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richard.goode(at)russiana
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 Posted: Tue Feb 20, 2018 8:04 am Post subject: Engine stumble in flight |
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Ernest – with your huge experience in these matters, possibly you could explain why you think I'm wrong!
Richard
Rhodds Farm
Lyonshall
Hereford
HR5 3LW
United Kingdom
Tel: +94 (0) 81 241 5137 (Sri Lanka)
Tel: +44 (0) 1544 340120
Fax: +44 (0) 1544 340129
www.russianaeros.com
I’m currently in Sri Lanka but this Mail is working,and my local phone is +94 779 132 160.
From: owner-yak-list-server(at)matronics.com [mailto:owner-yak-list-server(at)matronics.com] On Behalf Of Ernest Martinez
Sent: Tuesday, February 20, 2018 8:14 PM
To: yak-list
Subject: Re: Re: Engine stumble in flight
Wrong
On Tue, Feb 20, 2018 at 5:28 AM, Richard Goode <Richard.goode(at)russianaeros.com (Richard.goode(at)russianaeros.com)> wrote:
I'm sorry, but that is not correct! But over the last 25 years, I have experienced coil problems on at least as many aircraft. Logic will tell you that a coil failure in one magneto will leave the engine running perfectly well on the other magneto with a slight power loss. The practicality is different, and the engine will stop totally if the coil failure is serious. Of course it will then restart, but enough to give the pilot, and indeed any passengers, a fright.
Our own view is that, as has been said, the magneto gets very hot in operation. And of course the coil is inside, and worse still, the capacitor is inside the coil, which is intrinsically getting hot with the current going through the coil. In order to partially overcome this problem, we have developed coils with an external capacitor which will run rather cooler, and have had very satisfactory results with them. The capacitor is small; bonded to the outside of the coil and makes no difference to installation of the coil inside the magneto.
Richard Goode
From: owner-yak-list-server(at)matronics.com (owner-yak-list-server(at)matronics.com) [mailto:owner-yak-list-server(at)matronics.com (owner-yak-list-server(at)matronics.com)] On Behalf Of John B
Sent: 20 February 2018 07:13
To: Yak-List Digest Server <yak-list(at)matronics.com (yak-list(at)matronics.com)>
Subject: Re: Re: Engine stumble in flight
A coil failure in a magneto will feel the same as simply grounding the mag, or turning the mag "off." In other words, a coil failure with both mags "on" or "not grounded," will feel like nothing, other than, say, a five percent loss of performance. It won't cause a total engine failure. However, it is entirely possible for both magnetos to have intermittently failing coils. One is tired, and the other quits when it gets hot, so the engine stumbles, terrifying the pilot and passenger. The brief engine stumble rattles the coil enough for it to correct it's internal short, and the engine smooths out. Or, one has a spark plug wire problem on one mag, and a failing coil on the other. The engine runs fine, until it gets good and hot and the coil associated with the good spark plug wires fails. Terrifying!
Magnetos get very hot in use. Has anyone fashioned dedicated cooling blast tubes to the magnetos? What does the Sukhoi use, if anything?
We did the auto plug conversion, and immediately were rewarded with a better running engine. The auto plug conversion will reduce the weight of your airplane by a couple of pounds, which is also of benefit. The cost of the kit is nominal.
On Mon, Feb 19, 2018 at 11:26 PM, Walter Lannon <wlannon(at)shaw.ca (wlannon(at)shaw.ca)> wrote:
[quote]
--> Yak-List message posted by: "Walter Lannon" <wlannon(at)shaw.ca (wlannon(at)shaw.ca)>
I have a really hard time accepting that a coil failure in one mag. can cause the other mag to fail.
Have had only one definite coil failure. Occurred during pre-flight power & mag. check on a 1340 with American Bosch mags. Went dead as a doornail on that one but other just fine. New coil installed and back to normal.
Have had two instances of the Huosai wake up call (2 sec. of silence). Two different aircraft & engines, x-country at around 7500 ft. throttle fully open trying to maintain about 65% power, mixture up to throttle (max. lean). Maybe too lean!
Since then with a large throttle opening at altitude I don't go quite as lean and have not (so far) had a recurrence.
Don't know for sure but???????
Walt
--
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Ernie
Joined: 11 Jan 2006
Posts: 513
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| Posted: Tue Feb 20, 2018 8:12 am Post subject: Engine stumble in flight |
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I don't think you're wrong. I agree with you. I didn't see your post. I was responding to the original post.
On Tue, Feb 20, 2018 at 11:03 AM, Richard Goode <richard.goode(at)russianaeros.com (richard.goode(at)russianaeros.com)> wrote:
[quote]
Ernest – with your huge experience in these matters, possibly you could explain why you think I'm wrong!
Â
Richard
Â
Rhodds Farm
Lyonshall
Hereford
HR5 3LW
United Kingdom
 Tel: +94 (0) 81 241 5137 (Sri Lanka)
Tel:Â Â [url=tel:+44%201544%20340120]+44 (0) 1544 340120[/url]
Fax:Â [url=tel:+44%201544%20340129]+44 (0) 1544 340129[/url]
www.russianaeros.com
I’m currently in Sri Lanka but this Mail is working,and my local phone is [url=tel:+94%2077%20913%202160]+94 779 132 160[/url].
