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JL2A
Joined: 07 Apr 2015
Posts: 113
Location: Australia
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 Posted: Mon Jul 03, 2017 6:07 pm Post subject: Mag timing HS6A is the book wrong? |
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Someone that is in a workshop working on aircraft everyday says he times the HS6A as follows:
say 27d mag, max advance in book is 31d.
difference is 4d
multiply by 0.787 prop reduction = 3.1d at the propeller
The book says 5.5d +/- 0.7
His claim is that the chart published in the maintenance manual (and Craig Payne's publication on the matter) are wrong, they are dividing by 0.787 whereas it should be multiplied (the propeller goes through less angular distance than the engine)
Not being a quick thinker, at the time I could not fault his logic, simply saying we just did it by the book and have never had a problem.
This engine in question always drops 100rpm or more on a single mag. This is out of limits. Plugs etc are fine, it does it anytime, not just oily plug mornings.
Now this has got me real curious as like I said, can't fault his logic, but not being an expert maybe there is something else going on that is not accounted for here, that they knew about when publishing this chart... or did they?
Is the chart simply wrong and everyone has been running around with too-advanced HS6As for 60 years
Maybe they took into account the difference between static and dynamic timing?
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wlannon(at)shaw.ca
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| Posted: Mon Jul 03, 2017 8:49 pm Post subject: Mag timing HS6A is the book wrong? |
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Perhaps the question should be "which book is wrong?"
Start with the "Technical Specification for Service and Maintenance", Chap.
6, Power plant, Sec. 1, "Technical data of Huosai-6 Engine".
Page 122, item 42, shows Max. advance angle (CRANK) at 31 +/- 1* BTDC
This corresponds nicely with the Polish AI14 R (also 260 HP/TO) and the
Czech M462 RF (315 HP/TO) both at 30*BTDC.
Now to CHAP. 8 , Supplement. Sec, 1 Huosai -6 JIA Engine (285 HP/TO) -
Note 3, Pg. 189 clearly reduces the max. advance angle to 27*BTDC.
But then we have the PT6 Maintenance Manual which shows 31* for both Huosai
models! Which is correct? Damned if I know but I use 30* just cuz!
And then we have the M14P ---------- 75 more HP and a max. advance angle of
23*BTDC. Finally getting close to the real ones (P&W 985, 1340, etc. at
25*).
Walt
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JL2A
Joined: 07 Apr 2015
Posts: 113
Location: Australia
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| Posted: Tue Jul 04, 2017 1:48 am Post subject: Re: Mag timing HS6A is the book wrong? |
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I think my esteemed colleague woodja has come up with the answer:
| Quote: |
advance on magneto is calculated as the angle the advance moves on the device itself ,
nothing to do with piston , prop or anything ...thus ,
I read the magneto is geared at 1.125 internally. This from Tech specs ...
So 27 degrees of magneto advance only equals 27/1.125 , or 24 degrees of piston advance .
24 degrees from 31 +|-1 degree (from tech specs ..)
is the TDC degrees piston firing point ,
equals 7.0 degrees of piston advance required ,
which , multiplied by .787 equals
5.5 degrees of prop advance.
Remarkably close to the table ...
ie exact.
..And +/-1 degree of piston is , funnily , +-.7 degree of prop , coincidentally the limit variation... |
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woodja51
Joined: 13 May 2015
Posts: 40
Location: MELBOURNE AUSTRALIA
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| Posted: Tue Jul 04, 2017 1:59 am Post subject: Re: Mag timing HS6A is the book wrong? |
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I reckon this is the answer ...I already told Anatole, but for anyone wondering
How it's calculated here's some math. Also , something for those timing air start distributors , there is a paperwork out there stating the hole aperture is set at 1mm gap on the number 4 master / with prop at 9.5 ATDC. .
It should read 0.1 mm ... BIG DIFFERENCE?. FYI .
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yakman285(at)gmail.com
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| Posted: Tue Jul 04, 2017 2:28 am Post subject: Mag timing HS6A is the book wrong? |
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Huh?? Multiply not Divide the prop ratio? Must be the New Math they taught a few years back when Johnny was being educated. After 40 years of dumb down in the schools for Johnny. Johnny is a genius.
Rather than go into a long discourse about timing, My advice is to stick with what you know works.
Now, what are the effects on running too far advanced? The Bad: Heat, CHT's will be higher at climb power, Best Power will not be obtained. The Good: an efficient burn at low manifold pressures where a lean burn slows flame front progression. The Ugly: piston and exhaust valve erosion, evidenced by white powdery deposits and burn spots.
M-14P Series II owners are lucky. They can buy one of my Gearcase windows that allows them quickly and exactly determine where TDC is and calculate where the magneto points (fire) open. HS6A owners must use a Timerite or that prop. If using the Prop. make up a jig so that a digital level can be used to measure prop angle.
Keep Johnny away from the calculator while you figure out where to set the timing.
Craig Payne
 Virus-free. www.avg.com [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2][/url]
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wlannon(at)shaw.ca
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| Posted: Tue Jul 04, 2017 8:46 am Post subject: Mag timing HS6A is the book wrong? |
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Woodja51’s math is quite correct.
The only problem is it needs some explanation of the factors involved to be meaningful. If there is anyone really interested I would be happy to provide that.
Craigs “Good, Bad and Ugly” is also right on. One description of “Ugly” for the M14P is the installation of an auto advance mag. being incorrectly timed to the values of the stock fixed spark magneto.
