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Rotax 914 "what if"

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rparigor(at)suffolk.lib.n
Guest

Posted: Wed Jun 03, 2009 9:40 am Post subject: Rotax 914 "what if"

"What if" for some reason you can't land and need to fight gravity for a long time with a charging system that has quit.



You are runing on battery alone to run a fuel pump.



To extend flight can you turn on pump to fill float bowls

then turn off pump till engine sags, and turn on etc. etc. etc instead of letting pump just run?



2nd half of question is if the answer to above is yes, what might be the optimal MP to use?



Thanking in advance.

Ron Parigoris

Visit -  www.EuropaOwners.org

davidjoyce(at)doctors.org
Guest

Posted: Wed Jun 03, 2009 1:55 pm Post subject: Rotax 914 "what if"

Ron, You probably know, but it's worth saying perhaps for others that one 

914 pump works directly off the alternator. With main and alternator 

switches both off, it continues to pump. The only failure of the charging 

system that has appeared at all commonly on this forum is the rectifier 

failing, and with that scenario, switching off the alternator switch should 

leave the main pump working so that you can use your battery reserves on 

whatever radio or navigational gizmo makes most sense.

regards, David Joyce, G-XSDJ

---

paul.the.aviator(at)gmail
Guest

Posted: Wed Jun 03, 2009 2:12 pm Post subject: Rotax 914 "what if"

Hi Ron,



I seem to recall during my flight testing phase that when flying at the best L/D I used 1.8 gallons per hour.



My electrical system is fairly simple using the eBuss system.  I exchange the battery every other year, (Oddessy 625) and  I test the system capacity every annual inspection and with just using the power consuming devices connected to the eBuss. I get about 1:40 minutes until the buss voltage drops to 11.00 volts.

 

Hope this helps,



Paul

  [quote][b]

frans(at)paardnatuurlijk.
Guest

Posted: Wed Jun 03, 2009 2:33 pm Post subject: Rotax 914 "what if"

 	  Quote: 	
		   

 <davidjoyce(at)doctors.org.uk>

 

 Ron, You probably know, but it's worth saying perhaps for others that

 one 914 pump works directly off the alternator. With main and alternator

 switches both off, it continues to pump. The only failure of the

 charging system that has appeared at all commonly on this forum is the

 rectifier failing, and with that scenario, switching off the alternator

 switch should leave the main pump working so that you can use your

 battery reserves on whatever radio or navigational gizmo makes most sense.

 regards, David Joyce, G-XSDJ


	


If the rectifier fails, the pump can no longer be powered. The pump runs

on DC. The pump is connected directly behind the rectifier, but before

the switch.

If the rectifier fails, you have to continue on batterypower only.

Unless you have a dual alternator setup.

I consider a light weight additional alternator a worthy addition: the

weight involved with the additional alternator can be offset by a

smaller battery, as it is extremely unlikely that you will need the

battery during flight. Unless you have both alternators failing at the

same time...



-- 

Frans Veldman

rparigor(at)suffolk.lib.n
Guest

Posted: Wed Jun 03, 2009 3:50 pm Post subject: Rotax 914 "what if"

Hi David, Paul and FransI have aOdyssey PC545 battery and a total los 2200mA NiMh emergency battery. There is also a SD20S with a LR3C sitting on the vacuum pad. I also have an E-bus. Thx. for the input.I too think that if the regulator fails, internal Rotax generator will not run a fuel pump.Anyway, my "what if" is when flying with lots of fuel and  not too much in the way of landing areas I get some severe smoke in cockpit thought to be electrical in nature.In 10 seconds I can plumb electrons from my total loss 2200mA NiMh battery to a fuel pump.I would rather troubleshoot on the ground or at least over an area I can land if needed with a reasonable chance of sucess.Thus my "what if" question is can I extend the range of my total loss battery by turning on and off the fuel pump?"When" I am flying the AlCan highway will probably be when I need to retrieve this piece of "what if".Ron Parigoris   [quote][b]

frans(at)paardnatuurlijk.
Guest

Posted: Thu Jun 04, 2009 12:20 am Post subject: Rotax 914 "what if"

rparigor(at)suffolk.lib.ny.us wrote:



 	  Quote: 	
		   I have aOdyssey PC545 battery and a

 total los 2200mA NiMh emergency battery. There is also a SD20S with a LR3C

 sitting on the vacuum pad. I also have an E-bus. Thx. for the input.

 

 I too think that if the regulator fails, internal Rotax generator

 will not run a fuel pump.

 

 Anyway, my "what if" is

 when flying with lots of fuel and  not too much in the way of

 landing areas I get some severe smoke in cockpit thought to be electrical

 in nature.


	


Well, with a totally separated dual setup (as you could have as well, as

you also have dual alternators), it is just a matter of finding out the

bad system which should not cost more than two seconds (you do have an

amp-gauge, do you?) , and keeping the healthy system on and running the

associated pump. Any additional complexity will only increase the

failure points.



