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Engine RPM and propeller speed
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N642K

Joined: 23 Jul 2008
Posts: 84

Posted: Mon Aug 06, 2012 5:51 pm Post subject: Engine RPM and propeller speed

I have a digital tach on my M-14B powered CJ.  If it indicates engine crank RPM, are the displayed RPM limits corrected for the difference between crank and prop speed?



Thanks in advance.

Dabear(at)devere.us
Guest

Posted: Mon Aug 06, 2012 6:41 pm Post subject: Engine RPM and propeller speed

What is the tach and what are reading off of?



Bear



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N642K

Joined: 23 Jul 2008
Posts: 84

Posted: Mon Aug 06, 2012 7:22 pm Post subject: Re: Engine RPM and propeller speed

This is a Horizon Tachometer.  This from their website:



The P-1000 functions as two fully independent digital tachometers that monitor the signals received from the primary circuits of the aircraftâ€™s magnetos. The internal right and left tachometers independently determine engine RPM, which is then average and displayed for the pilot. The superior reliability of the tachometer design is due to the use of two separate magneto signals to generate two identical RPM readings.

wlannon(at)shaw.ca
Guest

Posted: Mon Aug 06, 2012 7:25 pm Post subject: Engine RPM and propeller speed

You are reading crankshaft RPM.



Walt



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viperdoc(at)mindspring.co
Guest

Posted: Mon Aug 06, 2012 7:44 pm Post subject: Engine RPM and propeller speed

Suspect you are reading the pulses off your P lead but don't know the type of tach and how it is wired Bear. So you should be reading the crank revolutions.

Doc



Sent from my iPad



On Aug 6, 2012, at 9:38 PM, "Randy" <Dabear(at)devere.us> wrote:



[quote] 

 

 What is the tach and what are reading off of?

 

 Bear

 

 --

viperdoc(at)mindspring.co
Guest

Posted: Tue Aug 07, 2012 7:05 am Post subject: Engine RPM and propeller speed

--

mark.bitterlich(at)navy.m
Guest

Posted: Tue Aug 07, 2012 7:16 am Post subject: Engine RPM and propeller speed

This is a great instrument and works very well.  That said, it works by connecting to the P leads of both mags.  Every person that has done this install  themselves (that I know) has usually ended up with increased radio noise from P lead EM radiation.  Be very mindful of this and use the very best in shielded wiring and installation procedures to avoid radio EMI issues with this device. 



Mark Bitterlich

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N642K

Joined: 23 Jul 2008
Posts: 84

Posted: Tue Aug 07, 2012 11:05 am Post subject: Re: Engine RPM and propeller speed

I agree, it's a great instrument.  But my question is about the difference between engine and prop speeds and the limits on the tachometer.  Are those limits corrected for the difference?

dsavarese0812(at)bellsout
Guest

Posted: Tue Aug 07, 2012 11:29 am Post subject: Engine RPM and propeller speed

Mike,

The Horizon tach ranges can be set to ANY specification you want by the 

manufacturer before delivery.  IE: If the max engine RPM is 2900, the 

tach red light can be programmed to come on at red line.  The other 

parameters, like 82% (2378 RPM) can also be pre programmed.



The original Russian tach, even though it reads in %, was engine RPM, 

not prop RPM.  The prop RPM is determined by the nose case gear ratio.  

In the case of the M14P, it is .658.  So in other words, no matter what 

the engine RPM is, the prop always runs at 2/3 the speed of the 

engine.   All you do is phone Horizon and tell them what parameters you 

want programmed into the tach and they will program it before delivery.



You will determine the limits on the Tach by the programming.

Dennis

A. Dennis Savarese

334-285-6263

334-546-8182 (mobile)

www.yak-52.com

Skype - Yakguy1



On 8/7/2012 2:05 PM, N642K wrote:

 	  Quote: 	
		   



 I agree, it's a great instrument.  But my question is about the difference between engine and prop speeds and the limits on the tachometer.  Are those limits corrected for the difference?





