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fuel consumption Jabiru 3300
"karel" wrote in message ... Out of curiosity I started to look for fuel consumption figures for the Jabiru 3300. I found a figure of 0.46 lbs/HP/hr which is not particularly meaningful to me. Moreover it said "at cruise power" without further specification. So I started to assume 65% powser for cruise, calculating from the rated power of 120HP this gives some 78 HP. So 78*0.46 gives me 3.6 lbs/hour, or 6 USG per hour or close to 23 liters/hour. Is this way of calculating correct and do the numbers seem reasonable? I had expected this engine to be less fuel hungry than the Lycomings &C... Do not Rotax claim something like 15 liters/hour? TIA PS do not tell me that the rated power of 120 HP is not for continued application, I knew that. Seems similar to the Rotax 914S. Isn't that a six-banger with 3.3 liter displacement? I'm surprised it doesn't use more fuel than that. It revs higher than your average Lycoming or Continental too. |
#2
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In article ,
"karel" wrote: Out of curiosity I started to look for fuel consumption figures for the Jabiru 3300. I found a figure of 0.46 lbs/HP/hr which is not particularly meaningful to me. Moreover it said "at cruise power" without further specification. So I started to assume 65% powser for cruise, calculating from the rated power of 120HP this gives some 78 HP. So 78*0.46 gives me 3.6 lbs/hour, or 6 USG per hour or close to 23 liters/hour. Is this way of calculating correct and do the numbers seem reasonable? I had expected this engine to be less fuel hungry than the Lycomings &C... Do not Rotax claim something like 15 liters/hour? Your method is correct -- but it is 36#/hr, not 3.6! Yes, it does work out to about 6 gph. BTW, 0.46 #/hp/hr is right in the ballpark for aircooled piston, gasoline engines. PS do not tell me that the rated power of 120 HP is not for continued application, I knew that. Seems similar to the Rotax 914S. |
#3
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karel wrote:
Out of curiosity I started to look for fuel consumption figures for the Jabiru 3300. I found a figure of 0.46 lbs/HP/hr which is not particularly meaningful to me. Moreover it said "at cruise power" without further specification. So I started to assume 65% powser for cruise, calculating from the rated power of 120HP this gives some 78 HP. So 78*0.46 gives me 3.6 lbs/hour, or 6 USG per hour or close to 23 liters/hour. Is this way of calculating correct and do the numbers seem reasonable? I had expected this engine to be less fuel hungry than the Lycomings &C... Do not Rotax claim something like 15 liters/hour? TIA PS do not tell me that the rated power of 120 HP is not for continued application, I knew that. Seems similar to the Rotax 914S. According to the Zenair web site: (seems a bit optimistic) Specifications: Jabiru 3300 A Displacement: 3300 cc. (200 cu.in.) Bo 97.5 mm. Stroke: 74 mm. Compression: 8.3 : 1 Prop Rotation: Clockwise Firing Order: 1 - 4 - 5 - 2 - 3 - 6 Power Rating: 100 hp @ 2750 rpm (see above) Fuel Consumption @ 75%: 5.0 US Gal/Hour (gph) Fuel: 100/130 Avgas or 92+ octane Mogas Oil: Aeroshell W100 (or equivalent) Oil Capacity: 3.5 qts. (3.75 l.) Spark: NGK D9EA (common automotive) My Cessna 150 manual (for a continental o-200) shows a spc of .448 for 75% (75 HP) operation. The above table works out to a SFC of .4 which looks low.( note they derate the J 3300 to 100 HP) your figure of .46 looks more real. Hey but who knows unless you've flown one! John |
#4
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23 liters for the 3300cc Jairu is conservative. My 80hp 2200cc Jabiru
uses only 13 liters per hour at 2500rpm cruise revs. Cheers, Joe karel wrote: So 78*0.46 gives me 3.6 lbs/hour, or 6 USG per hour or close to 23 liters/hour. Is this way of calculating correct and do the numbers seem reasonable? |
#5
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karel wrote: Out of curiosity I started to look for fuel consumption figures for the Jabiru 3300. I found a figure of 0.46 lbs/HP/hr which is not particularly meaningful to me. This is actually a pretty reasonable number. Most of the big bore lycomings are in this range, if I remember the discussions I have had recently on power and fuel consumption. The value being discussed here is "BSFC" or brake specific fuel consumption. This is part of the universal "truth" regarding horsepower in internal combustion engines. HP takes fuel. More HP takes more fuel. Is this way of calculating correct and do the numbers seem reasonable? I had expected this engine to be less fuel hungry than the Lycomings &C... Do not Rotax claim something like 15 liters/hour? As others have already pointed out, you had one decimal out of place.. (36 pph) but the rest of the math was about right.. As for the 15 liter per hour claim.. that is likely the power setting (and fuel flow) for max range/best economy. Airframe and engine manufacturers like to "play" with the numbers to suit their needs. None of this overrides the fact that you have to burn more fuel for more HP. With a BSFC of 0.45 (essentially the same as your engine, and similar to Lyc's and continentals). I am not positive at what mixture this is being computed at, but stoichiometric (1:14.7) seems to be the most logical. 250 hp = 18.75 gal/hr 200 hp = 15 gal/hr 150 hp = 11.25 gal/hr 100 hp = 7.5 gal/hr The way you can use this BSFC to your benefit is in evaluating engine efficiency claims on your own, independently of marketing claims. Your fuel burn for given power setting can be calculated. If an engine maker, particularly a new-comer, wont release their values, then their claims of power and efficiency should be viewed as suspect and with skepticism. Dave TIA PS do not tell me that the rated power of 120 HP is not for continued application, I knew that. Seems similar to the Rotax 914S. |
#6
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HI,
I've got about 200 hrs with this engine. Don't know what power settings I normally use, but fuel consumption has always been 5.5 to 6 gph.. Have fun John Sonex N130JX karel wrote: Out of curiosity I started to look for fuel consumption figures for the Jabiru 3300. |
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