What's the benefit of the 912iS over the 912ULS?

[kicktireslightfires]

I'm a student pilot and haven't even flown a FADEC yet so my knowledge is purely theoretical so please be kind. Just trying to learn! The way I understand it is that the 912iS is both fuel injected and has a FADEC. Let's take those one at a time.

FADEC:
This eliminates the mixture control, but the 912ULS already doesn't have a mixture control. So what exactly is the FADEC controlling/optimizing/making easier? What is the benefit of the FADEC in the 912iS vs no FADEC in the 912ULS? What are the Pros of the FADEC? For example, does it make the starting sequence easier/eliminate steps to prime the engine and you merely turn the key/push the button? What else does the FADEC make easier or harder?

Fuel injection:
As I understand it, the only benefit of fuel injection is that it saves fuel by using fuel more efficiently. But fuel injection is also more complicated that carburated so technically the fuel you save could end up canceling itself out by the extra maintenance cost/complexity?

Is there any other benefit to fuel injection besides a tiny fuel savings?

I under the carburated 912ULS will require a synchronization of the carbs roughly once a year/at the annual, but that supposedly takes less than an hour.

Fuel injected also means no carb heat control to deal with. But some planes with a 912ULS don't have a carb heat control, either. So inside the cockpit, they look the same.

It would almost seem carburated is better than fuel injected? Fuel injected is more complex, more that could break, minimal fuel savings when taking about small engine like the 912, more complex starting sequence (although it seems the FADEC wins here because from what I understand the FADEC simplifies the starting sequence), more weight, etc. A benefit to fuel injected would be no carb heat control to fuss with, but on a 912ULS plane without a carb heat control, it's moot.

Thanks in advance, everyone. Just want to better understand Pros and Cons of the 912iS vs. the 912ULS.

 

[Ghery]

Every plane I've flown, except for one, was carbureted. The one exception was the club's Piper Arrow, which had fuel injection. I haven't had trouble unique to either. Both have fouled plugs while on the ground to the point where I couldn't clear them. Instead of carb heat the Arrow had an alternate air intake. You pays your money, you takes your chances. Starting was different, but I don't know that the difference made much difference.

I haven't flown a plane with FADEC, so I can't make a comparison there. I guess it would be nice, but the older engines work fine for me. Maybe that's just because I'm old and glad they don't have a choke to mess with.

 

[Kent Wien]

The 912is gives you a 20% fuel savings which also translates into longer range. It is a heavier engine though. All your points are valid.

 

[Doctor Bob]

No cheap, worthless 50 cent floats that cost $100 per carb and come shipped in a plain brown bag that don’t seem to last very long.

As stated above, some LSA’s have small tanks or reduced useful load and every gallon saved counts.

 

[Capt. Geoffrey Thorpe]

The lack of a mixture control on the Bings doesn't mean that the engine would not benefit from improved mixture control. Decent electronic fuel injection (not the typical aircraft technology from the 1930's) will do a better job of maintaining the mixture and compensating for altitude. This can result in some improvement in fuel economy. Particularly at altitude. Many carburetor Rotax get away with no carb heat because they are picking up warmer under the cowl air. External cold air can give a bit more performance.
Which is more reliable? The electronic systems have had their teething problems, but for long term reliability, a carburetor is not the answer. Even NASCAR has (finally) given up on carburetors. About the only places you still find carburetors any more are aircraft and lawn mowers - but even the lawn mowers are starting to go with with electronic injection.

FWIW, I spent more than 30 years working on emissions / fuel economy / self diagnostics in the auto industry (carburetors back in the '70s and fuel injection starting in the '80s). There is a good chance the car you are driving today has my algorithms in it.

 

[ateamer]

How hard is it to synch carbs on a Rotax? I used to synch the carbs on motorcycles myself and found it easy. Is Rotax similar?

 

[Warmi]

How hard is it to synch carbs on a Rotax? I used to synch the carbs on motorcycles myself and found it easy. Is Rotax similar?

Yeah, most likely even the same carbs ( Bing )

 

[DaleB]

How hard is it to synch carbs on a Rotax? I used to synch the carbs on motorcycles myself and found it easy. Is Rotax similar?

It's not terribly difficult or time consuming. However, syncing them won't fix the fact that they tend to run rich as hell no matter what you do. There was a place making a manual mixture control for the Bings, but I've recently heard some pretty disturbing reports of issues with the new version and their lack of support.

I can come up with numerous proven, practical reasons to prefer fuel injection. I have heard only theoretical scenarios where a carburetor might be better.

 

[Warmi]

It's not terribly difficult or time consuming. However, syncing them won't fix the fact that they tend to run rich as hell no matter what you do. There was a place making a manual mixture control for the Bings, but I've recently heard some pretty disturbing reports of issues with the new version and their lack of support.

