Fuel pressure question?

[Buckaroo]

Today turning right from the upwind leg my fuel psi gauge dropped momentarily to 0 psi and flickered around 1 and 2 lsa just to return to its normal 3 to 4 reading in the mid green. 

In order for me to understand the system and feel more comfortable can folks explain this systems operations to me? 

1. If the gauge drops and stays at zero will I have engine failure? 

2. Gravity fed fuel to engine still requires fuel pump. 

3. How does fuel pump interact with psi on Dynan? 

[procharger]

If you were low on fuel might have had a air bubble get in your lines

[Buckaroo]

I just filled it. If the pressure reads zero on the dynan can one expect engine failure? 

[Anticept]

Fuel pressure drops are acceptable per rotax running modifications bulletin, for up to 5 seconds. Add a few seconds for the dynon to stabilize as it uses software smoothing.

[procharger]

Gas will still flow to carbs. I believe?

[Buckaroo]

8 minutes ago, procharger said:

Gas will still flow to carbs. I believe?

I believe!! ?

Ive grounded her until I find out the safety aspect of this! 

HELP please!

[Roger Lee]

I posted a test I did a few years back. With and without a fuel pump on the CT. Your engine will not quit. It may not have been a real fuel issue, but an electrical connection issue.

No fuel,pump and fuel hoses joined. Full throttle capable.

Pump in line, but off the engine. Will run approximately 5K rpm, but stutters after that.

[FlyingMonkey]

Yeah, these airplanes are notorious for little electrical gremlins.  I have had bouncing oil pressure (dropped to zero a time or two, that will get your attention!) and oil temp. Both were electrical issues.  Check grounds, wiring, and connections, especially at the fuel pressure sender itself.  

The fuel pressure on a CT can't *really* go to zero at the carbs unless:

A ) Airplane is out of fuel (you verified fuel state, so not this).

B )  You are inverted (you'd probably know).

C )  You have a completely blocked fuel line somewhere (unlikely).

D )  Gravity stops working (less likely).

[Buckaroo]

Thanks guys I feel better now and went flying this morning. It’s funny that the gauge stated flickering at the exact part of the fligh it did it the other day and then went back to normal. 

With regard to the fuel system in general it’s my understanding from this mornings discussion with a Rotax owner the following. 

The FD is gravity fed so you will have adaquate flow to the carbs even if the fuel pump fails. True or false?? He said the fuel pump has bypass fuel capabilities. I asked why have a fuel pump anyway. He said because Rotax has universal uses in different configurations. 

Is this paragraph true partly true or false.

 

[FlyingMonkey]

56 minutes ago, Buckaroo said:

Thanks guys I feel better now and went flying this morning. It’s funny that the gauge stated flickering at the exact part of the fligh it did it the other day and then went back to normal. 

With regard to the fuel system in general it’s my understanding from this mornings discussion with a Rotax owner the following. 

The FD is gravity fed so you will have adaquate flow to the carbs even if the fuel pump fails. True or false?? He said the fuel pump has bypass fuel capabilities. I asked why have a fuel pump anyway. He said because Rotax has universal uses in different configurations. 

Is this paragraph true partly true or false.

 

Pretty much all true.  I'm not sure if you will get full power without the pump, but probably pretty close.  The pump is designed to fail open, so a failed pump should not interrupt the flow.

Open the gascolator valve sometime in your hangar (with a bucket under it!) and see how much fuel flows out.  It's alot, enough to drain your tanks in about 20 minutes.  The engine can't use fuel that fast, so that should tell you what you need to know.

[Buckaroo]

3 minutes ago, FlyingMonkey said:

Pretty much all true.  I'm not sure if you will get full power without the pump, but probably pretty close.  The pump is designed to fail open, so a failed pump should not interrupt the flow.

Open the gascolator valve sometime in your hangar (with a bucket under it!) and see how much fuel flows out.  It's alot, enough to drain your tanks in about 20 minutes.  The engine can't use fuel that fast, so that should tell you what you need to know.

This is comforting information. Again the brilliancy of this wonderful engine.

[Tom Baker]

13 minutes ago, FlyingMonkey said:

Open the gascolator valve sometime in your hangar (with a bucket under it!) and see how much fuel flows out.  It's alot, enough to drain your tanks in about 20 minutes. 

I have checked the fuel flow meter on several different CT's when draining fuel. The flow rate is normally between 18 and 22 GPH. It takes about 15 minutes to fill a 5 gallon jug.

[FlyingMonkey]

5 minutes ago, Tom Baker said:

I have checked the fuel flow meter on several different CT's when draining fuel. The flow rate is normally between 18 and 22 GPH. It takes about 15 minutes to fill a 5 gallon jug.

My point was it's more fuel than the engine could ever use, I think you are right now that you mention the time to fill a 5g jug.

The only time a 912 uses 18gph is if the engine fire has burned through the fuel lines.   

[Buckaroo]

So on our FD’s is the fuel pump useless? 

[Anticept]

No, it's not useless.

Even old cessnas have fuel pumps on the engine.

Fuel pumps take an unknown variable, head pressure, and turns it into a known one, the acceptable operating range.

Yes, it will run without it. No, that is not a good idea.

[Buckaroo]

I know someone who had a leaky fuel pump on their Rotax and never knew it until finally they ran 100ll and saw the blue stains in the compartment. It was very slow but probably not a good situation corrected by the blue discovery! 

[patrickwiering]

On my last 3 hr cross country my fuel pressure went to 8.3 PSI for like 5-10 minutes. Than dropped back to normal. Also my first guess is that its an electrical problem. Anyone had the same experience?

 

[Buckaroo]

3 minutes ago, patrickwiering said:

On my last 3 hr cross country my fuel pressure went to 8.3 PSI for like 5-10 minutes. Than dropped back to normal. Also my first guess is that its an electrical problem. Anyone had the same experience?

 

With all this discussed that we’re dealing with a gravity fed system why would there even be high psi warnings set in the gauges? Seems to be if this is a non issue having red alerts could distract pilots and scare passengers!

 

[Tonfo]

My last 2 Flights My Fuel Pressure Gauge went from 9.6 for about 30 sec. then back to 5.6 Then the next flight went all the way up to 16.5 for about 1 min  then down to  8.6 for about 15 sec then down to 5.5 make me a little  uneasy so i've got the cowling off now waiting to get ahold of a A&P does anyone have a answer i'm not that great of a pilot 

[Roger Lee]

Most likely a poor connection. If it was a poor ground it would go low. It is possible to be the sender. It happened to me.

 

[Tonfo]

On 10/7/2018 at 3:37 PM, Tonfo said:

My last 2 Flights My Fuel Pressure Gauge went from 9.6 for about 30 sec. then back to 5.6 Then the next flight went all the way up to 16.5 for about 1 min  then down to  8.6 for about 15 sec then down to 5.5 make me a little  uneasy so i've got the cowling off now waiting to get ahold of a A&P does anyone have a answer i'm not that great of a pilot 

I THINK WE GOT IT FIXED, To make a long story short, took off the fuel sensor let about a cup of fuel drain out into a clear container,got about a spoon full of crap out of the lines cleaned everything up, put it backed together, checked it out, and i have had 2 flights with no problems.  Roger thanks for the feed back.