Design a SSTO that uses propellers or rotors instead of jets during atmospheric ascent

[It'snorocketscience]

Some people were saying that props and rotors aren't worth carrying around to and from Kerbin—a normal SSTO with a detachable Duna plane would be better, they said. Maybe. Maybe not.

A good prop plane setup will get you to 15k on Kerbin at 200 m/s or so. I will figure out how much dV that saves empirically tomorrow...

But what I love about the "prop SSTO to duna" concept is that the props are not dead weight on Duna. I've done some tests and found that, during ascent from Duna surface to orbit, a prop setup saves 200~300 m/s of dV, plus another 25-100 m/s depending on your engines (engine efficiency increases as atmosphere pressure decreases). There's also the bonus of props boosting your rocket TWR in the lower atmosphere, and the benefit of free Duna landings—no suicide burn or parachute spam required to come to a safe stop.

(The dV estimate was determined empirically. It assumes you have a propeller plane that can reach 200 m/s at 7.5k on Duna, and that you manage propeller blade pitch and drag very carefully.)

But there's a lot of room for improvement in that estimate. I made that estimate with a craft that had too many wings and fans for Duna. You read that right, I over-engineered my first Duna plane. The plane carries 7 tons of wings and propellers to haul 8 tons of fuel up to 7.5K (19.5 tons total), but a full load of fuel is complete overkill in my case—I only need full fuel tanks to escape Kerbin. Those extra wings and props added a fair amount of drag, which could've messed up my dV estimate.

Edited May 1, 2020 by It'snorocketscience
Edited for clarity.

[xendelaar]

On 4/29/2020 at 4:03 PM, Mephisto81 said:

This should work on Kerbin as well:

https://kerbalx.com/Mephisto/XE-01-APEX-Mk-VI-Eve-SSTO

 

nice design! are you saying that you're able to get into orbit using only 3,600 m/s delta v? My vessels need 4,700 to get into orbit. How did you manage to pull this off?  could you elaborate on the design? i see a lot of stuff nicely clipped behind fairings and casings.

12 hours ago, It'snorocketscience said:

Some people were saying that props and rotors aren't worth carrying around to and from Kerbin—a normal SSTO with a detachable Duna plane would be better, they said. Maybe. Maybe not.

A good prop plane setup will get you to 15k on Kerbin at 200 m/s or so. I will figure out how much dV that saves empirically tomorrow...

But what I love about the "prop SSTO to duna" concept is that the props are not dead weight on Duna. I've done some tests and found that, during ascent from Duna surface to orbit, a prop setup saves 200~300 m/s of dV, plus another 25-100 m/s depending on your engines (engine efficiency increases as atmosphere pressure decreases). There's also the bonus of props boosting your rocket TWR in the lower atmosphere, and the benefit of free Duna landings—no suicide burn or parachute spam required to come to a safe stop.

(The dV estimate was determined empirically. It assumes you have a propeller plane that can reach 200 m/s at 7.5k on Duna, and that you manage propeller blade pitch and drag very carefully.)

But there's a lot of room for improvement in that estimate. I made that estimate with a craft that had too many wings and fans for Duna. You read that right, I over-engineered my first Duna plane. The plane carries 7 tons of wings and propellers to haul 8 tons of fuel up to 7.5K (19.5 tons total), but a full load of fuel is complete overkill in my case—I only need full fuel tanks to escape Kerbin. Those extra wings and props added a fair amount of drag, which could've messed up my dV estimate.

awesome! so you went for a plane design. Very interesting.. can't wait to see it in real life. How long did it take to design the craft?

Edited May 1, 2020 by xendelaar

[Mephisto81]

Hi Xandelaar

it started with a video by realseek: he made an single stage to orbit from Eve sea level based on propellers, Vectors and Nervs. Basically, the propellers will bring the craft to about 15km above sea level. Vectors will provide high thrust supported by Nervs. When the oxidiser runs out, the Nervs have to carry the craft all the way to orbit.
As I found out, this is really, really tricky to pull of.
Kergarin made a version of his own, and Chargan put two crafts on KerbalX who managed to do this as well.
It took me weeks, to rebuild the craft from realseek just by reviewing his video. Same with the craft from Kergarin. A vessel from chargan was downloaded from KerbalX.
I can recommend this thread by Kergarin:

But rebuilding them was only part of the issue. To actually reach Eve orbit, the flying in atmosphere with propellers and the flight profile had to be almost perfect. Personally, I was not able to pull it off. With every craft from other creators, I fell a couple of hundred meters short.

