Throttle Linkage Geometry
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Throttle Linkage Geometry |
If you're having a lack of power symptom on
climb outs, you might want to check the throttle linkage
geometry. I know you may be thinking that can't be it!!!
I thought the exact same thing until I saw it with my own
eyes. Last October (1999) at Mr. Kolls event, VinceH and
I were trying to figure out why his Raptor would sag on
climb outs. Bill Meador showed us how to properly setup
the throttle linkage geometry. Afterwards, Vince's Raptor
no longer sagged on climb out. I think the reason I did
not have this problem was because I was using a high
speed servo. The concept behind it, is engine throttle/pitch
timing. The engine needs to lead ahead of the pitch. To
do this, we installed a longer servo arm. He had it setup
so the length of the arm gave end points of 100%,100%. We
used a long enough arm to make the end points 80%,80%.
This trades strength for speed and with the collective
set at 100%, 100%, this makes the throttle faster then
the collective. The next important point is to use the
arc of the servo correctly. These are NOT exact
measurements, I am just using clock positions so you can
get an idea how it works. If the low throttle is at an ~8
o'clock position, then as it travels counter-clockwise,
the link to the carb will not move much until the
throttle gets to the ~7 o'clock position due to the angle
of the linkage from the servo horn to carb. As the servo
horn travels from the ~7 o'clock to ~5 o'clock, the link
moves very fast. You need the servo to be fast on this
half so the engine can supply power just before the pitch
causes the extra load. The best example I've heard is
when you're driving a car up a steep hill, if you wait
for the car to start slowing down before you push the gas
pedal more, then you will have trouble getting over the
hill. However if you add more throttle just before the
car slows down, you won't have a problem getting over the
hill. If your collective servo and throttle servo are the
same speed this linkage geometry will make the throttle
servo move the linkage faster then the collective servo
moves its linkage. |
| PS: I can't tell you how many times I have had people tell me their fancy deluxe computer radio will do the same thing by adjusting the throttle curve. It will NOT. No radio can make your servo faster then what the servo was designed. The throttle curve in the radio only tells the servo what position to go to, not how fast to get there. |