Â
From: owner-yak-list-server(at)matronics.com (owner-yak-list-server(at)matronics.com) [mailto:owner-yak-list-server(at)matronics.com (owner-yak-list-server(at)matronics.com)] On Behalf Of Ernest Martinez
Sent: Tuesday, February 20, 2018 8:14 PM
To: yak-list
Subject: Re: Re: Engine stumble in flight
Â
Wrong
Â
On Tue, Feb 20, 2018 at 5:28 AM, Richard Goode <Richard.goode(at)russianaeros.com (Richard.goode(at)russianaeros.com)> wrote:
I'm sorry, but that is not correct! But over the last 25 years, I have experienced coil problems on at least as many aircraft. Logic will tell you that a coil failure in one magneto will leave the engine running perfectly well on the other magneto with a slight power loss. The practicality is different, and the engine will stop totally if the coil failure is serious. Of course it will then restart, but enough to give the pilot, and indeed any passengers, a fright.
Â
Our own view is that, as has been said, the magneto gets very hot in operation. And of course the coil is inside, and worse still, the capacitor is inside the coil, which is intrinsically getting hot with the current going through the coil. In order to partially overcome this problem, we have developed coils with an external capacitor which will run rather cooler, and have had very satisfactory results with them. The capacitor is small; bonded to the outside of the coil and makes no difference to installation of the coil inside the magneto.
Â
Richard Goode
Â
From: owner-yak-list-server(at)matronics.com (owner-yak-list-server(at)matronics.com) [mailto:owner-yak-list-server(at)matronics.com (owner-yak-list-server(at)matronics.com)] On Behalf Of John B
Sent: 20 February 2018 07:13
To: Yak-List Digest Server <yak-list(at)matronics.com (yak-list(at)matronics.com)>
Subject: Re: Re: Engine stumble in flight
Â
A coil failure in a magneto will feel the same as simply grounding the mag, or turning the mag "off." In other words, a coil failure with both mags "on" or "not grounded," will feel like nothing, other than, say, a five percent loss of performance. It won't cause a total engine failure. However, it is entirely possible for both magnetos to have intermittently failing coils. One is tired, and the other quits when it gets hot, so the engine stumbles, terrifying the pilot and passenger. The brief engine stumble rattles the coil enough for it to correct it's internal short, and the engine smooths out. Or, one has a spark plug wire problem on one mag, and a failing coil on the other. The engine runs fine, until it gets good and hot and the coil associated with the good spark plug wires fails. Terrifying!
Â
Magnetos get very hot in use. Has anyone fashioned dedicated cooling blast tubes to the magnetos? What does the Sukhoi use, if anything?
Â
We did the auto plug conversion, and immediately were rewarded with a better running engine. The auto plug conversion will reduce the weight of your airplane by a couple of pounds, which is also of benefit. The cost of the kit is nominal.
Â
Â
On Mon, Feb 19, 2018 at 11:26 PM, Walter Lannon <wlannon(at)shaw.ca (wlannon(at)shaw.ca)> wrote:
[quote]
--> Yak-List message posted by: "Walter Lannon" <wlannon(at)shaw.ca (wlannon(at)shaw.ca)>
I have a really hard time accepting that a coil failure in one mag. can cause the other mag to fail.
Have had only one definite coil failure.  Occurred during pre-flight power & mag. check on a 1340 with American Bosch mags. Went dead as a doornail on that one but other just fine. New coil installed and back to normal.
Have had two instances of the Huosai wake up call (2 sec. of silence). Two different aircraft & engines, x-country at around 7500 ft. throttle fully open trying to maintain about 65% power, mixture up to throttle (max. lean). Maybe too lean!
Since then with a large throttle opening at altitude I don't go quite as lean and have not (so far) had a recurrence.
Don't know for sure but???????
Walt
--
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GeorgeCoy
Joined: 02 Dec 2010
Posts: 309
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| Posted: Tue Feb 20, 2018 8:18 am Post subject: Engine stumble in flight |
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I believe that the coil failure actually fires the spark plug prematurely burning the fuel charge while it’s in the intake position that causes a small burn back through the intake system consuming the fuel charge and that’s why the engine quits because it has no fuel for a second or two. George Coy
Sent from my iPhone
On Feb 20, 2018, at 9:43 AM, Ernest Martinez <erniel29(at)gmail.com (erniel29(at)gmail.com)> wrote:
[quote]Wrong
On Tue, Feb 20, 2018 at 5:28 AM, Richard Goode <Richard.goode(at)russianaeros.com (Richard.goode(at)russianaeros.com)> wrote:
[quote]
I'm sorry, but that is not correct! But over the last 25 years, I have experienced coil problems on at least as many aircraft. Logic will tell you that a coil failure in one magneto will leave the engine running perfectly well on the other magneto with a slight power loss. The practicality is different, and the engine will stop totally if the coil failure is serious. Of course it will then restart, but enough to give the pilot, and indeed any passengers, a fright.
Our own view is that, as has been said, the magneto gets very hot in operation. And of course the coil is inside, and worse still, the capacitor is inside the coil, which is intrinsically getting hot with the current going through the coil. In order to partially overcome this problem, we have developed coils with an external capacitor which will run rather cooler, and have had very satisfactory results with them. The capacitor is small; bonded to the outside of the coil and makes no difference to installation of the coil inside the magneto.
