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Stock Contra-rotating Turboprop

NightshineRecorralis
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Azimech

Azimech

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It's a nice trip down memory lane, reminds me of my 2013 engine designs. If I had hollow parts back then ...

 

I can make a list for you where this design has merits and where it fails. To achieve something that can power an airplane or helicopter, a major redesign is needed.

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NightshineRecorralis

NightshineRecorralis

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4 hours ago, Majorjim! said:

Which ones?

Look at the dropdown menu :)

 

3 hours ago, Azimech said:

It's a nice trip down memory lane, reminds me of my 2013 engine designs. If I had hollow parts back then ...

 

I can make a list for you where this design has merits and where it fails. To achieve something that can power an airplane or helicopter, a major redesign is needed.

Well, you are the turboprop master, I made this as a POC, not designed to power anything. Still, that would be very nice of you!

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XB-70A

XB-70A

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Just now, NightshineRecorralis said:

It's in the picture of the craft in the SPH.

I think the best at this time will be to describe them directly :

- Infinite Propellant

- Infinite Electricity

- Unbreakable Joints

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Azimech

Azimech

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9 minutes ago, NightshineRecorralis said:

 

Well, you are the turboprop master, I made this as a POC, not designed to power anything. Still, that would be very nice of you!

  1. You have an unequal shaft/prop diameter between front and aft sections. Since diameter has a direct influence on torque conversion, the one with a smaller diameter will have less horsepower. That said, a smaller prop doesn't always result in less horsepower since it's often capable of running at higher speeds and it puts less strain on the bearing when changing direction.
  2. There's a lot of axial tolerance in the front section, at one point it jammed because the turbine blades got stuck against the I beams holding the landing gears.
  3. The rear thrust bearing is made of a single structural adapter, unable to cope with the axial thrust produced. I tested without cheats, obviously.
  4. Landing gears: friction control should be set to override and minimum. This reduces stress on everything and makes higher output possible. Also, disable steering. Great results can be achieved experimenting with spring/damper settings although 1.2 promises much better results since 1.1.3 still has bugs.
  5. Totally counter-intuitive: lowering the dampening improves the situation, which is opposite of what it should be. Usually I use a 1:2 to 1:3 ratio, 1 being the damper setting vs spring setting.
  6. Due to the distance of the blowers to the turbine blades, higher engine speeds are not possible. It's unknown if the bug of the expanding blades at higher speeds (typically above 25 rad/s) will ever be solved, in my case I exploited it and made a two-stage blower solution, one for starting the engine and revving up, one for high power, they hit the blades at 35 rad/s and higher.
  7. Higher blower count gives a more fluid torque conversion: think of your father giving you a push every time you passed him on the merry-go-round. This reduces low-frequency vibration. Personally I always go for 8 turbine blades per shaft for the same reason but ... I haven't done research in over a year on this topic. Usually I use a blower count the power of 10 and nearly always start with 20 for a MK3 sized engine.
  8. A heavier shaft means it's more susceptible to low frequency vibration but it's more stable overall. It also produces more bearing stress. That said, the high frequency vibrations of light shafts can result in a feedback loop (pogo) which ultimately results in broken bearing elements or clipping through, due to computational limits, with disastrous results. Not only that, parts with a higher mass have more collider integrity than the same parts with lower mass. I see this is as a severe bug. Personally I try to use the MK1 crew cabin because they have a high crash tolerance and are heavy, making less flexible joints (another strange, unrealistic property).
  9. The mid thrust bearing suffers from blocked landing gear.
  10. Having a probe core + battery on both shafts gives you the ability to use variable prop pitch. This invention made a turboprop renaissance possible and improves power & efficiency at all speeds and power levels.
  11. Using Editor Extensions Redux helps you with turboshaft design, it makes building much, much faster and easier. For example, I can slide whole assemblies back & forth 50 meters to give me the space I need. It also gives you the ability to "float" parts. The way you mounted the front shaft is the only solution using the standard editor. With EEX I attach a docking port at the rear then slide the whole assembly forwards, this way it's easier to center and I use less parts. It especially makes coaxials much easier to build.
  12. A single I beam at the rear does a great job as a thrust bearing for opposite thrust (when windmilling the engine at low/no power conditions). It actually does a great job as a thrust bearing with forward thrust, if you don't mind parts floating in mid air.
  13. Bearing clearance has a big effect on engine operation. Too much clearance means least amount of friction but high amplitude low-frequency vibration and a risk of blowers missing their blades creating a feedback loop. Too little clearance creates high frequency vibration without the feedback loop but with unacceptable power loss due to friction.
  14. Have patience when frustrated and wait for 1.2, it promises a huge improvement in landing gears (and therefore bearing technology).

 

I've taken the liberty to modify your design and tried to correct all of the above. It's far from perfect but I have limited time. It will give you something to improve on. These engines are difficult and take many hours to mature but provide a huge feeling of accomplishment, in my case much more than building a rocket.

And thanks for showing an interest in turboprop technology and coaxial in particular, both are my babies and seeing an old-school attempt gives me a great feeling. Plus we need more engineers IMHO :-)

Here's the modified version. You'll notice the front section turbine blades fitted much closer to the center, this gives more room for expansion at higher speeds. I've fitted all blowers directly to the tank then shifted them forwards, it's not optimal because the engine frame blocks a few. It runs without any cheats.
Download link: https://www.dropbox.com/s/fb8uxqlwvw09v0k/Contrarotating Turboprop MK2.craft?dl=0

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Azimech

Azimech

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1 hour ago, NightshineRecorralis said:

I tried to build a plane featuring the engine with some minor tweaks, it only got up to ~20ish m/s in stock aero, not fast enough.

