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AVGAS Alternative Engines

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glibejaja

I'm New Here
Hi all,

I'm currently looking into building my first homebuilt aircraft, and because I chose the most expensive hobby, I want to have some assurance about my future project. For background, I am looking to build a tandem seat aircraft primarily for aerobatic purposes.

With that in mind, I am under the belief that AVGAS (100LL) will disappear by the time my little RV will be complete (2030-2035). So, I'm looking at engines that would be able to run off the next best thing, whether that's MOGAS, 91UL, Jet-A1 or some sustainable aviation fuel (SAF).

I understand that Rotax is the best choice for versatility, however it’s not common to see Rotax outside of the RV-12 and that one RV-4. I heard Lycoming can take some high-octane UL fuel (100UL), can it do lower? Does anyone have any suggestions for engines that won’t be affected by the phasing out of 100LL (and potentially other fuels).
 
glibejaja said:
Hi all,

I'm currently looking into building my first homebuilt aircraft, and because I chose the most expensive hobby, I want to have some assurance about my future project. For background, I am looking to build a tandem seat aircraft primarily for aerobatic purposes.

With that in mind, I am under the belief that AVGAS (100LL) will disappear by the time my little RV will be complete (2030-2035). So, I'm looking at engines that would be able to run off the next best thing, whether that's MOGAS, 91UL, Jet-A1 or some sustainable aviation fuel (SAF).

I understand that Rotax is the best choice for versatility, however it’s not common to see Rotax outside of the RV-12 and that one RV-4. I heard Lycoming can take some high-octane UL fuel (100UL), can it do lower? Does anyone have any suggestions for engines that won’t be affected by the phasing out of 100LL (and potentially other fuels).
Click to expand...

Good news - you can use many Lycoming-type engines with good mogas. There are 100s on this forum that do so, and probably 1000s around the world. The main issues are compression and fuel system compatibility. If you build your fuel system right, and use a "normal" compression engine, you'll be able to run premium mogas without problem.
 
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Proper manipulation of the ignition timing will allow the typical Lycoming to run very well on auto gas. My 540 was built for the eventuality of 100LL going away.
 
Toobuilder said:
Proper manipulation of the ignition timing will allow the typical Lycoming to run very well on auto gas. My 540 was built for the eventuality of 100LL going away.
Click to expand...

Doing so, the SDS is a large part of that?
How did you address the 2 electric busses for sds redundancy?
Did you put an O2 sensor in your exhaust yet?

I’m looking to put the sds in my ,not built yet,RV8 O-360. I’ve held off on ignition and fuel just for the SDS and addressing different fuels. I have 9:1 pistons which I believe will be just fine with the SDS efi setup.

I’m not sure just electronic ignition(Pmags, etc) and mechanical fuel injection can fully address different fuels.

Thanks for any input.
 
Toobuilder said:
Proper manipulation of the ignition timing will allow the typical Lycoming to run very well on auto gas. My 540 was built for the eventuality of 100LL going away.
Click to expand...

I'm starting my RV-14A build, which will have an IO390 119 EXP (currently planning Pmags). Where do I learn what's required to build for the eventuality of 100LL going away?
 
AutoGas

I'm running 100% E10 93 oct autogas. the engine is a IO-360-B1B (vertical sump) with 8.4/1 compression.
The key to running ethanol autogas was solved by the automotive industries years ago. Keep the fuel under pressure from the fuel tank to the engine to eliminate vapor lock. Even 5psi block pumps constantly running in the wing roots will achieve this. Use ethanol compliant plumping (Teflon hoses everywhere). Avoid 90* turns in the fuel lines. Use 93 Oct autogas for an engine requiring a minimum of 91 oct. Keep the engine driven pump as it's ethanol compliant, and a good backup (in Brazil they use the same mechanical Lycoming pump with 80+% ethanol gas!). And replace all the quick drain "O" rings with hardware store butyl rubber equivalents.
You engine will thank you by running well past TBO for NOT running leaded fuels.....




glibejaja said:
Hi all,

I'm currently looking into building my first homebuilt aircraft, and because I chose the most expensive hobby, I want to have some assurance about my future project. For background, I am looking to build a tandem seat aircraft primarily for aerobatic purposes.

With that in mind, I am under the belief that AVGAS (100LL) will disappear by the time my little RV will be complete (2030-2035). So, I'm looking at engines that would be able to run off the next best thing, whether that's MOGAS, 91UL, Jet-A1 or some sustainable aviation fuel (SAF).

