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Recent Dead Stick Landing / Intake Flange Separated

JonJay

Well Known Member
An RV4 dead sticked into KTMK, Tillamook OR.
I was flying the Bucker and noticed him on the ramp with a buddies truck next to it, cowling off.
He said he flew into Pacific City, a small coastal airport about 20nm away. He said his engine was running rough at the time but making “good power”. He decided to take off and try to fly home, somewhere in Washington State. He performed a series of circles over Pacific City until he was at 10k feet, then headed north. He figured at 10k, he had options, and he needed it….
Still at 10k over KTMK, the engine dramatically got rougher, he decided to land. During decent, it quit altogether. I am told he made an excellent landing by my buddy who heard his emergency radio call and assisted in pushing off the runway to the ramp.
The intake flange had “fallen off” and was hanging on the tube. The flange bolts, of course, were gone. I had some spare bolts at my hangar and a gasket. Engine ran great and he was back in the air headed home.
I asked him who did his CI? He skirted the question.

Scott mentioned in another post something that applies here. These things don’t happen overnight. I have a hard time believing that the flange bolts were checked at his last CI, or how many prior? I rarely find mine have lost any torque at all in a years time.
 
I'm curious why the engine would quit with an intake flange off. Certainly would run rough with one cylinder super lean and mis-firing, but the other three cylinders should keep running 'ok'.
 
I'm curious why the engine would quit with an intake flange off. Certainly would run rough with one cylinder super lean and mis-firing, but the other three cylinders should keep running 'ok'.

I think what happens here is that there is a huge air leak on the affected cylinder, and atmospheric pressure air runs backwards to the point just after the carb or air flow sensor, then down to the other three cylinders. Meanwhile the reduced flow thru the venturi results in idle power fuel being delivered to the cylinders, and they’re way too lean for any significant power.
 
I'm curious why the engine would quit with an intake flange off. Certainly would run rough with one cylinder super lean and mis-firing, but the other three cylinders should keep running 'ok'.

One cylinder wasn’t super lean, no fuel/air was even making it there into the cylinder. The intake had a significant gap between it and the cylinder. Considering he had been running this engine rough for some time before it finally quit entirely.
Still, I thought the same thing.

Considering a carbureted machine, is it possible it was leaking so badly that the other cylinders were starved? Don’t know what his sump was or know enough even if I did on what could happen with basically one completely open intake tube. (Edit, Bobs post sounds reasonable. )
 
Pull one little vacuum hose off the intake manifold on your car and see how it runs !!! :eek: If it runs.

These intake tubes don't supply independent air sources to each cylinder, they're all connected via the manifold.

Happy to hear he got back down safe. More to learn, nuf said

Cheers
 
When all else fails, a primer may get you enough performance to get you on the ground.

If the plane was landed the first time due to rough running, and the cowl was removed to take a look. How hard would it be to see an intake tube bolt backing off.

A rough running motor usually means one cly is not hitting right or at all. So you would be looking for things that would affect one cyl. It would not be ignition, it has a back-up for everything. It would not be the carb, the motor was still running..... a loose carb would affect all cyl's. A clogged filter would affect all cyl's.

Short of a piston, ring or valve problem, the main thing left is intake tube. And that failure looks like it will take out the rest of the motor due to the easier path for the air to flow.

Just like Scott mentioned in the past "The motor was talking to you".
 
This is a great learning moment for the rest of us. When the engine starts behaving differently than it normally does, that is a sign. It could be an issue that will get worse in 100 hours or 100 seconds; You just can never know. The moral of the story here, IMHO, is don't ignore signs of change in engine behavior / performance.

Larry
 
With a 4 cylinder EGT/CHT monitor, a USB stick, and an upload to Savvy to look at the data, it should have been pretty obvious which cylinder to take a hard look at.

Hypothetically just looking at the monitor in flight should have worked as well... but sometimes it is much easier on the ground to think and focus on the analysis.

Sure glad he was circling over the airport and all is well!
 
Loosing one part in the induction system will cause the entire engine to run rough. Been there, done that. Lost one intake valve and turned into a very rough running, underpowered powered glider. Despite it happening over a 300' overcast, I made an airport.
 
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