Looking at 912 failure modes......

[Head in the clouds]

Sorry HITC,Didn't realise you know more than the manufacturer, Sierra also has a mechanical fuel pump, maybe you should write all the manuals.

 

Alf

Alf, I do apologise. I was unwell in bed yesterday and didn't write very clearly what I meant, so you misunderstood me.

 

I most certainly wasn't criticising you in any way, my comment was directed at whoever wrote that manual.

 

Consider the purpose of the electric fuel pump. It has two functions. To deal with the lesser known one first, it is essential at high altitudes if the fuel tank(s) are lower than the engine. In that event the electric pump is mounted low, near or in the tank because the low air pressure at altitude causes the mechanical engine pump to cavitate and so it cannot lift the fuel, instead the electric pump(s) must push the fuel up to the mechanical pump. This is the very typical case in many helicopters for example, where the tanks are under the cabin floor and the engine is on top of the cabin.

 

The use of the electric pump that we are most familiar with is to increase the safety of the take-off and landing phase of flight when an engine failure is most dangerous. It's a common myth that the mechanical pump requires some kind of extra assistance in pumping fuel at the time when the engine is consuming fuel rapidly i.e. running at full power in the climb. The mechanical pump, if working properly, can deliver way more than enough fuel for any engine power setting. So the only purpose of using the electric pump during take-off is just in case the mechanical pump fails at that time, or perhaps has a hole in the diaphragm and isn't working to full efficiency. If it has a hole then that should show on the fuel pressure gauge if one is fitted, but not all aircraft have them.

 

I think we would all agree that just about the worst time to have an engine failure is at about 300ft just after take-off and on climb. We're nose high so we can't see the landing area ahead all that well and that attitude also slows the plane very quickly after the failure. It's also a critical height for decision making about the turn-back or not.

 

Now lets say that the next flight we make in our Sierra just happens to be the one where the mechanical pump fails just as we lift off. We don't know it's failed even if we check the pressure gauge because the electric pump is holding the pressure up and the engine is running fine. We reach 300ft, clean up and switch the electric pump off. Now we have flaps up at just the wrong time because by switching the only working pump off we also caused ourselves an engine failure at the very worst possible time.

 

So what do you think? Is the manual right? I know it doesn't say you must turn the pump off but even by saying it is a permissible practice then folks doing things very diligently 'by the book' will actually be likely to cause themselves a potential crash. If they left the pump on until reaching the cruise (as all manuals I've read previously state) then the failure would happen at a safe height and still in the vicinity of the departure strip. The height would both give time to attempt a re-start with the pump switched back on again, which would likely be successful, or time to glide to a well prepared landing using a full circuit. Whereas attempting a re-start at 300ft would be more likely to make things even worse still so you'd really be committed to a rapid forced landing ahead onto whatever surface happened to be there.

 

 

[alf jessup]

HITC

 

Sorry your not feeling well

 

Yes I did interpret it differently than what you may have been trying to get at

 

No offence taken and hopefully same with you

 

Yes I understand your point but I fly as per the flight manual

 

You bring up some valid points which I take onboard and thank you for your input

 

Maj also brings up some good points regarding the use or over use of the electric pump

 

Hope your feeling better

 

Alf

 

 

[Mark11]

Why don't we need to turn on or off an electric fuel pump for a 912 powered trike?

 

 

[Guest Maj Millard]

To hopefully clarify things a little. The Rotax operators' manual states the following : (912ULS)

 

.......................................................................................................................................................................................

 

FUEL PRESSURE:

 

Max..................... 0.4 bar (5.8psi)

 

Min...................... 0.15bar (2.2psi)

 

Note: Exceeding the max admissable fuel pressure will override the float valve of the carburetor.

 

The delivery pressure of aan additional backing pump (eg: electric standby pump) must not exceed 0.3 bar (4.4psi) in order not to override the float valve.

 

...........................................................................................................................................................................................

 

Now I reckon the go is to have a fuel-pressure guage installed, otherwise your just guessing as to what is occuring when you turn the boost pump on or off. When buying/fitting a boost pump you must select one that fits the max pressure scenero, that the above recommends. They are available both in Facet ticker pumps, and Pierburg rotary valve pumps. One would assume the manufacturer of a new aircraft would know and respect these limits, and accordingly fit the correct boost pumps.

