CTLSi economy at altitude

[Ed Cesnalis]

As we here the CTLSi adventures on the other forum actual fuel usage is revealed. 3.5 gal / hour @ 120kts is claimed but a 590nm trip ( with winds ) takes 24 gallons.

 

Looks like real numbers at higher altitudes are 110 - 120 kts and 4 1/2 gallons @ 120kts.

 

Here's the math:

 

Metric: hour = 120kts = 3.5gal

 

Southbound with 20kt headwind 290 nautical miles Note 2.9 hours assumed to match metric above.

 

13 gal / 2.9 hours = 4.48 gallons / hour @ 120kts.

 

 

Northbound: claimed 330 miles due to going east into CA, even if they went as far as Mammoth Lakes millage would be limited to 300 nautical miles, so I'll bump the mileage up to 300 with 5 knot tailwind.

 

300nm / 125GS = 2.4 hours / 11 gal = 4.58 gallons / hour @ 120kts TAS

 

Rough Check

 

Round trip = 590nm, 24gallons used.

590 / 120 = 4.92 hours @ 120kts

24gallons used / 4.92 hours @ 120kts = 4.87 gallons / hour @ 120kts

Allow for winds 4 1/2 gallons / hour confirmed.

 

Conclusion:

 

Econo mode is not available at WOT, much like leaning on the 912uls is not available at WOT so economy suffers when cruising at high altitudes.

[Roger Lee]

So long as your under 92% throttle the 912is is runs in eco mode so that is where the savings are, but past that it has nothing over the 912ULS.

[josjonkers]

So long as your under 92% throttle the 912is is runs in eco mode so that is where the savings are, but past that it has nothing over the 912ULS.

In terms of fuel efficiency, Roger.

 

There are significant other benefits to the 912ULSi though.

[Roger Lee]

There are benefits for sure and it's a nice engine, but a few things the ULS does better from a user stand point. Like the ULS won't have a major fault that will shut the engine down or if you lost your fuel flow or pump power to them the engine shuts down in 1-2 seconds. You don't have to go to school to work on a ULS and you don't have to buy a dongle, but you'll spend $1087 for a dongle and you'll have to go to school because this isn't like any other engine out there that an A&P or LSRM has ever seen. There was a 65% redesign over the 912uls.

 

 

I'm not knocking the engine, it is a good engine, but I think both the ULS and the IS have pros and cons. Just plugging it in and trying to make things work with the computer program would be almost impossible without a class.

 

Some thing else no one knows. The two on board computers (Lane A and Lane track every start and every little thing that goes on with that engine 10 times a second for its 2000 hr. life. It records everything so you'll never be able to say you did this or that because the computer won't lie. Most don't know the friction torque test at the annual is gone. There is no more 30 degree play. It was all removed from the dogs.

 

 

It's a nice engine just different and there will be a learning curve. You will need to be taught its differences it won't be done by trail and error on this one. I'm glad I went to the class or I would be totally lost and I'm sure more classes will be needed along the way. It isn't even being taught here in the US yet. There are only 10 people in the US that I know can work on it (past changing oil and plugs) or who have had any training on the IS. FD has 6 of those. The one thing I do like is I can plug the computer in and run the program and it will tell me right where the problem is.

The problem with it for the experimental guys is wiring needs to be followed very strictly and any non compliance or changes causes problems. It does come with a nice wiring harness, but you need to connect and wire all other accessories just right.

[josjonkers]

One thing I did hear from the Rotec guys where they were installing the LSI into a lsa (not CT, but can't remember which one) is that because it runs "lean of peak" for optimum fuel efficiency it is running quite a bit hotter and they were struggling to dissipate the heat and prevent the engine from overheating.

[Roger Lee]

The temp numbers are to be pretty close to ours, but because there are many LSA some of those don't have very good cooling and air flow characteristics. Pipistrel,Vans, FD, and 1-2 others (I can't remember) are using it at this time. FD is leading the way in numbers in service and on order. I'm sure others are right on there heals. I think I heard the 400 number of IS engines out there world wide and adding more every day.

[sandpiper]

Roger Vans?? If they are it hasn't leaked out yet. What do you know?