Walt
From: Craig Payne (yakman285(at)gmail.com)
Sent: Tuesday, July 04, 2017 3:25 AM
To: yak-list (yak-list(at)matronics.com)
Subject: Re:Mag timing HS6A is the book wrong?
Huh?? Multiply not Divide the prop ratio? Must be the New Math they taught a few years back when Johnny was being educated. After 40 years of dumb down in the schools for Johnny. Johnny is a genius.
Rather than go into a long discourse about timing, My advice is to stick with what you know works.
Now, what are the effects on running too far advanced? The Bad: Heat, CHT's will be higher at climb power, Best Power will not be obtained. The Good: an efficient burn at low manifold pressures where a lean burn slows flame front progression. The Ugly: piston and exhaust valve erosion, evidenced by white powdery deposits and burn spots.
M-14P Series II owners are lucky. They can buy one of my Gearcase windows that allows them quickly and exactly determine where TDC is and calculate where the magneto points (fire) open. HS6A owners must use a Timerite or that prop. If using the Prop. make up a jig so that a digital level can be used to measure prop angle.
Keep Johnny away from the calculator while you figure out where to set the timing.
Craig Payne
Virus-free. www.avg.com
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JL2A
Joined: 07 Apr 2015
Posts: 113
Location: Australia
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| Posted: Thu Jul 06, 2017 3:52 am Post subject: Re: Mag timing HS6A is the book wrong? |
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| Quote: | | The only problem is it needs some explanation of the factors involved to be meaningful. If there is anyone really interested I would be happy to provide that. |
Please explain!
I find it meaningful in that it backs up the book figures and verifies that this other 'method' was indeed flawed.
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wlannon(at)shaw.ca
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| Posted: Thu Jul 06, 2017 9:13 am Post subject: Mag timing HS6A is the book wrong? |
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There was no disrespect intended in my post and I apologize if it was so
perceived.
I believe I opened with a clear statement that the formula was "quite
correct". This was in response to another posters questioning of the math.
I wondered how many readers of these posts actually understood (or cared?)
how the formula was derived. For example the factor "1.125" and it's effect
on the value of the magneto's advance feature and the reasons behind that.
eg: Four sparks magneto, number of cylinders, etc.
Cheers;
Walt
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JL2A
Joined: 07 Apr 2015
Posts: 113
Location: Australia
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| Posted: Fri Jul 07, 2017 1:16 pm Post subject: Re: Mag timing HS6A is the book wrong? |
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No disrespect taken. Just thought there was more to it than either myself or Matt had figured.
9 cylinders, 720d rotation of rotor to fire them all
9÷8=1.125
thanks CP!
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wlannon(at)shaw.ca
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| Posted: Fri Jul 07, 2017 2:43 pm Post subject: Mag timing HS6A is the book wrong? |
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Thank you;
Yes, 9 cyls., 720* Crankshaft rotation, 810* Mag. drive rotation. If it
were a standard 4 lobe rotor that also would turn 810* but it is a
compensated 9 lobe rotor (radial engines only) that turns 360* or 0.5 X
Crankshaft (Internally geared to mag. drive)
Walt
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jbsoar(at)gmail.com
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| Posted: Fri Jul 07, 2017 4:00 pm Post subject: Mag timing HS6A is the book wrong? |
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Timing issues...Gentlemen, would it be possible to condense this tribal knowledge into a manual that applies to both the CJ and Yak aircraft?
Step-by-step, using various methods?
John B
On Fri, Jul 7, 2017 at 4:16 PM, JL2A <info(at)flyingwarbirds.com.au (info(at)flyingwarbirds.com.au)> wrote:
| Quote: | --> Yak-List message posted by: "JL2A" <info(at)flyingwarbirds.com.au (info(at)flyingwarbirds.com.au)>
No disrespect taken. Just thought there was more to it than either myself or Matt had figured.
9 cylinders, 720d rotation of rotor to fire them all
9÷8=1.125
thanks CP!
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Viperdoc
Joined: 19 Apr 2014
Posts: 484
Location: 08A
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| Posted: Sat Jul 08, 2017 5:59 am Post subject: Mag timing HS6A is the book wrong? |
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Ah, mental masturbation...the book has always worked for me but I'm getting old and senile.
Doc
Sent from my iPad
| Quote: | On Jul 4, 2017, at 4:48 AM, JL2A <info(at)flyingwarbirds.com.au> wrote:
I think my esteemed colleague woodja has come up with the answer:
>
> advance on magneto is calculated as the angle the advance moves on the device itself ,
>
> nothing to do with piston , prop or anything ...thus ,
>
> I read the magneto is geared at 1.125 internally. This from Tech specs ...
>
>
> So 27 degrees of magneto advance only equals 27/1.125 , or 24 degrees of piston advance .
>
> 24 degrees from 31 +|-1 degree (from tech specs ..)
>
> is the TDC degrees piston firing point ,
>
> equals 7.0 degrees of piston advance required ,
>
> which , multiplied by .787 equals
>
>
>
>
> 5.5 degrees of prop advance.
>
> Remarkably close to the table ...
>
>
> ie exact.
>
>
> ..And +/-1 degree of piston is , funnily , +-.7 degree of prop , coincidentally the limit variation...
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=470679#470679
|
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Monika Miller
Joined: 03 Nov 2021
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