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=380312#380312

N642K

Joined: 23 Jul 2008
Posts: 84

Posted: Tue Aug 07, 2012 11:42 am Post subject: Re: Engine RPM and propeller speed

Thanks Dennis.  Once again you come thru with the answer.  I guess I need to look up the limits of the V530 and double check what is already programmed on my Horizon tach.

dsavarese0812(at)bellsout
Guest

Posted: Tue Aug 07, 2012 11:57 am Post subject: Engine RPM and propeller speed

The V530 limits are your engine RPM limits, which according to the 

manual is 2950 RPM.  I prefer to use 2900 though.



A. Dennis Savarese

334-285-6263

334-546-8182 (mobile)

www.yak-52.com

Skype - Yakguy1



On 8/7/2012 2:42 PM, N642K wrote:

 	  Quote: 	
		   



 Thanks Dennis.  Once again you come thru with the answer.  I guess I need to look up the limits of the V530 and double check what is already programmed on my Horizon tach.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=380323#380323

wlannon(at)shaw.ca
Guest

Posted: Wed Aug 08, 2012 8:06 am Post subject: Engine RPM and propeller speed

Hi Dennis;



I probably am wrong but I seem to recall from the manual that the operating 

T.O. RPM limit for the M14P was 2901 and the overspeed limit was 2950.

It appears that "N642K" may still not understand that the tachometer has 

nothing to do with the propellor.



Cheers;

Walt



--

N642K

Joined: 23 Jul 2008
Posts: 84

Posted: Wed Aug 08, 2012 8:40 am Post subject: Re: Engine RPM and propeller speed

Thanks Walt but I get it

dsavarese0812(at)bellsout
Guest

Posted: Wed Aug 08, 2012 9:03 am Post subject: Engine RPM and propeller speed

Hi Walt,

 From the M14P maintenance manual, here are the specs pertinent to this 

conversation.



Take-off rating is 2900 RPM +-1 (99%). "Given in brackets are nominal 

values of the crankshaft speed of rotation in percent against the unified

tachometer (99.4 % corresponds to 2900 r/min of the crankshaft)".



I have no idea where they come up with 99.4% corresponds to 2900 r/min. 

There are numerous misprints in the manual caused by translation. I'd 

stick with 99%=2900 period.

1.2. SPECIFICATIONS

1.2.1. Engine

Designation................................................................................ 

M-14P

Cooling system 

......................................................................... 

Air-type

Engine starting system 

............................................................. Air-type

Engine continuous operation time:

At take-off rating 

.............................……..………….................. Up to 5 min

At maximum permissible speed, of rotation .......... ................... 

Up to 1 min

At other ratings .................................. 

..................................... Not limited

Iverted engine operation:

Ratings ........................................... 

.........................................Nominal

Continuous operation time ......................... 

............................. Up to 2 min

Total time within service life 

..................................................... Up to 18 %

_/Maximum permissible speed of rotation ............... 

.................. 2950 (101 %) r/min/_

Acceleration (pickup) from 760 r/min (idle) to take-off

rating on stationary airplane .............. 

...................................... Up to 3 s

Maximum permissible crankshaft speed drop when

changing over to one-magneto operation at nominal

rating II and cruise rating I (low-pitch airscrew) .. 

..................... 85 r/min (3 %)

Number and arrangement of cylinders ................. 

................... 9, radial, single-row

Cylinder numbering .................................. 

............................... Counter clockwise if viewed from

rear cover side, top cylinder is Ho. 1

Cylinder bore 

............................................................................ 

105 mm

Piston stroke:

Cylinder No. 4 .................................... 

...................................... 130 mm

Cylinders Nos 3 and 5 

.............................................................. 130.15 mm

Cylinders Nos 2 and 6 ............................. 

................................ 130.23 mm

Cylinders Nos 8 and 9 ............................. 

................................ 130.39 mm

Cylinders Nos 1 and 7 ............................. 

................................ 131.25 mm

Total displacement .................................. 

................................ 10.161 1

Compression ratio ................................... 

................................ 6.3±0.1

Direction of rotation of crankshaft and airscrew shaft ...............LH

Engine dry mass ..................................... 214 kg+2%

NOTE: Engine dry mass does not include mass of the generator, 

compressor, fine

filter with pipelines, engine frame ring, exhaust manifold parts, 

tachometer generator.



