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RV-12iS with ULS motor pros/cons

DanFrazer

Member
I'm currently building an RV-12iS and just as I think about paint schemes often, I've also been contemplating installing the ULS motor instead of the iS version. With some recent discussion on electric fuel pump failures, and multiple attempts at replacing the pumps combined with the much more difficult accessibility vs. the ULS configuration, it's prompted me to actually write out my thoughts in a pro/con list format.

As with most airplane decisions, it's highly dependent on personal opinions and situations so I won't bother making this a poll. I welcome the group's additional thoughts from both ULS and iS drivers. What am I missing in the comparison?


Scenario: installing 912ULS motor in RV-12iS

Pros:
  • $5,000 cheaper
  • Better fuel system accessibility. With tailcone on, the 912iS configuration looks real tight and painful to access.
  • Better fuel system reliability. It's on top of my mind because of reading couple posts of repeated replacements AND poor access. If ULS boost pump fails - so what? Still have engine driven pump. If iS fuel pumps fail - no engine.
  • Simplicity? Something about a carbureted engine in an airplane makes me feel better. Maybe it's because most of my experience is in 65 hp cub engines :D
  • Ability to have map box. Not that big of a deal but I'll take more space where I can.

Cons:
  • Higher fuel consumption. ULS is already great at 4.5 gal/hour. Do I really care about saving another gal/hour? If fuel consumption was the only item of merit, it would take a lot of hours to pay back $5,000 in extra cost with less fuel consumption.
  • Lower resale value. How many RV-12iS with ULS motor? Not many I bet.
  • Carburetor maintenance/syncing.
  • Lower range. I'm not old, but I can't see myself sitting in a small plane for longer than 3 hours at a stretch anyway.
  • Lower ceiling. I'm a sport pilot and am limited to 10k feet anyway.
  • I like the appearance of the 912iS top cowl louvers. After reading through 37iS-U, it looks like the bottom cowl is mostly same.
  • Less electrical power from ULS engine. I only have the single landing light. Anything else I'm missing out on?

Thanks for your thoughts.
 
I'm currently building an RV-12iS and just as I think about paint schemes often, I've also been contemplating installing the ULS motor instead of the iS version. With some recent discussion on electric fuel pump failures, and multiple attempts at replacing the pumps combined with the much more difficult accessibility vs. the ULS configuration, it's prompted me to actually write out my thoughts in a pro/con list format.

As with most airplane decisions, it's highly dependent on personal opinions and situations so I won't bother making this a poll. I welcome the group's additional thoughts from both ULS and iS drivers. What am I missing in the comparison?


Scenario: installing 912ULS motor in RV-12iS

Pros:
  • $5,000 cheaper
  • Better fuel system accessibility. With tailcone on, the 912iS configuration looks real tight and painful to access.
  • Better fuel system reliability. It's on top of my mind because of reading couple posts of repeated replacements AND poor access. If ULS boost pump fails - so what? Still have engine driven pump. If iS fuel pumps fail - no engine.
  • Simplicity? Something about a carbureted engine in an airplane makes me feel better. Maybe it's because most of my experience is in 65 hp cub engines :D
  • Ability to have map box. Not that big of a deal but I'll take more space where I can.

Cons:
  • Higher fuel consumption. ULS is already great at 4.5 gal/hour. Do I really care about saving another gal/hour? If fuel consumption was the only item of merit, it would take a lot of hours to pay back $5,000 in extra cost with less fuel consumption.
  • Lower resale value. How many RV-12iS with ULS motor? Not many I bet.
  • Carburetor maintenance/syncing.
  • Lower range. I'm not old, but I can't see myself sitting in a small plane for longer than 3 hours at a stretch anyway.
  • Lower ceiling. I'm a sport pilot and am limited to 10k feet anyway.
  • I like the appearance of the 912iS top cowl louvers. After reading through 37iS-U, it looks like the bottom cowl is mostly same.
  • Less electrical power from ULS engine. I only have the single landing light. Anything else I'm missing out on?