I understand that Rotax is the best choice for versatility, however it’s not common to see Rotax outside of the RV-12 and that one RV-4. I heard Lycoming can take some high-octane UL fuel (100UL), can it do lower? Does anyone have any suggestions for engines that won’t be affected by the phasing out of 100LL (and potentially other fuels).
Click to expand...
 
DonMcKee said:
I'm starting my RV-14A build, which will have an IO390 119 EXP (currently planning Pmags). Where do I learn what's required to build for the eventuality of 100LL going away?
Click to expand...

Learn about octane rating and compression ratio, and how higher compression requires higher octane.
Learn that there are three different ways of measuring octane.
Search for calculators that show how much more HP you get with say 10:1 compression vs. 8.7:1 compression. Many hot rod oriented websites have these.

With enough ignition timing retard you can run lower octane.

So, some opt for higher compression than stock (to get performance), then retard the timing (to run on lesser fuel), which drops performance.

Bottom line, the higher the compression ratio the more you are tied to 100 octane fuels.

Oh, and just because some motorcycle engine says it runs 14:1 compression... on 90 octane... don't believe that is translatable to a Lycoming.

Enjoy the learning process!
 
glibejaja said:
With that in mind, I am under the belief that AVGAS (100LL) will disappear by the time my little RV will be complete (2030-2035). So, I'm looking at engines that would be able to run off the next best thing, whether that's MOGAS, 91UL, Jet-A1 or some sustainable aviation fuel (SAF).
Click to expand...

Pick your plane and Start building as you have plenty of time before you need to know what engine you are going to buy. A lot can/will happen in the next 5-10 years but not really predictable. Look how much has changed on a Lycoming in the last 80 years. Things under development now that look new and shiny are very unlikely to be around in 5 years.
 
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Lycoming

No need to look any further, Lycoming will do just fine.
Many advances have been made in fuel injection and ignition systems.
Most of these are none certified and do not have the blessing of "Mr Lycoming"

What you will see is two kinds of responses; those who use premium pump mogas in their Lycomings for years without issues and those who do not use mogas but know better and predict doom and gloom if you dare to use anything but certified lead polluting avgas.
You are right, 100LL will be phased out before too long and the new replacement will be even more expensive and who knows what the unknown devil will do to our Lycomings, only time will tell.

Hundreds of us have been using premium pump mogas without issues for many years and continue to do so in the face of sometimes harsh criticism.
There are a few modifications necessary to make mogas work properly.
Choosing the right Injection/ignition system and most of all designing a fuel system that runs cool, the same goes for the entire engine compartment.
Many of us have entered the "twilight Zone" of using mogas by filling up one tank with avgas and the other with mogas.It is an excellent way to experiment and verify that your system works even in the most extreme of circumstances.
Good luck pursuing your new adventure.
 
2theskyy said:
Doing so, the SDS is a large part of that?
How did you address the 2 electric busses for sds redundancy?
Did you put an O2 sensor in your exhaust yet?

I’m looking to put the sds in my ,not built yet,RV8 O-360. I’ve held off on ignition and fuel just for the SDS and addressing different fuels. I have 9:1 pistons which I believe will be just fine with the SDS efi setup.

I’m not sure just electronic ignition(Pmags, etc) and mechanical fuel injection can fully address different fuels.

Thanks for any input.
Click to expand...

The SDS EFI fuel system is essentially automotive, so that does make the compatibility issue with auto fuel "easy". Also, as others mentioned, proper attention to fuel system design elements (no 90's, pusher fuel pumps, cool routing, etc) is also important, whether EFI or mechanical FI. But finally, a correct initial curve is what really keeps the detonation demons at bay. I have dyno tested various curves and even a substantial retard when well ROP is almost no reduction in power.

THAT said, no, a Pmag is not capable of the reduction in initial curve to do this correctly. That product just does not have the flexibility of the SDS ignition products.
 
Toobuilder said:
The SDS EFI fuel system is essentially automotive, so that does make the compatibility issue with auto fuel "easy". Also, as others mentioned, proper attention to fuel system design elements (no 90's, pusher fuel pumps, cool routing, etc) is also important, whether EFI or mechanical FI. But finally, a correct initial curve is what really keeps the detonation demons at bay. I have dyno tested various curves and even a substantial retard when well ROP is almost no reduction in power.

