# Turbo Pipe Coupling Popped Off And HP Dropped Considerably

Discussion in 'General Experimental Aviation Questions' started by HomeBuilt101, Feb 19, 2018.

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1. Feb 19, 2018

### HomeBuilt101

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Hi All,

Second flight in the airplane…I was off to do a test flight with red yarn on my canard, main wing, and winglet to do some benchmark stall and performance testing prior to installing Vortex Generators (you can see a bunch of red yarn pieces taped to the left wing and canard) and o
ne of my silicon turbocharger couplings popped off and my Manifold Air Pressure immediately dropped from 42 inches to 29.3 inches causing my engine’s Effective Compression Ratio to also drop from 12.0 to 1 compression down to 7.0 to 1 compression (in a millisecond) and therefore causing my 12.0 to 1 happy face to turn into a 7.3 to 1 sad face at 200 feet AGL.

Someone at the airport caught it on youtube, I wont bore you with the return to landing flight details (I did do a write up on the YouTube video page if you are interested…

Yes I expected the engine HP to drastically reduce if the turbocharger pipe popped off however the amount of drop in HP was really surprising and the black smoke as seen inn the video was also surprising...hence the question in this post...The following post is what I THINK the reason for the drastic drop in HP and black smoke...however...if someone familiar with turbocharging systems can PLEASE back up my thinking or flat out correct me I would be most grateful...

The engine is a TIO-540 with 7.3:1 compression pistons and with 42 inches of MAP the Effective Compression Ratio of the engine is more like 12:1.

Using a generic horsepower calculator that I found online, I came up with the following numbers:

Engine Displacement (CID) is 540
Engine Revolutions Per Minute is 2700

At 12.0 compression ratio Computed Engine HP is 348

At 7.3 compression ratio Computed Engine HP is 194

So at first glance 194 HP should be plenty to make the airplane fly…

The way the turbocharger system on my airplane works…stolen from a Bellanca Viking and pretty much all of the airframe makers during that era used a similar system…is the exhaust gasses pass through the impeller of the turbocharger and connected to that same shaft is a compressor. The compressor pumps air into the intake system. Directly upstream of the Bendix opening is a fitting that taps air pressure and this air pressure is fed to the wastegate controller. The job of the wastegate controller is regulate the air pressure being supplied to the Bendix to 42 inches of mercury measured as Manifold Air Pressure (MAP).

If the air pressure drops below 42 MAP then the wastegate controller tells the exhaust wastegate to close farther and more exhaust gasses are forced into the turbocharger impeller and this will pump up more air. If the air pressure above the Bendix is more than 42 MAP then the wastegate controller tells the exhaust wastegate to open so that exhaust gasses will be dumped out before they can forced through the turbocharger…that is why my airplane has two exhaust pipes…the small one is the wastegate exhaust pipe and the larger one is the turbocharger exhaust pipe.

So why so much more smoke and so much less power?

The intake air pipe coupling that popped off was the coupling just before the last pipe that leads to the Bendix. When it popped off the forced air supply from the turbocharger no longer was being shoved down the throat of the Bendix but instead it was being dumped into the engine cowling and that is why my indicated MAP dropped from 42 MAP to 29.3 MAP.

I heard the pop and the air whooshing sound however at that point I could tell if the noise was coming from the engine compartment or from my shorts.

Since the wastegate controller saw the drop in pressure upstream of the Bendix it then told the exhaust wastegate to close as far as possible so as to drive more gasses into the turbo in an effort to bring the MAP back up to 42 inches.

When the wastegate closed completely, all of the exhaust gasses were forced through the turbo and this created a bunch of exhaust system backpressure. Since the mechanical compression ratio of the engine is only 7.3:1, the low compression pistons do not produce a great deal of power and therefore do not produce a great deal of exhaust pressure and since all of the exhaust gasses are now being forced into the turbocharger that “clogged up” exhaust system makes the situation worse so that is the reason for the great loss of power and my guess is that the engine was producing much less than 194 HP.

I’m sure the turbocharger was spinning much faster than it should so I first thought that it was oil being forced past the seals and burning that was causing the smoke however oil burning would be blue and this smoke was black so that should be an excessively rich mixture.

