skippydiesel

I take your point about fuel line losses due to constriction & friction. To a large extent this has been addressed by enabling the Boost pump to draw from the Header tanks. In practice this will mean using the Header (rather than Wing tanks) for TO/CO. The Header is right behind & slightly higher than the engine, so has the combined benefit of a shorter delivery line and a bit of gravity, to assist in fuel flow. I have never seen any where near 27L/hr on my two Rotax 912ULS engines. Yes that's what Rotax specifications say for max power ,however I think a real world figure might be more like 24 L/Hr

I don't think I disagreed with the idea that the aircraft should be able to fly without a Boost pump - just that mine gave every indication that it might not. I never tried a TO/CO without Boost pump, so I can't say what might have happened, however with mechanical + Boost pump, my fuel pressure dropped below 2 psi (the Rotax min). Engine never lost power/hesitated but my heart did. As mentioned , several fixes were tried, with limited success. Aircraft returned to workshop for a range of improvements (including fuel system) - yet to be tried/flown. One of the fuel mods, was the installation of a Boost pump fuel bypass (as per Rotax recommendation) - this will remove any tendency for the boost pump itself, to restrict fuel supply (one of the possible in-line restrictions to good flow). When its back in the air, I will try a full power climb, at altitude, without Boost pump , just to see what happens - let you know.

Fair enough. "Hi Skip, I'm not advocating no boost pump in your aircraft. I'm just suggesting that the fuel system should be able to work comfortably without it." - it does. "As to the Sportstar, I agree it's comforting to have the pump on in those critical phases of flight, but when I was last flying with an instructor in the RH seat, his comment was, "it's unusual, but follow the POH" ie. leave it off. " - There are times in life & POH's, when common sense should prevail, no matter instructions to the contrary. My advice use the Boost pump at all critical stages of flight. It costs nothing and may save your life. An unrelated example; I was taught to use carby heat when required. Many years after obtaining my PPL, I was flying with an instructor in Canada - his advice, use carby heat every time you initiate descent power and leave it on until returning to cruise/full power. I thought about it, made sense, cost nothing and adopted the habit and that's what I do now (when in an aircraft so fitted).

Hi Thruster, See above answer to RossK for responses to most of your observations. I think RossK was leaning towards the Sportstar concept (no Boost Pump) I cant accept that.

Hi RossK, "It seems that your fuel delivery system may have a lot of restriction (lines, connectors, pumps etc), which is limiting pressure and flow." Restrictions - for sure; Long (pipes) all the way to the wing tanks Failure to install a pump bypass as per Rotax installation advice Changes to the fuel system, is to plumb in my (new higher pressure) boost pump & bypass to my 40L header tank. Previously the boost pump would only draw from either wing tank. This change should have two benefits - header tank is pretty much on the same level (head) as the carbs/ engine & very much closer (frictional losses) to the engine. The downside to installing a bypass, etc, is many more joins, additional non return valve & convoluted pipe work. So far only ground check, will be interesting to see what happens on the first TO/CO. "POH actually says the boost pump is on only for start up and emergencies. It's off at all other stages of flight, including take off and landings." Can't agree with any of that. All my training requires; Boost On pre start / check pressure / Off / start engine - This is a check pump function & prime of carb float chamber Run up bay - Boost On / check combined mechanical/boost pressure / TO &/ CO to safe altitude / Off - This is to ensure continuity of engine function through the most critical phase of powered flight Pre landing - Boost On / Off after after landing - Again this is to ensure continuity of engine function, when in close proximity to very hard ground. "The boost pump is actually an optional extra for the Sportstar,... "" I can accept that a high wing/tank may have good fuel flow (engine continue to deliver power) even if mechanical pump fails, however a low wing does not have this inherent safety feature. "...the fuel system will work just fine relying on the Rotax pump alone." Sure - all of use who have forgotten to use the Boost Pump, at one time or the other, know this BUT what happens when the mechanical pump malfunctions????? I suggest it gets a tad quiet, followed by potential nasty noise a little while later. The Boost Pump is a low cost safety feature that all aircraft (in this class) should feature.

Anyone got any thoughts on the likelihood of a pump, with a higher flow & pressure, delivering a worthwhile improvement, in fuel transfer time, given that the piping (aluminium) will remain as is.