THAT said, no, a Pmag is not capable of the reduction in initial curve to do this correctly. That product just does not have the flexibility of the SDS ignition products.
Click to expand...

My parallel valve IO-360 with dual pMags runs just fine on 93 unleaded pump gas.

Carl

Carl.
 
Testing was done on the bone stock 320-B and it worked *as in no knock* with 91 octane.
https://www.tc.faa.gov/its/worldpac/techrpt/ar99-70.pdf
Read the doc and notice all the edge cases they pushed into. Then ask yourself, would I ever fly near those conditions? High CHT, high intake air, temp, high oil temp, etc.
Decision tree:
a) no, I can't ever see having high temps -> then this testing is of no interest to you
 
Another thing to keep in mind: if you use capacitive (instead of float-style) fuel senders, you will need to re-calibrate them whenever you switch fuel types. Or so I heard. Not a huge problem if you switch over once and never go back, but probably an annoyance if you go back and forth or mix fuels.
 
2theskyy said:
Do you use an engine bridge with your Pmags to further control some parameters for your 93 use?
Click to expand...

No. For the four cylinder pMag the “jumper in” timing curve has proven to work well with my standard compression engines. On the six cylinder pMag you set the timing curve on install to whatever you want.

My first RV started off life 20 years ago with another brand of EI. It provided timing readout and timing adjustment in the cockpit. Other than playing around with it the first few hours it was never touched. I can report I biased the timing down as CHTs were not what I wanted (the timing curve on these EIs was too aggressive). Those ignition were replaced with pMags at 300hrs after several failures with the original EI installs. The pMags have been flawless. I have them on all three builds.

The data I’ve read on engine timing demonstrates to me that for my type of flying a max of 9 degrees advance is the best operating curve. Note - the conditions to get that much advance is atypical - as in high altitude. Full power is at base timing (for me 25 degrees). You can retard the base to 2-3 degrees if you like and not loose much. Good way to make sure your engine is ok with pump gas.

Carl
 
SDS or EFII

As others have mentioned, automatic advance/retard electric ignitions along with high pressure fuel delivery systems such as SDS or EFII are the key to being able run alternative fuels such as auto fuel.

I have the standard 180hp 8.5:1 CR engine in my -8. I exclusively run auto fuel…unless I’m on a cross-country and can’t get it. I use both ethanol and ethanol free without a problem. As long as your plumbing is compatible with ethanol, the engine itself really doesn’t care what it’s burning.

It’s true, the higher the octane the better, but I run 90 all the time and my engine has never missed a beat. It’s definitely more critical to run higher octane if you have a high compression engine. The higher the compression ratio, the narrower the detonation margin becomes. With an electronic ignition, you have some control over detonation by manipulating the advance/retard, but compression ratio remains a big factor. I’m currently building a -14 which has an 8.9:1 CR 390 in it. I’ll have to pay a little more attention to the detonation margins, but I still plan on running auto fuel in it.
 
SDS/EFII

As others have mentioned, automatic advance/retard electronic ignitions along with high pressure fuel delivery systems such as SDS or EFII offer are the key to being able run alternative fuels such as auto fuel. These systems also make vapor lock a thing of the past…even when burning auto fuel.

I have the standard 180hp 8.5:1 CR engine in my -8. I exclusively run auto fuel…unless I’m on a cross-country and can’t get it. I use both ethanol and ethanol free without a problem. As long as your plumbing is compatible with ethanol, the engine itself really doesn’t care what it’s burning.

It’s true, the higher the octane the better, but I run 90 all the time and my engine has never missed a beat. It’s definitely more critical to run higher octane if you have a high compression engine. The higher the compression ratio, the narrower the detonation margin becomes. With an electronic ignition, you have some control over detonation by manipulating the advance/retard, but compression ratio remains a big factor. I’m currently building a -14 which has an 8.9:1 CR 390 in it. I’ll have to pay a little more attention to the detonation margins, but I still plan on running auto fuel in it.
 
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Toobuilder said:
"Fine" is not the same thing as "correct".
Click to expand...

The only way to be "correct" is to be certified - and this is EAB. Please don't be that guy.

It is quite possible to run 91+ octane autofuel without vapor lock or other problems - your modern automobile does it everyday. I would strongly suggest looking into the SDS or EFII products, personally I prefer SDS.

