In-Flight Fire – Maybe in the Rear Engine You Can’t See

[K337A]

It was amazing that Ford could build a B24 every 59.34 minutes when Willow Run was running at capacity. The Axis powers didn't stand a chance once the industry of the United States geared up for war. Costs went from $300,000 to $137,000. If any industry in the USA achieved that goal today the saving and efficiency would be taxed to make up the difference.

http://www.wondersofwwii.com/willow-run.html

"The problem with socialism is that eventually you run out of other people's money [to spend]."- Margret Thatcher


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[Ernie Martin]

Forgive me for hammering on this subject, but for those of you who have not yet acted on this, Aero-News Network is reporting an SR22 Cirrus down with two fatalities, with a local paper saying that the airplane caught fire shortly after takeoff.

Ernie

[Walter Atkinson]

Ernie:

Are you aware that if a SkyMaster that has an exhaust crack develop had an engine monitor that event would have been seen almost immediately by a pilot educated in interpreting the engine monitor data? This would allow immediate action by the pilot to mitigate the danger.

For educational purposes, would anyone care to describe what would be seen on an engine monitor in which the exhaust riser on the #2 cylinder developed a crack? IOW, how would you know you had an exhaust crack by looking at the engine monitor display?

This is a serious reason to have an engine monitor. It can save your life.

[Ernie Martin]

I agree: an engine monitor would provide near-instant information of an exhaust leak in a riser. As to how it would read, I need to think about it. There would be less resistance (freer flow) of the exhaust on that cylinder, but I can't instantly determine how that would affect CHT. On EGT for that cylinder, my initial (read: possibly wrong) reaction is that it would be cooler if the monitor probe is downstream of the leak (because the probe sees less gas) but I would not venture a guess if the probe is upstream of the leak*.

Ernie


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* I have an MS in Mechanical Engineering from Caltech but my combustion skills have atrophied from 20 years working on satellite communications and 20 years running or consulting for high-tech companies.

[Walter Atkinson]

Originally Posted by Ernie Martin

I agree: an engine monitor would provide near-instant information of an exhaust leak in a riser. As to how it would read, I need to think about it. There would be less resistance (freer flow) of the exhaust on that cylinder, but I can't instantly determine how that would affect CHT. On EGT for that cylinder, my initial (read: possibly wrong) reaction is that it would be cooler if the monitor probe is downstream of the leak (because the probe sees less gas) but I would not venture a guess if the probe is upstream of the leak*.

Ernie:

Kuddos. You have the right answer--the EGT will drop. The "why" does not come from the probe seeing "less gas." The drop is seen whether the probe is upstream or downstream of the crack. The closer to the crack, the greater the change that's seen.
The reason is the Boyle's PV = nRT. The gas leaving the cylinder is actually the same temp but the pressure in the exhaust drops due to the escaping gases, so the temp is lower as well ( P and T are on opposite sides of the equation, right? ).

As for the CHT change, there is usually no measurable change in the combustion event, so the CHT should not change -- UNLESS the leaking gas is blowing onto the cylinder head metal, then the CHT may be rising a LOT. The good news with a rising CHT is that the escaping gas is hopefully not squirting onto a fuel line!

This is really good stuff to know... it can save your bacon.

This is only one of the reasons I consider an engine monitor to be mandatory equipment.

There are so many ignition issues that can be discovered long before they would cause one to abort a flight from a faulty a run-up.