Landing spaceplanes on Duna.

[Ol’ Musky Boi]

So in preparation for a laythe space plane mission, I decided to fly 2 Kerbals to Duna and back as practice. Cos’ I’ve never really flown  space planes before you see. Anyways I’ve been trying to land the damned thing for an hour now and Its 1:20am, but I can’t seem to make my approach any slower than 200m/s. I did bring drouge chutes, but I foolishy positioned them at the back of the plane, so deploying them causes me to nosedive. Thinking about it now, I may need to pump some fuel further back, because my plane might have became front heavy after I completed my transfer burn. But screw it, I’m going to bed now. If you have any advice it would be appreciated.

[Mako]

Practice landing on Kerbin.

Seriously. Duna's atmosphere is rather thin compared to Kerbin and Laythe and that's probably why you're having trouble slowing down. Landing practice on Kerbin would give you a better idea of what to expect. I'm sure someone will correct me if I'm mistaken in this, but I've always tested Laythe landers/planes on Kerbin.

Good luck.

Edited April 14, 2018 by Mako

[Raptor9]

Yeah, Kerbin is a much closer analog to Laythe, both in gravity and atmospheric density.  Duna's atmosphere is so thin it requires a much higher landing speed, and is harder to slow down and change direction.  Plus only rocket engines work in Duna's atmo.

Duna:
- about 30% Kerbin's gravity
- very thin atmosphere providing little lift, however little drag
- no oxygen so only rocket engines work

Laythe:
- about 80% Kerbin's gravity
- atmosphere is slightly thinner compared to Kerbin, but produces adequate lift
- jet engine thrust will suffer a little, as if flying at high altitudes at Kerbin; however due to the lower drag and slower orbital velocity, I find it a little easier to get to orbit compared to Kerbin

I would practice flying the spaceplane around Kerbin to simulate the flight sequences between Laythe orbit and the surface, but you could still practice the interplanetary transfers to Duna and back before going all the way to Laythe.

Edited April 14, 2018 by Raptor9

[qzgy]

I concur with what the others here have already said. Basically any space plane that works on Kerbin will work on Laythe. Laythe actually is even better for SSTO'ing since the gravity is lower compared to Kerbin and the atmosphere is also smaller.

Duna needs quite specialized spaceplanes. The one time I managed, my craft was basically a flying wing with a nuke on the back for propulsion. Was decently difficult to land too though cause of the thin atmosphere.

[Bill Phil]

Rocket assisted landing, anyone?

Duna is a bad place to practice for Laythe. Kerbin works much better.

[DerekL1963]

You can also use a Sandbox save and the Hyperedit mod and practice on Laythe itself.  That's how I do all of my engineering development.

[Ixamus]

I have never done spaceplanes, but I fly modded aircrafts in Duna all the time. I land them like this.

Note that I have thrusters pointing downward since parachutes alone are not enough for safe landing. It's possible to land horizontally to Duna but it's difficult and often requires some kind of retrothrust to slow down. Having sensible stall speeds requires enormous wing area which makes flying at Kerbin very difficult. My is extremely slow at Kerbin.

Landing at Duna will be easiest in areas of low elevation. The midland sea is probably the best choice for horizontal landing and takeoff. It's also relatively flat.

But keep in mind that landing to Duna can often result this:

[KerikBalm]

I pretty much always do rocket assisted landings on Duna. Trying to add enough wing area to land slowly is not a good solution IMO, particularly since the low gravity makes any landing bouncy and ground friction takes longer to slow you down.

If you do it though, I usually deploy a drogue chute (drogue being the function, not the part name, a normal chute can work) right at touchdown, mounted as far back as possible, to slow my craft down without the use of wheel brakes. All that drag at the back also helps keep it point forward. during the rollout.

Here's an old Duna surface to Duna orbit spaceplane shuttle I made. It SSTO'd from kerbin with some strap on airbreathers (which it discarded in LKO, and I later recovered back at KSC).

