Turbos…I Want To Learn More

[TCABM]

Specifically, I want to understand more about wastegates and turbocharging vs turbo normalizing. This may turn into a lot of questions over; what I *think* I know is bound to be not entirely correct and impacts of things like compression ratios and compression testing are bound to come up. Bear with, I’m ignorant, not stupid.

As a starting point for me, I read this article https://www.avweb.com/ownership/mot...nd read that,that could grow cracks overnight.

From it I gleaned the manual wastegate adds another pilot control in the equation that allows the pilot to manually tune the boost to achieve given manifold pressure; basically a fourth knob. Is that a correct understanding?

Then, there’s the automatic wastegate. This system essentially regulates the exhaust flow (in a variety of ways) to effectively maintain a predetermined manifold pressure.

Those two dump exhaust before hitting it hits the turbo.

Finally, there’s the Continental system that doesn’t care about exhaust flow before the turbo and instead dumps excess boost after the turbo and before the intake.

Is that essentially correct?

Second, how does the wastegate system work in a TN setup? Is it just an automatic wastegate that’s set maintain 29” of manifold pressure until you climb high enough it can’t anymore or is it some other rube goldberg contraption the regulates the magic smoke flow?

 

[TCABM]

Not sure why this dropped in Technical Corner…tapatalk gremlin, I guess. @flyingron or someone else, can this be moved to Hangar Talk? Thank you.

 

[masloki]

From it I gleaned the manual wastegate adds another pilot control in the equation that allows the pilot to manually tune the boost to achieve given manifold pressure; basically a fourth knob. Is that a correct understanding?

I have a Rajay manual wastegate. This is correct.

Those two dump exhaust before hitting it hits the turbo.52;5

Not as written. The exhaust inlet is a Y with a butterfly valve. The more I twist the boost control the more exhaust is routed to the turbo. Any unneeded exhaust pressure is still sent down the the other pipe. It is very possible to overboost the engine with this setup leaving it to the pilot to not screw up.

There is an article floating out there comparing the Mooney M20K 231 and 252s which would be a good highlight of different turbos. Iirc, 231 had a manual wastegate and 252 moved to automatic.

 

[flyingron]

Not sure why this dropped in Technical Corner…tapatalk gremlin, I guess. @flyingron or someone else, can this be moved to Hangar Talk? Thank you.

Actually, Maintenance Bay would seem to be better... moving.

 

[Bill]

There is an article floating out there comparing the Mooney M20K 231 and 252s which would be a good highlight of different turbos. Iirc, 231 had a manual wastegate and 252 moved to automatic.

We were picking up the 201 from annual yesterday and the shop had both a 231 and 252 in there with the cowlings removed. While we waited for the paperwork to be completed, we walked back and forth to compare the engine installations. In additon to the automatic waste gate, the 252 has a better induction system design as well as an intercooler after the turbo. The 252 is a hotrod of a bird, capable of 190-200kts in the high teens and low 20’s, on about 13gph.

 

[RussR]

There is also a fixed wastegate, used in some Senecas and Turbo Arrows, as well as early Turbo Saratogas. If you push the throttle all the way up, the engine explodes. Good times when teaching go-around/engine failure actions to pilots used to just jamming the throttle all the way forward.

 

[Pinecone]

There is an article floating out there comparing the Mooney M20K 231 and 252s which would be a good highlight of different turbos. Iirc, 231 had a manual wastegate and 252 moved to automatic.

231 had a fixed waste gate, not a manual one. The 252 does have an automatic wastegate.

 

[Pinecone]

We were picking up the 201 from annual yesterday and the shop had both a 231 and 252 in there with the cowlings removed. While we waited for the paperwork to be completed, we walked back and forth to compare the engine installations. In additon to the automatic waste gate, the 252 has a better induction system design as well as an intercooler after the turbo. The 252 is a hotrod of a bird, capable of 190-200kts in the high teens and low 20’s, on about 13gph.

IMO the 252/Encore is the ultimate Mooney, and thus the ultimate airplane.

I cruise at 175 KTAS, 17,000 on 10.1 GPH.

 

[Pinecone]

Fixed wastegate - a settable (on the ground) bypass for some of the exhaust gas. Manifold pressure is controlled by the throttle. Depending on the setting and conditions, it is possible to overboost the engine.

Manual wastegate - pilot has a control over the wastegate, either with a separate control or linked to the throttle.

Automatic wastegate - the system takes care of the manifold pressure. You can get a mild overboost in cold temps. But mainly set and forget control of manifold pressure.

