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Fuel Injected 912 for RV-12?

S

sandpiper

Well Known Member
There was recently a 912i training class in the Bahamas where a rumor leaked out. A Rotax guy supposedly rattled off a bunch of manufacturers as 912i users and Vans was on the list. Didn't mention for which RV, just included Vans.

Any truth here?
 
The carburated 912 ULS is doomed my friends, sooner or later VANs will have no other choice than going 912 i: this is called progress!
 
The 912is has created a lot of interest and is clearly a very nice engine, but apart from getting rid of the carbs, what do people see as the big attraction? Similar power, more weight, more cost. Doesn't sound like a great leap forward to me. What am I missing?
 
Supposedly there is a 20% fuel saving over the ULS. Hard To believe, but I really don't have any personal knowledge.
 
Even if the 20% fuel saving is real, using our mogas cost of about $1.50/litre (about $5.25 $US/gal at the current exchange rate), by my quick estimate I'd have to fly around 700 hours to break even on the additional purchase cost (about $4k extra as I recall). I'd be doing well to reach that number in the next 10 years. You lucky guys in the US with much cheaper fuel would have fly half way to TBO to break even. Maybe the 912ULS will fall by the wayside eventually, but in the meantime I won't be spending too much time wondering how to alter the cowl and mount to fit the new engine in. I may be wrong, but from what Van's have said so far, they won't be doing that either.
 
RFSchaller said:
Supposedly there is a 20% fuel saving over the ULS. Hard To believe, but I really don't have any personal knowledge.
Click to expand...

I think the word supposedly is a correct word to use at this point. There is not enough real world experience to yet validate the new fuel economy claims. I don't doubt that it is better than the carbed engine, but I am not yet convinced it is 20% better.

Case in point...
If you fly an RV-12 with the carbed engine, at max continuous cruise power, you will not get the fuel economy that was typically published 6 years ago when Van's first started playing with the 912 in the yellow prototype.
Sure, you can match the claimed numbers, but at a reduced cruise speed.

So, is the 20% fuel flow claim, a reduction from what we know a carbed engine burns at max. cruise power, or a 20% reduction on what it was always claimed to burn?

As for the rumor? It is not true. There is no work being done to adapt the 912iS to the RV-12. Van's is still concentrating on trying to re coupe all of the $ spent during 5 + years of development (I say 5 years plus because there is still work going on developing improvements etc).

It may be true that eventually Rotax will force it to happen. If it does, it will require a lot more engineering (probably more than most people realize). Until then, Van's will likely soldier on selling more Rotax 912 engines in the USA per year than any other company (not making that claim, but I think it is pretty likely).
 
RFSchaller said:
Supposedly there is a 20% fuel saving over the ULS. Hard To believe, but I really don't have any personal knowledge.
Click to expand...

I find the 20% number very difficult to believe. It takes X amount of fuel to achieve X amount of hp. If the hp is the same, that says that these carburetors are EXTREMELY inefficient. While I believe that this carb set-up is somewhat inefficient, I can't believe it is that bad.

Just my $.02.
 
Mel said:
I find the 20% number very difficult to believe. It takes X amount of fuel to achieve X amount of hp. If the hp is the same, that says that these carburetors are EXTREMELY inefficient. While I believe that this carb set-up is somewhat inefficient, I can't believe it is that bad.

Just my $.02.
Click to expand...

In our bench running back in 2006, developing our EFI kit, the carbs did quite a good job of holding the mixture right around best power AFRs (around 12.8 to 1). The EFI engine can run LOP (approx 15.5 to 16.5 AFR) in cruise so I can see how fuel burn could be this much less. Remember there is no provision for leaning the Bing carbs manually so they are a compromise.
 
EFI

I know I will come under fire for this but........Not to excited about the E part of EFI considering some of the E glitches I had to overcome. The Bings have been around awhile. Carbs seem to fail gradually while E's seem to turn off.