Spoiler

Obviously, it lands using parachutes and rocket thrust. It uses its wings to glide right over the target area, so that chutes can be popped at the right time so that it lands close to a surface base.

Wings can work for very light craft, this one used modded electric motors (rescale of goliath and then .cfg file editing). It flew slowly enough to land without special tricks... but it won't go to orbit.

Spoiler

This next one was on a modded duna with a thicker atmosphere (but still rather thin), but it shows the stabilizing drogue chutes for a rollout, but probably deployed too early

This next one is a cargo spaceplane that could deploy and recover 2.5m rover payloads (like jumbo 64 tanks on wheels, or mining + ISRU rigs, 2.5m labs, etc), and used rockets to land. Not chutes were used so that it could operate without kerbals servicing it (although ISRU refuelling is very slow like that)

It uses its wings to slow down and change course.

RCS systems enable it to take on a very high AoA for more aerodynamic breaking:

And that high AoA also allows the lift rockets to slow it down... but the 2nd set  of lift rockets needs some tweaking depending on the payload to keep things balanced:

I later moved up to a 3x rescale, and also increased Duna's gravity to 0.376 G (the same as mars'), so my spaceplanes had to get bigger. This next one uses "ram rocket" engines that I modded for horizontal propulsion, but the rest of the craft is all stock (including the VTOL rockets).

Ok... its its not technically VTOL, but touching down with only 14 m/s horizontal speed is pretty good:

Getting it to orbit was a bit hard:

Spoiler

Launching from Kerbin, the ramrockets are in normal rocket mode:

The "ramrockets" that I made are a bit like rapiers that consume LF an O, and get 1440 atmospheric Isp, but the atmospheric mode only works above mach 0.4 and below mach 6, so rocket mode is used for the initial acceleration, and the final circularization

The air augmented thrust is saying air combustion failed because its only at mach 0.24

More massive Duna SSTOs landing in .376 G, with much more fuel mass because its 3x gameplay (these ones use the modded engines, but they really carried excessive amounts of fuel for those engines, and the design still worked when they were replaced with 3x pairs of aerospikes and 1 pair of vectors to maintain CoM)

These landings are rather exciting though...

On approach:

A rather extreme braking maneuver:

And another, but it will get the plane pretty close to the surface base:

A shot of one of the landings post- braking maneuver, begining near vertical descent and controlled with RCS:

This one is about to touch down, going a bit backwards:

touchdown:

and more descent an touchdown:

Spoiler

16.9 m/s... not bad

With surface refueling, and a stock sized system with stock gravity.... its definitely an achievable goal.

(note, that uses KPBS parts, but stock ISRU rovers work as well for refueling on the surface)

Spoiler

a deployment test of a fully stock mining + ISRU rover:

 

[Ol’ Musky Boi]

Thanks for the advice everyone, I didn’t really know what the gravity and atmospheric density on Laythe was like, so I assumed if I could get to Duna then Laythe would be no problem. I almost gave up my landing, but I decided to turn my plane around and try a suicide burn, and it worked! 2 Kerbals safely on the surface of Duna. 

[StarStreak2109]

The Lonesome Robots DADV also works just peachy for safe Duna landing.... It's a mix  between space planes and rockets...

 

[Ol’ Musky Boi]

Bear in mind I’m playing stock, (Apart from Kerbal engineer).

[Ixamus]

6 hours ago, KerikBalm said:

Wings can work for very light craft,

Question of weight is complicated one. I do believe that in theory you can fly very heavy crafts in Duna atmosphere simply by adding more wings and thrust. The requirement of thrust is still relatively low in comparison to what would be needed in Kerbin.

My own bigger dunaplane is relatively heavy. It uses three pairs of aeroplane main wings and to pairs of large delta wings to gain lift. It can get to orbit with aerospikes.

