Rotax 912iS or 912ULS for Sling 2 ???

[Warmi]

True, they are different in the sense that electronics only make sense if you are trying to replace/automate sufficiently complex mechanical behavior ( say altitude compensating carburetors ) and of course, nothing is perfect - vibration , all of that comes into play but ultimately, the basic principle still holds - the fewer moving parts , the better.

In other words, a simple mechanical switch based on some kind of binary action is probably more reliable than the same behavior implemented on a board and in software but once you move up there in complexity there is no comparison.

[ShawnM]

The Sling is a beautiful plane for sure, it looks A LOT like my SportCruiser. They say imitation is the best form of flattery.

[cam737]

ShawnM, I agree. The Sport Cruiser is beautiful! I just happen to fall in love with another.

Cam

[ShawnM]

Don't worry cam737 I wont tell your wife, your secret is safe with me.

The Sling is a beautiful plane as well. It does have some great features.

[WDD]

This thread got my curiosity up, so I e mailed Vans about their POV on their RV 12. I asked them about the differences in their new RV12iS version of the plane between using the ULS vs the iS engine.

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Hi Warren,

The only RV-12iS in existence right now, our factory prototype, had an empty weight of 780 lbs. That yielded a useful load of 540 lbs. The iS engine and systems are a bit heavier than the ULS. We haven’t built an iS fuselage with the ULS engine to weigh. But judging what we know of the ULS installed in the earlier version, the useful load of an RV-12iS with the ULS engine should be about 10-15 lbs. higher.

If you are considering going this way, I really feel compelled to offer my $.02. I have over 700 hours in the RV-12 ULS and about 60 in the RV-12iS with the iS engine. They both fly the same. Not a nickels difference in handling between them if anything at all. The iS version climbs about 100 FPM faster than the ULS. It operates more smoothly and does honestly use 25% less fuel than the ULS. I flew the iS out to OSH this last year. I flew along with our ULS version. Similar weights, same altitudes, same airspeeds, took off and landed at same time. The ULS used 60 gallons of fuel to get there. The iS used 45. Kind of hard for me to believe but it is the honest truth. Just some food for thought.

Hope this helps.

Mitchell Lock
President
Van’s Aircraft, Inc.
14401 Keil Rd. NE
Aurora, OR 97002
503.678.6545

[FastEddieB]

Thanks for posting that. It carries a lot of weight!

So to speak!

[3Dreaming]

How does cost factor in? The 25% reduction is fuel will save you about $7,500 over the 2,000 hour TBO based on a fuel cost of $3.00 per gallon. You will also save a little bit on carb maintenance. However there is other annual condition inspection maintenance. Plus the fuel pressure regulator is supposed to be replaced at the 5 year rubber replacement, and cost is $337.45. I think in most cases the added cost of the 912iS will be recouped by the fuel and maintenance savings over the 2000 TBO of the engine.

[drseti]

Current US price of the 912ULS is $16,995. The 912iS Sport is $23,286 (CA Power Systems pricing). So, in terms of fuel savings, it's probably a wash. Therefore, I would make decisions based on mission, weight, dongle cost, availability of iS mechanics, and how much one likes to resync dual carbs.

[MrMorden]

Current US price of the 912ULS is $16,995. The 912iS Sport is $23,286 (CA Power Systems pricing). So, in terms of fuel savings, it's probably a wash. Therefore, I would make decisions based on mission, weight, dongle cost, availability of iS mechanics, and how much one likes to resync dual carbs.

In doing the math, the 912ULS saves you those thousands of dollars *right now*, which can then be used/invested for other purposes. To get that money back from a 912iS, you have to keep and use the engine for its entire life. So I'd rather have $7000 now than $7000 inflation-adjusted (e.g. of less value) in however many years it takes to realize those fuel savings. Since twenty years down the road that $7k is worth half as much or less, it's not really a wash; the math clearly favors the 912ULS and savings now.

Of course, there are many reasons one might consider a 912iS engine over a 912ULS, but in my mind fuel cost savings are the least of them, and the worst reason to switch over to the newer technology.

[drseti]

I'm inclined to agree with you, Andy. Of course, there are those who will (rightly) point out that there is an intangible benefit to having the latest technology in hand right now. Whether that benefit outweighs financial considerations is very much a personal decision.

[Nomore767]

Mitch Lock's comments are very accurate. Mitch has a wealth of experience with the RV-12, and it was a demo flight with him in the, then, new SLSA demo plane that helped me decide to buy the RV-12 SLSA, with the ULS engine.

His figures and comments on the flight of the iS RV-12 flying along with the ULS airplane show that the only real difference was that the iS plane saved 15 gallons, which in my area is just under $40. The purchase cost of the iS though is quite a bit higher than the ULS SLSA, somewhere around $45k, which is not insignificant. The iS will come with some mods developed by builders but you can add some of them now on the ULS SLSA, as I've done.

Paul's comments about mission and what the iS RV-12 gets you is right on the money. I do feel that the new RV-12 is better in some regards, and that the iS type engine will be the wave of the future, and is more efficient in fuel burn, but as I said above, with autogas being much cheaper than avgas, and even the new UL fuels, that saving is really small compared to the increased maintenance cost, if you can find someone who has some experience with them.
I'd be a lot more interested in a Rotax that is more 'efficient' in terms of things like rubber replacement periods which would save more over the life of the engine and airframe. Carb synchs really aren't that frequent or difficult, for my mechanic anyway (not me!).

The empty weight of the iS RV-12 is really good considering the iS engine is heavier than the ULS. My SLSA has empty weight of 765 only 15lbs less than the iS which is real advantage for the RV-12 over competitive manufacturers.

Agree with MR Mordens comments about fuel savings. The benefit is minimal in $$, but I suppose it does help the environment. I plan on 5gph but usually get 4.8 mph. The iS typically gets 3.5gph in cruise and overall would be, in my view, closer to 4gph overall versus what I get. Again to me a minimal advantage. To max out the savings you'd have to look at going to TBO of 2000 hours. Ive had my plane almost 4 years and have about 400 hours so in 16 years when I'm 81 I'll be able to tell you how much I've saved.

If I was back in the market and trying to decide on either the ULS or the iS I'd be tempted to buy the latest and greatest model, as technology moves quickly, but the price difference would be a factor. I asked my mechanic for his opinion and he said he's worked on a lot of ULS engines in the past few years, and no iS engines. Of any manufacturer, not just Vans.

[MrMorden]

I'm inclined to agree with you, Andy. Of course, there are those who will (rightly) point out that there is an intangible benefit to having the latest technology in hand right now. Whether that benefit outweighs financial considerations is very much a personal decision.

My last paragraph was a disclaimer to that effect. We are on the same page.

[Nomore767]

Agreed!

[Wm.Ince]

Regarding the choice between ULS and iS, something that should not be overlooked is the demand on the aircraft electrical system.
Besides wing strobes and position lights, I believe the Sling is equipped with 2 taxi lights and 2 landing lights. If the autopilot is engaged, will the ULS easily handle that load or will the limit be pushed?

[drseti]

The 912 ULS generator puts out 15 amps. For avionics systems that put a heavy load on it, most of us supplenent this with the 20 amp aux gen.