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Vapor Lock RV-12 Rotax 912ULS

Actually, the latest KAI for the ULS installation uses a different cowl, different oil and coolant radiators and placement.

I'm playing devil's advocate here I guess, but I think removing the cooling shroud may be a significant factor in what you are experiencing.

"The troubles started when the mechanic opened his toolbox", author unknown.

Tony -

See Scott McDaniels comments regarding removal of cooling shroud on existing legacy RV-12... https://vansairforce.net/community/showpost.php?p=1405341&postcount=5

Looks like Van's vetted this pretty well.
 
Actually, the latest KAI for the ULS installation uses a different cowl, different oil and coolant radiators and placement.

A friend has Synergy build RV-12. He took delivery in 2018 and as far as we can see it has same cowling, oil, and coolant radiators. No fiberglass cooling shroud included in the build. Maybe I need to take closer look...
 
Actually, the latest KAI for the ULS installation uses a different cowl, different oil and coolant radiators and placement.

I'm playing devil's advocate here I guess, but I think removing the cooling shroud may be a significant factor in what you are experiencing.

My opinion is that shroud removed will have little if any influence on engine compartment temps after shut down compared to an RV-12 with it still installed.
 
Jim, Have you downloaded the Dynon logs for your incident and looked for any clues like oil temp, air temp, fuel pressure, flow rate, etc?

Easier said than done... I don't have capability to do serial port for D-180, and besides, the connector is buried in the tunnel.
 
I'll have a SkyView Classic for sale shortly, if interested in upgrading. ;) It would have a USB port.

No, actually, I bought Tony T's D-100 to make dual screens when he upgraded to HDX. I have screens supplemented by two mini iPads both running ForeFlight.

I need to keep pinching myself having come from J-3 Cub for 23 years - old dog / new tricks.
 
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To answer Jim Norcal’s question: I rewired my Nav Light switch (I don’t have lights) to be a fuel boost pump switch. I routinely secure the electric pump after reaching cruise altitude and turn it on for descent and landing. I also run it more in PHX summers when fuel line vapor causes high flow and low fuel pressure alarms. My engine has never stumbled.

Please spare me the breast beating and hand wringing over my decision to make the boost pump controllable. I have heard it all and stated my reasons. I don’t tell you how to customize your airplane, so spare me any opinions. After 1100 hours and 12 years I am confident in my approach.

BTW I put temperature witness strips on my ignition modules and voltage regulator (mine is on the original firewall location with no ducts). The V/R has reached 180F. The ignition coil strips show a scary 250F! PHX summers are a very harsh environment.
 
I flew one hour this morning with OAT – 37F so not much relevant to vapor lock. I landed at two outlying airports with taxi back for TO at each. I have one temperature probe mounted to right carb float bowl and it is pretty much showing under-cowl temp at that location. The second probe is now pinched against the Teflon hose stainless-steel braid underneath the Fire Sleave on the fuel line that feeds the T fitting before the carb split-off. I think this thermocouple is giving a very close reading to actual fuel temperature in the hose and temperature of fuel being fed to carbs.

Some observations from this morning’s flight:

• Airplane was cold-soaked in hanger prior to flight, so fuel in tank was same as OAT – 37F
• Fuel line temp is about 25F higher than OAT in cruise flight
• Fuel line temp immediately increases when throttle is reduced for landing – this was very surprising
• Fuel line temp increases during taxi ground ops - no surprise there
• Airplane was pushed back into hanger at end of flight and Fuel Line temp climbed to 121F within ten minutes with oil door open


Next Steps:

• Change SOP (Standard Operating Procedure) for Take-Off phase of flight. Going forward... all Take-Off’s will be monitored with right EFIS/EMS screen to display full-screen EMS showing Fuel Flow and Fuel Pressure with Fuel Pressure alarm set at 3 psig. Screen will not be changed to normal 2/3 EFIS - 1/3 EMS until cruise flight.
• Install Design Engineering 010669 Vapor Block Fuel Line Sleeve on all fuel lines FWF. Also install on bare aluminum manifold crossover tube.
• Install Lynn Manufacturing Flame Guard, 2100F Superwool Blanket with Heavy Foil on fuel T fitting fastened to manifold crossover tube.
• Continue monitoring Right Carb and Fuel Line Temperatures and mount digital display permanently in instrument panel on left side of Pilot EFIS just above fuse block.
• Need to fly when OAT ~ 80F
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When fuel flow is reduced, fuel is exposed to engine heat for longer time.

