[Stock Helicopters & Turboprops] Non DLC Will Always Be More Fun!

[Pds314]

Conundrum with using these aquatically is as follows:

They generate relatively constant torque for constant power, so for ex, an ideal Juno 8-blower engine with blower blades of radius 1 meter would generate 8 Juno-meters of torque. At full thrust, that's 160 kN*m.

This means that, to a good approximation, rpm=k*power, where k is an engine-specific constant.

So we can see that these engines are extremely susceptible to the Oberth effect. Power in is, much like in a rocket or jet, constant, but power out is directly proportional to RPM.

 

Unfortunately, not all this output power useful. For smaller engines or inefficient designs, shaft drag consumes a roughly constant fraction of the total power at all times. For any decent engine, propeller drag will be the limiting factor. This means blade pitch in an ideal engine should be at maximum L/D, since total engine drag will be relatively constant in all cases under equilibrium conditions, and drag torque will equal blower torque. The one major exception is the wobble of the engine, since part wobble drag seems to be highly non- linear and is probably not polynomial or even continuous.

 

Point is, high- torque applications like a paddle wheel on a boat mean you need a big engine that doesn't go fast. This is unfortunately not a simple thing to make, so the workaround is probably to gear it waaaayyy down.

 

Come to think of it, these engines should ALWAYS be better when geared down, at least as long as the engine isn't generating excessive internal drag. Constant torque at the engine becomes higher constant torque at the prop at lower RPM, but it should end up reaching the same RPM anyway due to the higher torque, or higher rpm due to lack of increased drag at that RPM. Basically, gearing it down should DRAMATICALLY increase engine output power.

 

Hmm.. Dang. Now I've started to consider automotive engines...

Edited April 22, 2016 by Pds314

[Pds314]

I think I found a stock way of measuring lift. "Upwards force." My current engine produces ~190 kN in the aerodynamics GUI. Pretty good for a dry mass of like eight five point six tonnes including props, excluding tanks, fuel lines and intakes.

Engine specs:

Blowers: 12*Juno
Torque radius: ~0.8 meters.
Peak thrust: 195 kN
Mass: 5600 kg with prop
Bearing: Internal-shaft avionics cone single-stage starting wheeless thin-rod bearing.
Ideal RPM=200-220.
Unloaded max RPM: 300.0, at 1% power, 300.0
Stability: As long as you don't let the engine fly apart by having it spin loose, I have yet to break it.
Never exceed RPM: unknown, at least 260 RPM
TWR: 3.55




Interestingly, it appears that there is an absolute, fundamental limit of 300 RPM (like, literally, 1799 plus change degrees/second). This has very important applications in Turboshaft design, and means that any power you dump into a turbine going at 300 rpm is instantly going into nonexistence. I'll confirm, but it is HIGHLY suspect that my engine has the same absolute RPM limit at 100% and 1% power. One other good thing about my 1% power test is it proves that the bearing design is not dragging significantly below 300 RPM, since drag is not a function of engine thrust, that means that when running correctly, it is over 99% efficient. You cannot make a less draggy bearing, at least for sub-300 RPM applications, if it's even possible to exceed 300 RPM.

Tried 0.6% thrust (1 blower at 5%, all others disabled). The speed went down to 1750 degrees per second, but was stable. Let it slow down and tried slowly increasing the thrust limiter until the speed started climbing without bound. It appears that my bearing design requires 1 blower at 3.5% thrust in order to function. That's about 500-something Newton-meters of shaft torque losses... compared to about 190000 Newton-meters of torque. Isn't efficiency awesome?

Edited April 22, 2016 by Pds314

[Pds314]

Yep. It is possible with a light enough object and great enough torque to exceed 300 RPM, but only temporarily. Even a rotating object in orbit isn't immune to the 300 RPM limit. Sadly, this will greatly limit the effects of gearing on engine output. 300 RPM is 5 Hertz, so that means if r=1 meter, the limit on the blade speed is 10*pi m/s. The only way around that is to go bigger, and if, like mine, your shaft drag is negligible, gearing only helps if it couldn't originally get to 300 RPM under load.

Note, however, that while 5 hertz might seem slow, that means a prop with a 12-meter radius will have supersonic bladetips, so it might not be THAT terrible.

Test that shows the fundamental rotational speed limit:

Edited April 22, 2016 by Pds314

[Pds314]

Experimenting with props that look more like pancakes of struts and whirling blades than engines. 710 kN out of 24 Junos! That's better than using the Junos directly!

Expanded the prop. I have got to say, I've never seen 24 Junos manage 1.1 MN before. Thrust efficiency of 230%!

(although, to be fair, power efficiency is much less, since the paddles are NOT going at the exhaust velocity of the jet).

