Mogas in the RV-4

So I'm thinking about the Peterson STC for my bought RV-4 so I can run Mogas at least part of the time. I have an O-320 D1A that Peterson says can run on premium (91) only. No problem so far. They make several suggestions on the experimental aircraft page that brings me here to the -4 builders forum with questions.

They recommend heat shielding on fuel lines under the cowl to help prevent vapor lock, no problem, I'll address it with the annual in April which is when I'll have the $240 decals 'installed' to make it mogas compatible if I go ahead with this.

They suggest fuel pumps at the tank to pressure feed fuel up to the hot cowl, again to prevent vapor lock issues. Not much I can do here. The -4 either has them or doesn't. So what is a typical -4 install with a carb. I'm guessing a single fuel pump under the cowl rather than 2 out at the tanks??? Anyone have an issue with the -4 on mogas and a single fuel pump under the cowl. So far my -4 seems to run cool but oil and cht's running low'ish doesn't mean the undercowl area is cool from a vapor lock standpoint.

Anyone out there with -4 experience and or mogas in an RV experience have any USEFUL thoughts on the issue. From what little I know about mogas it seems fine for the O-320 even at 160hp on premium. But what you don't know you don't know is what can kill you most often.

With the limited availability of mogas away from home I'll likely end up burning a 50:50 mix of mogas/100ll in the tanks from a practical standpoint anyway. But at some point a full tank of mogas is probably gonna happen so it's gotta be able to run it all the time if its going to run it some time.

Thanks in advance. In short I'm looking for reasons not to run mogas in a -4 from a design aspect specifically and what should be done to run it correctly if it can.

Grant

Are you sure that a homebuilt even needs a STC to run mogas??

No mogas STC required on a homebuilt. STC's don't apply to experimental aircraft. Technically the fuel tanks need to be placarded. I run 87 mogas in my O-360 and have done so for several hundred hours. No issues with mixing or running it straight.

Make sure the hoses are firesleeved, and if there are any 90 degree bends in the fuel system forward of the fuel selector try to reroute hoses and replace those fittings.

Mogas

I have an electric pump in each wingroot for FI'd 7a and no mechanical pump. Needless to say I am more comfortable with this arrangement from a VL perspective.

If you ever do want to hire an A&P to inspect your work and go this route feel free to hit me up to see how I did it.

Frank
Io360 8.5:1 Mogas only

Oregon Ethanol

Frank, what's your plan when all your local Oregon gas stations are mandated to contain 10% ethanol, like the northern part had mandated to have by Jan 15/08?

Done some resarch

I'm 90% convinced that 10% ethanol will be OK....At least up to say 12k'

In other wrds for most of my goofing off.

The one remaining piece I need to find out is if the Proseal will withstand ethanol....I keep meaning to call Flamemaster, just haven't gotten around to it yet.

Fuel system compatibility (AFP) and VL are a non issue as far as my airplane is concerned....Water dropping out of suspension looks like it can be mitigated by doing both a sump check and hygrometer test.

Looking at the research Baylor did with AGE 85, they sugest a Specific gravity of over 0.8 has too much water in it....Hence it may drop out of solution at altitude.

I need to read up on this last statement a little more but I tentatively think it will be OK to use.

Of course the final test will be a tank of 100ll/93 in one tank while gasohol run in the other for a few weeks.

Frank

Mark Frederick used to fly his rocket with one tank filled with E85, back about five years ago. I don't remember him having any problems. I think the problems with proseal softening had to do with MTBE, not ethanol. Now that MTBE has been legislated out of existence, proseal softening likely isn't a problem.

No STC Required

STC stands for Supplemental Type Certificate. Since an amateur-built doesn't have a Type Certificate, there's nothing to Supplement.

Good to know

rocketbob said:

Mark Frederick used to fly his rocket with one tank filled with E85, back about five years ago. I don't remember him having any problems. I think the problems with proseal softening had to do with MTBE, not ethanol. Now that MTBE has been legislated out of existence, proseal softening likely isn't a problem.

Click to expand...

Thanks!!

Frank

Mogas in RV4

Grant,

I set up my RV6 during construction to run mogas.

