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THX1138

How to use R121 Turboshaft Engine?

Question

I put on a R121 Turboshaft Engine on a plane but there is no staging for it and I don't seem to be able to turn it on. Why does it come under robotics and not engines?

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2 hours ago, RocketSquid said:

Oh, right, I should probably be adjusting my prop pitch and not just leaving it at a constant value. 

And don't assign anything to the main throttle axis group. Use custom axis groups instead.

When testing for best speed it soon becomes apparent that there is a very narrow window for optimum prop pitch. You will either need to get lucky to find this optimum setting or have switched on fine control (caps-lock). Main throttle keys do not seem to respond to the use of fine control but custom axis group keys do respond.

As an example, if I takeoff and have rpm limit on the main throttle the smallest change I can make with or without fine control is 4 rpm with a sharp tap on the throttle keys. With rpm limit assigned to a custom axis group, the smallest change I can make with fine control switched on becomes on average 0.2 with the same sharp tap. With prop pitch on a custom axis group the smallest change I can make is 0.5 (or two taps to make a change of 1). Best speed is achieved within a prop pitch window of 0.5 - 1.

After takeoff, reducing prop pitch will usually increase speed until a point is reached where either the speed starts to drop or the current rpm (not the rpm limit) starts to drop below 460. The value of the prop pitch at this point is worth remembering. When starting a sharp turn or a steep climb it may often be worth changing the prop pitch back to this value. Effectively you can control airspeed and power by only using the prop pitch.

But you need the current rpm to drop in order to reduce prop pitch to achieve the fastest speeds.

If say, in level flight, the current rpm does not start to drop and speed reduces when you reduce prop pitch from this value, you can force it  by reducing the rpm limit and further reductions in prop pitch should see a marked increase in speed. At some point the current rpm will usually drop below the rpm limit. Quite often though, the current rpm will drop by itself leaving you to concentrate on finding the optimum pitch for speed.

When trying to find the best settings for maximum range, only two things seem to affect fuel consumption - rpm limit and torque limit. Again it will be a benefit to be using fine control with nothing assigned to the main throttle keys.

On 7/21/2019 at 7:24 AM, THX1138 said:

As if landing a plane isn't hard enough. Literally unplayable!

I find landing to be pretty easy. I reduce rpm limit and torque limit if for no other reason than making sure I don't run out of fuel before landing then on final approach, increase prop pitch back to 100 and drop the landing gear. Speed drops dramatically but flying in under power still provides good control.

All robotic engines can have an action group key assigned to toggle the motor direction. So on touchdown, reverse the engines until stopped or nearly stopped then use another action group key to toggle prop deployment. This is much safer and much more effective than using brakes.

Like @aegolius I disengage the engines in the SPH so my usual setup is something like this

Action group 1 - Toggle engage engines
Action group 2 - Toggle engine power (full torque on/off)
Action group 3 - Toggle prop deployment
Action group 5 - Toggle motor direction
Custom axis group 1 - prop authority
Custom axis group 2 - rpm limit
Custom axis group 4 - torque limit

So takeoff is as simple (after engaging SAS with the 't' key) as 1,2,3.

If you want to see a hard to land plane, you can check out the landing at the end of the video below which was made for the Kerboprop Speed Challenge - which requires a landing back on the runway. And it wasn't hard. The optimum prop pitch for speed with this plane is 29.5 - note that the current rpm is only 220.7 at 298.6m/s -  while the value for the prop pitch I use to maneuver is 70 and you can see me increase it back to 70 as I start the vertical climb preparatory to returning to the runway and then back to 100 just before landing.

 

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They are under Robotics because they're basically the same as rotors just with different input resources.

That also means you need to control them like rotors, i.e. set RPM and torque either manually or through axis or robotics controller

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I've found it works well to set the thing up with motor disengaged, have an action button to toggle on and off, and then bind torque or RPM to the throttle.  (Some people seem to use the throttle for prop pitch as well).

Having the engine default to "on" seems to cause problems as physics kick in.

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Thanks but imagine if you had to set rocket thrust manually in the part menu whilst flying? As if landing a plane isn't hard enough. Literally unplayable!

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6 hours ago, THX1138 said:

Thanks but imagine if you had to set rocket thrust manually in the part menu whilst flying? As if landing a plane isn't hard enough. Literally unplayable!

You don't have to set the thrust manually. Just bind the RPM limit to the main throttle axis group, and the "activate rotor" action to the stage action group, and it will behave like any other engine.

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3 hours ago, RocketSquid said:

You don't have to set the thrust manually. Just bind the RPM limit to the main throttle axis group, and the "activate rotor" action to the stage action group, and it will behave like any other engine.

Well apart from having to manually adjust prop pitch for airspeed.  

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On 7/21/2019 at 3:38 AM, Foxster said:

Well apart from having to manually adjust prop pitch for airspeed.  

Oh, right, I should probably be adjusting my prop pitch and not just leaving it at a constant value.

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Posted (edited)

When I load onto the runway, the engine is already engaged so using that action button disengages the engine. If the engine is engaged, when I use the action button to toggle engine power, the engine disengages - the propeller starts to turn slowly but gets slower and slower until it stops. The engine cannot then be re-engaged until I toggle the engine power again. None of the other buttons help either. 

Never mind; I thought it used electricity, not liquid fuel.

Edited by THX1138

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