I have had my aircraft up to FL210 a couple times on 93 octane Walmart premium autofuel without issue and commonly fly it in the mid-upper teens for cruise, and regularly use it in the heat of summer in west Texas without vapor lock or hard start issues. It's not precisely simple, but yes it can be done.

Keep the fuel cool, and under pressure, and it won't boil. SDS accomplishes this with a pressurized fuel loop running 40+ psi and returning the excess to the tank - no chance for it get hot and want to boil. After a "hot" stop just turn the fuel pump on, wait about 10 seconds, and you have cool fuel at the injectors for a normal start, life is good.
 
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airguy said:
The only way to be "correct" is to be certified - and this is EAB. Please don't be that guy.

It is quite possible to run 91+ octane autofuel without vapor lock or other problems - your modern automobile does it everyday. I would strongly suggest looking into the SDS or EFII products, personally I prefer SDS.

I have had my aircraft up to FL210 a couple times on 93 octane Walmart premium autofuel without issue and commonly fly it in the mid-upper teens for cruise, and regularly use it in the heat of summer in west Texas without vapor lock or hard start issues. It's not precisely simple, but yes it can be done.

Keep the fuel cool, and under pressure, and it won't boil. SDS accomplishes this with a pressurized fuel loop running 40+ psi and returning the excess to the tank - no chance for it get hot and want to boil. After a "hot" stop just turn the fuel pump on, wait about 10 seconds, and you have cool fuel at the injectors for a normal start, life is good.
Click to expand...

The response was to a question I had asked about SDS on his plane. I did not take it nor do I think he meant it the way you portrayed your response. But I don’t want to speak for him on what he meant. There’s a lot of good info and advice in this thread so let’s not turn it into a certified vs experimental thread.

Thank you
 
airguy said:
The only way to be "correct" is to be certified - and this is EAB. Please don't be that guy...
Click to expand...

I was responding to a Pmag owner who does not personally suffer any ill effects due to the aggressive advance curve of his ignition. "it runs fine". This is a common sentiment among those who have not done the experimentation that I (and I presume YOU) have done to go beyond "fine" and attain "correct".

The point is simply to illustrate that just because your engine combination does not explode with a particular ignition curve does not mean it is performing well either. There can be a wide gulf between "correct" and "not exploding" (fine).

Some engine combinations are much closer to the bad end of that scale (as evidenced by the need to mechanically spoof the Pmag timing on AV engines, as one well known example), and others are further away. But in the end, "one size does NOT fit all", and when you are playing with compression and auto gas, it's a good strategy to choose the ignition and fuel hardware that can be tuned to accommodate those variables.

Or just follow other people and hope for the best.
 
Toobuilder said:
I was responding to a Pmag owner who does not personally suffer any ill effects due to the aggressive advance curve of his ignition. "it runs fine". This is a common sentiment among those who have not done the experimentation that I (and I presume YOU) have done to go beyond "fine" and attain "correct".
Click to expand...

Point taken, and I apologize for stepping into the middle of a conversation. I suppose I have a taken a bit of a "hair trigger" with those that like to say "You can't do that!"

Those who say something is impossible should not associate with those who are doing it.
 
Added benefit of unleaded fuel in a Lycoming...100 hr oil changes. Filter is still changed at 50 hrs though
 
This is a timely thread.

I too am worried that 100LL will even more expensive. At this point 100LL purchased off airport and pumped through my transfer tank in the bed of my truck and non-ethanol mogas is pretty close to the same price. So, other than the lead contaminating my oil there isn't really much savings. Where the real savings comes from is using the utter garbage that comes out of the local chevron station pump.

I'm not building an RV, and for reasons listed over here I decided to skip the EFI setup and go with airflow performance because it doesn't return to tank.

I have followed what N427EF has posted elsewhere on the forum where I have a small manifold after the mechanical fuel pump that bleeds 7-8gph back to the tank (to cool it and give a place for vapor to go) through a duplex valve as well as blast air to a mech pump shroud. I also installed the fuel pressure sensor and a fuel temp sensor in the same little manifold. Anyone else do this? Anyone have any thoughts about this setup?

I need to develop a test procedure during my initial hours to confirm operation before I can trust it so any ideas on how to do that would be welcome. I'm hoping that the post pump fuel temp will give me an idea of what is going on and alert me to issues before I have vapor lock.