I simply placed the fuel pump ( and the gascolator) in the wing root so they were in a cool spot. It also meant that the pump was doing more pushing than pulling, which reduces potential for vapor lock. I also firesleeved all the firewall forward fuel hoses and placed heat shields where appropriate. I plumbed a vapor return line from the carb fuel inlet back to the fuel tank via a valve, but have never used it. I can happily run premium unleaded in my O-320 D1A 160 hp Lycoming, but more often run a mix of avgas and unleaded. The exhaust and the plugs, as well as the oil, are much cleaner than on Avgas.

Martin

rocketbob said:

Mark Frederick used to fly his rocket with one tank filled with E85, back about five years ago. I don't remember him having any problems. I think the problems with proseal softening had to do with MTBE, not ethanol. Now that MTBE has been legislated out of existence, proseal softening likely isn't a problem.

Click to expand...

What is MTBE?

SvingenB said:

What is MTBE?

Click to expand...

Methyl tertiary Butyl Ether.

It was used as an octane enhacer in mogas, but no longer.

Bit more toxic than gasoline itself, and does not play well with the environment when leaked from underground storage tanks.

A question...

Harvey said:

Grant,

I set up my RV6 during construction to run mogas.

I simply placed the fuel pump ( and the gascolator) in the wing root so they were in a cool spot. It also meant that the pump was doing more pushing than pulling, which reduces potential for vapor lock. I also firesleeved all the firewall forward fuel hoses and placed heat shields where appropriate. I plumbed a vapor return line from the carb fuel inlet back to the fuel tank via a valve, but have never used it. I can happily run premium unleaded in my O-320 D1A 160 hp Lycoming, but more often run a mix of avgas and unleaded. The exhaust and the plugs, as well as the oil, are much cleaner than on Avgas.

Martin

Click to expand...

Do you have the boost pump in only one wng root and always start up, take off and land on that tank or is there a pump at each tank? If two boost pumps, do you have one switch for both pumps or 2 switches to select the the tank in use at the time?

Thanks the info.

Mogas in RV4

Hi Jim,

My set up is a variation of the usual Vans system, and based on one drawn by Tony Bingelis. It uses all Vans supplied components. Instead of the boost pump sitting inside the cockpit, it is in the wing root. Instead of the gascolator on the hot firewall, it also is in the wing root, where it is much, much cooler.

By pushing the fuel and keeping components cool, vapor lock is much harder to get. I have been flying the 6 this way for 4 years in temps up to 42 degrees C (over 30 C in the air) with no problems

Martin

ddurakovich said:

Methyl tertiary Butyl Ether.

It was used as an octane enhacer in mogas, but no longer.

Bit more toxic than gasoline itself, and does not play well with the environment when leaked from underground storage tanks.

Click to expand...

OK. I checked, and here in Norway it is used alot, up to 15%, and I see no signs of phasing it out, unless maybe more ethanol is used? I plan to use mogas. Are you sure it is the MTBE that destroys the tanks?

ALMOST impossible in fact

Harvey said:

Hi Jim,

My set up is a variation of the usual Vans system, and based on one drawn by Tony Bingelis. It uses all Vans supplied components. Instead of the boost pump sitting inside the cockpit, it is in the wing root. Instead of the gascolator on the hot firewall, it also is in the wing root, where it is much, much cooler.

By pushing the fuel and keeping components cool, vapor lock is much harder to get. I have been flying the 6 this way for 4 years in temps up to 42 degrees C (over 30 C in the air) with no problems

Martin

Click to expand...

If your run fuel lines close to exhaut pipes then it is still possible.

Remember also that a carbed engine only runs at 5 psi or so..My FI'd motor runs at 35+...Thus with both my electric pumps in the wingroots (and no mechanical pump to soak up heat from the engine block) VL is a complete non issue...

At least thats the theory...I did the same thing with a carb'd soob in a Zodiac and that never VL'd in 400 hours either. The high pressure FI'd sysytem has an even greater margin against VL.

Frank

Thanks for all the infomative replies. I'll have to investigate all the issues as far as 90 degree fittings and single or dual pumps. I have a single fuel pump switch and no placards as to start up or other times when the boost pump is used. Hopefully I have 2 boost pumps in the wing roots but it sounds like most have a single pump FWF. I know next to nothing about this plane other than it flies great. I'm going to have to do an owner assist inspection in April and get less dumb in the near future. Oregon is a bit far to go for the generously offered assistance, I'll probably do it with Troy Grover although he is not a fan of mogas.

And thanks for the No-STC needed answer to the unstated question. It was in the back of my mind to ask but the original post was getting long.

