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  #1  
Old 01-27-2022, 07:20 PM
DanFrazer DanFrazer is offline
 
Join Date: Sep 2020
Location: West Chester, OH
Posts: 15
Default RV-12iS with ULS motor pros/cons

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
  • 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.
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Dan Frazer
Sport Pilot
West Chester, OH

RV-12iS
Empennage Kit - Complete
Wing Kit - In progress
Fuselage - Ordered 10/16/2021
https://eaabuilderslog.org?s=dfrazer
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  #2  
Old 01-27-2022, 07:48 PM
rvbuilder2002's Avatar
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,792
Default

Quote:
Originally Posted by DanFrazer View Post
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
  • 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, butÖ..

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 wonít be 3.5 gallons per hour either, unless you are throttled back quite a bit. This would be possible on both if youíre 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 canít comment on why some people have struggled with fuel pumps, but I do know itís 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.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Hubbard, Oregon
Van's Aircraft Engineering Prototype Shop
FAA/DAR
RV-6A (aka "Junkyard Special ")
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  #3  
Old 01-27-2022, 09:47 PM
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jrtens jrtens is offline
 
Join Date: Apr 2018
Location: Utah
Posts: 271
Default

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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2019 12iS SLSA
Salt Lake Int'l

Last edited by jrtens : 01-29-2022 at 03:54 PM.
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  #4  
Old 01-28-2022, 06:57 AM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,701
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I own RV-12 SN120058. Iíve been flying for over 50 years and will turn 70 next year. Iíd 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 canít 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 canít get myself back out of the plane?

Iíll 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 Iím willing to pay the extra gallon of 93E10 at CostcoÖ
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 760

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father - CFI) - USAAF 1st Lt. Captain B-17H
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  #5  
Old 01-28-2022, 07:08 AM
JFCRV12 JFCRV12 is offline
 
Join Date: May 2015
Location: Liberty Township OH
Posts: 232
Default 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.
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  #6  
Old 01-28-2022, 08:14 AM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,792
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Quote:
Originally Posted by Piper J3 View Post
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).
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Hubbard, Oregon
Van's Aircraft Engineering Prototype Shop
FAA/DAR
RV-6A (aka "Junkyard Special ")
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  #7  
Old 01-28-2022, 08:21 AM
rvbuilder2002's Avatar
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,792
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Quote:
Originally Posted by Piper J3 View Post

I canít 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.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Hubbard, Oregon
Van's Aircraft Engineering Prototype Shop
FAA/DAR
RV-6A (aka "Junkyard Special ")
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  #8  
Old 01-28-2022, 08:30 AM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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Quote:
Originally Posted by rvbuilder2002 View Post
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?
__________________
-
Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 760

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father - CFI) - USAAF 1st Lt. Captain B-17H
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  #9  
Old 01-28-2022, 01:01 PM
NinerBikes NinerBikes is offline
 
Join Date: Dec 2018
Location: Granada Hills
Posts: 1,247
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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.
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  #10  
Old 01-28-2022, 06:24 PM
gasman gasman is offline
 
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Location: Sonoma County
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Quote:
Originally Posted by NinerBikes View Post
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.
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