Myself and 3 of my co CH750 builders have been planning to install the Rotax 912iS in our CH750s since the day that Rotax announced the release of the iS. Up to this point, there has been little information available so all of us have searched for scraps of info that can feed our hungary appetite for information.

We talked to our (Canadian) Rotax distributor at Oshkosh and as luck would have it, they had bought a CH750 kit to install a 912iS and use as a demonstrator. That was great news for us, so since then we have been waiting for the 750 to be built and flown. Rotech Research have contracted the newest Zenair Build Centre in Vernon BC which is right across the field from them to the build the airplane. The project is progressing, but no airplane goes together by itself so we somewhat impatiently wait to see a 912iS installed in a 750.

Today there was another tidbit of info released. Their build is a feature on the forum/information site. The site has many videos on Rotax tips, product information and reviews, etc and today they released a new series called "Rotax Builder Series". The video released today has an introduction to the series with a first look at the CH750 airframe and some of the issues with installing a 912iS in that airframe. The video is at If you wish to look at the video, this site is user pay site and has annual fee of $29.95.

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Thanks for your post! Its great to hear from someone who has flown with this engine. I have the long range tanks for my 750 and because the fuel suction outlet is not at the very back of the tank because of its geometry, I think there is going to be considerable unusable fuel when tested at the takeoff attitude as well as on a steep approach - which is the sort I'm partial to since I like the idea of being able to glide to the runway if the engine stops on final - something that a WWII pilot friend drummed into me.

The Flight design CTLS POH has a diagram of the carburretted fuel system, but not the injected system - but their sales brochure says they have added a 1.7 gal header tank. I note that according to its handbook, the carburetted CTLS  used "large diameter fuel lines" to feed the engine and I guess that is sort of like using a small header tank - you can see these on the diagram.

The CTLS handbook with diagram is downloadable here:

What I am inclined to do until someone comes up with a better idea is to replicate most of the latest Cessna 172 system - it uses a header tank, albeit small I think. That would mean

1. Install a 1.7 gal header tank.

2. Join my Two tank return lines together as a vent line so that either tank cap can vent the whole system. I don't think I need to vent the header tank if its designed correctly so that it can't trap air, I need to think about unintended fuel transfer between tanks. Maybe I vent the header tank to the main tank vent line, but that would mean putting three check valves in the system to prevent unintended fuel transfers.

3. Use an Andair simplex fuel selector with "Off", "Left", "Right" and "Both" positions to feed fuel to the header tank.

4. Put an Andair Gascolator with drain between engine and header tank on the front of the firewall like in a certified aircraft - assuming an andair gascolater will flow Sixty litres per hour..

5. If the header tank ends up as the lowest point, then put a drain valve on it.

6. Fit an "Emergency fuel shutoff valve" preferably like the Cessna one, in front of the fuel selector.

What could possibly go wrong?  :)

indeed, there is a lot to think about.... but we are also now into a new realm.  Sadly, events of today and tomorrow are pushing back our in aircraft tests... .but we are hopeful of an interesting option that may attract some people!

Rick Hayes of Hays Aero, Lapeer,Mich. is Pres. of the Mich. Ultralight Assoc. I don't live in Mich., but A) he is a hvy. Rotax repair center, 100 hr. inspect., etc. B) Just received 912 iS in crate-would be a good source for those applicable, although will install in different E.A.B. A/C model. I have a 5 gal. sq. alum. header tank, fed by (2) 9's, high wing: leading & trailing edge lines ea. wing @ L. outer, inner brass fittings, same 2 @ other side outer, inner 90 degree brass. Lower tank db. "Y" 2:1, then under seat to shut-off valve enroute to 912S. Center fitting is vent, exiting out & up to R. skylight ( w/same 90 tube as are on fuel caps.)Mission  was to = 23 gal. for range in Wyo.-Mont., + no concern wing siphoning, but vented this 5 gal. header, mounted in diff. E.A.B. (1st A/C was 701 w/914 turbo, 3rd -finishing 601XLB, hence thread.)Contact Hayes for 912iS ,good referral.

