IFR Turbo Decent and turbulance

[skidoo]

So I had a great flight a few days ago, some photos included. I had power back to about 65% and cruising at FL190. All temps are good and stable. Then ATC calls out "descend and maintain xxKft". So, I set the autopilot to descend at 500 fpm, and pull back some power, as much as 6" or more. Airspeed still increases from about 148kts to near 165 kts (TAS) to maintain the 500 ft/minute. This was fine as I was still in smooth air.

But, when it came time to descend below 10K below under the puffy clouds, as anticipated, it became fairly bumpy. So, I'm thinking this is too fast for bumps! Also thinking "shouldn't pull power back to fast or too far". Also thinking "need to maintain 500 fpm descent". I was taught not to pull the power so far back that the TIT is below the green. Instructor says add flaps and keep some power in it. Doesn't seem practical 50 miles out from the destination.

Any recommendations for the right balance of power, descent rate, etc...

 

[dukeblue219]

Well, you gotta do what you gotta do to get down. If you can't slow enough with power reduction because you need to protect the engine, then you need to add drag. I do not fly high-performance aircraft, but this is where speed brakes would be handy if you had 'em, or flaps if you're slow enough to deploy them, or even a bit of a forward slip I guess.

 

[Henning]

So I had a great flight a few days ago, some photos included. I had power back to about 65% and cruising at FL190. All temps are good and stable. Then ATC calls out "descend and maintain xxKft". So, I set the autopilot to descend at 500 fpm, and pull back some power, as much as 6" or more. Airspeed still increases from about 148kts to near 165 kts (TAS) to maintain the 500 ft/minute. This was fine as I was still in smooth air.

But, when it came time to descend below 10K below under the puffy clouds, as anticipated, it became fairly bumpy. So, I'm thinking this is too fast for bumps! Also thinking "shouldn't pull power back to fast or too far". Also thinking "need to maintain 500 fpm descent". I was taught not to pull the power so far back that the TIT is below the green. Instructor says add flaps and keep some power in it. Doesn't seem practical 50 miles out from the destination.

Any recommendations for the right balance of power, descent rate, etc...

Did you consider pulling the prop back instead of the throttle? Either will reduce power while one preserves heat.

 

[DavidWhite]

Did you consider pulling the prop back instead of the throttle? Either will reduce power while one preserves heat.

That's what I do flying airplanes with turbos.

 

[skidoo]

Did you consider pulling the prop back instead of the throttle? Either will reduce power while one preserves heat.

No, I didn't because I was already back to 2100 rpm's, cruising. When going VFR, I would anticipate beginning my descent earlier and would open the cowl flaps for a few minutes before, and then close them as I reduce power. But IFR, I am not used to the descend, level off, descend, level off on command yet for managing the power/temps. I think I am ok, just looking for maybe better ideas.

 

[Clark1961]

Hmmm, I don't have a green arc on my TIT so I don't pay much attention to it when the needle goes that direction.

At 65% power the heads should have been relatively cool. Descending from 190 to 100 at 500 fpm give you 18 minutes to get everything cooled. I wouldn't have worried about running 18 inches or so of power at that point.

Question, what power settings do you use in the pattern and what's the TIT then? What's the TIT on short final? You have to be able to go to full power at that point so I don't think the bottom of the TIT scale is a problem. Of course the real question may be what does the POH say?

 

[skidoo]

Hmmm, I don't have a green arc on my TIT so I don't pay much attention to it when the needle goes that direction.

At 65% power the heads should have been relatively cool. Descending from 190 to 100 at 500 fpm give you 18 minutes to get everything cooled. I wouldn't have worried about running 18 inches or so of power at that point.

Question, what power settings do you use in the pattern and what's the TIT then? What's the TIT on short final? You have to be able to go to full power at that point so I don't think the bottom of the TIT scale is a problem. Of course the real question may be what does the POH say?

I believe that the bottom of the TIT green is near 12". In training, I had to get down faster and needed less than that, hence the suggestion for adding flaps and keep some power in.

In the pattern, CHT is usually cooled to below 300F. I was cruising at about 365-370F. I have hear other turbo pilots say that they pull about 1" of MP per minute. If I did that, I would either not make 500 ft per minute or my AirSpeed would get way high...

