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does rotax need egt?

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Rowland_Carson

Joined: 04 Jul 2008
Posts: 155
Location: Cheltenham, England

Posted: Wed Nov 11, 2009 5:18 am Post subject: does rotax need egt?

Subject line nearly says it all.



I'm considering my panel layout and wondering if there's any point in 

including an instrument to show EGT for the intended Rotax 912S 

installation.



My initial reaction is that as there's no mixture control, EGT 

indication does not add much to the CHT/coolant indication that comes 

as standard. But I'm open to other opinions.



Has anyone found EGT indicators really important or useful in a Rotax 

912S installation?



regards



Rowland

-- 

| Rowland Carson  LAA #16532    http://home.clara.net/rowil/aviation/

| 1300 hours building Europa #435 G-ROWI  e-mail <rowil(at)clara.net>

davidjoyce(at)doctors.org
Guest

Posted: Wed Nov 11, 2009 6:04 am Post subject: does rotax need egt?

Rowland, I would strongly recommend fitting a Rotax Flydat or one of the 

more modern engine monitoring systems that will monitor EGTs, oil T & P RPM 

coolant temp and will flash a bright light at you if any of them depart 

marginally from the norm. You can then spend much more time looking out and 

making sure you don't ram something! And you save a lot of panel space. 

Regards, David Joyce, G-XSDJ

---

Rowland_Carson

Joined: 04 Jul 2008
Posts: 155
Location: Cheltenham, England

Posted: Wed Nov 11, 2009 9:25 am Post subject: does rotax need egt?

At 2009-11-11 14:04 +0000 David Joyce wrote:



 	  Quote: 	
		  I would strongly recommend fitting a Rotax Flydat or one of the more 

modern engine monitoring systems that will monitor EGTs, oil T & P 

RPM coolant temp and will flash a bright light at you if any of them 

depart marginally from the norm


	


David - thanks, I have already purchased a MGL box that does that 

sort of stuff (but in a lot less space than a Flydat). I guess I 

should have made that clear.



My query should therefore be re-stated as:



Should I bother to buy EGT probes for a 912S installation to use with 

my engine monitor instrument?



With no mixture control, if I saw abnormal EGT indications, what 

actions could I take in response?



regards



Rowland

-- 

| Rowland Carson          ... that's Rowland with a 'w' ...

| <rowil(at)clara.net>            http://home.clara.net/rowil/

| Twitter: rowland_carson      Facebook: Rowland Carson

davidjoyce(at)doctors.org
Guest

Posted: Wed Nov 11, 2009 11:54 am Post subject: does rotax need egt?

Rowland, I suspect you only get real value out of it if you monitor all 4 

EGTs, as in the Flydat. I am no expert but I would expect that ignition 

problems or compression problems in one cylinder would throw up unequal 

temps. so letting you know where to start looking for the problem.There is 

also the point that if your mixture control systemdoes go up the creek, then 

it might tell you so before the whole thing burns up!   I assume that 

gubbins in one carburettor can lead to leaning of that bank of cylinders. It 

also shows you whether your cylinder/exhaust cooling is even (which is not 

the case in mine - the front 2 are significantly cooler than the others), 

and presumably would give you warning that a baffle or some other part of 

the cooling system had come adrift.  Regards, David

---

air.guerner(at)orange.fr
Guest

Posted: Thu Nov 12, 2009 4:14 am Post subject: does rotax need egt?

Hi Rowland and  all,

  

 In my opinion,  EGT indication on any Rotax engine is useless. EGT indication is  extremely sensitive to the position of the probe inside the exhaust stack.  This is one of the reasons why, on any piston engine, the EGT indication in  itself cannot be used to determine whether a cylinder is running too lean or too  rich. The highest EGT cylinder is not necessarily the leanest. The only way to  determine the mixture condition is to pull the mixture control progressively and  monitor the EGT on all cylinders. The leanest cylinder is the one which  will reach peak EGT first. Of course you cannot do that on a Rotax as there is  no mixture control. The only thing EGT can do on a Rotax, in case of a big  engine problem, is to help diagnose which cylinder is the  culprit.       

 Additional comments:

 With the Europa XS cowling,  the EGT probes on cylinders 1 and 2  are cooled by direct ram air from the round intakes and this has proved to  affect their indication. 

 The Rotax Flydat has 4 EGT channels but shows EGT  on two cylinders at a time and switches automatically back and forth. That makes  EGT very uneasy to read. Any other engine monitor on the market is  certainly better. 

 My plane was fitted with a 914 with Flydat and 4  EGTs when I bought it. When I replaced the engine with the 912S five years  ago, I kept the Flydat but did not install EGT probes and it works for me.  