Just watched the second video of the 912 iS installation in a CH750 at I've learned that a header tank is considered necessary. The header tank is installed behind the left door post so its not going to be noticed much by the pilot although I guess it cuts the passengers vision a little.

I was most impressed by the short section showing flow testing at a Forty degree up angle. I've flown with an instructor in a CH701 who demonstrated the ridiculous attitude you can achieve and I am glad that this type of testing is being done for the CH750 install.

I emailed skytek to ask about their schedule. The only issue I noted for my plane so far is that they use half inch inlet and return lines from each fuel tank and the header tank and I've already plumbed my wings with 3/8 SS braided teflon hose. I can easily swap out the inlet line with half inch, but replacing the vent line with half inch is going to require signifigant grumbling, so I guess I have to wait and see what the experts think.

I like the Andair Gascolator mounted on the front of the firewall like a certified aircraft as well. There is a single "on off" fuel shutoff valve so I don't get to buy one of those cute Andair "left right both" valves but hey, I guess its one less thing to fiddle with and mess up.

The video is here:


From the time that this engine was announced, I felt that a header tank was necessary for this airframe. The flat bottoms tanks could easily unport like they have since concluded and shown in the video. I have four wing tanks installed in my 750 and have them controlled by 4 individual ball valves. This way I can have any combination of tanks feeding on or off to my header tank. My header tank is mounted under the pax seat and is vented back to the wing tanks to ensure that no air can be trapped in the header tank. I also have installed a optic level sender in the header tank in order to warn me if the header tank is not fully flooded. I have ran 3/8" aluminum fuel lines except for the vent line which is 1/4". I do not feel that the 1/2" line is necessary. I also feel confident in my design; my co-builders and I have put a lot of thought and mental energy into this design which we have had for a year now. When we first talked to Rotech about this at Oshkosh 2012, they felt our design was flawed. Since then, they have ended up copying us pretty closely. The only difference is the size of lines from the wing tanks to the header tank and that only has to have a max flow rate of 28 litres per hour not the 60 litres per hour that the fuel pumps cycle through. I will give them credit for having a deep sump intake port on the header tank which pretty much guarantees that fuel will continue to be delivered to the injectors if there is any fuel left in the aircraft. My header tank has a flat bottom and could unport if my 5 litre header tank had less than 2 litres. If my warning light illuminates, I am assuming that I am in an emergency situation and will be taking all necessary precautions to make an emergency descent and landing.

Geoff, I think you will be fine with the fuel lines that you have already installed. I am not going to change mine...

On another note, I am wondering what the UL Power guys are doing with their fuel injected fuel system design for the 750..? I know there are few guys installing them and have not heard them speak of a header tank. The Viking guys on the other hand have also realized that a header tank is pretty much a necessity.

Header tanks for fuel injected engines make a lot of sense - and having worked with them for a while, will install a header in all injected engines - and probably add to our carb installations too in future - the advantages outweigh the disadvantages for me, at least.

With all due respect to my Canadian colleagues, I feel that AN8 (1/2") lines are an overkill.  3/8" are plenty big enough, in my opinion.  Now, we should note that, as far as I am aware, the Canadians are not allowed 1/4" lines due to ice crystals.  So, if you want to go up from 1/4" to 3/8" in the warmer climates, I understand their logic in going from 3/8" to the 1/2" - which is amazingly safe and allows air to pass very easily, however, I have a different opinion, right or wrong!

Now, how is my opinion formed?  We have been flying the 912iS on our 701 test bed for over 6months.  We have tried several fuel systems based on the 3/8" lines in all areas. and are currently running tests with 1/4" lines from the main tanks to the header tank and 3/8" lines to the fuel pumps, engine and return.  We would not normally do this, but but we wanted to test it - and in flight (yes, we are serious about testing!).  We have several successful hours operations, at VERY extreme angles and at high temperatures.  We have installed visuals to observe the flow of fuel and of bubbles - and are comparing to the similar effects found with the CARB version of 80Hp.  We have demonstrated uncovered ports on the ground and in the air.  We have demonstrated in flight (not just on the ground) what happens... and it is very interesting!