What worked finally, was an approach with 4 Vectors  and 3 Nervs as opposed to the 3 vectors and 2 Nervs of realseek. This led to a higher thrust to weight ratio from the nervs.
To get bigger margins and to negate drag, lots of fuel tanks are clipped inside fairings.

The propellers are shielded from drag inside the service bays during rocket flight. As we all saw in the video from Lt. Duckweed and Stratzenblitz, 1.25m service bays are sufficient to shield R25 Propellers from drag, even if they stick out a little. As the center of lift is affected by the propellers and can move to different positions if service bays are opened or closed, I followed a similar layout as Chargan used: Build the propellers very close to the center of lift.
This way, the craft was flyable in all states.

The hardest part was to reach a certain speed with vectors: if you can reach 2.800 m/s when oxidiser runs out AND your aposapsis is high enough to buy you some time AND you have enough liquid fuel for your Nervs, you can make it to orbit. It took me roughly six weeks, where I spent every other evening in front of my PC to get to the point, until I had a craft, that could reach Eve orbit in a somewhat repeatable manner. 

You can get away with TWR of the vectors of slightly lower than 1, because the wings provide lift. You start out with horizontal flight and slowly transition to an s-curve. Ar max Q, you have to throttle down a bit to prevent overheating. Curiously, throttling back at max Q led to a higher velocity when oxidiser run out. When this happens, the Nervs will have to do the rest.
Basically, the difference between 2,800 m/s and the final 3,080 m/s have to be provided by the Nervs. With proper flying, more than 300 m/s are left over in a stable Eve orbit.

Interestingly, Chargan had a very peculiar ascent profile, where he was not able to fully establish an orbit at apoapsis. But he continued to burn his Nervs whilst the craft plummeted back to a suborbital trajectory, only to get to a stable orbit again on the other side of Eve. This happened to me as well several times with a previous craft.

Have fun!

 

[xendelaar]

On 4/27/2020 at 4:29 PM, KerikBalm said:

KA

  Reveal hidden contents

Its a VTOL tilt rotor on Kerbin that can lift an orange tank, but doesn't lift on Duna)

  Reveal hidden contents

  Reveal hidden contents

 

But none of that meets the challenge requirements of SSTOing from Kerbin. Even at 1x scale, I never did that much, I don't see the point in taking deadweight along for the ride when you can leave it in LKO and still recover it. I always aimed for reusable over SSTO... to the point that I stopped making SSTOs, and instead made re-usable 2 stage launchers (at 3x rescale, SSTOing is still possible with >10% payload fraction, but really long LV-N burns are needed. Time to orbit and payload fraction were much improved with re-usable 2 stage launchers).

How did I miss this post! Your build looks very sleek!

56 minutes ago, Mephisto81 said:

Hi Xandelaar

it started with a video by realseek: he made an single stage to orbit from Eve sea level based on propellers, Vectors and Nervs. Basically, the propellers will bring the craft to about 15km above sea level. Vectors will provide high thrust supported by Nervs. When the oxidiser runs out, the Nervs have to carry the craft all the way to orbit.
As I found out, this is really, really tricky to pull of.
Kergarin made a version of his own, and Chargan put two crafts on KerbalX who managed to do this as well.
It took me weeks, to rebuild the craft from realseek just by reviewing his video. Same with the craft from Kergarin. A vessel from chargan was downloaded from KerbalX.
I can recommend this thread by Kergarin

But rebuilding them was only part of the issue. To actually reach Eve orbit, the flying in atmosphere with propellers and the flight profile had to be almost perfect. Personally, I was not able to pull it off. With every craft from other creators, I fell a couple of hundred meters short.

What worked finally, was an approach with 4 Vectors  and 3 Nervs as opposed to the 3 vectors and 2 Nervs of realseek. This led to a higher thrust to weight ratio from the nervs.
To get bigger margins and to negate drag, lots of fuel tanks are clipped inside fairings.

