Research and Results for Fuel Supply Solutions Rotax 912iS

Finally we have reached the point where we consider that we have expressed how we have established our fuel system for the 912iS in our test bed CH701.  No, it does not contain all that we wanted to, but we feel that it conveys the points about what we have done, why we have done it and what we would prefer to do.

We LOVE LOVE LOVE the engine and the airframe combination.  It is a great airframe and a great engine.  A marriage of heavenly proportions, for us and what we use our aircraft for, at least!

It is not a short document... 14 pages long... but it does make great bedtime reading for those who are interested.  It demonstrates what we found, and how we approached it.  It does not contain some of the other things we tested, that relate to ALL the Zenith Aircraft, in relation to the 'fuel tanks levels' - which I can assure everybody are fantastically good and very well balanced, even if there are many comments about them not being (but that is another set of pages and calculations!)

In the meantime, if you are considering installing a Fuel Injected Engine, whether it is Rotax or Viking or UL or any other, please be safe, think about what you want to do, and make sure that you follow the engine manufacturers guidelines... in the mean time, enjoy this bedtime reading...  (link is below the thumbnail The%20Magic%20of%20Electronic%20Fuel%20Injection.pdf

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Comment by Jonathan Porter on March 25, 2013 at 5:54am

Cheers for the positive response, Joe!  Clearly, fuel systems are the challenge that get us all concerned! Do try to get the fuel tanks with 'return lines', if possible, it will make balancing and flow a little faster and it is the way we will go in the future - we are even looking at ways to get a common venting pressure to improve balance - but that is another story!  :-)

Comment by Joe Harrington on March 22, 2013 at 11:44pm

Jonathan, I have taken this long to respond because I wanted to re-read your document and take time to digest all that is in there. A very detailed document with lots of information. To me it looks like you have very much considered all the issues involved and addressed them all. Having actually been able to prove out your solutions in actual flight conditions "is where it is at". At this point your conclusions gives me confidence that we (our building group) are on the right track and our iS fuel system should work. We had concluded pretty much everything that you did in our process of discovery. Thanks again for putting your findings down on paper so we can all benefit from your work! Cheers, Joe

Comment by Jonathan Porter on March 15, 2013 at 5:17am

Thanks Geoff, as Raymond as pointed out, the prop makes a difference.  Imagine that the prop is like the tyres on your truck - they need to be the right ones for your application.... I operate mainly 'off road' others operate 'mainly in the city' then the variable pitch lets you change tyre type as you go!   I would be interested to hear how you get on with the Airmaster!

Comment by Geoff Klestadt on March 14, 2013 at 4:18pm

Thank you so much for this highly informative and well written piece!

I'm going to visit the Rotax agent shortly. I plan on using an Airmaster Constant Speed prop which is specifically designed for the Rotax, thus bypassing all the agonizing about propeller pitch, etc. From what I can tell, Once the CH750 is in the air a Rotax will provide enough power for its rated cruise speed and anything much more is only going to give more noise and a bigger fuel bill for minimal results. The CS propeller will give the aircraft a pretty good take off run and climb too.

Comment by Raymond Paul on March 7, 2013 at 6:54am
Hi Jonathan, I can add to your comment on props, we have a cheeth at our club with the std WARP drive prop, does a great job, but then they fitted the KIEV prop and wow this is just a completely diffrent plane now, running the 912S motor.
Comment by Jonathan Porter on March 5, 2013 at 10:51pm
In fact Jesse, like with all engines there is a balance between torque and Horsey Power. It's important to match the prop setup with the specific engine and air frame arrangement. I assure you we see the full horses on the Rotax engines! You should try different props and pitches on the same engine and compare the results -we are all learning and hopefully getting better results in all aspects of our flying experiences.
Comment by Jesse Hartman on March 5, 2013 at 3:08pm

I would like to see somone put a rotax or any other $22,000 motor on dyno.  I would bet that they are not hitting the horse power they say.  I'd even put money on it.

Comment by Ken Ryan on March 5, 2013 at 11:10am

Nice write up. Now I am starting to understand the limited flow bypass.

Comment by Bob McDonald on March 5, 2013 at 9:12am

The complicated fuel system required for fuel injection vs. benifits of a fuel injected engine is a tough sell for myself to buy into. The carburated version of the Rotax 912ULS has performed flawless in my (and many production aircraft) aircraft. At the reduced power setting that you operate to extend the range, the caburated engine will use the same fuel as the fuel injected version without the "snakes on a plane" fuel lines in the cockpit. (I know the snakes are a real hazard where you live). I know the prevention of carb icing is a benifit of the fuel injected engine, but again it has never been an issue in my part of the world. If fuel injection offered increased HP that would be a benifit I would want....presently the carb 100 hp = fuel injected 100 hp. I am sure that Rotax, and the many other builders considering the use of a fuel injected engine will benifit from the extensive R&D done by yourself. Excellent documentation and presentation of the lessons learned. Fly safe. 

Comment by Chumphol Sirinavin on March 5, 2013 at 12:22am
Thank you, Yaw Obruni. This is very well documented and quite informative. I may go for a Honda Viking engine sometime in the future.


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