Mogas in Aviation

The equations are readily available from many research papers online.
The PDF is a snapshot from the attached Spreadsheet.
The service ceilings are all rounded down to make them conservative.

It should be noted that the altitudes are the Pressure Altitudes experienced by the fuel within the hoses.
A fuel pump drawing from high above a belly tank or through a restricted filter, will lower the pressure (raise the Pressure Altitude) significantly.

The information is for academic purposes and should NOT be used for flight planning.
The Temp Scales and RVP Numbers can be freely varied.

Excellent!  I will study this and see how it correlates to the data from my incident.  In case you haven't seen the graph... its the "The Data Tells the Story" chapter. 

One Source of the equations used in the SpreadSheet Calculations.
Warning, Heavy reading.

Jeff,

I have a side project for your RVP Tester if you are willing.
If I remember you have a 912is.
During the testing of my 912is' fuel system, it was noted that the fuel returning to the tank had a lot of bubbles (Released Volatiles) in it.
There is an assumption that the released vapors (Butane) condense in the fuel tank and rejoin the fuel.
It would be interesting to see just how much this actually happens or does the released Butane just get vented overboard?

The experiment:
Procure a fresh tank of gas and test it for its actual RVP.
Then take about an hour's flight to beat up the fuel.
Then pull a sample from the tank and retest for a second RVP value.
It would be interesting to see how much the RVP decreases as the flight progresses.
The pumps move about 30 gal/hr, so after a long flight, the remaining fuel has been through the engine more than a few times.
It wouldn't be surprising if the last few gallons had an RVP in the 5-7 range.

Interested?

Hi Bill,

My apologies for interrupting & going of on a  tangent.

Your comment "..........it was noted that the fuel returning to the tank had a lot of bubbles (Released Volatiles) in it." 

confirms my earlier suspicion - the FI system is returning hot fuel to the tank. It would seem likely that the heat is causing the "lighter" fractions to separate as vapour ("bubbles") - hardly a desirable situation.

Its also likely that the returned fuel is raising the temperature of the in tank fuel, increasing the chances of fuel vaporisation within the fuel to engine delivery system - an additional undesirable situation.

A partial solution is a simple in line heat exchanger (cooler), fitted on the return line/befor tank, that would reduce some of the undesirable effect of heat on the fuel.