I can come up with numerous proven, practical reasons to prefer fuel injection. I have heard only theoretical scenarios where a carburetor might be better.

Carbs are never "better" in terms of performance... the only potential benefit of using carbs would be that , in some scenarios, they are simpler to troubleshoot and fix and don't need electricity to run.
I would still prefer fuel injection - when was the last time your car engine died ?

 

[DaleB]

Carbs are never "better" in terms of performance... the only potential benefit of using carbs would be that , in some scenarios, they are simpler to troubleshoot and fix and don't need electricity to run.

Nor does the fuel injection used in many aircraft.

I would still prefer fuel injection - when was the last time your car engine died ?

Exactly. And, as I said, while you can come up with a couple of theoretical scenarios where FI would fail, there are many good reasons why fuel injection is king of the hill for most things bigger than a weed whacker built in the last few decades.

 

[Cogito]

I've owned one plane with a 912iS and one with a 912ULS. Fuel burn for 912iS is 4 gph vs. 5gph for the ULS, on a cross-country that can easily mean an extra fuel stop. ULS is cheaper to purchase but ends up costing more over the life of the engine. ULS requires higher maintenance cost as well as higher fuel cost. You say fuel injection is more complicated, but that's not the case as far as pilot or maintenance technician, I flew my 912iS 1,500 hrs and never once had to even think about the fuel injection system. Never an issue. The ULS had to be constantly tweaked to keep carbs in sync as well as regular maintenance, rubber carb seals and diaphragms wear out and need to be replaced.

Carburetors are old technology, not well suited to different altitudes, step up to the 1980's and get a fuel-injected engine.

 

[Flocker]

Carburetors are old technology, not well suited to different altitudes, step up to the 1980's and get a fuel-injected engine.

+1. My plane has the 912iS. Trust me, you'll love it. PS - I'm an iRMT - feel free to PM me with any questions.

 

[Mike Blackburn]

I fly a 914ULS.
The carbs aren’t a problem unless you are sloppy with your shutdown and try and start the engine hot.
As long as you run the carbs mostly dry before shutdown you’re ok. Otherwise I find it tends to flood when starting warm.

then again there is no injected 914....

 

[ETres]

How hard is it to synch carbs on a Rotax? I used to synch the carbs on motorcycles myself and found it easy. Is Rotax similar?

The hardest part is having to get so close to a spinning prop. Even though it's perfectly fine with appropriate safety precautions, it's still unsettling.

 

[DaleB]

The hardest part is having to get so close to a spinning prop. Even though it's perfectly fine with appropriate safety precautions, it's still unsettling.

One of my least favorite things. You pray you don't have a momentary lapse of attention, and that your buddy inside the cockpit keeps his feet FIRMLY planted on the brakes.

 

[Warmi]

I fly a 914ULS.
The carbs aren’t a problem unless you are sloppy with your shutdown and try and start the engine hot.
As long as you run the carbs mostly dry before shutdown you’re ok. Otherwise I find it tends to flood when starting warm.

then again there is no injected 914....

There is .. 915is.

 

[Warmi]

The hardest part is having to get so close to a spinning prop. Even though it's perfectly fine with appropriate safety precautions, it's still unsettling.

Then don’t run the engine when adjusting - start , test, stop, adjust, start ,test ... etc

 

[ETres]

Then don’t run the engine when adjusting - start , test, stop, adjust, start ,test ... etc

That's no fun!

 

[C-1 PILOT]

Up until recently the 912 iS had issues with their gear boxes. Many required premature servicing. Eventually, late 2017-18, ROTAX came out with an improved gearbox and its a non issue. When I ordered my LSA, the factory recommended I build it with a ULS because of the problem at the time, which I did. I don’t regret it, as a couple of owner/builders with the iS experienced the gearbox problem, as well as other iS related electronic issues.

If I were to order a plane today, I’d go with a 912iS, as the early teething issues have been resolved by ROTAX.

 

[DaleB]

Then don’t run the engine when adjusting - start , test, stop, adjust, start ,test ... etc

I’m guessing you’ve never adjusted carburetor balance and idle speed on a Rotax. You just described an excellent way to make a 20 minute procedure into an all day project.

 

[Warmi]

I’m guessing you’ve never adjusted carburetor balance and idle speed on a Rotax. You just described an excellent way to make a 20 minute procedure into an all day project.

I do it every 3-4 months on my personal plane and it usually gets done in about 20 minutes with 2 people ( one in the cockpit starting/stopping the engine (me) and one adjusting ( who happened to be my wife ) - btw .. we both went to a Rotax owner maintenance training.

 

[smv]

FADEC is nice. I got all my multi-engine ratings in DA-42s. Kinda feels like I cheated.