Another question is the vapor lock and corrosion difference between non-ethanol and ethanol fuel. If they are the same, then I might be able to validate that the system works on junk fuel just fine, if not, I might be stuck with non-ethanol which is cheaper, but not cheapest.

If I had an RV with a single tank pickup I would have for sure run EFI and just pressurized the entire deal, but I want to put two full sized bikes, wife, cooler, astrophotography mount, and camping kit in the airplane and hit all of the PWN strips and since I already live in the PNW, going slower doesn't really matter as much.
 
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OK I as another RV-6A 0-360 driver converted it to SDS 120 hours ago and burn Costco premium with NO problems.
Yes I personally think leaded fuel is on it's way out. "Some day"
I really like the idea of the Andair 6 port fuel selection valve WITH the return to tank that is actually needed with the SDS system.
My engine starts immediately on a hot start. One blade and off we go.
Cold start is a few blades.
Yes I replaced all the fuel lines with Teflon braided lines and am real happy with the system.
Dual electric fuel pumps switched separately. Great filter setup.
Love the little lean/rich knob. Tune on the go if needed.
My luck varies Fixit
 
Strictly speaking, a duplex fuel valve is not "required" for a return style EFI like SDS, but it makes fuel management much easier.

One can port the return to a fixed tank, but you better make sure that tank has room for the returning fuel - just like the aux tank transfer on a 1956 Piper Tri Pacer. Get it right and you have access to all the fuel available - get it wrong and you dump all the aux fuel overboard.
 
Toobuilder said:
Strictly speaking, a duplex fuel valve is not "required" for a return style EFI like SDS, but it makes fuel management much easier.

One can port the return to a fixed tank, but you better make sure that tank has room for the returning fuel - just like the aux tank transfer on a 1956 Piper Tri Pacer. Get it right and you have access to all the fuel available - get it wrong and you dump all the aux fuel overboard.
Click to expand...

That's the way the new Bristell B23 does it. Returning permanently to the left tank. No duplex selector valve. This type of aircraft is now in use at many flying clubs, including the one I am a member of. It's flown by any random club member and no problems so far. This proofs that the concept works. Duplex valve would be nicer but it"s not really mandatory.
 
akschu said:
Another question is the vapor lock and corrosion difference between non-ethanol and ethanol fuel. If they are the same, then I might be able to validate that the system works on junk fuel just fine, if not, I might be stuck with non-ethanol which is cheaper, but not cheapest.
Click to expand...

That's a very interesting question. Is there any data/experience on the vapor lock part?
 
KayS said:
That's a very interesting question. Is there any data/experience on the vapor lock part?
Click to expand...

Other than from personal experience, I really can’t speak much with regards to corrosion, but after several years of running standard pump gas with ethanol, I haven’t noticed any. It could be because I cycle through quit a bit of it and no moisture has a chance to separate, but I haven’t personally seen any corrosion.

Regarding vapor lock, if the pumps aren’t having to pull the fuel uphill, it’s virtually impossible to vapor lock one of these high pressure/return fuel systems…regardless if the fuel ethanol or non ethanol. Remember, vapor lock is going to occur pre pump, (suction side) not post pump (pressure side).
 
KayS said:
That's the way the new Bristell B23 does it. Returning permanently to the left tank. No duplex selector valve. This type of aircraft is now in use at many flying clubs, including the one I am a member of. It's flown by any random club member and no problems so far. This proofs that the concept works. Duplex valve would be nicer but it"s not really mandatory.
Click to expand...

Interesting, never heard of that aircraft before. Trying to figure how I would consistently (I'm anything but consistent...) manage a fuel system like this. I assume it has very accurate fuel gauges.
 
Mark33 said:
Other than from personal experience, I really can’t speak much with regards to corrosion, but after several years of running standard pump gas with ethanol, I haven’t noticed any. It could be because I cycle through quit a bit of it and no moisture has a chance to separate, but I haven’t personally seen any corrosion.

Regarding vapor lock, if the pumps aren’t having to pull the fuel uphill, it’s virtually impossible to vapor lock one of these high pressure/return fuel systems…regardless if the fuel ethanol or non ethanol. Remember, vapor lock is going to occur pre pump, (suction side) not post pump (pressure side).
Click to expand...

I imagine few have actually read Lycomings position on alternate fuels, I hadn't

https://www.lycoming.com/contact/knowledge-base/insights

They seem to be more concerned with vapor issues rather than corrosive issues.
 
