled up and custom modded system, which makes flying on Duna a bit harder, as Duna's gravity gets increased 25% (0.3 G to 0.376 G -> ie martian gravity). The 3x rescale of body radius and SMA doesn't really affect flying on Duna. Terrain height got rescaled to 1.5x, and I made the atmosphere 90km high (1.8x) so the highest parts on Duna are in a little thicker air (but stronger gravity). THere was also a height offset lowering elevation a little so I could have some terrain below 0 meters (stock duna's lowest boing is 120 something meters), and have standing water at its lowest points.... Anyway... its still pretty comparable.

My first attempt to see how high my helo could fly ended in disaster, after climbing slowly at first, I kept adjusting blade pitch until I reached 30 m/s upward velocity. I did not adequately adjust blade pitch once climb rate slowed, and I found myself reaching a maximum height, then falling down, the fall reached over 70 m/s, and it took a while ot realize that I needed to lower blade pitch into negative values to maximize lift and get optimum blade AoA.

I was only able to slow my fall to 20 m/s before impact.

Flying around mostly horizontal went well, but that thin air means that you can't change your velocity very quickly, so you need to control your vertical descent rate well, or there simply won't be enough air to stop you.

Still, its perhaps too slow for my taste. I may want to make a horizontal prop plane with folding wings for faster traversal of Duna.

The rocket powered VTOL with a mk3 cargo bay that I'm using can get the science helo rapidly to the general vicinity of a desired location, but at 3x, its dV margins are thin, and I dislike straying from the equator in what is meant as a surface to orbit shuttle.