Thanks for your thoughts.

Not trying to push you one way or the other, but…..

Unless you run a ULS at a rather low economy power setting you will not be flying at 4.5 gallons per hour. And the iS version won’t be 3.5 gallons per hour either, unless you are throttled back quite a bit. This would be possible on both if you’re only interested in flying at low power, but you will not be anywhere close to achieving the cruise speeds that the RV 12 is capable of.

Higher Service ceiling can be of benefit when thought of relative to density altitude in the heat of the summer. Some better performance at higher altitudes will equate to better performance at Sport Pilot altitudes in the heat of the summer.

I can’t comment on why some people have struggled with fuel pumps, but I do know it’s not a chronic issue with iS equipped RV 12s. Additionally, there are ways to simplify maintenance and service access to the fuel system. One that works very well is to build a simple platform that has some hinges so that it can fold up, and design it in such a way that it makes a flat area for you to lay on from the seat back brace to the baggage bulkhead opening. This allows you to bridge over the fuel tank and the baggage area and just lie on it with your shoulders and head stuck through the baggage bulkhead open. This puts the entire fuel system within easy reach.

Other than those things, I think the rest of your list nailed it pretty well.
 
It seems a shame to miss out on some really great technology because you are concerned about the fuel pumps.

Yes there were some defective pumps in the past but the recent 12iS pump problems were due to a bad electrical connection which has been addressed in SB00041.

And there seems to be some misconception about fuel system maintenance.

First, the access panel is quite large so that you can easily see and access the fuel pump/filter assembly. Simply remove the seat backs (2 pins) and put a comforter over the fuel tank to make it a little easier on your mid section. A pillow in the baggage area is good too.

Second, the 12iS design makes it easy to remove the fuel pump/filter assembly from the aircraft. Don't punish yourself by trying to work on it in the airplane. (this is key)

If you follow the maintenance manual you will disconnect the wire harness and two fuel lines. Then take out six screws which hold the assembly to the bulkhead. Once out, it is easy to change the filter or pumps while it is on a table.

Bottom line - don't be put off by fuel pump or filter maintenance - it's just not that hard. :)
 
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I own RV-12 SN120058. I’ve been flying for over 50 years and will turn 70 next year. I’d like to still own, maintain, and fly my airplane for another ten years.

When I first saw photos of the 12iS fuel distribution manifold I thought it looked complicated and then I realized it was mounted on the backside of the baggage compartment bulkhead. I suspect that location was chosen, not for accessibility, but to offset the heavier 12iS engine with dual everything including two computers.

I can’t imagine me climbing over the structural angle beam and fuel tank in order to position a temporary skateboard to allow me to lay on my back and stick my body through a hole to service a major fuel component. Minimum requirement would be to do this at Annual Condition Inspection, and perhaps more often than that.

What if I cramp-up and can’t get myself back out of the plane?

I’ll stick with reliable carburation. The 912 is really two sperate and distinct power sources that are linked together buy a common crankshaft. Each half of the engine must be synched together to produce reliable smooth power. Once carbs are synched then very little maintenance is required going forward. At 750TT, I cruise just shy of 5500 redline and I’m willing to pay the extra gallon of 93E10 at Costco…
 
Love my ULS motor, but would build with an iS engine

Admittedly, I was in the iS engine or bust camp and was really the only envy between my RV12 and a new iS (except the great cup holder!).

But, I've come around to appreciate the simplicity of the ULS motor as well. Synching carbs is a non-issue...easy and quick. I do wish I could get a bit more range, but that's about it. If my fuel tank was 25 gallons it would be just about perfect. So, overall, I'm content.

With that said, if I were to build a 12is now, I would certainly go with the 912is without question. I do not think it's any less reliable or a liability. And, unless I'm building my forever plane, the resale on a 912is powered RV12 will certainly be more than the $5k difference of building it with a ULS motor now.
 
When I first saw photos of the 12iS fuel distribution manifold I thought it looked complicated and then I realized it was mounted on the backside of the baggage compartment bulkhead. I suspect that location was chosen, not for accessibility, but to offset the heavier 12iS engine with dual everything including two computers.