The propellers are shielded from drag inside the service bays during rocket flight. As we all saw in the video from Lt. Duckweed and Stratzenblitz, 1.25m service bays are sufficient to shield R25 Propellers from drag, even if they stick out a little. As the center of lift is affected by the propellers and can move to different positions if service bays are opened or closed, I followed a similar layout as Chargan used: Build the propellers very close to the center of lift.
This way, the craft was flyable in all states.

The hardest part was to reach a certain speed with vectors: if you can reach 2.800 m/s when oxidiser runs out AND your aposapsis is high enough to buy you some time AND you have enough liquid fuel for your Nervs, you can make it to orbit. It took me roughly six weeks, where I spent every other evening in front of my PC to get to the point, until I had a craft, that could reach Eve orbit in a somewhat repeatable manner. 

You can get away with TWR of the vectors of slightly lower than 1, because the wings provide lift. You start out with horizontal flight and slowly transition to an s-curve. Ar max Q, you have to throttle down a bit to prevent overheating. Curiously, throttling back at max Q led to a higher velocity when oxidiser run out. When this happens, the Nervs will have to do the rest.
Basically, the difference between 2,800 m/s and the final 3,080 m/s have to be provided by the Nervs. With proper flying, more than 300 m/s are left over in a stable Eve orbit.

Interestingly, Chargan had a very peculiar ascent profile, where he was not able to fully establish an orbit at apoapsis. But he continued to burn his Nervs whilst the craft plummeted back to a suborbital trajectory, only to get to a stable orbit again on the other side of Eve. This happened to me as well several times with a previous craft.

Have fun!

 

sounds like that challenge was frustrating and epic at the same time. thanks for sharing your tale with me. sounds to me this was a very difficult undertaking.  Don't know if I have the willpower to do this though, but I will give it a go.  

 

Edited May 1, 2020 by xendelaar

[It'snorocketscience]

11 hours ago, xendelaar said:

Quote

awesome! so you went for a plane design. Very interesting.. can't wait to see it in real life. How long did it take to design the craft?

 

I've spent about a week (15-20 hours) improving the same design and learning new things to improve it. It seems like each day I learn something new and use it to fix a problem, only to encounter the next problem and fail again.

I finally realized why getting to orbit is so hard with props and rotors. Props suffer from huge drag loses as you approach the 300 m/s zone just before breaking the sound barrier. (Drag naturally spikes near the sound barrier, but spinning wings suffer even more as their rotation speed causes different parts of the blades to break the sound barrier before other parts.) Helicopters have it worse—Google "helicopter speed limit".

Even if you shut off your rotors and props and adjust blade pitch during rocket flight, they still produce a lot of drag. At 15000m on Kerbin, 16 stationary large fan blades produce about 5-8 kN of drag altogether around the 350 m/s sound barrier. To put that number into perspective, each wing board and fuselage part produced 0.5-2 kN of drag each during the same conditions. That's awful—the rotors doubled the drag on my small craft.

Thankfully there's an easy solution. Place some hinges on your rotors, put the props on top, and set things up so that your props fold back (preferably into a fairing that encloses the rotor) at the push of a button. That should fix things, but I'll have to try it out tomorrow...

Edited May 2, 2020 by It'snorocketscience
Fixed formatting, improved clarity.

[xendelaar]

4 hours ago, It'snorocketscience said:

 

I've spent about a week (15-20 hours) improving the same design and learning new things to improve it. It seems like each day I learn something new and use it to fix a problem, only to encounter the next problem and fail again.

I finally realized why getting to orbit is so hard with props and rotors. Props suffer from huge drag loses as you approach the 300 m/s zone just before breaking the sound barrier. (Drag naturally spikes near the sound barrier, but spinning wings suffer even more as their rotation speed causes different parts of the blades to break the sound barrier before other parts.) Helicopters have it worse—Google "helicopter speed limit".

Even if you shut off your rotors and props and adjust blade pitch during rocket flight, they still produce a lot of drag. At 15000m on Kerbin, 16 stationary large fan blades produce about 5-8 kN of drag altogether around the 350 m/s sound barrier. To put that number into perspective, each wing board and fuselage part produced 0.5-2 kN of drag each during the same conditions. That's awful—the rotors doubled the drag on my small craft.

