Looking for cause of engine quit - Page 4

Blain · #31 01-04-2017, 12:38 PM

Quote:

Originally Posted by DanH

What Kurt said. Prudence requires an attempt to duplicate the problem. Sometimes it's not possible to do so, but when you can...

Your initial post says you had 30 psi with the boost pump on, and ran it at idle and 1500 RPM. Did you run it with the boost pump off? If it ran fine on the engine driven pump alone, with normal fuel pressure, I wouldn't bet on the leaky diaphragm as the cause of engine stoppage.

Here's a classic, a little piece of **** loose in a fuel system. This airplane had been assembled by a very good team, test flown repeatedly, then flown Texas to Alabama without a problem. The very next time it was flown it scared the snot out of James, followed by a LOT of hunting for a smoking gun.

http://www.vansairforce.com/communit...9&postcount=73

Did not run it with boost off. It was a ground start on damaged airframe. I limited it to just a few minutes. Never got out of cabin during run up or I may have saw fuel dribble. Really didn't even think of trying that at the time. I was just excited to have a running engine!

lr172 · #32 01-04-2017, 01:03 PM

There are two diaphragms, creating a chamber in between. This chamber has the overflow outlet. That outlet has a restrictor in it. It is designed so that this chamber fills with fuel when the main diaphragm leaks, allowing the second diaphragm to provide the backup pumping function (chamber fills with fuel, as Dan mentioned). The restrictor is sized such that enough pressure can still be exerted by the second diaphragm upon the gas in the main chamber (ruptured main diaphram and filled chamber allows upper diaphram to act as the main diaphragm). Some fuel is expelled through the restrictor on each pump cycle, so there may be some evidence of this if it happened.

Chkaharyer99 · #33 01-04-2017, 03:53 PM

Blain,

I found a youtube video that seems to be relevant to your questions regarding fuel starvation. The entire video is really good.

The part most relevant begins at the 11:20 mark and involves the cause and effect of air introduced into the fuel system.

"The Amazing Ubiquitous Diaphragm Fuel Pump"

https://www.youtube.com/watch?v=PYKo...ature=youtu.be

I hope this helps.

Blain · #34 01-04-2017, 07:57 PM

That was educational. It leads me to believe that if the chamber is full of fuel and draining overboard there may not be an open route for air to enter the pump.

sailvi767 · #35 01-05-2017, 07:13 AM

Quote:

Originally Posted by Ironflight

In addition to Dan's analysis on icing what most folks don't kow is that this was a short flight over the Sierra from Auburn - not hours in cruise. I would doubt that the fuel temp dropped more than a degree or two in the tanks during the flight. 11,500 sounds high to many folks - that's just a quick climb for those of us near Tahoe.

The original builder/pilot is our neighbor, so we know a little more than most about it. We were disappointed that their was no further investigation of the cause of the power loass - it remains a head scratcher. BTW - not a case of unporting - he had lots of gas - I stored over twenty gallons that came out of the plane after it was put back on its wheels for awhile.

Paul, was it AVGAS or auto gas?

Ironflight · #36 01-05-2017, 06:02 PM

Quote:

Originally Posted by sailvi767

Paul, was it AVGAS or auto gas?

Avgas, and very clean. After talking with the original owner, I believe that the leaking pump is a very high contender for the cause of this. Can we prove it? No - but I have heard no other more likely and reasonable solution. We will probably never be sure, but changing the pump like Blain is doing is the right thing regardless.

Paul

RV3bpilot · #37 01-05-2017, 07:48 PM

I know for sure that in my aircraft that if I use a steep decent with the throttle pulled all the way to an idle, and when the fuel tanks are less than 1/2 full, the fuel will move forward in the tanks uncovering the fuel pick-up. I have a sensor that goes off when air is coming into the fuel system.

Ironflight · #38 01-05-2017, 08:58 PM

Quote:

Originally Posted by RV3bpilot

I know for sure that in my aircraft that if I use a steep decent with the throttle pulled all the way to an idle, and when the fuel tanks are less than 1/2 full, the fuel will move forward in the tanks uncovering the fuel pick-up. I have a sensor that goes off when air is coming into the fuel system.

His descent wasn't steep enough to create a significant nose down attitude - 6,000 feet in about fifteen miles. And there was 2/3 fuel, so it would be pretty tough to unport the tanks.

BillL · #39 01-06-2017, 07:39 AM

This thread is looking like a game of battleship. So, Paul, is the"a" theory that that the mechanical pump failed, released debris then it plugged something downstream of that? The op said it had fuel pressure. It seems it would flow fuel with fuel pressure ( measured downstream of the pump) unless there is an obstruction. Even if the tank fuel was not low temp, the wing root connection could cool the fuel rapidly , but not through a 3/8" tube with 6-7-8 gph. That is pretty fast moving unless it was near the critical temp. Even if that were so, it would seem to plug the boost pump filter first, resulting in no fuel pressure.

So, is there any chance that the air filter was plugged with ice? No mention of the NTSB report or temps are posted here.

I would think taking the servo and distributor apart and inspecting and cleaning, or sending it to Don for same would be in order. Also, removing every single hose, tube and (or) ensuring it has no obstruction or debris, then doing a first flight style series of pressure (leak) and flow testing would be prudent to ensure that all (non icing) bases are covered. Just my 1 cent.

sailvi767 · #40 01-06-2017, 08:47 AM

Quote:

Originally Posted by Ironflight

His descent wasn't steep enough to create a significant nose down attitude - 6,000 feet in about fifteen miles. And there was 2/3 fuel, so it would be pretty tough to unport the tanks.

Ice in the fuel system could have certainly been the cause if the actual temp of the fuel was below freezing. Since we don't have a fuel temp gauge it's hard to know. Based on the flight profile the fuel could have been below freezing. If we knew the temp at the departure station and how long the aircraft sat their before the flight we could make a pretty good guess. Fuel icing brought down a British Airways 777 so it could be a factor.