 

[Jaybird180]

Your 500fpm command to the A/P dictated the actuation of down trim to obey your command at the selected power setting. The A/P was doing what it was told.

So I had a great flight a few days ago, some photos included. I had power back to about 65% and cruising at FL190. All temps are good and stable. Then ATC calls out "descend and maintain xxKft". So, I set the autopilot to descend at 500 fpm, and pull back some power, as much as 6" or more. Airspeed still increases from about 148kts to near 165 kts (TAS) to maintain the 500 ft/minute. This was fine as I was still in smooth air.

But, when it came time to descend below 10K below under the puffy clouds, as anticipated, it became fairly bumpy. So, I'm thinking this is too fast for bumps! Also thinking "shouldn't pull power back to fast or too far". Also thinking "need to maintain 500 fpm descent". I was taught not to pull the power so far back that the TIT is below the green. Instructor says add flaps and keep some power in it. Doesn't seem practical 50 miles out from the destination.

Any recommendations for the right balance of power, descent rate, etc...

 

[Henning]

As to adding flaps, what effect do flaps have on Va?

 

[Alexb2000]

182 or 206? I never worry or care about TIT when it comes to cooling. I watch the CHT's and I've noticed that the temps don't move dramatically in a powered descent like you described. With a Lycoming I've found I never have to worry about it. 80 degrees isn't going to matter and that's about the difference in CHT's I see.

Is your instructor basing this recommendation off of turbo aircraft generically or late model Cessna's with turbo Lycomings?

 

[skidoo]

182 or 206? I never worry or care about TIT when it comes to cooling. I watch the CHT's and I've noticed that the temps don't move dramatically in a powered descent like you described. With a Lycoming I've found I never have to worry about it. 80 degrees isn't going to matter and that's about the difference in CHT's I see.

Is your instructor basing this recommendation off of turbo aircraft generically or late model Cessna's with turbo Lycomings?

I believe he was basing that on generic turbo aircraft.

 

[skidoo]

As to adding flaps, what effect do flaps have on Va?

The instructor's suggestion to add flaps were to get down relatively fast without excessive speed and still maintain power in the TIT green. There was no consideration given for Va. The slower speed for the approach, I believe was to buy me more time to correct mistakes.

But, now I am looking for a balanced approach and considering Va for long descents into turbulence.

 

[skidoo]

Hmmm, I don't have a green arc on my TIT so I don't pay much attention to it when the needle goes that direction.

snip...

Here is a photo during cruise. The TIT has a lower green area. The POH doesn't say much about operating below this green level. But, an instructor expressed concern about doing so...

 

[douglas393]

IN my T182T I believe that lower edge is about 800 degrees. I can check when I get home, but it has not been an issue for me in descents. Though I have never knew there was a problem with that as much as problems with shock cooling, but then again everytime I think I have this engine management stuff figured out I find out everything I thought I knew was wrong!

 

[Alexb2000]

I just don't get the logic of the TIT and I can't find any reference too it in my POH. You could always call Lycoming about this, but I wouldn't worry about it.

Rather, in the scenario you described I would be more concerned about Va. You are probably near the end of the flight, so light weight where Va is less than published. If you were to add flaps that will further decrease Va. So that would be my concern entering possible turbulence.

 

[douglas393]

I just don't get the logic of the TIT and I can't find any reference too it in my POH. You could always call Lycoming about this, but I wouldn't worry about it.

Rather, in the scenario you described I would be more concerned about Va. You are probably near the end of the flight, so light weight where Va is less than published. If you were to add flaps that will further decrease Va. So that would be my concern entering possible turbulence.

Could he be worried about shock cooling. I believe, and again my understanding of engine management leave much to be desired as much as I read Irealize so much I do not know, that cooling the turbo too fast can lead to damage, as can running it too cold. As for Va, at his speeds he is well above the Va if he is in a t182t which is 110 kts. Again not sure what he is flying, though from the pictures it looks to be a cessna either 182 or 210.

 

[weilke]

My 5cents.

The turbo itself doesn't care how fast it cools down as long as it has oil pressure.

