The Unexpected Drop of MP at 12K Ft

[alim]

Re: The Unexpected Drop of MP at 12K Ft

Cable : I replaced mine after 18 yrs.
Did in 2000. Now again in 2018. It started showing signs of binding last yr.

Not every 2 yrs !

My main cable (installed) is the expen$ive Lycoming. I had ordered it last yr - took 3 weeks to show up from Lycoming. Just installed it this annual (a month ago).

I am carrying the Beechurst as a backup as well.

 

[carllee]

Re: The Unexpected Drop of MP at 12K Ft

Yes the compression ratio is lower on the TO360 7.3 to 1 vs the straight 360's compression ratio of 8.5 to 1 but that is not the issue.

Flying clean, 20" will get you to an airport - not fast but it should get you there.

Inspection of the wastegate, turbo, cable and rod ends should be regularly done. I do so at each oil change (takes a few minutes.)

Replaced every 2 years?

That cable is $1,200 dollars or so. Mine is 13 years and just fine.

I do expect that you will always point out the advantages of the hot shot

Hi Joel,

I think you just caught the end of the conversation I was having with Jason. He was asking if the TC/TCA would just become like a naturally aspirated airplane if the wastegate was stuck in the open position. Answer is no, and the issue "is" the compression ratio. The compression ratio is the reason the TO-360 won't run like an naturally aspirated airplane without the turbo.

The Lycoming performance chart for the TO-360 doesn't actually go down as low as 20", but you can kinda extrapolate from it that 20" would probably land you somewhere between 50 and 100hp. I guess whether or not that would get you to the next airport would depend on what phase of flight you're in.

I know you do your own maintenance, and know what to look for, so you can trust your equipment. Kelly, Vince, Moazzam, and others do the same, but for many aircraft owners maintenance means dropping the plane off at the mechanics shop for 1 week once a year. For those people I stand behind my 2 year replacement recommendation. The stories of failed wastegate cables are numerous, and a failure can be very dangerous. I was in one once when it happened!

Jason has a Hot Shot, so was trying to help him to understand

 

[carllee]

Re: The Unexpected Drop of MP at 12K Ft

Hi Alex,

Sorry, this should have been my first post on this thread.

I'm glad to hear you're ok, and your advise on prepping the wife is very good.

 

[Commander91gm]

Re: The Unexpected Drop of MP at 12K Ft

Hi Joel,

I think you just caught the end of the conversation I was having with Jason. He was asking if the TC/TCA would just become like a naturally aspirated airplane if the wastegate was stuck in the open position. Answer is no, and the issue "is" the compression ratio. The compression ratio is the reason the TO-360 won't run like an naturally aspirated airplane without the turbo.

The Lycoming performance chart for the TO-360 doesn't actually go down as low as 20", but you can kinda extrapolate from it that 20" would probably land you somewhere between 50 and 100hp. I guess whether or not that would get you to the next airport would depend on what phase of flight you're in.

I know you do your own maintenance, and know what to look for, so you can trust your equipment. Kelly, Vince, Moazzam, and others do the same, but for many aircraft owners maintenance means dropping the plane off at the mechanics shop for 1 week once a year. For those people I stand behind my 2 year replacement recommendation. The stories of failed wastegate cables are numerous, and a failure can be very dangerous. I was in one once when it happened!

Jason has a Hot Shot, so was trying to help him to understand

Carl



You are correct that it does not just become a naturally aspirated (and I might have missed a portion of the thread - which I try not to do ).


For me downwind leg is flown at 25" and if I get behind something way slower and want to slow it down a bunch I pull it back to 20" or less. No problem maintaining pattern altitude, just feel like I am flying a Cherokee.
In general the cable does show some clear symptoms of pending failure prior to actually failing. If throttle operation gets stiff than one needs to check. Haven't seen pictures yet but Alex's failure was at the carb and not the Watergate.
First time I ever heard of one failing that way.

Sure hope he provides pictures of the cable and routing before it is removed.


I still maintain that a properly maintained cable is good for way more than 2 years. Now if we were talking rod ends, than I would agree that 2 years is prudent.

 

[FS]

Re: The Unexpected Drop of MP at 12K Ft

If we're going to get analytical then let's bring out the charts.

Alex said he was at 12,000 feet when the wastegate cable broke, and the MP dropped to 20". On a standard day the barometric pressure at 12k will be about 19.02". So, I'd say his MP was pretty darn close to normally aspirated for that altitude, particularly if you consider gauge and reading error margins.

Granted, at 12k and 20" on that engine he's not getting much power, but you would expect the same from an NA 112 at that altitude. What he doesn't tell us is if MP increased as he was descending. I would expect that it did, given that the failure was on the exhaust side, not the inlet side. Without inlet blockage I can't see anything that would fix the MP at 20" from 12k down to sea level (and Tallahassee is pretty close to sea level, from what I know).

I will also disagree with the others that say the engine does not become normally aspirated. Of course it does. The impeller on the inlet side does reduce airflow, but it doesn't block it completely. Functionally, it's no different than the turbo-normalized engine. If it's not normally aspirated then it would be a dead engine, not a running engine. Where else is it getting air for combustion?

