REFLECTOR: It's been really quiet this week

Tue Feb 18 12:59:58 CST 2014

Brian,

7 GPH sounds like you are running at best power which can be spelled "detonation".  The factory CHT spec is for bayonet temp not gasket temp.  If your bayonet temp is good you're trying to solve a non existent problem.

Larry Coen
N136LC

From: Brian Michalk 
Sent: Tuesday, February 18, 2014 9:43 AM
To: Velocity Aircraft Owners and Builders list 
Subject: Re: REFLECTOR: It's been really quiet this week

Hmm, I am a proponent of reducing timing to lower CHT's, and have my mag and EI set to 28BTDC, advancing to 32BTDC above 2600 RPM.  The book value is 28-32 degrees.

I will retard it some more and we'll see what happens.

On the EI, I am running NGK Iridium IX plugs, with a fairly shallow reach.  I don't have the exact rating available at the moment.

I am seeing conflicting data.  My gasket thermocouples are reading redline temps on takeoff, but the bayonet thermocouples are reading cool.  Do you know what could be causing this?

On 2/18/2014 8:51 AM, John Dibble wrote:

  On 2/17/2014 11:44 AM, Brian Michalk wrote:

    I've been flight testing.  It's a slow process for me, since my engine design while Franklin based, has EFI and EI.
    I have been battling high CHT's even in the cooler weather, and am seeing positive results as the engine breaks in.

  Sorry for repeating myself, but I really think you need to reduce the timing advance to 24-25 degrees.  My anecdotal experience has been that any departure from the mag/massive electrode combination increases the detonation tendency for the Franklin engine.  Further, multiple changes compound the problem.  When I bought my plane it had one mag and one EI, both using massive electrode plugs.  I experienced minor detonation symptoms such as an occasional plug fouled with metal and an occasional high CHT.  When I switched to auto plugs for the EI, the symptoms worsened with more frequent plug fouling, erosion of the electrode and an occasional engine stumble right after takeoff, a real attention getter.  When I switched the mag plugs to fine wire, the engine stumbling became more frequent and I had to replace a cylinder and piston due to severe pitting.  I have eliminated the symptoms by reducing the timing advance.  I manually increase the EI advance once I'm above 9k for max power.  Maybe Mike W will comment also.

  John

    Specifically, I've been testing the forward CG limits, and have decided that my decision to move equipment as far forward as possible was a bad one.  I was intending to have Juanita be able to fly the airplane without ballast, but with my weight, I can't really carry much in the copilot seat.  I mounted a big Optima Red Top at a 15 inch arm location.  This weekend I relocated it temporarily to just forward of the whales tail, but for a permanent solution, I am looking at some of the really lightweight batteries that are out there, and am having a hard time making up my mind.

    Option 1: some lightweight lead/acid battery
    Option 2: an alternative chemistry

    For option 1, John mentioned the Braille batteries.  I looked online, and people seem to think that Braille is stretching their performance numbers, but if Velocity is using them, then that's a pretty good endorsement.  There are also Odyssey batteries that look pretty good as well.

    Option 2 for me would be the new LiFe (Lithium Iron) batteries that are used in some motorcycles, snowmobiles and jet skis.  Those are all pretty high vibration environments, which was my first concern.  Next, they are really incredibly lightweight.
    Now, when these batteries reach 13 volts, they are basically dead, with 30% capacity remaining.  They are fully charged at 14.3 volts, and appear to take a charging voltage up to 15 volts.  For me, I'd need to convert my internal regulated alternator to external, and bump up the voltage to accommodate these new batteries.
    Another down side is, like the LiPo batteries, these need to have the cells balanced.  There is a special connector that ensures all of the cells are charged to their proper voltage, but balancing a battery doesn't have to be performed for every charge.  I also think that rather than charging through the balancing port, a person could use a hobby grade balancer that places a load on cells to draw down their voltage, achieving the same goal.  Bulk charge through the terminals, then balance by discharging excess capacity.
    And another downside is that they like to be stored at something like 80% capacity.  This may be fine for our needs.  As long as they can start the plane, they can be charged at high currents, so within a few minutes after starting they would be at 100%.
    Okay.  For one final upside:  The higher operating voltage will spin a prop faster, and will have smaller voltage drop in your cables.  I'm solid state switching, losing a couple of tenths of volts across each solid state relay.  This bump up in voltage would really be nice for my electric gyros, which are always complaining about low voltage until I bring up the engine RPM's.

    LFX19A4-BS12MSRP: $199.95 
    SHORAI LFX Lithium-ion Powersports battery,19AH 12V, "A" polarity, Case Type 4
    Length 5.83" 
    Width 3.39"
    Height 3.46"
    Weight 2.32lbs
    CCA 285amps

    I would need two of those, which would put me at the lower end of my CCA requirements.
    www.shoraipower.com

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