[Jim Meade]

One thing I did hear from the Rotec guys where they were installing the LSI into a lsa (not CT, but can't remember which one) is that because it runs "lean of peak" for optimum fuel efficiency it is running quite a bit hotter and they were struggling to dissipate the heat and prevent the engine from overheating.

 

I'd like to see some numbers on this. When I was running my 520 Continental with Gami injectors lean of peak, the temperature curve was that as you leaned the temps went up until you were at the hottest point which was right a peak, naturally, where the fuel and air were balanced. Richer than that and you had more fuel than the air could support for combustion and the fuel helped cool the engine. Leaner than that and you had less fuel than the air could support and because you were burning less fuel the temps went down again. I'd typically run my hottest cylinder 50°F cooler than peak. This engine when running rich of peak was often run from 50° to 100° rich of peak. As I recall, best fuel economy was around 25° or 50° rich of peak but that was also hardest on the engine. Running rich of peak it was better to run 100°. My fuel burn at 50° LOP was 12.6 gph and I did about 155 KTAS at 8k-10k in a turbo Centurion. Running 100° ROP that engine would burn about 17-18 gph and the plane would cruise faster, but to be honest I flew it there so seldom that I can't quote a number.

 

It will be interesting to see more figures come on as to how much LOP they run and what the temps are.

 

For more discussion of LOP read John Deakin and Mike Busch on Pelican's Perch in AvWeb.

 

 

[paul m]

also see Mike Busch webinars on EAA website, especially the Advanced Leaning one

[FastEddieB]

I'm with Jim* and Paul.

 

There is nothing inherently "hotter" about LOP operations, in spite of what many mechanics wrongly feel.

 

Quick question: which is hotter, 75° ROP or 75° LOP?

 

Hint: it's a trick question

 

 

 

*except for this, maybe:

 

 

As I recall, best fuel economy was around 25° or 50° rich of peak...

 

As I recall, in my Cirrus as I went farther and farther LOP (within reason), NMPG went up and up. For max range (and hence best fuel economy) we'd end up quite lean of peak.

[FastEddieB]

BTW, some people take this sort of thing quite seriously!

 

(click to enlarge)

 

 

On a serious note, note how quickly CHT's drop off on the right of peak (leaner) than on the left of peak (richer).

 

Hard to conclude that LOP is somehow inherently "hotter", right?

[Dan Kent]

I know the engine had many differences and enhancements from the ULS, but just from a finacial standpoint it makes no sense to purchase this engine. FD is charging $12,800 more for the iS. If you save 25% fuel (which is probably overstating the real savings, FD says 21%), with the ULS burning on average 5 gph (iS 3.75 gph), Mogas would have to be over $5 a gallon to break even at TBO. This doesn't include the time value of the $12,800 if used elsewhere.

 

Flying to TBO, at least for me is a lot of flying and anything less just makes even less economic sense.

[FlyingMonkey]

Put another way, to break even on the additional cost of the iS engine based on fuel economy, you'd have to burn 3571 gallons of mogas at $3.50 per gallon. At 4gph that is 892 hours of operation, almost halfway into your engine's total life and about eight years of flying for most of us.

 

Don't get me wrong, I think the fuel injection is pretty awesome. But the benefits of the 912 series of engines to me have always been light weight and relative ease of maintenance. These advantages are mitigated in the iS version, and in my mind the additional efficiency benefits are not really a good trade-off.

[S3flyer]

I'm with Andy and Dan. The benefits just don't offset the weight increase (in a MTOW limited plane) and $$$ cost. I'm also aware that the maintenance on the iS is purported to be lower but only time will tell. I've pretty much had zero maintenance on my 912ULS between annuals save for replacing VDO sensors. Also, I may just be lucky but carb sync has been included in the cost of my flat rate annuals.

 

A large bit of thread creep here -- but I'd be hard pressed to buy a new LSA of any type today due to overall increased empty weight. My 5.5 year old Sting S3 was able to handle my mission of full tank, full cockpit (my wife and I), baggage (50-60 lbs) and one spoiled Shitz tsu. Pretty sure very few new LSAs these days can do that.

[Dan Kent]

Put another way, to break even on the additional cost of the iS engine based on fuel economy, you'd have to burn 3571 gallons of mogas at $3.50 per gallon. At 4gph that is 892 hours of operation, almost halfway into your engine's total life and about eight years of flying for most of us.