Ralph Inkster said:
Interesting, never heard of that aircraft before. Trying to figure how I would consistently (I'm anything but consistent...) manage a fuel system like this. I assume it has very accurate fuel gauges.
Click to expand...

I think it's just a math exercise like it is now.... Consume from the "return" side tank until you have excess headroom; switch to the other tank until the first tank is nearing full again.

The thing to watch is the rate at which each tank depletes. Assuming a 50% bypass, then a 10GPH fuel burn is actually pumping 20GPH out of the tank. On one tank, half goes back in, but on the other, 20 GPH goes out and NONE comes back (10 GPH goes back to the OTHER tank)
 
Toobuilder said:
I think it's just a math exercise like it is now.... Consume from the "return" side tank until you have excess headroom; switch to the other tank until the first tank is nearing full again.

The thing to watch is the rate at which each tank depletes. Assuming a 50% bypass, then a 10GPH fuel burn is actually pumping 20GPH out of the tank. On one tank, half goes back in, but on the other, 20 GPH goes out and NONE comes back (10 GPH goes back to the OTHER tank)
Click to expand...

Hi Michael
That or similar process would definitely work. I would still be unsure about a consistent output if a pilot overload situation plays in - heavy traffic, pattern work, rough air, bouncing gauges, dodging weather, etc. The return to feed tank method would be mentally easier for me.
 
No doubt it's easier to manage with a duplex valve. I spent a lot of time trying to convince myself I could manage the "fixed return" system when I went with EFI, but in the end the "one time" pain of the added modification time of duplex won out.
 
Toobuilder said:
I think it's just a math exercise like it is now.... Consume from the "return" side tank until you have excess headroom; switch to the other tank until the first tank is nearing full again.

The thing to watch is the rate at which each tank depletes. Assuming a 50% bypass, then a 10GPH fuel burn is actually pumping 20GPH out of the tank. On one tank, half goes back in, but on the other, 20 GPH goes out and NONE comes back (10 GPH goes back to the OTHER tank)
Click to expand...

Geeez... no need to make a doctoral thesis out of it. :D You just tell John Doe to keep in mind there should be some air in the left tank when running on the right one. And it can't hurt to have calibrated fuel gauges.
 
A lot less thinking involved with the Duplex valve and less to go wrong. Over 99% of our EFI customers have gone with the Duplex valve and I'd say virtually 100% on RVs.
 
Nothing to think about

As mentioned, the simplest installation to deal with a return system is an Andair
duplex valve.
What I don't like about the duplex valve is the considerable expense and an unavoidable rats nest of fuel lines converging in one place. In a RV-10 for instance, this valve tower extends about 6 inches down leaving almost no room for heater hoses etc.
A better option IMHO is to use an Andair valve for supply fuel and use Vans provided valve for return fuel. Mine are located in a tandem setup, standard location as per plans for the main valve and 5 inches behind it the return valve.
The only downside side is that you have to switch two valves every time you change the selector "I know, its a real chore".
In almost 800 hours of flying I haven't ever forgotten to move both selectors.
Worst thing that could happen, you'll pump your precious fuel overboard but you'll have a full tank when you realize it and you have at least 2 hours of flying time left to think about that mistake.
On the plus side, you'll have the benefit of transferring fuel from one tank to the other if for any reason you think you need to do that.
Fuel flow is metered past the return port and is of no consequence as long as you don't exceed a required minim fuel flow for full power operation.
In my case, 26GPH with a 50% safety margin 39GPH.
My Airflow performance boost pump delivers 46 GPH as tested minus 6 GPH return.
 
N427EF said:
As mentioned, the simplest installation to deal with a return system is an Andair
duplex valve.
What I don't like about the duplex valve is the considerable expense and an unavoidable rats nest of fuel lines converging in one place. In a RV-10 for instance, this valve tower extends about 6 inches down leaving almost no room for heater hoses etc.
A better option IMHO is to use an Andair valve for supply fuel and use Vans provided valve for return fuel. Mine are located in a tandem setup, standard location as per plans for the main valve and 5 inches behind it the return valve.
The only downside side is that you have to switch two valves every time you change the selector "I know, its a real chore".
In almost 800 hours of flying I haven't ever forgotten to move both selectors.
Worst thing that could happen, you'll pump your precious fuel overboard but you'll have a full tank when you realize it and you have at least 2 hours of flying time left to think about that mistake.
On the plus side, you'll have the benefit of transferring fuel from one tank to the other if for any reason you think you need to do that.
Fuel flow is metered past the return port and is of no consequence as long as you don't exceed a required minim fuel flow for full power operation.
In my case, 26GPH with a 50% safety margin 39GPH.
My Airflow performance boost pump delivers 46 GPH as tested minus 6 GPH return.
Click to expand...