Thankfully there's an easy solution. Place some hinges on your rotors, put the props on top, and set things up so that your props fold back (preferably into a fairing that encloses the rotor) at the push of a button. That should fix things, but I'll have to try it out tomorrow...

sounds like a great solution.  I read in several posts that you can place the rotors in a fairing to negate the drag. but in my tests, that also resulted in zero thrust.. so I don't know what I'm doing wrong. good luck with testing.

[It'snorocketscience]

5 hours ago, xendelaar said:

I read in several posts that you can place the rotors in a fairing to negate the drag. but in my tests, that also resulted in zero thrust.. so I don't know what I'm doing wrong. good luck with testing.

I think you have to offset the blades outside so that they are mostly outside of the fairing (be careful not to offset them too far—that will cause the blade tips to blades to break the sound barrier = bad). I believe KSP decides whether if a part is "hidden" by checking if its center of mass is inside a fairing/payload bay, or not. AFAIK the prop/rotors must produce drag if they are able to produce thrust, but fairings still have the benefit of eliminating drag caused by the electric motor.

[Mephisto81]

Regarding rotors, service bays and drag
 

Rotor inside service bay, service bay CLOSED: rotor is shielded from drag. Rotor cannot produce any thrust.

Rotor inside service bay, service bay OPEN: rotor is exposed to aerodynamic forces. Rotor can produce thrust.

 

It is possible to shield from drag, even when some small parts of the rotor are outside the closed fairing. Offsetting the blades is not needed. You can check this with aerodynamic forces displayed in action menues.

It is best to the "Display aerodynamic forces in action menues" or something similar in ALT+F12 --> Physics to check, whether or not a part is exposed to aerodynmaic forces.

If it is exposed, the numbers will change constantly. Even if the craft is standing still on the runway.

Same goes for hiding other parts in fairings: you can check whether or not an engine or tank is shielded from aerodynamic forces with this. For many engines, you can find a sweet spot, where the part is shielded from drag, but can produce normal thrust without heating the fairing up.

 

Here is a picture of a rotor assembly with open service bays. (Small motor, R25 Rotors, 1,25m service bays.) It can produce thrust with open service bay. When we transition to rocket flight, we power down the motors, lock it up and close the service bays to reduce drag. You can also see some fuel tanks sticking slightly out of the fairings. They are shielded form drag as well.

Edited May 5, 2020 by Mephisto81

[xendelaar]

22 hours ago, Mephisto81 said:

Regarding rotors, service bays and drag
 

Rotor inside service bay, service bay CLOSED: rotor is shielded from drag. Rotor cannot produce any thrust.

Rotor inside service bay, service bay OPEN: rotor is exposed to aerodynamic forces. Rotor can produce thrust.

 

It is possible to shield from drag, even when some small parts of the rotor are outside the closed fairing. Offsetting the blades is not needed. You can check this with aerodynamic forces displayed in action menues.

It is best to the "Display aerodynamic forces in action menues" or something similar in ALT+F12 --> Physics to check, whether or not a part is exposed to aerodynmaic forces.

If it is exposed, the numbers will change constantly. Even if the craft is standing still on the runway.

Same goes for hiding other parts in fairings: you can check whether or not an engine or tank is shielded from aerodynamic forces with this. For many engines, you can find a sweet spot, where the part is shielded from drag, but can produce normal thrust without heating the fairing up.

 

Here is a picture of a rotor assembly with open service bays. (Small motor, R25 Rotors, 1,25m service bays.) It can produce thrust with open service bay. When we transition to rocket flight, we power down the motors, lock it up and close the service bays to reduce drag. You can also see some fuel tanks sticking slightly out of the fairings. They are shielded form drag as well.

absolutely stunning man! what are those dark things popping out of the main stack? I had a lot of drag issues with my helicopter design. I think I needed quite some extra delta v to get into orbit of Kerbin because of it. your craft looks absolutely amazing btw.

Also, many thank for the explanation of the setup and testing methods.  

Edited May 6, 2020 by xendelaar

[Mephisto81]

@xendelaar You mean the fuel tanks? FL-TX 900 and FL-TX 1800 have these ridges at the side. If you clip enough of them into a fairing of the same diameter, the ridges still look out.

https://wiki.kerbalspaceprogram.com/wiki/FL-TX900_Fuel_Tank

https://wiki.kerbalspaceprogram.com/wiki/FL-TX1800_Fuel_Tank

1.875m radial size is a good compromise between drag and part count for mid-sized vessels, in my opinion. If we only had a proper service bay with doors for this size in stock...