Yes, I believe that is what is happening. Very surprising how quickly the fuel temp rises when throttle is reduced to near idle.

Going to be interesting to see fuel temp and under-cowl temp when weather gets warm...
 
I was removing the cowl for an oil change so I thought I would get these temp numbers to aid the discussion.

I flew 30 minutes in ambient 98f, 2 minute taxi, shut down & remove cowling. All temps checked with infrared gun.

Left carb bowl – 152f
Left carb fuel line as it enters carburetor – 164f
Fuel pressure sensor on firewall left side – 140f
Right carb bowl – 159f
Right carb fuel line as it enters carburetor – couldn’t get a good reading, too much in the way
Body of mechanical fuel pump on gear box – 140f
Fuel “tree” fittings on top of engine – 168f
 
This is louver I’m thinking about adding at rear top cowling to help extract heat during ground ops. Opening is 9” x 3.75”. Most likely mounted with fiberglass resin from bottom side and no fasteners.
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I for myself would be very, very careful with adjusting existing airstream. The louvre will suck air out of the cowl during flight, as well - unless you can shut it off in-flight. I once owned a KitFox/Jabiru combination and've had a major job to get the numbers right. Now with the '12 I'm so happy it has all been sorted out for me, I can only give my deepest respect for the designer and keep it the way many equal planes are happily flying at the moment.
I added to my SHUT-DOWN checklist OILDOOR - OPEN. About the same opening, works for me.
Curious to your findings, though.
 
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Yes, I understand concern for cylinder cooling, however, the 912 is primarily a liquid-cooled engine.

Jabiru is air-cooled and that presents multitude of problems; front cylinders Vs. back cylinders, air dams, pressure cowling, cooling very bottom of cylinders, etc.

On the ground, excess heat would spill out of top louver - prop blast will create venturi effect. Slip stream will do same thing in the air. The RV-12 cowling has no baffles to direct air flow. Air enters through two small (2.5”) round openings and finds its best way to exit bottom of cowling. Path of air flow is most likely very different on ground Vs. flying. Some air goes through cylinder fins but not very much. Hot air from both oil radiator and coolant radiator have to mix inside cowling with small amount of fresh air making situation worse.

As stated in my previous post, I’m just thinking about louver – it would be final step for controlling fuel line temperature. For now, I will monitor fuel pressure and fuel flow on take-off. This week I will add foil-backed thermal insulation to all fuel components FWF. I will continue with temperature measurement of fuel line and carb float bowl and mount digital display in instrument panel.

It might appear that I am overly concerned about vapor lock… well, I am. Making 180 turn at low altitude on take-off, with partial power, to land opposite direction on runway is not my favorite thing to do. People use the term “anal” when someone is obsessed with something. In this case it is relevant because you get a really good “pucker” when engine starts shaking violently and loses half power.

I’m going flying today – 34F and solid sun.
 
Why no some 100LL?

Jim,

If I had your experience, I’d be super anal too! And will be. Curious though, why not save the engineering headache (unless you really enjoy it) and just mix in 100LL in each tank during March, April, May when you may have winter gas + high OAT? That’s what I’ll be doing to keep it simple. I already change oil at 25hr intervals anyway just because.
 
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Jim,

If I had your experience, I’d be super anal too! And will be. Curious though, why not save the engineering headache (unless you really enjoy it) and just mix in 100LL in each tank during March, April, May when you may have winter gas + high OAT? That’s what I’ll be doing to keep it simple. I already change oil at 25hr intervals anyway just because.

The answer to your question is that vapor lock can occur with summer blend Mogas if under-cowl temps allow. So, I feel it necessary to understand and control fuel temperatures FWF regardless of fuel type used.

Rotax states preference for Mogas Vs. 100LL for the 9-series engines. I prefer not contaminating gearbox, overload clutch, and oil tank with lead.
 
Vapor lock is a condition where the gas vaporizes creating gas bubbles inside the gas line. It almost always occurs on the vacuum side of the fuel pump since the low pressure is more favorable to the gas vaporizing. Obviously high heat aids the ability of the gasoline to vaporize.

To solve this problem in automobiles the fuel pump was put inside the gas tank to eliminate the pump having to create a low pressure in the fuel line sucking the gas into the pump. Additionally sometimes a return line was used to keep the gas circulating in the lines.

