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914 fuel flows

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erichdtrombley(at)juno.co
Guest

Posted: Tue Jun 06, 2006 9:13 am Post subject: 914 fuel flows

Ken, 

Knowing your fuel system as I do, I concur the problem is not with the fuel flow sensor. 

I would verify that your manifold pressure gage is properly calibrated.  This would explain the excessive fuel flow per inches of mercury. 

I believe for each fuel flow you have listed the actual H.P. you are producing is actually greater than that corresponding to the M.P. listed.   

Erich Trombley

N28ET Classic Mono 914 

  

Time: 10:24:39 PM PST US

From: KENNETH D HILL <kandshill2(at)sbcglobal.net>

Subject: RE: [ Ken Hill ] : New Email List Photo Share Available!



Hi Simon,

   

  I wish they were.  I recently put over 1000 miles on N214KS and the fuel 

required

to fill the tank agreed to within .1/.2 gallons of what the gauge said I

used.  Plugs look normal.

   

  Ken



Simon Smith <jodel(at)nildram.co.uk> wrote:

      I think you figures might be a little suspect.  The Rotax 914 Operators 

manual

give Take off performance as 5800rpm, 39.9 inHG and 8.7 us gph.  Max continuous

as 5500rpm, 35.4 inHG and 7.2 us gph. (ref pages 8-2 & 10-1)

  Are you sure that your fuel flowe sensor is correctly calibrated?

   

  Are these airspeeds IAS or TAS?

   

  Simon

 



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jodel(at)nildram.co.uk
Guest

Posted: Tue Jun 06, 2006 10:12 am Post subject: 914 fuel flows

Surely, if the MP gauge is suspect the Airbox sensor/TCU would also  have to be in error by the same amount?  I initially queried the figures  because I assumed (and we all know how dangerous that can be!) that the Rotax  book fuel flows ought to be accurate.

  

 Simon

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rparigor(at)suffolk.lib.n
Guest

Posted: Tue Jun 06, 2006 11:07 am Post subject: 914 fuel flows

I have no flight time on a 914 as of yet. Do have a pretty good

understanding of the Bing type 64 though.



Go up in altitude and the mixture will richen up which = more fuel burn

for a given power setting compared to sea level. 



The constant depression carbs are somewhat altitude compensating, but not

complete. Turbo in boost is more compensating than normal aspirated.



Once flying I will be able to tell pretty good numbers on fuel flow as to

just how much thin air richens mixture at given RPM/MP. 



I have a fuel flow gauge, EGT, O2 sensor that drives a Mixture Monitor and

ability to lean things out.



Looking at color of spark plugs is not absolute as far as mixture. If you

want the best tell of mixture from the plugs, you need to be hard on motor

and turbo, and your skill of flying if a short wing mono with a right

quartering tailwind:

Run at desired power setting and altitude for a while, then shut motor off

right away and land deadstick without touching throttle position upon shut

down. 

When you change throttle position, power setting and altitude things can

easily change and interfere with your good read of plugs.



I am somewhat of a motorhead, don't like to put undo stresses on motors,

so am going with ability to fiddle and test without hurting anything.



If you really wanted to be extreme precise on getting mixture just so,

measure carbon monoxide of each cylinder as per Rotax instructions for

making sure the leanest cylinder is rich enough for full throttle, just

vary a bit for cruise settings. They recommend such a test if you modify

the intake system of a 914. IMHO installing a intercooler is modifying the

intake system. Eastwood sells just such a measuring tool.



Ron Parigoris

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erichdtrombley(at)juno.co
Guest

Posted: Wed Jun 07, 2006 7:59 am Post subject: 914 Fuel Flows

Simon, 

Can't say I agree with your assessment.  The MP gage in the panel is independent of the airbox pressure/TCU.  As part of the installation of a MP (electronic not analog) you are required to calibrate the sensor.  If the sensor is off by any amount from the true MP that the engine is really producing then you will be incorrect in you assumption of H.P.  For example if the pilot has not correctly calibrated the MP gage and it is reading 31" of MP, however, in reality the engine is producing 34" then that would explain the excessive fuel flow for a given MP reading.  Make sense.  Off course too rich of a mixture could also be the cause, however, with the Bing carbs this is unlikely.  My fuel flows per indicated MP are very close to the published figures in the Rotax manual.  Just my two cents. 

Erich Trombley

N28ET Classic Mono 914 

Time: 11:12:29 AM PST US

From: "Simon Smith" <jodel(at)nildram.co.uk>

Subject: RE: 914 fuel flows



Surely, if the MP gauge is suspect the Airbox sensor/TCU would also have 

to

be in error by the same amount?  I initially queried the figures because 

I

assumed (and we all know how dangerous that can be!) that the Rotax book

fuel flows ought to be accurate.



Simon



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Gilles.Thesee(at)ac-greno
Guest

Posted: Wed Jun 07, 2006 8:31 am Post subject: 914 Fuel Flows

Erich Trombley a écrit :

 	  Quote: 	
		  

 Simon,



 Can't say I agree with your assessment.  The MP gage in the panel is 

 independent of the airbox pressure/TCU.  As part of the installation 

 of a MP (electronic not analog) you are required to calibrate the 

 sensor.  If the sensor is off by any amount from the true MP that the 

 engine is really producing then you will be incorrect in you 

 assumption of H.P.  For example if the pilot has not correctly 

 calibrated the MP gage and it is reading 31" of MP, however, in 

 reality the engine is producing 34" then that would explain the 

 excessive fuel flow for a given MP reading.  Make sense.  Off course 

 too rich of a mixture could also be the cause, however, with the Bing 

 carbs this is unlikely.  My fuel flows per indicated MP are very close 

 to the published figures in the Rotax manual.  Just my two cents.




	


Hi all,



You need to check the MP gauge and the tachometer.

We checked ours during the flight tests, and our UMA tachometer read 

high by nearly 100 RPM at 5000 RPM. I mean, when it read 5000, the 

electronic calibration tacho read only about 4900 RPM.



Now, suppose yours says 5000 while the engine is turning at 5100 ? If I 

recall correctly, prop power varies with the cube of RPM...



FWIW,

Regards,

Gilles Thesee

Grenoble, France

http://contrails.free.fr

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jodel(at)nildram.co.uk
Guest

Posted: Wed Jun 07, 2006 11:08 am Post subject: 914 Fuel Flows

Hi,

  

 As I  understand it, at full throttle, the TCU will control the wastegate to give  39.9in HG.

  

 Rotax  say that at 5800rpm and 39.9inHG the engine will burn 8.7us  gph.

  

 To  burn more than 8.7gph the MP or the rpm must be higher or there is an error  in Rotax figures.

  

 If the  MP gauge is suspect, then for a gauge reading of 39.9inHG the actual MP must be  higher (to give a higher FF) but this is unlikely if the wastegate is being  correctly controlled hence my comment thta the airbox sensor/TCU must also be in  error.

 Of  course, as others have pointed out, Rotax rpm gauges are notoriously inaccurate  so could this be the culprit?

  

 Simon

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