Turbo normalized just means the boost is limited to sea level manifold pressure or 30 inches. Turbo charged or turbo supercharged is max manifold pressure higher than sea level pressure.

 

[TCABM]

Thanks all, especially @masloki and @Pinecone for helping clarify and simplify. I don’t want to deep dive on one platform yet.

Let’s talk overboost for a second. In my mind this is a condition that occurs when the turbo is creating more boost than is needed/desired. I’m assuming this is functionally indicated on the manifold pressure indicator, but I understand some systems uses a lamp to indicate an overboost situation.

Is that a fundamentally correct understanding?

 

[midlifeflyer]

I don't know if this will be helpful or not. When I was living in Colorado, I flew a number of different turbo models and taught in a few of them. This is a cut and paste of a compilation I wrote at the time. It's probably over 20 years old at this point and I won't vouch for complete accuracy.

---

The purpose of turbocharging is to allow an engine to operate over a wider range of manifold pressures independent (more or less) of cruise altitude. The turbo-charger extracts waste energy from exhaust gases and uses it to blow compressed air into the intake side of the engine.

New Terms
Critical Altitude: the highest altitude at which the trubo can maintain se level MP.

Critical periods

• Takeoff (especially in fixed wastegate systems). There is a wastegate lag that can cause overboosting if the throttle is not handled properly.
• Beginning the descent. The 1"/minute rule is common. Turbos tend to run very hot, so you want to reduce power on an incremental basis to lessen overcooling of the engine.
• After landing. Three minutes after landing for cooldown.

Wastegates
The engine has two throttle butterflies: One in the intake system and one in the exhaust. The latter is called a wastegate.

Four Types of Wastegate Systems
1. Manual (Aftermarket like the Mooney)
The advantage of a manual system is that you can turn the boost “off ” when you don ’t want or need it, which is not true of other systems. The disadvantage of manual wastegates is that a moment ’s inattention can (at least in theory) cause a major overboost. This can result in both detonation and a dangerous rise in CHTs .

2. Fixed (Turbo Arrow)
A fixed wastegate setup is just what it sounds like: The wastegate is hardwired in one intermediate position and left that way forever. The advantage is simplicity: the pilot has no wastegate control in the cockpit; just uses the throttle to modulate manifold pressure as usual. The disadvantage: you can’t turn the boost off when you don’t need it and you can ’t apply full boost when you do need it. You’re stuck with a compromise.

This kind of system (used on the Mooney 231, Piper Turbo Arrow, and Piper Seneca II/III) requires that the pilot use considerably less than full throttle on takeoff to avoid going past the MP redline (of 40 or 41 inches). Manifold pressure overshoot is a consideration but some of these systems have an overboost valve to prevent too much overboosting. It should be mentioned that turbochargers often don’t make it to TBO in this kind of setup -and engines run hot.

3. Mechanical Interconnect (CT182RG)

Mechanical interconnect systems offer some improvement over fixed wastegate setups but not much. In some systems, the throttle arm and wastegate butterfly are interconnected such that they move in tandem; this is the configuration used in the Turbo Saratoga and Turbo Lance. In other cases, the system is set up so that the wastegate only begins to close after the throttle butterfly has already opened all the way; this is the situation in the Cessna Turbo 182RG.

Simplicity and transparency to the pilot are the main goals of this system, but the possibilities for lag, rigging problems, and linkage play are numerous.

4. Automatic Controller

Automatic controller systems offer (arguably) the most elegant solution for wastegate control. Typically, the wastegate is hydraulically actuated (using engine oil),under the control of one or more aneroids which may or may not know what the pilot is doing with the throttle. Usually there is no mechanical connection between the throttle and the wastegate circuit, nor any separate turbo controls in the cockpit. The pilot merely advances the throttle to a particular setting, and the aneroids (by compensating for ambient air pressure)keep the manifold pressure at the commanded level. This kind of setup is found in the Cessna T210,T310/320,340A,402,414,421, etc.; the Baron 58TC/58P and Duke; Turbo Aztec E &F, Navajos, etc. The Piper twins use a variation on this theme called the density controller. The TIO540 engines in the Aztecs and Navajos that use this method have high redline manifold pressures (43 inches or so).Most of the big Continentals that use pressure controllers or slope controllers have somewhat lower redline MPs: 32.5 inches for the Turbo 310, up to 38.5 inches for some of the cabin twins.

 

[midlifeflyer]

Thanks all, especially @masloki and @Pinecone for helping clarify and simplify. I don’t want to deep dive on one platform yet.