Our plane has the electric fuel at the base of the fuel tank, gravity feeds the pump. The fuel leaves the electric pump under pressure and arrives at the manual pump in the engine compartment. The manual pump does not have to “suck” to get gas, it is fed from the electric pump. The manual pump further pressurizes the gas and sends it to the fuel “tree” located above the center of the engine. There is one branch of the tree runs excess gas back to the gas tank. Because of this return line there is always fresh, “cooler” gas in all the lines in the system to this point whenever the engine and / or electric pump are running.
From the tree a gas line goes to each carburetor bowl. These 2 lines are the only ones the whole system that don’t have recirculating gas. If vapor lock was to occur it would happen in these lines first since the gas isn’t getting replaced. The fact remains that the gas in these 2 lines is under pressure from both fuel pumps, (unless the electric one has been disabled), and pressurized fuel resists vapor lock.

A scenario that I think would easily lead to vapor lock would be a hot day, heat soaked engine compartment, weak or no electric fuel pump, and high fuel demand like taking off. The mechanical fuel pump will suck hard to keep up with the demand, the suction in the line from the gas tank that is moving through the hot engine, (no or little help from the electric pump), compartment will induce the fuel to vaporize. The mechanical pump will cavitate and starve the carburetors.
 
A scenario that I think would easily lead to vapor lock would be a hot day, heat soaked engine compartment, weak or no electric fuel pump, and high fuel demand like taking off. The mechanical fuel pump will suck hard to keep up with the demand, the suction in the line from the gas tank that is moving through the hot engine, (no or little help from the electric pump), compartment will induce the fuel to vaporize. The mechanical pump will cavitate and starve the carburetors.

Yes, I think that’s pretty much it.

So, what can we do to stack the odds in our favor?

Hot Day – Not much can done to alleviate. Fly instead during cool part of day?

Heat-Soaked Engine Compartment – Add thermal insulation to all fuel components FWF. Monitor heat build-up with digital temp display. Avoid prolonged / repeated ground ops. If practicing landings – do touch/go instead of full stop and taxi back. Open oil door after engine stop. Let engine cool ~ 30 minutes prior to flying. Possibly alter cowling to improve cooling air flow.

Weak / No Electric Fuel Pump – Verify electric fuel pump running and developing pressure prior to engine start. Verify mechanical pump add’l fuel pressure after engine start. Purchase / install FAC-40135 Facet Cube 12v Fuel Pump,1/8 NPT, 4.5-6 psi per Van’s Notification 18-07-12.

High Fuel Demand On Take-Off - Monitor Fuel Pressure and Fuel Flow during take-off phase of flight.

Alternative solution is to use 100LL or combination 100LL / Mogas.
 
A few years ago, I saw a Cassutt Racer with Cont 0200 land and pilot got out, opened oil door to permit cooling, and then the guy had a 12-volt fan he stuck over the oil door opening to suck out the heat. Fan ran on 12V buss with small plug accessible at the oil door opening.

RV-12 might benefit from this…
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So, what can we do to stack the odds in our favor? - Don't take up flying as a hobby, it is inherently dangerous.:)

Avoid prolonged / repeated ground ops. - yes, but if you find you have possibly overheated things, watch oil temp it is a good clue, maybe a full power run-up to clear the lines and carb bowl of over heated fuel. It takes 20 sec at full power to empty the bowls.

Verify electric fuel pump running and developing pressure prior to engine start. - this should be done regardless of vapor lock concerns.

Monitor Fuel Pressure and Fuel Flow during take-off phase of flight. - and set alarms if you have a system that allows that, the 15 second warning could make the difference.

Alternative solution is to use 100LL or combination 100LL / Mogas - I am not convinced that will guarantee no vapor lock issues, besides the down side of having lead deposits in the engine.

Keep in mind the problem we are trying to eliminate, (vapor lock causing a crash), is EXTREMELY rare with the RV-12 because it has a full time electric fuel pump and constant fuel re-circulation. I have only read about 1 crash that may have started with Vapor lock but sounds like there was more to the story. Typically you would get a rough running engine with loss of power that recovers quickly.

Yes it has caused deadly crashes in aircraft without the features I mentioned above, but that is not us.
 
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Keep in mind the problem we are trying to eliminate is EXTREMELY rare with the RV-12 because it has a full time electric fuel pump and constant fuel re-circulation.

Might not be as rare as we think. Several reports here in this thread, and since starting thread, I rec’d two PMs from guys not willing to go public.

