CTLSi economy at altitude

[FlyingMonkey]

I flew nonstop yesterday from 52F to KIOW (582nm) nonstop at 5500 ft. Took 5.6 hours with winds and ran about 5.3 gph most of the trip. Started out full tanks and landed with very little in site tubes. Computer said I could go another 85nm, little voice inside of my head saying, land now, land now. Just wondering if the iS would have made any difference. DA was 7500 ft for the majority of the trip.

 

At what RPM and speed were you flying?

[FlyingMonkey]

Based on specs, sure but the point of this thread is to look at real world results, like when flying out west where you need altitude you might be flying without being in econo-mode.

 

It will definitely be interesting in a year or so to see whether the theoretical fuel savings translate into the real world with how pilots are *actually* flying their aircraft. I have no doubt if pilots are careful in RPM management they can see nice gains, but I'd love to see some iS drivers do some careful analysis matching real fuel burns to various RPMs and altitudes.

[Jim Meade]

Forty years ago when the trucking industry started using wind deflectors, they were touted as saving fuel. Instead of driving with your foot on the floor doing 70 mph, you could back off some rpm and save fuel while maintaining 70 mph. Or you could drive with your foot on the floor and do 74 mph. Guess what happened?

[Ed Cesnalis]

Guess what happened?

 

You got my number! Back in 2006 Alan Wallace named me 'WOT Charlie Tango'.

 

The economy is already awesome, I'll take the extra knots.

[FastEddieB]

The LOP crowd says operating with a partially closed throttle is analogous to operating with a dirty air filter.

 

I bet if you had a mixture control, it might be "WOTLOP Charlie Tango"!

[FlyingMonkey]

You got my number! Back in 2006 Alan Wallace named me 'WOT Charlie Tango'.

 

The economy is already awesome, I'll take the extra knots.

 

Would you do the same if you were flying lower and making full power, burning 6+gph? No judgments, just curious.

[Ed Cesnalis]

75% for max continuous has always been my thinking so no, I throttle back when I get the chance to curise over the beaches or low valleys.

[Dan Kent]

Here's an interesting discussion on Van's concerning the 912i. I think someone from this forum actually started the thread. A page into the discussion a couple of folks that have experience with fuel injecting the 912 pipe in.

 

http://www.vansairforce.com/community/showthread.php?t=104216

[FlyingMonkey]

From that Van's discussion, post #23, here is the most interesting and correct thing I have seen on this topic:

 

"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."

[Roger Lee]

The difference between the FI setups made for the 912ULS is it's the same engine with only a different fuel delivery and no near as sophisticated duel computer and sensor system setup. The new 912is engine is 65% different design from the 912ULS. They question a 20% fuel efficiency. I'm here to tell you it's real although that also depends on the users use of the throttle too just like any thing else. None of these guys on Vans has had any training or has been privy to the new engine info so they are like most speculating.

 

I will say this that both engines have their pros and cons and each can shine depending on it's use.

[Ed Cesnalis]

There are lots of open questions especially concerning what happens at altitude. As Don @ Airflow points out ( vans forum ) there is no free lunch, you can save fuel running LOP but at the expense of power.

 

As Andy points out there may be some power recovered by timing adjustments but it can't be optimized without knock sensors.

 

The economy claim is ambiguous "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?"

 

Conclusion: At altitude both the carbed and FI versions require a power reduction to realize better economy even if max power available is less than 75%.

[FlyingMonkey]

Nobody is doubting the increased full efficiency. People *are* debating how much that increase will be in the real world among the entire fleet of iS engines. Neither going to Rotax school or flying a CTLSi for a few hours will tell us that. Only experience over dozens or hundreds of aircraft running for many hours will give us that information. Since we don't have it and won't for a couple of years, it is natural for people to speculate on what that experience will show, given what we know about the engine and physics.

 

I don't think anybody is knocking the engine. We're just in speculation mode because there are not enough flying to answer our questions definitively. In addition there are questions about whether the EFI system with its higher reliance on electronics will prove to be more reliable or less. All the redundancy is fabulous, but if ECUs fail often due to heat or vibration, the airplane is still going to spend a lot of time in the shop. Electronics fail. Fuel injectors fail. Fuel rails can get clogged. There are a lot of issues that may or may not show up with regards to this new system, and it's normal to discuss it and pick it apart and try to spot weak areas. It doesn't mean we think the engine is crap, it's just the kind of analysis people (especially pilots) do with anything new.

