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  • Mick Broom
    replied
    polini thor 250 fuel burn

    Paul ,
    I think this is another mystery to me and just as interesting as trying to work out how the wing flies!
    You obviously don't lose the options to save fuel once you have done the mechanical bits of adjusting the carbs and fuel curve.
    The question may be why try and establish the fuel burn in the first place and I suspect there are two answers , one is how far can I go and the other is how can I fly forever on the least fuel. Like most things in life the more you put into the question the more you get out and for me the first question would be nice to answer with the second more interesting question being asked afterwards.
    I need to understand lift and thermals which I am finding very difficult at the moment under the Chaser wing but got the impression that I was beginning to understand when flying the Shadow.
    One result of my winter travels is I have a lot of time up serious hills watching and feeling the wind effects but maybe the most noticeable was when on the Atlantic beach in Portugal watching the rollers coming in from America and flying my kite in storm conditions in what turned out to be very strong and very very stable air.
    Blisworth to Sutton and back yesterday ( just under two hours = just over 10 ltrs ) Cheaper than the Shadow and about the same speed.
    Tried a reading at 5000 foot in cold clean air , less revs and fuel , very cold decided it did not mean anything till the cab is sorted and its to high for me to travel places ;-)

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  • Paul Dewhurst
    replied
    polini thor 250 fuel burn

    Mick Broom wrote: Paul

    While I await this flat calm none thermic day to look at the fuel burn which this year may be some time!

    What you are really after is a speed / power relationship and to be useful would need to find the effects of different weights and air conditions on the results.

    In my limited experience I have needed very little power in flat calm conditions so assume the figures you would get would be the ideal best case with a drop off in results due to an increase in weight and turbulence.

    The effects of weight would be easy to obtain but what are the implications of turbulence as against thermals which again throw all the figures out of the window?

    Mick
    Turbulence is generally convection ( thermals) unless you make a habit of flying in the lee rotor of hills., or at very low level on windy days in the mechanical turbulence.

    So the effect it will have depends on where you are flying - if you are under a cloud street then you will get very good consumption in that bumpy bit of air, whilst flying in the calm bit in the blue holes will give you poor consumption in the predominantly descending air.

    It also depends on how you fly. If you nervously stir the pudding then you will generate drag and consumption will increase. If you fly smoothly and play a bit of flying my Macready rules ( slower in the lift and faster in the sink) you may do better than in smooth non convective air.

    Paul

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  • Guest's Avatar
    Guest replied
    polini thor 250 fuel burn

    Mick

    i'd agree, 300-400 more rpm needed for me, rough v calm.

    some of my figures:
    mid hang point, 49-51 cruise
    150 prop
    75kg fat controller
    calm
    5600-5700rpm
    egt 570-580
    5.6 lts/hr
    based on a take off and 1hrs careful cruise (who does that for fun)

    add 15kg of random camping kit(some of it badly packed), and i get 50-52 mph
    6lts/hr for the same flight.

    stick in some rough air, and some big climbs near full rpm and it get out of hand, but its still well rich on the main jet (egt down to 500)

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  • Mick Broom
    replied
    polini thor 250 fuel burn

    Paul

    While I await this flat calm none thermic day to look at the fuel burn which this year may be some time!

    What you are really after is a speed / power relationship and to be useful would need to find the effects of different weights and air conditions on the results.

    In my limited experience I have needed very little power in flat calm conditions so assume the figures you would get would be the ideal best case with a drop off in results due to an increase in weight and turbulence.

    The effects of weight would be easy to obtain but what are the implications of turbulence as against thermals which again throw all the figures out of the window?

    Mick

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  • Mick Broom
    replied
    polini thor 250 fuel burn

    Won't be this week then

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  • Paul Dewhurst
    replied
    polini thor 250 fuel burn

    If you are flying straight and level, and doing it in non thermic air and similar weight you should have a fixed relationship between speed and RPM. You can then plot a fuel curve that has some meaning ( if you have a good accurate fuel computer and spend some time settling into each speed and the correct matching RPM.