Edited April 22, 2016 by Pds314

[Pds314]

[Azimech]

So much to read and reply to! Pds314, are you a real engineer?

By the way, the max angular velocity was way worse in the 1.1 pre-release, I issued a bug report. They've solved it and NathanKell added the following line in the Physics.cfg at 89:

maxAngularVelocity = 31.416 // Max angular velocity of objects in radians / sec

So I'm going to change it and let's see what happens. Might result in weird kraken like behaviour though, as I once observed in 0.90.

Please take note that joint flexibility results in turbine blades expanding from the shaft at speeds above ~20rad/s, the eventual result being blade strike on various objects.

[Pds314]

1 minute ago, Azimech said:

So much to read and reply to! Pds314, are you a real engineer?

By the way, the max angular velocity was way worse in the 1.1 pre-release, I issued a bug report. They've solved it and NathanKell added the following line in the Physics.cfg at 89:

maxAngularVelocity = 31.416 // Max angular velocity of objects in radians / sec

So I'm going to change it and let's see what happens. Might result in weird kraken like behaviour though, as I once observed in 0.90.

Please take note that joint flexibility results in turbine blades expanding from the shaft at speeds above ~20rad/s, the eventual result being blade strike on various objects.

I'm a student. My major is software engineering, so... it's not really applicable here.

1.3 Mn by tweaking the rotor pitch!

Hmm.. I'm gonna try tweaking the physics as well. Maximum angular velocity is a kind of odd behavior to begin with. I wonder what happens if I take my engine blades up to supersonic speeds? =)

It seems to be able to push 1400 kN with careful control. Beyond that, things start going 'splode. 

Alright, 5000 Hertz should be way, way faster than any machine can go, right?

[Pds314]

alright, so the critical speed of my 12-engine is about 3k degrees/sec, or 500 RPM. At that point, the shaft breaks.

[Azimech]

Succes! I can run the engine at 35rad/s continuously. The limit for my current design appears to be 36rad/s, resulting in a massive RUD.

On the topic of gears: I'm not sure how 1.1 handles it but the last time I tried (during 0.90) it resulted in unacceptable loss of power due to collider friction.

[Pds314]

10 minutes ago, Azimech said:

Succes! I can run the engine at 35rad/s continuously. The limit for my current design appears to be 36rad/s, resulting in a massive RUD.

On the topic of gears: I'm not sure how 1.1 handles it but the last time I tried (during 0.90) it resulted in unacceptable loss of power due to collider friction.

Managed to get the shaft to 4.2k deg/s as it blew up. It seems to be shaft wobble that's causing this behavior, and not blade collisions.

Hmm.. now it seems to be having blade collisions or something. It suddenly loses like 500 deg/s at any given time and wobbles.

Edited April 22, 2016 by Pds314

[Azimech]

11 minutes ago, Pds314 said:

alright, so the critical speed of my 12-engine is about 3k degrees/sec, or 500 RPM. At that point, the shaft breaks.

Yeah ... you come to the limit of the crash tolerance of the part. I've been busy with creating bearings running pure on I beams, smoothed out by having a lot of them. Crash tolerance of 80m/s ... that's gotta work. Or are you already using such parts?

[Pds314]

25 minutes ago, Azimech said:

Yeah ... you come to the limit of the crash tolerance of the part. I've been busy with creating bearings running pure on I beams, smoothed out by having a lot of them. Crash tolerance of 80m/s ... that's gotta work. Or are you already using such parts?

No, lol. I'm using things like cube struts as structure and the avionics nosecone as bearings. The BLADES are atmospheric fluid spectro-whatever-majiggers. Not a single moving part or part that could come into contact with a moving part has a durability of even 10 m/s.

Hmm.. it seems like the shaft inevitably blows up past something close to 4k deg/s

Yeah. Tried my wheel-based design, it pulls out of confinement at 2k.

Edited April 23, 2016 by Pds314

[Pds314]

144 kN, below the speed limit, aircraft-compatible prop, tiny engine that weighs a bit over 4 tonnes with prop. 12 blowers. Do not exceed 300 RPM! It also has a (relatively) low part count of 94 (I think)



Certainly not the most powerful engine ever, but it fits comfortably in a Mk3 fuselage, and also fits in this fairing. If I had shaped it slightly differently, it would actually be aerodynamic. It's also a bit wobble-happy, so I'll have to work on stability issues.

I think this thing is small enough that I could use it for a plane that's reasonably small. Probably 20 or 30 tonnes? IDK, maybe less than that. At this point these things are comparable in TWR to the BAD-T engines, although they are bigger and consume VASTLY more fuel, lol. Who knows, if I manage to make it small enough, maybe the plane will actually be comparable in performance to the BAD-T dummy? Maybe I'll put them in a dogfight vs. each other?

