> >> Got the Velocity 20B back in the air on Monday for two flights
of about
> >> 30
> >> minutes each. >
> >
> >
> > Congratulations Al.
> >
> > Just one thing, are they coil packs I see on top of the engine?
> > If so please read Tracy Crooks email re operating
temperature. We don't
> > want another in flight engine failure, it rather spoils one's day.
> >
> > Ian Beadle
> >
> > Very good point Ian.
> > You are absolutely right. Here is a minor point on this subject.
> > I think Al is running a 2.17:1 PSRU so his RPM's may be less
> > than yours, hence the pulse rate will be lower. However I can't
> > say if it is low enough to keep the coils alive. We still need
> > to set up a pulse generator and measure the heat increase
> > on the coil surface as a function of pulse rate.
> >
> > In the mean time and before he flies it again Al should built
> > a box around the coils and feed in some cold air.
> >
> > Paul Lamar
>
>
> Hi Paul
> I rigged a circuit to test the coil pack with a 2.5 ms pulse at
equivalent
> of 9000 rpm. At 14 volts the heat generated was minimal. After
1/2 an
hour
> the temperature rise was just noticeable using the finger test.
> At 12 volts the spark was less intense. With a one ohm resistor
in series
> it was also less intense.
>
> The wiring on Al's alternator looks a bit odd. Shouldn't one of
the wires
go
> to the light?
>
> Ian
>
> Was that the RX8 coils or the GM V8 Ls1 coils?
>
> Well then I wonder why the coils are failing. Equivalent? Is that
> 9000 pulses per minute ... 150 pulses per second? What ignition
> system are you using? I wonder if your ignition system assumes
> a waste spark setup where it might be firing twice per revolution.
>
> Perhaps it is a Chinese quality control problem.
>
> I am also wondering if the type of high voltage spark plug
> wire has anything to do with it. Some wire has resistance
> to suppress radio interference.
>
> BTW when you had a coil fail was that the leading plug
> or the trailing plug? How well did the engine run?
>
> Paul Lamar ...No rotor no motor.
>
I haven't done any testing, so I'm just making a supposition here. I
suspect the real problem is the ambient temperature. I think Tracy was
reporting some fairly high temps before putting in the blast tube. Try
the test in an oven.
Bob W.
--
N93BD - Rotary Powered BD-4 -
http://www.bob-white.com
First engine start 1/7/06 - Special Airworthiness Certificate 10/1/06
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Good idea Bob. If under the hood is 200 F that might change
some solid state parameters. Doubtful but possible I guess.
It certainly changes the rate of
heat transfer from coil to air. Ian tested at room temperature
so the rate of heat transfer was high. In Al's case the rate
of heat transfer from coil to air is much lower. This allows
the transistors to build up more heat. One feeds on the other
so to speak. When the car manufactures tested these things
at an ambient of 300 F they ran them at half our pulse rate.
IMHO we need to test them in an over at different temps.
In Al's case if he is sure the ambient air temp will never get over
145 F he needs to test at the max pulse rate he is going to
see at 145 F. I think.
One would need a pulse rate generator that generated a 3 ms pulse
at about 100 pulses per second (6000 RPM). This can be built from
a Radio Shack 555 for about a buck or two.
http://www.talkingelectronics.com/FreeProjects/555/555Test-FREE.html
-----------------
I plan to continue the testing of coils 'in situ'. If one fails
prematurely
(whatever that is), I'll look at adding additional cooling. Of all the
other "firsts" in the installation that may be of concern, that one is a
ways down the list.
Al
Al got any pictures of your new cooling air scoops?
Paul Lamar
Do you have a way to put some instrumentation on it? That way if one
fails, you'll (we'll) know how hot is too hot...
Thanks,
Matt-
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