 

In my Lightwing which came from the factory with only the engine mechanical pump (elect boost pump optional) I recently fitted a new facet ticker pump with a max pressure of 2-3.5psi . I also fitted a fuel-pressure guage to the dash. Whilst flying today I took particular notice of my fuel pressures. I turn the boost on just before I go full power for take off, and off as soon as I think it is safe, which today was around 3-400 Ft. As I turn it off, I monitor the fuel-pressure guage. It drops to about 2.5 bar where it stops, and no lower. That's within limits at the bottom end. The pressure with boost on and full power, goes to around 7 bar which is 3 bar above max recommended, which is why I don't leave the boost on any longer than needed. I have a high intensity green LED light at eye level, so I don't forget it's on. I have had no indication of any problems with this set up for two years now which has included a flight to natfly and back , and down to Monto last year.

 

The Lightwing of course had excellent gravity flow from both wing tanks, and I always have both selected for takeoff/landing. Therefore if I forget to select boost pump on for takeoff (which occasionally happens), it's no big deal. I flew the aircraft for years with no boost pump fitted anyway !...

 

With Alf in the Sierra, which doesn't have a gravity flow situation, the boost pump is being used as a supply pump to take fuel slightly uphill to the engine driven pump, and possibly should be left on until level cruise is established, where the engine pump then is quite capable of supplying adequet fuel to the engine. From memory Tecnams have fuel-pressure guages fitted standard, and should always be monitored, especially in low power descent situations where the engine driven pump is also operating at the lower end of it's range..This is where I would certainly be closely monitoring the fuel-pressure guage, and flicking on the boost-pump as required...

 

.And so to summerize: Make sure your elect boost pump operates at the low pressure range, don't accept whatever the guy at the parts shop throws across the counter !...And fit a fuel-pressure guage so you can monitor fuel pressure being delivered to the engine at all times................................. ....Maj...

 

 

[Head in the clouds]

No offence taken and hopefully same with you....

No, of course not, I'll just be more careful with my wording in future...

 

Hope your feeling better

Yes thanks, bouncing again now... the joys of recurrent Ross River

 

To hopefully clarify things a little. The Rotax operators' manual states the following : (912ULS).......................................................................................................................................................................................

Note: Exceeding the max admissable fuel pressure will override the float valve of the carburetor.

 

The delivery pressure of an additional backing pump (eg: electric standby pump) must not exceed 0.3 bar (4.4psi) in order not to override the float valve.

 

...........................................................................................................................................................................................

Excellent post Maj, and the quote above really is the crux of the matter. If the combined pressure of the boost pump plus the mechanical pump operating at max engine rpm are set up so that they don't exceed the float valve limit then you can safely leave the pump on anytime. And in my case that would mean that I would use it just as advised in most aircraft POH I've seen (referring to non-gravity-feed systems) i.e. during all phases of take-off and landing, at all times above DA 8000 and at all times 1000ft AGL or below.

 

 

[alf jessup]

Why don't we need to turn on or off an electric fuel pump for a 912 powered trike?

Mark,

 

Because Airborne don't fit electric fuel pumps to the trikes, for what reason I am not sure as the fuel tanks are lower than the carbies.

 

Wal from Floods once told me the Pierburg pumps that used to be used on the 912's would out last the engine, not sure how good the A/C ones are they use now.

 

The Tecnam has a Pierburg mechanical pump on it as did my trike.

 

My electric pump runs at about .26 bar when on.

 

Cheers

 

Alf

 

 

[metalman]

To hopefully clarify things a little. The Rotax operators' manual states the following : (912ULS).......................................................................................................................................................................................

FUEL PRESSURE:

 

Max..................... 0.4 bar (5.8psi)

 

Min...................... 0.15bar (2.2psi)

 

Note: Exceeding the max admissable fuel pressure will override the float valve of the carburetor.

 

The delivery pressure of aan additional backing pump (eg: electric standby pump) must not exceed 0.3 bar (4.4psi) in order not to override the float valve.

 

...........................................................................................................................................................................................