Jersey
 
jersey said:
I know I will come under fire for this but........Not to excited about the E part of EFI considering some of the E glitches I had to overcome. The Bings have been around awhile. Carbs seem to fail gradually while E's seem to turn off.

Jersey
Click to expand...

What kind of EFI were you running?
 
Just Sayin

We developed our mechanical fuel injection about 5 years ago for the Rotax 912 (actually built one for the factory in 1988). These were installed in the Just Aircraft Highlander. Fuel burn was about 4-6% better for the same power as the carbs and the system made about 8-13% more power. So at full throttle the fuel burn was a bit higher then the carbs. To date there are 5 flying with one aircraft with more than 600 hours on it. A couple of years ago I got involved re-working a Highlander with a Rotax conversion that was turboed with an SDS fuel injection system. Lots of redesign of the systems and programming time getting the fuel curve dialed in as the engine builder did not do his homework getting the turbo control system, air intake, ignition timing and fuel curves dialed in. Cooling was a huge issue. After we got the installation running satisfactory, we ran comparisons against the mechanical set up we had in another aircraft. Other than better performance at altitudes above 7500 feet, take off at 800 feet was about the same and cruise fuel burn on the turbo installation at the same speed was around 10% more. But to be fair the turbo installation had a fixed pitch prop and the mechanical injected engine had an adjustable pitch prop. The turbo Highlander was heaver by 150 lbs also. I also do not know if the turbo engine was really making the HP the engine builder claimed. I suspect not, maybe the engine was a dog. We had the manually adjustable waste gate set to a 40? maximum. I put around 80 hours on this aircraft, got my tail wheel endorsement in it then the customer that owned it sold it to a guy in Canada. So a friend and I flew the Highlander to north of Calgary to deliver it. Fun trip, but the little Rotax was pretty tired when we got there.

So you can figure I?m a bit biased (no just the facts here:)). But figuring that Rotax spent millions of $ on the development of their engine management system I would suspect it would be superior to any after market EFI or mechanical fuel injection system around (I wish I had a few million to develop a cooler mechanical system). Although I have to agree with Mel, there?s no free lunch. It takes so much fuel to make a HP and a 20% reduction in fuel burn even at cruise power is way out there. I didn?t see that when we leaned the mechanical injected engine to best power at any altitude. And I certainly couldn?t lean the turbo engine to a .060 F/A and keep it alive.

Don
 
Another Data Point

We saw a 5-8% gain in hp with EFI over the carbs, this was mainly due to having no restriction in the intake system using a 54mm TB. WOT resulted in ambient pressure as far as MAP went. The carbs showed roughly .75-1 inch drop at WOT.

At the same AFRs we saw roughly the same fuel flows although the engine was making more power. The big difference was in EGT spread. 912s tend to have two lean cylinders and two richer ones. The EFI cut the EGT spread from 150F to 30F.

In testing different ignition timing values, we saw no noticeable change in hp at WOT at a fixed altitude.

We are fortunate to have over twenty 912s flying with our EFI in several countries since 2006 having accumulated something over 4500 flight hours (one training aircraft has over 1000 hours alone). Every user reports increased speeds/ more rpms (200-250 in most cases) over the carb setup they replaced. If they reduce speed to where they were before, they report 5-10% lower fuel flows over the carbs. Note that these systems are tuned for best power AFRs and not running LOP. They sport a variety of different intake plenum designs.

As we know on Lycoming and Continental engines, running LOP can easily cut FFs 20% over best power AFRs. You will see around a 30% reduction in fuel flow and around 7-9% reduction in power. We know that turbocharged Contis run just fine LOP in cruise. At altitude, the variable spark timing on the 912is may offer additional efficiency gains as MAP falls off.
Many clients are now lining up to have EFI fitted over the winter when the flying season slows down there after seeing the in flight results.

The OEM Rotax EFI system is very sophisticated even by modern automotive standards, having the sensor suite to run LOP automatically. I can only guess they have flogged several different engines for thousands of hours on the dyno to be sure that the durability is there. You don't introduce this technology to decrease reliability and hurt that hard won reputation. Rotax was working on EFI as far back as late 2004 I believe.
 
