In episode E204 of Behind the Prop, hosts Bobby Doss and Wally Mulhearn dive into the function of the blue knob in constant speed propeller systems. They explain it as the RPM selector that acts like a transmission by changing propeller blade pitch to maintain selected RPMs. The discussion covers fixed pitch versus constant speed props, the role of the governor, engine oil as hydraulic fluid for blade adjustment, manifold pressure management during climbs and descents, and why the POH is the final authority over instructor advice. They address checkride scenarios, common misconceptions like flying squared settings, oil leaks as engine emergencies, and the importance of using proper checklists rather than acronyms like GUMPS. The episode emphasizes understanding the full system for safe and efficient operations in complex aircraft like the Cessna 182T.
00:00:00
Behind the Prop Intro
All right, all right.
00:00:15
Bobby Doss
What's up, Wally? Hey, Bobby, how are ya? I am fantastic as always. Back to some teaching stuff, learning more about airplanes and what's in our airplanes and how they work. Today's episode is going to be called, What Does That Blue Knob Actually Do? if you've listened to the show, you know I fly a 182T with my family around the country, and I've spent a lot of time in that cockpit. And I've got three knobs, Wally. I've got a black one, a
00:00:45
Bobby Doss
red one, and a blue one, and I, I remember learning how to fly that plane many, many years ago. But I don't think I got a lot of teaching on the blue knob. We just kind of, I was just told what to do to get that high performance endorsement. and I do remember studying it for my commercial check ride. That blue knob is really, really important, but I don't think a lot of people understand how to use it. So let's do a little chit-chatting together and teach them how to use it today. That sounds good. So in most layman terms, what does the blue knob do, Wally? It changes gears. It's the transmission. It's the transmission of our
00:01:30
Wally Mulhearn
airplane. It basically changes gears. I, I, I grew up an airplane geek. My father was a pilot. my room in my house, last when I counted, I mean, the last time I counted, there were like, I want to say there were 87 Model airplanes hanging from my ceiling. And, it was, it was a dust nightmare about every month. I mean, about every year we'd have to take them all down and dust them. It was, it was, it was a sneeze, sneeze fest. But anyway, one of the models I had, not, not, not only did I just have these airplanes hanging from the ceiling, but over on the shelf,
00:02:15
Wally Mulhearn
I had a, a, a radial engine that my father had built. and it, it was complicated. It was, I wanna say seven cylinders, maybe nine, I, I don't remember how many cylinders was it, but it was pretty big. It was probably the diameter of this engine was about fourteen inches. It had a propeller on the pro, on the front, and it, you could actually change the angle of the blades of the propeller. So as a very young kid, this, this thing was sitting in my room and I would go over there and I would move the propeller and I just remember my father, just, he was,
00:03:00
Wally Mulhearn
he was always very good at, dummying down things for me, making them very relatable and, you know, I've tried to kind of carry on that kid condition. I don't know if I'm honoring it or not, but, anyway, he said, as you're changing the angle of the blade of that propeller, you're basically changing gears. cause, you know, back then every car my father ever had was a manual transmission, so that was, you know, that's just the way we, we operated back in the, the sixties and seventies. and so Very early on, I, I had the, the luxury of learning that. And that's,
00:03:45
Wally Mulhearn
that is basically what you're doing is you are change the angle of the blade of the propeller to choose how much of a bite of air that propeller takes each time around. So you can take little bites and spin it really fast, or you can take big bites and spin it slower. much like I think all of us can relate to this, we can, most people can relate to the gears on a bicycle. So we can, we can have the chain on that, that big, big gear and be pedaling really hard, but pedaling slower, or have the chain on the small gear
00:04:30
Wally Mulhearn
and it's easier to pedal, but you're gonna have to go, you're gonna have to pair, pedal at a higher cadence, if you will. you know, and that's another one of my passions is, is cycling, and I'm, I am realizing that I, me, you know, when you're on a bicycle, you, the person, is, are basically the engine. So when I'm on my bicycle, I'm the engine, and I'm, I'm realizing that I am now, I'm more efficient pedaling at a higher cadence, you know, 80, 85 RPM, but making it easier than back at 60 RPM, where it's really hard to pedal.
