- Jun 26, 2012
- Calgary, Alberta, Canada
Nope again. I guess you're not aware that a B-29 holds the USA manned piston absolute altitude record at 47, 910 feet, set in 1946...Errrr. We are talking about using auto engines at 35,000 feet and NOBODY is doing that now nor ever did. Even the 'high altitude' B29 Stratofortress was only certified to 32K.
The research and papers I presented clearly show that there WILL be serious issues with using volatile fuels at 35K and its simply dreaming to expect Mogas with a vapor pressure of up to 14PSI could ever operate at 3PSIA. It wont. It will boil away. If it was easy, everyone would have done it and you would have seen B29's flying at 40K. Its not easy which is why Avgas is specially formulated to have a higher vapor pressure and even with this high octane, still is altitude restricted.
Of course when flying at 25K/7PSIA or lower, Avgas and maybe even some Mogas is stable and wont boil. At these altitudes EFI systems work just fine. We are not debating that. We are looking at what happens when you go higher.
If you think you can simply port all the hot return fuel from your EFI regulator back to the main tank and shoot straight up to 35K, then good luck with that. Any heating of the fuel at 35K will simply boil it away faster than the lapse rate already will. And any pump, even auto EFI pumps will have a suction side trying to take a feed from that boiling fuel. Since none of these have vapor handling systems its not unreasonable to expect trouble.
Properly designed EFI DOESN'T add any significant heat with the fuel block exposed to ambient air as shown below. It will be COOLED by -65F air here.
Bruce Bohannon's record flight also set time to climb records in class at the same time so if anything, heat soaked fuel would have been pronounced here due to the rapid ascent. It wasn't, the fuel system performed just fine, even at 47,000 feet which is a LOT higher than what you posted originally. Quoted from your post- "As a start, it's not possible to use Avgas at above 22,000 feet easily as its Reid vapor pressure range is only 5.5 to 7 psi At 35,000 feet, standard pressure is only 3.5 psi so all your Avgas just boiled out of the tank and turned to vapor." Flyin' Tiger wasn't using any special pressurized tanks as Bruce said himself. I've explained why the fuel doesn't boil up there- very cold temps- not 100F where VP is measured. Vigilant1 brought this second point up previously.
Your theory has been shown to be wrong by real-world examples. What more can I say? Read my signature quote by Richard Feynman...
Mark never mentioned using Mogas in this thread that I can see. Maybe I missed that part. A cross country plane like this won't be using mogas because it has limited availability at airports. Mark knows this. It may use unleaded avgas if that comes into use, but that will have similar characteristics to 100LL.