bought the plane today

Guy Byars wrote:
I try and keep a 50/50 mix of av/auto gas in my Skylane. More avgas in the
winter, more autogas in the summer.


Shouldn't it be the other way around, if you're concerned about vapor
lock?

Autogas in winter makes starting much easier due to its higher vapor
pressure.

Autogas in winter makes starting much easier due to its higher vapor
pressure.


I have heard a lot of arguments about vapor lock, but I do not understand
how vapor lock could ever be a problem in a Cessna 182.

With the high wing configuration, the carberator will always have a positive
fuel pressure due to hydrostaic pressure. How can vapor lock *EVER* happen
in a Skylane? As an engineer, I don't see it happening.

Now, on the other hand, if you have a low wing airplane with a fuel pump,
then vapor lock is a very real problem.

But vapor lock in a high wing carberated engine.... not possible.

In article ,
"Guy Byars" wrote:

Autogas in winter makes starting much easier due to its higher vapor
pressure.


I have heard a lot of arguments about vapor lock, but I do not understand
how vapor lock could ever be a problem in a Cessna 182.

With the high wing configuration, the carberator will always have a positive
fuel pressure due to hydrostaic pressure. How can vapor lock *EVER* happen
in a Skylane? As an engineer, I don't see it happening.

Now, on the other hand, if you have a low wing airplane with a fuel pump,
then vapor lock is a very real problem.

But vapor lock in a high wing carberated engine.... not possible.

Au contriare, mon ami!
Piper Tripacer running avgas on a hot summer day can vapor lock.
It's all in how and where the plumbing is routed from the wing to the
engine.

Of course it's possible. On a hot day if the plane is flown and then
parked on the ramp with the cowling closed, the heat under the cowling
can be so intense that it can potentially vaporize the fuel in the fuel
lines forward of the firewall. If the engine is restarted shortly
afterwards it's possible to experience vapor lock. This problem will
be worse if higher vapor pressure fuel is used (such as winter blend
autogas).

The solution is surprisingly easy. During those short turn-around
always open the cowling immediately after the shutdown. That'll let
the heat escape and avoid the vapor lock.

Guy Byars wrote:

I have heard a lot of arguments about vapor lock, but I do not understand
how vapor lock could ever be a problem in a Cessna 182.

With the high wing configuration, the carberator will always have a positive
fuel pressure due to hydrostaic pressure. How can vapor lock *EVER* happen
in a Skylane? As an engineer, I don't see it happening.

Now, on the other hand, if you have a low wing airplane with a fuel pump,
then vapor lock is a very real problem.

But vapor lock in a high wing carberated engine.... not possible.

Of course it's possible. On a hot day if the plane is flown and then
parked on the ramp with the cowling closed, the heat under the cowling
can be so intense that it can potentially vaporize the fuel in the fuel
lines forward of the firewall. If the engine is restarted shortly
afterwards it's possible to experience vapor lock. This problem will
be worse if higher vapor pressure fuel is used (such as winter blend
autogas).

The solution is surprisingly easy. During those short turn-around
always open the cowling immediately after the shutdown. That'll let
the heat escape and avoid the vapor lock.

Guy Byars wrote:

I have heard a lot of arguments about vapor lock, but I do not understand
how vapor lock could ever be a problem in a Cessna 182.

With the high wing configuration, the carberator will always have a positive
fuel pressure due to hydrostaic pressure. How can vapor lock *EVER* happen
in a Skylane? As an engineer, I don't see it happening.

Now, on the other hand, if you have a low wing airplane with a fuel pump,
then vapor lock is a very real problem.

But vapor lock in a high wing carberated engine.... not possible.

Vapor lock is a starving of fuel at the carb bowl while a low
pressure-high temperature area in the fuel delivery system delivers
enough vapor that the fuel pump can't get to liquid fuel. You just
don't have that situation in a gravity system.

What you may be considering vapor lock in a gravity system may be fuel
boiling in the carb bowl due to radiated heat from the exhaust system.
This causes the float to sink in the "foam fuel". The bowl then
overfills, and the excess fuel is vented from the bowl into the air
intake, flooding the engine.

The key is that all aircraft carbs vent the bowl to the air intake,
allowing a way to flood the engine. This is not very well publicized.

TriPacers probably flood the second way. Cherokees could go either
way.

Does this jibe with any observations? Comments?

I recall some planes getting ito trouble on autogas when they went too
high in the summer.

Guy Byars wrote:

Autogas in winter makes starting much easier due to its higher vapor
pressure.



I have heard a lot of arguments about vapor lock, but I do not understand
how vapor lock could ever be a problem in a Cessna 182.

With the high wing configuration, the carberator will always have a positive
fuel pressure due to hydrostaic pressure. How can vapor lock *EVER* happen
in a Skylane? As an engineer, I don't see it happening.

Now, on the other hand, if you have a low wing airplane with a fuel pump,
then vapor lock is a very real problem.

But vapor lock in a high wing carberated engine.... not possible.