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DCBrown198

Active Member
Patron
Yesterday I took off from south Texas in a -10 that had sat in the hot sun all day. The airframe was hot, and so was the fuel in the tanks I suppose.

I topped off the tanks with 20 gallons of fuel from a fuel truck that had sun baked fuel in it as well.

My tunnel gets warm like many -10s.

For the first time ever my Dynon announced “fuel pressure” to me a couple of times during climb-out. By the time I looked at the pressure it had returned to normal. As I watched the pressure it would occasionally drop and then return to normal (elec fuel pump off).

Switching tanks seemed to remedy this for a bit, but then I got another pressure drop from the other tank as well.

After some time in 52 degree cool air in cruise the fuel pressure stayed rock solid for the remainder of the flight.

Is my situation uncommon or has it been observed by others on really hot days with hot avgas in the tanks? A little percolation happening in the line as the engine driven pump pulls the fuel towards it?

David
 
I’m assuming Avgas with mechanical FI; then you’re on track to the right cause. The first action (that time and every time) would be to turn the boost pump on and see the results. You may have been dancing closer to the edge of the cliff than you realized.

As for temporary items/approach, make sure your fuel filters are clean. Longer term solutions are numerous.
 
Years ago I used to have a similar issue. when I built the plane I used 90 degree elbows at the fuel selector, the tunnel exit and on the side of the fuselage in the root area. I replaced the entire fuel line with a continuous piece of straight aluminum tubing. I have not had a glitch since. I always climb out to cruising altitude with the boost Pump on. I know of several people who have had Tom at TS Flightlines, fabricate a flexible line to run from the tank to the selector
 
Thanks for the replies...

Yes, fuel injected IO-540. 100LL.

I left the elec. fuel pump off as I wanted to observe the pressure swings with the engine-driven fuel pump acting as the only pump. I observed enough "dips" to make me believe that there were vapor bubbles making it into the pumping process. My normal engine-driven fuel pressure is 28PSI. The elec. pump boosts it to @38 PSI.

I will confirm no contaminants in fuel filter, but I don't believe that is the issue.

There is a previous thread here, that discusses 100LL temps and vapor points. At sea level pressure 100LL begins getting a wee bit "steamy", if you will, around 105F. Put it under lower pressure and that temperature goes down.

David
 
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