Episode 87
SPC087 [BTC] Vroom, Vroom or What Does the Turbo Say?
In Episode 87, we join Bill and Kent as they discuss forced induction in general aviation, contrasting normally aspirated engines with superchargers, turbochargers, and turbo-normalizers, and explaining how turbos use exhaust-driven turbines and wastegates (automatic, manual—separate or throttle-linked—and fixed) to manage boost. They cover turbocharged vs turbo-normalized manifold pressure, the role of intercoolers in cooling compressed intake air, and operational considerations like avoiding overboost on takeoff/go-arounds, critical altitude (example: Seneca around 12,000 feet), and high-altitude issues including cooling challenges, pressurized mags, and pilot oxygen needs. They recommend FAA hypoxia training (including nitrogen-based options and a spatial disorientation simulator) and discuss descent and shutdown considerations, including turbo cool-down and the debate around shock cooling. Finally, they outline why pilots choose turbos (terrain, takeoff/climb performance, speed on long legs, weather/icing avoidance) and why some shouldn’t (cost, shorter TBO, more fuel burn, maintenance complexity, limited benefit on short legs, and discomfort using oxygen), using a Mooney vs Mooney Bravo comparison to illustrate time vs fuel tradeoffs.
Links:
Hope you enjoy the episode and thanks for listening! Visit the SPC website at https://studentpilotcast.com. Please keep the feedback coming. You can use the contact form on the website or send email to bill at student pilot cast dot com. The theme song for our episodes is "To Be an Angel" by the band, "Uncle Seth".
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Copyright 2008-2026, studentpilotcast.com and Bill Williams
Transcript
All right, everybody.
Speaker:Welcome back to another beyond the check.
Speaker:Right.
Speaker:I'm back here with Kent as usual.
Speaker:How are you doing, Kent?
Speaker:Excellent.
Speaker:It's always a good day when we get to talk about flying
Speaker:Oh, I'm so glad you're back to saying that.
Speaker:I love it.
Speaker:All right.
Speaker:So as usual, we're bringing a singular topic.
Speaker:What have you got for us today?
Speaker:all about forced induction turbos.
Speaker:Ooh, That's a manly topic right there.
Speaker:Turbos.
Speaker:We're
Speaker:Yes.
Speaker:kidding.
Speaker:The more
Speaker:Go fast.
Speaker:right?
Speaker:That's right.
Speaker:That's right.
Speaker:More stuff to break.
Speaker:Love it.
Speaker:Go fast.
Speaker:Go high.
Speaker:What it's all about.
Speaker:higher, farther, faster.
Speaker:That's, that's kind of the, thing that most pilots are into.
Speaker:It seems like, right?
Speaker:Excellent.
Speaker:All right, well, let's talk about it.
Speaker:I guess there's a few things beyond your check ride that you've learned
Speaker:about this, so, let's dive into it.
Speaker:Yeah.
Speaker:So, um, I guess let's start with just, what it is, um, and
Speaker:what some of the main types are.
Speaker:so most of us learn in something simple like a 172 and we call that
Speaker:normally aspirated where it's just breathing whatever the outside air is.
Speaker:a lot of people who are listening probably have some experience with
Speaker:turbos in vehicles, myself included.
Speaker:and you know, the applications are a little bit.
Speaker:vehicle on the ground, you're kind of looking to get as much as you
Speaker:can out of the engine that you have.
Speaker:and it works really well.
Speaker:I, I had a, a Volvo with a turbo in it a while back and really liked it.
Speaker:You know, I
Speaker:I haven't.
Speaker:a big V8 engine all the time, but I still had some power available
Speaker:to spare when I needed it.
Speaker:So,
Speaker:I haven't driven a normally aspirated engine in something like 12 years
Speaker:for my daily driver or my truck for that matter, because I've got
Speaker:a diesel and those are all turbo,
Speaker:all of them, but
Speaker:well, all, all the modern ones are,
Speaker:Yes,
Speaker:yeah, they
Speaker:used to have one from, from the eighties that, that didn't have a turbo.
Speaker:That was a dog.
Speaker:But, but yeah, it's, um, it definitely makes a huge difference.
Speaker:And, um, you know, you, you can feel that boost, but it's quite a bit
Speaker:different for an airplane, right?
Speaker:Because we're usually not going to the same um, that we are in a car.
Speaker:a different problem in an airplane.
Speaker:Good point.
Speaker:It's not that we're trying to get more out of the same size engine, for the most
Speaker:part, it's more that we are trying to keep our performance to a higher altitude.
Speaker:So somewhat of a different, a different problem there, but we're solving it
Speaker:using, the same tried and true method.
Speaker:so there's a few different types of forced induction.
Speaker:There's, superchargers, which are.
Speaker:Directly driven by the engine.
Speaker:and then, basically anything that we're talking about today forced
Speaker:induction wise has a fan somewhere in the intake is blowing and basically
Speaker:more air into the intake so that we can have more oxygen and fuel available
Speaker:to combust and make more power.
Speaker:so.
Speaker:Superchargers in some ways are pretty simple.
Speaker:They don't have any of the stuff on the exhaust side, but, for whatever
Speaker:reason, they aren't very popular either.
Speaker:I know that there is a supercharger STC available for the diamond star.
Speaker:but I'd have to honestly look to see what else there's been.
Speaker:you know, post world war.
Speaker:With it uses an actual supercharger.
Speaker:Yeah, it might be because they draw some of the energy from, the power
Speaker:strokes of the engine themselves, rather than just utilizing the exhaust,
Speaker:which is, um, sort of being expelled and wasted, if so to speak, anyway,
Speaker:I'm guessing that might be part of it.
Speaker:They've gone a little bit out of style in cars, too.
Speaker:my forced induction vehicle that was my daily driver maybe seven years ago.
Speaker:And before that was a Mini Cooper S convertible, and that was a supercharger.
Speaker:Even minis have gone to turbochargers now.
Speaker:but the hot hatch I drive now is a turbocharger.
Speaker:And what I've noticed, Kent, is that the turbo lag has mostly gone away
Speaker:in these modern turbos that used to be one of the things you had to wait
Speaker:for the turbine to spin up as you accelerated and those gases came out.
