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Rotax 912 - Fuel Injected or Carburetor?

M

mvanwyk

Member
I am getting a new factory-built RV-12 next year. I would like your opinions.
Do you prefer the fuel injected engine (Rotax 912 iS)?
Or, do you prefer the engine with carburetor (Rotax 912 ULS)?
Please explain why you prefer one over the other.
What are the upsides of each?
What are the downsides of each?
Can you share any experiences with one or the other?
 
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I may be mistaken on this but isn’t the fuel injected iS engine the only option available now? I know for kit builders with fuselages after 2017, vans will only allow you to buy the iS engine. I would imagine they would be doing the same with new SLSA orders.

I purchased the iS version and even if I had the choice of iS or ULS, I would choose the fuel injected one. No carbs to balance, full fadec, single lever operation. It should function like a modern car. I still don’t get why the rest of GA hasn’t left this old carburetor and analog tech in the dust. I get that they have their place, simplicity, cost. But I’d prefer to have the latest tech in my plane. Especially given the cost of what rv12s are now. If budget is a reason for one or the other, saving a few grand on a new 12 seems like not much of a savings percentage wise. Vans also touts a slight increase in performance and range with the iS.

Also if the uls engine option removes the center console that is in the standard iS airframe… I’d be inclined to keep the center console. Where do they put the choke lever in the iS airframe?
 
sc_pilot said:
I purchased the iS version and even if I had the choice of iS or ULS, I would choose the fuel injected one. No carbs to balance, full fadec, single lever operation. It should function like a modern car.
Click to expand...

Actually... the 912ULS (with antiquated carbs :D) is single lever control. No carb heat, no mixture control... only a throttle lever. The carbs are automatically altitude compensation to correct mixture. Work flawlessly... Engine always starts with one turn of the prop. I balanced my carbs 5 years ago and still in perfect synch. Engine now with almost 900TT.

Kind of like SB 244, California Right to Repair Act. No fancy electronic troubleshooting skills required....
 
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We look after aircraft fitted with both types at work, I would go for the injected engine.
The 100hr service for the injected engines is to look it over and change the oil.
For the carbed engine it is more involved, as well as changing the oil, checking carb float weights, balancing carbs, changing the mech fuel pump every (I think) 500 hrs.
The injected engine has a full Fadec so will report any problems (if you have the very expensive interface dongle).
Also I believe the injected engine burns less fuel.
 
^^^^^ You forgot to mention crawling back thru the baggage bulkhead to service high-pressure pumps and filters....
 
sc_pilot said:
Also if the uls engine option removes the center console that is in the standard iS airframe… I’d be inclined to keep the center console. Where do they put the choke lever in the iS airframe?
Click to expand...

Getting a little bit off subject here, but I don't think the console is engine dependent so much as it was part of a number of airframe upgrades to the 'is' version. Moot point since as you mention, new builds are is engine and airframe only. Anyway, after my first long cross country in the 12is, I could see a benefit in not having the console. I'm fine with it either way and like the throttle where it is, but that console doesn't make for the most comfortable leg positioning when sitting in the airplane for a few hours. I love the airplane in general and it's a small thing, but I was cursing that console a few time. :)
 
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iS

For the lower fuel flow. PLUS:
More electrical power available for more avionics and accessories.
 
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sc_pilot said:
...I may be mistaken on this but isn’t the fuel injected iS engine the only option available now?...
Click to expand...
I also may be mistaken, but I think buyers of factory-built have a choice.
I opted for fuel injected, but was just wondering what owners think.
If I received a bunch of "Nooooo! Stay away from fuel injected!!!" I might get on the phone and see if I could make a change. But, thus far I am OK with my choice.

Question:
Is fuel injected hard to restart when hot after flying?
 
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mvanwyk said:
Question:
Is fuel injected hard to restart when hot after flying?
Click to expand...

Not at all. The reason is FADEC.

When starting cold you place the throttle position between 45% & 50% and when restarting throttle position of 35% - 38% will do.
 
Well, considering today's announcement, I don't think I will be worrying too much about my factory-built Van's RV-12.
I put $5K down, and was scheduled for another $55K balloon payment in November.
Hey Van's, if you are reading this, I would like an immediate refund of my $5K, and you can forget me sending you another $55K.
I'll bet that the supply of Rotax 912s is low anyway.
They are being used in great quantity for War Drones. And War is big business.
 
You will be missing out on an economical and wonderful flying machine if you actually do cancel your order. Be patient.
 
