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Bing Carb Checks ----- FAA investigated fatal accident..

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frans(at)privatepilots.nl
Guest

Posted: Sun Sep 12, 2010 12:31 pm Post subject: Bing Carb Checks ----- FAA investigated fatal accident..

On 09/12/2010 07:32 PM, Guerner Remi wrote:

 	  Quote: 	
		   

 

 The reason for two carbs on the Rotax is not redundancy but performance.

 I am pretty sure that if one carb fails completely on the Rotax, the

 engine runs so rough that you had better stop it immediately and land. 


	


There is a solution to that:

http://www.flygas.info/en/kit-intake-manifold.html



This set replaces the balance tube between the carbs by a much larger

balance tube, so each carb can feed both halves of the engine. It also

doesn't matter much anymore if your carbs are balanced or not, you can

just loose a carb and the engine keeps running on 4 cylinders.



It also makes retrofitting fuel injection easier, as these inlet

manifolds have already the fuel injector bosses in them. You only have

to bore them out and tap a thread in them.

The new billet pump (see Rob Borgers reports) is capable of feeding an

injector system directly, as it can produce a sufficiently high

pressure. So all one need after that is four injectors and a universal

EFI-box. You keep the carbs, they are now just playing the role of

throttle body.

The nice thing with such a setup is that you can in flight switch

between carbs and EFI. So you keep the carbs as a backup.



I feel a project coming. 



Frans

rampil

Joined: 04 May 2007
Posts: 870

Posted: Mon Sep 13, 2010 8:30 am Post subject: Re: Bing Carb Checks ----- FAA investigated fatal accident.

Hi Frans,



I looked at that referenced Italian site for FlyGas.



They gave no indication that their mod had been operationally tested

in any way as of this data (Sep 13, 2010)



Their cross tube looks to be about an inch +/- in diameter. At about

a foot long, my back of napkin estimate is that there would be quite

a pressure drop across that tube at WOT, causing an imbalance in

MP across the engine.  Looks doubtful to reduce carb imbalance

vibration on that basis, but will likely cause an RPM related imbalance

of its own which would not be adjustable.



Before we jump on another bandwagon lets see some actual operational

data, preferably with an accelerometer quantifying vibration.



Cheers,



Ira

_________________
Ira N224XS

frans(at)privatepilots.nl
Guest

Posted: Mon Sep 13, 2010 9:47 am Post subject: Bing Carb Checks ----- FAA investigated fatal accident..

On 09/13/2010 06:30 PM, rampil wrote:



 	  Quote: 	
		   Their cross tube looks to be about an inch +/- in diameter. At about

 a foot long, my back of napkin estimate is that there would be quite

 a pressure drop across that tube at WOT,


	


Pressure drop? Both halves of the engine carry the same manifold

pressure. If there is no inbalance, the air inside the cross tube is

more or less static, although it will cancel out the intake pulses, so

the air will be thrown left and right but never actually leave the tube.

This is a good thing by itself, because it will soften the intake

pulses. This will even out the mixture between the front and rear cylinder.



Let me explain this further: I guess everyone knows that the front

cylinders of a Rotax get a different mixture than the rear cylinders.

Some people think it has something to do with the distance to the carbs.

Wrong. The reason is that the Rotax fires two cylinders at each side,

and then fires the cylinders on the other side. So at each engine halve,

you will find two intake cycles, and then nothing for a while (during

this time the other cylinders on the opposite engine half have their

intake cycles.

This means that the airflow in one carb has to accelerate at the first

intake cycle, and when that intake valve closes, the other cylinder has

its intake cycle. This cylinder benefits from the air already at speed

through the carb. All this has to do with inertia. For the first

cylinder, apart from the fact that is has the task to accelerate the

mixture after it came to a halt during the pause, the acceleration of

the fuel is lower than the acceleration of the air. So the first

cylinder at each engine halve gets a leaner mixture than the one that is

to fire just after it.



So, the idea of a balance tube is to keep the air up to speed, because

both engine halves have the same problem, but at alternating moments.

Balance tubes are common things in cars, both for the intake as well as

for the exhaust. But usually they have a much larger diameter.



But all this has nothing to do with carb imbalances, this is just an

additional advantage. So, let's go back to the claim that this larger

cross tube makes imbalances less obvious:



 	  Quote: 	
		   Looks doubtful to reduce carb imbalance

 vibration on that basis,


	


Never took the small balance tube away (for pneumatic carb balancing)?

Without the tube, imbalances become more obvious. Put the tube in, and

some of the imbalance is gone, because the tube allows some of the

mixture from the higher manifold pressure side to flow to the lower

manifold pressure side. Put even more tube in (i.e. a larger diameter)

and more mixture can flow through it, making the difference in MAP

between both halves even less, and thus lessening the imbalance.