Speaker:But I don't know how they these engineers do it, but they've
Speaker:gotten rid of most of that.
Speaker:It seems these days.
Speaker:so, yeah, I've had experience with both, but the, the yeah.
Speaker:The, superchargers just don't seem to be as popular.
Speaker:Interesting.
Speaker:I'm, I'm sitting here wondering as a pilot and someone who knows absolutely nothing
Speaker:about forced induction on ground vehicles beyond just the experience of using them.
Speaker:I'm sitting here going now, maybe they came up with some sort of a constant
Speaker:speed impeller for the, for the turbo.
Speaker:And maybe they're able to extract more from a slower moving exhaust stream, but.
Speaker:That sounds expensive and prone to breaking.
Speaker:Um, but you know, they actually have constant speed props on rubber band
Speaker:airplanes now, believe it or not.
Speaker:So
Speaker:Wow.
Speaker:these days.
Speaker:That sounds like a whole beyond the check ride topic on its own for the future.
Speaker:Yeah.
Speaker:If, if there were check rides for rubber band powered airplanes,
Speaker:but yeah.
Speaker:So the other thing of course is, um, and, and this is kind
Speaker:of split in two for aviation.
Speaker:you know, you were mentioning turbochargers for a car and there are
Speaker:airplanes with turbochargers as well, but another thing that is kind of a
Speaker:special type of turbocharger called a turbo normalizer on an airplane.
Speaker:the difference there is that a turbocharger on an airplane is
Speaker:going to give you a manifold pressure that's higher.
Speaker:than sea level pressure.
Speaker:Whereas a turbo normalizer is just going to essentially correct for
Speaker:your altitude and give you sea level pressure at a higher altitude.
Speaker:So, there's some differences in the engines as well.
Speaker:so, uh, Turbocharged engine uses lower compression pistons and then you're
Speaker:just cramming more fuel and air into a bigger space than whereas a turbo
Speaker:normalizer is often something that's kind of bolted on after the fact,
Speaker:there's a company called Ray J. that a whole lot of, turbo normalizing systems
Speaker:for GA in the 60s and 70s and, um, still tons and tons of those out there.
Speaker:So anyway, regardless of how, you know, of which system you're using turbocharger
Speaker:or turbo normalizer, of getting the power from the engine like you do with
Speaker:a supercharger, um, some sort of direct drive, a turbo is using a second fan
Speaker:that's in the exhaust side of things.
Speaker:Um, and I'm sure there are probably some Mechanics and pilots and stuff.
Speaker:We're going to scream at their headphones for this episode.
Speaker:I'm yes, I'm keeping things simplified.
Speaker:know, I'm not going to explain every last little thing, but, you know, we're going
Speaker:to talk about the basics, especially.
Speaker:Mechanically speaking, we're going to be talking a little more in
Speaker:detail about operational stuff.
Speaker:But yeah, it's,
Speaker:So essentially you have another fan in the exhaust side of things.
Speaker:and so your, your exhaust that's coming out of the engine is, is blowing
Speaker:through that and spinning the fan that's attached to a shaft that's attached
Speaker:to the other fan on the intake side.
Speaker:So, And then there's a bypass that's called the waste gate and that kind
Speaker:of controls how much exhaust goes through the fan or not, depending
Speaker:on how much power you're asking for.
Speaker:and different airplanes have a bunch of different types of these, a few
Speaker:different types of these wastegates.
Speaker:Right?
Speaker:there are waste gates, which is kind of more of a set it and forget it.
Speaker:there are some things that will.
Speaker:take care of the actual waste gate for you.
Speaker:are manual waste gates where you're more in direct control of the
Speaker:waste gate itself, as opposed to how much power you're asking for.
Speaker:and those are sometimes tied to your throttle and sometimes
Speaker:they're controlled separately.
Speaker:So, A couple of examples, a Comanche, Piper Comanche is one where you
Speaker:have direct control of the manual wastegate via its own control.
Speaker:So if you ever look in the window of a Piper Comanche at the throttle
Speaker:quadrant and you see four levers instead of three, That's a turbo Comanche.
Speaker:and so,
Speaker:One more control.
Speaker:one all the way forward and you need more power, while you just go over the
Speaker:waste gate one and you start pushing that forward and that gives you more power.
Speaker:and then, Cessna, for example, if you get a turbo one 82, the older ones, they
Speaker:have that, they have a manual waste gate that is, Tied to the throttle control.
Speaker:So you're kind of moving two controls at once there.
Speaker:and then
Speaker:So you, so for that, when you add throttle and it reduces the amount
Speaker:of air going through the wastegate.
Speaker:oh man, you're gonna make me think here, Well, I mean, basically the
Speaker:way, the way any of the waste gates work is, like I said, it's a bypass.
Speaker:right.
Speaker:boost you have or the more boost you need, the more closed the wastegate is going to
Speaker:It bypasses less air,
Speaker:Yeah.
Speaker:So in a Cessna, where the two are tied together, when you add
Speaker:throttle, you're opening the throttle butterfly and you are closing
Speaker:closing the waste gate.
Speaker:Yeah.
Speaker:Giving yourself more boost.
Speaker:Correct.
Speaker:Okay.
Speaker:But yeah, then the last type is the fixed waste gate where, there's always
Speaker:Basically a fixed, I'm trying to think whether it'd be fixed volume.
Speaker:It's not fixed volume because there's going to be different speeds of gases.
Speaker:But one way or the other, it's, you know, no moving parts in there, but having to
Speaker:control your manifold pressure and it's a little bit less direct control, um,
Speaker:Hmm.
Speaker:with an actual waste gate would be.
Speaker:so an
Speaker:Okay.
Speaker:would be a turbo arrow or a Seneca some of the Mooney's have that like the, M 20
Speaker:K Mooney's will have that system as well.
Speaker:actually not super common.
Speaker:I think I may have just listed all of them, but
Speaker:So, interestingly, if we look at the four you've talked about, that
Speaker:is the automatic and then two types of manual waste gate controls.
Speaker:but one of those.
Speaker:You know, has its own separate control and the other one's tied to the throttle.
Speaker:And then of course the fixed that has no control at all, it was set it and forget
Speaker:it at the factory, basically, that.
Speaker:There's really only one that the pilot has direct control over.