Richard Goode
From: owner-yak-list-server(at)matronics.com (owner-yak-list-server(at)matronics.com) [mailto:owner-yak-list-server(at)matronics.com (owner-yak-list-server(at)matronics.com)] On Behalf Of John B
Sent: 20 February 2018 07:13
To: Yak-List Digest Server <yak-list(at)matronics.com (yak-list(at)matronics.com)>
Subject: Re: Re: Engine stumble in flight
A coil failure in a magneto will feel the same as simply grounding the mag, or turning the mag "off." In other words, a coil failure with both mags "on" or "not grounded," will feel like nothing, other than, say, a five percent loss of performance. It won't cause a total engine failure. However, it is entirely possible for both magnetos to have intermittently failing coils. One is tired, and the other quits when it gets hot, so the engine stumbles, terrifying the pilot and passenger. The brief engine stumble rattles the coil enough for it to correct it's internal short, and the engine smooths out. Or, one has a spark plug wire problem on one mag, and a failing coil on the other. The engine runs fine, until it gets good and hot and the coil associated with the good spark plug wires fails. Terrifying!
Magnetos get very hot in use. Has anyone fashioned dedicated cooling blast tubes to the magnetos? What does the Sukhoi use, if anything?
We did the auto plug conversion, and immediately were rewarded with a better running engine. The auto plug conversion will reduce the weight of your airplane by a couple of pounds, which is also of benefit. The cost of the kit is nominal.
On Mon, Feb 19, 2018 at 11:26 PM, Walter Lannon <wlannon(at)shaw.ca (wlannon(at)shaw.ca)> wrote:
[quote]
--> Yak-List message posted by: "Walter Lannon" <wlannon(at)shaw.ca (wlannon(at)shaw.ca)>
I have a really hard time accepting that a coil failure in one mag. can cause the other mag to fail.
Have had only one definite coil failure. Occurred during pre-flight power & mag. check on a 1340 with American Bosch mags. Went dead as a doornail on that one but other just fine. New coil installed and back to normal.
Have had two instances of the Huosai wake up call (2 sec. of silence). Two different aircraft & engines, x-country at around 7500 ft. throttle fully open trying to maintain about 65% power, mixture up to throttle (max. lean). Maybe too lean!
Since then with a large throttle opening at altitude I don't go quite as lean and have not (so far) had a recurrence.
Don't know for sure but???????
Walt
--
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dsavarese0812(at)bellsout
Guest
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| Posted: Tue Feb 20, 2018 10:15 am Post subject: Engine stumble in flight |
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Bingo!!!!
Dennis
From: George Coy <george.coy(at)gmail.com>
To: yak-list(at)matronics.com
Sent: Tuesday, February 20, 2018 11:19 AM
Subject: Re: Re: Engine stumble in flight
I believe that the coil failure actually fires the spark plug prematurely burning the fuel charge while it’s in the intake position that causes a small burn back through the intake system consuming the fuel charge and that’s why the engine quits because it has no fuel for a second or two. George CoySent from my iPhone
On Feb 20, 2018, at 9:43 AM, Ernest Martinez <erniel29(at)gmail.com (erniel29(at)gmail.com)> wrote:
[quote]Wrong
On Tue, Feb 20, 2018 at 5:28 AM, Richard Goode <Richard.goode(at)russianaeros.com (Richard.goode(at)russianaeros.com)> wrote:[quote]I'm sorry, but that is not correct! But over the last 25 years, I have experienced coil problems on at least as many aircraft. Logic will tell you that a coil failure in one magneto will leave the engine running perfectly well on the other magneto with a slight power loss. The practicality is different, and the engine will stop totally if the coil failure is serious. Of course it will then restart, but enough to give the pilot, and indeed any passengers, a fright.
Our own view is that, as has been said, the magneto gets very hot in operation. And of course the coil is inside, and worse still, the capacitor is inside the coil, which is intrinsically getting hot with the current going through the coil. In order to partially overcome this problem, we have developed coils with an external capacitor which will run rather cooler, and have had very satisfactory results with them. The capacitor is small; bonded to the outside of the coil and makes no difference to installation of the coil inside the magneto.
Richard Goode
From: owner-yak-list-server(at) matronics.com (owner-yak-list-server(at)matronics.com) [mailto:owner-yak-list-server(at) matronics.com (owner-yak-list-server(at)matronics.com)] On Behalf Of John BSent: 20 February 2018 07:13To: Yak-List Digest Server <yak-list(at)matronics.com (yak-list(at)matronics.com)>
Subject: Re: Re: Engine stumble in flight
A coil failure in a magneto will feel the same as simply grounding the mag, or turning the mag "off." In other words, a coil failure with both mags "on" or "not grounded," will feel like nothing, other than, say, a five percent loss of performance. It won't cause a total engine failure. However, it is entirely possible for both magnetos to have intermittently failing coils. One is tired, and the other quits when it gets hot, so the engine stumbles, terrifying the pilot and passenger. The brief engine stumble rattles the coil enough for it to correct it's internal short, and the engine smooths out. Or, one has a spark plug wire problem on one mag, and a failing coil on the other. The engine runs fine, until it gets good and hot and the coil associated with the good spark plug wires fails. Terrifying!
