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Thread: W&B and MPH

  1. #1
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    Default W&B and MPH

    Hi Guys,
    I have just flown off the mandatory 25 hours in my EX 0041 and now have a full C of A, can carry a passenger as well as going anywhere. I have seen over the first 25 hours solo at 2250 rpm (50% power) 6.5 galls/hour and 95mph. I thought this was OK until I took my first passenger, he weighs about 220 lbs, at the same numbers 2250 rpm I am seeing 105mph.
    Has anyone else seen the same thing (80" X 50" prop) Is to a W & B thing that the trim when solo is causing more drag.

    Also what is that white stuff tat I see on the forum photo's, 90 deg.F here today, Melbourne Australia. (couldn't resist that.
    Regards Bruce Thomas

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    Default Re: W&B and MPH

    There is about 15 inches of that "white stuff" on the ground here and our temperatures have been running -10 dF at night and 0 dF in the day.
    besides that, our tail wires are defective and we can't fly.
    You are evil!

    I see about a 2/3 mph decrease in speed with a passenger. That's all.
    Have fun in the sun.
    Bill

  3. #3
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    Default Re: W&B and MPH

    Bruce

    Check the washout in your wings. E.V. was talking to me about the difference between his 1st and 2nd EX, so we (mostly E.V.) started looking into it. E.V. found that a slight change to the washout made a huge difference in the trim position while flying solo. E.V. will you chime in here.

    Mitch

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    Senior Member randylervold's Avatar
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    Default Re: W&B and MPH

    I believe that increased speed with a more aft CG is normal. With more weight aft the horizontal stabilizer doesn't need to produce as much downforce thus less induced drag and great speed with the same power.

    BTW, at those power settings you could get your fuel flow lower by leaning more aggressively.
    Randy Lervold

  5. #5
    Administrator Pete D's Avatar
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    Default Re: W&B and MPH

    I have seen 2-5 mph speed changes depending on the airplane and the size of the passenger. It seemed like the Sport Cub made more difference than the Carbon Cub but perhaps I was seeing rigging differences between particular airplanes rather than differences between models.

    For example, our company S2 I have seen 3-4 mph change just by swapping from the front/back seat with a larger passenger.
    Pete Dougherty
    Customer Support Manager
    Cub Crafters Inc

  6. #6
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    Default Re: W&B and MPH

    Thanks everybody for answering my questions, as usual a question usually raises more questions.

    As all commented a rear C of G will result in more speed, to Mitch, my dihedral is 1.4deg both sides (CC geometry 1.5deg)and wash out is .8deg both sides( CC .75deg) so I am pretty close to spec. Aren't digital levels marvelous.
    Perhaps EV could give his opinion on how washout changes effect solo speed.

    To Randy, concerning fuel flow numbers and aggressive leaning. I have a Dynon 180 so I know where peak EGT is and LOP or ROP, when I read the ECI Titan operation manual for the 340S engine I see on page 13 a note at the bottom of the page.

    NOTE: There are some that advocate operating on the lean side of peak EGT. Although theoretically acceptable, it is generally not possible to operate lean-of-peak with an engine using a carburetor. Additionally, ECI has found that engines operating lean-of-peak EGT have significantly higher instances of cylinder problems that costing much more than the fuel savings.

    I note that when I operate LOP at 2250rpm my Fuel Flow drops to about 5 gph and the EGT and CHT drop dramatically
    the engine continues to run sweetly, however I have that ECI note nagging in the back of my mind.
    With, is it 300 CC's flying now, I would greatly appreciate some comment on what power settings others are using and corresponding fuel flow at those rpm's and whether they run LOP or ROP . I understand that with each engine your mileage can vary, but a general guide as to what others are getting would be useful. eg a Cessne 182 at 2300 rpm and 23" Mp achieves 12.8 to 13.1 gph and 125 knots.
    With fuel prices as they are ( US$7.50/ gall here ) we are all trying to stretch our dollar as far as we can, so I hope this
    thread will be beneficial to all.
    Regards Bruce

  7. #7
    Senior Member randylervold's Avatar
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    Default Re: W&B and MPH

    Quote Originally Posted by Thomas View Post
    To Randy, concerning fuel flow numbers and aggressive leaning. I have a Dynon 180 so I know where peak EGT is and LOP or ROP, when I read the ECI Titan operation manual for the 340S engine I see on page 13 a note at the bottom of the page.

    NOTE: There are some that advocate operating on the lean side of peak EGT. Although theoretically acceptable, it is generally not possible to operate lean-of-peak with an engine using a carburetor. Additionally, ECI has found that engines operating lean-of-peak EGT have significantly higher instances of cylinder problems that costing much more than the fuel savings.

    I note that when I operate LOP at 2250rpm my Fuel Flow drops to about 5 gph and the EGT and CHT drop dramatically
    the engine continues to run sweetly, however I have that ECI note nagging in the back of my mind.
    With, is it 300 CC's flying now, I would greatly appreciate some comment on what power settings others are using and corresponding fuel flow at those rpm's and whether they run LOP or ROP . I understand that with each engine your mileage can vary, but a general guide as to what others are getting would be useful. eg a Cessne 182 at 2300 rpm and 23" Mp achieves 12.8 to 13.1 gph and 125 knots.
    With fuel prices as they are ( US$7.50/ gall here ) we are all trying to stretch our dollar as far as we can, so I hope this
    thread will be beneficial to all.
    Regards Bruce
    Bruce, the general rule is that you don't want to even attempt to run LOP at or above 75% power. The lower the power the less it matters. When you're down around 2100-2250 rpm or so you are in the 45-55% power range. All the experts would say that there's not much you can do to hurt things at those levels as long as the engine continues to run smoothly.

    On this issue, if you're after maximum efficiency you should consider installing the new perforated nozzle in your carburetor, it evens out the fuel flow across the cylinders and helps you run smoothly LOP. I've flown several planes now with it and I think it is the single best thing one could do to improve a CC340. I just took a look and couldn't find them in our web store but if you'll give David Bingham, our Parts & Accessories Manager, a call he can fix you up.
    Randy Lervold

  8. #8
    Senior Member EVRoosevelt's Avatar
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    Default Re: W&B and MPH

    My problem with #2 CCub was tail heavy I did notice when I was breaking the engine in at 2500 RPM I was indicating around 132 MPH which was a lot faster than #1. I rerigged (not sure if that is a real word) the wings and got the washout closer together and drooped the ailerons about 1/4" that fixed the tail heavy problem but I could never get up to 132 mph again.
    EV

  9. #9
    Senior Member randylervold's Avatar
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    Default Re: W&B and MPH

    Undroop your ailerons and you'll probably pick up some speed, less induced drag.
    Randy Lervold

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    Default Re: W&B and MPH

    Thanks for that Randy, I have been told that the new emulsifier tube will only fit the Marvel Schebler carby, I have the Avstar carby. Will it fit this model also.
    Regards Bruce

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