What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Vapor Lock

The other downside

Geico266 said:
Just thinking out loud here Frank, you are right about maintainance issues after the fact, but the longevity of the new pumps is pretty impressive. I doubt we would wear them out in an airplane application.

We use Walbro pumps in the diesel pickup truck world.

http://www.walbrofuelpumps.com/
Click to expand...

of in pump tanks is they would be limited to positive G acro...

Frank
 
frankh said:
of in pump tanks is they would be limited to positive G acro...

Frank
Click to expand...

True, unless you wanted to try to engineer a connection and a flop tube for them - and I'm not that adventurous. There are lots of issues that can go wrong there...
 
rocketbob said:
Not so... just get two Facet 40185 cube pumps @11.5 psi for each side, and run them in series; the 40185's don't have a pressure relief built-in, so you can boost pressure by running them in series AND you have the benefit of some redunancy there at partial pressure. On the bench I tested mine with a digital calibration gauge, and they put out 23psi @35GPH. This is the setup I'm using in the rocket, cost is $50 ea, $200 total. They only draw 1.6A apiece.

Eliminate that POS unreliable mechanical pump! :) And get rid of the fuel selector while you're at it.

I got mine from another fine aviation parts establishment:
http://www.yachtsupplydepot.com/mec...tate-electric-fuel-pump-40185/prod_23424.html

The specs are wrong on this page, its a 9-11.5psi pump. Mine put out 11.5psi each.
Click to expand...
Bob, what size ports do the 40185's have? Did you have to drill them out?
 
jarvis said:
Bob, what size ports do the 40185's have? Did you have to drill them out?
Click to expand...

Yes they have 1/8" NPT ports, and no I have not modified the pumps. I'll just use an adapter to bring them up to AN6. The pumps with 1/8" NPT fittings are rated at 32GPH.

FWIW, the Flowscan fuel flow transducers only have an 1/8" hole thru them, and those have been used extensively in aircraft.
 
Good point Bob

The occasional restriction does not make much difference to the overall pressure loss in a system...But if you assumed that because the floscan has a 1/8th hole therefore you can replace the entire fuel line with 1/8th pipe then you would be in for a rude awakening..Especially if you did this on the suction side of a pump.

So don't do that OK?..:)

Frank
 
Return line may help !

I had my engine builder install a return on the Precision fuel injection servo. It?s an elbow that screws in the top of the throttle body (fuel pressure port) with a very small hole in it. They tested it for several hours when they test ran the engine on the bench. They told me the return would pump back about 2 GPH and they could see bubbles in the clear return line, that they used for testing, if the fuel pressure was lowered below the recommended pressure. I guess there is two advantages:

- The fuel flow back to the tank will keep the fuel cooler, especially at idle, when the fuel flow is already very low. This should eliminate a vapour lock issue during landing.
- If bubbles have formed in the fuel, they will be at the top of the entry into the throttle body and will be pumped back to the tank (double stack Andair fuel valve).

I also installed a cooling shroud on the mechanical pump and have the Dynon fuel flow transducer between the injection servo and the FI-spider. I intend to put plenty of heat shields on the exhaust to keep the (already fire sleeved) fuel hoses cool. Of course I have the AFP boost pump, that will be running during take off and landing.

I am not flying yet, but I am confident this set up will be sufficient for running, risk free, on Mogas. However, extensive testing will tell if I am right.

Regards, Tonny.
 
Please forgive me

I hope this does not come out wrong..... Why are you fellas using MOGAS ? Is it because you are worried about 100LL going away within the next week? I am not trying to start anything I am just wondering.
 
$$$$$$$$$$$$$$$$$$$$$$

KirkGrovesRV8 said:
I hope this does not come out wrong..... Why are you fellas using MOGAS ? Is it because you are worried about 100LL going away within the next week? I am not trying to start anything I am just wondering.
Click to expand...