Hi BrendAn, In this instance, pressure is used as an indicating of flow. Rotax 9's require a pressure of between 2-7 psi. If flow is reduced (pump unable to maintain sufficient flow), pressure will drop. Its as simple as that.

OK - I now have a low hrs (50) cube boost pump, surplus to requirement, works fine just a bit low on delivery for mys system, see above for estimated performance - intersted?

Thruster - Boost Pump The Rotax advice of max 5 psi is specifically to reduce the chance of pump pressure overwhelming the float chamber valve. Rotax also advise the use of a #35 return flow restrictor, which in my application delivered 7+L/h back to the tank. The combination of fuel burn at max power (TO & CO) plus the return flow, came close to equalling the max flow from both mechanical & boost pump combined, leading to low pressure at this time. After determining that the system was working as expected, I looked for a way to improve the pressure - cheapest/easiest was to put in a smaller aperture return line restrictor reducing return flow to 5L/h this produced a small improvement but not enough. A reference, on Rotax Owner Forum, to RV's advice to RV 12 owners to install a pump with a higher pressure & flow spec grabbed my attention. On reading the RV advice document I quickly saw the parallel with my situation - hence the installation of the higher capacity pump and the reinstallation of the #35 restrictor jet. My Sonex is still undergoing a host of major/minor mods, the boost pump change being just one, so yet to see if there is a beneficial change in TO/CO fuel pressure. Transfer Pump Yes the transfer pump works BUT its so sloooooow! In my limited in flight fuel transfer experience, the longer it takes, the more likely the pilot will be distracted by other tasks/situations leading to venting fuel overboard - not good!. My dilemma is; the 50 US GPH pump (costly special order from The States) will make a transfer time difference BUT by how much?? given the physical restrictions inherent in piped systems. Yes my transfer methodology & rates have all been logged in the POH

Kasper you are a gentleman. Few questions; I aspire to the rounded edge/return however as with all matters "little aircraft" weight is of concern - what would you do? lightweight CGM over the edge enclosing the foam followed by lightweight glass cloth - please expand using every day terminology (if possible) as I will have to purchase these items and like to have some awareness that it is the right material for the job. cryo/super glue - This sounds to be a way of achieving a quick fix (🙃) - would a glue gun (which I have) be as good? plasticine - OK with vinyl ester? radius balls - having no balls (worn out 🤥) would guess that any spherical object, of the correct /acceptable dimension would do? As for a couple of hours to complete - be advised that the male mold, for the body of the scoop, took me about 10 days to make and this was with the aid of a jig/form (home made) to try & acheive symmetry and correct size.

Fiberglassing work, is possibly my least favourite task to do with aircraft modification. I am in the process of modifying my engine cowling to accommodate a relocation of my radiator (Rotax 912) in the hope it will improve engine cooling. The mod is a large scoop that, with styling/streamlining ,takes up about 2/3 of the original cowls underside. I have made a male mould in situ, created the bulk of the scoop but am at a loss as to how to create a professional looking leading edge- helpful suggestions ???

Debate seems to be lagging somewhat, to the point of despiraton ("Peeing while on long flights") so thought I would "shoot the breeze" on fuel pumps; (FYI most of this will be from my experience with Rotax 912ULS & my current aircraft Sonex Legacy/Rotax 912ULS) Boost/Back-Up/Auxiliary As one of the "fixes", addressing an ongoing problem with low fuel pressure on take-off/climb out, I have recently changed my no name Facet Cube knock off (estimated 3-5 psi, 30 US G/hr) for a genuine Facet Cube PN 40135, 4-7psi, 32 USG/hr (yet to be tried). The Rotax obsessed amongst you will observe, I have exceeded Rotax recommended Boost Pump Max pressure of 5 psi. Reason - RV have advised RV12 owners to retrofit & fitted latest 12's, with this pump. It seem this aircraft was experiencing the same problems as my Sonex/912. In my quest to improve fuel pressure at this critical time in flight ops, I have ensured filters are clean, vents are open, changed fuel return restrictor jet for a smaller one (now changed back to original). The jet fix certainly helped but not enough, so I hope the new pump will solve the problem. Transfer Pump My Sonex is fitted with a Facet Posi-Flow PN 60303. 7-10 psi, 34 US G/hr. Ssslllooowww! Despite its claimed flow rate, it takes around 20 minutes to deliver 30L. Have been researching potential upgrades; Facet Posi-Flow PN 60107. 7-10 psi 40 US G/hr - This would be a "drop in" replacement, as I imagine external dimensions are the same as the above (awaiting dimension confirmation from Facet) BUT only improves flow by about .5L/min Facet Cube PN 40307, 12-15 psi, 50 US G/hr - Significant step up in flow rate BUT two things are of concern ; 1. Dimensionally longer (between fuel IN/OUT sockets) so not a drop in 2. Given that there will be frictional losses, what sort of improvement am I likely to experience? Your constructive criticism will be most welcome Sorry about the imperial pressure & flow specifications - that's how Facet express them.

