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Throttle setting at higher cruising altitudes
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MarkWDavis

Joined: 03 Jan 2007
Posts: 104
Location: Syracuse, KS

Posted: Wed Nov 28, 2007 3:35 am Post subject: Throttle setting at higher cruising altitudes

I recall reading that the carburetor on the M-14P  is altitude compensating, but has an auto-rich feature when opened to full  throttle.  If that's true, how far back does the throttle need to be pulled  to get it out of the auto-rich mode and start leaning itself?  I was  bucking a 50 knot headwind yesterday and needed to reduce the time my beak was  pointed into it so I ran at 70% and the throttle just backed off of the forward  stop to where it started to reduce manifold pressure a couple of tenths.   Once again a GPS sure beats a stopwatch and a sectional to avoid sweating fuel  so much.

  

 Mark Davis

 N44YK

   [quote][b]

mark.bitterlich(at)navy.m
Guest

Posted: Wed Nov 28, 2007 1:11 pm Post subject: Throttle setting at higher cruising altitudes

The answer to that question that I got from Vladimir Yastremski is to

simply pull the throttle back to the point where you sign even the

slightest reduction in manifold pressure and then to leave it right

there.  



I've tried it.  It works.  



Mark Bitterlich

 



--

Mozam

Joined: 24 Nov 2006
Posts: 85

Posted: Thu Nov 29, 2007 6:39 am Post subject: Re: Throttle setting at higher cruising altitudes

I have a Fuel Scan unit in my TW that has proved to be very accurate.



During high altitude cruise (say above 6,000'), I cannot detect any evidence of this full throttle enrichment.



For example, at 9,500' with the prop at 65%,  I can place the throttle at the forward stop, note the fuel flow, then retard the throttle until the manifold pressure drops several inches (this is a couple inches of throttle movement), and I see very little change in fuel flow.



It appears to me that if there is any full throttle fuel enrichment, it is "disengaged" at "higher" altitudes.



Also, FWIW, I have found that RPM has a much greater effect on fuel flow than manifold pressure (throttle position).  In other words, pulling the prop back from 70% to 65% reduces the fuel flow more than leaving the prop at 70% and reducing the manifold pressure three or four inches.



So at high altitude with a nice tailwind I pull the prop back to 60% and put the throttle at the forward stop.  This results in a fuel flow of about 12.8 gal/hr.



Just my opinion (based on my Fuel Scan observations), I think the most fuel efficient M-14 throttle setting for cruise is to set the throttle at the boost limit for any given RPM setting.



Note:  Your mileage may vary, past returns are no guarantee of future returns, some assembly required, batteries not included, etc.



Cheers,

Steve Dalton

napeone

Joined: 10 Jan 2006
Posts: 36
Location: Birmingham, Al.

Posted: Thu Nov 29, 2007 2:23 pm Post subject: Re: Throttle setting at higher cruising altitudes

Concur with Mozam.

David H.

MarkWDavis

Joined: 03 Jan 2007
Posts: 104
Location: Syracuse, KS

Posted: Thu Nov 29, 2007 2:25 pm Post subject: Throttle setting at higher cruising altitudes

Steve and Mark,

     Thanks for the replies.  I have noticed it appears to be a bit leaner 

when running at 65% vs. 70%.  So, I've been running at 70% into headwinds 

and 65% with tailwinds.



Mark Davis

N44YK



---

mark.bitterlich(at)navy.m
Guest

Posted: Thu Nov 29, 2007 2:47 pm Post subject: Throttle setting at higher cruising altitudes

I did not have the instrumentation that Steve has when I came to the

belief that I stated, and I tend to defer to his testing.  However, this

directly contradicts what Vladimir told me and I also trust HIS judgment

beyond others as well!  



Makes me wonder if it might not be worthwhile to run the test again at

altitude but with higher RPM settings.  I wonder if Steve's test would

duplicate at 10,000 feet and say 85% on the RPM?  I would really like to

know the answer to this for sure in case I have somehow managed to

delude myself!   



Steve did say:  "I think the most fuel efficient M-14 throttle setting

for cruise is to set the throttle at the boost limit for any given RPM

setting.



To the best of my knowledge Steve, there are no "boost limits" to this

engine at ANY RPM.  



Mark Bitterlich

 



--

MarkWDavis

Joined: 03 Jan 2007
Posts: 104
Location: Syracuse, KS

Posted: Thu Nov 29, 2007 3:23 pm Post subject: Throttle setting at higher cruising altitudes

I think I'll just stick with backing the throttle off of the stop just 

a tad.  It doesn't appear to make a noticeable difference in power output 

and it might also save a little wear and tear on the engine.  Besides, it's 

still just natural for me to back it off a bit after 1,700 hours of making 

heat with J-52's that we could run all day at MIL minus 3%.  I'll be in 

black figures all of my life with my taxes after all the JP-4 and JP-5  I 

got paid to burn!