Magnetos get very hot in use. Has anyone fashioned dedicated cooling blast tubes to the magnetos? What does the Sukhoi use, if anything?
We did the auto plug conversion, and immediately were rewarded with a better running engine. The auto plug conversion will reduce the weight of your airplane by a couple of pounds, which is also of benefit. The cost of the kit is nominal.
On Mon, Feb 19, 2018 at 11:26 PM, Walter Lannon <wlannon(at)shaw.ca (wlannon(at)shaw.ca)> wrote:
[quote]--> Yak-List message posted by: "Walter Lannon" <wlannon(at)shaw.ca (wlannon(at)shaw.ca)>I have a really hard time accepting that a coil failure in one mag. can cause the other mag to fail.Have had only one definite coil failure. Occurred during pre-flight power & mag. check on a 1340 with American Bosch mags. Went dead as a doornail on that one but other just fine. New coil installed and back to normal.Have had two instances of the Huosai wake up call (2 sec. of silence). Two different aircraft & engines, x-country at around 7500 ft. throttle fully open trying to maintain about 65% power, mixture up to throttle (max. lean). Maybe too lean!Since then with a large throttle opening at altitude I don't go quite as lean and have not (so far) had a recurrence.Don't know for sure but???????Walt--
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jbsoar(at)gmail.com
Guest
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| Posted: Tue Feb 20, 2018 10:51 am Post subject: Engine stumble in flight |
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What exactly happens when a magneto coil fails? How would a mag fire a
spark plug prematurely, of the mag fires when the points open?
Can anyone explain this?
On Tue, Feb 20, 2018 at 10:18 AM, George Coy <george.coy(at)gmail.com> wrote:
[quote] I believe that the coil failure actually fires the spark plug prematurely
burning the fuel charge while it’s in the intake position that causes a
small burn back through the intake system consuming the fuel charge and
that’s why the engine quits because it has no fuel for a second or two.
George Coy
Sent from my iPhone
On Feb 20, 2018, at 9:43 AM, Ernest Martinez <erniel29(at)gmail.com> wrote:
Wrong
On Tue, Feb 20, 2018 at 5:28 AM, Richard Goode <
Richard.goode(at)russianaeros.com> wrote:
> I'm sorry, but that is not correct! But over the last 25 years, I have
> experienced coil problems on at least as many aircraft. Logic will tell you
> that a coil failure in one magneto will leave the engine running perfectly
> well on the other magneto with a slight power loss. The practicality is
> different, and the engine will stop totally if the coil failure is serious.
> Of course it will then restart, but enough to give the pilot, and indeed
> any passengers, a fright.
>
> Our own view is that, as has been said, the magneto gets very hot in
> operation. And of course the coil is inside, and worse still, the capacitor
> is inside the coil, which is intrinsically getting hot with the current
> going through the coil. In order to partially overcome this problem, we
> have developed coils with an external capacitor which will run rather
> cooler, and have had very satisfactory results with them. The capacitor is
> small; bonded to the outside of the coil and makes no difference to
> installation of the coil inside the magneto.
>
> Richard Goode
>
> *From:* owner-yak-list-server(at)matronics.com [mailto:
> owner-yak-list-server(at)matronics.com] *On Behalf Of *John B
> *Sent:* 20 February 2018 07:13
> *To:* Yak-List Digest Server <yak-list(at)matronics.com>
>
> *Subject:* Re: Re: Engine stumble in flight
>
> A coil failure in a magneto will feel the same as simply grounding the
> mag, or turning the mag "off." In other words, a coil failure with both
> mags "on" or "not grounded," will feel like nothing, other than, say, a
> five percent loss of performance. It won't cause a total engine failure
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
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picko
Joined: 20 Nov 2013
Posts: 13
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| Posted: Tue Feb 20, 2018 12:01 pm Post subject: Engine stumble in flight |
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We had the stumble , followed Richards advice, all sorted. Other opinions will extend the solving of your problem until you adopt Richards solution.
Al.
Sent from my iPad
On 21 Feb 2018, at 3:18 am, George Coy <george.coy(at)gmail.com (george.coy(at)gmail.com)> wrote:
[quote] I believe that the coil failure actually fires the spark plug prematurely burning the fuel charge while it’s in the intake position that causes a small burn back through the intake system consuming the fuel charge and that’s why the engine quits because it has no fuel for a second or two. George Coy
Sent from my iPhone
On Feb 20, 2018, at 9:43 AM, Ernest Martinez <erniel29(at)gmail.com (erniel29(at)gmail.com)> wrote:
[quote] Wrong
On Tue, Feb 20, 2018 at 5:28 AM, Richard Goode <Richard.goode(at)russianaeros.com (Richard.goode(at)russianaeros.com)> wrote:
[quote]
I'm sorry, but that is not correct! But over the last 25 years, I have experienced coil problems on at least as many aircraft. Logic will tell you that a coil failure in one magneto will leave the engine running perfectly well on the other magneto with a slight power loss. The practicality is different, and the engine will stop totally if the coil failure is serious. Of course it will then restart, but enough to give the pilot, and indeed any passengers, a fright.
Our own view is that, as has been said, the magneto gets very hot in operation. And of course the coil is inside, and worse still, the capacitor is inside the coil, which is intrinsically getting hot with the current going through the coil. In order to partially overcome this problem, we have developed coils with an external capacitor which will run rather cooler, and have had very satisfactory results with them. The capacitor is small; bonded to the outside of the coil and makes no difference to installation of the coil inside the magneto.