Speaker:All the others are either fixed or automatic in some way or
Speaker:another tied to the throttle.
Speaker:So interesting.
Speaker:yeah.
Speaker:Yeah.
Speaker:so a couple of potential issues that you introduce when you have a turbo.
Speaker:first of all, you have extra heat and is not something that's good for engines.
Speaker:It's something that we are constantly thinking about how to get rid of, right?
Speaker:but of course, when you're taking a gas and compressing it, You are
Speaker:increasing the temperature as well.
Speaker:so there are some airplanes that also have, an intercooler and bill, you gave
Speaker:a great description of this before.
Speaker:so go ahead.
Speaker:Why don't you tell them what an intercooler looks
Speaker:Sure.
Speaker:just to talk about what Kent is talking about.
Speaker:We recorded, this, beyond the check ride about a month ago,
Speaker:but we forgot to hit record.
Speaker:It happens to everybody at least once, I guess.
Speaker:And so I don't remember exactly.
Speaker:Yeah, so, I wasn't ready for this.
Speaker:I'm not exactly sure what I said before, but I will, I will tell you, because of my
Speaker:experience with forced induction in cars, front mounted intercoolers are really,
Speaker:are really common with turbocharged or any forced induction, really, because
Speaker:as you compress that air, as Kent was talking about, it heats up and the
Speaker:hotter it is, the less dense it gets, which is what we're trying to avoid by
Speaker:compressing the air in the first place.
Speaker:So, we want to keep that air as cool as possible.
Speaker:Not only not to, you know, introduce extra heat soak on the engine itself, but to
Speaker:also continue to improve that performance.
Speaker:And so the way an intercooler works is the air that is being
Speaker:forced through the turbo.
Speaker:So after the turbo gets forced through a, an intercooler, which looks a lot like
Speaker:a radiator, but it doesn't contain, it doesn't contain any coolant or liquid.
Speaker:It contains the air that's being forced through it from, from
Speaker:the, the forced induction device.
Speaker:In this case, most, mostly we're talking about a, turbo itself.
Speaker:And so the turbo fan pushes it through.
Speaker:It goes through all these fins that has, air running across the fins to
Speaker:cool down the air as much as possible before it then goes from the intercooler
Speaker:and gets put into the engine for mixture with the fuel and combustion.
Speaker:So that's how it works.
Speaker:Hopefully that's similar to what I said before, Kent.
Speaker:Yeah, that's actually more detailed.
Speaker:Really it was kind of the, the radiator analogy I thought
Speaker:Oh, yeah.
Speaker:Okay.
Speaker:description of it.
Speaker:And, so not every airplane with a turbo is going to have an
Speaker:intercooler, but, if you can get one that does have it, that's great.
Speaker:there are companies that have STCs for those sometimes, speaking of those,
Speaker:you know, fixed waste gates that we were talking about on the Seneca's and
Speaker:the turbo arrows and such, there's a company called Merlin that hopefully is
Speaker:still around that, makes intercoolers for those among other things.
Speaker:Um, you know, if you're shopping for an airplane with a turbo, get
Speaker:educated on whatever type of airplane you're looking at as to not only what.
Speaker:type of, forced induction system you have and how the waste gate works and
Speaker:all that, but whether or not it has an intercooler and whether or not you can
Speaker:add one if you want to after the fact.
Speaker:So, so, let's talk about a few operational things.
Speaker:Um,
Speaker:one thing that's really nice when you have a normally aspirated airplane is
Speaker:if you're taking off, but especially if you're going around, can kind
Speaker:of just take that throttle and.
Speaker:shove it forward.
Speaker:Um, you know, and the throttle control is all the way forward.
Speaker:That's your maximum manifold pressure.
Speaker:Easy peasy, lemon squeezy, as they say.
Speaker:when you start getting into things with a turbo, it's not so easy anymore.
Speaker:and same thing with that supercharger and that diamond.
Speaker:Um, if you have an automatic waste gate, then you're golden.
Speaker:But Any of those other types you have to worry about over boosting.
Speaker:Um, if you have that manual, you know, strictly manual separate wastegate
Speaker:control, like we were talking about the command, she's having,
Speaker:that's fairly easy to deal with because you can have that wastegate control all
Speaker:the way back and essentially just be using ambient air pressure for the most part.
Speaker:and so you can set that on final approach when you enrich in your mixture
Speaker:and move your prop control forward.
Speaker:and so you can be pretty ready for a go around in those two.
Speaker:and so those are fairly simple as well, but on either the fixed
Speaker:wastegate or on the, manual ones that are tied to the throttle, you can't.
Speaker:Push the throttle all the way up anymore.
Speaker:And so you a lot more careful about that.
Speaker:so just to consider.
Speaker:Um, let's see critical altitude.
Speaker:We haven't talked about that yet.
Speaker:That's a concept with a forced induction airplane.
Speaker:Um, and basically that's the altitude
Speaker:it's the maximum altitude where you can still maintain sea level power.
Speaker:So, for example, on the Seneca, if I remember right, it's about 12, 000 feet.
Speaker:and so if you're above 12, 000 feet, well, you can have that throttle
Speaker:control all the way forward again.
Speaker:and then as you climb, you start losing power just like a
Speaker:normally aspirated airplane would
Speaker:I was going to say, then you join the, the world of the normies where your
Speaker:manifold pressure goes down as you climb.
Speaker:kind of, but of course your manifold pressure is still higher than
Speaker:It's still higher.
Speaker:That's right.
Speaker:That's right.
Speaker:let's see, There's a few things to think about when it comes to
Speaker:operating at higher altitudes.
Speaker:Um, cooling is a little more difficult at higher altitudes
Speaker:because the air is thinner.
Speaker:So even though the air is colder up there, a lot less of it.
Speaker:And so, you might have more challenges keeping your cylinders cool.
Speaker:Um, so that's something that you'll always have to keep an eye on.
Speaker:Um,
Speaker:Yeah.
Speaker:I'd never, I had never thought of that.
Speaker:Yeah, with that thin air also sparks behave differently.
Speaker:it's easier for a spark to form and jump a particular gap.
Speaker:And some airplanes have pressurized mags available.
Speaker:and that will help the, The spark to be at the right time and the right strength.