Its all about the money for me. If I can spend 1/3 less on fuel I can fly 1/3 more. If I was wealthy I wouldn't care if it ran on Dom Perignon! :)
 
KirkGrovesRV8 said:
I hope this does not come out wrong..... Why are you fellas using MOGAS ? Is it because you are worried about 100LL going away within the next week? I am not trying to start anything I am just wondering.
Click to expand...

OK, rhetorical question :)

Why do you throw your money away burning avgas?

Every buck I save in flying my airplane, is another buck in my kids' college fund.
 
I have

an issue burning leaded fuel too..Lead in the atmosphere is a very bad thing..Why do it if you don't have too?

Frank
 
Pilottonny said:
I had my engine builder install a return on the Precision fuel injection servo. It’s an elbow that screws in the top of the throttle body (fuel pressure port) with a very small hole in it. They tested it for several hours when they test ran the engine on the bench. They told me the return would pump back about 2 GPH and they could see bubbles in the clear return line, that they used for testing, if the fuel pressure was lowered below the recommended pressure. I guess there is two advantages:

- The fuel flow back to the tank will keep the fuel cooler, especially at idle, when the fuel flow is already very low. This should eliminate a vapour lock issue during landing.
- If bubbles have formed in the fuel, they will be at the top of the entry into the throttle body and will be pumped back to the tank (double stack Andair fuel valve).

I also installed a cooling shroud on the mechanical pump and have the Dynon fuel flow transducer between the injection servo and the FI-spider. I intend to put plenty of heat shields on the exhaust to keep the (already fire sleeved) fuel hoses cool. Of course I have the AFP boost pump, that will be running during take off and landing.

I am not flying yet, but I am confident this set up will be sufficient for running, risk free, on Mogas. However, extensive testing will tell if I am right.

Regards, Tonny.
Click to expand...

Guys,
Loads of great info on this thread. I'd like to say that I spoke at length with Mr. Petersen of Petersen Aviation, holders of auto fuel STCs for 8.5 to 1 compression ratio Lycoming aircraft. (EAA's STC only covers 7 to 1 and 7.2 to 1 engines)
I wanted to know why he was able to STC fuel injected Continental engines, but not fuel injected Lycomings. We had a very long conversation (98% me listening and learning). He gave me the whole history of auto fuel in aircraft and improvements in auto fuel Reid Vapor pressure (thanks to the EPA) since the 1970s, when the STC tests were done.
He feels that any fuel injected Lycoming with a fuel return system like those used on Continentals and modern fuel injected cars, (and proposed by Tony) would have no vapor lock problems with auto fuel. The down side to this is using the expensive duplex Andair fuel selector to send the returned fuel to the tank in use.
I haven't done this, so this is a "try at your own peril" suggestion for the financially challenged. Another option would be to add a second Vans fuel selector and use it for the return fuel. You could "slave" it to the main fuel selector by use of two Heim joints riveted to a tube. Vans does this for some of our control linkages. Connect the linkage rod between the levers of the two fuel selectors. Just an idea and worth what you paid for it.
Charlie Kuss
 
Last edited:
Mr Petersen is probably right

But I still have to come back to the question of why put lipstick on a pig?

In other words why keep trying to make a hydraulically flawed system work when we could all be doing it the right way in the first place and (with a modification to my design discussed previousy) do it for less cost than a standard system.

The only two downsides I see of an all electric system is potential sensitivity to lightening strikes (but so is a twin EI system) and the fact the electrical system has to have redundancy..just like a twin EI system or pretty much any aiplane that flys in IMC..Hardly difficult or costly to do these days.

Seems to me the forces of inertia continue to bolt mechanical fuel pumps on the backs of engines when in reality they should be relagated to the trash can like Vacuum pumps and dynamos should be.

