Setting the throttle curve

	Setting the throttle curve Last updated 11-29-2006
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For a description of what a throttle curve is, go to the Frequently Asked Questions page <here>.

Two steps describe the throttle curve setup:
1. Adjust the throttle point at hover to give the rpm you want.
2. Adjust all other points to give the same rpm.
The key phrase is "Constant RPM". The end result should be that the head speed is the same at all throttle stick positions (with the exception of the bottom point in the normal flight mode).

NOTE: On the JR 9303 it uses a 7 point curve. This can be confusing. What I do is a seperation of 8 and 10. So for normal mode I will have 15,42,52,50,58,68,100

1. Normal flight mode throttle curve - click <here> to read about pitch ranges

If you are just starting out then normal flight mode is the only one you need to setup. When I setup this mode I start with 20,40,50,60,100 for the five points of the throttle curve. The bottom point is set to 20% for radios with a digital type throttle trim. If the radio has a mechanical trim then I set the bottom point to 0%. The top point is set to 100% to start with. This can change later in the setup. The middle point is set to 50% for all helicopters. If the radio has a five point curve then I set the 1/4 stick point to 10% less then the middle (50-10=40%) and the 3/4 stick point to 10% above the middle (50+10=60%). The 10% around middle will make the hover smooth and will also help to keep the throttle up on steep descents.
So now that the points are set in the radio (and all other setups on the helicopter have been done) I get ready to crank the helicopter. I start with setting the radio to the throttle curve menu and on the bottom point waiting to be adjusted. I then crank the helicopter and adjust the bottom point to give a good idle. A good idle is a speed just low enough to not turn the rotor blades.
*For the following step you need to have 5 degrees pitch at center stick.
Next I work on setting the middle point. I hover the helicopter and note if the stick is below center, centered, or above center. If it hovers at center stick then you are ready for the next step. If it hovers below center then lower the middle points. If it hovers above center then increase the middle points. Now the limit for changing the middle points is +/-10%. If you need more then it is not a radio problem, it is an engine tuning problem. If it hovers below center then richen the engine. If it hovers above center then lean the engine. Remember that if you have a five point curve then keep the 1/4 and 3/4 points 10% from the middle point. So if you move the middle point then move the other two points by the same amount.
The only point left is the top point. From hover do a full power climbout and if the rpm increases then either the main needle on the engine is too lean or the top throttle point needs to be lowered. Initially I will go for the engine adjustments but if that makes a bad effect on the flight mode 1 then I will lower the top throttle point. If you are new then you should assume it is an engine adjustment before moving the throttle point.

Here are some sample throttle curves:
weak 30 size = 20, 50, 60, 70, 100
strong 30 size = 20, 40, 50, 60, 100
50 size = 20, 30, 40, 50, 80
60 size = 20, 40, 50, 60, 80
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You may notice a trend here, it has to do with power to weight. The higher the power to weight the lower the middle points are. Another thing you will notice is the top point is not always 100% on the more powerful engines. Yes, we could add more pitch on the top end and bring the throttle back up to 100 without exceeding the rpm set at hover and while that is great for drag racing it leads to other problems for normal and 3D flying. First you increase the pitch range making it a little less precise and second you cause the blades to now be able to reach stall angles (remember that the cyclic stick input plus the collective input is the total pitch).
In the samples I list the 1/4 and 3/4 points are are 10% above and below the middle point. Setting these two points close to the hover point gives a smooth hover by making the collective less touchy in the center area. Now this is for 1/2 stick hover. I do not like 3/4 stick hover for reasons stated <here>, but if you do then do the same, but instead of using the 25% and 75% points you will have to use 62% and 87% points. You will only be able to do this with the high dollar radios like the JR 10X and the Futaba 9Z.
The values in the list at the top are close starting points. What you need to do to refine them is to get the helicopter in a hover and see if the head speed is what you want. Normal flight mode should be 1600 rpm. If your head speed is higher then bring all three middle points down. So if you have 20,40,50,60,100 then try 20,37,47,57,100. This keeps the 10% difference around the middle point.

Tip: A common problem is during a descent the engine goes to idle. This is because the 1/4 point is too low. This is another reason I use the 10% technique. This can also be caused by the bottom pitch being too high. If you are flying around enough to run into this problem then you should be using a lower pitch, try -2 degrees and as you get more comfortable with this then go to -4. You should not need to go any lower then that for normal flight mode.

FAQ: Why is the bottom throttle point not at 0? Because 0 represents 'engine off' and that is not what you want the engine to do when you are flying around and move the stick all the way down :) The throttle points represent the stick positions. So for a 5 point throttle curve you have 1)stick at bottom 2)stick 1/4 up 3)stick in the middle 4)stick 3/4 up 5)stick at top. The values at each of these positions represent where you want the throttle arm on the engine to be. So with the throttle stick at the bottom and the throttle trim up then you want the throttle arm to be open enough to acheive a good idle speed.

2. Flight mode 1 (aka Idle Up 1, aka Stunt mode) - click <here> to read about pitch ranges

Here are some sample throttle curves:
weak 30 size = 100, 74, 62, 74, 100
strong 30 size = 100, 60, 50, 60, 100
50 size = 100, 50, 42, 50, 100
60 size = 100, 60, 50, 60, 100
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Just to restate what was mentioned above:
1. Adjust the throttle point at hover to give the rpm you want.
2. Adjust all other points to give the same rpm.
The key phrase is "Constant RPM". The end result should be that the head speed is the same at all throttle stick positions. There is no magic here, let's use the example of a 3D V-curve setup like listed above. This is of course with a -9,0,+9 pitch curve. Start by hovering at 3/4 stick and adjusting the 3/4 throttle point until you acheive the head speed you want. For a 30 size you want to setup for 1900 rpm. For larger blade helis 1800 to 1850 for good response with the more radical maneuvers. Now that you have the hover rpm set you can duplicate this value for the 1/4 point, remember this is a v-curve. To set the middle point you start with a hover up high then move the throttle stick to center position. Listen to the rpm and adjust this point to again get the same rpm as you had at hover. If you have problems of overspeeding when coming down during tail slides or a knifeedge then lower the middle point a little more. The top and bottom points will usually be 100%, but this is not a given. It is based on things like engine tuning, top end pitch, head speed you run, engine strength, and gearing. There are also situations that limit the usable carb range due to faulty designs that cause leaning in the mid range. All this will be covered in my advanced tuning page (this page has not been uploaded yet due to difficulties I am having in expressing all of the concepts in words).