SSTjumbo From , joined Dec 1969, posts, RR: Posted (9 years 9 months 3 weeks 4 days 21 hours ago) and read 6344 times:
My understanding of vapor lock is the following:
In a fuel injected aircraft, a hot engine or nearby exhaust manifold can cause the liquid fuel being pumped through the fuel lines to vaporize, or as most people say, boil over. Thus, two things happen: one, the fuel pumps aren't designed to efficiently pump fuel vapors, and two, the pressure in the fuel lines as a result of the vapor attempting to occupy more space can cause the fuel not to flow through the injector and into the engine. Also, this can be caused by enough air being trapped in the fuel line either by improper venting or running a tank dry before switching.
One question, can vapor lock occur when an engine is running? If so, what's the appropriate procedure to take? Run the aux fuel pump? I know it can occur before start-up, and I'm assuming that it then takes quite some time to restart the engine as the vaporized fuel is forced out of the line. Please, if there's any flaws in what I'm stating, correct me! That's the entire purpose of this post, I need education when it comes to vapor lock. Thanks!
KYIPpilot From United States of America, joined Oct 2003, 1383 posts, RR: 6
Reply 1, posted (9 years 9 months 3 weeks 4 days 20 hours ago) and read 6307 times:
I've always wondered that too. This past summer a Piper Arrow crashed at a local airport and the NTSB says it was vaporlock, but the engine quit just after takeoff, while they were airborne. Any ideas?
Illini_152 From United States of America, joined Jan 2001, 1000 posts, RR: 2
Reply 2, posted (9 years 9 months 3 weeks 4 days 19 hours ago) and read 6284 times:
One that I know of is an issue with early model 172's without vented fuel caps. They are placarded for single fuel tank operation in cruise above 3000'. They were having venting problems with the tanks, and this was the "fix". Later models received vented fuel caps on the right tank in addition to the main vent in the left tank.
Generally though things like that are ironed out before an aircraft is certified, so it is not all that common
Happy contrails - I support B747Skipper and Jetguy
411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 4, posted (9 years 9 months 3 weeks 3 days 20 hours ago) and read 6200 times:
The only large radial engines used on US civil aircraft that were fuel injected (CurtisWright turbo-compound series) did indeed have fuel vapor problems early on in their development.
This was solved by using a higher output (flow) engine driven fuel pump.
The TCM fuel injected series engines used on twin Cessna aircraft (including the GTSIO series used on my aircraft) have an engine driven fuel pump that delivers substantially more fuel than the engine uses...the excess is returned to the respective tank, from the fuel divider on top of the engine.
This helps prevent vapor associated problems when the engine is running.
However, TCM recommends that aux (electric) fuel pumps be used at higher altitudes (on LOW)...CE421 and AeroCommander 685 aircraft in particular.