Mark Davis

N44YK



---

wlannon(at)persona.ca
Guest

Posted: Thu Nov 29, 2007 3:24 pm Post subject: Throttle setting at higher cruising altitudes

Mark Bitterlich wrote;



 	  Quote: 	
		   To the best of my knowledge Steve, there are no "boost limits" to this

 engine at ANY RPM.



 Mark Bitterlich


	


Mark;



There are varying RPM/manifold pressure limits for every engine with a 

variable pitch propellor.

Probably the easiest (but not recommended) way to find the first one is to 

attempt a take-off with the prop control at low RPM.



Walt

mark.bitterlich(at)navy.m
Guest

Posted: Thu Nov 29, 2007 3:51 pm Post subject: Throttle setting at higher cruising altitudes

Really.  Well Walt, I am not so sure you are right about that, but I am

always ready to stand corrected and learn something that I did not know

before.  



My M-14 Manual says that you can operate this engine at full throttle

with the engine reduced to the very minimum RPM setting available at ANY

altitude.  And ... I've read every available operating manual on this

engine that I can find.   



So what is the limit you are speaking of with the M-14P ???  



Mark

--

brian-1927(at)lloyd.com
Guest

Posted: Thu Nov 29, 2007 4:12 pm Post subject: Throttle setting at higher cruising altitudes

On Nov 29, 2007, at 6:39 AM, Mozam wrote:



 	  Quote: 	
		   So at high altitude with a nice tailwind I pull the prop back to  

 60% and put the throttle at the forward stop.  This results in a  

 fuel flow of about 12.8 gal/hr.



 Just my opinion (based on my Fuel Scan observations), I think the  

 most fuel efficient M-14 throttle setting for cruise is to set the  

 throttle at the boost limit for any given RPM setting.


	


That is true for most recip engines, i.e. run maximum MAP to minimize  

pumping losses and modulate RPM to control power output.



Brian Lloyd                         3191 Western Drive

brianl AT lloyd DOT com             Cameron Park, CA 95682

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



PGP key ID:          12095C52A32A1B6C

PGP key fingerprint: 3B1D BA11 4913 3254 B6E0  CC09 1209 5C52 A32A 1B6C

Mozam

Joined: 24 Nov 2006
Posts: 85

Posted: Thu Nov 29, 2007 4:27 pm Post subject: Re: Throttle setting at higher cruising altitudes

 	  mark.bitterlich(at)navy.m wrote: 	
		  .



To the best of my knowledge Steve, there are no "boost limits" to this

engine at ANY RPM.  



Mark Bitterlich

-- 	




Hi Mark,



I agree, I have never seen any either.  



Perhaps not the best choice of words on my part.  What I was trying to say was to use the max manifold pressure that the manual lists for a given power setting.  For example, the manual lists "Cruise 1" power as 64% RPM and 735 mmHg (29").  I *think* that using less than 735 mmHg in this case reduces engine efficiency.



But, I do not know if using more throttle would be an actual "over-boost" situation.



Cheers,

Steve

Mozam

Joined: 24 Nov 2006
Posts: 85

Posted: Thu Nov 29, 2007 4:33 pm Post subject: Re: Throttle setting at higher cruising altitudes

 	  mark.bitterlich(at)navy.m wrote: 	
		  I did not have the instrumentation that Steve has when I came to the

belief that I stated, and I tend to defer to his testing.  However, this

directly contradicts what Vladimir told me and I also trust HIS judgment

beyond others as well!  



Makes me wonder if it might not be worthwhile to run the test again at

altitude but with higher RPM settings.  I wonder if Steve's test would

duplicate at 10,000 feet and say 85% on the RPM?  I would really like to

know the answer to this for sure in case I have somehow managed to

delude myself!   

-- 	




Mark,



I agree, Vladimir (and others) have a wealth of knowledge about these engines.



I have only looked (and not found) this "max throttle enrichment" at high altitude.  Perhaps the carb only operates this feature at lower altitudes?



I will experiment further and report my findings.  Any excuse to go fly is a good one!!    



Cheers,

Steve

mark.bitterlich(at)navy.m
Guest

Posted: Thu Nov 29, 2007 4:47 pm Post subject: Throttle setting at higher cruising altitudes

Thanks Steve, I'll sure be interested in your results. 



Mark

 



--

brian-1927(at)lloyd.com
Guest

Posted: Thu Nov 29, 2007 4:48 pm Post subject: Throttle setting at higher cruising altitudes

On Nov 29, 2007, at 3:49 PM, Bitterlich, Mark G CIV Det Cherry Point,  

MALS-14 64E wrote:



 	  Quote: 	
		   

 Point, MALS-14 64E" <mark.bitterlich(at)navy.mil>



 Really.  Well Walt, I am not so sure you are right about that, but  

 I am

 always ready to stand corrected and learn something that I did not  

 know

 before.



 My M-14 Manual says that you can operate this engine at full throttle

 with the engine reduced to the very minimum RPM setting available  

 at ANY

 altitude.  And ... I've read every available operating manual on this

 engine that I can find.



 So what is the limit you are speaking of with the M-14P ???


	


I don't think there is one for the M14P or the Huosai. There are RPM  

limits but not MAP limits (that one can reach).