Edited April 23, 2016 by Pds314

[Azimech]

I had a little fun using my engine from my newest airplane as well, to convert it into a heli. First try lifted off and went up at 5m/s. Not bad. Now the rest but that's something for tomorrow or next week. It's 3:37AM over here and I need to go to bed. Goodnight :-)

21 minutes ago, Pds314 said:

144 kN, below the speed limit, aircraft-compatible prop, tiny engine that weighs a bit over 4 tonnes with prop. 12 blowers. Do not exceed 300 RPM! It also has a (relatively) low part count of 94 (I think)



Certainly not the most powerful engine ever, but it fits comfortably in a Mk3 fuselage, and also fits in this fairing. If I had shaped it slightly differently, it would actually be aerodynamic. It's also a bit wobble-happy, so I'll have to work on stability issues.

I think this thing is small enough that I could use it for a plane that's reasonably small. Probably 20 or 30 tonnes?

I'll reply to ya in depth tomorrow, and a whole lot of other posts as well :-)

[Pds314]

Hmm.. ~160 kN*meters of torque at 290 rpm, that's 160000*290/60*pi*2 watts. That's.. Yeah, that's like.. 7000 HP? Should be pretty decent in something that weighs 20 tonnes.

In fact, why stop there? Why not have 2! Or 4! Build a 50-tonne (dry) mega-superfortress!

Edited April 23, 2016 by Pds314

[Pds314]

On my phone. Will post pic later, but I've managed to tweak that engine and prop so ut should work extremely well for planes. I've tried various configurations, some which generate >150 kN thrust at up to 365 RPM, and others which generate a stable 220 kN thrust.

Edited April 23, 2016 by Pds314

[Azimech]

For anyone interested, here's how you disable jet engine smoke. When using a lot of blowers, the smoke gives a big performance hit, depending on the machine.

[Pds314]

48 minutes ago, Azimech said:

For anyone interested, here's how you disable jet engine smoke. When using a lot of blowers, the smoke gives a big performance hit, depending on the machine.

Oh, by the way, I was messing around with my compact engine and in stock, it seems to incapable of taking off a 20- tonne plane. Maybe I'm setting the pitch wrong?

[Azimech]

4 minutes ago, Pds314 said:

Oh, by the way, I was messing around with my compact engine and in stock, it seems to incapable of taking off a 20- tonne plane. Maybe I'm setting the pitch wrong?

Could be the case, switch on F12 and compare the lift/drag lines. During 0.90 it was easy, in 1.x every speed has it's best pitch setting, even while accelerating on the runway. Did you try my airplane?

[Pds314]

4 minutes ago, Azimech said:

Could be the case, switch on F12 and compare the lift/drag lines. During 0.90 it was easy, in 1.x every speed has it's best pitch setting, even while accelerating on the runway. Did you try my airplane?

I haven't yet. I definitely had to adjust a lot on the runway. I tried maintaining 1800, 1700, 1500 and 1400 deg/s, but it just seems to not go over 30 m/s.

[Azimech]

5 minutes ago, Pds314 said:

I haven't yet. I definitely had to adjust a lot on the runway. I tried maintaining 1800, 1700, 1500 and 1400 deg/s, but it just seems to not go over 30 m/s.

I think you'll find using V.O.I.D. much easier for reading engine speed than the stock readout, if you don't mind thinking in rad/s.

I'd like to examine your engines/airplane, I might have a few tricks to get them airborne.

[Azimech]

And here's the first early prototype flight of a stock turboshaft helicopter in 1.1. Like always: an ork to control and a joy to crash. It uses the same powerplant as my turboprop airplane and features a very early version of cylic control.

 

Edited April 23, 2016 by Azimech

[Redshift OTF]

Keeping the dream alive I see. It's almost a tradition to defy the latest patch and get something flying. What's changed to make these engines better in the latest version of KSP?

Also, a side question, did they change all the graphics in the latest version? My VAB and SPH look, well, not to my liking and my FPS is taking a big hit. It's like the lighting is all wrong.

[V7 Aerospace]

1 hour ago, Redshift OTF said:

Keeping the dream alive I see. It's almost a tradition to defy the latest patch and get something flying. What's changed to make these engines better in the latest version of KSP?

Also, a side question, did they change all the graphics in the latest version? My VAB and SPH look, well, not to my liking and my FPS is taking a big hit. It's like the lighting is all wrong.

I believe that the lighting engine has changed as a result of Unity 5. I think I may also be experiencing the same FPS problem, it's not a constant FPS drop, but instead it seems to be a bit jumpy sometimes, and less jumpy other times. Just one of the few teething issues of the new update. 

[FlipNascar]

Fine, I'm game. Time to start kluding away at some stuff again... Some sort of turbine thingy coming soon™.