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2 Answers

Why is the throttle open 1/4inch when start up engine C172

Asked by: 1023 views , ,
Aircraft Systems, Student Pilot


I'm progress in PPL in South Korea.

My question is 'Why is the throttle open 1/4inch when start up engine C172'

Of course, it need open the throttle open for smooth start engine. but why 4/1 inch?

There are many option, like a 3/1 inch or 5/1 inch.

I don't know why specific length of open throttle. Thx.


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2 Answers

  1. Best Answer

    Russ Roslewski on Apr 13, 2017

    There’s no magic to 1/4 inch. 1/3 inch, 1/5 inch, 1/2 inch will all work just fine. The idea is you just have to have the throttle open “a little”. But since everybody’s definition of “a little” is different, they give you a number – 1/4 inch.

    I have yet to have anybody measure it before starting, so your estimate of 1/4 inch is likely different from mine. But if the engine starts, it was good enough.

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  2. John Scarry on Apr 13, 2017

    The next time you fly, pay attention to where the throttle is when you taxi at normal speed, do your runup, and when idling at 800-1000′ RPM. My guess is that at 800 RPM the throttle is about ¼”. If you start the engine with the throttle where it would be for runup, you would start up at ~1700 RMP. Not good.

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