Marc,

Is this the system where they increased the fuel line sizes to
something like 3/4" to permit vapor flow 'upstream' back to
the mains from the sump?  I have read that this was the
fix on late 210s to solve a random 'burp' of the engine,
apparently due to vapor buildup in the header trying to
counterflow uphill and momentarily blocking the fuel flow
downhill.   They found this with extensive mockups with
transparent fuel lines.

Bill
Long EZ builder & pilot
BSME, MSME

marc wiese wrote:

I don't know what the fix was for the late model 210 burps but

essentially

both model planes have the same configuration (same wings!). Both were
gravity fed, and the backflow depended on hp and model of injection

system.

The C177 200hp did not have the 210 problems but still a crossvent
inter-tank connection was added later. The vents are run from each of

the

sumps to the tops of each of the tanks, yes, with other venting

connections

along the way. Very complicated and wierd.

I think the issue was the extra heat in the return fuel with the larger

engines.

Cessna couldn't force the vapor to flow only in "vents" and the fuel to

only

flow in "fuel lines", (how do it know?) so they had to make the fuel

lines

large
enough to permit vapor bubbles to counterflow back to the tanks while

leaving

the gravity downflow of the fuel undisturbed.  Took them a lot to find

it.

Since the
flow blockage was momentary and cleared as soon as the bubbles made
it to the tank, and fuel flow immediately re-established by gravity it

was

very hard to trouble shoot.  I think it took years to find.

  Kids don't try this at home, even the professionals screw it up

occasionally.

  Fuel systems don't do what you think they will.  They lied when the

said

  liquids always run downhill and pumps just make it harder to predict.

Bill
Long EZ builder & pilot
BSME, MSME

tommayer wrote:

Could the lack of problem in the C-177 have been because it had a Bendix
injection system, while the C-210s all had Continentals?  The Bendix systems
I'm familiar don't have return lines. Tom Mayer

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