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  1. #1
    tweedy's Avatar
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    Need Help with Fox 15 Davis Conversion

    Just finished a Sig LT-25 with Fox 15 Davis Diesel Conversion and am having a hard time getting even close to the 10500 rpm with a 10-6 prop quoted on the davis performance chart I would be happy with 9000rpm but am not able to get anything over 6000rpm. What should I really expect?

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    RE: Need Help with Fox 15 Davis Conversion

    Tweedy Is your fuel ok?? Also make sure not over rich and overcompressed... martin
    also steel liner I think, know piston is iron may need a little run time to seat in
    is the liner in correct orintation in case

    A call to Bob Davis would not hurt either go to the source

  3. #3

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    RE: Need Help with Fox 15 Davis Conversion

    Tweedy

    Here is an earlier thread on the Fox .15 BB with DDD conversion head:

    http://www.rcuniverse.com/forum/m_11..._3/key_/tm.htm

  4. #4
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    RE: Need Help with Fox 15 Davis Conversion

    Hard to say for sure, but you might need to break the engine in good though.
    One thought is what is the fuel you are using? That could affect performance a lot in some cases.
    You could also check to make sure the cylinder sleeve is aligned properly in the crankcase. Maybe it moved a little when they were putting the head on the engine.
    Club Saito #722, Sig Kadet Brotherhood #80, GlowHead Brotherhood #14,
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    RE: Need Help with Fox 15 Davis Conversion

    Tweedy EarlWB stated same thoughts give them a try martun

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    RE: Need Help with Fox 15 Davis Conversion

    I would be surprised and amazed if a .15 with a 10-6 would do over 10,000 rpm.  I have glow GP and LA .40's that pretty much only do that.  I think a 9" prop would be more suited, or even an 8".  I am not a diesel buff, but realize their potential is good on large props too.
    Glow Head Hood # 7

  7. #7
    tweedy's Avatar
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    RE: Need Help with Fox 15 Davis Conversion

    β€œYou could also check to make sure the cylinder sleeve is aligned properly in the crankcase”
    I think this might be the likely culprit will try running it again in the morning.
    β€œI would be surprised and amazed if a .15 with a 10-6 would do over 10,000 rpm.”
    I’m just going by what the Davis Diesel performance chart is quoting, I would be happy to see 9000 rpm. Before the conversion it was turning a Kavan 8-4 nylon at 15500rpm.
    We are at 6000 ft. elevation I am using a J-Tec baffle less manifold with a carbon fiber arrow shaft extension on the exhaust with a I.D. larger than stock exhaust.

  8. #8

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    RE: Need Help with Fox 15 Davis Conversion

    Tweedy after you check the cylinder alignment** try a 9x6 prop and go from there martin

    you are at 6000 ft I am about 60-100 that has effect

    ** Have a gut feeling the cylinder is off alignment

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    RE: Need Help with Fox 15 Davis Conversion


    ORIGINAL: tweedy

    Just finished a Sig LT-25 with Fox 15 Davis Diesel Conversion and am having a hard time getting even close to the 10500 rpm with a 10-6 prop quoted on the davis performance chart I would be happy with 9000rpm but am not able to get anything over 6000rpm. What should I really expect?
    I don't get this at all, on the DDD site it gives an MVVS 21 doing 9800 on a 10X 6 prop and the smaller Fox 15 is supposed to do 10500 with the same prop?

    And -
    http://www.rcuniverse.com/forum/m_37...tm.htm#3748241


  10. #10
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    RE: Need Help with Fox 15 Davis Conversion

    I don't have any converted fox engines, but try a 9x5-9x6 prop instead. A 10x6 is a good match for .20-.25 diesels.


  11. #11
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    RE: Need Help with Fox 15 Davis Conversion

    You would need to use the same fuel DDD did. You also do not know which brand or type of prop DDD used to match it up. Then you have to have the same ambient temperature, altitude, barometric pressure, and humidity levels used when DDD did the engine runs too. The OP is in Cedar City Utah which sits at about 5,840 feet altitude but DDD is in Smyrna, TN which is at about 940 feet altitude. Thus engine performance would suffer a lot at the higher altitudes. There is a significant performance loss being higher up like that.
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    RE: Need Help with Fox 15 Davis Conversion

    It sounds more like a missprint to me (should possibly have been a 9x6 prop), I can't really see any .15 engine spin a 10x6 at 10500rpm. That would take a strong .20-.25 engine.

