Ibra Posted August 11, 2020 Report Posted August 11, 2020 (edited) It's mostly engine specific not type, if I have Rotax Mooney, I will gladly put Mogas, UL91, SP98, SP95, F3 or even two-stroke oil mix in it for other engines in hot days and high density altitude, I would be very careful, I no longer put Mogas on the D31 Turbulent with a WW engine let alone a Lyco engine Mooney ! Whatever those STC says, you will need Mogas with higher MON octane rating (not RON rating) but usually lower octane or detonation is not the biggest problem in normal operations on non-turbo engines (as long as compression ratio is bellow 1:8), the elephant in the room is ethanol alcohol and other aromatics in auto fuel that will eat your rubber fuel lines, well unless if you have a Rotax engine, they are the only engines I am aware that are designed to run on any Mogas with vapour lock return line when engine is running (even at FL200 pressure & 100F temps) and they also have alcohol filter for their fuel lines when the aircraft parked, anything else is at risk ! Once a friend got stuck in Scotland as Oban did not have 100LL, luckily his aircraft had a normally aspirated carbureted Lyco engine, he filled up with SP98 petrol from the gas station (which has ver low octane of MON88 vs 100LL) plus some lead additive, his engine did run fine to make it to the next place 80nm nearby, his aircraft says MON100 is the minimum The D31 has WW 1600cc Beettle engine (so by default should takes Mogas than Avgas), but the only time it failed me it was on 6000ft DA on Mogas, the type is a vintage that hand-start with flimsy mixture control, Mogas water vapour lock & too rich mixture were the usual suspects Apparently, while it's a car engine with Mogas, there are not that many WW Beettle cars driving above 6kft Now we have "fuel fresh, clean, water and alcohol free, tank temp less than 20C and fly below 5000 ft" written somewhere Most Conti & Lyco on Mogas may need to run with 10% avgas mix regularly and 100% avgas 10h after overhaul On 8/9/2020 at 3:50 AM, Raptor05121 said: What interesting is on the M20C, the TCDS states 100LL minimum, but on an M20D, same airframe and engine, states 91/96 octane minimum. I was not expecting that to be airframe related, any reasons why? difference in fuel system? or fuel flow? On Octane rating, I met many people in UK that stated that running their engine with SP98 gas is fine as their aircraft engine can takes 91 octane, turns out they were running it on 88 octane for years ! Edited August 11, 2020 by Ibra
Raptor05121 Posted August 11, 2020 Report Posted August 11, 2020 5 hours ago, Ibra said: I was not expecting that to be airframe related, any reasons why? difference in fuel system? or fuel flow? Absolutely nothing. They are 100% identical aircraft sans the landing gear
carusoam Posted August 11, 2020 Report Posted August 11, 2020 Keep in mind the M20D as delivered... Fixed pitch prop... when updated to M20C status... it got the variable pitch equipment added to it... Since then the valve diameters have changed for both.... (a stem dimension) Not sure if this is meaningful to gasoline choice, but... the engines were not identical when delivered... And the valves are an important reason for the lead to be there to begin with.... PP thoughts only, not a mechanic... Best regards, -a-
Recommended Posts