 	  Quote: 	
		   Before we jump on another bandwagon lets see some actual operational

 data, preferably with an accelerometer quantifying vibration.


	


Fine, if there is such data. If there isn't, we'll have to revert to

basic physics and engine knowledge.



I might install a larger cross tube some day (not for the cross tube

actually, but for the option to fit fuel injectors), and I will let you

know what I find.



Frans

rampil

Joined: 04 May 2007
Posts: 870

Posted: Mon Sep 13, 2010 10:47 am Post subject: Engine Engineering (was Bing carb recall

Hi Frans,



I mentioned the cross tube since you had mentioned the failure of a carb

and that both sides could be fed through the single carb and the"fat"

cross tube. Outside that scenario, there should normally be little flow

and resistive drop.



I am not sure what a cross tube does to "soften" the incoming air pulses.

The flow rate is mainly determined by the linear speed profile and the 

fixed surface area of the downgoing piston with the major flow restriction

at the intake valve orifice. The extra compliance of the cross tube is

probably only a small increment to the supply through the carb unless 

the butterfly is nearly closed.



Sadly there is no public detailed spec on the Rotax 9xx series, but I do

try to relate its operation from what I learned from Charles Taylor, John Heywood, and Will Pulkrabek's books.



For most pilots wanting to learn a bit more about their engines (I.e.,

Lycosaurus types), John Schwaner's Engineering Manual is great! Full

of easy to read facts, not conjecture or rumor from a very experienced A&P. (www.sacskyranch.com)

_________________
Ira N224XS

air.guerner(at)orange.fr
Guest

Posted: Mon Sep 13, 2010 12:02 pm Post subject: Bing Carb Checks ----- FAA investigated fatal accident..

Hi Frans,



Looks like an interesting modification.  But I am wondering if there is any inconvenience with this system. If not, why did Rotax design the engine manifolds with a small balance tube?

Remi



<<<<There is a solution to that:

http://www.flygas.info/en/kit-intake-manifold.html



This set replaces the balance tube between the carbs by a much larger

balance tube, so each carb can feed both halves of the engine. It also

doesn't matter much anymore if your carbs are balanced or not, you can

just loose a carb and the engine keeps running on 4 cylinders.>>>>>>>

   [quote][b]

frans(at)privatepilots.nl
Guest

Posted: Mon Sep 13, 2010 12:26 pm Post subject: Bing Carb Checks ----- FAA investigated fatal accident..

On 09/13/2010 08:47 PM, rampil wrote:



 	  Quote: 	
		   I am not sure what a cross tube does to "soften" the incoming air pulses.


	


Ok, I will try to explain some more.

The firing order of the Rotax is 1-4-2-3. The intake order is of course

similar.

Now, let's see what happens.

For ease of explanation, we will start with cylinder 4. The order we

will follow is thus 4-2-3-1.



Intake of #4 opens. Air starts to accelerate through the carb.

At the moment #4 closes, intake #2 opens. This cylinder is on the same

carb as #4. The air is already up to speed through the carb, it only has

to take the next exit.

Intake #2 closes. As on this side of the engine there are no more

intakes, and we now have to wait for the two cylinders on the other side

of the engine to complete their intake cycle, the air comes to a

screaching halt. There is nowhere to go for the air, all intakes on this

side are closed!



At the same time #2 closes, intake #3 opens. This one is on the other

carb. The air has been come to a stop there, because while the engine

was working on #4 and #2, this carb had no throughput at all. So intake

#3 has the task to start accelerating the air. When #3 closes, #1 opens,

same bank, so the air can just go through. And when #1 closes, this bank

is done, air comes to a stop, and we switch over to intake #4. The whole

cycle repeats itself here.



Ok, now with the balance tube. This will fit in between previous paragraphs.

At the moment intake #2 closes, there are no open intakes on that side

anymore. The air however is at speed, and due to inertia the air wants

to keep going. (keep in mind that the engine runs at 5000 rpm, and at

this speed, inertia of the gasses plays a significant role). Luckily

there is a balance tube, and the air still rushing through the carb

(remember, there is a whole column of air up to speed from the airbox

that doesn't know that intake #2 just closed) takes the only exit

remaining: the balance tube.

At the moment intake #2 closed, intake #3 opens. This one is at the

other side. Luckily, there is just a bunch of air arriving through the

balance tube! This air fills up the gap, at the moment the air through

the carb of #3 has to start moving. Of course the flow through the

balance tube doesn't last very long, but at the moment it ceases, the

column of air through its own carb has just accelerated enough to take over.



