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Throttle Non-Linear


FlyingMonkey

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Hey all...

 

Craig's discussion of the trim wheel stiffness on our training CTSW lead me to write about another quirk of this airplane...the throttle. It seems very non-linear in travel to RPM mapping. I'd say the first third of the throttle is *very* responsive, bordering on too much so. That first third will probably get the engine from idle to about 4500rpm.

 

The middle third of throttle travel seems to have very little effect on rpm, almost a dead zone, the entire middle range maybe going from 4500rpm to 4800rpm. The final third goes from 4800-ish to WOT, about 5400rpm.

 

Is this normal for the CTs? It's not really a problem once you figure it out, but it is pretty non-linear across the whole throttle travel.

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Hi Andy,

 

It's not just the throttle and carbs are rarely linear. First you are transitioning from the idle circuit to the main jet. Then with our altitude adjusting carbs air pressure plays a part, then prop speed and engine torque add to the fray. Wheel drag on the ground and all the flight forces in the air.

 

So bottom line exact throttle position can change when a number of these items or all of them are in play.

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Sorry I asked! :lol:

 

I understand (most) of the variables, but it just seems different from the throttle response in the same engine in the Tecnam P92 I trained in. That airplane had a very linear throttle response. It did have a push/pull throttle knob instead of a lever, so the cabling was probably much simpler. I don't find the CT to be "bad" it's just different and I find myself skipping over the center part of the throttle travel if I need to make more than a 100-200rpm change to get to the "meat" of the response at either end of the range.

 

Would fuel injection make this better? :ph34r:

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OK, Help me on this one,

If the aircraft wheels were sitting on conveyor belt, the speed of which at all times precisely matched the forward speed of the aircraft, would the aircraft take off? If so at what point?

 

It all depends on how non-linear the throttle is!

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Airspeed is dependent on all combined factors of air density, wind, prop, engine rpm assuming level flight and the non-linear throttle factors highly into this enumeration. Major complications are introduced when you introduce sports science to an aviation issue even if the testing is done in the gym environment.

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The non linear throttle in the CT is amplified as compared to the Tecnam because of the length of the throttle lever. Insteasd of a 1 to 1 ratio in the Tecnam it is more like a 2-1 ratio between the throttle and the carbs.

 

It took some getting used to on my 1st flight, I was creeping it way to slowly. Now I like it because it is easly to be precise, I never even noticed the non-linear issue.

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It took some getting used to on my 1st flight, I was creeping it way to slowly. Now I like it because it is easly to be precise, I never even noticed the non-linear issue.

 

I don't have a problem with it either, just saying what the difference is between it and the Tecnam.

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I liked the CT throttle from the beginning. Only had to adjust tension once in 6 years. It's always smooth and stays exactly where I put it.

 

RV-12's, like the one I am building have a throttle that requires a large amount of friction each time you move it. Otherwise it creeps to full throttle. It looks like the throttles on Cessna's and has the same friction lock but is constantly requiring attention. Some builders are solving the problem with weaker springs. Others, like myself, are opting for a vernier throttle. All after the airworthiness certificate is issued of course!

 

Anyhow, I have a lot of appreciation for the CT throttle and wouldn't change it for anything.

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Roger is correct again. Airspeed is dependent on all combined factors of air density, wind, prop, engine rpm assuming level flight.

 

I think you forgot the di-lithium crystals captain!

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