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rv6ejguy said:
Remember there is no provision for leaning the Bing carbs manually so they are a compromise.
Click to expand...

There is a kit available to lean the mixture of the Rotax carburetors.
One pilot showed me his installation in an Europa with a 912.
More info: HACman

HACmanDial_1.jpg
 
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And yet another data point

I guess what I?m saying is that from a marketing standpoint they can say there is a 20% decrease in fuel burn. The reality is that leaning the mixture 20% from best power F/A is an 8% reduction in HP. So if you had a 180 HP engine running 16 GPH then leaned the mixture 20% leaner (12.8 GPH) the engine would make 166 HP. Likewise just reducing the throttle to 166 HP keeping the same F/A the engine would use 14.7 GPH. That?s a 13% reduction in fuel flow. So the real difference is only a 7% gain in fuel economy by leaning the mixture. The problem here is that you can?t run the engine at 7% lean let alone 20% lean at the manifold pressure to make full power. Aircraft engines have been running LOP for a long time. Big radials ran like this all the time in the 40?s and 50?s to extend their cruise performance. So this is no big revelation.

We have 2035 FM units in the field. 90% of these are in aircraft installations and have overhauled over probably twice that many Bendix fuel injection systems in our 29-year existence. I would guess there are over 1.5 million flight hours on the FM systems. We have accumulated thousands of hours of dyno and test stand time running on various engines from 2-stroke, rotary and 4-stroke, turbo, supercharged, Nitrous, alcohol, 80 HP to 2500 HP engines. It?s amazing how similar all this stuff acts. Physics is always present. And this holds true even for the Rotax. As Ross stated in his observations with the addition of his EFI on the Rotax 912 (5-8% gain in HP and 5-10% reduction in fuel burn for the same power) was pretty much the same change that we saw with our mechanical system (8-13% gain in HP and 4-6%r reduction in fuel burn) on the Rotax 912.

So again, there?s no free lunch. What kind of value do you get for your dollar?


Don
 
rvbuilder2002 said:
I think the word supposedly is a correct word to use at this point. There is not enough real world experience to yet validate the new fuel economy claims. I don't doubt that it is better than the carbed engine, but I am not yet convinced it is 20% better.

Case in point...
If you fly an RV-12 with the carbed engine, at max continuous cruise power, you will not get the fuel economy that was typically published 6 years ago when Van's first started playing with the 912 in the yellow prototype.
Sure, you can match the claimed numbers, but at a reduced cruise speed.

So, is the 20% fuel flow claim, a reduction from what we know a carbed engine burns at max. cruise power, or a 20% reduction on what it was always claimed to burn?
Click to expand...

Don at Airflow said:
I guess what I’m saying is that from a marketing standpoint they can say there is a 20% decrease in fuel burn. The reality is that leaning the mixture 20% from best power F/A is an 8% reduction in HP. So if you had a 180 HP engine running 16 GPH then leaned the mixture 20% leaner (12.8 GPH) the engine would make 166 HP. Likewise just reducing the throttle to 166 HP keeping the same F/A the engine would use 14.7 GPH. That’s a 13% reduction in fuel flow. So the real difference is only a 7% gain in fuel economy by leaning the mixture. The problem here is that you can’t run the engine at 7% lean let alone 20% lean at the manifold pressure to make full power. Aircraft engines have been running LOP for a long time. Big radials ran like this all the time in the 40’s and 50’s to extend their cruise performance. So this is no big revelation.

We have 2035 FM units in the field. 90% of these are in aircraft installations and have overhauled over probably twice that many Bendix fuel injection systems in our 29-year existence. I would guess there are over 1.5 million flight hours on the FM systems. We have accumulated thousands of hours of dyno and test stand time running on various engines from 2-stroke, rotary and 4-stroke, turbo, supercharged, Nitrous, alcohol, 80 HP to 2500 HP engines. It’s amazing how similar all this stuff acts. Physics is always present. And this holds true even for the Rotax. As Ross stated in his observations with the addition of his EFI on the Rotax 912 (5-8% gain in HP and 5-10% reduction in fuel burn for the same power) was pretty much the same change that we saw with our mechanical system (8-13% gain in HP and 4-6%r reduction in fuel burn) on the Rotax 912.

