Aviation Training Tip: Manifold Pressure Gauge and Tachometer

0:00After watching this quick tip video, be sure to check out our website at Wi-Fi-CFI.com. Our online aviation courses include Study Courses for the private pilot, instrument rating, commercial pilot, CFI, CFWI, and multi-engine app on Study Courses. All of these include videos, podcasts, quizzes, flashcards, audiobooks, practice FAA exams, check-ride workbooks, and more. We also have courses for just the check-ride lesson plans. These are to teach on those flight instructor check-rides. We've got the CFI, the CFWI, and the MEI add-on lesson plans. They all come in PowerPoint, PF, and dot formats, word formats. They're downloadable, customizable, printable. They've got animations, diagrams, images, included quizzes, and more. Additionally, we have teaching courses. If you're a flight instructor already and you want to teach your students, you can teach your private pilot instrument rating, commercial pilot, CFI initial, and CFWI add-on students with

1:03flight syllabi, lesson plans, homework assignments, binders and tracking, quizzes, logbook audits, endorsements, and more. And you can try every single one of our courses for free for as long as you would like at Wi-Fi-CFI dot com. Manifold pressure gauge is next. There's some misconceptions about what the manifold pressure gauge is. What it does is it measures the pressure of the fuel air mixture inside the intake manifold. That's what it does. It is measuring how much pressure is at the intake manifold. So, if we increase our throttle, we're going to get a manifold pressure increase. This needle is going to go up. If we decrease our throttle, we're going to get a manifold pressure decrease. This needle is going to come down. What if,

2:05then that's all pretty self-explanatory, right? But what if the engine is just sitting there not running? It's sitting on the ramp. You've got your airplane turned off and you're sitting at your parking spot at the airport. It is not going to show zero. This manifold pressure gauge, you can go out, if you've got one in your airplane right now, you can go out and look at it on the ramp. It is not going to be showing zero. It will be indicating whatever the outside ambient pressure for you the day is. Because it is measuring, that's what it's measuring. It is measuring that pressure and there's never zero outside air pressure. If there was, we'd all be dead. We'd be in a vacuum, right? And that's not how Earth's atmosphere works. So, you can go out. If the engine is not running, the manifold pressure gauge will indicate whatever the outside pressure is. Now, we go out there. We see it sitting at whatever it's sitting at. Then we go ahead and start our engine. Once we start the engine, what you're going to see is that the manifold pressure actually

3:06decreases a bit to less than ambient. That is because now we're sucking air through our manifold pressure gauge. And when we, anytime we accelerate air, which you'll learn about in your principles of flight lesson, kind of Bernoulli's principle, is that anytime you accelerate air through an area, it's pressure decreases. When you start your engine, you're not going to see this needle bump up. You're going to see it go down because now all of a sudden we're sucking air through the intake manifold. Air is moving faster through the intake manifold and increased air velocity always equates to less pressure. And that is Bernoulli's principle. That is a scientific principle. If we think about it now, we're up flying in all of a sudden. We have an engine failure or an engine power loss. The manifold pressure is going to increase back to ambient. It's not going to go down to zero. This manifold pressure gauge won't go to zero. You're up flying.

4:07So you have a catastrophic engine failure. Your engine stops running. This is not going to go down to zero. It is going to go to whatever the ambient pressure is. It'll increase to ambient pressure because now we're not sucking air through the manifold anymore. So the velocity is slowed down, which means the pressure increases. And we'll see that increase back to ambient. That's how the manifold pressure gauge works. And a lot of students sometimes will kind of get confused on that. But once you work with it a little bit, you'll see how it works. And you'll get more familiar with it. Engine start. Okay, we talked about that. Engine failure will actually register as an increase on and so forth. The techometer. The governor automatically adjusts the propeller blade angles necessary. We already said this. Okay, actually, we kind of already went through all this. So I don't think we need to go through it yet. This was just my example of increasing propeller loads or decreasing propeller loads, changing from straight into a little flight to a climb. Right, propeller

5:10slows down. It flattens the blades to help the propeller speed back up again.