Speaker:Um, then finally, of course, we've been talking about the airplane
Speaker:the whole time, but we forgot we need to pressurize the pilot too.
Speaker:So, and what we're talking about there, of course, is the partial pressure
Speaker:of oxygen that you're breathing.
Speaker:so either you need to be in a pressurized airplane, which would be really nice.
Speaker:but usually in piston airplanes, with a few exceptions, of course, but usually
Speaker:in piston airplanes, we're talking about breathing 100 percent oxygen, through
Speaker:either a cannula or even a mask up higher.
Speaker:So that's just something to be aware of.
Speaker:You should probably go and take the oxygen chamber course somewhere.
Speaker:I took the opportunity to go do that in Oklahoma City a few years ago,
Speaker:and it was an excellent experience.
Speaker:you know, got to see FAA headquarters down there in Oklahoma City.
Speaker:the instructors from the FAA were really, really good.
Speaker:I'm, I'm sorry that I missed Loopy.
Speaker:Kent.
Speaker:Yeah, it's, I don't know.
Speaker:I, I'm not that entertaining when I'm loopy, but, I do have a picture of one of
Speaker:the guys I went down with, having just a really, really dopey smile on his face.
Speaker:Um, you know, we didn't go super high.
Speaker:They don't take you up into the thirties or anything like that.
Speaker:Um, you know,
Speaker:could get dangerous.
Speaker:is, right.
Speaker:And they, they don't want to get it, To the point of danger.
Speaker:What they want to do they, they actually kind of want it to come on slowly.
Speaker:So they
Speaker:Mm-Hmm.
Speaker:. Mm-Hmm.
Speaker:I forget if it was 18 or 25, 000 feet that they topped out at, but
Speaker:where, you know, you can't for too long without, breathing some oxygen.
Speaker:Um, and they basically have you sit at that higher altitude for several
Speaker:minutes and kind of progressively get worse and worse and worse until you
Speaker:finally throw up your hands and say, all right, I got to put the mask on.
Speaker:And they encourage you to, to do that as soon as you really
Speaker:understand how you feel.
Speaker:Because the point is not to show you how dumb you can get.
Speaker:The point is for you to recognize what your
Speaker:Right?
Speaker:are.
Speaker:Because everybody's a little bit different.
Speaker:Um, You know, they talk about, starvation for air where you, you
Speaker:just feel like you can't breathe enough being one of those symptoms.
Speaker:And, of course the stuff where you kind of get stupid,
Speaker:Feel euphoric.
Speaker:Yeah.
Speaker:right?
Speaker:Yeah, there are a handful of different symptoms and everybody
Speaker:experiences it differently.
Speaker:And the whole point of the course is for you to learn
Speaker:what hypoxia feels like to you.
Speaker:So that when it happens for real, you can recognize it and take
Speaker:care of it early enough that it doesn't, you know, knock you out.
Speaker:Um, and so I wouldn't even say that I experienced one of those symptoms, you
Speaker:know, more so than the others, but I, I kind of do have this general feeling.
Speaker:I can recognize that's different from other things I feel and I can recognize
Speaker:it now as hypoxia, you know, my heart will kind of be beating a little
Speaker:hard in my chest and, you know, I'll need to breathe a little more and,
Speaker:Mm-Hmm.
Speaker:of have that, it's not a, like I said, none of them really jump out for me.
Speaker:So, which honestly could make it worse, because
Speaker:Mm-Hmm.
Speaker:you don't have something that's way out of whack, you might think, oh, I'm fine.
Speaker:But now I'm able to say, okay, well, when I have these few things happen
Speaker:together, know that that's hypoxia.
Speaker:That's not just, you know, I didn't get enough sleep last night or whatever.
Speaker:It's, um,
Speaker:Well, that's a great thing to have experience with, to be able to recognize.
Speaker:Yeah.
Speaker:And I guess that's the whole point of the exercise.
Speaker:So if you're going to go out and buy a forced induction airplane that's
Speaker:not pressurized or even if it is pressurized, and you're going to go
Speaker:out and fly at high altitudes, I highly recommend that course from the FAA.
Speaker:So,
Speaker:I think they do something similar at Air Venture too.
Speaker:yeah, one of the, what they do bring to AirVenture, they don't, they
Speaker:don't bring the hypobaric chamber, to AirVenture because, it's probably
Speaker:pretty heavy and hard to move.
Speaker:But, and I was just about to talk about this is, if you have some sort
Speaker:of, physical issue that prevents you from being able to intentionally go
Speaker:to a pressure, you know, where it's 20, feet, they have another option.
Speaker:And that is that instead of changing the pressure, they change the amount.
Speaker:of oxygen.
Speaker:And so they basically displace some of the oxygen by adding extra nitrogen
Speaker:into this box that they bring along.
Speaker:So yeah, that's what they bring to Oshkosh is the, the nitrogen box.
Speaker:so you, you can get those same feelings of hypoxia without actually
Speaker:having to change the pressure.
Speaker:Um, along with that whole course, by the way, they also will do the
Speaker:spatial disorientation simulator, which they might bring to Oshkosh as well.
Speaker:I don't, I don't know that I've heard of that being there, but I think it's small
Speaker:enough that they could if they wanted to.
Speaker:Um, And what that is, is it's essentially a, a box big enough for you to sit in
Speaker:and there's a flight simulator, on the inside, it's all mounted on a swivel.
Speaker:And so what they do is you get inside this box you start flying the flight simulator
Speaker:what they do is the swivel starts to turn ever so slowly and they accelerate it at a
Speaker:rate that's so low that you can't feel it.
Speaker:And so over the course of several minutes, you'll start turning around and
Speaker:they're not going to let it get to where it's a centrifuge kind of situation or
Speaker:Yeah,
Speaker:It doesn't have to turn all that much.
Speaker:right.
Speaker:to turn.
Speaker:And so they're probably getting to where it's maybe doing.
Speaker:or 30 RPM, I would guess at most, you know, that means every two or three
Speaker:seconds you're turning around they have the process of accelerating you, they have
Speaker:also accelerated the fluids in your ear.
Speaker:Yep.
Speaker:And what they'll do is they'll have their guys acting as their traffic
Speaker:control and instructor and everything.