Plan Plan & Plan - Land every 2-3 hrs, wee break and a walk around Oh! and don't start drinking the inflight liquids until you know you are only 30 minutes from a full stop.

Mine has only got 45 flight hours so am still getting used to it. Goes like a "bat out of hell" - back in the "shop" for cooling system rethink (almost done).

Hi Area-51, Thanks for the terrific critique (with illustrations' for us simple folk). I was planning on wing root fairings/flairs for my new Sonex (similar performance to the Europa illustrated)- not so sure now.

Sales ??? - I suspect most aircraft manufacturers build to order (or very close to it). You may be lucky and score a factory demo but they are few and far between. Alos they are usually "loaded" with most/all the extras that you can order, so are likely to be as costly as the new "povo" job (which will probably fly better because its lighter)

Hi Kyle, Tangential thought; A carb control system that uses a profiled (prevents attachment rotation) rod mounted across the bulkhead, with three Borden (or pull/push) cable attachments; One that can be mounted anyhwher on the rod (secured in position using grub screws or similar) corresponding to straight (or close) to throttle location in cockpit. Two aligned with carb throttle actuating system Advantages: Adaptable to a very wide range of Rotax 9 powered aircraft. Only the cable lengths vary according to installation differences. Short cables to carbs aligned with system, allow for engine movement, do not inhibit carb vibration damping, prevent cable binding and once adjusted for carb balance less likely to need further adjustments.

Not sure what he is getting at - I fly out of The Oaks. You are correct regarding the charts, circuit height and the minimum overfly altitude BUT it is not uncommon to have aircraft overly (particularly those inbound to Camden) below this altitude. As I see it, Camden Tower will instruct (amongst other things) the inbound aircraft to maintain heading and altitude not below 1800ft - way too many pilots, anticipate this instruction and are already on decent to 1800ft thus entering The Oaks "airspace". Adding to this, is the likelihood that the Camden in bound aircraft is on Tower frequency 120.1 & Sydney Centre area frequency 124.55 not on / monitoring / overflying call The Oaks 126.7

At first glance (yet to be a second) it seemed very much to be reinvention ie nothing very new/revolutionary - was I wrong?

I am sure I would find you to be wonderfully scented. The only point I am trying to make is, that you don't seem to acknowledge the apparent durability, despite your technical misgivings, of the Rotax 9 range - is it marketing hype? or is it engineering excellence?

You are correct however this changes little, as most if not all mechanical systems undergo an evolutionary/improvement process during their production life. We know that you deep and abiding reservations about Rotax engines technical fitness. "their layout" - I assume you are referring to your frequent observations on twine carb, carb above, induction, high rpm/gearbox ? "cooling" - just the heads? - would you like them better if the barrel was included? OR is it liquid cooled aero engines in general? "oil plumbing" - I agree, not conventional but works, why the beef? "price of parts" - I haven't looked at the price of the equivalent Ly/Con parts of late, they used to be significantly more expensive, than Rotax. You may be comparing with Jab, this I give you without hesitation but then look at the reputation. Unless we have all been completely brain washed by Rotax (?) & the negative press on Jab it would seem that most Jabs (& Ly/Cons) will require "major surgery" well before TBO, while Rotax will not - in my mind this likely balances the cost equation. One one further point - service items - shop around (as I do) - parts not so expensive after all. This is not the case for those who do not make the effort or to lack the confidence to do so, then OM IS expensive as are most aircraft parts. "lied or failed to elaborate" - Of course not but you don't need to - as I said your tone would seem to be fairly consistently negative/disparaging towards the Rotax offerings. "not everyone can afford one" - True, but then there are not to many aspects of powered flight, in the 80hp and above, that can be considered cheap. While I may wish that there were no financial hurdles, to all who may aspire to own/fly a small (or large) aircraft, that's not the way the World seem to work - I cant afford a private jet (not sure that I aspire to own one, cant be much fun to fly). I support your KISS principals Nev but also recognise that efficiencies may also come from some compromise in this philosophy - I am sure I have heard/read somewhere that this is one of the ways technology advances - simplicity, followed by complexity, before refinement back to simplicity.