00:05:15
Bobby Doss
And when I got back into riding the bike, I was like a 65, cadence type person, but I've, I've, the data proves it, that I'm more efficient up around 80, and maybe our airplane engines are more efficient that way. So, and who knows? Yeah, well, I know who knows, the POAs knows, the manufacturer knows, and we'll get into that later on as well. Absolutely. In part one, let's talk about why change the propeller pitch at all. Most of us probably learned how to fly in a Piper Warrior or Archer or a Cessna 172 or something similar. And those are all fixed pitch props. Why, why isn't every
00:06:00
Bobby Doss
plane got one, you would say? And I think the, I think we all probably started learning how to ride a bike on a single gear bike. I remember being the guy who tried to ride wheelies and do all that stuff. And I had a sprocket and I had a wheel in the back that had one size gear. And if I thought I was, if I thought my parents did the right thing, I had that free, free wheel where I could spin backwards, right? Like it was this fancy gear. But net net. We all probably started riding a bike with a fixed pitch gear system, meaning one option. And as we grew up and got smarter, we might have got a three speed back in the day, or maybe a ten speed or a twelve speed. And they are very, very similar. And it is about
00:06:45
Bobby Doss
power versus cadence, or in the airplane world, RPMs. And to me, the simplest form is the blue knob is me setting the RPMs. There's a lot of stuff we're going to talk today about that is doing all the work that you're talking about, changing that gear system inside that nose cone and how all of the rest of the system works. That that's the part that I just don't think people really understand. And I just don't think I understood it either early on in my commercial training or early on in my high performance training. Because it's, I think it's confusing and complicated and not too many people know how to explain it easily. And that's what we're going to try and do here. On 172, you got, they've compromised, right?
00:07:30
Bobby Doss
They've made a prop that's fixed, it's, it's a set pitch, and it's intended to do a okay job climbing and a really good job cruising in most cases, or it's built to climb really well and be so-so during cruise. And you, you normally pick that pitch, or you buy the prop with the pitch that you want to get the advantage of more easy cruise or better climbing performance. we have one plane that's got a cruise, prop on it. Out of all the planes, the other ones are more leaning towards the climbing performance, and everyone thinks that plane's underpowered. They just don't understand the prop. They don't understand that it's gonna climb less, but actually outperforms all the other planes in
00:08:15
Bobby Doss
cruise, and that's by design. It's that pitch. Well, when you get to a, a constant speed prop, you get to change the manifold pressure and the RPM setting. On what the POA says in most cases, but you are in control of that, that 10 speed, you know, in cruise in sixth gear, which is you at 80, 80 RPMs in cadence with your feet, Wally, but you're getting so much better performance across the concrete. And I just don't think people understand how that works. Yeah. So at the simplest form, I think the way to pitch it in this show is the blue knob is the RPM selector. and we're going to dive deeper into it
00:09:00
Wally Mulhearn
and talk about it, but it's controlled by something that is managing that. There's a governor up there, and manifold pressure and oil and all these other things we're going to talk about. But just for everyone listening, know that the blue knob is the RPM selector as we begin this conversation. How often can an applicant operate the propeller correctly but not explain what the system's doing in your check rides, Wally? a lot. You know, more than, more than, than I would like. Now,
00:09:45
Wally Mulhearn
I, it, it's a different world, but, you know, back, back in the day, I hate to keep saying, well, back in the day, well, but I'm gonna say it, back in the day, to, you know, to get a commercial pilot certificate, you were required to have ten hours of complex time. Complex, you need three, three, three things to make a complex airplane. You gotta have movable flaps, a controllable pitch propeller, and a retractable landing gear. since, I don't know, maybe ten years ago, we, we, the FAA came up with this category called technically advanced airplanes. So it's possible for us to, get a commercial pilot certificate with never having flown on an air,
00:10:30
Wally Mulhearn