Let’s talk overboost for a second. In my mind this is a condition that occurs when the turbo is creating more boost than is needed/desired. I’m assuming this is functionally indicated on the manifold pressure indicator, but I understand some systems uses a lamp to indicate an overboost situation.

Is that a fundamentally correct understanding?

I've seen a combination of both an overboost light and a MP redline. Turbo Arrow is an example.

 

[EdFred]

IMO the 252/Encore is the ultimate Mooney, and thus the ultimate airplane.

I cruise at 175 KTAS, 17,000 on 10.1 GPH.

Except when you try and fly it into and out of a real strip with passengers. That's when the Comanche steps in to carry out 2 of your passengers to a nearby field while you, flying out solo, scrape the tree tops.

 

[TCABM]

Except when you try and fly it into and out of a real strip with passengers. That's when the Comanche steps in to carry out 2 of your passengers to a nearby field while you, flying out solo, scrape the tree tops.

You know what Mooneys and Comanches have in common, right?

Neither is still in production. Al Mooney had a certain je na sais qua about his designs.

 

[EdFred]

You know what Mooneys and Comanches have in common, right?

Neither is still in production. Al Mooney had a certain je na sais qua about his designs.

Yeah, it's just that the power to weight ratio just doesn't cut it when you have obstacles.
Takeoff roll is significantly higher, and the climb-out is lacking as well.

 

[Pinecone]

And they have the same wing.

 

[Pinecone]

Thanks all, especially @masloki and @Pinecone for helping clarify and simplify. I don’t want to deep dive on one platform yet.

Let’s talk overboost for a second. In my mind this is a condition that occurs when the turbo is creating more boost than is needed/desired. I’m assuming this is functionally indicated on the manifold pressure indicator, but I understand some systems uses a lamp to indicate an overboost situation.

Is that a fundamentally correct understanding?

Yes. And if that happens, you just pull the throttle back a bit.

With a fixed waste gate you get more pilot input. If you change the RPM, that changes the exhaust volume which changes the boost, which changes the exhaust volume. So a lot more tweaking.

 

[TCABM]

Alright, I think I have a basic understanding. Now, let’s talk about some turbo engine fundamentals.

I expect lower compression cylinders are desired in turbo applications because, well boost and intake air temps are part of the equation. But a stock O-320 is already a low compression ratio cylinder at 7:1 or 8.5:1

The six cylinder Conti TSIO 360 is 7.5:1; which is relatively lower than their IO-360 at 8.5:1.

Maybe engineer @Ted can help me understand why a 1.0 differential is all that’s needed for the TSIO360. More fundamentally though is why put the 7:1 cylinders in the O-320 other than to maximize utilization of common assemblies like barrels, cranks, con rods, etc.

 

[masloki]

but I understand some systems uses a lamp to indicate an overboost situation.

Oddly enough, my manual specifies a low oil pressure lamp only (which keeps the turbine spinning freely) and its optional with an oil filter. STCs and 1960s engineering, amiright?

Except when you try and fly it into and out of a real strip with passengers. That's when the Comanche steps in to carry out 2 of your passengers to a nearby field while you, flying out solo, scrape the tree tops.

Ouch. My F model had no issues getting out. Getting in with some screaming wind shear. …. That was my first flight ever though where I had to lower my nose for cooling. It was hot that weekend!

Yes. And if that happens, you just pull the throttle back a bit.

With a fixed waste gate you get more pilot input. If you change the RPM, that changes the exhaust volume which changes the boost, which changes the exhaust volume. So a lot more tweaking.

100% this. There’s definitely tweaking in the climb. And any time you do a climb or descent, in the maneuver and the level off. Not bad - just something to monitor and adjust. For the low price of climbing at 500-700 fpm to 20K.

Maybe engineer @Ted can help me understand why a 1.0 differential is all that’s needed for the TSIO360.

I’d like to learn more. The Lyc IO-360 is on the high side and on my model, NA, they set timing to 20’ to cool it off. My IA confirmed that is how they leave the factory even though the original timing was 25’. Nothing in my STC changes the timing.

 

[EdFred]

Oddly enough, my manual specifies a low oil pressure lamp only (which keeps the turbine spinning freely) and its optional with an oil filter. STCs and 1960s engineering, amiright?

Ouch. My F model had no issues getting out. Getting in with some screaming wind shear. …. That was my first flight ever though where I had to lower my nose for cooling. It was hot that weekend!

100% this. There’s definitely tweaking in the climb. And any time you do a climb or descent, in the maneuver and the level off. Not bad - just something to monitor and adjust. For the low price of climbing at 500-700 fpm to 20K.

