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

[Azimech]

2 minutes ago, Gman_builder said:

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

Do you see the leading edge of the wing? Fuel tanks in precise the wrong attitude: lots of drag. And it's a compound wing, extra drag.

In the future, when fluid dynamics become reality, everything changes.

Edited July 21, 2016 by Azimech

[Gman_builder]

10 minutes ago, Azimech said:

Do you see the leading edge of the wing? Fuel tanks in precise the wrong attitude: lots of drag. And it's a compound wing, extra drag.

In the future, when fluid dynamics become reality, everything changes.

That is why FAR style errordynamics could benefit KSP a lot. But that would essentially render all turboprops useless again. I think there is just to little support for this kind of craft ATM to really do anything magical with them. A lot of people don't get into turboprops because the bearing alone can be to much of a buggy challenge for some people.

I guess the necessary knowledge to build them comes with a lot of experimentation and experience.

[Azimech]

9 minutes ago, Gman_builder said:

That is why FAR style errordynamics could benefit KSP a lot. But that would essentially render all turboprops useless again. I think there is just to little support for this kind of craft ATM to really do anything magical with them. A lot of people don't get into turboprops because the bearing alone can be to much of a buggy challenge for some people.

I guess the necessary knowledge to build them comes with a lot of experimentation and experience.

FAR doesn't make turboprops useless, just much harder. I've had stock helicopters & planes flying with FAR in 0.90 and before.

Before the public release of my first stock turboshaft craft, I made this video:

 

[Gman_builder]

1 minute ago, Azimech said:

FAR doesn't make turboprops useless, just much harder. I've had stock helicopters & planes flying with FAR in 0.90 and before.

Before the public release of my first stock turboshaft craft, I made this video:

 

Ya that's what I mean. In the same way the transition from KSP 0.90 to 1.0 made turboprops significantly harder and much more inefficient. The same way FAR would. FAR doesn't like big flat surfaces, like most turboprops have and the built in RPM limiter that cant be changed makes reaching high enough RPM and having little enough drag to fly extremely difficult. We would essentially have to completely change our designs.

[Azimech]

Just now, Gman_builder said:

Ya that's what I mean. In the same way the transition from KSP 0.90 to 1.0 made turboprops significantly harder and much more inefficient. The same way FAR would. FAR doesn't like big flat surfaces, like most turboprops have and the built in RPM limiter that cant be changed makes reaching high enough RPM and having little enough drag to fly extremely difficult. We would essentially have to completely change our designs.

Built in RPM limiter? I'd have to contact ferram4 about this.

And here's an animation:

Animation is not real time, obviously.

[Gman_builder]

Just now, Azimech said:

Built in RPM limiter? I'd have to contact ferram4 about this.

Ya it is limited to the same 31.something rad/s and it can't be adjusted like stock can. So if you install FAR to try to built turboprops with it your basically back to square one with even more challenges.

[Pds314]

2 hours ago, Gman_builder said:

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.

Well, yeah, but a car engine just has to spin the wheels, which weigh a lot less than the car. Nonetheless, you're still moving an entire car or an entire plane.

Let's take a look at a plane and a car, shall we?

I have a 2005 Kia Optima. They are not a great car. They are a cheap car, but not a great one. It looks very much like this, but this picture is from Wikipedia:

It weighs 1500 kg. It has an I4 piston engine with 199 Newton Meters of engine torque at 3000 RPM and decreasing above that, with output power peaking at about 103000 watts at 5500 RPM. In first gear (automatic shiftable), this is equivalent to about 750 Newton meters on the wheels, at about 800 RPM. In fourth gear, it's equivalent to about 188 Newton Meters max torque at about 3200 RPM.

Now compare this to the Cessna 172:



Which has also a 4-cylinder piston engine in an I4 configuration, but one which operates at 2400 RPM and produces simultaneously 120 KW and 480 or so Newton-meters of torque runnign on direct drive. The plane weighs about 770 kg without fuel, passengers or cargo.

So basically, the Cessna's torque is at parity with my car in second or maybe third gear. Lower static torque. Higher torque at speed. Aero engines are not lacking in torque, as a rule anyway. Also consider that the car is designed to be able to run at up to 6500 RPM before redlining, still producing good torque up to 5500 rpm, whilst the Cessna's engine is designed for high torque at 2400 rpm.

