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1. 03:52 AM - Re: Momentary Power Loss (A. Dennis Savarese)
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| Subject: | Re: Momentary Power Loss |
Richard is 100% correct. You have one of the coils going TU. The
symptom typically occurs between 20 and 40 minutes of the flight. When
the coil fails, the engine seems to stop for "one heart beat" and then
picks up again. If the CHT starts to approach 200C, the coil will fail
more frequently. The only way I have ever been able to duplicate the
symptom is to purposely get the engine very hot on the ground by running
it with the cooling louvers closed and watch the engine temps increase.
There is no guarantee on the coil failing. But I was able to make a
suspicious coil fail by doing this .When the engine first begins to
misfire, turn the mag switch to 1 or 2 and determine which mag is
failing. Then replace the coil in the suspect mag. Quite honestly,
save yourself a lot of trouble and just bite the bullet and buy 2 new
coils from Richard or the Yak Collection.
As far as pressure carburetor icing, yes it can happen. Here's a great
article and graph which shows the temperature and dew points where
carburetor icing can occur, including pressure carburetors. What I found
most interesting was the VERY small window for pressure carburetor
icing. https://www.boldmethod.com/learn-to-fly/systems/carb-ice/
A. Dennis Savarese
334-546-8182
www.yak-52.com
On 8/30/2021 7:44 AM, Richard Goode wrote:
>
> I have to begin by saying that I'm completely biased on this topic, but this
symptom is extremely common and quite specifically caused by a breakdown of the
capacitor inside the coil through a combination of heat and age. The symptoms
you describe are absolutely typical, although no one has ever been able to explain
why the whole engine momentarily stops, given that one presumably has one
good coil and magneto. But it does! And if you continue to fly, it will slowly
get worse until the engine will completely stop for several seconds, always
after he to soak through to the magneto so typically after 25/30 minutes of
flight. As I wrote, we are biased since we have, after a lot of research, developed
a totally new coil with an external capacitor so does not have this problem
of the capacitor overheating inside the coil of hotwire and indeed for which
we have obtain full certification from EASA (European FAA) for these coils.
We have them in stock with John Warwick of the YakCol!
> lection in San Diego to avoid excessive courier costs from Europe. I have also
prepared a more detailed paper on this topic and can send it to anyone if
you ask us by email.
>
> Richard
>
>
> RICHARD GOODE AEROBATICS
> Rhodds Farm, Lyonshall, Hereford, HR5 3LW, UK
> Tel: +44 (0)1544 340120 Fax: +44 (0)1544 340129
> e-mail: richard.goode@russianaeros.com
> www.russianaeros.com
> WORLD LEADERS IN RUSSIAN SPORTING AIRCRAFT & ENGINES
> In partnership with Aerometal Kft, Hungary.
>
> -----Original Message-----
> From: owner-yak-list-server@matronics.com <owner-yak-list-server@matronics.com>
On Behalf Of Stressmerchant
> Sent: 30 August 2021 11:58
> To: yak-list@matronics.com
> Subject: Yak-List: Momentary Power Loss
>
> --> <mike_beresford@yahoo.co.uk>
>
> I had a little heart-stopping moment on a routine flight yesterday. I was at
about 2,000 ft on cruise settings when the engine very briefly cut, and then
resumed as if nothing had happened. No warning, no odd behaviour afterwards, just
a second of no power. The same thing happened about 5 minutes later, although
I had the impression that the second time the power did not die completely,
just cut back and then resumed.
>
> CHT, Oil temp, oil pressure, fuel pressure all normal.
>
> Some searching through the archives here suggests that it could be the coils
starting to go. I did wonder about carb icing, but the inlet temp was above freezing.
>
> The aircraft is due for annual maintenance next week, so if something needs changing
this would be a good time to do it.
>
> Any ideas about other potential causes?
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=503006#503006
>
>
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