I live in the northern part of the country and now worry about winter fuel operation when temps get warm. I’d be equally worried if I lived in the south with daily temp extremes reaching 100F. And, if I operated a flight school, I’d caution about ground ops…
 
What I meant when I said it was rare was, it is rare that it had been the cause of a crash.
 
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What I meant when I said it was rare was, it is rare that it had been the cause of a crash.

Not so sure of that either. Most of the time NTSB doesn’t even travel to accident site. Don’t think vapor lock is high up on list of possible causes...
 
Jim,

Only the cylinder heads are water cooled. I think a better approach would be a hinged cowl flap at the bottom aft end of the bottom cowling. That would probably cause stress on the cowling. Maybe a mister ring like the big boys at Reno?

In the end it seems easier to just set the alarm clock earlier and fly before it gets too hot.😁

Rich
 
We had issues with this in a flight school plane. It seems to be caused by a too low (or was it high?) Reid Vapor Pressure in the winter-blend auto fuel. Mixing the mogas with avgas has stopped the problem, since it moves the RVP in the right direction.

We also open the oil door and place a fan there to pull out the hot air in-between flights.
 
If I decide to add louver to rear of top cowling, I will buy another remote temperature sensor to monitor two cylinders for air cooling. Rotax 912 Installation Manual says maximum permitted cylinder wall temp on hottest cylinder is 392F (200C).
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Oil door gust lock

Hey Jim, apologies if this is too far afield of your vapor lock thread.

Here is an effective way to keep the door open even in strong winds.;)

It's not my invention, stole the idea from a hangar neighbor who made something similar for his -7.

i-MdkN9Jb-L.jpg


Material List:
(1) 2600-3W CAMLOC WING STUD
(1) CAMLOC 2600 RECPT
(1) CAMLOC 2600-LW RETAINING WASHER
(2) ANA426AD3-4.5 RIVET
(1) 1" X ~12" SCRAP 2024-T3 040 OR 060
 
I started this thread to highlight a potential problem that many may be unfamiliar with. All posts are relevant and certainly welcome. Forum is an invaluable tool to promote safety, understanding, and learning. I consider myself fortunate to be a part of this large group…
 
Seagull -

Interesting… Photo shows cowling with two NACA type inlets in front, and then what appears to be an elevated diffuser at rear of top cowling, perhaps to spill excess heat.

I might not be too far off the mark with thought of adding louver at rear of RV-12 top cowling…
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Seagull -

Interesting… Photo shows cowling with two NACA type inlets in front, and then what appears to be an elevated diffuser at rear of top cowling, perhaps to spill excess heat.

I might not be too far off the mark with thought of adding louver at rear of RV-12 top cowling…
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These inlets are likely installed in these locations for the same reason that I previously mentioned that the louvers are in those locations on the RV-12iS cowl.
The ignition coils are directly below those points and are specifically list by Rotax as being "Heat Sensitive Components", and they have a maximum component temp. specified.

It should be noted that in this document were it says

one or more of the following variables.
-Fuel system design
-Engine cowling design
-Fuel quality
-Seasonal adjustment on fuel
-High ambient temperatures


Taking it at face value; seasonal adjustment of fuel and/or high ambient temperatures can be consider a cause of vapor lock in and of them selves without that meaning that the cowl or fuel systems designs are to blame.

The RV-12 POH and FTS have specific info on the subject of operations in higher temps.
One that pilots often ignore is taking steps to avoid elevating the temp. of the fuel in the tank. A hot day with sun beating down on a fully closed canopy can elevate the cockpit temps to pretty extreme values. This in turn is heating the fuel within the tank.
 
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So, today I started adding insulation to the fuel lines FWF. I started with the feeder line for the left carb to see how Design Engineering Vapor Block Fuel Line Sleeve contours around fuel line radius bend. I installed a single wrap using small cable ties and then added a second wrap over it – again using cable ties to hold it in place. Fuel lines should be very well insulated with fiberglass Fire Sleave and two layers of fiberglass with foil liner. I use Thomas & Betts Ty-Rap Cable Tie with Stainless Steel Locking Device – very high quality. To convince the foil wrap to go around tight bend you need to snip and tuck a little bit but final job looks good.
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These inlets are likely installed in these locations for the same reason that I previously mentioned that the louvers are in those locations on the RV-12iS cowl.
The ignition coils are directly below those points and are specifically list by Rotax as being "Heat Sensitive Components", and they have a maximum component temp. specified.