Speaker:And they'll have you turn to some headings and stuff while they're accelerating you.
Speaker:And then eventually, They'll like give you a new squat code or something like that,
Speaker:but they have the transponder mounted all the way at the bottom of the panel
Speaker:You have to look down.
Speaker:And as soon as you take your head and go like this and you're
Speaker:turning, whoa, you know, the world just goes topsy turvy on you.
Speaker:It's That was a good experience to have too.
Speaker:Yeah,
Speaker:like I said, in the longest way possible, definitely recommend going to FAA
Speaker:headquarters and doing the, training
Speaker:you got to take care of the pilot to not just the mags and the cooling.
Speaker:exactly.
Speaker:what, can, what about, descents in a forced induction
Speaker:airplane or a turbo airplane?
Speaker:Anything to consider there?
Speaker:Well, depends who you ask.
Speaker:So
Speaker:This is where, this is where it can get controversial.
Speaker:this, this can get downright religious in some cases, but, depending on who
Speaker:you ask, some people will say there is such a thing as shock cooling.
Speaker:And if you've ever taken a, how do you do this?
Speaker:You take a glass or something and you heat it up and then throw it in the freezer
Speaker:or something like that and it cracks?
Speaker:I don't know.
Speaker:I've never done
Speaker:Something like that.
Speaker:I don't know.
Speaker:things, things can crack with extreme enough temperature changes.
Speaker:And some people believe that you can crack cylinders that way.
Speaker:Um, and so they go to great lengths to do things like, I'm only
Speaker:going to pull back a half inch of manifold pressure every minute.
Speaker:Or, um, you know, I'm going to run speed brakes the whole way down so that I can
Speaker:keep a higher power setting and all that.
Speaker:I'm on the side where I don't that I necessarily believe that shot
Speaker:cooling is a big enough issue to cause huge problems with an engine.
Speaker:On the other hand, you can be nice to your engine anyway.
Speaker:I think we already talked about this when we talked about planning your descents.
Speaker:That's right.
Speaker:I still, I don't go to quite the extreme.
Speaker:I just said, you know, I'll, I'll pull like three inches of
Speaker:manifold pressure at the same time.
Speaker:But if you, Something to think about, you know, you don't want to come
Speaker:screaming into the pattern at 200 knots and then yank the power back to idle.
Speaker:Um, so even
Speaker:then shut the engine down.
Speaker:yeah, right.
Speaker:Well, some of the people who say, Yeah, shock cooling is not a thing.
Speaker:We'll point out rightfully so that the fastest your engine cools down is
Speaker:right after you shut it down anyway.
Speaker:So,
Speaker:That's right.
Speaker:there's not a whole lot we can do about that, but anyway,
Speaker:Although there generally is a procedure for, for cool down when
Speaker:she land in a turbo airplane.
Speaker:Right.
Speaker:yeah.
Speaker:And that is more around, cooling the turbo itself.
Speaker:So that's something that you do have to think about because the
Speaker:turbo is mostly cooled by oil flow.
Speaker:And so you're pumping engine oil through there
Speaker:If the turbo, think about how hot a turbo must get, you know, your exhaust gas
Speaker:temperatures are going to be, you know, north of 1500, even a normally aspirated
Speaker:airplane, when you're leaned for cruise.
Speaker:Um, and you know, I was just looking at the, Mooney Bravo.
Speaker:P O H here.
Speaker:And there's like, they're talking about 1650 and 1750 being limits for your
Speaker:turbine inlet temperature on the turbo,
Speaker:I mean, I, I would venture to say,
Speaker:gas is going into the, into the fan on the exhaust side.
Speaker:And so things are going to get hot,
Speaker:Kent, I, I think I may even be safe in saying that that air is hotter than the
Speaker:air coming out of us most of the time.
Speaker:maybe
Speaker:I give that about a body even odds on that one.
Speaker:But I can say that I have been in a 414 and I've, you know, you can see the turbo
Speaker:glowing, through the fins and the calling.
Speaker:Um, at least I think that was
Speaker:That's hot.
Speaker:was a long,
Speaker:hot.
Speaker:That's hot.
Speaker:but yeah, I could, I could see the turbo glowing.
Speaker:and so yeah, those things get really, really hot.
Speaker:And you can imagine that if you kept power in right till the
Speaker:end, um, you know, Now you have something that's really, really hot.
Speaker:It's getting cooled by engine oil and you notice some, there's obviously
Speaker:some airflow happening there too, but, the, the primary cooling is coming from
Speaker:the engine oil and you have bearings that have to support this shaft.
Speaker:That's going many thousands of RPM.
Speaker:And now you're going to shut the thing down and whatever oil is in there is
Speaker:going to be absorbing a lot of heat.
Speaker:so yeah, cooling down the turbos.
Speaker:Definitely something that you have to pay a lot of attention to.
Speaker:and this is one of those things where those, those fixed wastegates
Speaker:are really kind of awful.
Speaker:If you think about, you know, the other types of wastegates, you can
Speaker:essentially get to the point where most of the exhaust is going through, the
Speaker:bypass and not going through the fan.
Speaker:Whereas a fixed wastegate, even when you're at idle.
Speaker:You still have exhaust gases that are going through that turbo fan.
Speaker:so, you know, those are, those are pretty hot.
Speaker:And on those, you have to have, the throttle at like all the way idle for
Speaker:at least five minutes before you shut down the engine, which means that
Speaker:you might sit there with a line guy standing in front of you, why on earth
Speaker:you haven't shut your engine down, or, you know, you might have passengers
Speaker:in the back saying, I don't know.
Speaker:Why can't we shut these engines off and get off this darn airplane, you know?
Speaker:Yep.
Speaker:Yep.
Speaker:so, yet another thing to think about.
Speaker:Well, can't.
Speaker:one of the things I actually like about the, I'll call it the Comanche
Speaker:setup, for the third time here.
Speaker:but the, manual wastegates where you actually have direct control of it.
Speaker:With those, can essentially, not completely, but you can almost shut
Speaker:the turbo off in a way, and you know, like when you're coming down from
Speaker:altitude and you don't need all that power anymore, you're gaining manifold
Speaker:pressure as the air is getting thicker,
Speaker:Just send as much as you can out through the waste gate, right?
