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3 Answers

Static runup

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Aircraft Systems

I'm confused as to how and why a static runup is done. The instructions given are as follows, "Prior to takeoff from fields above 3000 feet elevation, the mixture should be leaned to give maximum power in a full throttle static runup" for the 172RG. From what I get it is used to compensate for decreased air density, but can't seem to visualize how its done...

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3 Answers



  1. Chris Polek on Jun 04, 2014

    Your POH for the airplane should list what the maximum static RPM is. Since you have a Constant speed prop in a 172RG it would probably be around 2700 rpm maybe a little less since the prop tends to spin faster when in forward flight. The propeller has excess air built up around it when the plane is sitting still which loads it down. when you start your takeoff roll the prop rpm will usually increase around 50 to 100 rpm as you approach rotation speed. I suggest flying with an instructor or another pilot as they do the takeoff and you concentrate on the Tachometer so you can see this minor speed change. To set your mixture for takeoff from not only fields with elevation above 3000 feet also any field with a density altitude of above 3000 feet. Set the brakes advance the power to full and if your not in the range of the max static rpm of what the POH says adjust the mixture until the speed increases to the bottom end of the limit. then reduce the power to idle but leave the mixture there for takeoff. If you have a long enough runway and as you get more comfortable with the airplane you can make this adjustment on takeoff roll

    As for the first part of your question. Typically the only time a static run up is done is during maintenance or any inspections to make sure the engine can achieve it’s maximum static rpm that would be a requirement for airworthiness of the airplane. But if you for any reason suspect that the engine does not make full power I would do one the same time you do your magneto checks. just be careful of where you are parked as you taxi into your run up area be aware of the condition of the ramp and what is around you. If you know your density altitude is above 3000 feet chances are you will not achieve full static rpm because the air is too thin and the engine is set up to run on the rich side for cooling. So now you have too much fuel so by leaning out the mixture you have the engine set up for the proper ration fuel/air to achieve maximum power for takeoff. typically bellow 3000 feet most engines will achieve this ratio with the mixture rich only in the thinner air above 3000 feet will you need to make this adjustment.

    Hope this helps

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  2. Mark Kolber on Jun 04, 2014

    How i;’s done: You hold the breaks while going to full power on the throttle. In this case “static” just means “not moving.”

    And “maximum power” means the maximum rpm the aircraft is capable of at that density altitude. There are guidelines that will tell you how much power is lost just from the altitude increase – about 3% per 1,000′), but for practical purposes it means you start will a full mixture. As you lean, RPM will increase and then, when you become too lean, it will start decreasing. Your goal is to use the sequence to find the point where RPM is at its highest.

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  3. psequeira on Jun 05, 2014

    Thanks a ton Chris and Mark. All clear now!

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