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

[Gman_builder]

9 hours ago, Pds314 said:

Well, mach number is a problem in stock KSP, but I suspect not as much as IRL. We also have the benefit of having very little in the way of power limitations. I.E. Even the Thunderscreech or whatever still had "only" 6000 HP, which, while vastly more than any WW2 fighter or modern turborprop attack aircraft (I'm thinking of the Super Taco here, 1600 HP), is still way, way less than what we can do. As long as we're willing to build big enough, our engines should allow for pretty excessive thrust. Remember the Varpulis has 115000 HP, which is about equivalent to 20 thunderscreech engines, granted, at much lower RPM.

Also, not sure if the Thunderscreech could be rebuilt today faster. We now understand propfan engines better, which use exotic blade geometries to help reduce transonic drag. Further still, we now understand the area rule, which means that these things would be much sleeker at mach speeds.

Also, I suspect a modern equivalent to the Thunderscreech would be a pusher prop, and may well have the propeller inside the mach cone, thereby not needing a true supersonic prop, just a very big and powerful one. Alternatively, one might opt for a series of ducted fans similar to the compressor on a low bypass turbofan, which are definitely capable of exceeding mach 1. (I.e. I'm pretty sure the exhaust from the dry mode of an F-35 or F-22 escapes at something along the lines of Mach 3 or 4).

Our engines produce a lot more horsepower but they are also A LOT bigger and heavier. And a lot more inefficient and have lower RPM. So there really is no performance difference when we are talking about top speed. Also. As you know, Juno's can't really break the sound barrier so as long as we use them in our engines we are pretty much limited to subsonic regardless of RPM. If we go supersonic the thrust from the Juno's will just drop off past unusable levels.

[Pds314]

11 minutes ago, Gman_builder said:

Our engines produce a lot more horsepower but they are also A LOT bigger and heavier. And a lot more inefficient and have lower RPM. So there really is no performance difference when we are talking about top speed. Also. As you know, Juno's can't really break the sound barrier so as long as we use them in our engines we are pretty much limited to subsonic regardless of RPM. If we go supersonic the thrust from the Juno's will just drop off past unusable levels.

Really? I thought the Junos did this? Thrust slightly improves from Mach 1.0-1.65 or so, and then begins falling off, reaching half thrust by Mach 2.15

 

The Panther is better:


The Whiplash is better still, with thrust increasing considerably well before Mach 1.
  

 

And the Rapier is even better:

Though considering that none of them are small, you'd need a massive engine to get an advantage from the rapid increase in power and fuel consumption of supersonic jets.

It's also worth mentioning the altitude curves of these engines, since, if you can reach the upper atmosphere, supersonic engines are exceedingly powerful relative to the amount of lift and drag everything has. The problem then is that you may not have any increase in thrust because a correctly-sized prop for running supersonic engines in the upper atmosphere would be much bigger than a correctly-sized prop for running them in the lower atmosphere, and you cannot increase RPM either. Increasing prop pitch to compensate helps, but not much.

One idea would be to climb using an efficient engine and enter a steep dive, then switch to supersonic engines that allow speed maintainance above Mach 1.

Edited July 20, 2016 by Pds314

[Gman_builder]

25 minutes ago, Pds314 said:

Really? I thought the Junos did this? Thrust slightly improves from Mach 1.0-1.65 or so, and then begins falling off, reaching half thrust by Mach 2.15

 

The Panther is better:


The Whiplash is better still, with thrust increasing considerably well before Mach 1.
  

 

And the Rapier is even better:

Though considering that none of them are small, you'd need a massive engine to get an advantage from the rapid increase in power and fuel consumption of supersonic jets.

It's also worth mentioning the altitude curves of these engines, since, if you can reach the upper atmosphere, supersonic engines are exceedingly powerful relative to the amount of lift and drag everything has. The problem then is that you may not have any increase in thrust because a correctly-sized prop for running supersonic engines in the upper atmosphere would be much bigger than a correctly-sized prop for running them in the lower atmosphere, and you cannot increase RPM either. Increasing prop pitch to compensate helps, but not much.

One idea would be to climb using an efficient engine and enter a steep dive, then switch to supersonic engines that allow speed maintainance above Mach 1.

I have never gotten a Juno powered aircraft above Mach 1 and I am 90% certain thrust drops off significantly at speeds greater than Mach 1. Try it yourself. I once made a airplane under a ton powered by 2 Juno's and it reached Mach 0.95 but wouldn't go any faster.

[Pds314]

4 minutes ago, Gman_builder said:

I have never gotten a Juno powered aircraft above Mach 1 and I am 90% certain thrust drops off significantly at speeds greater than Mach 1. Try it yourself. I once made a airplane under a ton powered by 2 Juno's and it reached Mach 0.95 but wouldn't go any faster.