The cylinder heads care about cooling down too fast if they are (too) hot to start with. The only empiric data about head cracking is from glider tug operations that go from 'hot and slow full power' to 'divebombing' with no intervening cooldown. The skydiving operators that have a minute or longer jump-run at a intermediate power setting see very few cylinder cracks. If you are already quite cool in cruise, maybe the first power reduction shoud be stepped, but to wait religiously for 2min before going from 21in to 19in achieves nothing.

 

[skidoo]

snip... everytime I think I have this engine management stuff figured out I find out everything I thought I knew was wrong!

That is where I get, questioning what I thought I knew. The POH for my T182T shows a Green range of 1350 to 1685F.

 

[skidoo]

snip.. As for Va, at his speeds he is well above the Va if he is in a t182t which is 110 kts. Again not sure what he is flying, though from the pictures it looks to be a cessna either 182 or 210.

Actually, in looking back at my photo, I was cruising near Va at about 109KIAS. Va at my weight was probably about 105 KIAS. So, I just need to slow down a little when in turbulence, but still maintain a proper descent. And, yes I am flying a T182T as well.

When in IR training, 20 deg flaps, plus power just in the bottom of the green would give me about 95KIAS and 500 fpm. It just doesn't make sense for me to do that (put the flaps down) while 50 miles out. So, I am wondering if there is something I am missing when considering turbulence as well. It always seemed bumpy during training anyway...

 

[Henning]

Here is a photo during cruise. The TIT has a lower green area. The POH doesn't say much about operating below this green level. But, an instructor expressed concern about doing so...

Did you ask him, "Why?"

 

[Alexb2000]

Actually, in looking back at my photo, I was cruising near Va at about 109KIAS. Va at my weight was probably about 105 KIAS. So, I just need to slow down a little when in turbulence, but still maintain a proper descent. And, yes I am flying a T182T as well.

When in IR training, 20 deg flaps, plus power just in the bottom of the green would give me about 95KIAS and 500 fpm. It just doesn't make sense for me to do that (put the flaps down) while 50 miles out. So, I am wondering if there is something I am missing when considering turbulence as well. It always seemed bumpy during training anyway...

That was my earlier point. You were slightly above Va by your estimation and if you add any flaps then you are even further above it. Given the choice between entering a turbulent area above Va or letting my TIT fall out of the green, I'll take the former every time.

The thing about turbulence is you don't know how bad it will be until it is. I've never regretted being at or below Va when entering turbulence even when it wasn't required (99% of the time). If my engine only goes to 1990 hours because of "shock cooling" vs. my wings folding that's an easy one also.

 

[douglas393]

Actually, in looking back at my photo, I was cruising near Va at about 109KIAS. Va at my weight was probably about 105 KIAS. So, I just need to slow down a little when in turbulence, but still maintain a proper descent. And, yes I am flying a T182T as well.

When in IR training, 20 deg flaps, plus power just in the bottom of the green would give me about 95KIAS and 500 fpm. It just doesn't make sense for me to do that (put the flaps down) while 50 miles out. So, I am wondering if there is something I am missing when considering turbulence as well. It always seemed bumpy during training anyway...

As I was thinking about this after I got home, one of the things I realize I do when I am descending is after I pull the throttle back and trim(which is rarely needed) and then I reset mixture to peak TIT. I have never needed the flaps to descend and have descended at speeds of 90 kts and 500 fpm. Next time I will check the TIT but my recollection is that it has been in the 1400 range.

 

[skidoo]

Did you ask him, "Why?"

Yes. He just said that it is not healthy to the turbo if operating below the green for long durations. He has a lot of turbo experience, but I'm not 100% convinced that it is fact or if it is fact, how significant it is...

 

[skidoo]

That was my earlier point. You were slightly above Va by your estimation and if you add any flaps then you are even further above it. Given the choice between entering a turbulent area above Va or letting my TIT fall out of the green, I'll take the former every time.

The thing about turbulence is you don't know how bad it will be until it is. I've never regretted being at or below Va when entering turbulence even when it wasn't required (99% of the time). If my engine only goes to 1990 hours because of "shock cooling" vs. my wings folding that's an easy one also.

Excellent point!

 

[weilke]

In some turboprops, there is a recommendation/limitation against running too low of a temperature (ITT) as it can lead to sulfidation of the turbine blades. I am not aware of a similar limitation on any of the commonly used turbochargers. I wonder if the fear of the lower limit of the TIT range is a bleed-over from turboprop operations.