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    RE: Need Help with Fox 15 Davis Conversion

    TWEEDY if cylinder thing ok chuck a 9x6 on and see what you get best regards martin

    JUst looked at the data sheet on the Taipan 15 props
    10x4 apc 9800
    graupner 9x5 10300
    apc 9x4 12500
    graupner 8x-5 13000

    granted classic design but still a 15

    MVVS 15D 8x4, 8x5,9x5

    10x6 equals low revs on a 15


  14. #14
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    RE: Need Help with Fox 15 Davis Conversion

    I would agree with you all too. I think it might be a typo as well. A 10x6 seems a little too large to turn 10K rpms.
    I need to fire up and run my Fox .15 sometime and see what it does.
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  15. #15
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    RE: Need Help with Fox 15 Davis Conversion

    Thanks Guys:
    Had the plane out this morning, and it was the cylinder sleeve alignment that was causing the problem. Put in a flight of 45 minutes and still had half a tank of fuel left when I landed, power was adequate and seemed to improve as the flight went on, so I suspect it is still breaking in. It was also idling much better when I landed than when I took off, just ticking over, I had to pinch off the fuel line to get it to quit. Prop was a 10-6 Kavan I’ll have it out again tomorrow and post numbers with several different props.
    Thanks again for the help
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  16. #16

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    RE: Need Help with Fox 15 Davis Conversion

    Tweedy glad its solved, the cylinder alignment was the most logical based on the symptoms martin

    about 45 minutes air time and land with a half tank left, Ha try that on glow sure it made an impression on you club buds

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    RE: Need Help with Fox 15 Davis Conversion

    Love that inverted installation Tweedy. Where's the exhaust outlet?

    Scenic background too.

  18. #18
    tweedy's Avatar
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    RE: Need Help with Fox 15 Davis Conversion

    See the black line below the blue stripe exiting the Fuselage in front of the Stab it ends about 1" aft of the elevator T.E. it's a carbon fiber arrow shaft.


  19. #19

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    RE: Need Help with Fox 15 Davis Conversion

    Tweedy nice Mr Clean special all out the "stack" not over the plane martin


  20. #20

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    RE: Need Help with Fox 15 Davis Conversion

    Nice ...

    What is the covering? Airspan?

  21. #21

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    RE: Need Help with Fox 15 Davis Conversion

    Here is its "big brother" a 50 fitted with r/c fox carb the black one is a Perry carb bigga muffler
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  22. #22
    tweedy's Avatar
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    RE: Need Help with Fox 15 Davis Conversion


    ORIGINAL: fiery

    Nice ...

    What is the covering? Airspan?
    Graphics done wwith a CAD program (DeltaCad), Printed on Dollar Store tissue, applied with Nitrate Dope, then silk, then topped off with a sprayed coat of Klass Kote. If I did it again I think I would put the tissue over the silk also well over $100.00 of ink.

  23. #23
    tweedy's Avatar
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    RE: Need Help with Fox 15 Davis Conversion


    ORIGINAL: fiery

    Love that inverted installation Tweedy. Where's the exhaust outlet?

    Scenic background too.
    In the background in the gap between the wing and stab is the runway of the Cedar City Airport, our flying field is at the base of the hills in the distance.

  24. #24
    tweedy's Avatar
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    RE: Need Help with Fox 15 Davis Conversion


    ORIGINAL: AMB

    Tweedy glad its solved, the cylinder alignment was the most logical based on the symptoms martin

    about 45 minutes air time and land with a half tank left, Ha try that on glow sure it made an impression on you club buds
    I'm a diesel NUBE I've known of them all my life but the first one I have ever seen run was the Enya !! That I put in a Royal Coachman earlier in the year most of the guys in the club had had no idea a model diesel engine even existed.

  25. #25
    tweedy's Avatar
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    RE: Need Help with Fox 15 Davis Conversion


    ORIGINAL: fiery

    Nice ...

    What is the covering? Airspan?
    these were also printed on tissue
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