 Regards

  

 Remi Guerner

 F-PGKL

 

<<<<<< as there's no mixture control, EGT  

indication does not add much to the CHT/coolant indication that comes 

as  standard. >>>>>>>>

     [quote][b]

raimo.toivio(at)rwm.fi
Guest

Posted: Thu Nov 12, 2009 11:05 am Post subject: does rotax need egt?

Remi,

  

 just curious: why did you replace the engine  (914T) and went to 912S ?

  

 Raimo OH-XRT 152 hrs

 [quote]   ---

grahamsingleton(at)btinte
Guest

Posted: Thu Nov 12, 2009 1:22 pm Post subject: does rotax need egt?

Remi Guerner wrote:

 	  Quote: 	
		   Hi Rowland and all,

  

 In my opinion, EGT indication on any Rotax engine is useless. EGT 

 indication is extremely sensitive to the position of the probe inside 

 the exhaust stack. This is one of the reasons why, on any piston 

 engine, the EGT indication in itself cannot be used to determine 

 whether a cylinder is running too lean or too rich. The highest EGT 

 cylinder is not necessarily the leanest. The only way to determine the 

 mixture condition is to pull the mixture control progressively and 

 monitor the EGT on all cylinders. The leanest cylinder is the one 

 which will reach peak EGT first. Of course you cannot do that on a 

 Rotax as there is no mixture control. The only thing EGT can do on a 

 Rotax, in case of a big engine problem, is to help diagnose which 

 cylinder is the culprit.       

 Additional comments:

 With the Europa XS cowling,  the EGT probes on cylinders 1 and 2 are 

 cooled by direct ram air from the round intakes and this has proved to 

 affect their indication.

 The Rotax Flydat has 4 EGT channels but shows EGT on two cylinders at 

 a time and switches automatically back and forth. That makes EGT very 

 uneasy to read. Any other engine monitor on the market is certainly 

 better. 

 My plane was fitted with a 914 with Flydat and 4 EGTs when I bought 

 it. When I replaced the engine with the 912S five years ago, I kept 

 the Flydat but did not install EGT probes and it works for me.

 Regards

  

 Remi Guerner

 F-PGKL



Remi
	


We had a Classic with a Grand Rapids EIS and 4 EGTs. I soon noticed that 

EGT varies in an unusual way with throttle setting. The mixture is 

affected by throttle position because of the effect of momentum on the 

fuel droplets, which tend to go to the front cylinders at WOT and the 

rear at part throttle.

One thing is apparent, the very high EGTs the Rotax has in normal 

operation. This means the exhaust system is under considerable thermal 

stress.

I tend to the feeling that EGT is worth having for diagnostic reasons 

but difficult to understand on the Rotax.

Graham

budyerly(at)msn.com
Guest

Posted: Thu Nov 12, 2009 1:55 pm Post subject: does rotax need egt?

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  Well put Graham.

 It is a diagnostic tool of which you have no control over from the  cockpit...

  

  

 Bud Yerly

 [quote]   ---

air.guerner(at)orange.fr
Guest

Posted: Fri Nov 13, 2009 4:34 am Post subject: does rotax need egt?

Raimo,

 This is an old story. You can read the article I  wrote on this subject in the June 2005 issue of EF.  

 To make it short: I found the 914 to be very far  from satisfying my own standards of reliability and safety for an aircraft  engine. I have 430 hours now on the 912S and this replacement is the best  decision I have made since I own this aircraft.  

 Remi

  

 <<<<<just curious: why did you replace the engine (914T) and  went to 912S ?>>>>



     [quote][b]

rampil

Joined: 04 May 2007
Posts: 870

Posted: Fri Nov 13, 2009 8:18 am Post subject: Re: does rotax need egt?

Hi All,



I have all four cylinders monitored for the past five years and

have finally found a good use for them!



Based on data from several long cross country trips, I have decided to

add a mixture control!



Take a peak ( sic!) at the table I enclose.  If you have different data,

please let me know

Rotax Efficiency.pdf

Description:

Download

Filename:

Rotax Efficiency.pdf

Filesize:

37.19 KB

Downloaded:

521 Time(s)

_________________
Ira N224XS

jpg12305

Joined: 16 Jul 2008
Posts: 23

Posted: Sat Nov 14, 2009 1:23 am Post subject: Re: does rotax need egt?

 	  rampil wrote: 	
		  

Take a peak ( sic!) at the table I enclose.  If you have different data,

please let me know 	




If I properly understand, this demonstrates that fuel consumption increases very significantly with altitude, right? 



I have heard/read a lot of different things about altitude compensation for the Bing carbs. Some say there is compensation by design, some that there is no compensation at all, and some that there is only partial one.



I would think now the second statement is the right one! 



My own experience (without having a flowmeter nor CS prop) is that I have never seen an apparent MPG increase by flying high.