 

Not to be argumentative, but I think your example just calculates the additional expense of the CTLSi @ $3.50 per gallon, not the difference between the 2 engines.

 

My calculation would be a delta of 1.25 gph (25% less of 5 gph) @ $3.50 per gallon, would be a savings of $4.375 per hour of operation for the iS. $12,800 divided by $4.375 would mean that you would have to fly over 2,900 hours to break even (close to 11,000 gallons, or nearly $40,000 in fuel (@ $3.50 per gallon)). TBO is 2,000 hours so you'll never catch up without even taking into account the time value of the $12,800.

[Ed Cesnalis]

I need the WOT, there is almost no savings for me.

[FlyingMonkey]

Not to be argumentative, but I think your example just calculates the additional expense of the CTLSi @ $3.50 per gallon, not the difference between the 2 engines.

 

My calculation would be a delta of 1.25 gph (25% less of 5 gph) @ $3.50 per gallon, would be a savings of $4.375 per hour of operation for the iS. $12,800 divided by $4.375 would mean that you would have to fly over 2,900 hours to break even (close to 11,000 gallons, or nearly $40,000 in fuel (@ $3.50 per gallon)). TBO is 2,000 hours so you'll never catch up without even taking into account the time value of the $12,800.

 

Okay, you make my case stronger, I defer to your numbers.

[Duane Jefts]

Dan johnson flew from fla to Mount Vernon Il in a Si at 5050rpm, 120mph, 75% power, and 4.1gph. Coming from him, that should end the fuel burn in the Si discussions.

[S3flyer]

Dan johnson flew from fla to Mount Vernon Il in a Si at 5050rpm, 120mph, 75% power, and 4.1gph. Coming from him, that should end the fuel burn in the Si discussions.

Which isn't that different that what I'd get at the same RPM in my Sting with my fuel burn being around 4.7gph.

[FlyingMonkey]

Which isn't that different that what I'd get at the same RPM in my Sting with my fuel burn being around 4.7gph.

 

Yeah, at a half gallon per hour it would take you a few to recoup the extra cost of the iS engine...

[Jim]

Dan johnson flew from fla to Mount Vernon Il in a Si at 5050rpm, 120mph, 75% power, and 4.1gph. Coming from him, that should end the fuel burn in the Si discussions.

 

Which is not significantly better than what my CTSW gets at gross weight and that speed.

[paul m]

Are we really debating 4 vs 5 gallons? I know pilots as a whole can be pretty cost conscious but that seems a little extreme. Getting the fuel injected engine can be about a few things, but that can't be the primary reason. At the current price difference, you can never justify the cost on that. It's heavier, there are fewer people who can work on it, it can shut down on you, it requires a couple of mins of warm up before you can even turn on the avionics. Against that, you get a little better fuel economy (unless you never fly below 92% like Ed), you can't get carb ice, engine starts are smoother...and the real benefit.....it looks cool. Justifying its cost makes no sense. We often say that about airplane ownership as well.

[FlyingMonkey]

it requires a couple of mins of warm up before you can even turn on the avionics.

 

I have not heard that, what's that all about?

[chanik]

BTW, some people take this sort of thing quite seriously!

 

(click to enlarge)

 

 

On a serious note, note how quickly CHT's drop off on the right of peak (leaner) than on the left of peak (richer).

 

Hard to conclude that LOP is somehow inherently "hotter", right?

 

Oooh, that thing looks great. Where do you get those shirts? I've been wanting to see some real numbers on the 912iS for awhile. BTW, my CTSW on #1 needles burns 4.6gph at 5K RPM and 3000' turning 120kts TAS.

[paul m]

I have not heard that, what's that all about?

 

Per the AOI,

you start engine with GEN A, you then wait for min oil temp (122) to engage GEN B which requires you to go to 3,000 rpm for 10 seconds. It says it can take 2-5 mins to get to 122 depending on OAT. You then turn on avionics. If you turn on avionics before GEN B engaged, you are using batttery. "This can drain the battery very fast." I don't have any real world experience yet with the "i", so if anyone knows differently please correct me.