Richard Goode
From: owner-yak-list-server(at)matronics.com (owner-yak-list-server(at)matronics.com) [mailto:owner-yak-list-server(at)matronics.com (owner-yak-list-server(at)matronics.com)] On Behalf Of John B
Sent: 20 February 2018 07:13
To: Yak-List Digest Server <yak-list(at)matronics.com (yak-list(at)matronics.com)>
Subject: Re: Yak-List: Re: Engine stumble in flight
A coil failure in a magneto will feel the same as simply grounding the mag, or turning the mag "off." In other words, a coil failure with both mags "on" or "not grounded," will feel like nothing, other than, say, a five percent loss of performance. It won't cause a total engine failure. However, it is entirely possible for both magnetos to have intermittently failing coils. One is tired, and the other quits when it gets hot, so the engine stumbles, terrifying the pilot and passenger. The brief engine stumble rattles the coil enough for it to correct it's internal short, and the engine smooths out. Or, one has a spark plug wire problem on one mag, and a failing coil on the other. The engine runs fine, until it gets good and hot and the coil associated with the good spark plug wires fails. Terrifying!
Magnetos get very hot in use. Has anyone fashioned dedicated cooling blast tubes to the magnetos? What does the Sukhoi use, if anything?
We did the auto plug conversion, and immediately were rewarded with a better running engine. The auto plug conversion will reduce the weight of your airplane by a couple of pounds, which is also of benefit. The cost of the kit is nominal.
On Mon, Feb 19, 2018 at 11:26 PM, Walter Lannon <wlannon(at)shaw.ca (wlannon(at)shaw.ca)> wrote:
[quote]
--> Yak-List message posted by: "Walter Lannon" <wlannon(at)shaw.ca (wlannon(at)shaw.ca)>
I have a really hard time accepting that a coil failure in one mag. can cause the other mag to fail.
Have had only one definite coil failure. Occurred during pre-flight power & mag. check on a 1340 with American Bosch mags. Went dead as a doornail on that one but other just fine. New coil installed and back to normal.
Have had two instances of the Huosai wake up call (2 sec. of silence). Two different aircraft & engines, x-country at around 7500 ft. throttle fully open trying to maintain about 65% power, mixture up to throttle (max. lean). Maybe too lean!
Since then with a large throttle opening at altitude I don't go quite as lean and have not (so far) had a recurrence.
Don't know for sure but???????
Walt
--
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Yakjumper
Joined: 28 Nov 2016
Posts: 21
Location: Germany
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| Posted: Tue Feb 20, 2018 1:24 pm Post subject: Re: Engine stumble in flight |
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Hello,
a fellow Yak pilot got grounded on a remote airport due to a coil failure last year. Coils were not available over here in Europe, they had to be made.
So I ordered a spare set and put them in the shelf, just in case.
It turned out that they are just refurbished. Old core, new windings.
Are there any improvements or are there different type of coils on the market ?
Can the design be improved to reduce failures ?
thx
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mark.bitterlich(at)navy.m
Guest
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| Posted: Tue Feb 20, 2018 1:26 pm Post subject: Engine stumble in flight |
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An intermittent in the primary would do just that. The primary builds a field, the primary wire opens, the field collapses. In other words an intermittent in the primary would be just like the points opening early. You would not necessarily have the same peak voltage, but there would be enough. It's possible a breakdown in insulation could do it as well.
Mark
--
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Looigi
Joined: 20 Apr 2015
Posts: 80
Location: Christchurch, New Zealand
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| Posted: Tue Feb 20, 2018 4:04 pm Post subject: Re: Engine stumble in flight |
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I have been reading the comments here with keen interest and I would like to thank you for all your advise.
Having a mag that fires prematurely is extremely uncool! I am just thinking of Richard's recent picture of a bent rod!
In our case the engine just stopped firing, rather than stopped turning. The pilot said it was like someone had turned the mags off for a second or two.
I am not sure it is relevant, but I pulled the plugs and one of them had a lot of oil and crap in it. That might cause one cylinder to produce less power if it stopped firing, but not the issue we are having.
I have spoken to one of the guys in our electrical bay at work about this. I will pull the coils out and we can cook them up on the oven and put a meter on them and see what happens to the resistance.
I understand that those with much more experience on here have said that the bad mag takes out the other one. I am not doubting they are right, but I am struggling to wrap some logic around that as the only commonality between the two mags are the cockpit switches and the ignition harness. Could a dodgy coil in one mag send a spike down the P lead and arc across the switch to the P lead of the other mag and disrupt it somehow? Just a thought.
Cheers
Chris
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nigel.willson(at)yakdispl
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| Posted: Tue Feb 20, 2018 5:46 pm Post subject: Engine stumble in flight |
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Chris
I can categorically state I have had the exact identical issue.
The coil is to blame and Yes., it defies logic but it causes a complete loss of power for a very very short time period.
Forget testing the coils. You are wasting your time. They ARE (or st least one of thrm) IS the issue.
Forget replacing them with original Russian coils off the shelf... it's a calendar age issue not an in service hours of use issue.
