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Fuel starvation in a constant turn?

ArVeeNiner

ArVeeNiner

Well Known Member
Something occurred to me the other day and I haven't figured out the answer.

In a turn, with the low wing tank selected, does the fuel slosh down hill and away from the fuel pick up? If so and if the turn is persistant is there a chance of fuel starvation? I'm thinking that this just isn't an issue but why? Could it be that since the turn is coordinated, the fuel just doesn't move much outboard? How about in a slip?
 
ArVeeNiner said:
Something occurred to me the other day and I haven't figured out the answer.

In a turn, with the low wing tank selected, does the fuel slosh down hill and away from the fuel pick up? If so and if the turn is persistant is there a chance of fuel starvation? I'm thinking that this just isn't an issue but why? Could it be that since the turn is coordinated, the fuel just doesn't move much outboard? How about in a slip?
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In a sustained slip this could be an issue. In a coordinated turn it isn't. As far as your airplane knows it is in straight and level flight with a slightly heavier load.

Well I've already edited this message 4 times in 2 minutes. Let's say for all practical purposes a coordinated turn should not affect the amount of usable fuel. Actually there are some differences in level flight and a coordinated turn.
 
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Correcto, as long as A/C is coordinated the vector of G's is straight down. The tanks think they are on a level surface and if G's is above 1 you actually have increased head pressure. I've never had an RV tank unport, but you can do it pretty easy in a cherokee (if you try).
 
Your assumption is correct. In a coordinated turn the fuel will ride in the tanks in the same position as straight & level flight. In a slip, it depends how much you slip it how far the fuel will displace.
 
Think coordinated turn.

I believe if you are in a coordinated turn, normal G force keeps your fuel where is was in your wing tanks. Not necessarily so if you are skidding.
 
Thanks

Thanks! That's what I thought. With most of my time in high wings I just never thought about that before.
 
As everyone has said, in a coordinated turn, the bottom of the tank does not change from what it is sitting on the ground.

I may be the only one to have tested this. I wanted to only have enough fuel in the tanks to fill the containers I had before doing the Service Bulletin on safety the fuel pickups. I had enough containers to store 9-gallons of fuel. I desired to only have about 5-gallons on one side when I landed. I circled the airport at 3,000 AGL in a left turn while burning fuel out of the left tank. Since I have fuel flow in addition to fuel pressure, I ran till I saw a drop in fuel flow and a decrease in fuel pressure. As soon as that happened, I switched to the other tank then landed.

Back in the hangar, I drained the left tank and got less than 8-oz of fuel out. The other tank that I thought I had 5-gallons in actually turned out to be 8.5 gallons.

Yes what everyone one is saying about coordinated flight is true. I tested it.
 
And it doesn't matter if high-wing or low-wing. I tested this in my C172 a couple years ago while doing some photography with relatively low fuel (actually I was flying, wife was doing photography). I put the airplane in a slip and held it for a couple minutes and pretty soon.... cough.... cough.... the engine stopped for a minute. It was obvious what the problem was, although I quickly switched tanks as well.

greg
 
I ran a tank empty to calibrate my dip stick. At 2200 rpm, I ran the tank out of gas, and when the engine quit, I switched tanks and did not turn on the electric pump....... The motor fired in three seconds! No altitude lost, just a slight deccrease in speed for a few seconds.
 
gasman said:
I ran a tank empty to calibrate my dip stick. At 2200 rpm, I ran the tank out of gas, and when the engine quit, I switched tanks and did not turn on the electric pump....... The motor fired in three seconds! No altitude lost, just a slight deccrease in speed for a few seconds.
Click to expand...

Was this with a carbed engine or FI?

Bevan
 
Today's quiz:
What happens to the fuel if the wings are designed with anhedral? Where should the fuel pick-up be located?
Terry, CFI
RV9A N323TP
 
Anhedral

terrykohler said:
Today's quiz:
What happens to the fuel if the wings are designed with anhedral? Where should the fuel pick-up be located?
Terry, CFI
RV9A N323TP
Click to expand...