Speaker:right, and,
Speaker:Yeah.
Speaker:you know, so you can just Keep pulling that back.
Speaker:And really not going to be wanting to run at a hundred percent power or anything.
Speaker:So at some point, you know, if you start getting below, you know, seven,
Speaker:eight, nine, 10, 000 feet, you'll probably have that waste gate wide open.
Speaker:And at that point, now you're really helping that turbo cool down for that
Speaker:Mm hmm.
Speaker:of your descent as well.
Speaker:So,
Speaker:Interesting.
Speaker:Another thing I like about that particular setup.
Speaker:Well, as a pilot, who might own a, you know, a turbo normalized
Speaker:airplane, it sounds like that pilot needs some extra things to consider.
Speaker:there's going to be extra things to check in the annual.
Speaker:additional costs because additional parts means that other thing, you
Speaker:know, things more things to fail.
Speaker:you got to manage the extra heat, maybe an extra control lever.
Speaker:you got to think about some different things.
Speaker:So the big question is why go through all that trouble?
Speaker:Why do people, why do people, want to fly a turbo airplane?
Speaker:Now I have flying out here in the West.
Speaker:I have my favorite reason why I would like to have a turbo,
Speaker:but why, why do we want turbos?
Speaker:Why do we need them?
Speaker:Well, there are several reasons to have them.
Speaker:you know, the most obvious is if you are out West in the mountains and, know,
Speaker:if you're based at Leadville, Colorado.
Speaker:You probably want a turbo.
Speaker:remind me to bring Leadville back up in a second when I talk about
Speaker:why you don't want a turbo though.
Speaker:but yeah, if you have significant terrain around you and you have, departure
Speaker:procedures that you need to follow that tell you, you know, you got to
Speaker:climb in the hold until you get to this altitude before you can go anywhere.
Speaker:Yeah, you're probably going to want a turbo.
Speaker:Of course, you know, because of all the stuff we talked about with
Speaker:turbos and ground vehicles, people associate them with performance.
Speaker:And so there are a lot of people who well, I want to go fast.
Speaker:So I want a turbo.
Speaker:Well, there is truth to that.
Speaker:Um,
Speaker:Mostly because it can let you go higher.
Speaker:right.
Speaker:That's kind of what it comes down to, right?
Speaker:allowing you to maintain more power at a higher altitude.
Speaker:So you get a faster true air speed.
Speaker:Um, but.
Speaker:that also means you have to get up to the higher altitude and come back down.
Speaker:And so you have to be flying legs that are long enough to make that worthwhile.
Speaker:Yeah.
Speaker:That makes sense.
Speaker:if, it's normal for you to be flying hundreds of miles at a time, then yeah,
Speaker:turbo can be a great thing for you.
Speaker:Um, so I would say, Um, I guess we didn't really specifically call out takeoff
Speaker:performance, but that's kind of the third reason is if you are at a field
Speaker:that, you know, is at a higher altitude, especially higher density altitudes,
Speaker:and you need to get faster speeds on takeoff to be able to get off the ground.
Speaker:and you need to have the power to do that, obviously.
Speaker:So,
Speaker:Yeah.
Speaker:I've got a,
Speaker:with shorter runways.
Speaker:Yeah, you probably want to consider a turbo.
Speaker:So those are really the three big things take off performance, climb performance
Speaker:and then speed on longer legs are the reasons to really get a turbo.
Speaker:probably the primary one that has made me want to turbo, even though I'm essentially
Speaker:a flatlander living in Wisconsin here.
Speaker:I have been cruising at 15, 000 feet in my Mooney, is normally aspirated and
Speaker:I've There's been a layer below me at 13, 000 and then 13, 500 and then 14,
Speaker:and then, you know, climbing up towards me that I was pretty sure had ice in
Speaker:it and I do not have a de iced Mooney.
Speaker:So, I was sitting there looking down and going, Oh boy.
Speaker:I want to risk trying to climb to 17, 000?
Speaker:so that is the, the additional thing there is just operationally
Speaker:speaking, mostly weather.
Speaker:in addition to the terrain, of course, that we talked about
Speaker:already, you may want to go higher for, for that sort of reason, or
Speaker:Yeah.
Speaker:Cause I
Speaker:through an icy layer as quick as possible.
Speaker:Yeah.
Speaker:So, so yeah, I guess in a situation like that, a couple thousand, 4, 000 feet,
Speaker:if you could go higher efficiently and quickly could mean the difference between
Speaker:being out of the icing and in it, right?
Speaker:Yeah.
Speaker:Interesting.
Speaker:I'm at, 5, 000 feet and I decided I need to climb to 9,
Speaker:000 feet to get out of the ice.
Speaker:That's one thing.
Speaker:If I'm at 15, 000 feet and I need to climb to 19, 000, you know,
Speaker:now I'm probably in trouble.
Speaker:Okay.
Speaker:Interesting.
Speaker:is, my ceiling is still 20, 000 feet.
Speaker:And it's
Speaker:It'll really start to climb slower to get there.
Speaker:Yeah, exactly.
Speaker:Interesting.
Speaker:so you
Speaker:way.
Speaker:Yeah, way back when, I was training, to get my private pilot license.
Speaker:and I may have talked about this on the podcast at some time in the past
Speaker:when I covered this solo flight, one of my solos took me up north into the
Speaker:mountains and I landed at, Prescott, Arizona, which is quite a bit higher
Speaker:than the Phoenix Valley in elevation.
Speaker:And it was summer.
Speaker:If most people remember, I did my private training in the
Speaker:summer because I'm an idiot.
Speaker:And, I remember thinking that was the first time I thought, boy,
Speaker:it sure be nice to have a turbo normalized airplane up here.
Speaker:So I was on my solo, one of my solo cross countries.
Speaker:And luckily I was the only one in the airplane, but I was taking off.
Speaker:From Prescott headed south and there's a mountain range there and I remember
Speaker:thinking to myself several times You know the tower had me headed straight
Speaker:out to the south and I kept thinking I didn't have a lot of experience of
Speaker:course at the time and I kept thinking am I higher than those mountains yet?
Speaker:I'm not really sure.
Speaker:And I was climbing very, very slowly.
Speaker:So yeah, out, out in the mountains or high elevation airports, having
Speaker:a turbo would certainly be helpful to help you clear terrain easier.