The location of the fuel pump manifold is actually to meet some of the many installation design requirements specified by Rotax in the 912iS install manual. It was not for W&B.

I can't say that all other aircraft using the 912iS meet every requirement set by Rotax, but the RV-12iS does (a lot of effort was invested in the design to assure that).
 
I can’t imagine me climbing over the structural angle beam and fuel tank in order to position a temporary skateboard to allow me to lay on my back and stick my body through a hole to service a major fuel component. Minimum requirement would be to do this at Annual Condition Inspection, and perhaps more often than that.

I can't either, but that is not what I described (I am assuming you are commenting on my suggestion on how to deal with fuel system access).

What I described is a platform that when installed, is at the same level as the top of the seat back brace and longerons. While facing aft and kneeling on the seat pan area, you just slide your elbows across the platform and lay on it facing downward. Pretty easy for most anyone that is still limber enough to climb in and out of the pilots seat.
 
What I described is a platform that when installed, is at the same level as the top of the seat back brace and longerons. While facing aft and kneeling on the seat pan area, you just slide your elbows across the platform and lay on it facing downward. Pretty easy for most anyone that is still limber enough to climb in and out of the pilots seat.

Any pictures of someone actually doing this maneuver?
 
The 912IS configuration will add still another 25 pounds to your plane.

My 2012 RV-12 with Skyview, solid blue imron paint job (basic) AP, interior and wheelpants, weighs 772# with the ULS motor.

You'll be pretty close to 800# with dual HDX, non fancy paint. Add in another 119# for full fuel tank and that's about 920# with a gross of 1320# That leaves 410# for you and passenger.

Retired Americans aren't known for being that svelte, add in a $100 hamburger run and some left overs, and the margin might be thin to non existent.

If the 25# is a consideration, the Rotax ULS motor allows more leeway.
 
The 912IS configuration will add still another 25 pounds to your plane.

My 2012 RV-12 with Skyview, solid blue imron paint job (basic) AP, interior and wheelpants, weighs 772# with the ULS motor.

You'll be pretty close to 800# with dual HDX, non fancy paint. Add in another 119# for full fuel tank and that's about 920# with a gross of 1320# That leaves 410# for you and passenger.

Retired Americans aren't known for being that svelte, add in a $100 hamburger run and some left overs, and the margin might be thin to non existent.

If the 25# is a consideration, the Rotax ULS motor allows more leeway.

Going with Van's numbers, the RV 7 would have 418# left with full tanks. So, the 12 is doing really good for what it is.
 
What I described is a platform that when installed, is at the same level as the top of the seat back brace and longerons. While facing aft and kneeling on the seat pan area, you just slide your elbows across the platform and lay on it facing downward. Pretty easy for most anyone that is still limber enough to climb in and out of the pilots seat.

I’m trying visualize someone sliding on their elbows and then laying face-down on a board suspended above the baggage floor and then trying to work on a fuel manifold with redundant pumps and filters located on the backside of the baggage compartment bulkhead.

I would say a cellphone at the ready and pre-dialed for 911 would be prudent.

I’d really like to see a picture of this, or better yet, a video…

I'm still limber enough to climb in and out of the pilots seat. See RV-12 Ingress / Egress here.... https://drive.google.com/drive/folders/171i-weJWZgyHvXDjX8BtP4s-qO8pwF9d?usp=sharing
-
 
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I would say a cellphone at the ready and pre-dialed for 911 would be prudent.

:D

Jim,

Like you, the first time I saw a pic of the assembly on the backside of the bulkhead I thought well this is not going to be fun trying to change that fine filter.

Fortunately, the engineers were thinking the same thing so instead of fastening the pumps and filter directly to the bulkhead, they fastened them to a bracket. That bracket is then fastened to the bulkhead with six screws from the forward side. (another good idea)

So it is fairly easy to remove the fuel pump/filter assembly from the plane and then change the filter on a table.