I’d like to learn more. The Lyc IO-360 is on the high side and on my model, NA, they set timing to 20’ to cool it off. My IA confirmed that is how they leave the factory even though the original timing was 25’. Nothing in my STC changes the timing.

Your plane is a little lighter than Kent's. And the PW ratio is probably a bit better.

 

[masloki]

Your plane is a little lighter than Kent's. And the PW ratio is probably a bit better.

I think you just called me skinny or Kent not.

 

[flyingcheesehead]

Specifically, I want to understand more about wastegates and turbocharging vs turbo normalizing. This may turn into a lot of questions over; what I *think* I know is bound to be not entirely correct and impacts of things like compression ratios and compression testing are bound to come up. Bear with, I’m ignorant, not stupid.

I was going to write up a whole thing, but @masloki, @Pinecone, and @midlifeflyer pretty well covered the basic workings.

Automatic wastegates are great, manual wastegates can be nice, fixed wastegates suck. IMO, of course. I'm not a fan of the manual wastegates controlled by the throttle lever either (a la Cessna TR182 for example).

I kinda like the manual Rajay system used on the turbo Comanches and Twin Comanches - You can almost treat it like a normally aspirated engine for takeoff and landing, and then just tweak the wastegate knob in climb and cruise for the desired results, and you can essentially remove all boost by the later portions of the descent and give the turbo a chance to cool down before landing.

Except when you try and fly it into and out of a real strip with passengers. That's when the Comanche steps in to carry out 2 of your passengers to a nearby field while you, flying out solo, scrape the tree tops.

Well, considering that on a paved strip my plane can get out of any place it can get into, maybe your real strip needs to be mowed shorter.

Since I had to find this thread myself, you can go and find the thread where I talked nice about the Comanche. But, you did get me curious, given the similarities of our birds.

Mooney M20R: MGTOW 3368, hp 280, wing 174.9sqft, 12.02 lb/hp, 19.26 lb/sqft, Vs0 59kt, Vs1 66kt Vx 85kt.
Mooney M20C: MGTOW 2575, hp 180, wing 174.9sqft, 14.31 lb/hp, 14.72 lb/sqft, Vs0 49kt, Vs1 58kt Vx 70kt.
Comanche 250: MGTOW 2800, hp 250, wing 178sqft, 11.2 lb/hp, 15.73 lb/sqft, Vs0 56kt, Vs1 62kt, Vx 73kt.

So, the Comanche has the best power to weight ratio and will accelerate the quickest. It's much closer to the M20C than the M20R in wing loading and in Vx speed.

Now, why can the smaller Mooney get out of 6Y9 OK while the bigger one struggles? They both use the same airfoil, NACA 63-215 at the root and 64-412 at the tip (Comanche is a similar 64A215 throughout). The M20C accelerates more slowly due to its power loading, but its Vx is about at my rotation speed. In addition, the M20C can retract landing gear immediately - "When safely airborne and in good control" according to the POH - and if it has the manual gear system, can also do so almost instantaneously. The M20R, on the other hand, has a higher Vx. It also has a 3-part gear door, including some inner doors that aren't present on the C and open up during the retraction sequence:

Because of the extra drag of the door and the rear portion of that section of the wheel well at higher angles of attack, the M20R is one of the birds where you keep the gear down until clearing obstacles, so I have a bunch of extra drag that probably eliminates a good chunk of my power loading advantage over the M20C.

So, a Comanche or Bonanza or M20C will all get off of shorter runways than my M20R. The tradeoff is that I can go faster on less fuel, which is what I need to do 99% of the time. Someday hopefully I'll be able to stuff a Citabria or something like that in the back corner of the hangar for when I feel like landing at shorter grass strips or turning upside down.

 

[Pinecone]

Alright, I think I have a basic understanding. Now, let’s talk about some turbo engine fundamentals.

I expect lower compression cylinders are desired in turbo applications because, well boost and intake air temps are part of the equation. But a stock O-320 is already a low compression ratio cylinder at 7:1 or 8.5:1

The six cylinder Conti TSIO 360 is 7.5:1; which is relatively lower than their IO-360 at 8.5:1.

Maybe engineer @Ted can help me understand why a 1.0 differential is all that’s needed for the TSIO360. More fundamentally though is why put the 7:1 cylinders in the O-320 other than to maximize utilization of common assemblies like barrels, cranks, con rods, etc.

Low compression O-320s are designed to run on 80/87 AVGAS which is no longer available. The O-320 also came in a high compression version that makes 160 HP (versus 150 for the low compression). IIRC, it was for 91/96 AVGAS which hasn't been available for a LONG time.