with an airplane that has a controllable pitched propeller. And that's, that's what the regulation is now, so it's legal and, you know, we, we accept it. it wasn't the case twenty years ago. one of the problems is, you know, we don't have, there are just not as many, single engine complex Training type airplanes. There aren't many Cessna 172 RGs out there anymore. There aren't many Piper Arrows out there anymore. So to get a true complex airplane, you know, single engine, you've got to step up to a, you know, a Beechcraft Bonanza
00:11:15
Wally Mulhearn
or something like that, and that's really not conducive to going out and being a training airplane. So a lot of times the applicants, when we, if, if we end up talking to this, now, as an examiner, as an examiner, we are required on a commercial checkride to pick three systems to talk about. and in the ACS, right offhand, I don't have it in front of me, there are probably about twelve systems listed. We, we are required to pick three. and one of them is the propeller. I can't say I always ask about the propeller. but
00:12:00
Wally Mulhearn
maybe there are some examiners who that's, that's kind of their thing. I will tell you this, on every one of mine, I'm going to ask about the electrical system, and I think everybody who's ever listened to a couple of episodes of this show will know that. But, it, to me, it's, it is tough. It's tough for me to ask an applicant questions about something that they have never really, really been exposed to. and there's a lot of theory in it. you know, and so it, I mean, it's, it's possible that there, there's a CFI out there who really
00:12:45
Wally Mulhearn
doesn't have the experience. So now they're teaching A new student who doesn't have the experience and you know we got babies teaching babies so it's maybe not the most ideal scenario so me as an examiner do I pound it do I get really in depth on it no I don't I don't we will talk about it I will ask you know you know I'll I'll ask well what's what's inside that propeller hub and you know I get I get the book answers they'll talk about gears and everything and I I ask about lubrication and they'll say yeah it's it's lubricated
00:13:30
Bobby Doss
by oil and I said okay so do we have a separate oil system and I don't know about twenty percent of the time the the applicant will tell me yeah yeah we have a separate oil system I said so we have engine oil and then we have propeller oil And, and they, they kind of stop, usually right there, and they'll go, go, so, well, wait a minute, no, no, I don't think that's right. So, you know, that's something we talk about. So, you know, is, well, oil, oil quantity is important in any engine, so maybe this is a, is a bad statement, but it's more important in a airplane that has a controllable pitch propeller, because we're now,
00:14:15
Bobby Doss
I mean, that, that, that oil's doing more than just lubricating the engine. It's also, you know, it's lubricating the propeller. That's a great point to jump into part two. Like, let's follow the blue knob. We're going from governor to engine oil to prop hub. So what's moving the blue knob? What's moving when the blue knob starts to move, right? You're really, you're setting the RPMs. We called it the RPM selector in the beginning, but that blue knob is actually doing something else. It's moving something else. What is it moving? It's moving what's called a speeder spring, which forces the governor into the right place. That governor is kind of like
00:15:00
Bobby Doss
the gears on the back of a bicycle, but it's going to keep the RPM setting that you want. So if you move it to a certain distance or setting, telling the engine or the system that you want 2300 RPMs, that governor is going to check what the prop is spinning, and if it's spinning at 2400 RPMs, it's got to do something to slow it down. And to do it, it does what? It makes it take a bigger bite of air. It's, it's making it slow down and get to 2300 RPMs. And what I don't think I understood early on is that, okay, I nose the plane over, in a single engine plane, the prop's going to spin, or sorry, a single pitch prop is going to start spinning faster simply because
00:15:45
Bobby Doss
of the airflow over it. But in a constant speed prop, it's going to do what it needs to do to stay at 2300 RPMs. It's almost a thing of magic. and then- Is that why we call it constant speed? That is amazing, isn't it? a couple of situations where we could break that rule a little bit, but I, we'll get into those too. But the oil from the engine is what it's using for hydraulic fluid to change that. I mean, that's a lot of pressure. You got to think of how much weight are we pulling? A 182, max gross weight, 30 400 pounds, and we're going to pull that through the fluid in the air, the air, and it's got to pull us at 8,000 feet. It's going to be a lot of force that it's doing
00:16:30
Bobby Doss
