DA40 Fuel Pump Operation

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Re: DA40 Fuel Pump Operation

Postby smoss » Fri Mar 16, 2018 2:44 am

Colin- thread drift, but why is the prop cycling potentially harmful? The one time I forgot to do it in the past, when went to full throttle for takeoff, there was a noticeable hesitation in the prop, at which time I immediately recalled I had forgotten that step... perhaps it was totally unrelated, but seemed directly related.
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Re: DA40 Fuel Pump Operation

Postby pietromarx » Fri Mar 16, 2018 5:09 am

Having just replaced a Hartzell composite prop due to an undisclosed lightning strike that happened before purchase, I can tell you that I have closely examined what Hartzell, my A&P, and everyone else says about a prop. Unexpectedly spending $20k on something focuses the mind.

Hartzell and my A&P are extremely clear: at least 3 times is the thing to do. I've seen props which are sluggish until the 3rd, even 5th time through. The goal isn't the number inasmuch as making sure that the prop changes pitch smoothly.

Deaken is somewhat ambiguous as his pieces says, "How many times should you cycle the prop? If the RPM drops smoothly and properly, once is enough. The fresh oil will probably cause the piston to move a good deal and when it comes back to the low pitch stops, most of the "old" oil will be pushed out. If you really want to feel good, do it twice, to get even more of that "old" oil out of there. Three times is gross overkill, in my opinion, but a lot of people do three times, or more. In reality, there are tiny bleed holes that allow a constant flow of warm oil to both sides of the prop piston, so even if you take off with cold oil in there, it will quickly be replaced with nice slippery warm stuff. On some of the big old props on the radials, in extreme Arctic conditions, the oil would congeal faster than the bleed ports could replace it, but I doubt you'll find any modern props with this problem. I should note for completeness that many of the props on the big radials might require many more cycles to achieve a smooth RPM drop when cold. In freezing temperatures, it may take up to ten cycles. There's a lot more to the mechanism, and a lot more oil involved."
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Re: DA40 Fuel Pump Operation/check after maintenance

Postby ThomasD » Fri Mar 16, 2018 11:16 am

Free and correct? EVERY TIME.

I very much agree with this one. One time when I collected the airplane after maintenance, the control column was a bit 'sticky' in one direction. Turns out that the maintenance company had undone the earth bonding strap on the right aileron and whomever had put it back had left it rotated so that it snagged on the small fairing - something that I now always check pre-flight, that these earth bonding strips won't snag.
And pretty poor of the maintenance company not to do a 'full and free' check before releasing it back to me.

Another one I caught after maintenance (different company): the left wing was taken off to replace the inboard fuel sensor - so a careful inspection of the left wing, top and bottom of course? Yes, but I also found that the outboard inspection cover on the underside of the RIGHT wing was dangling loose - seems that the maintenance company undid both left and right wing inspection covers underneath the wings, both inboard and outboard, for comparison, and forgot to put one back on. In theory they were only touching the left wing, nothing else.
Taught me to do a thorough check of the whole plane, inside and out, no matter what the maintenance company has done - they could have touched anything while doing the work.

[Apologies for the thread drift.]
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Re: DA40 Fuel Pump Operation

Postby Tom Davis » Sat Jul 14, 2018 10:13 pm

ThomasD wrote:I agree with Gordsh and others - I do the same. (Plus pump on at final approach as well.)

FYI one thing that I do not do [which is recommended in the POH] is to switch on the fuel pump when changing tanks in flight, if I am 3,000' or above.
I have never had a hiccup of the engine when just switching in-flight left-right or vice-versa without the pump on, so I don't do so (as the pump appears to have a quite limited life).

Formerly I did not turn on the fuel pump when changing tanks, but about 18 months ago I was flying out of KAVL (Asheville, NC) and switched tanks at about 9,000 feet above sea level (about 4,000 above ground level) and got an alert about low fuel pressure. Since then I have switched on the fuel pump when changing tanks. For what is worth, my 2005 vintage DA 40 is in the shop for what I believe will be a new fuel pump. The old pump has about 1200 hours on it.

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