But because the Bendix was just seeing 29.3 MAP it should have simply reduced the fuel flow being pumped up to the injectors accordingly…however…since the fuel injectors on a turbocharged engine have a shroud around them that is normally pressurized by a pipe system that taps the same 42 MAP air (this is needed to atomize the fuel being squirted out of the injectors)…and since those hoses were still intact…and since the Bendix was now sucking air as opposed to the normal condition where the air is being forced into the throat of the Bendix…my guess is that the negative air pressure from the pipes before the Bendix was sucking air down from the fuel injector nozzle shrouds and that caused the injector nozzles to no longer atomize/ spray the fuel but instead to just squirt/dribble the fuel into the engine and this would cause the engine to burn the same volume of fuel but much less efficiently.

Does anyone who has experience with aircraft turbocharger systems have any thoughts to share…other than to tell me to ensure that the silicon couplings are clamped down more tightly???

I am going to make sure that the ends of each pipe has a larger lip on it…don’t want that to happen again…Just say’in…

THANKS!!!

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2. Feb 19, 2018

### Turd Ferguson

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That is actually fairly common installation method and usually much more trouble free than the exhaust side of the turbocharger.

3. Feb 19, 2018

### D Hillberg

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An intake pipe bead roller is needed to 'flange' the intakes. as for the rich condition the bendix is seeing more draw and no pressure from the turbo, you gave it a sea level headache...

4. Feb 19, 2018

### Mcmark

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Not knowing the aircraft Turbo FI but surmising that the FI is mechanical not EFI I don’t see how it would know to to reduce the fuel flow.
My guess is the black smoke is unburned gas.
My experience with a draw thru turbo had the turbo locking up (alcohol) from volume and then power would drop with the fuel choking the spark out. Basically be like closing the butterflies but leaving the fuel WFO.
The only possible way you might’ve made more HP was to lean it which goes against any reasonable thinking low and slow trying to climb.

5. Feb 19, 2018

### rv6ejguy

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You figured out what happened pretty correctly.

The fuel metering will be way off with the pipe disconnected so it was super rich (black smoke), this would have cost a bunch of hp. You won't have normally aspirated power with the induction pipe off as the turbine presents a lot of restriction. Might have been making 150hp at the most.

Also, I might worry that you could have overspeeded the turbo as it would have gone sky high with no wastegate signal.

As suggested above, you need good beads on the turbo pipes. T bolt clamps can exert more clamping force than standard hose clamps but both work fine with proper pipe beads.

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6. Feb 19, 2018

#### Well-Known MemberHBA Supporter

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BTW, good job of getting it back on the ground without incident, especially since the pattern seems to have been busy at the time!

7. Feb 19, 2018

### TFF

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In simple numbers a naturally aspirated engine will pull about 27 inches at sea level. Perfect would be 29 but there are losses. Every time you can add 27 inches you double the engine output. Subtract the same is same in power reduction. If you are relying on that power to be there, you don't want to loose it. Simple subtracting and you can figure what hp you had.

8. Feb 19, 2018

### rv6ejguy

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Turbocharged engines gain a significant part of their power from boost acting on the piston during the intake stroke as well. You can't just look at MAP to calculate hp loss in this case. The turbine back pressure losses and resultant charge dilution during valve overlap also reduces power noticeably.

Any FI engine which is pulling less than barometric pressure MAP WOT at SL could benefit from a larger throttle body to reduce this power loss. Some of the Bendix servos are quite restrictive.

9. Feb 19, 2018

### TFF

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I'm not trying to be scientifically perfect but just in a relative way. Not talking about perfecting turbocharging. The op was surprised to Loose that much power

10. Feb 19, 2018

### rv6ejguy

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My point was, you'll lose a lot more power when this happens than just the loss in MAP suggests. Let's use 27/42= .64 X 348HP= 224hp. Obviously if this was the case, he would not have staggered around the pattern when the pipe blew off. I'd say he would lose closer to 200hp which would put him around 150hp left. Climb would be pretty marginal, as it was. The ultra rich mixture could have put several (or all) cylinder into a rich misfire condition, further reducing the power or even shutting the engine right off.

Last edited: Feb 19, 2018
11. Feb 19, 2018

### BJC

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Rule Number 1: When things go wrong, first, fly the airplane.

Nice job, especially for the second flight in a new airplane.

BJC

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12. Feb 19, 2018

### pictsidhe

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Did the turbo survive?

13. Feb 20, 2018

### fmartin_gila

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Fully agree with this entire post. Many years ago I had the same thing happen on a Diesel truck and it seemed that about 2/3 of the HP instantly disappeared. On inspection, the turbo had turned excessive RPMs and the bearings had to be replaced in a rebuild. The T type clamps are the only way to go when dealing with the added pressure, along with beads on the flanges to ensure the hoses stay in place.

Fred

14. Feb 20, 2018

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