Speaker:Definitely now I mentioned something about Leadville a minute ago
Speaker:Oh yes.
Speaker:Leadville for those of you who don't know Leadville, Colorado is the highest
Speaker:elevation airport in the United States public use at least there might be
Speaker:some private ones that are higher
Speaker:Believe it's almost 10, 000 feet, right?
Speaker:Nine something.
Speaker:934 feet standing on the ground.
Speaker:and that place is where I have my record density altitude at takeoff.
Speaker:the first time I left Leadville was in a 182 and the density
Speaker:altitude was 12, 200 feet
Speaker:Normally aspirated 182, I might add, right?
Speaker:aspirated one day to correct.
Speaker:And so, you know, normal takeoff was about 650 or 700 feet
Speaker:in that airplane, at gross.
Speaker:And I was At least a few hundred pounds under gross.
Speaker:And we were rolling down that runway for 2000 feet.
Speaker:So tripling at least your takeoff role is what that looks like.
Speaker:Um, but for those who think they need a turbo who live in higher places like that,
Speaker:um, sure if they're still in operation, but there at least was a flight school,
Speaker:maybe still is, at Leadville, Colorado, that uses normally aspirated 172s.
Speaker:And not only were they normally aspirated, they were the older,
Speaker:geared continental engines that were 145 horsepower sea level.
Speaker:it is possible to fly normally aspirated airplanes out of higher, higher fields.
Speaker:Given
Speaker:I,
Speaker:length and
Speaker:Yep,
Speaker:really nice long runway.
Speaker:and and a valley to the south.
Speaker:I believe that allows you to not have to clear terrain right away
Speaker:So so that helps too, but but yeah, imagine Imagine training doing
Speaker:your primary training in Leadville.
Speaker:I didn't know that there was a flight school there that used these 172s,
Speaker:but Imagine doing your initial flight training there and then someday
Speaker:going somewhere else and thinking what has happened to the airplane
Speaker:Yeah.
Speaker:Somebody
Speaker:it fly so well?
Speaker:low lead.
Speaker:Yeah, those are going to be, careful climbout pilots.
Speaker:I'll tell you that they're going to get a lot of practice climbing in high density.
Speaker:That's, that's pretty awesome.
Speaker:Yeah, So before we finish up, now that we've talked about turbos all day,
Speaker:let's talk about why you don't want one.
Speaker:All right, let's do it.
Speaker:And
Speaker:the topic properly.
Speaker:Yeah, well, will say that I have thought long and hard about this, and despite
Speaker:there having been times where I wished I had a turbo, I have decided that for
Speaker:the most part, for me, it's a bad idea.
Speaker:and I think that, If you're not in one of those groups of people we
Speaker:talked about earlier, you know, where you're either based high somewhere
Speaker:or with a lot of terrain around you, or you're of always flying the long
Speaker:legs, you probably don't want a turbo.
Speaker:I guess I could put an asterisk on there and say some of the things about that,
Speaker:Comanche setup again, the, you know, one of the ones that has a
Speaker:directly controllable, wastegate.
Speaker:Okay.
Speaker:Maybe you could still use that.
Speaker:Unfortunately, that's not an option for me, with the Mooney there.
Speaker:Just is no setup like that.
Speaker:for an airplane that is like mine.
Speaker:Um,
Speaker:so the reason you probably don't want a turbo.
Speaker:First of all, you do have additional cost.
Speaker:sometimes the purchase price is on the used market.
Speaker:Maybe roughly the same.
Speaker:However, you mentioned the maintenance before that's a big one.
Speaker:TBOs on, on turbo engines are shorter.
Speaker:you're going to be burning a lot more fuel.
Speaker:You know, I was just, looking at a particular route before, we started the
Speaker:show here, kind of one of my favorite.
Speaker:flights I've ever had in the Mooney, flew home from Santa Fe, New Mexico,
Speaker:all the way back to Wisconsin.
Speaker:and this is normally aspirated, out of Santa Fe, you kind of have to
Speaker:get up to 13, 000 feet for terrain.
Speaker:So I knew I had to climb that high anyway, but I, I had enough performance to do
Speaker:it despite being normally aspirated.
Speaker:And I just decided what the heck I'll stay up here.
Speaker:You know, there were some pretty decent tailwinds up higher.
Speaker:And so, I flew a, uh, You know, almost 900 mile leg, at 13, 000 feet.
Speaker:I was truing 172 knots on 10.
Speaker:1 gallons an hour.
Speaker:So I made it home from Santa Fe in 4 hours and 37 minutes, and
Speaker:I burned 53 gallons of fuel.
Speaker:Ha
Speaker:That's incredible.
Speaker:driving, you know,
Speaker:Yeah.
Speaker:and I decided to kind of look at, look at the performance charts
Speaker:and see how I, I fared against the performance charts for my airplane.
Speaker:And then also compare that to the performance charts on a Mooney Bravo,
Speaker:which is essentially the same airplane as mine, only turbocharged and the Bravo
Speaker:could have flown that leg, up higher.
Speaker:And it would have saved in a, you know, four and a half hour flight, it would
Speaker:have saved 21 minutes and it would have burned an extra 21 gallons of fuel.
Speaker:So, Is that, you know, even cheap fuel these days is, you know,
Speaker:generally around five bucks a gallon.
Speaker:So you're talking about an extra a hundred bucks to save 20 minutes.
Speaker:Yeah.
Speaker:that's on a, you know, that, that is a leg that a turbocharged airplane
Speaker:is going to do really well at.
Speaker:And so, yeah, there's some, definitely some additional fuel costs there.
Speaker:so definitely something to be aware of if you think you want a turbo.
Speaker:part, part of the reason it only saved 21 minutes is because of the
Speaker:there would have been some extra time, right, to climb to that higher
Speaker:altitude, where you're going slower.
Speaker:You're not in cruise yet.
Speaker:Although the climb was faster.
Speaker:With the turbo.
Speaker:So, or, or would be faster, I would say.
Speaker:So I actually looked at a few different altitudes and whether
Speaker:it was the same 13, 000 feet or,
Speaker:okay.