But in general, peak cylinder pressures are a function of MAP. At  

really low RPMs you can complete combustion at an earlier crank angle  

before the combustion chamber volume has changed as much so you can  

get higher peak cylinder pressures at high MAP and low RPM. This  

translates into higher main bearing pressure due to combustion.  

(OTOH, higher RPMs result in higher main bearing pressure due to  

accelerating the moving mass.) So I can imagine an engine having a  

max MAP spec for a lower RPM. I recall that this is the case for most  

of the big radial engines. I suspect Pappy can name these limits for  

the 1820 for us.



Regardless, you aren't going to hurt your M14P or Huosai engine by  

leaving the throttle all the way forward and changing power by  

changing RPM. The only question is whether or not there is an  

enrichment circuit in the carb at full throttle. I think that having  

a fuel-flow gauge and having it NOT show a noticeable reduction in  

fuel flow when the throttle is pulled back a skosh puts this one to  

bed also.



Brian Lloyd                         3191 Western Drive

brianl AT lloyd DOT com             Cameron Park, CA 95682

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



PGP key ID:          12095C52A32A1B6C

PGP key fingerprint: 3B1D BA11 4913 3254 B6E0  CC09 1209 5C52 A32A 1B6C

mark.bitterlich(at)navy.m
Guest

Posted: Thu Nov 29, 2007 5:03 pm Post subject: Throttle setting at higher cruising altitudes

This is not a reply to your posting Brian, but just a reply in general.

In my earlier post, I did not mean to imply that manifold / RPM

relationships were unrestricted on EVERY airplane, just that such

restrictions did not always exist for any engine with a variable pitch

prop as Walt was mentioning.  I distinctly remember reading that you can

be at full power on the M-14P, and I mean WFO, and pull the prop back to

ANY RPM setting while leaving the throttle wide open.  This surprised me

enough that I questioned it and had it verified by a number of both

written and verbal (all Russian) sources. But if anyone has any written

source that specifies differently, I would be happy to be proven wrong.

This is to me not a matter of who is right and who is wrong, but WHAT is

right and WHAT is wrong. 



Mark

 



--

wlannon(at)persona.ca
Guest

Posted: Thu Nov 29, 2007 5:33 pm Post subject: Throttle setting at higher cruising altitudes

Hi Mark;



I don't have the M14P manual to refer to but Steve has just posted the 

Cruise 1 setting of 64% and 735 mm/hg. This is a recommended limit.

Granted that as altitude increases the throttle must be opened to maintain 

the desired MP. Since these engines have a low blower ratio compared to an 

"altitude" engine the full throttle altitude will be reached very quickly. 

In fact it is actually sea level but only with the power settings given in 

the manual.

I absolutely agree with Steve's first post to use max. manifold pressure for 

a given RPM. He has revised it a bit to a given power setting rather than 

RPM but I think he means the same. The "power setting" is a combination of 

RPM and MP.

I'm sure you would agree that at sea level a power setting of full throttle 

and 1450 (50%)RPM could be fairly described as over boosted.



Cheers;

Walt



---

N13472(at)aol.com
Guest

Posted: Thu Nov 29, 2007 6:58 pm Post subject: Throttle setting at higher cruising altitudes

In a message dated 11/29/2007 5:34:25 P.M. Pacific Standard Time,  wlannon(at)persona.ca writes:

  	  Quote: 	
		  absolutely agree with Steve's first post to use max. manifold pressure    for 

a given RPM. He has revised it a bit to a given power setting rather    than 

RPM but I think he means the same. The "power setting" is a    combination of 

RPM and MP.

I'm sure you would agree that at sea level a    power setting of full throttle 

and 1450 (50%)RPM could be fairly described    as over boosted.



Cheers;

Walt



	


 

  

 Walt, does not the Cj-6A manual say that Max power is 2350 rpm M/P  ambient + 85 mm ?   

 Tom Elliott  

CJ-6 NX63727

Sandy Valley  NV

3L2

702-723-1223





Check out AOL Money & Finance's list of the hottest products and top money wasters of 2007.

  [quote][b]

wlannon(at)persona.ca
Guest

Posted: Thu Nov 29, 2007 7:18 pm Post subject: Throttle setting at higher cruising altitudes

Hi Tom;

  

 Yep. But referring on this thread to the M14P. Trust all is well  with you.

  

 Best:

 Walt

 [quote]   ---

viperdoc(at)mindspring.co
Guest

Posted: Thu Nov 29, 2007 7:38 pm Post subject: Throttle setting at higher cruising altitudes

Huh?

Doc



--

MarkWDavis

Joined: 03 Jan 2007
Posts: 104
Location: Syracuse, KS

Posted: Thu Nov 29, 2007 7:55 pm Post subject: Throttle setting at higher cruising altitudes

Doc,

    I use 65% to take the free ride of the tailwind.  70% to reduce the time 

the headwind has to work on me.  Navy technique we used.  In significant 

headwinds we always ran at near military power settings.  Max endurance AOA 

with a strong tailwind when trying to stretch range.



Mark Davis

N44YK

---

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