Get hold of Jill at M14P and get her replacement coil mod kit and you will NEVER look back AND have complete peace of mind. We did this and have never had any issue since.
Trust the advice of this list... bite the bullet and go down this route Rather than waste further time and uncessary expense. Jill's solution is very effective and is not expensive.
Regards,
Nigel Willson
Flying Instructor & Examiner | Airshow Organiser | Display Pilot
http://yakdisplay. com
Tel. 07809 116676
Sent from my Samsung Galaxy S7 - powered by Three
-------- Original message --------
From: Looigi <cdoburton(at)gmail.com>
Date: 21/02/2018 00:04 (GMT+00:00)
To: yak-list(at)matronics.com
Subject: Yak-List: Re: Engine stumble in flight
--> Yak-List message posted by: "Looigi" <cdoburton(at)gmail.com>
I have been reading the comments here with keen interest and I would like to thank you for all your advise.
Having a mag that fires prematurely is extremely uncool! I am just thinking of Richard's recent picture of a bent rod!
In our case the engine just stopped firing, rather than stopped turning. The pilot said it was like someone had turned the mags off for a second or two.
I am not sure it is relevant, but I pulled the plugs and one of them had a lot of oil and crap in it. That might cause one cylinder to produce less power if it stopped firing, but not the issue we are having.
I have spoken to one of the guys in our electrical bay at work about this. I will pull the coils out and we can cook them up on the oven and put a meter on them and see what happens to the resistance.
I understand that those with much more experience on here have said that the bad mag takes out the other one. I am not doubting they are right, but I am struggling to wrap some logic around that as the only commonality between the two mags are the cockpit switches and the ignition harness. Could a dodgy coil in one mag send a spike down the P lead and arc across the switch to the P lead of the other mag and disrupt it somehow? Just a thought.
Cheers
Chris
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=478154#478154
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cjpilot710(at)aol.com
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| Posted: Tue Feb 20, 2018 7:16 pm Post subject: Engine stumble in flight |
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Been reading all the stuff here on engine stumble in flight. I had this same thing a number a years ago and turned out to be the ignition harness. I had even chased coils, points, plugs etc etc. The insulation on the ignition wires in the tube breaks down with age. You start to get cross firing. The only way I found it was using a high tension tester. It turns out 3 of the wires were bad. I yanked off the old system and went with auto plugs and wires. Not one problem since.
BTW I put Payne's electronic system and found it worked great. Better fuel burn and smoother. However since I had zeroed time by Barrett, I haven't hooked up the system as I wanted to get a little time on the engine. Then I bent two rods! A longer story there.
Jim "Pappy" Goolsby
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Looigi
Joined: 20 Apr 2015
Posts: 80
Location: Christchurch, New Zealand
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| Posted: Sun Feb 25, 2018 8:01 pm Post subject: Re: Engine stumble in flight |
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Ok, so to add to the story.....
On Sunday I pulled the two magneto coils out of my machine.
I did a simple continuity test on the bench with a multimeter across the primary and then the secondary windings of both coils thinking I could at least compare the readings. The coil from the right magneto tested open circuit intermittently on the secondary winding. To be honest I had planned to put them in the oven at home to cook while the War Office was at work so I wasn't expecting to find a fault so easily.
I am going to replace the faulty coil tomorrow and see how he goes from there.
There are many on here with brains bigger than mine so can I put a theory up for comment?
If the coil on my RH mag failed, like it has in the secondary (high tension) winding, could that send a burst of HT energy down the P lead, and jump the terminals of one of the 3 switches in that circuit, back down the LH mag P lead to the primary winding of the LH magneto coil, disrupting the magnetic flux of the 'good' mag?
Thoughts??
Chris
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dsavarese0812(at)bellsout
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| Posted: Mon Feb 26, 2018 3:01 am Post subject: Engine stumble in flight |
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I seriously doubt there is any possibility of that happening. George's explanation a few days ago is quite accurate regarding what happens when a coil is failing.
Dennis
From: Looigi <cdoburton(at)gmail.com>
To: yak-list(at)matronics.com
Sent: Sunday, February 25, 2018 11:04 PM
Subject: Re: Engine stumble in flight
--> Yak-List message posted by: "Looigi" <cdoburton(at)gmail.com (cdoburton(at)gmail.com)>
Ok, so to add to the story.....
On Sunday I pulled the two magneto coils out of my machine.
I did a simple continuity test on the bench with a multimeter across the primary and then the secondary windings of both coils thinking I could at least compare the readings. The coil from the right magneto tested open circuit intermittently on the secondary winding. To be honest I had planned to put them in the oven at home to cook while the War Office was at work so I wasn't expecting to find a fault so easily.
I am going to replace the faulty coil tomorrow and see how he goes from there.
There are many on here with brains bigger than mine so can I put a theory up for comment?
If the coil on my RH mag failed, like it has in the secondary (high tension) winding, could that send a burst of HT energy down the P lead, and jump the terminals of one of the 3 switches in that circuit, back down the LH mag P lead to the primary winding of the LH magneto coil, disrupting the magnetic flux of the 'good' mag?
Thoughts??