 

Now I reckon the go is to have a fuel-pressure guage installed, otherwise your just guessing as to what is occuring when you turn the boost pump on or off. When buying/fitting a boost pump you must select one that fits the max pressure scenero, that the above recommends. They are available both in Facet ticker pumps, and Pierburg rotary valve pumps. One would assume the manufacturer of a new aircraft would know and respect these limits, and accordingly fit the correct boost pumps.

 

In my Lightwing which came from the factory with only the engine mechanical pump (elect boost pump optional) I recently fitted a new facet ticker pump with a max pressure of 2-3.5psi . I also fitted a fuel-pressure guage to the dash. Whilst flying today I took particular notice of my fuel pressures. I turn the boost on just before I go full power for take off, and off as soon as I think it is safe, which today was around 3-400 Ft. As I turn it off, I monitor the fuel-pressure guage. It drops to about 2.5 bar where it stops, and no lower. That's within limits at the bottom end. The pressure with boost on and full power, goes to around 7 bar which is 3 bar above max recommended, which is why I don't leave the boost on any longer than needed. I have a high intensity green LED light at eye level, so I don't forget it's on. I have had no indication of any problems with this set up for two years now which has included a flight to natfly and back , and down to Monto last year.

 

The Lightwing of course had excellent gravity flow from both wing tanks, and I always have both selected for takeoff/landing. Therefore if I forget to select boost pump on for takeoff (which occasionally happens), it's no big deal. I flew the aircraft for years with no boost pump fitted anyway !...

 

With Alf in the Sierra, which doesn't have a gravity flow situation, the boost pump is being used as a supply pump to take fuel slightly uphill to the engine driven pump, and possibly should be left on until level cruise is established, where the engine pump then is quite capable of supplying adequet fuel to the engine. From memory Tecnams have fuel-pressure guages fitted standard, and should always be monitored, especially in low power descent situations where the engine driven pump is also operating at the lower end of it's range..This is where I would certainly be closely monitoring the fuel-pressure guage, and flicking on the boost-pump as required...

 

.And so to summerize: Make sure your elect boost pump operates at the low pressure range, don't accept whatever the guy at the parts shop throws across the counter !...And fit a fuel-pressure guage so you can monitor fuel pressure being delivered to the engine at all times................................. ....Maj...

Did a few laps in the eurofox this arvo, and the pump pressure is in the right range , I was just doing circuits so I didn't bother turning it off at, gotta say I cannot think of an aircraft I've flown that is more fun and more rewarding than the eurofox taildragger, if I could get the damn balance ball to sit anywhere near the middle I'd be 100% happy ,but I did a half a dozen circuits and tried a few different profiles, long flat final, flying up to the numbers and slipping off the height , big circuits ,real tight ones , an engine out from downwind, and mucked around keeping the tail up in a fast taxi, I've gotta say the little bugger makes me look good,,,,now where can I get my grubby mitts $95k

 

Met

 

 

[Guest Maj Millard]

Could agree more Met, it is great to see development like this on aircraft types over the years, which no doubt takes the base design lite years ahead in useability, quality, safety and durability. Good to hear all is well with the fuel pressures. I may just have to do the same later to check mine aslo ........any excuse will do !! I would also like to try a Eurofox in fact I wouldn't mind getting a tow endo on one.....Have you noticed any additional tendancy for the Eurofox to bounce on landing with the new main gear legs (more than normal I mean)..................Cheers....... Maj...

 

 

[alf jessup]

I've gotta say the little bugger makes me look good,,,,now where can I get my grubby mitts $95k

Met

Met,

 

At the bank mate they got plenty lol, they lent me some for my Tecnam no probs now I just gotta pay it back.

 

But like I said to my wife, this life is not a trial run gotta do what I want to this time around cause I aint going to know if there is a next time round until this time round finishes.

 

Now thats enuf rounds !!!

 

Alf

 

 

[metalman]

Could agree more Met, it is great to see development like this on aircraft types over the years, which no doubt takes the base design lite years ahead in useability, quality, safety and durability. Good to hear all is well with the fuel pressures. I may just have to do the same later to check mine aslo ........any excuse will do !! I would also like to try a Eurofox in fact I wouldn't mind getting a tow endo on one.....Have you noticed any additional tendancy for the Eurofox to bounce on landing with the new main gear legs (more than normal I mean)..................Cheers....... Maj...