to take a bigger bite of air, and that, that oil is being used as hydraulic fluid to change the pitch of those blades. In my 182, there's three blades. I'm sure there's a lot of four-blade systems out there. I'm sure there's some, are there very many two-pit, two-blade constant speed props out there, Wally? there, there are, you know, some of the, the big pipers, the Cherokee sixes, a lot of them will have two-blade propellers, but I, I would say it's definitely in the minority. I also feel like if you know the system well, then you start to understand what on speed, over speed, and under speed means. I think everyone's afraid
00:17:15
Bobby Doss
to over speed it. there's, probably a common phrase that's used is don't, don't have more RPMs than you have manifold pressure. Well, that's like the old, old days, the philosophy. I think the engines were built differently. But many POHs now have that as a setting. It's a, it's a cruise setting that you can have 2,400 RPMs and 23 inches of manifold pressure. I hear way too many times when people fly with me that, I was taught to fly it squared. Well, okay, well, why were you taught to fly it squared? And do you know if the POH says that that's a good setting to fly it squared? I, my cruise setting is 23 inches
00:18:00
Bobby Doss
of manifold, sorry, 23, yeah, 23 inches of manifold pressure. And the other way around, my bad. 23, 100 RPMs and 24 inches of manifold pressure. and that's what my book says to fly my 182. That's a good economical cruising. That's a turbocharged airplane, right? It is not. Oh, it's not. Okay. Okay. No. It's just the T. It's the 182T. Everyone thinks it's turbocharged, but it's not. but as you get to higher altitudes, the man, the air pressure changes, so manifold pressure is going to change. And at some point, you kind of just run out of throttle. Like, you just don't have any more to give it. another thing that I think people don't do well is, as they climb, they don't do their checklist usage.
00:18:45
Bobby Doss
And what happens to that manifold pressure as I go up? It just constantly ble constantly bleeds off some. And so you have to constantly be managing that. a great use of checklists will will make that happen for people. Well, here's a question that that I I will I I ask most of the people this question. I say, okay, if we go out to our airplane right now that has a manifold pressure gauge, what is that manifold pressure going to read right now if we walk out in the hangar or out on the ramp and look at the airplane? And I would say, and I, you know, of course the engine is not running. Most people are going to tell me zero. Okay. That kind of sounds like the obvious
00:19:30
Bobby Doss
answer. Okay, and this was a question that my, I, I remember this. I just, driving in the car, I, I learned so much from my father driving in the car. I guess that was the only time I was the, the captive, victim. I couldn't, I couldn't run away. But I remember my father saying, if the engine is not running, what is your manifold pressure gauge gonna read? And I knew, I mean, the obvious answer is zero, okay? The engine's not running, it's gonna read zero. That's kind of the obvious ignorant answer, okay? And by the fact that my father was asking me that, I knew that could not have
00:20:15
Bobby Doss
been the answer. So, I mean, I, I used a little bit of gamesmanship, and I sat there and I thought about it, and I thought, wow, it's, it's, manifold pressure is measured in inches of mercury. Is there anything that we do that's We do every day, every flight, many times on a flight, where we deal with inches of, of mercury. We do, our altimeter setting. So right now, if you were to go out and look at your manifold pressure gauge, it's gonna indicate whatever, see that whatever the pressure is outside. That's the truth. And the higher you go, the less it gets, and the more you have to add to it if you wanna stay at that setting that the POH told you to fly
00:21:00
Bobby Doss
at, or that you chose to use out of the POH. we kinda blew through part three, which is this whole manifold pressure and altitude stuff, but it, it truly is one of the things, when you get to more performant aircraft, you cannot set this stuff and just forget it. There's, the, all things like the outside pressures are going to change and make you take action. Same thing coming down. So if I set it and I had full, full throttle in, then I've got 23 inches or 24 inches at, at altitude. As I come down, that manifold pressure is going to keep rising the whole time, and I don't want to cause stress on the engine and that governor to try and let the RPM stay at the same that I've set
00:21:45
Bobby Doss