So again, there’s no free lunch. What kind of value do you get for your dollar?


Don
Click to expand...

Thanks Don,
You did a much better job raising the question, than I was able to in my previous post.

Claims can be made... but unless specifics are given regading those claims, it is nearly worthless information.
 
Don at Airflow said:
I guess what I?m saying is that from a marketing standpoint they can say there is a 20% decrease in fuel burn. The reality is that leaning the mixture 20% from best power F/A is an 8% reduction in HP. So if you had a 180 HP engine running 16 GPH then leaned the mixture 20% leaner (12.8 GPH) the engine would make 166 HP. Likewise just reducing the throttle to 166 HP keeping the same F/A the engine would use 14.7 GPH. That?s a 13% reduction in fuel flow. So the real difference is only a 7% gain in fuel economy by leaning the mixture. The problem here is that you can?t run the engine at 7% lean let alone 20% lean at the manifold pressure to make full power. Aircraft engines have been running LOP for a long time. Big radials ran like this all the time in the 40?s and 50?s to extend their cruise performance. So this is no big revelation.

We have 2035 FM units in the field. 90% of these are in aircraft installations and have overhauled over probably twice that many Bendix fuel injection systems in our 29-year existence. I would guess there are over 1.5 million flight hours on the FM systems. We have accumulated thousands of hours of dyno and test stand time running on various engines from 2-stroke, rotary and 4-stroke, turbo, supercharged, Nitrous, alcohol, 80 HP to 2500 HP engines. It?s amazing how similar all this stuff acts. Physics is always present. And this holds true even for the Rotax. As Ross stated in his observations with the addition of his EFI on the Rotax 912 (5-8% gain in HP and 5-10% reduction in fuel burn for the same power) was pretty much the same change that we saw with our mechanical system (8-13% gain in HP and 4-6%r reduction in fuel burn) on the Rotax 912.

So again, there?s no free lunch. What kind of value do you get for your dollar?


Don
Click to expand...

No, what I am saying is there is roughly a 30% reduction in fuel flow from best power AFRs to about 50 to 100F LOP (12.5 vs about 17) and roughly an 8% power loss at the same time so roughly a 22% gain in SFC. I am not making any claims from a marketing position, just what people see in real life on their aircraft. The EFI is better than the carbs and experiences vary somewhat.

I posted here in response to another post doubting a 20% reduction in fuel burn for the typical mission profile on the 912is. The EFI will save on warmup, taxi, cruise and descent over the carbs which deliver AFRs of around 10.8 to 13.2 across the power range in our testing at 4000 MSL and tend to run somewhat richer at high altitudes. We don't see a 20% reduction with our system because we don't run LOP in cruise like the 912is does.

I think many people here see the benefits of LOP operation on their Lycomings and as you say, most engines are pretty similar in operation. Running a Lycoming LOP vs. best power can easily increase MPG 20%.

Let's also remember Rotax is controlling ignition and can run the spark timing right up to just short of detonation for maximum cylinder pressure at all times. This is likely to show some FF benefits at cruise and more so at high altitude over fixed timing. This is even more critical running LOP so fixed and mechanical systems simply can't do the job as well as modern electronics with this balancing act of AFR vs. timing.

Now the question of economics comes in. What is the payback time for the system if you burn 10, 15 or 20% less fuel? Depends on usage. If you don't fly much, probably not worth it. If you fly 200 hours per year, you might make your money back in 3-5 years.

I think it is accurate to say that neither Don nor I have the resources of Bombardier/ Rotax but from my 35 years in this field and 20 years in the EFI manufacturing business, I can believe in the possibilities that Rotax is claiming given the sophistication of their system.
 
rv6ejguy said:
Let's also remember Rotax is controlling ignition and can run the spark timing right up to just short of detonation for maximum cylinder pressure at all times.
Click to expand...