Remember, whilst they just need to turn the prop, they also need to turn it hard enough to generate enough thrust to keep airborne. A Cessna generates some 900 lbs of static thrust, whereas my car generates about 550 lbs of static force.

Edited July 21, 2016 by Pds314

[Azimech]

Oh we're posting cars now? Mind if I post mine too?

[Gman_builder]

Just now, Azimech said:

Oh we're posting cars now? Mind if I post mine too?

Lol I'm in as well

[Pds314]

18 minutes ago, Azimech said:

Oh we're posting cars now? Mind if I post mine too?

Mostly just trying to explain how cars actually don't have more torque than planes, using mine as an example.

In any case, for turboshaft cars, the big problem is that unless it has a gearbox, you get enormously powerful engines running at peak power to generate ordinary amounts of torque at tiny RPM.

So for example, I made a little 2-blower turbo-tractor



And it really can't get the efficient RPM range. 7.3 m/s and maybe 12 rads/s. Also skids around like mad and tends to explode. If I only had a gearbox and some wheels that didn't want to skid like mad...

Edited July 21, 2016 by Pds314

[Azimech]

This is Flying Frankenstein, my own car, the one I've assembled myself but based on a Citroën BX GT. It had a carbureted engine with 5 manual, I've given it a turbodiesel with automatic, digital dashboard and a panel at the ceiling with 12 switches for power, engine control and starting. It already had self-leveling hydro-pneumatic suspension and 80 bar power brakes. Bought it 10 years ago, transformed it into it's current form 2 years later. It's 31 years old and it's my wish to keep this driving for as long as possible, at least another 20 years. It's maintenance costs are very low because I'm my own mechanic.

For those unfamiliar with Citroën's world famous hydropneumatic suspension: It's self-leveling, and the car is parked so it's in it's lowest position.

 

Seems Imgur or the forum cuts the pictures when embedding atm.

 

Edited July 21, 2016 by Azimech

[Pds314]

7 minutes ago, Azimech said:

This is Flying Frankenstein, my own car, the one I've assembled myself but based on a Citroën BX GT. It had a carbureted engine with 5 manual, I've given it a turbodiesel with automatic, digital dashboard and a panel at the ceiling with 12 switches for power, engine control and starting. It already had self-leveling hydro-pneumatic suspension and 80 bar power brakes. Bought it 10 years ago, transformed it into it's current form 2 years later. It's 31 years old and it's my wish to keep this driving for as long as possible, at least another 20 years. It's maintenance costs are very low because I'm my own mechanic.

For those unfamiliar with Citroën's world famous hydropneumatic suspension: It's self-leveling, and the car is parked so it's in it's lowest position.

 

Seems Imgur or the forum cuts the pictures when embedding atm.

 

LOL. Only reason I used my car as an example is to have an example that's sufficiently not Cherrypicked for the RPM and torque typically used in cars.

Edited July 21, 2016 by Pds314

[Azimech]

1 minute ago, Pds314 said:

LOL. Only reason I used my car as an example is to have an example that's sufficiently not Cherrypicked for the RPM and torque typically used in cars.

Yeah I'm a bit silly at times.

[Pds314]

I suppose using very small wheels would allow better turbocars in the sense of fuel efficiency, but the the problem is that the torque radius of an ungeared, uncanted axle must be smaller than the wheel radius.

Edited July 21, 2016 by Pds314

[Gman_builder]

38 minutes ago, Pds314 said:

Well, yeah, but a car engine just has to spin the wheels, which weigh a lot less than the car. Nonetheless, you're still moving an entire car or an entire plane.

Let's take a look at a plane and a car, shall we?

I have a 2005 Kia Optima. They are not a great car. They are a cheap car, but not a great one. It looks very much like this, but this picture is from wikipedia:

It weighs 1500 kg. It has an I4 piston engine with 199 Newton Meters of engine torque at 3000 RPM and decreasing above that, with output power peaking at about 103000 watts at 5500 RPM. In first gear (automatic shiftable), this is equivalent to about 750 Newton meters on the wheels, at about 800 RPM. In fourth gear, it's equivalent to about 188 Newton Meters max torque at about 3200 RPM.