Without question he did the right thing by getting on the ground quickly, not knowing what had actually happened.

 

[Commander91gm]

Re: The Unexpected Drop of MP at 12K Ft

If we're going to get analytical then let's bring out the charts.

Alex said he was at 12,000 feet when the wastegate cable broke, and the MP dropped to 20". On a standard day the barometric pressure at 12k will be about 19.02". So, I'd say his MP was pretty darn close to normally aspirated for that altitude, particularly if you consider gauge and reading error margins.

Granted, at 12k and 20" on that engine he's not getting much power, but you would expect the same from an NA 112 at that altitude. What he doesn't tell us is if MP increased as he was descending. I would expect that it did, given that the failure was on the exhaust side, not the inlet side. Without inlet blockage I can't see anything that would fix the MP at 20" from 12k down to sea level (and Tallahassee is pretty close to sea level, from what I know).

I will also disagree with the others that say the engine does not become normally aspirated. Of course it does. The impeller on the inlet side does reduce airflow, but it doesn't block it completely. Functionally, it's no different than the turbo-normalized engine. If it's not normally aspirated then it would be a dead engine, not a running engine. Where else is it getting air for combustion?

Without question he did the right thing by getting on the ground quickly, not knowing what had actually happened.

Way more analytical then I ever get but very well said!


Totally agree.

 

[Airotto370]

Re: The Unexpected Drop of MP at 12K Ft

Way more analytical then I ever get but very well said!

That's our Frank! Why we keep him around. Plus the parts thingie!

 

[alexnor]

Re: The Unexpected Drop of MP at 12K Ft

Great job Alex. Good reminder to practice glide scenarios....

We fight these wastegate cables all the time. Did it break at the rod end or the cable itself? Did you notice it working stiffer than usual in the flights preceeding this one? I know you did a complete overhaul after you bought the airplane. Did they refurb the cable?

Sure would be helpful to us if you got a pic showing the break location before they remove the cable from the airplene.

They don't fly well at 20" do they? k

I missed answering the rest of your question. We had to rent a car to drive 4 hours so we could fulfill our business commitments. Although I saw the broken cable I didn't do a detailed inspection. I will be there for the repair and intend to do that and take pictures that I will share.

Cable was new with 118 hours on it. It was not stiff at any time. All was normal.

 

[alexnor]

Re: The Unexpected Drop of MP at 12K Ft

Hi Alex,

Sorry, this should have been my first post on this thread.

I'm glad to hear you're ok, and your advise on prepping the wife is very good.

Thank you Carl. I appreciate it!

 

[carllee]

Re: The Unexpected Drop of MP at 12K Ft

If we're going to get analytical then let's bring out the charts.

Alex said he was at 12,000 feet when the wastegate cable broke, and the MP dropped to 20". On a standard day the barometric pressure at 12k will be about 19.02". So, I'd say his MP was pretty darn close to normally aspirated for that altitude, particularly if you consider gauge and reading error margins.

Granted, at 12k and 20" on that engine he's not getting much power, but you would expect the same from an NA 112 at that altitude. What he doesn't tell us is if MP increased as he was descending. I would expect that it did, given that the failure was on the exhaust side, not the inlet side. Without inlet blockage I can't see anything that would fix the MP at 20" from 12k down to sea level (and Tallahassee is pretty close to sea level, from what I know).

I will also disagree with the others that say the engine does not become normally aspirated. Of course it does. The impeller on the inlet side does reduce airflow, but it doesn't block it completely. Functionally, it's no different than the turbo-normalized engine. If it's not normally aspirated then it would be a dead engine, not a running engine. Where else is it getting air for combustion?

Without question he did the right thing by getting on the ground quickly, not knowing what had actually happened.

Ok, now you're using the term "naturally aspirated" to mean that any engine regardless of their internal parts will run the same if given the same MP. That's not true. Obviously it becomes "naturally aspirated" without the turbocharger because all it gets is the natural air pressure that surrounds it, but it doesn't perform the same way as an engine that's designed to run in a naturally aspirated environment. The TO-360 is designed to run always boosted by the turbocharger. Full power is achieved at 44" MP. There is simply no way that an engine that makes full power at 44" is going to make as much power at 20" as an engine that makes full power at 28" will make at 20". That's what I meant when I said "it wont become a naturally aspirated engine if the turbo quits". The pistons won't automatically change themselves, the cam won't change itself, the carburetor won't adjust itself, the timing won't adjust itself, the governor won't adjust itself, it won't grow a cold air intake. It will be "naturally aspirated", but it wont be a naturally aspirated engine.

You can see from the attached chart that even if, as you say, the MP increased as he descended, and it probably did, he still could only expect a maximum of 130-140hp. With 2 people on board, fuel, and luggage that's not enough to do a go-around.

Alex absolutely did the right thing - treat it like a glider.

 

[alexnor]

Re: The Unexpected Drop of MP at 12K Ft

If we're going to get analytical then let's bring out the charts.