This is of course a simplified explanation, you'd better think of all

this as pressure waves. To complicate things further, the column of air

rushing in that finds all doors shut, bounces back. This backwards

pressure wave interferes a moment later with the start of a new inlet cycle.



So, this is what a balance tube is for. Maintaning a smooth air stream

is more efficient and is easier on the carbs. Usually this translates in

more power, and a more even distribution of density and mixture.



Unfortunately, the balance tube of the Rotax is very small, and probably

doesn't do much at WOT.



Frans

frans(at)privatepilots.nl
Guest

Posted: Mon Sep 13, 2010 12:40 pm Post subject: Bing Carb Checks ----- FAA investigated fatal accident..

On 09/13/2010 09:55 PM, Guerner Remi wrote:

 	  Quote: 	
		   Looks like an interesting modification.  But I am wondering if there is

 any inconvenience with this system. If not, why did Rotax design the

 engine manifolds with a small balance tube?


	


Looks like a question that fits into the same category as some other

questions:

1) Why is the carb attached to a flange that often ruptures and we have

to inspect regularly? Why don't they fix it? On how many cars do the

carbs once in a while just fall off?

2) Why did Rotax not install a carb heater on the 912?

3) Why does Rotax still sell a voltage regulator which is not up to its

task?

4) Why is the TCU data cable a RS232 and not an USB, and do I have to

find a DOS computer to read out the engine parameters? Why can't they

write a decent program for their clients who pay a lot of money for this

engine?

5) Why did Rotax not install a billet pump on the 914, and forces us to

rely on two electrical fuel pumps instead?

6) Why do I need to manually disconnect the wastegate servo in case the

system starts surging, and is the TCU unable to recognize and solve the

problem on its own? How many cars exhibit this behaviour?



Etc.



Of course, Rotax may have had a reason for this one. But then again,

they might have not.

The whole balance tube looks as an afterthought, something they came up

with after the design was ready and the molds for the intake manifold

where already done. So there we have it, way too small, floating in the

air, and it gave them a good opportunity to attach two springs to it to

prevent the carb from falling off when the famous flange ruptures.



Who knows?



Frans

fklein(at)orcasonline.com
Guest

Posted: Mon Sep 13, 2010 1:09 pm Post subject: Bing Carb Checks ----- FAA investigated fatal accident..

On Sep 13, 2010, at 1:36 PM, Frans Veldman wrote:



 	  Quote: 	
		   1) Why is the carb attached to a flange that often ruptures and we  

 have

 to inspect regularly? Why don't they fix it? On how many cars do the

 carbs once in a while just fall off?

 2) Why did Rotax not install a carb heater on the 912?

 3) Why does Rotax still sell a voltage regulator which is not up to  

 its

 task?

 4) Why is the TCU data cable a RS232 and not an USB, and do I have to

 find a DOS computer to read out the engine parameters? Why can't they

 write a decent program for their clients who pay a lot of money for  

 this

 engine?

 5) Why did Rotax not install a billet pump on the 914, and forces us  

 to

 rely on two electrical fuel pumps instead?

 6) Why do I need to manually disconnect the wastegate servo in case  

 the

 system starts surging, and is the TCU unable to recognize and solve  

 the

 problem on its own? How many cars exhibit this behaviour?



 Etc.


	


Frans...All excellent questions...



 	  Quote: 	
		  >  On how many cars do the carbs once in a while just fall off?


	


..I'll just bite my tongue and resist further comment...afterall, I'm  

still building...



Fred



do not archive

frans(at)privatepilots.nl
Guest

Posted: Mon Sep 13, 2010 1:38 pm Post subject: Bing Carb Checks ----- FAA investigated fatal accident..

On 09/13/2010 11:03 PM, Fred Klein wrote:

 	  Quote: 	
		  >>  On how many cars do the carbs once in a while just fall off?

 

 ...I'll just bite my tongue and resist further comment...afterall, I'm

 still building...


	


Don't get me wrong. I'm happy with my Rotax 914. It is a nice and

reliable engine. But it doesn't mean that it is perfect, or that nothing

can be improved upon.

I think there is a lack of competition here. Why should they improve it?

It sells anyway.



Do they actually still have a development department? Or have they left

years ago because they harvested enough money? Is that why there is no

EFI version of the 914, no Windows version of the TCU-program, etc?



Frans

grahamsingleton(at)btinte
Guest

Posted: Mon Sep 13, 2010 2:20 pm Post subject: Bing Carb Checks ----- FAA investigated fatal accident..

Fred

I have to smile, why indeed. Why did they not have a proper breather on the coolant collector bottle. If they had I might not have got a black eye and some broken bones.

We must keep on learning and sharing information.

