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AW: 914 Fuel Pumps.

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gottfried.komaier(at)gmx.
Guest

Posted: Wed Feb 22, 2006 2:05 pm Post subject: AW: 914 Fuel Pumps.

Mike,



Here is the way I'll doing. I have the mechanical pump as a standby-pump on

the engine. The fuel is going through the pump  all the time in bypass, that

means all the fuel which is going through the mechanical pump goes via a

electrical valve back to the tank. In an electrical emergency, the valve

closes and the pump keeps the engine running up to ~2000m and ~55% power.

The fuel-pressure (Airbox pressure + 0,35 bar) is secured up to this

altitude and power setting. You can check the Airbox-Differential-pressure

with the new "uma"-gauge. www.umainstruments.com This instrument is the only

indicator for the fuel pressure on 914 engines which makes sense.



For checking the bypass-system the electrical pumps can switched off

momentarily after engine start.



Regards,



Gottfried



-----Ursprngliche Nachricht-----

Von: owner-europa-list-server(at)matronics.com

[mailto:owner-europa-list-server(at)matronics.com] Im Auftrag von MICHAEL

PARKIN

Gesendet: Mittwoch, 22. Februar 2006 21:52

An: Europa-List(at)Matronics.Com

Betreff: 914 Fuel Pumps.




--> <mikenjulie.parkin(at)btopenworld.com>



I am not sure whether it was Europa or not, but I heard that someone was

investigating putting the manual fuel pump on the 914 with electrical back

up pumps for the high demand situation.  Sounds like a good idea to me.



Does anyone know anything about it.



regards,



Mike

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gottfried.komaier(at)gmx.
Guest

Posted: Wed Feb 22, 2006 2:14 pm Post subject: AW: 914 Fuel Pumps.

Tony,



all the 914 have the eccenter for the pump-drive installed.This is the

status since around 2003. I can't say how the situation was before.



Regards,



Gottfried



-----Ursprngliche Nachricht-----

Von: owner-europa-list-server(at)matronics.com

[mailto:owner-europa-list-server(at)matronics.com] Im Auftrag von Tony

Krzyzewski

Gesendet: Mittwoch, 22. Februar 2006 22:56

An: europa-list(at)matronics.com

Betreff: Re: 914 Fuel Pumps.






With regard to putting a mechanical pump back on to the 914.



I investigated this some time ago and found that non of the pump drive

gearing is present in the 914 gearbox so it would be a major mod



Tony.

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tonyk(at)kaon.co.nz
Guest

Posted: Wed Feb 22, 2006 5:22 pm Post subject: AW: 914 Fuel Pumps.

Gottfried



Thanks for the update re the pump fitting. Mine is an earlier engine and all I have is an empty space under the cover where the mechanical pump would sit.



Tony

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mikenjulie.parkin(at)btop
Guest

Posted: Wed Feb 22, 2006 7:58 pm Post subject: AW: 914 Fuel Pumps.

Tony,



My aircraft predates 2003 also - another busted flush I guess.



regards,



MP



---

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gottfried.komaier(at)gmx.
Guest

Posted: Thu Feb 23, 2006 2:22 am Post subject: AW: 914 Fuel Pumps.

Patrick,



The reason why the mechanical pump is the backup and not the other way round

is easy to explain:

The mechanical pump do not deliver as much pressure as the electrical one.

On the 914 you will need an fuel pressure of

                                 Airboxpressure + 0,25 bar , 3,63

psi(normal)

                                 Airboxpressure + 0,15 bar , 2,18

psi(minimum)

                                 Airboxpressure + 0,35 bar , 5,08

psi(maximum)



At Take Off the engine produce an manifold pressure of 1350 hPa = 39,9 in.Hg

= 19,6 psi



That means, you need a max. Fuel pressure at the carburetor of 24,7

psi!!!!!!

The mechanical pump delivers 0,15 bar up to 0,4 bar(5,8 psi). Do you see

that difference?!



That's the reason why the mechanical pump can feed the engine only up to

~2000m with ~55% power and can works in this situation only as an EMERGENCY

equipment to bring you with reduced power to an airfield. . (Better than

nothing!!!)



You have a fine explanation of the Fuel pressure system in the Maintenance

Manual on pages 34&35



I hope this helps and bring a little light in the complicated 914 fuel

system. This is one of the reason, why the 914 is 

so much expansive vs.the 912S



All the best,



Gottfried





-----Ursprngliche Nachricht-----

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[mailto:owner-europa-list-server(at)matronics.com] Im Auftrag von

BEBERRY(at)aol.com

Gesendet: Donnerstag, 23. Februar 2006 10:16

An: europa-list(at)matronics.com

Betreff: Re: 914 Fuel Pumps.