I know in FAR, I've gotten Juno-powered vehicles supersonic. Just a minute.

[Gman_builder]

3 minutes ago, Pds314 said:

I know in FAR, I've gotten Juno-powered vehicles supersonic. Just a minute.

Ya that's in FAR. Where turboprops don't work.

[Pds314]

6 minutes ago, Gman_builder said:

Ya that's in FAR. Where turboprops don't work.

Well, they work, they're just limited to 31.4 rads/s. Also, FAR is pretty unforgiving about big flat faces like virtually every turboprop has.

 

The big problem is that if Junos can't go supersonic, we're gonna need engines that can outperform their own blowers at mach 1. Varpulis at 230 m/s gets on the order of 110 kN... Out of about ten times that much thrust.

 

While it's relatively simple to make, for example, a helicopter rotor that gets higher static thrust than the blowers would, it's very difficult to do the same at mach 1 without the engine being huge.

Edited July 20, 2016 by Pds314

[Gman_builder]

9 minutes ago, Pds314 said:

Well, they work, they're just limited to 31.4 rads/s. Also, FAR is pretty unforgiving about big flat faces like virtually every turboprop has.

 

The big problem is that if Junos can't go supersonic, we're gonna need engines that can outperform their own blowers at mach 1. Varpulis at 230 m/s gets on the order of 110 kN... Out of about ten times that much thrust.

 

While it's relatively simple to make, for example, a helicopter rotor that gets higher static thrust than the blowers would, it's very difficult to do the same at mach 1 without the engine being huge.

yee

[Azimech]

4 hours ago, Pds314 said:

@Azimech Didn't you somehow make a single-engined coaxial rotor system awhile back?

Sure did :-)

 

https://kerbalx.com/Azimech/77-Industries---CTR3-10

https://kerbalx.com/Azimech/Stock-Coaxial-Helicopter-77I--CTR3-Sky-Crane-10

Uh oh ... going down memory lane :-P

First ever coaxial: https://kerbalx.com/Azimech/77 Industries - Coaxial Turboshaft Rotor 012

This was a minimal helicopter back in 0.90: https://kerbalx.com/Azimech/77I-3H1

Largest helicopter ever built: https://kerbalx.com/Azimech/Largest-Stock-Helicopter-77-Industries-77I-5H2U

And the first ever turboshaft helicopter: https://kerbalx.com/Azimech/77 Industries 77I-5H1

[Pds314]

Hmm. It seems that there may be an effective limit on prop thrust. Putting large props like helicopter rotors on small engines like the screacher 2x1 seems to give optimal efficiency well below the max RPM, and also seems to have a lower or equal maximum thrust output for smaller props with peak L/D close to max RPM.

Thinking through this, it seems like the most likely explanation is that generating X amount of drag on a prop Y meters in effective radius consumes X*Y torque. Torque is the fixed resource, so a static prop 2 meters in effective radius can only rev until it generates half the drag of a prop 1 meter in radius.

Worse, drag comes at a lower RPM. Effectively, to get the same RPM, the drag area needs to be reduced by a factor of 4.

What this effectively means is that, below the RPM limit of a given bearing with no shaft drag, larger props are probably not better in any way past a certain point, especially since increasing blade count seems to be a completely practical way to improve static thrust, again, to a point.

Edited July 20, 2016 by Pds314

[Brownie352]

Well.. Maybe you need to make better planes ex flying wings  /prop engines behind and front im thinking something like the ho 229 and do 335

[Gman_builder]

11 hours ago, Pds314 said:

Hmm. It seems that there may be an effective limit on prop thrust. Putting large props like helicopter rotors on small engines like the screacher 2x1 seems to give optimal efficiency well below the max RPM, and also seems to have a lower or equal maximum thrust output for smaller props with peak L/D close to max RPM.

Thinking through this, it seems like the most likely explanation is that generating X amount of drag on a prop Y meters in effective radius consumes X*Y torque. Torque is the fixed resource, so a static prop 2 meters in effective radius can only rev until it generates half the drag of a prop 1 meter in radius.

Worse, drag comes at a lower RPM. Effectively, to get the same RPM, the drag area needs to be reduced by a factor of 4.

What this effectively means is that, below the RPM limit of a given bearing with no shaft drag, larger props are probably not better in any way past a certain point, especially since increasing blade count seems to be a completely practical way to improve static thrust, again, to a point.

uhuh......uhuh......

ya I know what some of those words mean.

[Pds314]

3 hours ago, Gman_builder said:

uhuh......uhuh......

ya I know what some of those words mean.

