# Why does airspeed increase with more throttle if RPM stays the same?

Given a constant speed propeller, the RPM will stay the same because of the governing system which changes the blade angle. But in cruise flight if you add more power and keep the RPM's the same, there is an increase in airspeed.

So when there is an increase in throttle/MP and more fuel/air mixture goes to the cylinders, does that extra combustive force attempt to spin the shaft faster and thus the blade angle increases and takes a "bigger bite of air"? Or is there some aspect of increased torque force pushing harder against the air?

I prefer the first explanation but I have heard some form of the second one being used, but in a more complete way. I honestly can't remember how that was described and I think I just misunderstood that explanation. What am I missing?

• Re "Or is there some aspect of increased torque force pushing harder against the air?" -- why the word "or" in this sentence? Aren't "attempt to spin the shaft faster"/ "takes a "bigger bite of air" and "increased torque force pushing harder against the air" fully compatible concepts? Seems like this is essentially just two different ways of saying the same thing. Commented Dec 4, 2022 at 1:26
• Could you perhaps improve the question by isolating one particular variable that you are trying to understand whether it stays constant, or doesn't, when the throttle position is changed? LIke, I dunno, just brainstorming here, total momentum change of air flow as it moves through the prop disk? Volume of air moved? Average velocity change of air? Or perhaps simply torque applied to prop shaft? Don't want to rewrite your question for you, but seems like you have presented two sentences that are not clearly different, and are asking "which is true?" Commented Dec 4, 2022 at 1:32

## 1 Answer

Yes, your assumption as stated below is correct. There's really no simpler way to explain it than that.

So when there is an increase in throttle/MP and more fuel/air mixture goes to the cylinders, does that extra combustive force attempt to spin the shaft faster and thus the blade angle increases and takes a "bigger bite of air"?