REFLECTOR:Rough Rider

[Scott Derrick]

Chuck Jensen wrote:
> still doesn't seem right.  I don't understand why there should be such a
> sharp drop-off in engine operation at 1000 rpm when the booster is secured.
> Shouldn't the engine run the same on the ramp whether the booster pump is on
> or not?  Isn't the booster pump just insurance during TO/LD in case of main
> pump failure and not required for normal ramp operations?

At idle the pump pressure will effect your fuel flow a lot more than at 
full throttle. Or I should say the engine will notice the difference a 
lot more.  Its the increased fuel flow that is cooling the injector 
lines and reducing or eliminating the fuel vaporization.

> 1) seems like a credible culprit (hot engine and all) but the likelihood
> that the slight amount of additional pressure from the booster would be just
> the amount needed to overcome the vapor lock is possible, but small?

Try this.  Hot engine at idle.  Turn on boost pump, note increased fuel 
flow and engine performance(smoothness), Turn off boost pump, increase 
throttle so your fuel flow is the same as it was with the boost pump on, 
  note engine performance.  Is it the same as it was with boost pump on 
and throttle set at low idle?

> this line of thought, is it possible to have a chronic continuous partial
> vapor lock would always behave the same...cause rpm drop, rough ops but
> never completely stops the engine?

at idle yes,  the first old automotive injection systems had this 
problem too.  Since we almost always run our aircraft engines at full 
throttle or near enough its just not a problem really.

Scott