Chris
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=478262#478262
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Looigi
Joined: 20 Apr 2015
Posts: 80
Location: Christchurch, New Zealand
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| Posted: Mon Feb 26, 2018 12:42 pm Post subject: Re: Engine stumble in flight |
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Yep, George's theory sounds plausible. If the primary circuit winding went open circuit at the right time then the magnetic flux would collapse and one plug could fire prematurely. That could consume the charge in the intake pipes and the engine would hesitate until it is refreshed, but wouldn't there also be a backfire out the carb?
In our case George's theory doesn't fit what was observed. It is the secondary winding that is intermittently open circuit and there was no backfire. Also, when the engine restarted, there was a big cloud of smoke as the unburnt fuel in the cylinders was consumed.
Please don't misunderstand me here, I am not claiming to be right about my theory either but here is my reasoning...
At the time of our event he was 800' up, 700mm manifold pressure and 70%RPM, dirty side down in a stable cruise enjoying the scenery.
The pilot reported the engine quit, "Just like someone had turned the mags off." When he returned to the airfield I had him do an extensive ground run where of course the engine performed flawlessly.
My first reaction was that it was a fuel issue, but I went through the fuel system with a fine tooth comb and I found nothing amiss. Sunday here was a 29C (84F) clear day and no other normal signs so carb ice can be ruled out.
In the Yak-52, if you ignore the cylinders themselves, there are only four components in common with both magnetos.
1. The ignition harness,
2 & 3. The mag switch in each cockpit,
4. The 'Start Selector' switch in the rear cockpit.
Cross firing in a harness usually causes rough running, not a dead cut so I discounted that as a possibility. Whatever goes wrong in one magneto somehow effects what happens in the other one, hence my thoughts about the cross arcing across a switch.
I have been working on round engines for many years now but I definitely don't claim to be an expert. I have a good engineers understanding of how they work and how to fix them, although most of my experience is on P&W engines. I suspect the solution to finding the cause here is to find the man with a good designers knowledge of how these Russian lumps tick.
It would be nice to pin this down to a demonstrable, repeatable defect and come up with a permanent fix....
Haha, Right..... I am off to preflight the pigs!
| dsavarese0812(at)bellsout wrote: | I seriously doubt there is any possibility of that happening. George's explanation a few days ago is quite accurate regarding what happens when a coil is failing.
Dennis
From: Looigi <cdoburton>
To: yak-list(at)matronics.com
Sent: Sunday, February 25, 2018 11:04 PM
Subject: Re: Engine stumble in flight
--> Yak-List message posted by: "Looigi" <cdoburton>
Ok, so to add to the story.....
On Sunday I pulled the two magneto coils out of my machine.
I did a simple continuity test on the bench with a multimeter across the primary and then the secondary windings of both coils thinking I could at least compare the readings. The coil from the right magneto tested open circuit intermittently on the secondary winding. To be honest I had planned to put them in the oven at home to cook while the War Office was at work so I wasn't expecting to find a fault so easily.
I am going to replace the faulty coil tomorrow and see how he goes from there.
There are many on here with brains bigger than mine so can I put a theory up for comment?
If the coil on my RH mag failed, like it has in the secondary (high tension) winding, could that send a burst of HT energy down the P lead, and jump the terminals of one of the 3 switches in that circuit, back down the LH mag P lead to the primary winding of the LH magneto coil, disrupting the magnetic flux of the 'good' mag?
Thoughts??
Chris
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=478262#478262
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http://wiki.matronics.com====================
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wlannon(at)shaw.ca
Guest
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| Posted: Mon Feb 26, 2018 10:07 pm Post subject: Engine stumble in flight |
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Looigi, et al;
George, Jan, Mark, Richard and Vic I believe are all on the right track. I
think all believe the capacitor (condenser) is the source of the problem and
after a considerable time "back to the books" I most certainly agree.
Like you all my time spent working on and flying radials has been on P&W
engines almost invariably with Bendix mags. Over 60 years (85 four days
ago) and never heard of such a problem!
I knew the capacitor was there to inhibit arcing of the points but really
had no idea how it worked (electrical is not my long suite). In the Bendix
mags. the primary
capacitor is wired in parallel with the points. Capacitors (so I read) can
be subject to leakage depending on charge level, capacitor type, size, high
temperatures. age, etc.
As Vic or Richard pointed out being buried between the coil windings seems
like the worst possible place to install it. I can't picture how it can be
wired in parallel
in such a location.
The scenario I think goes like this: The cap. is fully charged and for some
reason leaks across the plates. That charge by-passes the points and
energizes the primary/secondary circuit firing spark plugs totally out of
sync. Apparently the cap. can release that full charge in a millisecond
and then go back to normal.
For what it's worth;
Walt
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j.mevis(at)computer.org
Guest
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| Posted: Mon Feb 26, 2018 11:30 pm Post subject: Engine stumble in flight |
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Hello Walt,
The capacitor does more than avoiding sparks on the points.
It also must help the primary circuit to swing up the energy:
Dielectric energy in the capacitor is transfered into magnetic energy in
the coil and vice versa.
Comparable to what happens into an oscillator circuit.
So indeed, the good working of the capacitor is a must for a flawless coil
functioning.
Nobody knows why the Russians implemented an internal capacitor but they
must have had their reasons for that.
This internal capacitor is not much more than two tiny sheets of metal
wrapped up with insulation material in between.
The frustrating thing about this problem is that we¹ll never know exactly
what happens until someone knowledgeable finds the time/money to have a
thorough look at it in a lab.
