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Rodr

Rotax 912

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To be honest skippy, I've not heard of a uls using such low fuel usage as yours. My mate with an IFA prop Flight Design CT, which is pretty slippery,

 

doesn't get that low.

 

When I'm in fast cruise, I get about 17/18 as per rgmwa (5200-5300) and 15lph at 5000 as per Kyle. These are pretty much standard figures from everyone I know.

 

I don't mean to be rude but you're sure it's a uls and not ul 80 hp? I can't get my head around those figures....

 

 

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Back in the day I flew C 172"s 145 - 180 hp, fixed & retractable undercarriage & fixed & CP prop's with real world air speeds from about 110 - 132 knots. Cant remember all of the POH fuel consumption figures but 32 Lph sound familiar. Compared with the "Great Sling" that's pretty good for an old technology spam can. Proves that looks alone doesn't make for a great aircraft.

 

 

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That would be about right and you have 4 POB.. With retract and C/S you are cooking with gas, but it's cost and maintenance.. Hire and smile. .Nev

 

 

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Every 912ULS uses the same amount of fuel to produce the same horsepower if setup to spec. You need manifold pressure readings to know what is going on. Rotax recommend cruise at not below 5000 rpm and idle not below 2000. John.

 

 

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Revs alone won't indicate horsepower. MP is helpful or fuel flow as a ballpark, all other things being equal. A torquemeter does the job. Torque and rpm equals Horsepower. Nev

 

 

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I use the Bolly Optima 72 inch prop not the 68 inch like most do. So mine is setup to have WOT at 5600 in level flight which gives me around 98 knots... at 5000 rpm I get a good 85 to 86 knots. Whatever I get from there is it. Takeoff climb at 65kts is about 5200 rpm as soon as I get to 70kts I am backing off the throttle as it gets to 5300. I usually never climb out above 65 to 70 knots I find thats fine and gives me heaps of headroom if the noise ever stops

 

 

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It will be interesting to see when I get the Rans going or possibly earlier as I am getting a big bore kit for the 100hp Rotax...I may do a engine swap into the Sav to see how it goes since the Rans kit wont be here until probably mid next year then I have to build it . That will make it 1484 cc with 88mm pistons. This should give me 114hp and hope with a different tuned exhaust should get that up towards 120hp. It will still have carbs on it and not injected.

 

 

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You can expect to shorten the life of the clutch and redrive parts. That's probably manageable. Good luck with it. Nev

 

 

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To be honest skippy, I've not heard of a uls using such low fuel usage as yours. My mate with an IFA prop Flight Design CT, which is pretty slippery,doesn't get that low.

 

When I'm in fast cruise, I get about 17/18 as per rgmwa (5200-5300) and 15lph at 5000 as per Kyle. These are pretty much standard figures from everyone I know.

 

I don't mean to be rude but you're sure it's a uls and not ul 80 hp? I can't get my head around those figures....

I cruise at 4800-5200 for an indicated speed of 100 -110 knots (depending on pressure altitude & load) CT's are a bit like Harley's & Quarter Horses - mostly good marketing. Not saying there is anything wrong with them, but in my totaly unbiased opinion (ha!) the hype exceeds the delivery.

 

I log my real fuel consumption (whole of trip) against Hobbs hours at every refuelling - my figures are not from a Mizer or computer but actual measured litres put into the tank.

 

ATEC aircraft are the most under appreciated UL's on the Australian market - performance figures are real and are able to be demonstrated to anyone who would care to come along.

 

 

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Rgmwa, this sounds more like what I would expect, although I am confused by 17 & 19 Lph. What Lph you flight plan at?

I flight plan at 19. I did a long trip recently (over 4,000nm). Tacho time was 45.0 hrs and I used 773 litres giving 17.2 lph average. Time spent warming up, taxying, descending/climbing etc all affect the average fuel consumption so 19 lph is about as near as I can determine for steady cruise. I have a fuel flow meter, but it's only as good as its calibration, and in any case only measures fuel going to the engine, not fuel going back to the tank via the return line. Even in steady flight it can fluctuate between 16 and 20 lph for no apparent reason so I don't rely on it.

 

 

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Just for interest, Vans publish these performance figures for the 912iS and 912ULS respectively in the RV-12, based on their testing:

 

Range (7500’ @ 5500 rpm) 630 miles 433 miles

 

Range (7500’ @ 5000 rpm) 605 miles 435 miles

 

Tank capacity is 20 US gal, all useable. Miles are statute miles.

 

These show that the iS is significantly more fuel efficient than the ULS.

 

 

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It would have to be more efficient. The two carb set up is no where near optimal. The carbs are crude and the manifolding wrong. It has to fit in the space rather than feed properly. Nev

 

 

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For anyone that is interested, here is a spreadsheet for my Eurofox 3K with a Rotax 912ULS and a 3 blade FITI ground adjustable propeller. It details my actual fuel flow data points at various altitudes, speeds (IAS & TAS) manifold pressure, and RPM. I've got my reported fuel flow calibration k-factor within 3% of actual refuelling quantities over a number of cross country trips.

 

In nil wind conditions, I usually get 6 nautical miles per litre of premium unleaded petrol at 110 knots TAS at 5500 - 6500 feet. I tend to flight-plan conservatively for 105 knots TAS @ 19 litres per hour, and a 10% variable reserve on top of my fixed reserve.

 

Eurofox fuel & speed performance vs Altitude.xls

 

Eurofox fuel & speed performance vs Altitude.xls

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Just for interest, Vans publish these performance figures for the 912iS and 912ULS respectively in the RV-12, based on their testing:Range (7500’ @ 5500 rpm) 630 miles 433 miles

 

Range (7500’ @ 5000 rpm) 605 miles 435 miles

 

Tank capacity is 20 US gal, all useable. Miles are statute miles.