as well with the blue knob. And so you have to be thinking about these things, and you have to read your book, and you have to know what it says in that book. Don't just fly something that someone told you to fly. I had a great instructor. There was an assistant chief back in the day, his name was Geo. sounds like he's moving on to bigger and better things in, in his next step in life. Recently, I talked to him, but he taught me that manifold pressure, just like your dad did, that it's going to read a number when you sit in the plane and it's not running. And I was the same kind of way, like there's zero pressure in there. Well, no, we're all feeling pressure right now. We've just got used to living with it and we don't think about it. so you got to manage it, you got to
00:22:30
Bobby Doss
use your checklist, you got to know what you're doing or what it's the system's telling you to do so that you can say, stay in your safe space and in the numbers you want to be in. So let's talk about those normal operations and then what happens when it talks back to you a little bit. What, what, what is the plane wanting during the takeoff and climb portions, of a flight, Wally? What does, what does the blue knob want? What does the plane want the blue knob to be? it, it's easy, it's full forward, full forward. And when you say full forward, I think my multi-engine training is probably where I really learned this the most, but full forward, what does that mean to the prop? Is it, is it
00:23:15
Bobby Doss
flat? Max RPM. So it's flat, it's, it's, it's gonna cut through the air as quick as it can, because the prop is nothing more than an airfoil. You want it to create as much lift as possible. You wouldn't take your flat, you wouldn't take off with full flaps, right? Yeah. And that's the best example I can come up with, but you want that blade to go and spin as fast as it can spin, with the least resistance. I'm just having all these, brainstorms right now, and I'm, I, I, I'm. I, I, honestly, I, I just now thought about this during this podcast, flying an airplane is just like riding a bike. It really is. I mean, so if you're sitting on a flat surface and you're gonna
00:24:00
Bobby Doss
go, you're gonna ride two thousand feet and then you're gonna go up a big hill, you, you, you want to be in, you know, once you start going up that hill, you're gonna wanna be in the smaller gears to make it easier on you who is the engine, okay? It's gonna be more efficient. You don't wanna be in the big gears. Yeah, so you're climbing, you're, you're pedaling as fast as you can, making it easy on your legs and your engine as you can, and then when you get to that top of the hill, And you get to take a deep breath and squirt some water in your mouth, you're going to want that gear to get back to your
00:24:45
Bobby Doss
ideal ratio, whatever that is. You said 65 before, now you're at 80. Whatever that ratio is, and that's found in the POH. So you're going to want that setting to be where the engine uses the least amount of fuel and provides the right amount of power for the right amount of true airspeed. You're going to get what the book tells you you're going to get, and it's pretty amazing how efficient those engines can run at a RPM setting and pull you through the air at cruise. And you're probably using a lot less fuel than you think you are on a constant, or sorry, a fixed pitch prop propeller. But a descent, same thing, we're going to probably Change this,
00:25:30
Bobby Doss
manifold pressure, but the RPMs are gonna stay the same. We're gonna pull out some power and then the RPMs are gonna stay the same because we've got that governor doing all the work for us. And if I'm going downhill, I don't want to be pedaling as fast as I can at that point. If I wanna speed up, I wanna take a lot of bite and let that, let that manifold pressure, my engine, pull me through there at a much higher speed to hopefully catch the guy in front of me or whatever that analogy would be. but I just don't think people understand the system and how it works. let's talk a little bit of checkride, Wally. When I'm in the checkride with you, and I, and you ask me that question, and I say, it's
00:26:15
Wally Mulhearn
the RPM selector, are we done talking about it? Probably not. you know, we're, we're gonna, we're gonna, you know, I, I do, again, I, I'm throwing out some, some, Easter eggs here for my check rides, but we're gonna talk about, I'm gonna ask about the lubrication, how it's lubricated, if it's lubricated, again, is it a separate oil system, and, you know, where, where does that oil come from? you know, what are we checking on the pre-flight, and, and, you know, one of the things is, is no oil around the hub kind of stuff. you know, and, and everything that we would check
00:27:00
Wally Mulhearn
on a, a 172 prop, you know, smoothness and all that, that kind of stuff. I was always taught to check the cowling, you know, rub the cowling with my hand to make sure there was no residual oils up there. There should not be any residual oils in the middle of the cowling, and obviously if there was any residual oils up there, you might have a leak coming from that prop. And it's not a prop problem. This is what I don't think, is we talked through a few of the, the bad things that could happen with a constant speed prop. If you're flying along and your windshield starts getting a little bit of oil splattered on it, and your RPMs start to change without you moving that blue knob, that's, that's not a prop problem. You no longer are worried about