We operate over hostile terrain and really want a really safe system.  We are already flying with over 150litres of fuel on board for our long missions (4 tanks, individually switched, generally all 4 on at once when below 100 litres uptake, self balancing via the header tank) and need to remain airborne for 8 hours or more at times.  We love the iS for its low consumption (we are averaging less than 13lph).  However, we also want a system that is reasonable and reliable - and wanted to explore the retrofit market potential.  

Personally, I do not like the header tank installed on the door side, it appears vulnerable in an accident, but it does give excellent air-bleeding - there is always a compromise with everything we do. I also like to see my fuel flow (we have flow monitoring on all our installations for obvious reasons).  We have installed our prototype in the baggage area for monitoring (and we monitor fuel temperature too - remember it gets hotter when it flows around the engine and back to the header tank!)

Viking has a lot experience with header tanks (and provdided our test unit, but we use it differently - we are also using the same concept on our aerial dispersal programmes).  Viking has nice header installations for the 701 and a special one for the 750... take a look at their ideas.  you will note that they DO NOT appear to install a return to the main tanks... something we are also looking at, but believe that a return to the main tanks is advantageous for many reasons...

Later this week I expect to load up some pictures, diagrams, calculations and some video of our installation, not for others to say 'this is good or bad' nor for others to blindly copy, but to share what we have found works for us in our situation - in a retrofit condition - on a CH701 and our reasoning and test results - we will post a 'teaser' here and be submitting to an Aviation Journal for publication (so you got it first on the Zenith Aero site ;-) ).  

In the meantime, keep on taking in all the comments and observations - they are all valid and we can all learn from each other... only do what you are happy with - for it is your installation.... your plane.... your solution ..... your life!

*NB LO = Left Outboard, LI = Left Inboard, RO, RI = Right Outboard and Inboard - then there is a master switch after the header tank on the way to the teflon coated gasco on the way to the pumps!  The wires are from test equipment and the masking tape holds the temperature probe in place - we will soon dispense with that, as you will read why in the report!

Hi Jonathan,

I really like hearing what you have to say on this subject. You actually have one of these engines and even better, have flown with it. I really look forward to reading your report. It seems that my thinking may be on track based on your opinions of Rotech/Skytech's design and installation. I am even more hopeful that my system will work without problems right off. I am, however, prepared to treat my installation as a prototype and I will be putting my aircraft through a full testing regime. Your info definitely improves my odds of getting things right. THANK YOU!

Here's what I decided on, after considering many shapes, sizes and locations.


WOW! That will work!  Watch the W+B! Also ensure good air venting on your lines, avoid air traps !  

Very interesting approach!! I assume you are filling from the wing tanks?

How many litres?

About 3.5 gallons, with 3/8 hoses from each wing tank, 1/2 inch out the bottom of header to fuel pumps, mounted on firewall. Hoses from wings drop straight down to the belly, where there are drains, and from there slope continuously upward to header tank. I also strengthened the top shelf of the baggage so that the appropriate weight of survival gear can be permanently carried to fine tune the balance. There is room behind the panel for Dynon screen and V6 Comm. Top of the header tank is vented back to each wing tank (1/4 inch up each of the V tubes, and a sight gauge is centered on the panel.

Hi Ken, 

Well that shows you how awake I was with my last post. I forgot that you were using a UL engine and have installed a header tank. Your system looks great. Two of our guys have installed the 912 ULS and constructed header tanks closely resembling yours. Both the feeder lines and the vent line are routed along the upper firewall/cockpit windshield cage brace. I think their tanks are about the same size as yours'. Is UL Power recommending a header tank?



 Could you post some pictures of your header tank design?  I chose to place a header tank under the passenger’s seat also and vent it back to the wing tanks.  I previously posted pictures of my installation under the 750 topic of header tank below.




I am flying with the UL 350i and have about 50 hours on it.  The fuel system is working well for me.


I am interested to see what others are doing.


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