[xendelaar]

1 hour ago, Mephisto81 said:

@xendelaar You mean the fuel tanks? FL-TX 900 and FL-TX 1800 have these ridges at the side. If you clip enough of them into a fairing of the same diameter, the ridges still look out.

https://wiki.kerbalspaceprogram.com/wiki/FL-TX900_Fuel_Tank

https://wiki.kerbalspaceprogram.com/wiki/FL-TX1800_Fuel_Tank

1.875m radial size is a good compromise between drag and part count for mid-sized vessels, in my opinion. If we only had a proper service bay with doors for this size in stock...

ah, now i see. Thanks! yeah, I love the 1.875 tanks as well, but i find the lack of adapters very frustrating..

[It'snorocketscience]

After 15 craft iterations, plus weeks of crashes and learning and tuning, I finally completed my own challenge. The "Duna Phantom" Duna-capable SSTO is here:

While it was exceptionally hard to build, I think it shows that prop planes can be a viable way to explore other atmospheres. As far as Duna planes go, this plane is a dream to fly at both Kerbin and Duna... relatively speaking. Not many kerbals were killed in the making of this craft.

I'm happy with how this spaceplane turned out. The props and wings save about 550 m/s of dV when leaving Duna! (A normal Duna ascent to orbit costs 1450 m/s, but this plane only needs 900 m/s when starting from a 6km cruising flight.) But Kerbin ascent is a different story. I have no idea what is the optimal SSTO path you guys use. This thing barely escapes Kerbin on its way to Duna, even with 4850 m/s of dV. Could someone tell me if using one nuke for a 15 ton plane is bad?

Image album:

Spoiler

Craft at flight ceiling (before lighting rocket):

 

Craft beginning ascent:
Note the props sheltered inside a bay to reduce drag.

 

Craft ascent continued:

 

Craft in LKO:

 

Craft at Duna top speed and flight ceiling:
Note the half-empty tanks - liquidfuel has been dumped to make takeoff easier.

 

Landed on Duna:

 

Duna orbit:

 

Return to KSC:

Stats and optimizations:

Spoiler

Craft with fairing removed:

 

• Name: Duna Phantom
• Mass: 15.6t wet, 8.4t dry - about half fuel!
• Launch cost: 40k with fuel
• delta-V: 4880 m/s
• Kerbal capacity: 1 chair
• Flight envelope: 35-180 m/s on Kerbin (takeoff-11.5K), 45-120 m/s on Duna (takeoff-6K, half empty)
• Propulsion: 1 Nuke + 2 tiny rotors x 4 big ducted fans

To get this thing off the ground, I had to make a ton of optimizations. Here's a short list:

• Angled wings up by 5 degrees to improve lift-to-drag ratio and takeoffs.
• Used a barebones ISRU setup to save weight - a jr. drill and ISRU running with 3 fuel cells and 2 radiator panels. The wings act as passive radiators so lighter radiators can be used.
• Used a barebones rotor/motor setup to save weight - 2 tiny rotors and 8 big fans, powered a single FLT-100 fuel tank and 3 fuel cells. The range is actually quite good - I estimate 800-1000km of range on Duna. A service bay covers the props when not in use, reducing drag.
• Used wing strakes to save weight - Seriously, these things are OP. They're a two-in-one wing that act like fuel tanks!
• Manually tweaked landing gear friction so that the craft skids and slides instead of tipping over when landing - this is super helpful on Duna's rough terrain.

 

I'll post a video and .craft file later. Right now I've got to simplify the plane so you can fly it without reading the instructions.

Edited June 21, 2020 by It'snorocketscience
Added images and more info.

[xendelaar]

17 minutes ago, It'snorocketscience said:

After 12 craft iterations, plus weeks of failing and learning and tuning, I finally completed my own challenge. The "Duna Phantom" Duna-capable SSTO is here:

While it was exceptionally hard to build, I think it shows that prop planes can be a viable way to explore other atmospheres. As far as Duna planes go, this plane is a dream to fly at both Kerbin and Duna... relatively speaking. Not many kerbals were killed in the making of this craft.