Now compare this to the Cessna 172:


Which has also a 4-cylinder piston engine in an I configuration, but one which operates at 2400 RPM and produces simultaneously 120 KW and 480 or so Newton-meters of torque runnign on direct drive. The plane weighs about 770 kg without fuel, passengers or cargo.

So basically, the Cessna's torque is at parity with my car in second or maybe third gear. Lower static torque. Higher torque at speed. Aero engines are not lacking in torque, as a rule anyway. Also consider that the car is designed to be able to run at up to 6500 RPM before redlining, still producing good torque up to 5500 rpm, whilst the Cessna's engine is designed for high torque at 2400 rpm.

Remember, whilst they just need to turn the prop, they also need to turn it hard enough to generate enough thrust to keep airborne. A Cessna generates some 900 lbs of static thrust, whereas my car might generate about 1000 lbs of static force.

Interesting, but what I am saying is this.

My car, a 2012 Volkswagen Jetta weighs roughly 1500kg and runs on a straight 5 engine producing 170 horsepower at 5700 RPM and 177 lbs/ft of torque 4250 RPM.

Similar to the Cessna's engine but the difference is this.

Engine in the car is linked directly to the wheels through gears and axles, and the wheels also support the weight of the entire car(obviously) so the engine has to move the WHOLE WEIGHT of the vehicle. Whereas in a aircraft all the engine has to do is spin the propeller. Which weighs a small fraction of the weight of the entire aircraft.

So this is how I measure it.

Weight that has to be moved per engine:

Aircraft engine: However much a prop weighs(100 pounds maybe)

Car engine: Weight of entire car(I.E. 3019 pounds)

 

So the car engine uses MORE TORQUE to move the vehicle. Especially during acceleration.

I don't know how to factor in air resistance on a prop and how that affects engine torque and power output but I imagine it is very little especially at the slow speeds of a Cessna 172.

 

I'll be here all week folks

 

I like your car Alex....

Edited July 21, 2016 by Gman_builder

[Pds314]

20 minutes ago, Gman_builder said:

Interesting, but what I am saying is this.

My car, a 2012 Volkswagen Jetta weighs roughly 1500kg and runs on a straight 5 engine producing 170 horsepower at 5700 RPM and 177 lbs/ft of torque 4250 RPM.

Similar to the Cessna's engine but the difference is this.

Engine in the car is linked directly to the wheels through gears and axles, and the wheels also support the weight of the entire car(obviously) so the engine has to move the WHOLE WEIGHT of the vehicle. Whereas in a aircraft all the engine has to do is spin the propeller. Which weighs a small fraction of the weight of the entire aircraft.

So this is how I measure it.

Weight that has to be moved per engine:

Aircraft engine: However much a prop weighs(100 pounds maybe)

Car engine: Weight of entire car(I.E. 3019 pounds)

 

So the car engine uses MORE TORQUE to move the vehicle. Especially during acceleration.

I don't know how to factor in air resistance on a prop and how that affects engine torque and power output but I imagine it is very little especially at the slow speeds of a Cessna 172.

 

I'll be here all week folks

Well, sorta.

The turning the prop part isn't hard. It's the fighting air resistance part that's hard. Remember, as a rule, if a prop isn't generating meaningful air resistance, it probably isn't generating meaningful lift either.

So yeah, while the prop is spinning up from 0 to 2400 rpm, you don't need a lot of torque to make that happen.

But basically, somehow or other, you're draining 120 kilowatts of power and 480 N*meters of torque into the prop. It wouldn't matter if the prop weighed 100 grams, it isn't the propeller spinning on the shaft generating resistance, but the air being thrown around by the propeller. Divide 900 lbs by the static L/D of the prop blades, which is probably like 6 or something, and you get the amount of drag on the prop blades (this is 150 lbs between them based on my guess L/D). This drag is, on average, 70% of the way down the blades, which are about a meter in radius (give or take an inch or two) and therefore ends up with about 345 foot lbs or about ~466.9 N*meters of torque.

Which is pretty good. My initial guess led to an error of about 3%.