TATs (Deakin, Braley) recommendations for the operation of their turbocharger installations reference keeping the TIT at peak for the descent by reducing rpm to a minimum and adjusting fuel flow for max TIT. If you read through the entire thing, this is NOT done for the turbo but rather to keep the CHTs from dropping too quickly. If your CHTs have already dropped (through power reductions in cruise), that factor becomes less important.

It is the heads that crack, not the turbine blades or charger housing (some will even argue whether temp swings are a factor in the head-cracking issue).

 

[Henning]

Yes. He just said that it is not healthy to the turbo if operating below the green for long durations. He has a lot of turbo experience, but I'm not 100% convinced that it is fact or if it is fact, how significant it is...

It's not. Don't throw a bucket of water (or gas ) on a glowing hot turbo, that's about it.

 

[taters]

A reality of Turbos is decent planning like big boy airplanes...500fpm is for Cessna 150's. 1000 FPM is more like it.

-Using a 3 degree profile multiply your altitude by 3 (ex 18,000 =54 miles)
-Ad a zero to your planned decent Ground Speed/2 (ex 180(0)/2=900 fpm

This will allow you to stage cool properly and still not be high in the terminal area.

You said in the original post this doesn't seem practical..it absolutely is~! Yes you will come down fast so you have to plan for some deceleration at the bottom of your decent...Again you have to lost the mentality of 500FPM..it is a bogus tactic in a fast/high plane.

 

[Alexb2000]

A reality of Turbos is decent planning like big boy airplanes...500fpm is for Cessna 150's. 1000 FPM is more like it.

-Using a 3 degree profile multiply your altitude by 3 (ex 18,000 =54 miles)
-Ad a zero to your planned decent Ground Speed/2 (ex 180(0)/2=900 fpm

This will allow you to stage cool properly and still not be high in the terminal area.

You said in the original post this doesn't seem practical..it absolutely is~! Yes you will come down fast so you have to plan for some deceleration at the bottom of your decent...Again you have to lost the mentality of 500FPM..it is a bogus tactic in a fast/high plane.

My passengers ears don't like 1,000 FPM from the FL's. Sometimes mine don't either.

 

[Kelvin]

I negotiate descent at pilots discretion and when I get it...I fly "my plan"...not his...I get this clearance about 80+% of the time...

I pull back MP to 25" and raise the prop to 2450-80 rpms...leave mixture alone...I do use speed brakes from time to time when I want to save my pax's ears...I have even resorted to putting out 20 degrees of flaps..but that is an extreme in my view...

I am flying a Lyc 540 with twin turbos...

 

[Kelvin]

A reality of Turbos is decent planning like big boy airplanes...500fpm is for Cessna 150's. 1000 FPM is more like it.

-Using a 3 degree profile multiply your altitude by 3 (ex 18,000 =54 miles)
-Ad a zero to your planned decent Ground Speed/2 (ex 180(0)/2=900 fpm

This will allow you to stage cool properly and still not be high in the terminal area.

You said in the original post this doesn't seem practical..it absolutely is~! Yes you will come down fast so you have to plan for some deceleration at the bottom of your decent...Again you have to lost the mentality of 500FPM..it is a bogus tactic in a fast/high plane.

500 fpm is not going to get you down from 18-20K very fast...

 

[taters]

My passengers ears don't like 1,000 FPM from the FL's. Sometimes mine don't either.

Then you either need a 1.5 degree profile which starts about 100 miles out at 500 FPM, or slow down to about 100 knots over the ground.....that's whats not practical and why many flight level planes are also pressurized.

Decent planning has to be a very deliberate part of your flight plan or you are going to wind up embarrassingly high and scrambling to get the thing down at the expense of a shock cooled or backdriven engine

 

[Ted]

A reality of Turbos is decent planning like big boy airplanes...500fpm is for Cessna 150's. 1000 FPM is more like it.

