I've been requested by several Zenith builders to make this post so builders can ask questions about UL Power Aero Engines and I can respond publicly so other builders gain the benefit of the the exchange.


To start with here is a link to Zenith's webpage showing the Engine and FWF Kit pricing.





Robert Helms

General Managar

UL Power North America, LLC


573 434 0075


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     Sounds like a great opportunity for info to be shared. Anxious to follow your posts.     Jerry

Thanks Jerry.  You can also follow us on Facebook at http://www.facebook.com/ulpower.

I guess I'll fire off the first question:

Currently I have my CH 601 wings open to install the upgrade package. I seriously consider a UL Power powerplant, so this would be the perfect time to take my fuel tanks out and send them to Zenith to have fuel return fittings installed.

Will you be working closely with Zenith to come up with drawings, hardware and recommended practices for the routing of the fuel return lines? Or is the builder more or less on his own to figure this out.





Thanks Hans.  You raise an excellent point.  With Fuel Injection you need fuel return lines because the fuel pump delivers a lot more fuel to the engine than is required for operation.  We have a Fuel Connection Kit which Zenith Aircraft incorporated into their FWF Kit.  It returns the fuel thru a check valve and back to the Fuel Selector Valve.  The Valve in the FWF Kit that Zenith uses returns the fuel to the selected tank (i.e. if you are running off the "right" it returns the fuel to the "right.").  I do not know how Zenith recommends the routing of the fuel lines back to the tank.   All the tanks they ship now have fuel return line fittings in case the  builder wants to utilize UL Power.  Zenith is also making fittings available if you want to have the tanks welded locally.  I suggest you contact Roger for the recommended solution.


Note: it is possible to use a header tank in lieu of returning the fuel to the tanks but it is recommended to return the fuel to the selected tank.


Warning: Do not simply return the fuel from the engine back to the inlet side of the fuel system downstream of the selector valve because the fuel is warm having gone thru the fuel pump and this may cause vapor lock.

Robert: Thanks for starting this Q&A discussion. 

Since the announcement of the fuel injected Rotax 912iS engine we have had many questions about how the UL Power engines compare to Rotax.  It would be useful to see a side-by-side comparison.



Thanks Seb.  I noticed another member started a discussion about the Rotax announcement at the following link:




It is very difficult to obtain specific information about the Rotax 912iS.  Their marketing material simply makes generic comments like "less fuel,"  "less polution," "more efficient," and  "less weight per horsepower."  It is interesting to note, however, they make these comments in comparison to their own 912ULS, the Lycoming IO-233, the Continental O-200 and the Jabiru 3300 but there is absolutely no reference to any of the UL Power engines.  Why is this?  Because UL Power has three engines that produce more power, weigh less and cost less than the 912iS.  Here is a comparison based upon information I've gathered to date.  I would love reliable data if anybody knows more than I've listed here.




Suggested Retail  $ 24,917.70 

Plus you need to add the engine monitoring at a suggested retail price of $3,893.50

Does this mean you add these two numbers together to get the total price?  I don't know.

Weight?  I cannot find a published total weight but a reliable OEM source said the 912iS is heavier than the UL350iS (which has 30 more horsepower).





160 Pounds





173 Pounds





173 Pounds


As I gain more information about the Rotax 912iS I will post it here (it is interesting to see the "iS" after the 912.... it makes it sound like a UL Power engine... albeit impossible with the gearbox).

is there information on how many 350is engines are out there, how many hours flown, and what their reliability has been in terms of engine failures? Can this be compared to Rotax?.

The UL engines are certainly neat. When are we likely to see some actual performance numbers in a CH750 airframe?

Has anybody fitted a constant speed propeller to a UL350is? I note that the engine puts out 130 HP at 3300 rpm what I don't understand is how efficient the engine would be in cruise at say, 2500 rpm without a CS prop. I guess this is a moot point under the American LSA regs that prohibit CS props.

Hi Geoff,


William Yahner has a CH 750 with the UL350iS.  He says at gross weight he's off the ground in 100 feet and climbing about 800 fpm.  I have not flown with him so I can't validate his numbers and I do not know how this compares to other engines.  I've flown in Zenith's 650 demonstrator with the UL350iS and the take-off and climb performance was very nice.  With the GA Whirlwind installed the take-off rpm at full throttle is about 2800rpm.  At cruise in the 650 Roger reports he's doing about 118kts at 2850 rpm and burning about 6.8 gph.  When they throttle back they do about 100mph at 2200rpm and burn about 4 gph.  It depends a lot on how you have the prop adjusted (it's the ground adjustable model).


Several people have installed constant speed props but as you said it is kind of moot with the LSA regs.  With our new six cylinder engine the question is a lot more relevant so we are meeting with the various prop companies to see what they have to offer in terms of electric c/s props.

What prop is William Yahner using on his 750? The installation manual that is on the main UL-Power website (page 55):


says that for the 350iS the maximum prop diameter is 1650mm (65 inches) but I know that some have used longer propellers. What is UL Power's official position on using propellers longer than the 65 inches that is stated in their literature?


William sold his 750 and I don't know what prop he was using.  I met with Sensenich and they are interested in designing a prop for the 750 with the UL350iS.  William still has his 701 with the UL260i and he is using a Sensenich 64" two blade prop and he loves it.  The item number is 2A0J5R642N.  Sensenich would like for someone to try this prop on the UL350iS also (and I think they are talking with Roger at Zenith about doing such).

Hi Guys. spent about a week with UL power in Belgium doing engine builds, maintenance and installation courses.

After we built a 260iS engine, I was quite amazed to see that they actually run the engine (260iS) with a 68 inch prop on the test stand. It reved quite eagerly to 2800rpm! a 68 inch prop can run all the way 3300 rpm and still be subsonic, but fairly close to rpm tip limits. Usually its the prop design that limits rpms ( inertial loads etc). Was very interesting to see it all and experience it first hand.

After each engine is assembled, the engine is put on a test stand and runups done. The ECU, wiring harness used for that specific engine is used on the test stanb for connections and these items are then also shipped with the engine!

Now, the run ups.

Each engine has a set prop they use for runups. (260is -68", 350 iS 68")

Each engine must reach a set rpm with the prop installed and the same prop is used on all the engines with the same pitch. In this way they test each engine to see if it reaches its power and torque on the stand. If it dos not reach the rpm's it is removed and checked.

Therefore, the props for each engine are benchmarking tools.

What this is all about is the that the 260is engine uses a 68" prop and similarly the 350 has a bigger prop. Not the 65inch. Its up to prop manufacturers to bring out larger props for the engines and have them approved on the engine. I know of one prop manufacturer that allows there wood props but not there Ground Adjustables as yet to be used. Similarly, there is a variable pitch manufacturer testing there blades on the 350iS at the moment for approval as well.


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