Mmm bouncing on landing,,,I have NO trouble doing that all by myself :-)

Actually with the 26 inch tyres it's almost impossible to do a bad three pointer, wheelers take a bit of finesse though, as the wheels touch you can't pitch forward cause all that rubber has to catch up, after the wheels are rolling the tail drops a bit and you can then pin it as per normal, the gear legs seem pretty nice ,a lot more damping than bungee gear.

 

Yeh Alf, it the paying it back that's the thing, the guy who has the Eurofox has it on line but being a taildragger it's not getting the use that he needs for it to pay,

 

Met

 

 

[dazza 38]

Mmm bouncing on landing,,,I have NO trouble doing that all by myself :-)Actually with the 26 inch tyres it's almost impossible to do a bad three pointer, wheelers take a bit of finesse though, as the wheels touch you can't pitch forward cause all that rubber has to catch up, after the wheels are rolling the tail drops a bit and you can then pin it as per normal, the gear legs seem pretty nice ,a lot more damping than bungee gear.

Yeh Alf, it the paying it back that's the thing, the guy who has the Eurofox has it on line but being a taildragger it's not getting the use that he needs for it to pay,

 

Met

Its a shame that the guys Eurofox isnt used enough. It would be nice to have one to fly up here.

 

 

[Guest Maj Millard]

Back to 912 stuff.......................Just recieved my new carb-mount rubbers from Floods (Pt No 267789)...it could be my imagination, or the fact that they are new, but it looks like they may have gone back to the harder rubber compound, as opposed to the softer which seem to crack/fail more often.

 

The clamps which were gold colour are now silver. Still made in Japan..no other obvious changes. Any comments on this ?...I'll fit the newies this week, and remove my spare set of old hard-compound ones, which I've run for the last 15 hours or so since I found the newer soft-compound one's cracked (after 222 Hrs).............................Maj...

 

 

[pmccarthy]

Thanks for this thread. I was taught more than 40 years ago to establish a positive rate of climb and then, not below 300 feet, flaps up and pump off. I have always flown low- wing. I have tended in recent years to leave the pump on a bit longer until I can see a place for a forced landing within range, so it depends on terrain and trees. It helps greatly to have a pressure gauge when you switch it off to see that the pressure is still there. In the Texan the pressure just drops about 10% but still in the middle of the gauge.

 

 

[Guest Maj Millard]

Hi PMC, yes I fitted a fuel-pressure guage to my 582 Drifter years ago for the same reason, to make sure I still had pressure after I turned off the boost...it is reassuring, beats sitting there for a bit wondering doesn't it. I feel it's almost a required guage in an aircraft really and especially if you operate a boost pump....................................Maj...

 

 

[eightyknots]

I feel it's almost a required guage in an aircraft really and especially if you operate a boost pump....................................Maj...

I agree Maj, all aircraft built today should have them and a strong encouragement should be give to retrofit them to older aircraft.

 

 

[storchy neil]

about time 912s have to have return line to tank the:angry: repairer of my aircraft did not have the manuals to my aircraft and there for put lives at risk as it does not have return line to tank at the flying school when it was on cross hire

 

read your manuals dont be like me and assume that your aircraft is as the manual says neil

 

 

[Head in the clouds]

about time 912s have to have return line to tank ......

Is this right? I'm just installing my first 912, it's a 912ULS3 and I didn't know anything about a fuel return line to the tank. I've just gone through sections 14-16 of the installation manual and can't find anything about it. Can someone add further info please? Where would the return line originate from? The only fuel line info I can find shows the manifold (splitter) with one line in from the pump(s) and two lines out, one going to each of the carbies. And it says to keep them cooler than 35C to prevent vapour locking. What have I missed?

 

 

[storchy neil]

read rotax manual from the disc page 14 - 3 check out digram hih neil

 

 

[Head in the clouds]

read rotax manual from the disc page 14 - 3 check out digram hih neil

Neil, thanks, I had completely missed the reference to that. I wonder why that manifold with it's restricted orifice and barb for the return line is not provided as part of a new engine installation kit since they state that it's a piece of equipment that is "essential for operation of the fuel system".

 

I've not come across such a thing before in other fuel systems unless they're fuel injected, and quite clearly it's the .014" diameter orifice that needs adjusting (make it larger) in these cases where aircraft are suffering excess fuel pressure problems.