Dennis



A. Dennis Savarese

334-285-6263

334-546-8182 (mobile)

www.yak-52.com

Skype - Yakguy1



On 8/8/2012 11:04 AM, Walter Lannon wrote:

[quote] 



 Hi Dennis;



 I probably am wrong but I seem to recall from the manual that the 

 operating T.O. RPM limit for the M14P was 2901 and the overspeed limit 

 was 2950.

 It appears that "N642K" may still not understand that the tachometer 

 has nothing to do with the propellor.



 Cheers;

 Walt



 --

markdavis(at)wbsnet.org
Guest

Posted: Wed Aug 08, 2012 11:16 am Post subject: Engine RPM and propeller speed

His confusion may be from the fact that he has an M-14B with an M-14P nose 

case and standard Russian paddle blade prop on it, so the engine for all 

practical purposes is the same as an M-14P regarding RPM limitations. 

Engine RPM is engine RPM regardless of the nose case gear ratio.



Mark Davis

N44YK (w/M-14P, but also a spare M-14B in hangar with an M-14P nose case on 

it.)

---

brian(at)lloyd.com
Guest

Posted: Wed Aug 08, 2012 1:07 pm Post subject: Engine RPM and propeller speed

On Wed, Aug 8, 2012 at 12:13 PM, Mark Davis <markdavis(at)wbsnet.org (markdavis(at)wbsnet.org)> wrote:

 	  Quote: 	
		   --> Yak-List message posted by: "Mark Davis" <markdavis(at)wbsnet.org (markdavis(at)wbsnet.org)>

 

 His confusion may be from the fact that he has an M-14B with an M-14P nose case and standard Russian paddle blade prop on it, so the engine for all practical purposes is the same as an M-14P regarding RPM limitations. Engine RPM is engine RPM regardless of the nose case gear ratio.

 	




And any tach that uses the impulses on the p-leads is using crankshaft RPM (probably a better name than "engine RPM") and not prop or output shaft RPM.

FWIW: p-lead pulses per crank rotation = number-of-cylinders/2

 

-- 

Brian Lloyd, WB6RQN/J79BPL

3191 Western Dr.

Cameron Park, CA 95682

brian(at)lloyd.com (brian(at)lloyd.com)

+1.767.617.1365 (Dominica)

+1.916.877.5067 (USA)

 

  [quote][b]

viperdoc(at)mindspring.co
Guest

Posted: Wed Aug 08, 2012 1:51 pm Post subject: Engine RPM and propeller speed

And...who's on first? To really confuse... a M-14 DHPF with an M-14 P nose case?!! Along with a few other minor but significant changes to allow for the prop governor accessory drive. 

Doc

--

wlannon(at)shaw.ca
Guest

Posted: Wed Aug 08, 2012 7:21 pm Post subject: Engine RPM and propeller speed

Hi  Dennis;



Thanks for the info.

I agree, 2900 RPM (99%) period is a good number.   I would not set up the 

governor for the max. allowable of 2950 but would regard that as an 

accidental overspeed limit.



Walt



--

dsavarese0812(at)bellsout
Guest

Posted: Thu Aug 09, 2012 3:44 am Post subject: Engine RPM and propeller speed

Totally agree with you Walt.

Dennis



A. Dennis Savarese

334-285-6263

334-546-8182 (mobile)

www.yak-52.com

Skype - Yakguy1



On 8/8/2012 10:19 PM, Walter Lannon wrote:

[quote] 



 Hi Dennis;



 Thanks for the info.

 I agree, 2900 RPM (99%) period is a good number. I would not set up 

 the governor for the max. allowable of 2950 but would regard that as 

 an accidental overspeed limit.



 Walt



 --

GeorgeCoy

Joined: 02 Dec 2010
Posts: 310

Posted: Thu Aug 09, 2012 5:28 am Post subject: Engine RPM and propeller speed

And then there was the guy with a homebuilt (name and type to remain

anonymous) who used a prop tach to set up his tachometer. Had the prop

turning at 2950 RPM . About 60 hrs later he was informed of his mistake. As

far as I know now 9 years later and over 500 hrs it is still  running

fine...



--

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