If NACA inlets are used on the 912iS to cool sensitive electronics on top of the engine, with no air flow problem through the cylinders, then it seems to me that the same inlets could be added the 912ULS installation to add cooling, particularly during ground ops.

I would be interested to know more about the rear of the top cowling in the photo (see pink arrows) of post #84 above. It appears to be a raised section probably with an outlet on the back side – almost like a mirror image of the rear section on the RV-12 bottom cowl.
 
If you have burned leaded fuel in your plane, do not transfer it into your car.
Even very small amounts of lead will ruin catalytic converters.
 
If NACA inlets are used on the 912iS to cool sensitive electronics on top of the engine, with no air flow problem through the cylinders, then it seems to me that the same inlets could be added the 912ULS installation to add cooling, particularly during ground ops.

NACA inlets are not used on the 12iS top cowl.
They are louvers and are located well fwd on the cowl.
Will engine cooling be different with louvers at the back vs at the front?
I don’t know. We never did any testing with that configuration.
 
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If NACA inlets are used on the 912iS to cool sensitive electronics on top of the engine, with no air flow problem through the cylinders, then it seems to me that the same inlets could be added the 912ULS installation to add cooling, particularly during ground ops.

I would be interested to know more about the rear of the top cowling in the photo (see pink arrows) of post #84 above. It appears to be a raised section probably with an outlet on the back side – almost like a mirror image of the rear section on the RV-12 bottom cowl.

You might consider those sexy iS louvers. They look like they are for air flow to escape. You could place them toward the back but some more serious experimenting is needed to make this stuff all work. These look a lot better than that outhouse vent you posted :rolleyes: jes kiddin' :D

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These look a lot better than that outhouse vent you posted

Duly noted... :D

For the heck of it I looked up “outhouse vents” on Amazon. The vent I got is listed. Spent an hour looking at privy vents. I guess vapor lock is a concern there also.

This Pandemic sheltering-in-place is really ruining my social life…
 
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Duly noted... :D

For the heck of it I looked up “outhouse vents” on Amazon. The vent I got is listed. Spent an hour looking at privy vents. I guess vapor lock is a concern there also.

Ha, ha, this makes my day.
 
You might consider those sexy iS louvers. They look like they are for air flow to escape. You could place them toward the back but some more serious experimenting is needed to make this stuff all work. These look a lot better than that outhouse vent you posted :rolleyes: jes kiddin' :D

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That IS cowl got more holes in it than my practice rivet sheet! lol

Of course just thinking out loud but I wonder if you get too much cooling do you risk the odds of carb ice in our normally aspirated versions? Not usually a problem on the 912 but we all agree we have a pretty warm, tight engine cowl otherwise.
 
I ran across this and found it to be an interesting read.. Yes, it's an old study, but interesting none the less..

https://www.fire.tc.faa.gov/pdf/ct86-21.pdf

Good find. I do think our tank heats up under that bubble canopy in the sun - esp here in AZ.

I added the higher pressure Facet fuel pump when Van's came out with it because I noticed fuel pressures dipping into the red on occasion on those hot days. That plus topping with 100LL when I get the chance has helped out immensely.
 
Did you have continuously occurring vapor lock that was fixed with the 100LL or you just feel better using it?

I never had any power loss. Just fuel pressure indications. At the time i was pretty much using Premium auto gas all the time. 100 LL might be the sole fix needed i dont know. I can only say the two things I have done that appeared to fix the problem.

I replaced my Kavlico last year too since mine appeared on the affected list. Don't forget to remove that purple gasket too.

Also fuel pressure line removal and flush procedure on Page 13-9 RV-12 MM is supposed to be done annually or 100 hrs. Occasionally I get a little gunk coming out of there.

With the 5 year Lockwood rebuild of the carbs, the new R floats, my 912 seems to be running very nicely (knock on wood).

https://www.vansaircraft.com/service-information-and-revisions/n-2018-07-12/
 
Job is continuing... Today I wrapped right carb fuel line and output line from mechanical pump. Everything FWF is going to have two wraps of foil-backed fiberglass insulation including return line to tank and fuel pressure hose. I may even insulate side of oil tank nearest the right carburetor. For now, mechanical pump will remain uninsulated – pump is near cowling front air inlet.

First photo shows single wrap of insulation and second photo shows completion with both wraps applied.
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