Remember that the car has inertia as does the plane. A car engine doesn't need to lift a car, it needs to push a car. A person can push a car, albeit not fast. A plane engine doesn't precisely need to lift a plane either, but push it so that the wings can lift it. An anecdote that the restaurant on top of the Space needle is spun by a motor little more powerful than that of a sowing machine comes to mind. Originally, the motor was 1 HP, but is now 1.5 HP. That's less than a person peddling a crank can potentially yield.

Ultimately, both vehicles must in order to accelerate produce more forward force than the oncoming drag. A car generates about 1/50th of its weight in drag at all times on typical Asphalt, so in order to maintain speed, it must overcome this drag due to rolling resistance. This means that whether your car is at 30 m/s or 1 m/s, it is generating about 300 Newtons of rolling resistance.

Cars also generate aerodynamic drag. A typical car has a drag coefficient of perhaps 0.35, with new cars and sedans being better in this respect than older cars and SUVs. Let's say a Sedan has a frontal area of 3 square meters and a drag coefficient of 0.33, rounding off the numbers at about 1 m^2 Cd*A

And for simplicity's sake, the atmosphere is 1 kg / m^3.

This means that atmospheric drag is roughly v^2/2 N of drag.

So a car at 10 m/s generates 50 Newtons of air drag and 300 of rolling resistance. A car at 20 m/s generates 200 of air drag and 300 of rolling resistance. A car at 30 m/s generates 450 of air drag and 300 of rolling resistance, etc.

And of course the "lift" of a car is always its weight on a level road.

So this means that the L/D of a car is effectively 50 stopped, 30 at 44 mph, 13.6 at 88 mph, etc.

Whereas a plane must deal with LID as well.

Cars don't need a lot of force to get moving. Planes do.

Edited July 21, 2016 by Pds314

[Gman_builder]

1 minute ago, Pds314 said:

Well, sorta.

The turning the prop part isn't hard. It's the fighting air resistance part that's hard. Remember, as a rule, if a prop isn't generating meaningful air resistance, it probably isn't generating meaningful lift either.

So yeah, while the prop is spinning up from 0 to 2400 rpm, you don't need a lot of torque to make that happen.

But basically, somehow or other, you're draining 120 kilowatts of power and 480 N*meters of torque into the prop. It wouldn't matter if the prop weighed 100 grams, it isn't the propeller spinning on the shaft generating resistance, but the air being thrown around by the propeller. Divide 900 lbs by the static L/D of the prop blades, which is probably like 6 or something, and you get the amount of drag on the prop blades (this is 150 lbs between them based on my guess L/D). This drag is, on average, 70% of the way down the blades, which are about a meter in radius (give or take an inch or two) and therefore ends up with about 345 foot lbs or about ~466.9 N*meters of torque.

Which is pretty good. My initial guess led to an error of about 3%.

Ya I understand, but I think part of the equation is the fact that props are specifically designed to have as little drag as possible in flight. That's why we increase the pitch on our props in KSP, to minimize drag.

A prop is essentially a rotating wing. So when the aircraft is stationary, there is little pitch on the prop. This is because lift(thrust) is maximized and drag is minimized through the prop rotating directly into the airflow. No speed, equals no forward airflow. When you are at high speed, the leading edge of the prop is still pointing into the airflow, so there is little affect on the RPM of the engine. High speed equals high forward airflow.

Given there may be more torque being utilized to keep the prop running, it is not like the torque on a car's engine either cruising or accelerating.

I have to go feed someones cat so i'll be back in 20 minutes. I will explain my idea further.

[Pds314]

18 minutes ago, Gman_builder said:

Ya I understand, but I think part of the equation is the fact that props are specifically designed to have as little drag as possible in flight. That's why we increase the pitch on our props in KSP, to minimize drag.

A prop is essentially a rotating wing. So when the aircraft is stationary, there is little pitch on the prop. This is because lift(thrust) is maximized and drag is minimized through the prop rotating directly into the airflow. No speed, equals no forward airflow. When you are at high speed, the leading edge of the prop is still pointing into the airflow, so there is little affect on the RPM of the engine. High speed equals high forward airflow.

Given there may be more torque being utilized to keep the prop running, it is not like the torque on a car's engine either cruising or accelerating.

I have to go feed someones cat so i'll be back in 20 minutes. I will explain my idea further.

