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Low CHT

 
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glipaz



Joined: 11 Jan 2011
Posts: 107

PostPosted: Mon Jul 11, 2022 11:13 am    Post subject: Low CHT Reply with quote

Hey friends. I have a low time M-14P on my Nanchang. I typically have low CHTs in the 140C range even with gills closed. Fly out of SoCal so not a cold climate. I know Richard Goode tends to point to the suction jet and being too rich, but know that I also only get around 35gph fuel flow with WOT. I have increased the suction jet as large as I can to raise temps but not get a lean surge at altitude.
Thoughts?
Gil


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richard.goode(at)russiana
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PostPosted: Mon Jul 11, 2022 10:10 pm    Post subject: Low CHT Reply with quote

Hello Gil,

Interesting. To be honest I would first suspect the sender underneath the
spark plug. It is a very imprecise way of temperature measurement that can
be helped by rarely cleaning the cylinder head and the sending ring itself.
And then which suction jet have you got fitted? And the engine as a standard
M 14 P?

Please let me know and with regards

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(at)russianaeros.com
www.russianaeros.com
WORLD LEADERS IN SOVIET & CHINESE RADIAL AIRCRAFT ENGINES
In partnership with Aerometal Kft, Hungary.

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Vic



Joined: 12 Aug 2008
Posts: 113
Location: Southern Bavaria

PostPosted: Tue Jul 12, 2022 4:08 am    Post subject: Re: Low CHT Reply with quote

Hi Richard,
off topic, but I had no luck so far trying to contact you about a set of hoses for a 18 T. Do my emails bounce back to somewhere ? I don´t get error warnings when sending so still head scratching . . .

Vic


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richard.goode(at)russiana
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PostPosted: Tue Jul 12, 2022 5:08 am    Post subject: Low CHT Reply with quote

Hi Vic,

Richard was in email correspondence with you yesterday regarding hoses. You last emailed us today at 01:26 our time and Richard replied to you at 06:58. Did you receive that email? Are you trying to reply to that one? I'll resend it to you again now. We don't have many filters on our emails, so people don't usually struggle to reach us.

Kind regards,

Wendy
RICHARD GOODE AEROBATICS
Rhodds Farm, Lyonshall, Hereford, HR5 3LW, UK
Tel: +44 (0)1544 340120 Fax: +44 (0)1544 340129
e-mail: richard.goode(at)russianaeros.com
www.russianaeros.com
WORLD LEADERS IN SOVIET & CHINESE RADIAL AIRCRAFT ENGINES
In partnership with Aerometal Kft, Hungary.

--


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Vic



Joined: 12 Aug 2008
Posts: 113
Location: Southern Bavaria

PostPosted: Tue Jul 12, 2022 5:57 am    Post subject: Re: Low CHT Reply with quote

Hi Wendy,
thank you sooo much, your mail landed in my own spam files !! I should check this more often - well, old age I guess. Years ago there was a notice when anything arrived in spam, but no longer for some reason, now that´s computer business . Does that make sense , cannot see this.
I will send details to you today.

cheers
Vic


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glipaz



Joined: 11 Jan 2011
Posts: 107

PostPosted: Tue Jul 12, 2022 7:29 am    Post subject: Re: Low CHT Reply with quote

Vic, thanks for blowing up my thread.

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Vic



Joined: 12 Aug 2008
Posts: 113
Location: Southern Bavaria

PostPosted: Tue Jul 12, 2022 12:58 pm    Post subject: Re: Low CHT Reply with quote

Two postings from me ? I said why, because I was unable to contact Richard . So go on with your topic . . . .

Vic


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Ttail



Joined: 24 Jun 2013
Posts: 118

PostPosted: Tue Jul 12, 2022 6:36 pm    Post subject: Re: Low CHT Reply with quote

Gil.
My engine (M14PF) came with 1.3mm suction jet fitted. This was changed to a 1.5mm suction jet so slightly leaner. No issue controlling CHT's to say 180C. Also picked up a lesser fuel burn at crz power settings. FF reduced by 4L hr.


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Sean Trestrail
ttail[at]internode.on.net
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PostPosted: Tue Jul 12, 2022 11:42 pm    Post subject: Low CHT Reply with quote

These engines are surprisingly "individual" when choosing a suction jet. That is that two engines of seemingly identical specification can require suction jets 0.1 mm or even 0.2 mm apart. But from my experience I would suggest that for an M 14 PF that a 1.3 mm suction jet is probably correct. But I'd also say that a 1.5 mm (larger means leaner since they are compensating jets) is too lean. Then, as I said before, the CHT measuring probe under a sparking plug is an incredibly imprecise way of measuring temperature. But it makes a huge difference if it is really clean as indeed its "seat" onto a cylinder head. Then I would suggest comparing its reading with an accurate external CHT measurement. And, finally, I wouldn't be concerned about fuel flow. I feel too many people have expensive electronic fuel flow measurements and then become obsessed by them. Engine performance and cylinder temperature are, to my mind, the only important factors!
RICHARD GOODE AEROBATICS
Rhodds Farm, Lyonshall, Hereford, HR5 3LW, UK
Tel: +44 (0)1544 340120 Fax: +44 (0)1544 340129
e-mail: richard.goode(at)russianaeros.com
www.russianaeros.com
WORLD LEADERS IN SOVIET & CHINESE RADIAL AIRCRAFT ENGINES
In partnership with Aerometal Kft, Hungary.

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glipaz



Joined: 11 Jan 2011
Posts: 107

PostPosted: Wed Jul 13, 2022 10:18 am    Post subject: Re: Low CHT Reply with quote

Thanks Richard! My suction jet is 130 on my standard M-14p. It’s not a PF.
Accel jet is 060. I don't use the stock CHT sensor. I have an Electronic International multi-cyl instrument. I’d like CHTs to be at least 170C.
Gil


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Ttail



Joined: 24 Jun 2013
Posts: 118

PostPosted: Wed Jul 13, 2022 2:58 pm    Post subject: Re: Low CHT Reply with quote

" I feel too many people have expensive electronic fuel flow measurements and then become obsessed by them. Engine performance and cylinder temperature are, to my mind, the only important factors! '[i]

The reduction in FF was an observation not an "obsession". Its also kind of nice to have a second independent fuel qty system.

The reason the jet was changed in the first place was consistently low CHT (on all cylinders). After the change CHT is far more manageable.


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PostPosted: Wed Jul 13, 2022 11:26 pm    Post subject: Low CHT Reply with quote

Hello Sean,

Of course I had no idea who this might be, and "obsession" might be too strong a term. But remember that the Russians have been using these engines for 50 years without any kind of fuel flow measurement and don't seem to do too badly.

Certainly I have seen pilots adjusting suction jet purely on the basis of fuel flow; ignoring cylinder temperatures and engine performance! Why I have no idea. But the fundamental problem is that this CHT measurement system is not precise and so dependent on a good contact with the cylinder head which so many people do not provide.

And I know from long experience that suction jet sizes can make significant differences to CHT.

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(at)russianaeros.com
www.russianaeros.com
WORLD LEADERS IN SOVIET & CHINESE RADIAL AIRCRAFT ENGINES
In partnership with Aerometal Kft, Hungary.

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