Eve and jets

[kerbal fella]

So I'm gonna send a plane to Eve ahead of my lander and I need to know, do jets work on eve?

 

[FTLparachute]

No, but if you have Breaking Ground you can use the propellors.

[Duke MelTdoWn]

I prototyped such an Eve SSRT with propellers. It still needs to get a lot bigger to work for Eve and I have not tested it there yet.

Some considerations I had along the way:

- Put the propellers inside service bays. Close them when you switch to rocket motor to reduce drag.
- Use counterrotating propellers to cancel torque.
- Use fuel cells (inside forward service bay) to energize the propellers. This causes less drag than using e.g. OXSTAT solar panels.
- Use some super efficient engines like Vector or Dart.

Some open questions I have:
- How fast can you fly on Eve before aerodynamic forces tear up deployable solar panels?
- How high can you fly on propellers in Eves atmosphere?

Edited Wednesday at 10:34 AM by Duke MelTdoWn

[kerbal fella]

10 hours ago, Duke MelTdoWn said:

I prototyped such an Eve SSRT with propellers. It still needs to get a lot bigger to work for Eve and I have not tested it there yet.

Some considerations I had along the way:

- Put the propellers inside service bays. Close them when you switch to rocket motor to reduce drag.
- Use counterrotating propellers to cancel torque.
- Use fuel cells (inside forward service bay) to energize the propellers. This causes less drag than using e.g. OXSTAT solar panels.
- Use some super efficient engines like Vector or Dart.

Some open questions I have:
- How fast can you fly on Eve before aerodynamic forces tear up deployable solar panels?
- How high can you fly on propellers in Eves atmosphere?

Its gonna be a unmanned scout drone to find a landing spot

 

[Vanamonde]

Air breathing engines do not work, but as people have said, wings and propellers work even better and are a viable alternative. 

[umbra humanus]

You should make a helicopter with propellers  for Eve. Not that it is practical, but it is a cool idea.

[KerikBalm]

On 2/12/2025 at 11:26 AM, Duke MelTdoWn said:

- Put the propellers inside service bays. Close them when you switch to rocket motor to reduce drag.

Meh, I just put their pitch to 90, and lock the rotation to reduce drag

On 2/12/2025 at 11:26 AM, Duke MelTdoWn said:

- Use fuel cells (inside forward service bay) to en questions I have:

I use a combo of those and batteries and small solar panels, so that I can recharge and fly around if I run out of fuel on eve's surface and need to fly back to the fuel station 

On 2/12/2025 at 11:26 AM, Duke MelTdoWn said:

- How fast can you fly on Eve before aerodynamic forces tear up deployable solar panels?

Not sure, I tried this, I think the angle is important, but even keeping gigantors horizontal to their airflow didn't get me anywhere close to fast enough 

On 2/12/2025 at 11:26 AM, Duke MelTdoWn said:

- How high can you fly on propellers in Eves atmosphere?

Depends on your wingloading and power to weight ratio for the props.

Obviously I can make something that flies higher on props if I don't have to lug a bunch of rocket fuel and engines up (ie, something like a U2)

For my orbital designs, I think I was getting to about 10 or 11k

[KerikBalm]

On 2/13/2025 at 2:58 AM, umbra humanus said:

You should make a helicopter with propellers  for Eve. Not that it is practical, but it is a cool idea.

Practical for what purpose? Eve's thick atmosphere makes helos work very well. Quite practical for biome hopping.

I would use tilt rotors though, for faster horizontal speed, while still being able to stop and hover to get where you want for science collection (like finding a BG surface feature)

On 2/12/2025 at 10:07 PM, kerbal fella said:

Its gonna be a unmanned scout drone to find a landing spot

 

Landing spot for what?

Eve's thick atmosphere makes it quite easy to land even large craft (if you can get them to the lower atmosphere without being destroyed by heat and dynamic pressure)

Are you looking for a flat spot at high altitude for easier ascent? Intersection of multiple biomes for science?

Long flat spot for landing a larger aircraft?

On 2/12/2025 at 11:26 AM, Duke MelTdoWn said:

- Put the propellers inside service bays. Close them when you switch to rocket motor to reduce drag.

- Use some super efficient engines like Vector or Dart

Two more comments:

Those service bays are draggy when open, and will degrade it's prop flight performance. I don't know how that trades with the drag from higher altitudes but also higher speed when you switch to rockets for a spaceplane design.

