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Turbine Throttle Curves

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Turbine Throttle Curves

Old 10-14-2018, 02:04 PM
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bushong572
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Default Turbine Throttle Curves

I've been flying jets for a couple of years now and have been running the stock (Kingtech) throttle curves on all of my turbines 60n,70n, 85n, 140n. The default is "half expo''. I've been thinking about going to "linear" on all of them. Any suggestions????
Old 10-14-2018, 04:56 PM
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mongo
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it will not be what you are used to, and for that reason, you will probably not like it at first. it will not hurt anything to make the change on one engine, and see if you can live with it. then go from there.
Old 10-15-2018, 03:38 AM
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I don't know why anyone would use a throttle curve or expo on a turbine. It isn't a Walbro carb.
Old 10-15-2018, 03:51 AM
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Most of the thrust from a turbine comes in the highest few thousand RPM.

People use the thrust curves to make the thrust response more linear (e.g. half thrust at half stick). Otherwise it can get difficult to set part thrust settings in the small amount of usable throttle throw at the the top of the stick movement.
Old 10-15-2018, 08:07 AM
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Having been an ATP Turbine Capt for twenty years, and flown these for the past 12+ years, I know that the max thrust is in the last ten percent. But we probably temp out more then max engine rpm. Even full scale at altitude, due to temping out, most of the time the rpm doesn't get to 100%. Usually 92-96%. Only ones that I remember getting to 100% were the Garretts. I still don't see the benefit, other than for the 3D guys that might be hovering or high alpha. The curve that you are using, from half stick down to idle is linear? And half stick above with the curve? Which brings up the subject of derating these engines. If you are lowering the top 10 percent of the rpm thrust, the derated turbine isn't producing the thrust that one might think.
Old 10-15-2018, 09:54 AM
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Model turbines are rarely flat-rated (at least at ‘normal’ density altitudes).

If you download the RPM/EGT figures from a typical model turbine flight then you will almost always see the turbine achieving the max RPM that is set in the ECU. The EGT more often than not doesn’t get hot enough to limit at the max EGT.

We are not taking about de-rating here, we are talking about a throttle curve. We also aren’t talking about different ‘curves’ below and above half throttle.

At full throttle you will still be demanding max RPM. The point of the throttle curve is to alter the thrust output so that, for example, rather than having the ECU demanding 50%RPM at half throttle, you set it so that it gives you the RPM that equates to 50% thrust.

If you’re happy with the response of thrust to stick position on your turbine then there is no need to change it. Some people prefer not having a tiny stick movement (the top 10% as you mention) making such a big thrust change. It is those people that benefit from changing the throttle curve.
Old 10-15-2018, 10:22 AM
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On my JetCentrals I always use Linear. Otherwise, like stated above, all the power happens at the top of the stick travel.
Old 10-15-2018, 12:47 PM
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Thanks for the replies...………
I think I will change to "linear" I don't like how most of the thrust is at the top of the throttle stick
Old 10-15-2018, 03:47 PM
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Originally Posted by bushong572 View Post
Thanks for the replies...………
I think I will change to "linear" I don't like how most of the thrust is at the top of the throttle stick
I have even added a throttle curve, where at 50% input you get around 55-60% output to make it feel even more linear on the stick. Experiment until you get the feeling you like
Old 10-25-2018, 12:18 AM
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i really dont see any needs to use expo and curve for turbines.
Old 10-25-2018, 08:18 AM
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Originally Posted by VS.T View Post
i really dont see any needs to use expo and curve for turbines.
Don't use them then
Old 10-25-2018, 09:47 AM
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I have not used curves in awhile, but I am thinking of going back to them to help my son transition to turbines. Here is the curve I used 15 years ago,

http://www.rcuniverse.com/forum/496210-post6.html
Old 10-25-2018, 11:36 AM
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I prefer linear thrust and can usually tell pretty quickly if I'm flying something without a throttle curve. I also use the same curve for my EDF jets as they have the same power characteristics. Linear also gives some rough sense of how much thrust you're using just by where the throttle stick is.

In : Out
100 : 100
87.5 : 95
75 : 89
62.5 : 81
50 : 71.3
37.5 : 58.5
25 : 43
12.5 : 24
0 : 0

Or:

100 : 100
75 : 90
50 : 78
25 : 62
0 : 43
-25 : 17
-50 : -14
-75 : -52
-100 : -100

Turn Expo on. Make minor adjustments to each point to make the curve a smooth arc.

Last edited by Thud_Driver; 10-25-2018 at 11:44 AM.

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