Turbo engines are designed to run on 100LL (or 100/130 in the past).

In the past, there were 4 grades of AVGAS. This was simplified to two then to one. The grades have two numbers. The first number was lean octane rating and the second was rich rating. The rich rating allowed higher power for take off, climb, and for military - combat. The lean rating was for cruise. Not really useful for normally aspirated, but allowed higher boost for takeoff, climb and combat in turbocharged engines/

80/87 - Red - For low compression engines. It was the last to go away (early to mid 80s). Most planes that are designed to use this can run MOGAS.
91/96 - Brown - For higher compression, normally aspirated engines. Was the first to go away (early 60s).
100/130 - Green - For turbocharged and higher compression. Replace by 100LL
100LL - Blue - Lower lead than 100/130.
115/145 - Purple - Used by the military and airlines. Now only available for special events. There was a batch made each year for Reno air races. The USAF used it into the 80s, but it was not commercially available for many years before that.

Now we have:

UL91 - mainly in Europe, basically a premium auto fuel, without alcohol and tighter controls.
UL94 - Similar to 100LL without the lead. Should be usable in those planes designed for 91/96
G100LL - FAA approved unleaded AVGAS that is usable in all airplanes. Interestingly, in the old nomenclature, this would be 100/160

 

[Tokirbymd]

Don’t forget the Merlyn waste gate controller add on. Touted as “automatic” it actually uses oil pressure and an aneroid to keep upper deck air pressure around 2” higher than selected MAP. Improves on the fixed wastegate designs for Mooney, Arrow, and Senecas. Allows higher critical altitude or max altitude with full MAP, but bypasses the turbo at lower settings so you “may” preserve some turbo health and longevity.

 

[Lon Stratton]

There is also a fixed wastegate, used in some Senecas and Turbo Arrows, as well as early Turbo Saratogas. If you push the throttle all the way up, the engine explodes. Good times when teaching go-around/engine failure actions to pilots used to just jamming the throttle all the way forward.

The early Turbo Saratoga does not have a fixed wastegate. It moves in sync with the throttle. True, you don't just firewall the throttle on takeoff or go arounds. You just learn how to use the equipment properly. Had 2 of these engines go past TBO so far.

 

[Larry in TN]

I don't have a lot of time flying turbos but I did fly the C-207 and C-402 on Grand Canyon tours in 1990. Both had Continental engines, IIRC, though the details have faded.

When I'd go into work I'd always hope to be assigned the C-402 but sometimes fly the C-207. It seemed like a real dog, and flew like an old pickup truck with bag suspension. One morning, I had the 207 and was departing the Grand Canyon airport (GCN) behind a loaded C-172. May have been the 180hp version. I was cleared for takeoff once he was 3,000' down the runway and airborne. My doggy 207 passed him before reaching the end of the ~7,000' runway. For me, that really highlighted the roll the turbocharger played, even if I had become accustom to even better performance.

 

[Checkout_my_Six]

At sea level....my turbo Bonanza has a "longer" takeoff roll than a similar N/A plane. It takes more time to make power.

 

[RussR]

The early Turbo Saratoga does not have a fixed wastegate. It moves in sync with the throttle.

Fair enough. It's been a few years, I must have been confused with the others.

 

[TCABM]

So continuing the general discussion, turbos add heat and pressure on the intake side does anyone monitor the charge air temp or is it just watch the EGT/TIT?

I would think EGT/TIT is most important for the turbo itself, but for the engine itself the intake temp seems to be important for longevity, especially in a TN setup.

 

[masloki]

So continuing the general discussion, turbos add heat and pressure on the intake side does anyone monitor the charge air temp or is it just watch the EGT/TIT?

I would think EGT/TIT is most important for the turbo itself, but for the engine itself the intake temp seems to be important for longevity, especially in a TN setup.

For that side, you still monitor CHTs. I do see a very real difference when flying boosted and correlated to the boost amount. On the other hand, you are using more boost where the air is colder so it isn’t a big deal to keep the engine cool.

 

[Pinecone]

So continuing the general discussion, turbos add heat and pressure on the intake side does anyone monitor the charge air temp or is it just watch the EGT/TIT?

I would think EGT/TIT is most important for the turbo itself, but for the engine itself the intake temp seems to be important for longevity, especially in a TN setup.

The fixed waste gate Mooney 231 is required to have a Compressor Discharge Temp gauge. So the answer is YES, you do monitor charge air temp on some installations.

On my 252, no, it is not instrumented to do so.