Frank
 
I'm running a PS-5C pressure carb in my Rocket, and like the early Bonanza's that used this carb, the return line goes to the right tank - no duplex selector. Why bother with a complicated return setup when the amount is only 0.3-0.4 GPH. One of the reasons why I chose to go this route was because of the return line, which constantly purges the throttle body with cool fuel. One complaint about return lines is that most systems require another fuel flow transducer on the return line. I built my own engine montor, and am handling this in the code by computing an offset based on the fuel pressure; so no additional fuel transducer is required in my case.

After SNF I am going to do some extensive flow/pressure testing with the 40185 pumps in series and will report back.
 
Why do we want to run Mogas? Stupid question!

No, serious now, Avgas is approx. EUR 2,30/ltr :eek: (approx. $ 11,65/gal.) and Mogas is EUR 1,11/ltr :) (approx. $ 5,60/gal), over here at the moment! (it has even been worse!). At an average of 30 ltr/hr and 2.000 hrs., that makes a difference of EUR 71.400,- ($ 96.390,-), more or less the price of a new RV6/7/9, every time you overhaul the engine! :D

A free new plane with your engine overhaul, go figure!
 
Environment to!

I do not have kids, do you? Do you want them to survive the next 50 years or so?
No,no,no,....... do not stop flying! Just stop using leaded fuel! That will help a lot too!

Did you know that you wll burn approx 2% less fuel if you are flying on Mogas? That also helps (not you on your own, of cource, but you have to look at the bigger picture). Thousands of gallens of fuel (and unnecessary exhaust gasses) may be saved if all GA aircraft would fly on Mogas.
 
Fuel flow transducer on metered side!

Bob, I have placed the fuel flow transducer after the return-line, in the line from the servo to the spider, so there is no need for a second fuel flow transducer (to subtrakt the return to the tank) or a calculation of a constant return. Aparently this is better for avoiding vapour lock also (reduce friction in the suction lines).

Regards, Tonny.
 
Pilottonny said:
Bob, I have placed the fuel flow transducer after the return-line, in the line from the servo to the spider, so there is no need for a second fuel flow transducer (to subtrakt the return to the tank) or a calculation of a constant return. Aparently this is better for avoiding vapour lock also (reduce friction in the suction lines).

Regards, Tonny.
Click to expand...

Yes Tonny its really not a problem on a FI setup, but I should have clarified that its a problem on a carbureted setup because there's not a metered fuel line.

OTOH, theres a bit of fuel in the metered fuel line that doesn't get purged, hence why I thought the pressure carb is superior in that regard. How evenly I can get fuel distribution remains to be seen, but I've thought up a few tricks that I will be testing in my carbed RV-6 soon.
 
Bob

Just out of interest..Do you know that Matronics has a little box that will subtract the readings from two floscan flowmeters to give a corrected output?

Built just for the purpose of subtracting return from total flow to give actual burned.

Output is the same as a single floscan and maybe read with a Dynon or any instument that can count the pulses.

Frank
 
Fin tubing

Has anyone thought of using fin tubing for fuel lines. Might help to keep the fuel lines cooler. Just a thought. I haven't been thinking about this really, so don't hold it against me if it's stupid.
 
finned tubes?

Finned tubes would actually absorb more heat North of the firewall...Hence would make the situation worse.

Frank
 
frankh said:
Just out of interest..Do you know that Matronics has a little box that will subtract the readings from two floscan flowmeters to give a corrected output?

Built just for the purpose of subtracting return from total flow to give actual burned.

Output is the same as a single floscan and maybe read with a Dynon or any instument that can count the pulses.

Frank
Click to expand...

I can easily do the same thing in my code, if I wanted to add another flowscan transducer. I have a table in my code I look up the offset to the current flow based on pressure. The Saratoga I fly has a fuel flow meter, and all it does is measure metered fuel pressure at the divider, and report that pressure as GPH.
 
vapour lock in stock system

I'm curious if all the great minds that have commented here could dumb it down for me???

If I have a totally 'stock' RV-9a, with a low compression carbed 0-320, what is the best track to running mogas?