 	  Quote: 	
		   Thus my "what if"

 question is can I extend the range of my total loss battery by turning on

 and off the fuel pump?


	


Sure, there are several things you can do. There is no magic number in

duty cycle here, as it depends on the state of the fuel filters,

altitude, power setting, etc. You can run the pump on a 50%-50% duty

cycle and see what happens, and adjust the duty cycle accordingly.

Better would it be to use a feed-back system, using the return flow as

an indication how much electricity you can safely spare.

You can also make a switched power supply for the fuel pump, and run it

on reduced voltage, again adjusting the fuel pump power related to the

fuel return flow.



But I feel that all this kind of trickery will only increase the chances

of failure.

What's wrong with two totally separated systems, each with its own

alternator, battery and fuel pump? This eliminates every single failure

point. You are already almost there, with two fuel pumps and two

alternators. Just add a second battery (I use two 8Ah batteries, so

essentially I have just split the normal battery into two smaller ones

so I have no weight penalty), and of course a second main power switch.



Once you are there, it is easy to use the additional redundancy

everywhere. I have the CHT's and coolant temperature indicators each on

a separate bus. Just like the NAV and GPS. And the attitude indicator

and turn indicator. Etc. I can loose an entire bus without too much

worries, will always keep at least one fuel pump, some navigation

instruments, and some engine instruments (enough to locate and reach the

nearest landing strip).



It is so easy to set it up like this, once you have two fuel pumps and

two alternators anyway.



Oh, and just in case I experience multiple failures (suddenly fuel pump

A stops, and alternator B dies as well) I have a last card to play: a

cross-over switch between both buses which essentially ties both buses

together. Of course this violates the dual setup approach, so it is only

used in a genuine emergency, if no other options remain. It is a "all or

nothing" last resort.



BTW This is not intended as a "my system is better than yours" but an

invitation to either shoot bullets in my approach, so I can fix any

overlookings and improve my system, or to help you to improve your system.



-- 

Frans Veldman

jan_de_jong(at)casema.nl
Guest

Posted: Thu Jun 04, 2009 12:33 am Post subject: Rotax 914 "what if"

Hi Ron,

You are asking a carburetion question.

When you stop the fuel pump the pressure across the carburettor fuel 

input valve goes from positive (5 psi I believe)  to negative actual 

boost pressure I would think.

I would guess that the only way to keep the engine running is by 

removing all boost and even then you would have extremely low fuel pressure.

All in all I would not like to count on it working.

Regards,

Jan de Jong

m.j.gregory(at)talk21.com
Guest

Posted: Thu Jun 04, 2009 1:03 am Post subject: Rotax 914 "what if"

The pressure from the fuel pump is needed to get the fuel into the carburettor.  Once the fuel is in the float bowl, the engine will be able to use it whatever the boost pressure until the float bowl runs dry.  

   

Regards,  

   

Mike  

Europa Club Safety Officer  

   

--

air.guerner(at)orange.fr
Guest

Posted: Thu Jun 04, 2009 5:37 am Post subject: Rotax 914 "what if"

Ron,

  

 The 914 would probably be able to run for a few  minutes without fuel pressure, until the carb bowls are empty, provided that the  manifold pressure is below ambient pressure. This MP would therefore depend on  altitude. Any manifold pressure higher than ambient pressure  would push the fuel back to the tank and the engine would quit as soon as  the fuel pump is turned off. Then the low MP may allow the engine to come  back to life.

  

 Regards

 Remi Guerner

  

 

 	  Quote: 	
		  >>>To extend flight can you  turn on pump to fill float bowls

then turn off pump till engine sags, and  turn on etc. etc. etc instead of letting
	


pump just run?



2nd half of  question is if the answer to above is yes, what might be the optimal

MP to  use?<<<<<<<<<



    [quote][b]

kevann(at)gotsky.com
Guest

Posted: Thu Jun 04, 2009 6:38 am Post subject: Rotax 914 "what if"

That's why you should consider redundant charging systems. A second 

alternator and regulator.

While in phase 1 flight testing I ran the main tank dry to see what it's 

like to switch the fuel selector to reserve and restart. While running 

just 1 pump it sure seemed like a long time to restart, and that was at 

3,000' over the airport!

I have not tested your "what if".



Kevin



Europa XS Mono-Wheel

Inter-cooled Rotax 914

Airmaster Prop

On Wed, Jun 3, 2009 at 9:22 AM , rparigoris wrote:



 	  Quote: 	
		   

 <rparigor(at)suffolk.lib.ny.us>



 "What if" for some reason you can't land and need to fight gravity for 

 a long time with a charging system that has quit.



 You are runing on battery alone to run a fuel pump.



 To extend flight can you turn on pump to fill float bowls

 then turn off pump till engine sags, and turn on etc. etc. etc instead 

 of letting pump just run?



 2nd half of question is if the answer to above is yes, what might be 

 the optimal MP to use?



 Thanking in advance.