Graham

From: Fred Klein <fklein(at)orcasonline.com>

To: europa-list(at)matronics.com

Sent: Monday, 13 September, 2010 22:03:43

Subject: Re: Europa-List: FW: Bing Carb  Checks ----- FAA investigated fatal  accident..



--> Europa-List message posted by: Fred Klein <fklein(at)orcasonline.com (fklein(at)orcasonline.com)>





Frans...All excellent questions...



 	  Quote: 	
		  >  On how many cars do the carbs once in a while just fall off?


	


..I'll just bite my tongue and resist further comment...afterall, I'm still building...



Fred





 

  [quote][b]

josok-e

Joined: 29 Jan 2010
Posts: 16
Location: Ivalo Finland

Posted: Tue Sep 14, 2010 1:44 am Post subject: Re: Bing Carb Checks ----- FAA investigated fatal accident.

Two years ago, one day before my second birthday, we happened to be at the same table with the brass of the Rotax factory in Wels. And of course the question about injection popped up. The anwser was that yes, they were working on that, and their main difficulty was to make the efi programmers understand that in case of any error the engine was not to shut down, but continue running, They also suggested that there was an injection engine up and running. 

Rotax probably still fails to find a programmer that will and can do that special job. As for the other items to be improved: Remember there is a certified engine. Getting a new certification because parts change seems to be very costly... Changing parts on non-certified engines and divert from the approved stuff could be very costly because of the US liability threats.

air.guerner(at)orange.fr
Guest

Posted: Tue Sep 14, 2010 5:04 am Post subject: Bing Carb Checks ----- FAA investigated fatal accident..

Hi, Justin,



This confirms what Jerry said. Good to know!



Remi



<<<<Thus I can say that a Rotax 912s will give 4000 rpm on the  

starboard carb o

nly. >>>>>

air.guerner(at)orange.fr
Guest

Posted: Tue Sep 14, 2010 5:42 am Post subject: Bing Carb Checks ----- FAA investigated fatal accident..

Frans,



Here are my answers to some of your questions below:



1) Why is the carb attached to a flange that often ruptures and we  

have to inspect regularly? :

  the problem with the rubber flanges is  known to happen on basic  

microlight installations where each carb have its own air filter with  

no further mechanical support. The carbs then oscillate vertically and  

flex the rubber flange, leading to fatigue rupture. When you are using  

a properly supported airbox this does not happen.  However with the  

914 it is a different story as the internal pressure will tend to  

disconnect the carbs and the airbox.



2) Why did Rotax not install a carb heater on the 912?

Lycoming and Continental are not supplying a carb heat system ether.   

Carb heat installation is usually designed and made by the aircraft  

manufacturer.  However Rotax offers an optional airbox fitted with the  

provision for hot air for the 912 series. It work fine on my Europa.



3) Why does Rotax still sell a voltage regulator which is not up to  

its task?

  From my experience the Ducati voltage regulator works fine as long  

it is cooled properly.  There are two ways to do it: on a metal  

aircraft, bolt the regulator to the structure which will act as an  

heat sink.  On composites, provide fresh air with a SCAT ducting to  

the cooling fins of the regulator casing.



Remi

F-PGKL Monowheel, 912ULS, 800 hours

rampil

Joined: 04 May 2007
Posts: 870

Posted: Tue Sep 14, 2010 8:25 am Post subject: Re: Bing Carb Checks ----- FAA investigated fatal accident.

Nice discussion guys!



Be careful though about manufacturing questions!



If one had the temerity to ask why Lycoming and Continental still

use cork gaskets that melt in ethanol when they could see it coming for 

10 years, one might get into a "real" flame war!

_________________
Ira N224XS

fklein(at)orcasonline.com
Guest

Posted: Tue Sep 14, 2010 8:09 pm Post subject: Bing Carb Checks ----- FAA investigated fatal accident..

On Sep 13, 2010, at 2:33 PM, Frans Veldman wrote:

 	  Quote: 	
		  --> Europa-List message posted by: Frans Veldman <frans(at)privatepilots.nl (frans(at)privatepilots.nl)>



On 09/13/2010 11:03 PM, Fred Klein wrote:

 	  Quote: 	
		  

...I'll just bite my tongue and resist further comment...afterall, I'm

still building...

	


Don't get me wrong. I'm happy with my Rotax 914. It is a nice and

reliable engine. 

	




Frans,

...not at all surprised that you feel that way...and I believe your feelings expressed above mirror those of (literally) hundreds of other Europa owners. And I admire your open mind and innovative thinking behind the mods you've done, on your cooling system for example.

My reluctance to make further comments was solely based on my building around an alternative fuel-injected engine, with the outcome of that decision being still uncertain...I'm grateful for my high tolerance of ambiguity.

Fred

 [quote][b]

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