 

It's better than talking about how to land again.

[Ed Cesnalis]

...My wife got 3.4gph on her trip from KVGT to KCXP with a 5kt tailwind running an average of 5200-5300 rpm at 8500 feet into and out of California across the Sierras....

 

It is very hard for me accept your claims. You claim you need 12,000' just to fly to Truckee yet your wife can cross the much higher sierra in California at 8,500'?

 

You said her flight was 330 miles and 11 gallons so at 3.4gph it was a 3.23 hour flight or real close to 100mph yet you repeatedly claim 3.5gph @ 120kts, your not even in that ballpark.

[Roger Lee]

Another issue being addressed,

You are going to have to have the computer diagnostic cable hook-up changed. FD split the cable and should have been a single cable, but not a huge deal, but you'll need a splitter. Plus you need to have a 120 ohm resister between pin 2&7 in each cable or if a single cable it still needs to be there.

[Tom Baker]

I flew a CTLSi for a little bit a couple weeks ago. The fuel burn was better than my CTLS, but I didn't se the 20% better number that you are saying.

[Roger Lee]

While you guys are batting around fuel economy just remember this has huge variables. Prop pitch (big factor), take-off styles, cruise rpms (another big factor), type of plane (SW or new LS).

 

You have two very different engines and would need to setup everything the same to truly compare fuel economy. Even the guys on Vans with the after market FI system is comparing apples and oranges. Of the approximate 400 engines out flying they are getting much better economy, but again that is subjective from each person reporting because they have an entirely different set of variables.

Rotax ran these on a stand at the factory so all variables could be controlled between the two engines which never are the same in the field. It does better, okay so my Prius gets better fuel mileage than your 1 ton truck. It is what it is. the 912is is different from the 912ULS. The FI is redesigned by 65% over the ULS. It's just different.

 

We all know the FI will do better at altitude with power and fuel adaptation so who cares if one saves a little more fuel. That was the same with cars when they went from carbs to FI and now it's the standard. We own and fly what we have and we all like what we have.

 

The FI wins with better fuel economy no argument. any real and actual numbers will be owner subjective and influenced by the variable.

 

We should euthanize this 95 page debate they may end in the year 2025.

[Ed Cesnalis]

What does 65% redesign mean?

 

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.

 

Your quote here says there is no savings at max available power when below 75%, and now you are saying there is savings enough discussion.

 

You are correct that many variables are involved but some are self defeating, for instance mixture is a variable and when the 912i is LOP it is saving fuel, some of the savings is from no longer running rich and some are from a power reduction that is the result of being LOP. Savings are therefore at the expense of cruise speed to a point.

 

Its the 120kt @ 3.5gph using high altitude western routes that is the most questionable, in this case compromise is required. I wouldn't want to personally

take on the expense of an upgrade and find that the savings don't apply to me after I spend the money.

[Roger Lee]

A 65% redesign means that that new engine is 65% different from the 912ULS design. Internal and external part are veary different. For example even though the gearbox looks the same the dogs inside are different and the 30 degree movement when the crank is locked is gone.This is one reason (along with many others) I said no one will be able to work on this without some type of class. The throttle position is monitored and when over 92% the 912is gets no better than the ULS and actually worse. Once you throttle down under 92% the computers help things out by going into eco mode. The savings between the two engines will happen because the 912is can meter fuel more efficiently and as you climb in altitude can make finer adjustments to the fuel system.This is only if everything and everyone was created equal and we all flew the same.

 

That isn't going to happen so there will always be discrepancies. We both know that the fuel injected will do better at altitude and can meter fuel more efficiency.

 

We might as well leave it at that.

Any claims past that are subjective from plane to plane and varied from plane to plane.

 

This discussion between all you guys has no exact answer it will always vary.

 

No different than one owner of a car claiming he gets better fuel economy than the other with the same car or the auto MFG making its MPG claim. Results will vary is all they say.

 

All claims here are going to vary. Just agree to disagree.