1. does my engine need SOME lead? I think it's about 25 years old. does a mix of Avgas and MoGas really STAY mixed?

2. If I just run my electric fuel pump full-time, and it's on the cabin floor, nearly always below the fuel level in the tanks, am I likely to avoid Vapour-lock in most conditions?

3. what are the key points to address if running mogas with ethanol? sounds like there are only a couple of rubber O-rings to replace?

thanks!
 
flyboy1963 said:
I'm curious if all the great minds that have commented here could dumb it down for me???

If I have a totally 'stock' RV-9a, with a low compression carbed 0-320, what is the best track to running mogas?

1. does my engine need SOME lead? I think it's about 25 years old. does a mix of Avgas and MoGas really STAY mixed?

2. If I just run my electric fuel pump full-time, and it's on the cabin floor, nearly always below the fuel level in the tanks, am I likely to avoid Vapour-lock in most conditions?

3. what are the key points to address if running mogas with ethanol? sounds like there are only a couple of rubber O-rings to replace?

thanks!
Click to expand...

1. Lycoming says that standard compression, non-turbocharged engines can be run on mogas. Mogas and avgas do stay mixed.

2. You will likely avoid vapor lock with the electric pump running full-time, but if your system is properly designed you would not have to do this.

3. The common culprits are the o-rings on the fuel drains which can be replaced with vitron rings and the rubber gaskets on the resistor-type fuel level float mechanism. These can be eliminated entirely.

As an update to my conversion to mogas..... I initially had a problem with vapour lock during long climbs. I have since replaced three 90-degree fuel fittings with straight fittings and have put a blast tube on the mechanical fuel pump. I regularly run 100% mogas and have not had any VL issues since making these modifications. I have saved so much money that I no longer send my grandchildren down to the street corner to sell Chicklets to support my 100LL habit. ;)
 
mogas etc.

thanks Smokey,
all good info from an experience user!.....I think I'll order some new o-rings and get ready for Mogas in the spring!
 
Vapor lock

Hi evry one. I have an RV-8 with an o-360 with a mech fuel pump and a cube boost pump. My aircraft ran fine on a one hour trip then sat in the 90deg sun for 3 hours. I went to run it up on take off and eperianced a vapor lock issue and got way worse when I turned on the boost pump, Carb ice was not an issue. I have read your posts and will do some investigating but I just thought I would sign up and see what yuo had to say. Thank you. FYI..I did not build the airplane.
Mark
 
more info pls

Were u using mo or av? I must assume MO given you have subscribed to this post. Obviously, in the future, have one wing with pure av, the other with mo. If the mo was intended for autos, you r not the first one to experience this. My friends and I theorized that it tool some time for the mo in the wing to cool off after sitting in the sun but I have no idea if that's the cause. I've seen the issue go away after 15 min of flying but my electric pump always kept pressure > 3lbs. Yours did not which is alarming.

I do know of another test which may help. After your final landing on pure mo, turn off the electric pump and let your instruments (hopefully an EMS) report fuel pressure. If < 2lbs, welcome to the world of mo designed for autos. I resolved that issue by adding 40% av all the time with mo. Instead of saving a buck a gallon, I save less but breaking an airplane is simply not worth the savings so conduct more tests at alt. Safety first.
 
ronschreck said:
......

As an update to my conversion to mogas..... I initially had a problem with vapour lock during long climbs. I have since replaced three 90-degree fuel fittings with straight fittings and have put a blast tube on the mechanical fuel pump. I regularly run 100% mogas and have not had any VL issues since making these modifications. I have saved so much money that I no longer send my grandchildren down to the street corner to sell Chicklets to support my 100LL habit. ;)
Click to expand...

Where the three 90 degree fittings in front of, or behind, the firewall?