You must not have had or didn't read the requirement in your 135 ops manual to perform climbs and descents in non-pressurized aircraft at no greater than 700 FPM unless impractical for safety considerations. We did for our Navajo, and it didn't give a crap about turbos or not because our passengers' ears didn't, either. So simply saying it's turbo'd, do faster climbs and descents is a blatently incorrect statement. If pressurized, sure, but then you can keep your cabin ROC below 500 FPM. We still routinely do 500 fpm climbs/descents with the 310, especially with the baby. Just me? Sure, I'll do 1000+, but my ears don't care.

Now assuming that your passengers don't have ear issues, then you will likely want to descend quicker from the flight levels, but speed is an important consideration. Some people start doing power reductions early so they can remove power slowly and still get the descents they want.

 

[Alexb2000]

Then you either need a 1.5 degree profile which starts about 100 miles out at 500 FPM, or slow down to about 100 knots over the ground.....that's whats not practical and why many turboish planes are also pressurized.

Why? I do it all the time. What advantage is there in coming down faster? If ATC asks for more I'll give it to them if I can. More often they want me down early for traffic so they start me down way out there.

Remember the OP is flying a T182T.

 

[Ted]

Why? I do it all the time. What advantage is there in coming down faster? If ATC asks for more I'll give it to them if I can. More often they want me down early for traffic so they start me down way out there.

Remember the OP is flying a T182T.

That's my question. Descent planning can be 100+ nm out. I'm planning my descent throughout the flight, and make my calls to get what descent I want. Usually I end up hitting the pattern right at my 18" desired without needing to bust ear drums. By descending at a faster airspeed, I make up some of the time I lost in climb.

Turbines are a bit different. Because of operational considerations (mostly fuel burn), staying high until the last possible moment makes more sense. Of course, you also have pressurization, so 2k+ fpm drops won't hurt anyone's ears. Of course I've done 2k+ fpm in the 310 and other planes, but I'm careful with passengers. Some will start screaming in pain if their ears aren't used to it or they have ear problems - BTDT on a 1000 fpm drop.

 

[taters]

You must not have had or didn't read the requirement in your 135 ops manual to perform climbs and descents in non-pressurized aircraft at no greater than 700 FPM unless impractical for safety considerations. We did for our Navajo, and it didn't give a crap about turbos or not because our passengers' ears didn't, either. So simply saying it's turbo'd, do faster climbs and descents is a blatently incorrect statement.

-I flew cargo P135 so not in the GOM, moreover not all manuals are equal as you have more or less stated

-The obvious point Im making here is that turbos tend to fly higher, need time and distance to be stage-cooled and that involves specific decent planning that is different than a garden variety single etc

 

[Ted]

-The obvious point Im making here is that turbos tend to fly higher, need time and distance to be stage-cooled and that involves specific decent planning that is different than a garden variety single etc

And when he's descending at a higher airspeed than he wants to aim for 500 fpm, what makes you think that 1000 fpm is somehow going to aid in that attempt to cool the engine properly? An unpressurized turbocharged piston plane isn't one of the "big boys" when it comes to pressurization, and passenger comfort is a very real concern for those of us who fly passengers that aren't boxes (even if they are in cages).

 

[taters]

And when he's descending at a higher airspeed than he wants to aim for 500 fpm, what makes you think that 1000 fpm is somehow going to aid in cooling the engine properly ?

probably the same reasons you do since you stated you come down 1000FPM as well...an engine can still be stage cooled at a decent rate of more than 500 FPM....not hard at all. if the OP wants to use 500 FPM great..just understand the distance involved in doing that.

 

[Ted]

probably the same reasons you do since you stated you come down 1000FPM as well...an engine can still be stage cooled at a decent rate of more than 500 FPM....not hard at all. if the OP wants to use 500 FPM great..just understand the distance involved in doing that.

I stated that I'll do it when it makes sense. But your statement of "500 FPM is for Cessna 150s" is out of line. Even in the turbine world we've done 500 FPM descents when it makes sense.

 

[chartbundle]

With the fully automatic wastegate on the 182 G1000 I flew a couple weeks back it was basically: 2000 rpm, 25" MP , Mixture to keep TIT up(seemed to stay at 1400-1500) and a 600FPM descent at the top of the green. But this was only from 10,000 or so, haven't had a chance to try it from higher.

 

[taters]

I stated that I'll do it when it makes sense. But your statement of "500 FPM is for Cessna 150s" is out of line.

Bullocks