00:27:45
Wally Mulhearn
how do I make the RPM setting correct. What are you worried about in that scenario, Wally? In that scenario, I'm, I'm worried about a loss of oil. That's an engine emergency is what that is. I mean, that, that is a full blown emergency situation. It is not another container of oil that's driving that prop. You, you are going to lose all the oil in your engine over time if you don't take action. And there's not, you ain't gonna get out there and change that, the, the gasket right then. You gotta get on the ground, as fast as possible. Right. So, if your applicant, or gave you, you got a scenario of some sort, and they said the RPM stayed constant, so my power stayed
00:28:30
Bobby Doss
constant, is that a correct answer? Absolutely not. No. And I just think I might have thought that early on, I hate to admit how dumb I was as a, as a rookie pilot, but power and RPM on a constant speed prop have, have nothing to do with one another. much like a 12 speed, if we both got on the same bike, I have a feeling your engine's a little bit better than my engine, cause I haven't ridden a bike in 10 years. so it's not gonna be, it's not gonna work out to be the same thing, but we might both spin it at 60, 60 cadence, but you're gonna be going a lot faster than me, I can assure you, cause you're going to be taking a lot bigger bite in that air, as the example says it, right? So, 60
00:29:15
Bobby Doss
second blue knob test. We, we've talked about it. You listening, think about these questions, and then I'm going to give you the answer, or Wally give you some of these answers. Actually, we'll alternate these questions, Wally, if you want to. If I were to say, what's the blue, what blue knob selects, it's the RPM. You take the next one. The throttle primarily controls engine power and manifold pressure. So, think of the black knob is really what's setting that manifold pressure. and I think when you take off, you would go prop, obviously, full forward, and you'd push that throttle in, and as
00:30:00
Bobby Doss
you got to your cruise or climb setting, you would probably set your RPM and then manifold pressure. Or would you go the other way around with that, Wally? In your Saratoga, do you set power, then prop, or prop, then power? are you talking about, for takeoff, I mean, it is, we do, the Saratoga's a turbocharged airplane, so we don't have the luxury of just going full forward on the throttle. 36 inches of manifold pressure is our max, so we, we aim for 33, so I push it up to 33. If it goes up to 34, 34 and a half, that's fine. I mean, we don't micromanage it on the runway. Maybe, you
00:30:45
Wally Mulhearn
know, there's, there's bigger fish to fry. So that's why I shoot for 33. but yeah, I mean, as, as probably about thousand feet, twelve hundred feet, I'm gonna leave the throttle up there at 33 inches of manifold pressure, and I'll pull the, the, the, prop back to 2500 RPM. So typically, you know, just There's so many different variables in it. How, you know, I'm, I'm looking at, at my, my EGTs, I'm looking at my cylinder head temperatures, and, you know, summertime, it's hot in the back of the airplane, so if we're trying to get up to
00:31:30
Wally Mulhearn
an altitude faster, so I, I may keep the power up and climb at a greater rate of climb using a higher power setting to get up there quicker, just, just simply for comfort. But I'm also looking at, my CHTs and my EGTs, To, you know, to baby the engine, and, and I, I do baby the engine, maybe a little bit too much, but anyway, that's, that's an expensive thing out there. I was going to say, if people don't own engines, they wouldn't know why you baby it, because they're very, very, very, very, very, very, very expensive. Yeah. The next question in our 60-second test was, what, what moves the blades hydraulically? We've talked about it, and this is a typical system, but it is the oil that's in the engine. So that engine oil becomes the hydraulic
00:32:15
Bobby Doss
system to let that system manage the pitch of those props. Right. And, and, and we, you know, we, we've mentioned this, you've mentioned it several times, the, that controller inside that pub is, is called the governor. I, I, I don't know where or how that came about, but that's just one of the mysteries of the world. to me, I, if, if it were me, I would, I would call it a controller in there, but it's a governor, so it governs the, the output. So we talked about this as well, but what, as a normally aspirated airplane climbs, what tends to happen to manifold pressure? And this is meaning
