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Thread: Cruise performance table (5.2.6 of the EX POH) above 80hp

  1. #1
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    Default Cruise performance table (5.2.6 of the EX POH) above 80hp

    Does anyone have the complete table? Or a link to it?

    I understand the LSA restriction at 80hp but what about the rest of us?

    Thanks,



    -- martin

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    Senior Member Dan L's Avatar
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    Default Re: Cruise performance table (5.2.6 of the EX POH) above 80hp

    I asked a somewhat similar question here:
    http://www.cubcraftersforums.com/sho...hlight=Leaning

    I didn't get the answer I was hoping for but have come up with some numbers I use at over 80 hp power settings. And I'm not a 1340 gross weight plane. I'll get them from the hangar.
    Flying Carbon Cub EX #11 since 2011

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    Default Re: Cruise performance table (5.2.6 of the EX POH) above 80hp

    Thanks Dan,

    I'm very much enjoying my new cub, but am surprised by the paucity of solid technical data. My previous aircraft was an RV.

    Regards,



    -- martin


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    Default Re: Cruise performance table (5.2.6 of the EX POH) above 80hp

    Hello All,

    Still searching with no success. Anybody have any tips on where else to look?

    Thanks,



    -- martin


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    Default Re: Cruise performance table (5.2.6 of the EX POH) above 80hp

    You won't be far out using rules of thumb.

    Drag coefficient won't reduce much as you go faster. You'll lose a bit of wing drag and trim drag but the Cd of wheels, struts, cowls etc won't change. So assuming it is constant, power required will increase with speed cubed (doubling power is roughly 25% speed increase).

    Weight effect is much smaller. 10% weight needs about 1 degree extra incidence which is typically 3-4% extra wing drag. I would guess power required would increase about 2-3%.

    But higher weights will usually give a more aft CG so reducing trim drag.

    Propeller efficiency will also vary with speed as its airfoil will be decreasing angle of attack.

    So assuming galls/hour increases as speed cubed and MPG increases as speed squared and you won't be far out.

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    Default Re: Cruise performance table (5.2.6 of the EX POH) above 80hp

    Thanks Mark,

    Much appreciated.



    -- martin


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    Default Re: Cruise performance table (5.2.6 of the EX POH) above 80hp

    Is there a rule of thumb for rpm vs fuel flow assuming level flight with a fixed pitch prop?

    Regards,



    -- martin


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    Default Re: Cruise performance table (5.2.6 of the EX POH) above 80hp

    Unfortunately altitude and airspeed have too big an influence on that. You may have a rule for one altitude, but it won't work when the altitude changes.

    But, if you have manifold pressure, there is an approximation:

    add together rpm/100 and MP in inches Hg. e.g. 2300 RPM and 23" gives you 46.
    Max SL power would be 2700 and 30" =57
    Divide 46 by 57 and square the result is the approximate percentage power i.e. 65%
    If it's a 180 HP engine that's 65% of 180 =117 HP
    Fuel flow is about 0.45lbs per HP hour fully leaned, up to .6 lbs fully rich
    So 117 HP * .45 = 52.65 lbs/hr or 8.8 galls/hr

    Fully rich may be 20-30% higher.

    You can refine that calculation by going to the engine power tables and getting the actual power for various RPM, MP combinations.

    So in flight you just add RPM/100 to MP and look at your table of that number vs fuel flow.

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