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upgrading from carburated to fuel injected engine on a almost completed RV12-iS/ULS

Major-Tom

Major-Tom

Active Member
Late change of plans....
Since October 2018 I am building a RV-12is. The built comes along very nicely and without any problems. The kit quality is great and with excellent engineering down to the smallest details. What helps a lot to keep a steady pace while building, are the complete and accurate construction manuals. So best to do exactly like Vans says, when you want a quick built. That is the pure truth and I did until the avionics and engine kit. General electric and MGL / Trig Avionics was fun to do. Now the firewall is ready to hang the engine. My RV-12iS was supposed to get a carburated Rotax 912 ULS engine. It has all the fuel lines, the gascolator, the faccet fuel pump installed like in the plans chapter 27U for RV-12iS/912ULS. All electric cables and flight control cables and tubes are completely installed on top the fuel lines in the center tunnel. Now it comes: one week ago I was able to get my hands on an almost brand new 912iS Sport. It has 2 hours on it, but was sitting in a box for 6 years. Since I am building something like full experimental ( E-AB instead of ELSA) I have all the options:


1. remove all flight controls, cables etc. that are in the way to get to the fuel lines. Remove the complete fuel system. Then place a big order at vans and start all over with chapter 27iS.



2. leave all like it is. The fuel lines stay, the gascolator acts as drain point and coarse filter. Even the boost pump stays in and wired. Start with the modifications at the two blue AN6 fittings at the firewall. Place the fuel pump duo, the fine filter and the bypass at a low position firewall forward. The faccet fuel pump could provide 5psi and 30 - 40 Gph if vapor look should ever be a problem and does not slow the fuel flow when inactive. I am not sure if the Vans gascolator can provide the 25 Gph needed for the 912iS. But it should be more than enough???


3. leave the return line in but remove the supply side of the fuel system. Make a new fuel line from the tank direct forward to a shut off valve and a gascolator firewall forward mounted, like it is done and proven concept in all the RV-12 before the iS Upgrade. Fuel pumps etc. firewall forward.


What do you think? Most interesting: what did people do, who installed alternative engines like Viking or UL-Power?
Thanks for you input.
 
You may get better information here...

VAF Forums > RV Firewall Forward Section > Alternative Engines
 
Every engine has different installation requirements.
What was required for a UL Power engine will not match what is required for a Viking engine. Same goes for the 912iS.

The extensive system differences designed for the iS version of the RV-12 were done for very specific reasons. In simplest terms, it was to meet all of the installation requirements defined by Rotax.

I think it is easy to understand that if the legacy systems for the ULS engine could have been used, it would have made no sense to go to all of the effort to redesign the airplane around the new systems.

I suggest you look through the Rotax 912iS Installation Manual (available on RotaxOwner.com) and see what all is required for an installation.
About the only requirement that the ULS system meets is that it has a fuel tank that can supply fuel to the rest of teh required systems.


Major-Tom said:
Late change of plans....
Since October 2018 I am building a RV-12is. The built comes along very nicely and without any problems. The kit quality is great and with excellent engineering down to the smallest details. What helps a lot to keep a steady pace while building, are the complete and accurate construction manuals. So best to do exactly like Vans says, when you want a quick built. That is the pure truth and I did until the avionics and engine kit. General electric and MGL / Trig Avionics was fun to do. Now the firewall is ready to hang the engine. My RV-12iS was supposed to get a carburated Rotax 912 ULS engine. It has all the fuel lines, the gascolator, the faccet fuel pump installed like in the plans chapter 27U for RV-12iS/912ULS. All electric cables and flight control cables and tubes are completely installed on top the fuel lines in the center tunnel. Now it comes: one week ago I was able to get my hands on an almost brand new 912iS Sport. It has 2 hours on it, but was sitting in a box for 6 years. Since I am building something like full experimental ( E-AB instead of ELSA) I have all the options:


1. remove all flight controls, cables etc. that are in the way to get to the fuel lines. Remove the complete fuel system. Then place a big order at vans and start all over with chapter 27iS.