00:33:00
Bobby Doss
you've said it, what's going to happen? You're going to lose some of it. You're going to decrease it. Yeah, it's going to go down. It's, it's, it's the, it's, you're, you're going to lose, lose the power. And, and again, I, I, I keep comparing this to a bicycle. If you're out on a bicycle and you're riding uphill, you're gonna be getting a loose power. You are. You're gonna get tired, and that's essentially what it does. At some point, at some point in time, you, and again, normally aspirated engine, non-turbocharged is what we're talking about, which is probably what most of the listeners are flying. you know, at some point, that throttle is gonna be full forward. And, and there's not anything you can do to increase
00:33:45
Wally Mulhearn
that manifold pressure. You know, you may start it out at 25 inches, 2,500 RPM, and, you know, the manifold pressure decreases about an inch per thousand feet. So, if you don't touch the throttle at, you know, at, at 5,000 feet, you're probably gonna be around, down around 20 inches of manifold pressure. So, can the RPMs remain constant while I change that power setting? Yeah, yeah, absolutely. That's why it is a constant speed prop. can a prop system oil leak become a bigger problem for the entire plane? Yeah, absolutely, and, and that's what we talked about. You're,
00:34:30
Wally Mulhearn
there's only one oil system in that airplane, so now you've got cylinder problems, you've got, you've got big problems. Oil, oil to an airplane is what blood is to the human body, you know. If we have a blood pressure problem, the, the human body is eventually gonna, not gonna work anymore, so. And then what's the final authority for all settings in, in this? Is it what my CFI told me to set it, or should I get that information from somewhere else? Yeah, I, I, I just, I go back to that. I remember when I bought my Saratoga, the, the guy told me how to start it, and, we went in and we did the transaction. I got back in the airplane,
00:35:15
Wally Mulhearn
and I did exactly what he told me. The thing started right up. We flew halfway home, spent the night, got out the next morning. I did exactly what he told me, and it didn't start. And I thought, oh my gosh, what am I gonna do? And then I found this book called The POH in the back of the seat back pocket, and I looked up this procedure called cold start, and the engine fired right back up. And, you know, at that point, I was a very experienced pilot. I don't think I was an examiner at that point. Maybe, maybe I was. I, I, I don't really remember. It was about the same time. But it, it was, it was a dull moment, like, what an idiot. What a freaking idiot. You know, just, just read the book. It's in the book. It is in there. and, and just
00:36:00
Wally Mulhearn
be careful, you know. I have I, I do use a, secondary checklist, an aftermarket checklist for my Saratoga and for the, the 120, I, I use it. But I have gone through and I have really made sure that, that they jive, that, that we're not missing anything from the POH on, in this checklist. But my point is, this, these checklists, for the Saratoga, it's, it's really a booklet. It's more than just a checklist. It has all the power settings in there and everything, and, you know, I've kind of cross-referenced and, and, they're, they're pretty much spot on. So what I've
00:36:45
Wally Mulhearn
seen at the flight school and what I've heard you say a little bit is that most pilots, they're just memorizing the book. Maybe it's because they haven't had the experience and they don't really know. Hopefully this podcast helps some people understand the system and what's really going on. But remember, the blue knob selects the RPM, the governor senses RPM, and meters the engine oil or hydraulic fluid, the thing that's using is hydraulic fluid, so that the propeller can change blade angle. Then the throttle changes the engine power settings and manifold pressure tells us what's happening at the intake side. Altitude and other things can change this equation. Just know what you're doing with your system to manage it and don't just do whatever a
00:37:30
Wally Mulhearn
flight instructor or someone told you to do with it. if you ever see a little bit of oil on the windshield, it's going to be a really bad day. Do what you can to get on the ground. just know where the blue knob goes. To get you what you want, the performance you need when you have your plane in flight. Anything else to close with, Wally? Let, let me just say this. I, I am see, sensing, well, not sensing, I am seeing a trend with a lot of the, and I, I'll just say a lot of the bigger flight schools. and they are teaching their students, maybe they're not teaching, but this is what I'm getting on check rides.