    Paul

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  • Mick Broom
    replied
    polini thor 250 fuel burn

    Been up again today.
    Observed the obvious in that linking the results to the revs does not work very well because the power and fuel depends on the load on the prop and you can get a big difference depending on speed for fuel used at set revs.
    Will think about this?
    I was surprised I could achieve a climb rate of 760Ft/min.
    Sight gauge still needs a bit of work. I believed it and promptly run out of fuel but don't tell anyone as its a bit embarrassing having done the same trick 20 years ago in the Shadow. :shakehead:

    https://www.youtube.com/watch?v=gTJUSe2e60w

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  • Mick Broom
    replied
    polini thor 250 fuel burn

    Weather and experience is slowing down my progress on this but as a snap shot of results so far while I try and discover why the camera will not switch on to record it all.
    Dragon Chaser ( early wing as they are all slightly different ( god bless Ben).
    Pilot a lardy 76Kg with kit ( must get that down a bit )
    18Lts fuel
    Later Bing carb, set up as supplied but with the needle on max weak setting.
    water 74C , small rad with no thermostat
    EGT about 600
    CHT less than 100
    Not got the prop number in front of me.

    Max power 7500RPM =12.4Ltrs /hour

    6000 RPM = 4.8Ltrs/hour
    6200 RPM = 5ltrs/hour
    6500 RPM = 6ltrs/hour

    Straight and level flight at about 55MPH = 6200RPM
    Reduces to just over 6000RPM when the fuel is low.

    I will add to this when I have more and refine the figures where necessary.

    Mick

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  • Guest's Avatar
    Guest replied
    polini thor 250 fuel burn

    hi mick

    i was out fuel testing again today, testing with the trike fully loaded. 5700rpm give 5.7litres. interestingly flying constant rpm for 45mins i noticed the egt wandering down. back on the ground, found the other float had started to sink.

    i've got 3 conflicting sets of test results for 5400rpm

    i got into a similar domestic problem with the washing when i was doing mixture testing a month back :-)

    col

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  • Mick Broom
    replied
    polini thor 250 fuel burn

    Hi Colin,
    How are you progressing with this.
    I should be able to contribute in the near future with figures from my Dragon after I have checked the flow meter and adjusted the carbs.
    3.8 litres per hour at 5000 rpm and 6 litres at 6000 rpm so far till I blew the washing off the line ;-)
    Looking for brownie points, still its not as bad as when I melted something in the oven
    Early days and lots of fun

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  • Guest's Avatar
    Guest replied
    polini thor 250 fuel burn

    paul,

    thanks

    i have set about doing some structured testing, but i just thought i'd ask to see if anybody else has done something already.

    cheers

    colin

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  • Paul Dewhurst
    replied
    polini thor 250 fuel burn

    You are just going to have to do some testing Colin.

    If you don't have a fuel computer start by topping up to a known level. Starting, warming , taking off and climbing to 1000 or other defined level then gliding back in on idle for landing. Top it. Back it back up measuring how much fuel you have used.

    Then takoff and go back to that level and fly straight and level at your chosen speed for at least 30 mins starting your stop watch when you start the straight and level flying. Arrive back in the overhead and stop the watch. Glide down on idle. Top back up measuring fuel. Subtract the amount you found you used on the first flight and you have the fuel burn for the time straight and level at you chosen speed.

    Repeat for a spread of speeds. Draw a graph of the results.

    Do this a number of times to refine the data for top accuracy.

    Make sure you travel a distance over a range of terrain when doing this, or you risk doing big circuits in areas of constant lift or sink skewing the results.

    Paul

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  • Guest's Avatar
    Guest replied
    polini thor 250 fuel burn

    thanks john,

    i did speak to paul, they did most of their comp work before the switch to the bing carb. i'll see what i can work out

    cheers

    colin

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  • johnkendall
    replied
    polini thor 250 fuel burn

    Ben and paul must be the people to speak to. Most users are paramotors at the moment, they have completely different fuel consumption figures to usdue to wing design and the likes. My 200 gives around 5litres per hour with a fox wing. With a more efficient wing it can be as low as 3.

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  • johnkendall
    replied
    polini thor 250 fuel burn

    Ben and paul must be the people to speak to. Most users are paramotors at the moment, they have completely different fuel consumption figures to usdue to wing design and the likes. My 200 gives around 5litres per hour with a fox wing. With a more efficient wing it can be as low as 3.

    Leave a comment:

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