[Ed Cesnalis]

...I own one, and I fly one. None of the discussion here bears any resemblance to reality ...

 

So we ended up on the header tank on the last 50 miles in with the big red low fuel light on reducing the throttle to 3800 and using the altitude to make the last five miles..

 

If there was no header tank, we would have run out of fuel (about 1.2 useable)....

 

Every time I hear that story the hairs on the back of my neck stand up. I know that approach, I have been flying it for decades. What triggers your low fuel light, you are implying that you had only 1.2gallons from 50 miles out or at least that you landed with less than 1.2gal, is that true?

 

Did you have to declare an emergency to use Class B for your high slipping approach? What were your thoughts as you are doing this over the densely populated city?

[FlyingMonkey]

I agree here..."we would have run out of fuel"...how? Do you just ignore the fact that the sight tubes are empty and keep flying because you "should" have enough fuel? When you see the tubes barely showing fuel and know you have many more miles to travel, doesn't this demand that you divert to the nearest airfield?

 

I think you should completely forget about the header tank and consider the airplane empty of fuel when the sight tubes show 1/5 or less fuel in them. The way you tell this story is as if you think the great header tank feature of the CTLSi salvaged some kind of unforeseen, completely unexpected situation. The reality is you ignored your fuel state until it was well past critical and only luck saved you from an off airport landing.

[FastEddieB]

Which is safer...

 

...a plane with 11 gals each side, or...

 

...a plane with 10 gals each side and a 2 gal header tank?

 

My fear is that the header tank is being seen as some sort of "reserve" that can get you out of a jam.

 

It's not - usable fuel is usable fuel.

[Doug G.]

Not only that, you are required to have at least 1/2 hour of reserve for VFR day flight. I personally plan an hour on long trips. You do not have the right to endanger yourself, anyone fling with you, or people on the ground because of a poor pre-flight, or a failure to properly calculate your fuel burn. You got lucky, there are others who don't realize they were lucky too.

[Ed Cesnalis]

A 65% redesign means that that new engine is 65% different from the 912ULS design...

 

Once you throttle down under 92% the computers help things out by going into eco mode. ...

 

We both know that the fuel injected will do better at altitude and can meter fuel more efficiency.

 

...

 

Just agree to disagree.

 

65% different, sounds like marketing to me, how can they use such a number without any math to determine it? Plug in the number you want for the effect you desire I think.

 

Your next 2 statements are in conflict no? I know that my normal cruise altitudes in any direction are 10,500 , 11,500 , or 12,500 as they have always been. At those altitudes flying below 92% throttle only makes sense if you want to fly at 55% to 65% power. It makes the 120kt @ 3.5gph claim or expectation highly suspect. We don't have to agree to disagree at all, these things can be determined.

 

At first the claims were 20% faster due to a 20% expected increase in power. I wouldn't buy that and pointed out that it takes an 8x power increase and that this is a 100hp engine. So now those high speed expectations are gone and eventually any expectation of 120kt @ 3.5gph at altitude will likely be lost as well.

 

These conversations are great, I have learned that the FI uses LOP in Econo mode, that timing optimization must be limited and 92% throttle is a limitation that would defeat benefit starting above 7,500'.

 

Before we call it and agree to disagree we should be at disagreement, at this point there is agreement that the FI has fuel saving technology and that the results and limitations have yet to be quantified.

[Duane Jefts]

When the header tank drops below its 1.6 gal mark it illuminates the light in the cockpit. When you look at the header tank itself there is a fuel remaining sight tube that shows you exactly what is left in the tank.

[Ed Cesnalis]

Which is safer...

 

...a plane with 11 gals each side, or...

 

...a plane with 10 gals each side and a 2 gal header tank?

 

My fear is that the header tank is being seen as some sort of "reserve" that can get you out of a jam.

 

It's not - usable fuel is usable fuel.

 

Ah but Eddie, in a CT it is

 

...a plane with 17 gals each side, or...

 

...a plane with 17 gals each side and a 1.2 gal header tank?

 

so his claim could be true. Since the wing tanks have sight tubes and he had a low fuel light on 50 miles out I"m guess the only fuel he had remaining was in his header tank and perhaps some sloshed outboard in a wing.