Right, but at some point there are also the hard laws of physics to contend with. An ideal actuator disk a meter in radius at sea level can't actually get 4000 Newtons of thrust without a certain minimum input power. The bare minimum is to accelerate all that air to around 32.6 m/s, which takes about 65 Kilowatts, minimum. Add in that props are notoriously bad at stalled thrust and you can see why our efficiency is around 55%. Actually, if we increase the thrust desired to the maximum static thrust of 4500 Newtons, we're more like 65% efficient, which is about what you'd expect for something like this.

Edited July 21, 2016 by Pds314

[Pds314]

Interestingly, if we compare my KSP Screacher 2x1 engine to an ideal actuator disk 4 meters wide (the prop diameter), we get an interesting result The engine has, at 50 rad/s, about 700-800 kW of power and gets about 30 kN statically with the right prop.

Interestingly, the result is that it needs about 680 kW to do this. I suspect, however, that rather than super-efficient props, the reason it is capable of such a feat is either prop expansion or lack of blade interaction. With this in mind, it could be possible to build props in KSP but not in real life which are physics-defyingly efficient.

Similarly, my engine gets 360 kW thrust power from about 60% of max RPM with the same prop. This is again an indication that the props are highly efficient for their size.

(Now if only I could get 2 Megawatts of thrust power out of the Screacher 6x1...)

Edited July 21, 2016 by Pds314

[Gman_builder]

2 minutes ago, Pds314 said:

Interestingly, if we compare my KSP Screacher 2x1 engine to an ideal actuator disk 4 meters wide (the prop diameter), we get an interesting result The engine has, at 50 rad/s, about 700-800 kW of power and gets about 30 kN statically with the right prop.

Interestingly, the result is that it needs about 680 kW to do this. I suspect, however, that rather than super-efficient props, the reason it is capable of such a feat is either prop expansion or lack of blade interaction. With this in mind, it could be possible to build props in KSP but not in real life which are physics-defyingly efficient.

I wonder if something like a power turbine could be utilized in KSP to drive cars and mechanical devices that don't fly.

 

[Pds314]

6 minutes ago, Gman_builder said:

I wonder if something like a power turbine could be utilized in KSP to drive cars and mechanical devices that don't fly.

 

The biggest problem here is that the game has no fluid dynamics.

[Gman_builder]

2 minutes ago, Pds314 said:

The biggest problem here is that the game has no fluid dynamics.

well

 

s h i t

I can't think of a better way to reduce the torque on the turboshaft besides designing a geared transmission which is all but impossible.

[Pds314]

11 minutes ago, Gman_builder said:

well

 

s h i t

I do wonder, however, if you could make what one might call an over-unity turbine. Real-life wind turbines are limited to about 59% efficiency, and more like 45% in real life where things are not magically perfect, but I'm not sure about KSP turbines and props. It might be possible to build a device which, upon being moved through the air, turns a shaft, moving it through the air, turning the shaft more, increasing RPM and therefore thrust, etc etc until the Mach barrier reduces efficiency.

I.e. At 100 m/s, it generates enough torque to make meaningful thrust, which outweighs drag. This may or may not be possible with KSP's aerodynamic (or errordynamic, if that works) model. Essentially, this would be using a wind turbine to drive a fan to accelerate the wind turbine to drive the fan. Infiniglide turbine would I suppose be another name for this device.

The electrical version is this:

Edited July 21, 2016 by Pds314

[Gman_builder]

1 minute ago, Pds314 said:

I do wonder, however, if you could make what one might call an over-unity turbine. Real-life wind turbines are limited to about 59% efficiency, but I'm not sure about KSP turbines and props. It might be possible to build a device which, upon being moved through the air, turns a shaft, moving it through the air, turning the shaft more, increasing RPM and therefore thrust, etc etc until the Mach barrier reduces efficiency.

Hmm, interesting concept, but i'm not sure how one would go about building that.

[Pds314]

2 minutes ago, Gman_builder said:

Hmm, interesting concept, but i'm not sure how one would go about building that.

It would be pretty simple to build an experimental version: make a thing with wings that also has other wings. Try to build it in such a way that the lift off some of the wings is enough to generate thrust with the other wings.

The question is whether KSP physics are sensible enough to disallow such absurdity.