I was relieved to see the procedure in the maintenance manual and very grateful for someone who was thinking ahead! :)
 
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Thanks everyone for the feedback. I didn't realize how you could remove the entire fuel pump assembly with 6 screws, from the forward side of the bulkhead. That sounds a lot easier than trying to unclamp the fuel pumps while still attached to the bulkhead. I plan to stay on the 912iS course I think.
 
Just curious...Does anyone know of an RV-12iS that was built (or is under construction) with a 912 ULS engine?
 
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Is , being fuel injected , will not have issues starting in cold weather - not so with ULS …. If you plan to fly in winter , it makes a lot of difference.
 
Not quite sure where warmi is coming from with his first post to VAF….. The 912ULS with Bing64 carburetor is wonderfully easy to start in warm or cold weather. The enrichener (airplanes do not have choke) is very affective even at temps below freezing. Engine always starts within a couple blades of turning. The enrichener circuit is easily modulated to produce smooth operation as the engine begins to warm.

As with all aircraft engines, preheat is advised to allow faster cranking in cold temps. The 912 has very close piston / cylinder clearance and cold congealed oil along the piston skirt will reduce engine cranking speed. Best to preheat either ULS or iS engine to help battery and one-way roller clutch on starter motor with cold-cranking. Also good if cold-soaked battery gets warmed slightly from the engine preheat.
 
The 912ULS with Bing64 carburetor is wonderfully easy to start in warm or cold weather. The enrichener (airplanes do not have choke) is very affective even at temps below freezing. Engine always starts within a couple blades of turning. The enrichener circuit is easily modulated to produce smooth operation as the engine begins to warm.

100% this. There *may* be other reasons to knock the ULS (balance carbs, fuel efficiency) vs. the 912is, but Cold/Hot starts certainly isn't one. The Rotax has been a revelation since coming over from Lycoming world. It's just starts every time no matter what on a blade or two. Took this video this past Saturday. It was 14 degrees when I got to airport and estimated 18 degrees when I started. Snow day at KHAO

Admittedly, airplane was in a hangar, but not heated and forgot to turn on pre-heater. I'd estimate hangar temp to be in low 20s as it was 0 degrees the night before. Not to mention airplane sat a bit outside hangar while I waited for hangar bi-fold to completely close because the access door on the bi-fold swung open and I needed to close it before getting in plane (doh!).

Airplane started right up no sweat
 
Only cold weather starting issue I've had with the ULS is when the dumb pilot is so cold he skips over the pre-start checklist too fast and forgets to switch on the two ignition switches. Engine needs them on I've lea...., I mean that dumb pilot has learned.

BTW, do recommend EZHEAT for Rotax system for preheater, reliable and inexpensive.
 
Is , being fuel injected , will not have issues starting in cold weather - not so with ULS …. If you plan to fly in winter , it makes a lot of difference.

Not sure what issues you are having, I lived in Maine for 6 years and flew with temps as low as -10 and no back in PA with temps in the the 10-30 range in the winter with no issues at all and really great performance :D
 
Is , being fuel injected , will not have issues starting in cold weather - not so with ULS …. If you plan to fly in winter , it makes a lot of difference.

Ahh,yeah that's totally not true at all.
I dont care what the temp is my ULS starts so fast that you cant even hear it crank,its like touch the key and bang its running.
 
Not sure what issues you are having, I lived in Maine for 6 years and flew with temps as low as -10 and no back in PA with temps in the the 10-30 range in the winter with no issues at all and really great performance :D

It is not about flying, it is about starting …I won’t even bother starting below 30 degrees without pre-heating.

On a more general note … after 400 hours flying behind 912uls ,if I were to purchase a Rotax equipped plane again , I would certainly go with the IS version ( preferably 915 but that’s another story )
The engine has been generally quite reliable the only problem being carbs - heavy floats as well as one time partial engine out due to debris in the carb bowl ( mostly likely maintenance issue).

Thankfully , the engine out episode was on the ground ..
https://youtu.be/PCmdNnOrXOc
 
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