On the outboard ends of the tank. The bonus is that it would still feed fuel in a spin. :eek:

John Clark
RV8 N18U "Sunshine"
KSBA
 
The winner from yesterday's quiz is John Clark. John, you may collect your prize any time over the next 12 months. When you arrive at KPTK, advise ground that you want Foxtrot row. From there you will be transported to a fabulous $3.00 breakfast at Everybody's Cafe with the Pontiac RV guys.
Regards,
Terry, CFI
RV9A N323TP
 
Breakfast

Terry,
I'm honored to be the recipient of your generous award. Might be able to collect around the end of July. ;)

John Clark
RV8 N18U "Sunshine"
KSBA
 
High wing, low wing

I should have said "since my time has been mostly in a specific high wing which had a fuel valve that only gave you the option of ON or OFF". I had a 1951 Aeronca Sedan that I had for 6 years and it was like this. As I sit here about to make the statement that the Aeronca was exempt from these problems I'm thinking that this isn't the case.

Let's say that I had low fuel and went into an extended slip (something that I did quite regularly). Initially, the fuel would slosh to the low side of both wings. The fuel in the high wing would eventually transfer to the low wing. BUT, the fuel in the low wing would slosh away from the fuel pick up. I guess that until the fuel from the high wing got to the low wing, there would be a chance that the pickup would start sucking air. This is something that I never thought about but I never experienced it either.

So, unless we are in an extended slip situation with low fuel, we shouldn't have a problem I guess.

Greg Arehart said:
And it doesn't matter if high-wing or low-wing. I tested this in my C172 a couple years ago while doing some photography with relatively low fuel (actually I was flying, wife was doing photography). I put the airplane in a slip and held it for a couple minutes and pretty soon.... cough.... cough.... the engine stopped for a minute. It was obvious what the problem was, although I quickly switched tanks as well.

greg
Click to expand...
 
Unuseable Fuel Quantity Tests

This topic brings me back 30 years ago when I briefly worked for Cessna Aircraft in Wichita. One of my projects was to conduct unusable fuel quantity tests for the Cessna 404 Titan. The engineers wanted a tank design to reflect about 5 gallons unusable fuel. We had a mock-up tank of the existing prototype installation on the floor of the hangar. The objective was to come up with a published figure to place in the POH.

According to certification requirements, it required 35 seperate flight parameters to test the unusable fuel quantity. Many of these flights had to be repeated. We flew in a variety of pitch attitudes, angle of bank, and coordinated and uncoordinated flight.

For example, we would put just enough fuel into one tank to get us out to the practice area and perform the stated manuever. The manuever could be a 1/2 ball skid, level flight, 15 degree bank turn. We would maintain that attitude until the engine coughed. Switch back to the good tank. Return to the field, empty the tank, and measure the results.

If the results didn't meet the target figure, we would walk over to the mock up, look at the tank baffling and lightening holes, make funny airplane gestures with our hands analyzing the problem, then tell the technicians to move this or that, or make a another hole here or there.

We go drink coffee for a couple of hours, they would make the mods to the tank. Then we would go flight test again. This process, for a certified aircraft was very laborious and costly.

This thread topic brought back some pleasant memories.

Regards,
 
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Tom, I'm curious why the engineers wanted 5 gal unusable fuel? Seems like a significant weight penalty to me (especially if there are two tanks = 60 pounds!).

greg
 
That's not much fuel for a twin-engine piston cargo carrier with a total horsepower of 750hp. Empty weight of 4800+ and max takeoff weight of 8400, I'm thinking they were trying to get the unusable fuel DOWN to five gallons a side. Those would be some good sized fuel tanks, usable fuel is listed 2064 pounds - you'll have lots of baffles and puddling spots in the tanks to deal with. 60 pounds of fuel is only 12 minutes at full power for that bird.

http://www.airliners.net/aircraft-data/stats.main?id=152
 
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airguy said:
That's not much fuel for a twin-engine piston cargo carrier with a total horsepower of 750hp. Empty weight of 4800+ and max takeoff weight of 8400, I'm thinking they were trying to get the unusable fuel DOWN to five gallons a side. Those would be some good sized fuel tanks, usable fuel is listed 2064 pounds - you'll have lots of baffles and puddling spots in the tanks to deal with. 60 pounds of fuel is only 12 minutes at full power for that bird.

http://www.airliners.net/aircraft-data/stats.main?id=152
Click to expand...

Airguy,

I couldn't have stated that better myself...thanks!

Regards.
 
DAGO said:
...According to certification requirements, it required 35 seperate flight parameters to test the unusable fuel quantity. Many of these flights had to be repeated. We flew in a variety of pitch attitudes, angle of bank, and coordinated and uncoordinated flight...
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This goes to point out that what the factory airplane world calls unusable fuel is entirely different that what just about everyone in the homebuilt world calls unusable fuel.

Lots of us homebuilt people find out how much fuel is left when the engine quits in level flight but that is nothing like what is described above.
 
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