Glad to hear the grandkids not longer are in servitude...:)
 
No 90s

Thx to Gil, I have no 90 degree fuel line bends, a heat shield over the gascolator & insulated lines, but still experience vl issues when the wing sits in the sun. The latest batch of mo measured only 6.0 on the Peterson scale and it seems to vl even more, so av is always mixed in. With av mixed in, I have no vl issues but my flying in the Tucson summer starts @ 5am and ends before 7am when it's still relatively cool.
 
Vqpor lock

We've been using mo gas exclusively (E10 included) in the Searey amphib (Rotax), our 182, and RV 10. Also help a friend who trains and tows banners with 172s, with mogas, all here is warm Florida, and never experienced vapor lock. There must be some other issue. weakening pump (mechanical), fuel line restriction, un insulated lines, low pressure......
 
FLYONE said:
Hi evry one. I have an RV-8 with an o-360 with a mech fuel pump and a cube boost pump. My aircraft ran fine on a one hour trip then sat in the 90deg sun for 3 hours. I went to run it up on take off and eperianced a vapor lock issue and got way worse when I turned on the boost pump, Carb ice was not an issue. I have read your posts and will do some investigating but I just thought I would sign up and see what yuo had to say. Thank you. FYI..I did not build the airplane.
Mark
Click to expand...

Since the boost pump makes it worse, it's likely pneumatic lock. Vapor in the lines can force excess fuel past the needle valve in the carb, or boiling fuel in the carb can cause the float to sink. Either way, the result is an overly rich mixture. A vapor return can help with the first problem, but not the second. Fuel injection is the only solution for that one.
 
Rad the entire thread this evening, thanks for all the great comments and advice! I have bookmarked this for my -10 build for sure.
 
Great thread, learned a lot.

I'm probably going to go with an IO-320 for my 9A. How does the fuel injection effect the chances of Vapor Lock?

-Dan
 
ronschreck said:
<snip> BTW, are there not some corrosion issues with running ethanol-blend fuel?
Click to expand...

Since this thread has been revived . . .there are real facts and data behind elimination of modern ethanol corrosion issues. They were very real and very bad. It is true that they have been eliminated at the manufacturing plant.

The early ethanol plants (circa 1994) were not required to have a continuous monitoring system for acidic content. Cargill and ADM made 90% of all ethanol as an additive at that time. The manufacturing process adds acid to accelerate the mash fermentation process (like the old batteries in hillbilly stills) then a water wash process removes the acid. Some plants did not have good controls and allowed the acid laden ethanol out on the market. My engineering group worked with Cargill and ADM to propose, and get, the ASTM testing standard modified to make it a continuous process measurement rather than the batch process being used. This change pretty much eliminate all corrosion due to the ethanol content over the following 12 months that the standard allowed for compliance.

More background: At the time (mid 1990's) my engineering group was developing catalysts for large diesels that sprayed pure(denatured) ethanol in front of a catalyst bank to reduce NOx by 90%. We had field testing sites that purchased 10,000gal tanks of ethanol. The first one was ok, but then we started to eat up everything. Pumps especially. We had a 5 gal can of the stuff shipped back to us and it dissolved the chrome off the pull out spout of the 5 gallon can, and in the process of eating the container neutralized itself. Struggling for a while, I sent a guy with a glass container and brought a sample back. It was 500 times over the acid limit of the standard. yes, five hundred. So- the old tales of corrosion were true and were nearly impossible to trace. The large batch sizes and the fact that we stored it in stainless steel tanks kept the acid from neutralizing itself in normal steel tanks, allowing the team to get to the root cause.

PS: one must still ensure that elastomers are compatible and pressure/temp of fuel is adequate to prevent vapor formation, but corrosion should not be a concern.
 
Bill,
excellent info and great write up.

Dan,
Fuel injection is your friend when it comes to vapor lock issues.
More pressure on the fuel means higher boiling point of fuel.
Along with a few modifications you can virtually eliminate the possibility of vapor lock.

Been burning 91 octane E10 in my Rv-10 at all times and under any conditions.
 
You must log in or register to reply here.
Back
Top