It's 2023...get the injected one, which I believe is your only option.
Plenty to read here about carb issues. In fact, getting the 12iS was a determining factor in my final decision to build the 12iS version. I did not want any more carbs.

:eek:

BTW: Rotax is king at mass production. There have been no shortages of Rotax engines that I've ever heard of.

I wouldn't worry about Vans, they will be fine. They have a very unique and quality product that no one else can touch.
 
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It’s interesting to read about so many pilots that prefer steam gauges over glass panels because of their ability to work without a computer but will quickly adopt computer controlled fuel injected engine.

I have 1300 hours / 8 years on my 912ULS. Since changing to the blue floats I have had zero carb problems, and they have never been rebuilt. The float valves were replaced at 1100 hrs. I check carb balance every 100 hrs but seldom have to adjust. Maybe mine are an exception. If you are the kind of owner that has someone else do all your maintenance I would buy an injected engine. There is virtually nothing to repair just parts changing, they have the expensive dongle to troubleshoot. If you are mechanical inclined the carburetors are user serviceable.
 
I also wonder, with Van’s severe economic problems, how soon they will be able to dedicate resources to fixing the 912iS radiator problem and issuing a SB. It could be along wait... One guy said he’s on his fourth radiator.
 
seagull said:
It’s interesting to read about so many pilots that prefer steam gauges over glass panels because of their ability to work without a computer but will quickly adopt computer controlled fuel injected engine.

I have 1300 hours / 8 years on my 912ULS. Since changing to the blue floats I have had zero carb problems, and they have never been rebuilt. The float valves were replaced at 1100 hrs. I check carb balance every 100 hrs but seldom have to adjust. Maybe mine are an exception. If you are the kind of owner that has someone else do all your maintenance I would buy an injected engine. There is virtually nothing to repair just parts changing, they have the expensive dongle to troubleshoot. If you are mechanical inclined the carburetors are user serviceable.
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Well how many modern vehicles ( of any kind ) with piston engines use carburetors - are they all missing on joys of user serviceable cabs ?
 
warmi said:
Well how many modern vehicles ( of any kind ) with piston engines use carburetors - are they all missing on joys of user serviceable cabs ?
Click to expand...

Now a days automobiles are seldom serviced by owners. When automobiles stop they park easily. My main point was the Bing 64 is a very low maintenance reliable carburetor. The carbureted engine is simple compared to an injected one. The fuel system on carbureted engine will run without any battery power. The 912is requires 2 alternators and 2 batteries to make it safe.
 
Seagull - you live in CA and adhere to SB 244, California Right to Repair Act. No fancy electronic troubleshooting skills required.... :D
 
Piper J3 said:
Seagull - you live in CA and adhere to SB 244, California Right to Repair Act. No fancy electronic troubleshooting skills required.... :D
Click to expand...

I live in CA because it feels so good every time I fly out of the state. It’s like hitting yourself because it feels good when you stop. But that’s a topic for another day. :D
 
mvanwyk said:
I am getting a new factory-built RV-12 next year. I would like your opinions.
Do you prefer the fuel injected engine (Rotax 912 iS)?
Or, do you prefer the engine with carburetor (Rotax 912 ULS)?
Please explain why you prefer one over the other.
What are the upsides of each?
What are the downsides of each?
Can you share any experiences with one or the other?
Click to expand...

Less than 5%.. my FAA database search shows less than 2% (but their database is a mess.. so lets round up to 5%) of RV-12iS builders chose the ULS engine option. I'd be surprised if the factory assembly team has actually ANY experience building a RV-12iS kit with the ULS option.

Benefits to the 912iS are less problems with sinking carb floats, no carb synching every xxx hours, and increased fuel efficiency (I think it was 30%?) -- the latter having a varying degree on your operating costs..the more you fly, the more you save.

Drawbacks to the 912iS is that its $5000 more expensive. Its electrical system is more complicated to understand (lawn mower vs. car engine) - but once you understand how it works, its a non-issue.

Other issues like the radiator is common to both engines and will be solved by the time yours goes into production.
 
rcarsey said:
Less than 5%.. my FAA database search shows less than 2% (but their database is a mess.. so lets round up to 5%) of RV-12iS builders chose the ULS engine option. I'd be surprised if the factory assembly team has actually ANY experience building a RV-12iS kit with the ULS option.
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I think it is way less than even 2 percent (it is probably typos in the database that make it look like more).