If going with my suggestion to just feather the props to 90 and lock the rotors, it's best to have "pusher" props, as then the blades act like fins, and having fins on you nose is bad for stability (but good if they're at the back)

I don't much care for dart engines on eve, though I may use them on the core stage of a cross feeding rocket only design.

Eve has a thick atmosphere, reducing drag is very important. Dart TWR is not great, but another spec few people talk about is thrust to cross section ratio. The dart's is terrible, the vector's is amazing. High ratios for this mean you can have long thin stacks with sufficient thrust, and thus minimize drag.

I'm not sure how important this is if you climb first with props into thinner atmosphere, but it's very important for rocket only designs: vectors FTW.

Lastly, I don't think I ever got an Eve SSTO working, with or without Breaking Ground.

- But I did get a reusable 2 stage space plane working with a cargobay (the rear ramp section, and 2nd longest cargobay part) with >16 tons to orbit capacity.

The first stage has the props, plus rockets: goes suborbital- undocks 2nd stage, which gets to orbit, then I have to quickly change back to the suborbital 1st stage before it falls back in the atmosphere and gets deleted, and fly it back to refuel from a surface base.

After deployment of the payload, the orbital stage glides back to the fueling base, and then docks with the 1st stage, then the fueling base (wheeled) fills them up, ready to go again 

[Duke MelTdoWn]

Good point on the cross section to thrust ratio of the Dart. And I might look into a two stage solution like you suggested. Some tests of props in service bays vs. other placements also seem in order.

Wanted to add that there is a non-standard construction technique (some might call it an exploit) to reduce drag of rocket engines (and Rapiers). You can cap the backside of the engine with a nose cone, then rotate the nose cone 180° forward and translate it. This causes the game engine to think that the backside of the engine is completely covered (as if it were in the middle of the stack), reducing the overall drag. You are trading the drag created by the blunt backside with the drag of the nose cone. On a Rapier, this cuts overall drag approximately in half.

 

[KerikBalm]

Pics of an eve 2 stage that I tested. The docking port between the orbiter and carrier would need to be changed for a shielded docking port, but then I couldn't build it as a single ship, and having to dock them together (while landed on the ground) each time I test would be annoying.

Spoiler

 

 

 

Probably could still be improved a lot, it was just proof of concept.

I rarely play on stock eve, or even stock scale

[Lt_Duckweed]

On 2/12/2025 at 4:26 AM, Duke MelTdoWn said:

- How fast can you fly on Eve before aerodynamic forces tear up deployable solar panels?

Not fast enough for them to be usable on this kind of craft sadly, their dynamic pressure limits are just too low.

On 2/12/2025 at 4:26 AM, Duke MelTdoWn said:

- How high can you fly on propellers in Eves atmosphere?

Most Eve SSTOs seem to centralize around a peak altitude figure of 16km, give or take 1km or so, at a speed of around 130 m/s, give or take 5 m/s.  Generally, the most efficient designs then enter a very shallow dive in order to trade 0.5-1 km of altitude for another 20-30 m/s of forward speed, which doesn't sound like much, but really does help, since that 20-30 m/s is cut off of the most inefficient portion of the flight, where the Vectors/Mammoths (the only real choices for this sort of craft) are sucking down large amounts of fuel for very little acceleration, since you are still fully loaded down at max weight.

9 hours ago, KerikBalm said:

Those service bays are draggy when open, and will degrade it's prop flight performance. I don't know how that trades with the drag from higher altitudes but also higher speed when you switch to rockets for a spaceplane design.

This is a common misconception, the high drag people anecdotally see with open service bays is from the stuff inside the bay.  The only additional bay drag is from the frontal cross section of the doors, which is minimal.  The trade of completely removing the drag and CoP effects from the props is extremely worthwhile.

On 2/12/2025 at 4:26 AM, Duke MelTdoWn said:

- Use fuel cells (inside forward service bay) to energize the propellers. This causes less drag than using e.g. OXSTAT solar panels.

Fuel cells are a great option (and what I generally use) but I have also seen a successful SSTO design that powered the props with the large OXSTAT panels placed inside the service bays and arranged for minimum drag at the fight regime for peak altitude/speed (counterintuitively, if you rotate the panel so that the long side is facing prograde with an AoA of near 0, it's quite low drag).  The drag penalty was surprisingly small, and it gives you the benefit of not being on a timer for ascent.

Edited 14 minutes ago by Lt_Duckweed