First flight with new internal muffler (EGG)

[David-aviator]

Well, after 17 pages, I think it is time to end this. Actually, I thought it had died from lack of interest.

Even though the last couple of posts are sorta back on track, the thread has gotten so far off from the original post it isnt even recognizable anymore.
__________________
Mike Starkey
Rv-10, VAF 909
panel installed,
officially a "No
Smoking" zone

Actually, Mike, I was going to post one last message today - sort of an evolutionary wrap-up of the EGG history thread - but you beat me to the punch by a few hours.

When I first started flying this engine a major concern was fuel temperature and vapor lock, and rightly so. At least 2 airplanes bit the dust due to inadequate attention to the possibility of vapor lock. One with winter fuel on a hot spring day and one after a landing and subsequently taking off with time on the ground for the engine compartment to warm up due to residual heat and no air flow. At the time the fuel pumps were mounted on the forward side of the firewall out of a consideration to keep high pressure fuel out of the cabin. The real weak, weak link was the area before the fuel pumps where gravity fed fuel came through the firewall. To keep engine compartment temps to a minimum, the mufflers were mounted external.

To illustrate how far we've come, I flew today for the first time with a new internal muffler, a real heat generator in the engine compartment if ever there was one. The external torpedo mufflers are gone and so is the vibration they created with the bottom forward skin. The fuel system did not vapor lock - so how come?

The primary reason is the fuel pumps are now located in a tunnel on the cabin floor just forward of the fuel valve. All fuel going forward is under pressure and as a matter of physics, fuel under pressure does not vapor lock. (that's why modern autos have fuel pumps in fuel tanks) That's not to say it couldn't vapor lock before the pumps, but that doesn't seem to happen at all with 100LL in any RV and won't happen with MOGAS if vapor pressure is checked when adding it. 100LL always checks at about 62 kPa's with the Hodges system and MOGAS can vary from 36 (minumum) to the mid 50's depending on the time of the year and the blend. If MOGAS is the fuel of choice, it's vapor pressure must be checked - I have found some at less than 36 kPa's.

Moving the fuel pumps out of the engine compartment to the cabin floor is a calculated risk. I finally decided to do it about 3 years ago because I was going nuts worrying about heat forward of the firewall. I worry much less about a fuel leak in the cabin than I did about vapor lock forward of the firewall.

So the question today was, would the internal muffler affect oil and/or coolant temperatures? Jan invented the internal muffler, it is a rectangular stainless steel box with baffles but no material and with two headers in and one pipe out. It is held in position just below the oil pan by the headers coming off the engine exhaust manifolds and 2 small straps on an aft flange attached to the engine mount structure.

It works. I think it is quieter, there is no floor vibration, and oil and coolant temperatures were normal. I haven't flown since mid February and it was very nice to be aloft one more time. The best check of such a modification is a climb to 8500 - all temps were normal at level off with a take off OAT of 71F.

In one respect, the Subaru fuel injection system is better than that used with Lycoming. It is impossible for the system to vapor lock after shut down due to a tiny bypass feature invented by Jan. The reason Lycoming fuel injected systems are difficult to start with a heat soaked engine is the fuel rail vapor locks. That does not happen with the Subaru, it starts instantly any time, at least mine does.

Enough "history" for one night.

[DGlaeser]

I made the first flight of my Egg H6 powered RV7a (with internal muffler) last Saturday (3/29).
Everyone hanging around the airport commented on how smooth and strong the engine sounded. It felt the same way inside
The OAT that day was 32F, and my temps were not a problem (oil - 175, coolant 200, gearbox 160). I have a James Cowl modified to have a cowl flap. Right now I'm using a loaner Sensenich ground adjustable prop, waiting for a Quinti/Sensenich CS prop.