Alex said he was at 12,000 feet when the wastegate cable broke, and the MP dropped to 20". On a standard day the barometric pressure at 12k will be about 19.02". So, I'd say his MP was pretty darn close to normally aspirated for that altitude, particularly if you consider gauge and reading error margins.

Granted, at 12k and 20" on that engine he's not getting much power, but you would expect the same from an NA 112 at that altitude. What he doesn't tell us is if MP increased as he was descending. I would expect that it did, given that the failure was on the exhaust side, not the inlet side. Without inlet blockage I can't see anything that would fix the MP at 20" from 12k down to sea level (and Tallahassee is pretty close to sea level, from what I know).

I will also disagree with the others that say the engine does not become normally aspirated. Of course it does. The impeller on the inlet side does reduce airflow, but it doesn't block it completely. Functionally, it's no different than the turbo-normalized engine. If it's not normally aspirated then it would be a dead engine, not a running engine. Where else is it getting air for combustion?

Without question he did the right thing by getting on the ground quickly, not knowing what had actually happened.

MP increased a little at lower altitude but it was not significant. Since I was not sure of the cause, and the engine did not like when I moved throttle forward, I only moved it back when the landing was assured. Outside of that I treated it as a glide. It would have been easier if I could have known the cause but during the emergency it was safer to fly the plane and be conservative just in case.

 

[kgrant]

Re: The Unexpected Drop of MP at 12K Ft

... and the engine did not like when I moved throttle forward, I only moved it back when the landing was assured. Outside of that I treated it as a glide. It would have been easier if I could have known the cause but during the emergency it was safer to fly the plane and be conservative just in case.

Since our throttle link to the carb and wastegate cable move together, increasing the throttle without the wastegate moving was pushing WAY too much fuel at the engine. I'm surprised it didn't die. k

 

[carllee]

Re: The Unexpected Drop of MP at 12K Ft

The engine did not like when I moved throttle forward, I only moved it back when the landing was assured. Outside of that I treated it as a glide. It would have been easier if I could have known the cause but during the emergency it was safer to fly the plane and be conservative just in case.

The throttle is directly linked to the wastegate, so the carburetor is set-up to work with the boost that the turbo provides. The engine wont run the same with 20" natural air pressure as it will with 20" boosted pressure. You might have been able to push the throttle further forward if you moved the mixture back at the same time, but I don't know - the carburetor is just not set up to run that way.

 

[carllee]

Re: The Unexpected Drop of MP at 12K Ft

Since our throttle link to the carb and wastegate cable move together, increasing the throttle without the wastegate moving was pushing WAY too much fuel at the engine. I'm surprised it didn't die. k

Brilliant minds think alike

 

[Commander91gm]

Re: The Unexpected Drop of MP at 12K Ft

I missed answering the rest of your question. We had to rent a car to drive 4 hours so we could fulfill our business commitments. Although I saw the broken cable I didn't do a detailed inspection. I will be there for the repair and intend to do that and take pictures that I will share.

Cable was new with 118 hours on it. It was not stiff at any time. All was normal.

Would be helpful if you can get pictures before it is removed to see how it was installed.
A picture of the broken cable after it is removed will be interesting but not of much value in determining what happened.

 

[Commander91gm]

Re: The Unexpected Drop of MP at 12K Ft

The throttle is directly linked to the wastegate, so the carburetor is set-up to work with the boost that the turbo provides. The engine wont run the same with 20" natural air pressure as it will with 20" boosted pressure. You might have been able to push the throttle further forward if you moved the mixture back at the same time, but I don't know - the carburetor is just not set up to run that way.

Using TIT temperature should allow you to lean for any configuration. Even at high altitude airports leaning is required for takeoff because of the excessive amount of fuel that the carb feeds which is of no use in till the turbo spools up.

 

[alexnor]

Re: The Unexpected Drop of MP at 12K Ft

Would be helpful if you can get pictures before it is removed to see how it was installed.
A picture of the broken cable after it is removed will be interesting but not of much value in determining what happened.

I will definitely work on this and update everyone in about a week when the parts come in.

 

[alim]

Re: The Unexpected Drop of MP at 12K Ft

Alex - do you have a JPI or GEM onboard ?

It would be great to get a download of engine params from the failure flight ...

ps. I know you're busy w/ dealing with the issue, etc - but if you have it - I am sure the board is interested

 

[painlesspotter]

Re: The Unexpected Drop of MP at 12K Ft

I can't imagine this scenario with a panic on the right seat. Its a good wife conversation to have in the comfort of one's home to get them in the mind set for when an emergency happens. I am glad we had it at a while back and she followed through.

Alex
My wife, over 4 decades, uses rosarie beads and has worn out a few sets. She is always ready. It is just the price of going shopping in exotic places.
John P.

 

[alexnor]

Re: The Unexpected Drop of MP at 12K Ft

Alex - do you have a JPI or GEM onboard ?

It would be great to get a download of engine params from the failure flight ...

ps. I know you're busy w/ dealing with the issue, etc - but if you have it - I am sure the board is interested

I have a JPI EDM 830. It will take a little time but when I get the plane back I can certainly do that.