Basically, very much unlike in real life, you can't use tiny weak engines to make a big helicopter blade generate good lift by gearing them, unless you actually gear them.

[Gman_builder]

6 hours ago, Pds314 said:

Basically, very much unlike in real life, you can't use tiny weak engines to make a big helicopter blade generate good lift by gearing them, unless you actually gear them.

Well I mean if you up-gear it enough you will generate more speed out of a smaller engine and vice-versa. Like, attach a big gear directly to your engine and mesh it with a tiny gear. You will get more speed out of the engine now. Considering how aircraft engines don't really need to generate very much torque, like a car, a small low powered engine would work fine with up-gearing. But gears don't really work too well in KSP at high speed so.  

[Pds314]

13 hours ago, Gman_builder said:

Well I mean if you up-gear it enough you will generate more speed out of a smaller engine and vice-versa. Like, attach a big gear directly to your engine and mesh it with a tiny gear. You will get more speed out of the engine now. Considering how aircraft engines don't really need to generate very much torque, like a car, a small low powered engine would work fine with up-gearing. But gears don't really work too well in KSP at high speed so.  

Yeah. Seriously, a light, compact, rugged, low part count gear system capable of 50 rads/s engine-side would be amazing. Of course, if it did 80 rads/s engine side and 50 prop side, that would be better.

 

As for aero engines not needing much torque, I'm not so sure. The torque on the prop shaft of a Griffon Spitfire reached something like 6000 foot-lbs, which is why both Griffon and Merlin Spitfires were considerably geared down from the 3000 or so RPM and 2500 or so foot-lbs of the engine. (or like 1700 for the Merlin)

 

Like, that's not quite as much as a Screacher 2x1, but it's at nearly thrice the RPM.

Edited July 21, 2016 by Pds314

[Gman_builder]

1 hour ago, Pds314 said:

Yeah. Seriously, a light, compact, rugged, low part count gear system capable of 50 rads/s engine-side would be amazing. Of course, if it did 80 rads/s engine side and 50 prop side, that would be better.

 

As for aero engines not needing much torque, I'm not so sure. The torque on the prop shaft of a Griffon Spitfire reached something like 6000 foot-lbs, which is why both Griffon and Merlin Spitfires were considerably geared down from the 3000 or so RPM and 2500 or so foot-lbs of the engine. (or like 1700 for the Merlin)

 

Like, that's not quite as much as a Screacher 2x1, but it's at nearly thrice the RPM.

Well its not like a car. In a car the engine has to propel the entire vehicle via 4 tires. But a aircraft engine just has to spin the prop. Which weighs a lot less than the entire plane. Same goes for helicopters. In my 4 wheel drive turboshaft car I used a engine straight out of @erasmusguy's latest plane. That plane goes 70 something m/s and the car does 4 m/s. So I mean, torque is not really a factor in KSP turboprops.

[Azimech]

Some more cleaning up and it's done.

 

[Gman_builder]

1 minute ago, Azimech said:

Some more cleaning up and it's done.

 

Part count must be horrendous

[Azimech]

7 minutes ago, Gman_builder said:

Part count must be horrendous

Yep, 634.

[Gman_builder]

Just now, Azimech said:

Yep, 634.

h o l y s h I t

How do you play with that much lag omfg let alone fly It to the north pole lol. That flight must have taken days IRL.

[Azimech]

1 minute ago, Gman_builder said:

h o l y s h I t

How do you play with that much lag omfg let alone fly It to the north pole lol. That flight must have taken days IRL.

Hyperedit ;-)

[Gman_builder]

Just now, Azimech said:

Hyperedit ;-)

Oh that makes sense. But seriously, it looks beautiful. What's the flight time and speeds?

[Azimech]

38 minutes ago, Gman_builder said:

Oh that makes sense. But seriously, it looks beautiful. What's the flight time and speeds?

Thanks man! Max speed is probably 130 m/s (with 40 juno's). Flight time is poor, probably 30 minutes.

[Gman_builder]

3 minutes ago, Azimech said:

Thanks man! Max speed is probably 130 m/s (with 40 juno's). Flight time is poor, probably 30 minutes.

Why so slow? How much does it weigh?

[Azimech]

1 minute ago, Gman_builder said:

Why so slow? How much does it weigh?

Current mass is 74 tons, the airframe produces a lot of drag because of all the detail.

[Gman_builder]

30 minutes ago, Azimech said:

Current mass is 74 tons, the airframe produces a lot of drag because of all the detail.

Ya that makes sense. But it's only 27 tons heavier than my latest plane and is over 100 m/s slower.... hmm seems slower than it should be

Edited July 21, 2016 by Gman_builder