The International Cessna^® 170 Association

Grady and BL,

Before you get your panties in a wad, the original bubble of doom was is a '53 170. Mayday is talking about another bubble of doom.

Pretty sure now that BL has mentioned helicopters, we'll be trouble shooting one of their problems. One thing I know though I've never had a bubble of doom in a helicopter cause they don't have gascolators.

MoonlightVFR wrote:Seven months I have been following this subject "Air bubble of doom"

Over 4,000 views this forum,

And then , and then I learn the subject was not about a C170 at all!

It was an issue with a 170! I just found this thread looking for an answer to the same problem with my 175, whe I found my issue I felt it as my duty to report back! Sorry for the confusion.

It's all good and all on the net for future trouble shooters

Bruce says that helicopters don't have gascolators! I knew there must be something wrong with them.

blueldr wrote:Bruce says that helicopters don't have gascolators! I knew there must be something wrong with them.

Well to qualify the statement, not the turbine powered models I fly. At least they are not gascolators like we are accustom in our 170. There are sumps in the tank. 5 of them on the current model I fly.

MoonlightVFR wrote:Seven months I have been following this subject "Air bubble of doom"

Over 4,000 views this forum,

And then , and then I learn the subject was not about a C170 at all!

I am the original poster of this thread, and I know it's been a while since this thread started but I can verify the plane is still a 1953 170B. It hasn't morphed into a 175 or helicopter. Unfortunately not a 180, either. (I still love me a nice 170 like mine, just need more oomph and zoom for what I do.)

However, no more recurring air bubble with the latest configuration. I had to fly it a while to be sure... so haven't posted. But I think I'm ready to claim it's a done deal. Will post with photos when I get a chance, soon. In a location with crazy slow internet so it won't work from here.

Any bubble should disappear up thru the fuel-delivery system on a healthy, tight fuel system. The only air can be from a lower source if not the gascolator itself.
This would be explained by the leaky fuel-measurement system hoses, and it would also be explained by the leaking gascolator-sump valve.

I once (not on a 170) experienced a consistent loss of engine power during takeoff. It would happen every time unless the fuel boost pumps were on "HI". (It was a model that did not require pumps on for takeoff.)
It turned out to be the inner-liners of the rubber fuel delivery hoses were collapsing from the engine's fuel demand during takeoff. The collapsing liners would further restrict fuel delivery at high fuel-flow demand at takeoff power.

Moral: If a loss of power occurs in a gravity system which does not indicate leakage, it's possible the inner fuel hose liners have collapsed.
Good mx practices will replace standard engine-compartment, flammable-fluid-carrying hoses every 5 years or engine overhaul, whichever first occurs.
The so-called "Teflon" hoses may be good until engine overhaul.
Hoses may be ordered from Aircraft Spruce to duplicate your existing hose. I recommend having your new fuel hose "fire-sleeved".

http://www.aircraftspruce.com/catalog/a ... ey=3010399

George, that all sounds reasonable. The fuel hoses were newly made with all new parts when the fuel flow sensor was installed, and then just to make sure they weren't causing the air, new ones were made to replace those. No change. Only when a single hose was used (eliminating the fuel flow sensor) would the air bubble go away. So that was back to the stock configuration.

However, no air bubble ever appeared after we dispensed with the fuel sensor bracket and just installed the sensor "floating" in-line with the two short hoses for a nice continuous path from gascolator to carburetor. I checked with EI and that is a perfectly acceptable installation.

Photos will help illustrate the difference in the flow path for the two configurations. But through the various tests, the hoses do not seem to have been the issue. In this case. (And they are indeed fire sleeved.)