I'm happy with how this spaceplane turned out. The props and wings save about 550 m/s of dV when leaving Duna! (A normal Duna ascent to orbit costs 1450 m/s, but this plane only needs 900 m/s when starting from a 6km cruising flight.) But Kerbin ascent is a different story. I have no idea what is the optimal SSTO path you guys use. This thing barely escapes Kerbin on its way to Duna, even with 4850 m/s of dV. Could someone tell me if using one nuke for a 15 ton plane is bad?

Images:

  Hide contents

Stats:

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• Name: Duna Phantom
• Mass: 15.6t wet, 8.4t dry - about half fuel!
• Launch cost: 40k with fuel
• delta-V: 4880 m/s
• Kerbal capacity: 1 (chair)
• Flight envelope: 35-180 m/s on Kerbin (takeoff-11.5K), 45-120 m/s on Duna (takeoff-6K, half empty)
• Propulsion: 1 Nuke plus 2 tiny rotors x 4 big ducted fans

 

I'll post a video and .craft file later. Right now I've got to simplify the plane so anyone can fly it without reading the instructions.  

wow! such a slick design! I was wondering when you would show us your vessel! It's very impressive! Amazing that so little wing span is needed to fly a 15 ton craft on duna! What kind of speed do you need to have enough lift there? Can't wait to see your video! This is extraordinary stuff!

[It'snorocketscience]

19 minutes ago, xendelaar said:

wow! such a slick design! I was wondering when you would show us your vessel! It's very impressive! Amazing that so little wing span is needed to fly a 15 ton craft on duna! What kind of speed do you need to have enough lift there? Can't wait to see your video! This is extraordinary stuff!

The wings are larger than you think. The wing strakes have a "relative wing area" of 1, according to the SPH menu. This craft has 14 of those wings, so it has a wing area of 14 and weighs 15.6t. For comparison, the Aeris 3A has a wing area of 5 and weighs 8.5t. So my plane actually has more wings for each unit of mass than the Aeris 3A.

I also pushed the rules a bit and only did plane takeoffs and landings at low altitude. Duna's low-lying canyons go down to 200 meters on the altimeter and have much thicker air... I did the math and Duna's canyon air should be as dense as Kerbin's air 8km up. That's pretty handy!

Edited June 21, 2020 by It'snorocketscience
Fixed a typo.

[It'snorocketscience]

On 4/28/2020 at 12:42 PM, Lt_Duckweed said:

So a while back @Stratzenblitz75 and I did a collab project where we flew a 2 Kerbal part clipped monster of an SSTO from Kerbin to Jool "surface" and back via refuel pitstops at Pol -and Laythe.  Looking through the challenge rules I think it qualifies.  I wouldn't consider this an entry though, just want to show that it is possible (or at least was, props got nerfed in 1.9 so this craft would need a serious redesign)

[Video]

Have you guys had the chance to test it in 1.9? If not, do you have a .craft file I could use to try? It looks like piloting it is quite challenging, but I would like to try it anyway. Also, if the prop TWR is good enough, it should work on Eve or maybe Duna.

 

On 4/29/2020 at 10:03 AM, Mephisto81 said:

This should work on Kerbin as well:

https://kerbalx.com/Mephisto/XE-01-APEX-Mk-VI-Eve-SSTO

Spoiler

@Mephisto81 I was reading through the older posts, and realized I might've missed your post... is this a challenge entry? If it can make it to LKO without dropping any stages then it's set. I also would be very excited to see this if it's a working Eve prop SSTO.

By the way, I must thank you a ton for the service bay tip. It cured my headache from trying to deal with prop drag! 

[Lt_Duckweed]

7 hours ago, It'snorocketscience said:

Have you guys had the chance to test it in 1.9? If not, do you have a .craft file I could use to try? It looks like piloting it is quite challenging, but I would like to try it anyway. Also, if the prop TWR is good enough, it should work on Eve or maybe Duna.

Unfortunately I can't share the craft file, as that is reserved for Stratz's patreon.  It would most definitely work on Duna thanks to the huge wing area and large number of props, (plus you could just directly zoom away on nerv power alone, it has right about 1 twr in rocket mode) except for the fact that it doesn't have wheels.  You would need to land it vertically and then take off vertically, which would require very flat ground.  As for eve, the nuke twr is far too low, so it wastes most of its fuel trying to get supersonic, then runs out well short of orbit.  We haven't retested this craft in 1.9, but all my other Jool sstos broke so this one would too.  If the goal is just to get to low Jool orbit from it's 0 altitude that is definitely still doable, the margins on that are way more forgiving than on this craft.