Thanks again guys.

PS, how hard would it be to track down all the fittings to check for 45 vs 90? Or put another way, how likely is it that there are fittings between the tanks and FWF area that might be hard to locate?

Fittings are a non issue

There are three ways to go on fittings, and flexible hoses....

1) Genuine Aeroquip hardware...or the like from Vans or Aircraft Spruce.

2) Same thing but from speed shops such as Summit Racing......Seems very quality gear

3) Go to your local hydraulics shop and buy steel fittings...They are called JIC threads and this is exactly the same as aircraft stuff except its made from steel and thus heavier but considerably cheaper...You won't get firesleeved hoses but you can buy firesleeve and they can assemble the firesleeve over the top of the hose.

Sounds like you have a carbed RV4?..If so the boost pumps in the wingroots is much easier because you don't need a pressure regulating valve when using the Facet pumps.

For me personally if you have two boost pumps then the mechanical pump is more of a liability than useful...This assumes each pump supplies adequate fuel (should easily) and each ump is wired independantly.

You will then have the same system I had on my old Zodiac and as I said I had 400 hours on the airplane before I sold it.

Frank

I dont see you need wing root pumps (or have the space).

Grant - I just read this thread and am a little concerned that no one has stated the way VANS intended things. They put the fuel pump inside the fuse just after the selector valve. Since the pump is level with, or below the level of the fuel in the tanks you are hardly likely to get vapour lock in that section of the system. VANS then pushes the fuel forward to a firewall forward gascolator and then to the mechanical pump. (I think you will have quite a problem on a -4 finding room for a pump at the wing root by the way.)

Because I think one of these days I may find myself running on Mogas, or not running, I have brought the gascolator inside the cabin so it does act as a cooking pot. I plan to use it more as a filter than anything else. I will use the wing drains to check for water. Otherwise mine is close to standard.

There are some pictures here.

http://gikonfuse.blogspot.com/2008/01/fuel-system-inside-fuselage-is-complete.html#links
and here
http://gikonfwf.blogspot.com/2008/01/baffles-exhaust-stays-fuel-and-carb.html#links

I am in the UK so its not so hot, but even with the gascolator on the firewall in VERY hot weather I only ever had a brief problem on start up once on a -9a I used to have.

Good luck.

Ah, very good. Now I know what to look for when I get the covers off. I agree that VL before the pump in that configuration is darn near impossible without a significant heat source in that space. Wing root pumps would be ideal but I don't see a problem with VL behind the firewall and below the tanks.

Thanks again.

Hi Steve,

Whilst I agree that changing anything from the Van's plans is inviting trouble, relocating the boost pump from inside the cockpit to outside in the wing root is very straight forward. The difference in distance is something like a few inches..
Moving it to the wing root gets the pump and its connections out of the cockpit and into an even cooler location. I even fitted the gascolator in the wing root, so there is sufficient room. Another benefit is that I was able to place the gascolator upstream (ie before) the pump, so that the pump gets filtered fuel.
The Facet pumps are very susceptible to damage from debris.

I am very happy with the result.

Cheers

Martin

Martin, are you talking about the wing root of a -4? You dont say what you built. I know we are on a -4 thread but I am impressed if you have. Just want to be sure. Steve.

RV7a

In each forward wingroot section I got

A high pressure fuel pump (much bigger than a Facet)
Pressure relief valve.
Prefilter on suction side of pump
fuel supply (flop tubes)
fuel return to tank
fuel supply to engine.

I don't use a Gascolator.

Each pump is switched independantly and does not have an engine driven pump.

Frank

Brand

Frank

I know you have provided this info before but what brand and model of pumps did you use? My AFP high pressure pump is on its last legs and looking at your setup as an alternative.

My pumps came from NAPA

Part # is 2P74028

They now have an upgraded version of this pump for about $130.....You will see NAPA lists them at 5psi pumps...This is a mistake in their catalogue...They will run at 100psi happily.

This is the same pump that Tracy Cook at RWS has been running in his fi'd RV4 without issue.

The thread on one end is a #3 ORB (O ring boss) which is 3/8UNF thread. I tap these out to 7/16ths (#4 ORB) as the fitting is beefier but that is optional.

The fittings provided are 5/16ths barbed hose...I'm OK with that for the inlet but change the fitting for flared fitting on the discharge.

Frank