     

 

Why should the mechanical pump ( if you can fit one) be the 'back up  pump?



It would seem sensible to adopt general G.A., practise and  have a

permanently running mechanical pump and electrical back ups which  are used

only for take off and when below 3000ft on the  approach.?????

 

Patrick

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BEBERRY(at)aol.com
Guest

Posted: Thu Feb 23, 2006 2:37 am Post subject: AW: 914 Fuel Pumps.

Thanks Gottfried for your explanation - very useful for a non techie  ( at 

least on fuel systems, pressures etc)..

 

Patrick

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Gilles.Thesee(at)ac-greno
Guest

Posted: Thu Feb 23, 2006 1:40 pm Post subject: AW: 914 Fuel Pumps.

 	  Quote: 	
		  That's the reason why the mechanical pump can feed the engine only up to

~2000m with ~55% power and can works in this situation only as an EMERGENCY

equipment to bring you with reduced power to an airfield. . (Better than

nothing!!!)



  



Gottfried and all,
	




Not sure I clearly understand your setup : are you intending to add a 

mechanical pump to the two electrical pumps ?

So that is 3 fuel pumps, correct ?

Have you already run your engine with the mechanical pump ? If I recall 

correctly, no one mentioned the possibility of upsetting the delicate 

enrichment algorithm that protects the engine against detonation. The 

need for the wastegate servo "disconnect switch" might come from 

instabilities when the TCU little brain loses control.



I tried not to modifiy the Rotax 914, but designed the electrical 

architecture so that each pump has a truly independent source of power. 

This way I can insure  redundant fuel delivery.



Regards,

Gilles Thesee

Grenoble, France

http://contrails.free.fr

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gottfried.komaier(at)gmx.
Guest

Posted: Thu Feb 23, 2006 4:38 pm Post subject: AW: 914 Fuel Pumps.

Mike,  



thank you for your discussion-input. As we see, the mechanical fuel pump

helps only in an electrical total failure (which will be on an 914-driven

aircraft an "EMERGENCY") and can bring you in this situation - and only in

that - safely to the ground.

To see the fuel pressure of the mechanical pump more exactly, we have to

consider that the pressure would be higher as laid down in the manual,

because there is no open return line back to the tank. This means, the

available power-situation would be better in an emergency. 



Regards,



Gottfried    



-----Ursprngliche Nachricht-----

Von: owner-europa-list-server(at)matronics.com

[mailto:owner-europa-list-server(at)matronics.com] Im Auftrag von MICHAEL

PARKIN

Gesendet: Donnerstag, 23. Februar 2006 23:57

An: europa-list(at)matronics.com

Betreff: Re: 914 Fuel Pumps.




--> <mikenjulie.parkin(at)btopenworld.com>



 	  Quote: 	
		   At Take Off the engine produce an manifold pressure of 1350 hPa = 39,9 

 in.Hg = 19,6 psi



 That means, you need a max. Fuel pressure at the carburetor of 24,7 

 psi!!!!!!

 The mechanical pump delivers 0,15 bar up to 0,4 bar(5,8 psi). Do you 

 see that difference?!




	




Gottfried,



But that 24,7 psi includes the local atmospheric pressure.  Consider

pressure at sea level on an ISA day.  If the atmospheric pressure was 1013

hpa, then the fuel pump pressure required would be (1350+250)-1013 = 587 hpa

(8.5psi) this as you correctly say is beyond the capability of the

mechanical fuel pump. (Ref - Maintenance Manual p34).  However, that is a

max power calculation.



If one considers the max continuous condition as quoted in the operating

manual - 5000 rpm, 31 in/hg, the situation with just the mechanical pump

would be considerably better and certainly sufficient to continue to a

diversion without a problem - all be it at a fairly low altitude.



Example:



Condition - 75% power, 5000 rpm, 31 in/hg.   Air box pressure = 1049 hpa.



therefore fuel pump pressure required  at 1000 ft (ISA day) - (ambient

pressure = 976 hpa)



        (1049+250)-976 = 324  hpa   which is 4.7 psi.



Using the minimum pressure required of 0,15 bar a calculated fuel pressure

required from the mechanical pump would be 3.2 psi.



Plainly, pressure altitude is the driving factor here.



kind regards,



Mike  (G-JULZ)

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