Speaker:I believe the, I have to look, I looked at, the optimum time and the optimum
Speaker:fuel burn, One of one, one of those was at 17, 000 and one of them was
Speaker:at 21, 000 and the result was pretty much the same at all three altitudes.
Speaker:today and the winds are pretty similar at all the altitudes today.
Speaker:So, obviously, you know, if you have a situation where the winds at 10, 000
Speaker:or knots tailwind and you know, you get up to 10, 000, 20 or 25, 000 and
Speaker:you've got a hundred knot tailwind.
Speaker:Well, you know, yeah.
Speaker:That day it's beneficial.
Speaker:that only works in one direction, right?
Speaker:If you're going the
Speaker:Right.
Speaker:day, that turbo is not doing you any good
Speaker:That's right.
Speaker:down low to get out of the headwinds anyway.
Speaker:Right.
Speaker:Yeah.
Speaker:so.
Speaker:You know, that's, that's one thing to consider is that, that, you know,
Speaker:the extra costs with fuel as well as the maintenance and the engine
Speaker:overhauls, potentially being earlier.
Speaker:And,
Speaker:the other thing is if you fly a lot of short legs, you know, I kind of,
Speaker:um, all over the board, I like to go on long trips in my airplane.
Speaker:you know, at least before the pandemic, I was doing usually about Four or
Speaker:five good, long, you know, thousand mile trips, one way thousand mile
Speaker:trips in the airplane every year.
Speaker:so that's when you start going, well, gee, you know, if I had a turbo,
Speaker:maybe I could knock off, know, a half hour, maybe even more if I
Speaker:can find some favorable winds, but
Speaker:Or, maybe even delete some of your stops, you know, if you're going fast enough.
Speaker:Yeah.
Speaker:stop is, is one of the biggest differences in speed you'll be able to find anywhere.
Speaker:so, you know, maybe if you want to get places fast, finding an airplane
Speaker:with really good range is as important as finding something that goes fast.
Speaker:Yeah.
Speaker:Good point.
Speaker:I can skip a fuel stop and you can't, I will beat you
Speaker:Yeah.
Speaker:Yeah.
Speaker:Interesting.
Speaker:Good things to be thinking about.
Speaker:Hmm.
Speaker:fuel for me is seven hours and 20 minutes.
Speaker:and so as long as I can manage to sit in the airplane for a long
Speaker:time, I can go places pretty quick.
Speaker:you know, I've, I've come back from the West coast in one day, um, a few times.
Speaker:And I think we actually talked about that before on one of the other episodes.
Speaker:But, anyway.
Speaker:The other thing I like to do, though, is I just like to fly around and go for 100
Speaker:hamburgers and, you know, once in a while I'll take the airplane when I go to visit
Speaker:my parents who are really like about 100 and I guess it's about 100 miles away.
Speaker:So I'm staying close enough on a lot of my legs the turbo would be a detriment
Speaker:on those legs because comparing, my airplane to the Bravo again, I'm
Speaker:actually faster below 10, 000 feet.
Speaker:you know, I don't have any restriction in my exhaust from a turbo peeing in there.
Speaker:it's not a huge difference, but It's there.
Speaker:so, you know, if, if both airplanes are at 10, 000 feet, it'll pretty
Speaker:much be a wash in terms of speed.
Speaker:cruise speed.
Speaker:That is, you know, the, the turbo will get up to 10, 000 a little
Speaker:faster, but you know, my climb rate below 10, 000 is really good too.
Speaker:So, really that turbo would only be advantageous to me
Speaker:if I was going up to 20 feet.
Speaker:And to do that, you have to be flying a long leg.
Speaker:I've kind of run a whole bunch of numbers trying to see what that looks like.
Speaker:And it seems like a good rule of thumb is that you want at least
Speaker:half of your flight to be in cruise.
Speaker:My airplane takes about, you know, down low or I'm developing lots of power.
Speaker:I figure it's taking me, eight miles per thousand feet just for climbing descent.
Speaker:Um, and so that means for every thousand feet I climb for the
Speaker:trip, I need to be going 16 miles.
Speaker:So on a 160 mile leg, then that means it would be a wash
Speaker:for me to have a turbo or not.
Speaker:So you really want to start getting an advantage from the turbo.
Speaker:You got to be going, you know, 300, 400 miles at a time, and then you start
Speaker:to see a speed advantage on the turbo.
Speaker:And I just fly enough legs that are shorter than that.
Speaker:It just, Doesn't make as much sense.
Speaker:So about what your, what your missions are and all that.
Speaker:for me also, I've just kind of found that I really don't like breathing oxygen.
Speaker:It really drives me out in a hurry.
Speaker:you know, you maybe as a. Arizona native where the air just is that way might
Speaker:be a little bit different for you.
Speaker:Um, you know, that's another thing that people should maybe try before
Speaker:they go and buy an airplane that they think they're going to fly up there.
Speaker:I've just found it highly unpleasant after about a half hour, an hour
Speaker:on oxygen, you know, my sinuses are just burning because there is
Speaker:zero moisture in that oxygen tank.
Speaker:So, but
Speaker:Yeah, I
Speaker:that's, just a few things to think about.
Speaker:And,
Speaker:I think you did a good job covering all of it.
Speaker:Pros, cons, things to think about.
Speaker:Love it.
Speaker:Um, any last things you can think of?
Speaker:Nope.
Speaker:Nope.
Speaker:I think we beat this horse to death.
Speaker:All right.
Speaker:Excellent.
Speaker:Well, thanks again, everyone for watching.
Speaker:in the recording of this episode.
Speaker:Thanks everyone for again, watching and listening.
Speaker:And we always want to hear from you, if there's any disagreements or, any
Speaker:things we missed, let us know about it.
Speaker:We'd love to hear your turbo stories, things that you like about it and so on.
Speaker:So let us know.
Speaker:You can always reach out to us, on the contact page on the website,
Speaker:which is at studentpilotcast.
Speaker:com.
Speaker:Or you can send an email easily to Bill at StudentPilotCast.
Speaker:com and that'll get to both of us.
Speaker:And, with that, we'll end this one for now and, hope you have a, a
Speaker:great time in your turbo or your normally aspirated engine airplane.
Speaker:So keep it flying.
Speaker:We'll see you later, Kent.
Speaker:See ya.
