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Fuel economy - is 7 L/hr normal for a fat bloke?


stuartasutherland
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Hi, now I've been up a few times I can judge how much fuel I'm using.

Generally using 3.5L for each 30 min flight. Just looking for comment on whether this is normal or is there something I can look at to get it improved.

Parajet Macro - 2 blade wooded prop

Dudek Synthesis 34

I weigh 100kg naked and a bit more with clothes on.

I'm suffering a bit from vibration at the moment - could that reduce the fuel economy? (Prop balancing issues - details on my other post).

Anyway, comments welcomed.

Many thanks

Stuart :|

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No that's not normal - I get 3.5l per hour (or better) from a 230cc Kobra paramotor and 34m Nucleon. Similar weight to you or slightly heavier.

Is your plug black & sooty ? Any idea what rpm your motor is at on a level cruise ? The parajet 3 blade carbon prop might help a little bit.

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That plug actually looks fine (from that angle), but really you need to judge it from the colour of the porcelain part way down from the electrode. Also that probably shows your idling mixture if you let it idle at all before switching off - you need to do a 'plug chop' after high revving under load for at least 2 minutes (preferably a steady climb above your landing field then kill the engine immediately before drifting down to land).

There could be other reasons for the high fuel burn other than mixture, such as worn or stuck piston rings, worn or grooved cylinder bore, leaking or coked up exhaust to name a few. Do you know how many hours are on the engine ?

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The shorter prop you put on would also be a bit less efficient perhaps than the original. From what I gather, the bigger the prop, the more efficient it is.

I would think that the vibration is definately wasting energy to some degree, but no idea if it is enough to make any difference to your fuel burn.

My FB simonini states 3L/hr burn and I a getting around 4.5L/hr in practice, using a 29m non reflex wing with trims on all the time (no bar). Im 86kg. I think flying style makes a difference though and reckon I could get it down to 3.5 if I kept trims in, stayed lower and was lighter on the throttle. A larger more modern wing would also improve things quite a lot (mine is 12 years old!).

I also heard that an iridium tipped plug improves efficiency, but doubt the difference is significant.

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In 2008 I had a brand new Macro for the tip to tip and spent a month testing fuel burn etc for flight planning. Looking in my flight log where i recorded some of the the fuel burn it reads:

6.25 ltrs hour

5.23 ltrs an hour

5.5 ltrs hour

5.31 ltrs hour.

I weigh a bit more than you and was flying a medium size Action at the time. So i would say 5.5 to 6.5 is about normal. Technique does make a difference.

Make sure the tank is the actual size you think it is. Some of the small Parajet tanks actually only hold 8.5 ltrs instead of 10 which we found out while testing. Some of the early clear tanks had thicker walls than the black tanks but were made in same size mould making the contents less.

The large Macro tanks we used on tip to tip held 13.75 ltrs if you tilted them slightly to fill right up, and on the first test flight of the large tank which was on 23.06.2008 I flew 68.8 miles in 2 hours 31 mins before running out of fuel approaching my field as planned. The flight record described very lively conditions. Returning 5.5 ltrs hour.

Be carefull you don't lean off and seize your engine. been there and done that :cry:

Just spoke to Dan Burton who has swopped his Walbro carb for a Bing carb with pump, and is now getting 4Ltrs an hour instead of nearer 6 and sometimes was more on his revo 2 which in my opinion is to small for him.

Regards.

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No that's not normal - I get 3.5l per hour (or better) from a 230cc Kobra paramotor and 34m Nucleon. Similar weight to you or slightly heavier.

Is your plug black & sooty ? Any idea what rpm your motor is at on a level cruise ? The parajet 3 blade carbon prop might help a little bit.

3 blade props will burn more fuel for sure. Larger 2 blades is better for economy. You need to get it balanced as it will cause damage to your machine.

Regards.

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3 blade props will burn more fuel for sure. Larger 2 blades is better for economy.

I find the opposite - the Helix 3 blade prop as supplied by Kobra for the Simonini Evo is quieter, more economical, efficient & powerful than the 2 blade glassfibre prop I bought as a spare (which is wider, greater pitch but a tiny bit shorter) although the 2 blade prop is a lot thicker which may effect its efficiency.

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Whitters, thanks a lot for that info - really helpful. I have one with the 14L tank (Simon's old one). I've marked the tank with lines after putting in exact amounts so should be an accurate measurement.

As my technique gets better I'm sure I can improve down within the range 5.5 to 6.5 (with out leaning the engine!)

My prop is currently with Pete B getting checked for balance.

Appreciate your thoughts.

Thanks

Stuart

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Whitters, thanks a lot for that info - really helpful. I have one with the 14L tank (Simon's old one). I've marked the tank with lines after putting in exact amounts so should be an accurate measurement.

As my technique gets better I'm sure I can improve down within the range 5.5 to 6.5 (with out leaning the engine!)

My prop is currently with Pete B getting checked for balance.

Appreciate your thoughts.

Thanks

Stuart

First one is done and tested on my motor

it was 10 grams out in the cord (the weight of a pound coin)

Second one now done

will try to post tomorrow if I can get to the post office

Pete

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  • 2 weeks later...
  • 3 weeks later...
In 2008 I had a brand new Macro for the tip to tip and spent a month testing fuel burn etc for flight planning. Looking in my flight log where i recorded some of the the fuel burn it reads:

6.25 ltrs hour

5.23 ltrs an hour

5.5 ltrs hour

5.31 ltrs hour.

I weigh a bit more than you and was flying a medium size Action at the time. So i would say 5.5 to 6.5 is about normal. Technique does make a difference.

Make sure the tank is the actual size you think it is. Some of the small Parajet tanks actually only hold 8.5 ltrs instead of 10 which we found out while testing. Some of the early clear tanks had thicker walls than the black tanks but were made in same size mould making the contents less.

The large Macro tanks we used on tip to tip held 13.75 ltrs if you tilted them slightly to fill right up, and on the first test flight of the large tank which was on 23.06.2008 I flew 68.8 miles in 2 hours 31 mins before running out of fuel approaching my field as planned. The flight record described very lively conditions. Returning 5.5 ltrs hour.

Be carefull you don't lean off and seize your engine. been there and done that :cry:

Just spoke to Dan Burton who has swopped his Walbro carb for a Bing carb with pump, and is now getting 4Ltrs an hour instead of nearer 6 and sometimes was more on his revo 2 which in my opinion is to small for him.

Regards.

My last few flights I've managed to average 6 litres / hour.

This gives me a 2 hours duration plus a wee reserve.

8)

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