 

These show that the iS is significantly more fuel efficient than the ULS.

I don think anyone doubts the improved fuel efficiency of the 912iS - what is debatable id the cost effectiveness of purchasing an iS, compared with a ULS, for most RAA users. Flight schools and other high hour (fuel) users may be able to justify the significantly higher cost of an iS as their break even period may be only a few years.

 

 

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I don think anyone doubts the improved fuel efficiency of the 912iS - what is debatable id the cost effectiveness of purchasing an iS, compared with a ULS, for most RAA users. Flight schools and other high hour (fuel) users may be able to justify the significantly higher cost of an iS as their break even period may be only a few years.

How much does a fuel injected 914 cost?

 

 

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For anyone that is interested, here is a spreadsheet for my Eurofox 3K with a Rotax 912ULS and a 3 blade FITI ground adjustable propeller. .................................................................................................................................................................................................................................................................................................................................................................................... I.

 

  • Not sure how you manage to get a better fuel consumption at 110 knots (18.3 LPH) compared with your planed 105 [email protected] LPH.
     
  • Not many pilots talk in fuel consumed over distance - to many variables
     
  • Great spread sheet, but with a fixed pitch prop, at your target 19 LPH, I would have expected much greater variations in RPM & Manifold Pressure, from near sea level to 9500 ft.
     
  • Why do you have your Auxiliary pump on below 3500ft??
     

 

The only real world fuel consumption figures are those noted at the end of a flight (hours) compared with how much fuel you have to put back into the tank (Litres) to bring the level to the same point as when you started.

 

 

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  • Not sure how you manage to get a better fuel consumption at 110 knots (18.3 LPH) compared with your planed 105 [email protected] LPH.
     
  • Not many pilots talk in fuel consumed over distance - to many variables
     
  • Great spread sheet, but with a fixed pitch prop, at your target 19 LPH, I would have expected much greater variations in RPM & Manifold Pressure, from near sea level to 9500 ft.
     
  • Why do you have your Auxiliary pump on below 3500ft??
     

 

The only real world fuel consumption figures are those noted at the end of a flight (hours) compared with how much fuel you have to put back into the tank (Litres) to bring the level to the same point as when you started.

I get a wealth of data from the Dynon Skyview, but to be fair, the spreadsheet is merely a collection of (constantly updating) data points (from photos like the attached) over 2 flights on different days across a range of altitudes, temperatures, QNH etc etc. Lots of variables involved, but good enough for some fairly good predictability when flight planning future trips.

 

The Auxiliary pump was mistakenly left on for the early part of that flight test (it is capable of being left on long-term). I tend to only turn it off after I’ve climbed past 2000 AGL to give me time to rectify any (unlikely) negative fuel-surge surprises necessitating re-starting. That’s never happened yet, but I usually notice a momentary fuel pressure drop in the gauge when I switch it off each time.

 

Distance per litre is a quick visual reference for me, along with the Range readout (vs Distance to Go readout), and wind vector display. It helps me find the optimum altitude under actual MET conditions, all during climb out, and throughout a cross country trip.

 

From this recent photo, I read a data point of 110 KTAS @ 17 lph, 5260 RPM, MAP 20.1, 9500 ft (DA 10492 ft) OAT 8 degrees, QNH 1024

 

I calibrated the k-factor for the Dynon fuel-flow by my record-keeping of actual fuel to fill at the pumps along my trips.

 

83116237-60BB-4886-B382-49A86F8119CC.jpeg.3fb63a1ac19d7c5c6956fe604962157f.jpeg

 

 

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I think it is all about rpm. My 15 l/hr was at 5000 rpm. I well expect 18-19 l/hr T 5200 rpm.

 

 

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...The only real world fuel consumption figures are those noted at the end of a flight (hours) compared with how much fuel you have to put back into the tank (Litres) to bring the level to the same point as when you started.

Ok here is another data point: YLIL to YCBA, 4.2 hours wheels-off to landing, 70.52 litres at the pump to re-fill (16.79 litres per hour).

 

It is rather consistent with the real time readout on the Dynon Skyview.

 

 

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I don think anyone doubts the improved fuel efficiency of the 912iS - what is debatable id the cost effectiveness of purchasing an iS, compared with a ULS, for most RAA users. Flight schools and other high hour (fuel) users may be able to justify the significantly higher cost of an iS as their break even period may be only a few years.

I agree. The iS package from Vans is $5,000US more than the ULS. I don't know what Bert Flood charges for the iS but I'm sure it will be a lot more than the ULS. It's also difficult enough to find trained Rotax mechanics locally, and those with iS experience will be even more scarce. It may be different in Europe, but I think that for us in Australia the ULS still makes a lot of sense. However, the iS is certainly a nice engine with impressive performance and if I was building again I could be tempted to try to find the extra cash. Fortunately, I'm not building.

 

 

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There is no injected 914?

 

The 915 is a turboed and modified 100hp injected (ULS) engine. .140hp.

 

 

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I think it is all about rpm. My 15 l/hr was at 5000 rpm. I well expect 18-19 l/hr T 5200 rpm.

Yep!! RPM & Load - load as in climb but also prop pitch to achieve air speed at a given RPM.

 

My prop is a ground adjustable two blade Fiti which I have pitched for advantage climb - so at cruise (100 -110 knots) it is a bit on the fine side (lightly loaded).The load is reflected in manifold pressure (if you have a gauge).

 

 

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