00:38:15
Wally Mulhearn
People are not using their checklists. They're coming up with all these little gimmicks, and I'm just gonna call it gimmicks, acronyms. And what we get all the time, what I get all the time is GUMPS, GUMPS, GUMPS, gas, undercarriage, mixture, prop. I think S stands for switches. That's fine if you want to use that, but let, let's take a 172. Gas, undercarriage, well, the undercarriage is welded, okay? And if it's not there, there ain't anything you can do about it, okay? mixture, yeah, we need to, we need to deal with the mixture. P, props, well, we don't, we don't have a prop control.
00:39:00
Bobby Doss
We don't have a blue knob on that 172. So already, four of the things that we've mench, mentioned, we don't even, or two of the four on that, that airplane, we are not, we don't have on our airplane. and, and, but people are thinking, or Teaching or, or whatever, they're thinking that that is a checklist. That is not a checklist. If you go in the ACS for every landing, every takeoff for private, commercial, and instrument, one of the skills elements is uses or completes, it, it, it says, I believe it says completes the appropriate checklist. Gumps
00:39:45
Bobby Doss
is not a checklist. And, and here's why I say this. Okay, Gumps, G U M P S, that's five things. You're gonna eventually outgrow your 172. You're even gonna outgrow your 182. You're gonna start flying airplanes that have more things that are important on the landing checklist. You might fly an airplane that has an air conditioner, and in, in most cases that air conditioner needs to be off for landing. And the reason it needs to be off for a landing is it's preparing for a Go around. So if you do have to go around, you have that extra power. You may have an airplane that has cowl flaps. You may have an airplane that has a yaw damper. And, and all those things are on the
00:40:30
Bobby Doss
checklist. And what we're doing is we are memorizing checklists. And I, I use the analogy, there's an, an old saying, give a man a fish, you feed him for a day. Teach a man how to fish, you feed him for life. Well, I, I apply that to checklists a little bit, and this, this doesn't, it's not a hundred percent, so don't hold me to it, but learn how, memorize a checklist, you can fly one airplane. Learn how to use a checklist, you can fly any airplane. Okay, so we need to be using these checklists. There are things on the checklist, so don't, don't just, and, and I get it. And a, and a 172, especially a non-carbureted 172, there's
00:41:15
Bobby Doss
not a whole lot on the landing checklist, you know. you know, especially if you're just staying in the pattern. The mixture's already forward, your, your landing light's already on. There's not a whole lot to do, but it's a discipline. It's a mindset. I've flown every non-four-engined Boeing that there is, the 727, 37, 57, 67, 777, 787. There are three things on our landing checklist, speed brake, gear, flaps, three things. I've memorized it. I know it. I've got thousands of hours in those airplanes, but we still pull out the checklist. It's the right thing to do. Amen. And with that, we'll wrap this episode up, and you now know what that blue knob does. As always, fly
00:42:00
Bobby Doss
safely, and stay behind the prop.
00:42:02
Behind the Prop Outro
Sorry, I, I kind of.