I would be interested in seeing some other data confirming yours.



Jean-Paul

Europa 332 - France

hurstkr(at)redzone.com.au
Guest

Posted: Sat Nov 14, 2009 2:41 am Post subject: does rotax need egt?

 	  Quote: 	
		   Attachments:



 http://forums.matronics.com//files/rotax_efficiency_125.pdf


	


Hello Ira,



Thank you for posting those figures . . . interesting indeed.  60% increase

in fuel consumption flying at 9,000 ft as opposed to 3,000ft while TAS

increases 33%.



I note the increase in fuel consumption is almost linear from 3K to 7K ft

while the increase between 7K and 9K is double that between 5K & 7K.  I

imagine 22.6" MP at 9K would be wide open throttle so I'm wondering if this

kick in the consumption is because of power jets coming into play.

Regardless, there is nothing that can be done about it with things as they

are so I can certainly understand your desire to install a mixture control.

I look forward to hearing how you accomplish this.



Sorry I am unable to supply any comparative data yet.



BTW, your MPG figures appear to actually be NMPG so your actual MPG is still

way ahead of any motor vehicle travelling at 146 MPH.  Realizing that may

make you feel better No?



Somewhere  I saw once that Rotax actually do have true altitude compensating

carburettors but for the life of me I cannot recall where I saw that.



Cheers

Kingsley

davidjoyce(at)doctors.org
Guest

Posted: Sat Nov 14, 2009 5:12 am Post subject: does rotax need egt?

Kingsley, For what it's worth my 914 mono XS + speed kit has given the 

following figures in careful trials:

At 2000ft    100 kts  TAS    12 litres/hr

                     110 "          "        13  "

                     120  "         "        14  "

                     130   "       "          18  "

                     140   "         "         23  "

At 10,000ft  150  "        "          21  "

        This suggests that unlike the 912S, the 914 is able to adjust 

adequately for altitude, and I suppose that should be no surprise.

    Regards, David Joyce, G-XSDJ

---

frans(at)paardnatuurlijk.
Guest

Posted: Sat Nov 14, 2009 6:31 am Post subject: does rotax need egt?

David Joyce wrote:



 	  Quote: 	
		          This suggests that unlike the 912S, the 914 is able to adjust

 adequately for altitude, and I suppose that should be no surprise.


	


It doesn't adjust, it has a turbo. And the turbo keeps everything

pressurized, including the carbs. The engine, nor the carbs, would

notice the difference between 2.000 and 10.000 feet.



Frans

grahamsingleton(at)btinte
Guest

Posted: Sat Nov 14, 2009 4:44 pm Post subject: does rotax need egt?

jpg12305 wrote:

 	  Quote: 	
		   If I properly understand, this demonstrates that fuel consumption increases very significantly with altitude, right? 



 I have heard/read a lot of different things about altitude compensation for the Bing carbs. Some say there is compensation by design, some that there is no compensation at all, and some that there is only partial one.



 I would think now the second statement is the right one! 



 My own experience (without having a flowmeter nor CS prop) is that I have never seen an apparent MPG increase by flying high.



 I would be interested in seeing some other data confirming yours.



 Jean-Paul

 Europa 332 - France



   

There is a mod for mixture control, I know the UK agents (Nigel Beale at 
	


SkyDrive) tried it and they may offer a mod. It involves adjusting the 

overpressure on the carb float bowl, which has a significant effect on 

mixture. Don't try this at home without consulting a Rotax expert.

You definitely need EGT to see what's happening.

Graham

hurstkr(at)redzone.com.au
Guest

Posted: Sun Nov 15, 2009 1:19 am Post subject: does rotax need egt?

 	  Quote: 	
		   At 2000ft    100 kts  TAS    12 litres/hr . . . . . . At 10,000ft  150  " 

 "          21  "


	


Hello David,



Thank you for the extra food for thought.  As I say, I'm only an observer in 

all this but I enjoy trying to understand what is going on and some accurate 

figures are interesting to compare.



As a further point of interest, do you have the MP settings and RPM for each 

of the figures quoted?



Cheers

Kingsley

ami(at)mcfadyean.freeserv
Guest

Posted: Sun Nov 15, 2009 3:24 am Post subject: does rotax need egt?

By way of comparison for a normally aspirated engine (912S), in a full power 

climb from 2000' to 6650' (at OAT +5C (at) 2000' and QNH 1005), fuel flow 

dropped from 4.0 to 3.7 imp.GPH.

I've not worked out the percentage power loss due to air density, but would 

guess that this was more than the % drop in fuel flow. Engine speed was a 

constant 4800rpm throughout. No EGT data available, which would have shown 

any richening of the mixture with altitude (as I recall, EGT does usually 

get less with altitude on this engine, but not greatly).



Duncan McF.

---

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