SL-00078 and Updates to RV-12 POH and RV-12iS POH/FTS Published

[Bob Y]

I unscrew the Schrader valve and use a syringe to add the fuel.

[Mark33]

I watched and enjoyed the YouTube presentation, but I'm still a little bit confused as to why Ron experienced vapor lock.

I don't know exactly how the 12's are plumbed, but if the fuel pickup is in the bottom of the tank and sitting in liquid fuel, and the electric fuel pump(s) aren't having to pull fuel uphill, and the liquid fuel is basically free-flowing to the pump inlet, how can they vapor lock or cavitate? Vapor lock can only happen at the pump inlet (suction side) and if the pumps have liquid being fed to them, they're going to pump, regardless of the fuel temperature. Once the fuel exists the pumps, the fuel pressure regulator takes over an maintains a constant 45 psi in the fuel rail and across the injectors.

Those of us that run an SDS or EFII setup and also run car gas, are basically in the same boat. I run car gas in my -8 almost exclusively and I've never once experienced even a hint of vapor lock. It doesn't matter if it's winter or summer, hot starts or cold, high altitude or low, my airplane has never missed a beat.

So is there something about the way the 12 is plumed that's different than the typical SDS or EFII installation, or am I missing something here?

[csmith3603]

I have read the SL-00078 document. Wow.

The Rotax 912 ULS has only one fuel line and the Rotax 912iS
has two fuel lines & circulating (cooling).

Why did the RV-12iS Rotax 912 iS Fuel system get compared equally to the RV-12 Rotax 912 ULS model?

They are not the same. Where are the RV-12iS vapor lock stories?

Why no comment on Hight Octane Unleaded Ethanol free fuel?

Call Roger Lee at 520 349-7056

[Piper J3]

I see your profile lists RV-9… so perhaps you are not familiar with 912ULS. This engine has a single fuel delivery system with return flow to the tank (I believe you are calling this circulating / cooling). The comparison to 912iS is an acknowledgement that Vapor Lock is a real concern with elevated temperatures when using winter-blend Mogas where responsibility for safe operation is on the ownness of the pilot / operator. Vapor Lock can happen in any engine including Lyc and Cont when conditions are ripe. Knowledge is the key to safe operation…

[Piper J3]

Originally Posted by Mark33

Vapor lock can only happen at the pump inlet (suction side) and if the pumps have liquid being fed to them, they're going to pump, regardless of the fuel temperature.

So is there something about the way the 12 is plumbed that's different than the typical SDS or EFII installation, or am I missing something here?

Yes, you're missing a lot... RV-12 with Rotax 912ULS has a low-pressure fuel delivery to normally-aspirated carburetors. Fuel lines are run topside on the engine and are easily heat-soaked. Fuel can "boil / vaporize" in the fuel lines and/or carb float bowls.

[Brantel]

Originally Posted by pstraub

I just bought 50 gallons of mogas two days ago(93UL, ethanol-free) but I have no idea if the blend is summer or winter. I am in East TN and obviously not quite May 1st yet. It would be great to measure the RVP per SL-00078. Does anyone know of a reasonably priced RVP tester? (if there even is such a thing!) Thanks!!

If you don’t mind, we’re do you purchase your fuel?

Thanks!

[Mark33]

Originally Posted by Piper J3

Yes, you're missing a lot... RV-12 with Rotax 912ULS has a low-pressure fuel delivery to normally-aspirated carburetors. Fuel lines are run topside on the engine and are easily heat-soaked. Fuel can "boil / vaporize" in the fuel lines and/or carb float bowls.

I know that low pressure fuel systems are ripe for vapor lock in a high temperature environment, but I was under the impression that Ron’s fuel system was a high pressure one, which also incorporated a return line. I’ll have to go and watch the video, but I know in his presentation he talked about and showed where his fuel pressure normally runs about 45 psi. but showed where that pressure dropped to around 12-15 when the vapor lock was occurring. I may also be mistaken in thinking that Ron has the iS model. If his has carburetors, I know the fuel can boil in the bowls and the floats can sink.

[pstraub]

Pioneer Market, 480 Erwin Hwy, Tusculum, TN 37745

Originally Posted by Brantel

If you don’t mind, we’re do you purchase your fuel?

Thanks!

[docjjrmd]

It seems to me that the 912 really would like Swift 94UL or 100R or GAMI 100UL. Fuel costs are a concern and I realize that drives many to mogas along with the increased maintenance cost of 100LL with Decalin. However, maybe we are being pennywise here because a hiccup at 300 ft on take off can get real expensive in a hurry and not just in dollars! - JJR

[j4cbo]

Originally Posted by docjjrmd

It seems to me that the 912 really would like Swift 94UL or 100R or GAMI 100UL. Fuel costs are a concern and I realize that drives many to mogas along with the increased maintenance cost of 100LL with Decalin. However, maybe we are being pennywise here because a hiccup at 300 ft on take off can get real expensive in a hurry and not just in dollars! - JJR

For me it's not a cost issue - I don't like putting lead in my airplane (because it's nasty stuff, bad for humans and bad for engines), but the nearest airport with 94UL is 600nm away, and neither 100R and G100UL have hit pumps anywhere yet as far as I'm aware. So mogas is the only remaining option.