I think it is about 3 customer built airplanes total.

There have been zero factory built SLSA's built with a ULS engine.
 
Fuel-injected all the way.

I've been fighting carb problems for the last year, and I really wish I had the raft of sensors in the 912is to tell me what exactly was going on. I've personally been in an RV-12is where a lane fault was thrown during runup and stopped us from flying with what turned out to be a clogged injector.
A BUDS dongle will let you dump out all the error codes logged by your aircraft.

Side benefits:
You'll get a higher service ceiling with the -iS as the Bing carbs run out of leaning capability around 8k feet.

You'll get the EarthX LiFePo4 battery which is more reliable and has more usable capacity than the lead-acid battery for the ULS (Vans specifically states that using the lighter battery will cause CG issues on the ULS).

If you wanted to be maximally experimental, the -iS has an easier pathway to a constant-speed prop as the governor for Airmaster/E-Props just taps into the CANBUS to get engine RPM.
 
rvbuilder2002 said:
The specified gross weight for all RV-12's, ULS or iS, is 1320 lbs.
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What I meant to ask;
What is the empty weight difference between the is and ULS assuming they both have the same equipment, radios, interior kit etc. including earth x battery? Or said another way is the usable weight different?
 
seagull said:
What I meant to ask;
What is the empty weight difference between the is and ULS assuming they both have the same equipment, radios, interior kit etc. including earth x battery? Or said another way is the usable weight different?
Click to expand...

The useful load for a ULS equipped 12iS would be slightly higher if all other details were the same.
I am not positively sure but my memory is telling me it was around 10 pounds.
 
seagull said:
What I meant to ask;
What is the empty weight difference between the is and ULS assuming they both have the same equipment, radios, interior kit etc. including earth x battery? Or said another way is the usable weight different?
Click to expand...

It would be interesting to know weight difference ULS Vs. iS as installed in the RV-12. I'm thinking an add'l 20# for dual CPU, injector rails, fuel pump/filter assembly, wiring harness, etc.
 
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seagull said:
Scott,
I have never heard this before. Was this in place when you were at Van’s?
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The page for the Odyssey battery on the Van’s storefront specifically states

This battery is included in the kit for any RV-12/12iS that is equipped with a Rotax 912 ULS engine. The RV-12iS utilizes the EarthX battery only when the Rotax 912 iS Sport engine is installed. For weight and balance reasons, we do not approve exchanging these batteries between the aircraft with the different engine models.​

Reliability-wise, LiFePo4 batteries have more usable capacity than SLA, and draining them wont fause the long-term damage that will occur when doing that to a Lead-Acid. The only thing I can see as a downside is that you cannot charge them when the cells are below 0°C, though the battery management system will prevent this until they warm up.
 
NORDO Industries LLC said:
The page for the Odyssey battery on the Van’s storefront specifically states

This battery is included in the kit for any RV-12/12iS that is equipped with a Rotax 912 ULS engine. The RV-12iS utilizes the EarthX battery only when the Rotax 912 iS Sport engine is installed. For weight and balance reasons, we do not approve exchanging these batteries between the aircraft with the different engine models.​
.
Click to expand...

If the issue is a because of a CG problem then I would expect some of these lighter propellers to also be a no-no. They are 5-7 pounds lighter with an arm that is double that of the battery.

On my plane a weigh and balance calculation with a 180# pilot, full fuel and 50# in the baggage area. By removing 10# from the nose wheel, (forward of the battery location) it puts the CG at the rear most allowable location, still safe to fly. If I had 50# of baggage it would go in the passenger seat anyway.
 
seagull said:
If the issue is a because of a CG problem then I would expect some of these lighter propellers to also be a no-no. They are 5-7 pounds lighter with an arm that is double that of the battery.

On my plane a weigh and balance calculation with a 180# pilot, full fuel and 50# in the baggage area. By removing 10# from the nose wheel, (forward of the battery location) it puts the CG at the rear most allowable location, still safe to fly. If I had 50# of baggage it would go in the passenger seat anyway.
Click to expand...

May be true, but Vans Aircraft didn’t supply any of those lighter propellers as a standard part of the kit.
They do supply the battery as a standard part, and because they know the light weight battery will have a major impact on the aircraft center of gravity. They do not supply that for one equipped with the ULS engine.

A lot of different things can be done to manage center of gravity for flight, but it cannot be assumed that every pilot will take the time to do so. Configuring an aircraft with a marginal empty center of gravity is not a good idea.
 
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