 Ron Parigoris

 Visit -  www.EuropaOwners.org

frans(at)paardnatuurlijk.
Guest

Posted: Thu Jun 04, 2009 7:49 am Post subject: Rotax 914 "what if"

Cori Hayth wrote:



 	  Quote: 	
		   While in phase 1 flight testing I ran the main tank dry to see what it's

 like to switch the fuel selector to reserve and restart. While running

 just 1 pump it sure seemed like a long time to restart, and that was at

 3,000' over the airport!


	


I did some tests too, but without flying. I found, to my astonishment,

that selecting the reserve tank by itself doesn't solve the problem. If

I don't turn the secondary fuel pump on at the same time, the fuel

pressure won't come up, probably because the primary pump sucked air in,

and with the low fuel level, the fuel will not by itself flow to the pump.



So, I tested what happens when you run the main tank dry with both fuel

pumps on. As you can guess, both fuel pumps swallow air, and after

switching to reserve, it takes a very very long time before they develop

fuel pressure again.



So, better not to forget to switch off the secondary fuel pump when not

needed.



Oh, and the order is also important: first select the reserve tank, and

only then switch on the second fuel pump!



-- 

Frans Veldman

rparigor(at)suffolk.lib.n
Guest

Posted: Thu Jun 04, 2009 8:55 am Post subject: Rotax 914 "what if"

Hi Frans and allFirst I have a request from group.If someone is comfortable, if you don't mind could you try in cruise with a 914 turning on and off fuel pump and report how long engine will run till it slumps and how long it takes to fill carb back up for another cycle. Again if you don't mind try with slight lower than ambient MP and higher.I believe that because airbox pressure is plumbed to the sealed float bowls that even if the needle valve opened and some air pushed backwards through it, motor will run till float bowls are dry. In other words i think airbox plumbing can overcome needle valve leak.I suspect that one side of engine will slump before the other.Frans as far as having two separate systems as you have, if the cockpit filled with smoke thought to be electrical in nature, which system would you turn off?I am a reasonable troubleshooter, and anything I fly, I make sure I am intimate with working of my machine and try and armchair different scenarios.There is nothing wrong with having a dual system as you have, just to make second side nice and worthwhile you need a second battery that is heavier than I care for.BTW on my system I have on the passenger headrest an Anderson power pole connector that I can easily plug in any battery I wish to, including a lead acid and have, or not have it hooked to charging system.My approach is stone simple for smoke in cockpit thought to be electrical in nature, shut down everything, run one pump on a separate battery if feasible and land. If not feasible then try e-bus with alternator and generator shut down and go from there.Ron Parigoris   [quote][b]

kevann(at)gotsky.com
Guest

Posted: Thu Jun 04, 2009 1:48 pm Post subject: Rotax 914 "what if"

That makes sense. I had not thought that out.

Thanks, Kevin



Europa XS Mono-Wheel

Inter-cooled Rotax 914

Airmaster Prop

On Thu, Jun 4, 2009 at 7:37 AM , Frans Veldman wrote:> Oh, and the order 

is also important: first select the reserve tank, and

 	  Quote: 	
		   only then switch on the second fuel pump!



 -- 

 Frans Veldman

frans(at)paardnatuurlijk.
Guest

Posted: Thu Jun 04, 2009 2:46 pm Post subject: Rotax 914 "what if"

rparigor(at)suffolk.lib.ny.us wrote:



 	  Quote: 	
		   Frans as far as having two separate systems as you have,

 if the cockpit filled with smoke thought to be electrical in nature, which

 system would you turn off?


	


The one with the wrong Amp-reading. In Europa's, everything is usually

low-power. The biggest power hog in my machine is the strobe power

supply, good for almost 5 Amp's. Now, even with 5 Amp's, it is difficult

to generate much smoke. If there is smoke, you can be pretty sure that

one of the systems show an amp-reading that is way out of limit. Knowing

what is normal for your machine is helpfull either.  Apart from that,

I have everything fused. I have no problem short-cutting any wire in my

aircraft, there is nothing that is not fused, everything is safe here

(except for the starter, but as it is not used during flight, it can not

generate much smoke.)



 	  Quote: 	
		   There is

 nothing wrong with having a dual system as you have, just to make second

 side nice and worthwhile you need a second battery that is heavier

 than I care for.


	


My two batteries are together lighter than many single system batteries.

The point is: with a dual alternator setup, you don't need batteries

during flight, only for starting. The batteries are not part of my

back-up scenario. If the alternator dies, I always have another

electrical bus, with a running alternator. (Unless the engine quits, but

in that scenario you don't need power for very long, a small battery

will be sufficient because you probably won't stay aloft very long. 

) So, the batteries can be fairly small and light.



 	  Quote: 	
		   My approach is stone simple for

 smoke in cockpit thought to be electrical in nature, shut down everything,

 run one pump on a separate battery if feasible and land.


	


It is not much different. You see, you only lack a dual battery, but

actually you have already a separate battery, except that you need to

plug it in manually.



-- 

Frans Veldman

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