The main problem I have experienced with planes being too heavy is the Kraken. If I load my plane full with fuel and try to use physics warp the plane starts to wobble violently and disassembles itself. I have not yet figured out if there is universal weight limit for Duna aeroplanes and physics warp, or if the problem is my design or the autopilot mod I use.

[KerikBalm]

Well, its just a matter of wings per unit mass... but as you go with heavier craft, it becomes increasingly hard to add enough wings without part clipping (sure you can have 50 wings clipped into the space of 1, but I don't do that). If you don't part clip, then you have weird biplane designs, triplanes, tandem wings, etc. If you just go for a large wingspan and thick chord, then it becomes very likely that you'll clip a wing on the ground because of the size of your craft relative to terrain features.

You can SSTO down to the surface of Tylo and back up to orbit, stock Duna is super easy in comparison... so its really easy to have enough TWR and dV to spare to do a propulsive landing (it might even cost you less fuel than it would cost to haul those wings around all over the place).

[juanml82]

I've done a few Duna planes in the past:

Use retrorockets for slowing down if you want to do an horizontal landing - airbrakes simply won't slow you down

You'll need plenty of wing. But you also need to consider the rolling terrain. A wide plane is very likely to crash stuff into the ground so put landing gear at the wing tips and use structural panels as bumpers, so you can hit the ground at 50 m/s without breaking anything

A plane that flies well in Kerbin shouldn't behave well in Duna and viceversa.

Use rcs or vernier thrusters to manuever, as control surfaces are of limited use

Edited April 14, 2018 by juanml82

[GluttonyReaper]

10 hours ago, Ixamus said:

-snip-

I have to ask, why is your Duna so... purple?

[Ixamus]

1 hour ago, GluttonyReaper said:

I have to ask, why is your Duna so... purple?

First of all it's Duna's icecap. I have also changed the lighting setting significantly darker to see the ground features. Otherwise the scenery would often be just pure white. I believe that made the purple color more visible.

[StarStreak2109]

22 hours ago, Ol’ Musky Boi said:

Bear in mind I’m playing stock, (Apart from Kerbal engineer).

Yeah, okay. You can still take it as a reference, tho...

[n.b.z.]

One way to get an idea of the difficulty of landing on Duna, before actually flying there, is to practice landing somewhere high in the mountains on Kerbin.

While you still have higher atmospheric density on Kerbin, you add the factor of unvafourable Terrain. If you can't land your plane in Kerbin's mountains, that same plane will be difficult to land on Duna.

Drogues in the back are actually a good idea if you really don't want to spend fuel to slow you down. But on Duna, you need the big chutes (such as the blue radial ones) to act as drogues. Having them in the back will keep the plane pointed straight, in case your nose-wheel contacts first and knocks your craft into a pitch-up motion.

Ideally, they should be mounted in the back and a bit above the vertical position of the Center-of-Mass. This way, the chutes "want" to orient the plane in a slight nose-up attitude, 5 or 10 degrees, like the flare for a landing.

[Ol’ Musky Boi]

6 minutes ago, n.b.z. said:

One way to get an idea of the difficulty of landing on Duna, before actually flying there, is to practice landing somewhere high in the mountains on Kerbin.

While you still have higher atmospheric density on Kerbin, you add the factor of unvafourable Terrain. If you can't land your plane in Kerbin's mountains, that same plane will be difficult to land on Duna.

Drogues in the back are actually a good idea if you really don't want to spend fuel to slow you down. But on Duna, you need the big chutes (such as the blue radial ones) to act as drogues. Having them in the back will keep the plane pointed straight, in case your nose-wheel contacts first and knocks your craft into a pitch-up motion.

Ideally, they should be mounted in the back and a bit above the vertical position of the Center-of-Mass. This way, the chutes "want" to orient the plane in a slight nose-up attitude, 5 or 10 degrees, like the flare for a landing.

I had four droughts at the back, two at the top and bottom, I only used the top ones for my attempted landing, but they were small and didn’t do much. In the future I’ll probably use retro-rockets for Duna landings.