DA40 Fuel Pump Operation

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Rich
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Re: DA40 Fuel Pump Operation

Post by Rich »

For certification, I'm sure the electric would pump has to deliver sufficient fuel to substitute for the mechanical. I'll double-check the data plate on my spare Dukes (as it has sat unused for years in the hangar), but I seem to recall the flow rate was far more than the Lycoming consumes at any power setting.
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Re: DA40 Fuel Pump Operation

Post by pietromarx »

Rick wrote:This has me wondering now... Does anyone know of any instance of a mechanical fuel pump failure in an IO-360 engine, or how to look for such a thing? This would be the ultimate source of information on how well the electric pump performed, if it has ever happened.
That's exactly my question. I've had bad electric pumps (which fail, by the way, during critical phases of flight), but I've never heard of an engine-run fuel pump failing in a Diamond.

I always turn on the electric fuel pump with some tentativeness. They seem to fail at turn-on and when they're supposed to be the backup. Not inspiring.
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Re: DA40 Fuel Pump Operation

Post by Rich »

Rich wrote:For certification, I'm sure the electric would pump has to deliver sufficient fuel to substitute for the mechanical. I'll double-check the data plate on my spare Dukes (as it has sat unused for years in the hangar), but I seem to recall the flow rate was far more than the Lycoming consumes at any power setting.
Checked this afternoon. Nameplate shows 23.5 GPH @ 14 PSI, with deadhead pressure at 18 PSI.
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Chris
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Re: DA40 Fuel Pump Operation

Post by Chris »

pietromarx wrote:I always turn on the electric fuel pump with some tentativeness. They seem to fail at turn-on and when they're supposed to be the backup. Not inspiring.
I'm curious if anybody has had a failure with the Weldon replacement pumps. The original Dukes were quite fragile, to say the least, but I don't think I've heard of many problems with the Weldon.
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Re: DA40 Fuel Pump Operation

Post by Chris B »

Chris wrote:I'm curious if anybody has had a failure with the Weldon replacement pumps. The original Dukes were quite fragile, to say the least, but I don't think I've heard of many problems with the Weldon.
Yes. I had mine fail recently at about 1500 hrs. I usually use the pump above 10k, so it probably had 250 hrs of run time.

It would pop the breaker after a few seconds. The initial failure was at night, so I didn't notice until the next morning when the pump would not run at all. Since the resistance across the terminals is ~1/2 of the new pump, I assume that the windings developed a short.

I plan to keep a spare in the hangar so that this one never fails again. ;)

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Re: DA40 Fuel Pump Operation

Post by TimS »

I trained in a Cirrus SR20; and then transitioned to an Aerostar. Both of these planes teach fuel pump on for run up, idle test, low altitude flight and first hour of high altitude. If installed, the Aerostar even suggests low pressure pumps on for flight above 10K. Here is why:
Both electric and mechanical pumps have a bypass, however the electrical pump is significantly stronger because it is required to overcome vapor lock in flight and provide fuel to the engine at a greater distance while maintaining power.

If the electric pump fails in can be in one of two ways. Providing too much fuel or too little fuel pressure to overcome vapor pressure cavitation by the mechanical pump or the bypass for the mechanical pump. If the pump provides to much fuel you can flood the engine and prevent you from making full power, or cause backfires, or other issues. If you get cavitation you have vapor pockets in the fuel line which can produce interesting pauses in power or eventual silence. The result was it is considered critical to do the run up with the electric pump; since you do not want to discover these issues on the runway, at rotation or the immediate climb segment.

Now, if the mechanical pump fails, the fuel pressure drops some, but the engine is still able to make full rated power, with adequate detonation margins and no vapor lock in the fuel lines. Depending on power setting, it may make the engine slightly less rich, but will continue to run. Further, since the checklist has you keep the fuel pump on till in cruise or at least a few thousand ft off the ground. When you shut off the electric and the engine goes quiet because the mechanical pump failed, it is easy enough to turn it back on.

Note: This is a complete different design and philosophy than you see in Beech and some other vendors. In those designs, the electric is supplemental and is only to be used when the mechanical fails.

The point being, think through a failure analysis, and how you can spot trends. For example, during run up in the Cirrus, I spotted that the fuel flow and pressure did not match previous values so I did a full power run up; the engine would skip and sputter. The pump was fine, but I had some crud partially blocking the fuel filter.

Lastly, I have not gone through the design analysis on the DA-40 fuel system, so.....

Tim
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Re: DA40 Fuel Pump Operation

Post by CFIDave »

The fuel systems of Continental (e.g., Cirrus SR22, older SR20s, or Beech Bo/Baron) vs. Lycoming are designed very differently, so it's not surprising that different procedures are used for run-up, takeoff/landing, starting, etc.

On Lycoming DA40s the system is quite simple with the electric pump in-line/in series with the engine's mechanical pump, to provide multiple uses:
- To prime the engine for cold starts,
- To provide additional pressure at higher altitudes (e.g., greater than 10,000 feet),
- To act as a backup in case the mechanical pump should fail during critical phases of flight (e.g, takeoff and landing),
- To maintain fuel pressure when switching between L and R tanks (although this is no longer common practice among many DA40 owners attempting to minimize fuel pump use; to my knowledge there's never been an engine stoppage caused by not using the pump during fuel tank switching).
On a Lycoming, the electric fuel pump is "supplementary" to the engine's mechanical pump.

The fuel system on Diamond JetA diesels is a much more complex design with re-circulation of unused fuel from the common rail back into the tank, parallel electric pumps in case one fails, a bypass valve around the electric pumps' fuel filters in case they get clogged, etc. -- not at all like the simpler Lycoming fuel system. An electric fuel pump AND the engine's mechanical high pressure fuel pump for the common fuel rail must both be running all the time; unless at least one of the parallel electric fuel pumps is operating, the engine will quit.
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Re: DA40 Fuel Pump Operation

Post by gordsh »

Rich wrote:In my plane operating the fuel pump switch is not what one would think of as muscle memory. I'm unclear to me how the G1000 switch layout is, but the switch in mine is right next to the avionics master and looks just like it. So my muscle memory is to look down and confirm which switch I'm about to operate and then do it. Otherwise :oops:
Rich, here is a pic of the fuel pump location in the XLS and I assume its the same for all the G1000 equipped DA40's. Its situated next to the Pitot Heat switch so no harm done if you click the wrong one but I always glance down anyway and because its so noisy I am used to hearing it as well.
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Re: DA40 Fuel Pump Operation

Post by TimS »

CFIDave wrote:The fuel systems of Continental (e.g., Cirrus SR22, older SR20s, or Beech Bo/Baron) vs. Lycoming are designed very differently, so it's not surprising that different procedures are used for run-up, takeoff/landing, starting, etc.
Dave,

My point was Cirrus using a Continental, and Aerostar with a Lycoming actually use the same operational procedures (except for cross feed).
And based on your posting, I would think following the AFM and having the fuel pump on during run up makes sense.

Tim
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Re: DA40 Fuel Pump Operation

Post by pietromarx »

Has anyone has experienced a failure of the engine-driven *mechanical* pump on a Lycoming? I've not heard of one, but maybe someone has?

There is a piece on Aviation Consumer that implies they're pretty reliable ... http://www.aviationconsumer.com/issues/ ... 795-1.html

Thanks
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