2. leave all like it is. The fuel lines stay, the gascolator acts as drain point and coarse filter. Even the boost pump stays in and wired. Start with the modifications at the two blue AN6 fittings at the firewall. Place the fuel pump duo, the fine filter and the bypass at a low position firewall forward. The faccet fuel pump could provide 5psi and 30 - 40 Gph if vapor look should ever be a problem and does not slow the fuel flow when inactive. I am not sure if the Vans gascolator can provide the 25 Gph needed for the 912iS. But it should be more than enough???


3. leave the return line in but remove the supply side of the fuel system. Make a new fuel line from the tank direct forward to a shut off valve and a gascolator firewall forward mounted, like it is done and proven concept in all the RV-12 before the iS Upgrade. Fuel pumps etc. firewall forward.


What do you think? Most interesting: what did people do, who installed alternative engines like Viking or UL-Power?
Thanks for you input.
Click to expand...
 
Thanks Scott, of corse I already did as suggested. The installation manuals of various 912 engines are under my pillow for some time now and I'm not new to this engines. Be assured that I am more than confident, all has been perfectly designed to meet all Rotax requirements. Surely Vans engeniers did not jump to conclusions, but considered different approches to meet or better surpass every single requirement and have choosen the best one for us builders. I just can't stop to wonder what the second best choice was?

Do you thing there is a pressure drop / fuel flow diagram aviable for the blue gascolator?


Thanks Jim, you may be right. Possibly someone can move this topic.
 
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Major-Tom said:
Thanks Scott, of corse I already did as suggested. The installation manuals of various 912 engines are under my pillow for some time now and I'm not new to this engines. Be assured that I am more than confident, all has been perfectly designed to meet all Rotax requirements. Surely Vans engeniers did not jump to conclusions, but considered different approches to meet or better surpass every single requirement and have choosen the best one for us builders. I just can't stop to wonder what the second best choice was?

Do you thing there is a pressure drop / fuel flow diagram aviable for the blue gascolator?


Thanks Jim, you may be right. Possibly someone can move this topic.
Click to expand...

Here is just one example of what I was talking about.....

A bunch of testing was done to evaluate the performance of the Gas-5 gascolator if used on an RV-12iS.

The testing proved it was nearly worthless.

The 912iS engine has a very high constant fuel flow looping through the entire system fuel system and then back to the tank via a return path.
High enough that the gascolator wasn't even able to remove any water that was purposefully induced into the fuel for testing.

Rotax specifies a specific micron value of filtration up steam of the electric fuel pumps. Changing the screen in the gascolator to the correct micron value induces a lot of unacceptable flow resistance because of the small screen size.
 
rvbuilder2002 said:
Here is just one example of what I was talking about.....

A bunch of testing was done to evaluate the performance of the Gas-5 gascolator if used on an RV-12iS.

The testing proved it was nearly worthless.

The 912iS engine has a very high constant fuel flow looping through the entire system fuel system and then back to the tank via a return path.
High enough that the gascolator wasn't even able to remove any water that was purposefully induced into the fuel for testing.

Rotax specifies a specific micron value of filtration up steam of the electric fuel pumps. Changing the screen in the gascolator to the correct micron value induces a lot of unacceptable flow resistance because of the small screen size.
Click to expand...


Thank you Scott, this is the kind of high quality information I was hoping to get. Could you possibly tell me the main reason for the pumps behind the baggage bulkhead? I would guess it is to prevent vapor lock issues in nose high attitude.
 
Major-Tom said:
Thank you Scott, this is the kind of high quality information I was hoping to get. Could you possibly tell me the main reason for the pumps behind the baggage bulkhead? I would guess it is to prevent vapor lock issues in nose high attitude.
Click to expand...


Weights and balances, moment of arm, is my guess.
 
It was done to comply with one of Rotax's many installation requirements, and somewhat dictated by where the fuel tank is located, related to those requirements.
 
rvbuilder2002 said:
It was done to comply with one of Rotax's many installation requirements, and somewhat dictated by where the fuel tank is located, related to those requirements.
Click to expand...


This would have been my guess. Otherwise Vans might have placed the complex pump and filter assembly, where it could be inspected more easily, I guess. You know, I love the RV-12is, but I hate the pumps in this dark place.
 
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