@Azimech, Do you have any suggestions?AkYbx6B.jpg

fUZ1t4n.jpg

Nice attempt! Be sure to modify the Physics.cfg line 89 in the KSP root folder, change it to 50. More angular velocity means more power/speed.

One more: instead of building a frame consisting of I-beams nowadays I usually go for MK3 cargo bays because they're stiffer and you can exchange 20+ parts for a single one. Yes, it's much heavier.

Edited by Azimech
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Azimech

Azimech

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Just now, NightshineRecorralis said:

I have it set as 150 for a SAS helicopter I built previously, would that affect anything?

There's a PhysX/Unity/KSP limit of 51rad/s, above it physics go gaga. NathanKell is aware of it and who knows ... we might get a solution in the future.

I forgot ... with the modified design, pressing action group 1 starts the engine/decouples the shafts. You'll see a puff of smoke as the separator is placed inside the fuel tank and destroyed immediately.

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Azimech

Azimech

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2 minutes ago, Majorjim! said:

Aww... We need more skilled rocket/payload builders! ;-)

 have you ever posted a rocket to the forum? 

I have ... not a lot of people were interested though. Because I want a new -meaningful- job and haven't finished school, I figured I need to create stuff which is away from the well-trodden path.

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Majorjim!

Majorjim!

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18 minutes ago, Azimech said:

I have ... not a lot of people were interested though. Because I want a new -meaningful- job and haven't finished school, I figured I need to create stuff which is away from the well-trodden path.

I'm not sure I understand.. What do you mean you want a new job and haven't finished school? 

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Azimech

Azimech

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5 minutes ago, Majorjim! said:

I'm not sure I understand.. What do you mean you want a new job and haven't finished school? 

Well ... due to circumstances in life I ended up with leaving school without any diploma, having a low self-esteem and a general distrust of my parents ... who's good advice I could heed if they weren't blackmailing each other. So after then I've had numerous unsatisfying jobs while using the internet to develop my skills in any direction until I discovered I could actually do something ... creating stuff in a virtual world. So that's where I want to go ... I want a job in (game|virtual world|3D print) design.

Sorry if I'm polluting this topic with my personal musings, I could keep them to private chats in the future.

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klond

klond

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2 hours ago, Azimech said:

Well ... due to circumstances in life I ended up with leaving school without any diploma, having a low self-esteem and a general distrust of my parents ... who's good advice I could heed if they weren't blackmailing each other. So after then I've had numerous unsatisfying jobs while using the internet to develop my skills in any direction until I discovered I could actually do something ... creating stuff in a virtual world. So that's where I want to go ... I want a job in (game|virtual world|3D print) design.

Sorry if I'm polluting this topic with my personal musings, I could keep them to private chats in the future.

 I'm glad you shared this with us.  If it's any help, this here group recognizes your hard work.  We know you care about people and can be very dedicated and driven.  Future employers are going to see all these qualities.  You'll be alright eventually.

 Enough ego stroking.  We've totally derailed this new engineer's posting.

Keep up the good work, NightshineRecorralis! 

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Majorjim!

Majorjim!

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5 hours ago, Azimech said:

Well ... due to circumstances in life I ended up with leaving school without any diploma, having a low self-esteem and a general distrust of my parents ... who's good advice I could heed if they weren't blackmailing each other. So after then I've had numerous unsatisfying jobs while using the internet to develop my skills in any direction until I discovered I could actually do something ... creating stuff in a virtual world. So that's where I want to go ... I want a job in (game|virtual world|3D print) design.

Sorry if I'm polluting this topic with my personal musings, I could keep them to private chats in the future.

Right.. ok. I was just not sure how not finishing school had anything to do with what you build in KSP. Thanks for the explanation.

 

On 08/29/2016 at 2:40 PM, NightshineRecorralis said:

Cheats were enabled

Just keep tinkering man. Don't be discouraged by failures and try to do things in new ways, to be creative. Most importantly keep building! This stuff is not that had once you get the hang of how parts work together in KSP. :wink:

Just now, Gman_builder said:

This topic exploded

*Dives for cover

Edited by Majorjim!
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NightshineRecorralis

NightshineRecorralis

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4 minutes ago, Majorjim! said:

 

Just keep tinkering man. Don't be discouraged by failures and try to do things in new ways, to be creative. Most importantly keep building! This stuff is not that had once you get the hang of how parts work together in KSP. :wink:

 

Azimech has kindly produced a variant that doesn't require cheats, it's up there somewhere, in a dropbox folder.

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Majorjim!

Majorjim!

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Just now, NightshineRecorralis said:

Azimech has kindly produced a variant that doesn't require cheats, it's up there somewhere, in a dropbox folder.

Yeah I saw that he posted one. My advice is take his advice but don't download the one he made. Make one yourself with the advice. You will learn more and faster if you build it yourself and therein lays the satisfaction of building.

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NightshineRecorralis

NightshineRecorralis

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Just now, Majorjim! said:

Yeah I saw that he posted one. My advice is take his advice but don't download the one he made. Make one yourself with the advice. You will learn more and faster if you build it yourself and therein lays the satisfaction of building.

Precisely what I did, everything turned out almost identical except for length and engine layout, most others were practically the same :/

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