That's a great idea to deal with the return, I think. Was so afraid of the duplex I didn't install a return line. Plumbing the single storey was painful enough. Will reinvestigate the topic as I plan to switch to mogas entirely. Till now I have 100 % avgas in one tank for takeoff/landing and using the cheap stuff for cruise in the other one.
 
Mogas Return

So why is a return flow necessary if the fuel to the engine is ALWAYS under pressure? Seems like an additional place for a failure mode. In over 2000 Hrs of operation on just 93 oct E10 gas, I've never had a return flow to the selected tank. If you have the fuel pressurized out of, or near the tank source, it's almost physically and mathematically impossible to get a vapor lock. This is how the auto industry solved the problem many years ago....





KayS said:
That's a great idea to deal with the return, I think. Was so afraid of the duplex I didn't install a return line. Plumbing the single storey was painful enough. Will reinvestigate the topic as I plan to switch to mogas entirely. Till now I have 100 % avgas in one tank for takeoff/landing and using the cheap stuff for cruise in the other one.
Click to expand...
 
Belt and suspenders

I agree with Fred and I have friends who fly without issues just as Fred describes.
Seems like an additional place for a failure mode.
Click to expand...
True as well, a bit of an insurance policy but I think it is probably not needed and yet most of the modern systems like EFFI and SDS use return lines as far as I know.
In over 2000 Hrs of operation on just 93 oct E10 gas, I've never had a return flow to the selected tank.
Click to expand...
I would most certainly not argue with someone who has as many hours on 93 E10.
I am aiming to do the same
 
Fred.Stucklen said:
So why is a return flow necessary if the fuel to the engine is ALWAYS under pressure? Seems like an additional place for a failure mode. In over 2000 Hrs of operation on just 93 oct E10 gas, I've never had a return flow to the selected tank. If you have the fuel pressurized out of, or near the tank source, it's almost physically and mathematically impossible to get a vapor lock. This is how the auto industry solved the problem many years ago....
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Speaking only from an SDS/EFII perspective, they both utilized a high pressure fuel rail and a fuel pressure regulator which maintains a constant fuel pressure and fuel flow to the electronic fuel injectors. All of this is controlled via vacuum/manifold pressure and is required to deliver the proper amount of fuel based on engine demand. The electric fuel pumps supply a lot more fuel than is ever required by the engine, so the mass majority of the fuel is returned back to the tank from which is was taken.
 
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Fred.Stucklen said:
This is how the auto industry solved the problem many years ago....
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The auto industry DOES have a return - but the pump is inside the tank so you don't see it. The electric fuel pump is cooled by the fuel flowing through it. Very low flow rates without any return can result in high local fuel temps at the pump.

If a person were to source an automotive-style fuel pump that lives in the tank and provides pressurized fuel out, then you would indeed be in the same world of fuel supply. Our tanks are pretty shallow compared to automotive tanks, so finding one that will fit may be a trick.
 
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Bonanzas

Beechcraft has been returning excess fuel to a tank for a long time. My 1956 G35 has a pressure carburetor which operates at 13 psi and 10 gph of fuel is always being returned to the left main tank. Understanding and knowledge of that is essential to operation but has never been an issue for me or others that I know. It takes an *engaged pilot but we should all be engaged all of the time. Modern fuel senders, fuel flow meters, fuel totalizers and an engaged pilot should make fuel management a nonissue IMO.
 
rmarshall234 said:
... It takes an *engaged pilot but we should all be engaged all of the time. Modern fuel senders, fuel flow meters, fuel totalizers and an engaged pilot should make fuel management a nonissue IMO.
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And when you find the secret to achieving that, put it in a bottle and you'll have more money than Bill Gates and the Tesla guy!
 
rv8ch said:
And when you find the secret to achieving that, put it in a bottle and you'll have more money than Bill Gates and the Tesla guy!
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Amen. These days they all want to follow the magenta line while they take a nap and then autoland.
 
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