Sport Pilot Talk

designrs wrote:Yeah, but if it's vapor restriction or a bad clamp / seal on a fuel line then I suppose it doesn't matter how many fuel pumps you have pumping. Pushing it at a few hundred feet AGL is not fun. Thinking I need a solution to troubleshoot and resolve the problem.

Have you considered asking your Rotax mechanic to fly with you in the conditions you're questioning? Perhaps they could then actually see what you're describing for themselves?

My RV-12 has the Dynon SkyView and you can take screen shots and download them to your PC etc and even e-mail them to whomever you want. I've done that and sent it directly to Dynon Tech Supprot and they say t's very helpful. If you could screen-shot your EMS when the issue is occurring then they could see it.

drseti wrote:

designrs wrote:What should I do?

Climb out with your aux (electric) fuel boost pump on, at least until you get to what you consider a safe re-start altitude, should the engine actually quit.

What you're talking about is a fuel pressure 'indication'. You haven't mentioned whether it's triggering an alarm/alert/caution in your EMS and neither does the engine seem to mind so far as it appears to be running well, and at a time where you require full power.

drseti wrote:Howard, what you describe is a perfect example of Daniel Bernouli's principle.

Sorry Paul, my plane is built in USA and the engine is Austrian (?)…so don't know who this Bernouli is and I'm not sure he has any principles at all if he's involved in aviation.

I took the plane up yesterday and had a great flight. Fuel pressure dropped when I was at altitude, and continued even after flipping on the electric pump, so I pushed it at full-throttle climb to see how low the fuel pressure would go. It really just bobbled around 2.0 and then stabilized at 3.X in a minute or two.

Yes, it triggers an alarm at 2.2 psi.

Did some research. Lots of people having these issues. Seems more common with the new style fuel pump with the drain hose.

Some check points:
1) make sure the fuel pump drain hose is inside the cowling and clipped back about 12" from the firewall.
2) fuel pressure sender (clean, especially the hole, or replace)
3) check banjo bolt at fuel return diverter
4) check for overly tight ties on fuel lines
5) check for electrical grounds
6) check fuel filters, gascolator etc.
7) possibly consider attaching a manual gauge to check system

Supposedly the motor runs just fine at 1.X psi.
Fuel pressure gauges are optional equipment.
Plenty of people probably live with this issue without even knowing it.

SportCruiser / PiperSport Owners: US Sport Aircraft offers a fuel reroute option which is suppose to help.

One rumor speculated that the new style fuel pump design may cavitate.

Further details at the following links:
http://www.rotax-owner.com/en/rotax-for ... essure-low
http://www.rotax-owner.com/en/rotax-for ... l-pressure
http://www.rotax-owner.com/en/rotax-for ... 0&start=40

* Disclaimer: I am not a mechanic or otherwise certified to give advice. The above are simply my findings while researching as an owner.

I have been hearing more about this

I just don't know why. I would need an RV12 to study a while and take some measurements. This could even be electrical.in RV12's. I doubt it is everyone's Corona fuel pump because this seems more prevalent in the RV12's and we're not hearing about this across the board. Possibly a fuel hose too close to a hot exhaust pipe? There has to be something different.

Thanks Roger. I have a SportCruiser. Evaluated the aircraft last night with my mechanic. US Sport Aircraft offers a LOA for a fuel line reposition. Basically it moves one fuel line (feed line to main fuel pump) away from the heat of the motor (under the carbs) to a higher position (over the carbs). Looks like I will do this mod.

Another solution (also requiring an LoA if an SLSA) is to firesleeve all fuel lines if not already done. That extra insulation can prevent heat from vaporizing fuel in the lines.

I'm my case, all fuel lines are already sleeved.

I'd really like to know more about how the existing fuel return to tank valve / connector functions. Does it constantly bleed back? Or only if pressure exceeds X. Can anyone explain?

It is constant. Pressure should be reasonably steady within a few tenths. Many fuel pressure readings are wrong.

Flying home yesterday in my RV-12 (912uls) my fuel pressure dropped into caution for about a minute before returning to green/normal. It dropped from around 4 to 2.8 .
Warm day, 3500', 5200rpm, airplane had sat in 85f sun for almost 3 hours with oil cooler door propped open and started first time on slightly open throttle (no choke).

Yep, I checked online for a photo of the Vans RV-12 motor installation and found this:
http://www.vansaircraft.com/images/rotax_lg.jpg

Notice that the fuel line to the mechanical fuel pump is run low.

My SportCruiser installation is similar and US Sport Aircraft is offering a LOA to move the fuel line high, basically above the carbs to reduce vapor restriction. I will most likely do this mod.

Wonder if VANS will follow with similar LOL after vapor restriction issues.

Nomore767 wrote:Flying home yesterday in my RV-12 (912uls) my fuel pressure dropped into caution for about a minute before returning to green/normal. It dropped from around 4 to 2.8 .
Warm day, 3500', 5200rpm, airplane had sat in 85f sun for almost 3 hours with oil cooler door propped open and started first time on slightly open throttle (no choke).

Do you have the old mechanical fuel pump (gold color) or the new fuel pump (with the drain hose)?

My engine is a 2014 912 ULS and I believe the RV-12 I have has a Facet ES 40105 in addition to the engine driven pump.

Vans have the aux rigged to run all the time.

I'm not completely sure if my mechanical pump has a drain but the picture you posted looks like mine and I have Teflon hoses.

In the winter the fuel pressure would drop off a little after applying full power and rise again as I throttled back in cruise climb. Engine never faltered.

Running exclusively on 93 non-ethanol auto-gas.

.......