Thanks for your input,
Jan
On 27/02/2018, 07:07, "Walter Lannon" <owner-yak-list-server(at)matronics.com
on behalf of wlannon(at)shaw.ca> wrote:
[quote]
Looigi, et al;
George, Jan, Mark, Richard and Vic I believe are all on the right track.
I
think all believe the capacitor (condenser) is the source of the problem
and
after a considerable time "back to the books" I most certainly agree.
Like you all my time spent working on and flying radials has been on P&W
engines almost invariably with Bendix mags. Over 60 years (85 four days
ago) and never heard of such a problem!
I knew the capacitor was there to inhibit arcing of the points but really
had no idea how it worked (electrical is not my long suite). In the
Bendix
mags. the primary
capacitor is wired in parallel with the points. Capacitors (so I read)
can
be subject to leakage depending on charge level, capacitor type, size,
high
temperatures. age, etc.
As Vic or Richard pointed out being buried between the coil windings
seems
like the worst possible place to install it. I can't picture how it can
be
wired in parallel
in such a location.
The scenario I think goes like this: The cap. is fully charged and for
some
reason leaks across the plates. That charge by-passes the points and
energizes the primary/secondary circuit firing spark plugs totally out of
sync. Apparently the cap. can release that full charge in a millisecond
and then go back to normal.
For what it's worth;
Walt
--
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cjpilot710(at)aol.com
Guest
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| Posted: Tue Feb 27, 2018 6:11 am Post subject: Engine stumble in flight |
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Looigi,
I would not dismiss the wiring harness so easily.  A little history.  During WW2 when Grumman aircraft was flight testing the Hellcat, the story goes that at altitude the engine would start to stumble and actually quit.  However as the airplane descended, the engine would start running again and would be performing normally for the landing.  Testing showed no problems.  The problem was design.  The Hellcat ignition harness was not pressurized.  The very air around the wiring harness was "helping" with the insulation between the wires at low altitude.  At high altitude, the wire's insulation was not enough to contain the current.  I am fairly sure if any of us were able to get our Yak or CJs to the Hellcat's altitudes we would have the same problem.Â
My point is the factory wires in the harness, their insulation brakes down with age. Â Not all wires brake down at the same time and place and with heat changes so can change in cross firing. Â
Jim "Pappy" Goolsby
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mark.bitterlich(at)navy.m
Guest
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| Posted: Tue Feb 27, 2018 9:27 am Post subject: Engine stumble in flight |
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Pappy is absolutely correct, and there have been many instances of M-14's cross firing with the stock Russian ignition harness contained within the RF Shield tubing and mesh flex couplings. The shielding design was flawless. The insulation material used on the ignition wire itself, not so much. Many attempts to fix this design were made, including replacing the Russian wire with American made silicone insulated wires. In the end, Dennis came up with the automotive plug and wiring design which totally solved the problem, albeit without the 100% shielding that the tube and mesh design had.
It is easy to forget that a lot of us suffered from exactly the problems that today are ascribed to bad mag coils, that were back in the day also caused by a bad ignition harness. I think that is probably because most of us have gotten rid of the darn thing, especially after trying to snake a new wire through the blasted thing.
That said, the gripe where the engine just stops running for a second or two, then resumes perfect operation, .... especially after getting hot ..... has become a classic sign of the mag coil, after dozens of cases where it has been the proven cause.
Mark
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Lancer
Joined: 21 Apr 2016
Posts: 30
Location: Cairns, Australia
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| Posted: Mon Mar 05, 2018 10:00 pm Post subject: Re: Engine stumble in flight |
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| Vic wrote: | | Remember, the alu foil capacitor is wound between primary and secondary windings within the coil - the worst place to put a capacitor. My guess is that the dielectric material and materials in the coil wires may age and since the electrical properties of components will become unsuitable to operate. |
I figured the capacitor was wound into the coil but wasn't sure and yes it's not the best place to have it located...Thanks Vic
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Vic
Joined: 12 Aug 2008
Posts: 113
Location: Southern Bavaria
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| Posted: Tue Mar 06, 2018 3:46 am Post subject: Re: Engine stumble in flight |
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In the photo you can see the aluminium foil of the capacitor, the primary windings are not there, just the HT wires around it.
There are a lot of good ideas in this thread, we certainly know effects from HT harness and sparkplug troubles. But I can tell you, nothing of that all is depending on time and temperature like a failed coil cum capacitor. When we had this stumble first time for real we were thinking along old mogas from last season that may have gone duff. So we had avgas for next flight - and that took us some more flights till we realized that time was that matters. It was about half an hour each time till that stumble showed and could be induced spectacularly on the ground after landing, setting revs to min. 80 percent: You cannot fail to notice for sure !! With a cold engine NOTHING showed when doing the mag test in preflight. So it became crystal clear after realizing the critical time lapse for the effect that the real problem was the coil. I could demonstrate that anytime in my oven by watching the spark length with the hot coil ! A cold bad coil produces exactly the same spark like a good one.
Just why the engine misses for a complete second on all cylinders in flight is not totally logic to me. Burning into the inlet system with an open valve is hard to imagine. You usually get no ignition without compression in a gasoline engine. While that effect is not yet well explained I continue to be worried about a situation when the engine may not pick up again after that stumble !
Vic
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