 

Good info, thanks again.

 

 

[storchy neil]

just to keep you on your toes also hih did you see that peice about egt that it has to fitted to rotax engine

 

neil

 

 

[Guest Maj Millard]

Neil and others, the fuel return provision was fitted to the 912S which is the certified engine, and is not generally fitted to the 912ULS. It is not absolutly necessary on all instalations. My 912ULS in the Lightwing doesn't have it, or need it. Many other 912uls that I have seen don't have it....I am familiar with the device as a lot of the Storches had certified 912S engines which were obtained by Nestor, after another manufacturer that they were destined for went belly up.

 

On the other hand if you have a ULS that has it , or you wish to fit it to a uls engine I can't see it doing any harm if installed correctly. CAUTION: Do not overtighten the banjo-bolt that holds the lot together (10 NM or 90 inch pounds max) otherwise you will snap it, and a replacement is costly......Neil, the 14-3 page you mention is from the 912S instalation manual is it not ? ...................................................Maj...

 

 

[Head in the clouds]

just to keep you on your toes also hih did you see that piece about egt that it has to fitted to rotax engineneil

Thx again, no haven't seen that yet either. My new project is very complex enclosed pusher so the pplant installation at this stage has been a case of put it in place and build the metal cowling around it so I haven't concentrated on the systems except their wiring and inbound plumbing. I'm thinking the 'return line' really doesn't need to return to tank but just recirculate back to behind the pumps to act as a (rather poor) form of pressure relief valve. Any thoughts about that?I did wonder if I had just not noticed the fuel manifold so I checked its co-ordinates, 385 back from the prop flange ctre, 50 below it and 110 to the right of it is the position for its clamp. That puts it clashing with the ignition units and my engine certainly doesnt have one or the supposed mount for its clamp. Surely someone knows more...

 

Can folks with 912s please look at their fuel delivery lines, do they go to a manifold with a split to carbies then a takeoff for pressure gauge and another for a return line? Or simply a T piece to each carby and a takeoff somewhere for the gauge?

 

Logically the fuel system does need an adjustable relief valve, this business of buying the right pump is too iffy, we're talking small pressures and small differences that will cause potentially catastrophic flooding of a perfectly serviceable engine. So we need properly adjustable control, or preset control as offered by this restriction in a return line... so where has this unit gone? The manual I recd with my new engine is Revn1 2007...

 

This is important folks, it may be the reason for planes coming down from overpressure. My brand new 912 has not been supplied with this ESSENTIAL manifold and no mention of it was made by Floodys, and its not obvious in the manual.... why? And I asked for Everything I Need, and was encouraged to buy a bunch of instruments, which I did, and the thousand dollar airbox etc, but no mention of the manifold with pressure relief, or a pressure gauge...

 

Apologies if there are typos or any mad autocorrects - phone txting...

 

EDIT - sorry and also Thx Maj, our posts crossed...

 

 

[Head in the clouds]

About the S or ULS thing, no - my supplied manual, for the ULS, Very Clearly states the item 4 manifold, with restricted orifice return line is ESSENTIAL for operation of the fuel system... as far as I interpret it anyway i.e. it says all 912 engines must have it, no exceptions are mentioned. Maybe we 'uncertified' operators are supposed to notice this veiled info and buy the item separately, if so why isn't it in the package list? Personally I'd just install a simple spring and ball relief valve...

 

 

[Guest Maj Millard]

It obviously isn't essential for suitable 912 ULS operation...I have been flying succesfully now for 705.9 hrs without it, and so have many others that I know of !......the .014 " orifice and return to the fuel tank is designed to eliminate vapor lock in the fuel supply system, not to act as an over-pressure relief device. That is one reason it is situated at the top of the system. Lets face it, do you really think enough fuel is going to be forced through a 0.014 " orifice to eliminate overpressure to the carbs, if a high-pressure elect pump is fitted or used, against recommendations ??. .............................................Maj...

 

 

[Guest Maj Millard]

HITC,........I feel that the confusion is because certain things have been lost in the German-English translation, and it just doesn't read as it should..They probabily ment to convey that it is 'essential' you don't suffer any vapor locks !!!...................................Maj....