".........your unsubstantiated comment that the 912 g/b will definitely last 600 plus hours" I don't recall saying/writing this. FYI - The Sprag Clutch (SC) can be replaced without removing the gear box. I have replaced one, don't recall any special tools but the aforementioned dodgy memory, may be in play. The SC was one of the Rotax weak points being particularly susceptible to the forces generated by the earlier engine start system (now mitigated by the Soft Start ignition) and the failure of some pilots to replace a weak start battery, as soon as identified as such.

No offence Blue but I realy dislike unsubstantiated statements like this. Reason; they and possibly the reports you have read/heard, are without context (history - service, usage, prop type, number of similar failures, as a percentage of total in use, etc). All mechanical "things" (technical term for man made object with moving parts) are subject to wear and failure that may be accelerated by poor usage. These days. most will have some sort of in service life expectancy, either through testing or experience - I have not heard of Rotax 9 gear box or engine general failures at 600 hrs or anywhere near this operational time. From geriatric memory - Rotax recommend that the gearbox be inspected (may require servicing) at 600 hrs for engines run on AvGas and 1200 hrs for those run on ULP (reasons are common knowledge) Nev You comments are without doubt based on his extensive experience & training - fair enough however your "tone" (subjective attribute, conferred by reader/me) does seem to be biased against Rotax 9's, in that some of his technical observations (while accurate) do not appear to negatively effect the service life of these engines. To me there can only be two possible reasons: Rotax are good at promoting their engine & hiding its defects ie most of us believe they are one of the few aircraft engines (in their class) that generally make it (pass) TBO without major "surgical" intervention - this may be marketing hype & not be true. Rotax engines somehow transcends the conventional engineering wisdom of the past (at least in some respects) -if this is correct, it would mean that you might have to re-examine your training/knowledge.

Cant agree Nev - I hesitate to say my opinion is fact but history tells us the US is a very difficult market to crack (not just for aviation). That Rotax are "in" at all is likely to do with shear persistence/Canadian association and possibly the use of their engines in military drones and skidoos etc and the grudging realisation that for aircraft in the sub 700kg TO range there is probably nothing better ("better" covering a range of posative attributes). Of course Rotax is slowly working its way up the aircraft size/weight range, could there be a 200hp in the works? I would also question quite how much Rotax aircrafts are "in" - some of the US Forums have a distinctly anti Rotax "flavour". As for air cooled direct drive - nothing wrong with it, if you don't mind the inbuilt inefficiencies eg need for fuel cooling, big bore/low rpm engines, relativly high noise, vibration & fuel consumption/hp. I learnt to fly behind an air-cooled engine - its was great! I just happen to feel that but for the US market holding back development, better options would likely have arrived before now. Asides from an unhealth relationship with guns, the Americans seem obsessed with large bore engines - to me this is a cultural, not rational, position.

Speak for yourself🙃 I'm a post WW2 Euro baby = thrift in almost all I do. The reason LYCon still sit on the throne, is because they are made by Uncle Sam, who has the largest & most partisan market, on his doorstep. Any aviation product, developed / made outside the US, has almost insurmountable difficulties in breaking into that market ,which just happens to be the largest single markets of its kind. This also means that products from within, pretty much dominate the rest of the aviation World. One of the consequences, is the persistence of "traditional" (I'm trying to be nice) products way past their use by date.