No they can't. Their system has provision for knock sensors, but they are not installed. Without that they are risking detonation unless they use fixed, overly conservative fuel and timing curves. If they try to really retard or advance the timing for a specific engine in a particular regime, they will end up blowing up a lot of engines that are running under different conditions.

I saw an interview with a Rotax engineer a while back that said the "phase II" EFI engine will include knock sensors and dynamic timing.
 
MrMorden said:
No they can't. Their system has provision for knock sensors, but they are not installed. Without that they are risking detonation unless they use fixed, overly conservative fuel and timing curves. If they try to really retard or advance the timing for a specific engine in a particular regime, they will end up blowing up a lot of engines that are running under different conditions.

I saw an interview with a Rotax engineer a while back that said the "phase II" EFI engine will include knock sensors and dynamic timing.
Click to expand...

I skimmed the same article perhaps and missed the Phase II part. Thanks for the correction!

Something I find interesting is that Rotax is claiming the same HP as before where Don and me both saw some tangible gains in our testing. Would be interesting to see a 912S vs. 912is swap in the same aircraft, same prop with some previous performance numbers. On the MCR aircraft, people are seeing 10-15 knots with the EFI over the carbs which is pretty amazing although they are very clean airframes. Some with FP props are having to repitch with the EFI as they see as much as 300 more rpm in flight.
 
Engine of the future!

First off I don't want to be the launch customer because I'm sure that there will be some initial problems but in a year or two this will be a superb engine.

Why I would prefer 912SI
Burns less fuel, 2000 hours saving 1 gall per hour equates to a $8000 savings over the life of the engine at $4 per gallon. Even if you only save .5 gals that's $4000 saved.
This engine, if runs as advertised will be just like a modern auto engine. On board engine control computer will monitor every aspect along with letting you know when something is wrong via diagnostic software.
No maintenance on carbs, saves $2000 over life of engine. Carbs should be checked every 200hrs at a cost of $250 (includes shipping and labor)
How about those rubber cups that hold the carbs on, those retail for $150 per pair.
No more sensor problems, has one connection for all sensors. IE EGT jumps when transmitting. Fuel pressure goes to zero then returns to normal, etc.
Can down load computer data similar to auto to trouble shoot.
No more split throttle cable with springs! Yahoo!
No more balance carbs or buying carb balancer, more money saved.
More amps for electricity without adding alternator.
This technology in an aircraft engine puts continental and lycoming to shame.
Glad some body is out there advancing aircraft engines to a modern level of technology.

Now all that being said I still think the 912 ULS is a great engine but I can see just like as avionics advances have made flying much easier this engine will do the same.
Oh and the weight is not that much heavier, you have more accessories like high pressure fuel pumps so when time comes and they stop making the 912 ULS then Vans engineers will sit down and make it happen.:D
 
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I was wrong!

Earlier on this thread I predicted the demise of the 912 ULS in favor of the 912iS: what do I know?
It looks like what is going to happen is the demise of the 912iS in favor of the 912iS Sport and it only makes sense considering the small changes involved.
The question is: After so many $$$ and so much time spent in the 912iS development, why did Rotax not see it coming?
Another question is: Why did Rotax changed the name as the retrofit from iS to iS Sport is so straightforward?
May be this just boils down to a matter of pride?
Anyway, this makes me feel good about my good ol' 912 ULS :D
And kudos to VANs who did not fall into this trap! (Not an excuse to delay further the engineering needed to adapt the -12 to the iS Sport, you got a 2 years reprieve so now is the time!)
Wrong again?
 
Never be an "early adopter".

If the "Sport" is here already, can the Super Sport be far behind?

Bob Bogash
N737G
 
and now I'm waiting eagerly for Skyview V11.....

Where is the DISLIKE button when you need one::D;)

Bob Bogash
N737G
 
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