[xendelaar]

On 6/21/2020 at 10:33 PM, It'snorocketscience said:

After 15 craft iterations, plus weeks of crashes and learning and tuning, I finally completed my own challenge. The "Duna Phantom" Duna-capable SSTO is here:

While it was exceptionally hard to build, I think it shows that prop planes can be a viable way to explore other atmospheres. As far as Duna planes go, this plane is a dream to fly at both Kerbin and Duna... relatively speaking. Not many kerbals were killed in the making of this craft.

I'm happy with how this spaceplane turned out. The props and wings save about 550 m/s of dV when leaving Duna! (A normal Duna ascent to orbit costs 1450 m/s, but this plane only needs 900 m/s when starting from a 6km cruising flight.) But Kerbin ascent is a different story. I have no idea what is the optimal SSTO path you guys use. This thing barely escapes Kerbin on its way to Duna, even with 4850 m/s of dV. Could someone tell me if using one nuke for a 15 ton plane is bad?

Image album:

  Reveal hidden contents

Craft at flight ceiling (before lighting rocket):

 

Craft beginning ascent:
Note the props sheltered inside a bay to reduce drag.

 

Craft ascent continued:

 

Craft in LKO:

 

Craft at Duna top speed and flight ceiling:
Note the half-empty tanks - liquidfuel has been dumped to make takeoff easier.

 

Landed on Duna:

 

Duna orbit:

 

Return to KSC:

Stats and optimizations:

  Reveal hidden contents

Craft with fairing removed:

 

• Name: Duna Phantom
• Mass: 15.6t wet, 8.4t dry - about half fuel!
• Launch cost: 40k with fuel
• delta-V: 4880 m/s
• Kerbal capacity: 1 chair
• Flight envelope: 35-180 m/s on Kerbin (takeoff-11.5K), 45-120 m/s on Duna (takeoff-6K, half empty)
• Propulsion: 1 Nuke + 2 tiny rotors x 4 big ducted fans

To get this thing off the ground, I had to make a ton of optimizations. Here's a short list:

• Angled wings up by 5 degrees to improve lift-to-drag ratio and takeoffs.
• Used a barebones ISRU setup to save weight - a jr. drill and ISRU running with 3 fuel cells and 2 radiator panels. The wings act as passive radiators so lighter radiators can be used.
• Used a barebones rotor/motor setup to save weight - 2 tiny rotors and 8 big fans, powered a single FLT-100 fuel tank and 3 fuel cells. The range is actually quite good - I estimate 800-1000km of range on Duna. A service bay covers the props when not in use, reducing drag.
• Used wing strakes to save weight - Seriously, these things are OP. They're a two-in-one wing that act like fuel tanks!
• Manually tweaked landing gear friction so that the craft skids and slides instead of tipping over when landing - this is super helpful on Duna's rough terrain.

 

I'll post a video and .craft file later. Right now I've got to simplify the plane so you can fly it without reading the instructions.

I would love to see video of you completing the mission. when are you planning on releasing it?

 

[It'snorocketscience]

On 7/8/2020 at 2:13 PM, xendelaar said:

I would love to see video of you completing the mission. when are you planning on releasing it?

 

Probably not for a while . I got a lot of work to do this month, plus flying and filming a prop plane is time-consuming because props can't spin with timewarp active.

Also, on a side note, the fairing improvements in 1.10 are super handy - you can eliminate drag from exposed engines but leave a hole in the back for the rocket flames to come out. (It was possible to hide rocket engines inside fairings before 1.10, but they look horrendous to me .) 

[It'snorocketscience]

I know this is an old thread, but this just came out on Stratenblitz's channel:

So with this thing, you can reach orbital speeds with nothing but props, and push yourself into orbit with ion engines. This is big! Somebody's gotta build a Jool SSTO with this

In my case, I probably won't be using it as I don't like buggy tech, and it's somewhat... well, ugly, to be frank. Stock parts are strong enough as they are, in my opinion.