Van's Air Force
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Fuel Flow Tests
- Thread starter bret
- Start date
Robert Anglin
Well Known Member
That is a good one
When we contacted FSDO to get an inspection, we found that the local office was asking for a fuel flow test to be posted in a Log as one of the check off items on their list. We simply put it in the flight level attitude and did the test for both tanks. Ours is injected so it came out to a little over one gallon a minute. I call FSDO back and asked if that was OK and how they wanted it put in the Log. The answer was, they were looking for 150% of the flow rate at the maximum fuel flow at full power for the engine in that airframe. I rounded it off to one gallon per minute and was told just write it as being 60 gallons per hour in the log. I have heard that from a safety point and that of the requirements across the pound that just like in part 23 you should add the pitch angles to the test, but FSDO told us we where find in just the fight level set point. You may wish to check with your DAR or FSDO office and see what they like to see as well as what you are comfortable with. It is a very good idea to check you whole fuel system very well before your first flight. you will not regret being careful on this point. Hope this helps. Yours, R.E.A. III #80888
When we contacted FSDO to get an inspection, we found that the local office was asking for a fuel flow test to be posted in a Log as one of the check off items on their list. We simply put it in the flight level attitude and did the test for both tanks. Ours is injected so it came out to a little over one gallon a minute. I call FSDO back and asked if that was OK and how they wanted it put in the Log. The answer was, they were looking for 150% of the flow rate at the maximum fuel flow at full power for the engine in that airframe. I rounded it off to one gallon per minute and was told just write it as being 60 gallons per hour in the log. I have heard that from a safety point and that of the requirements across the pound that just like in part 23 you should add the pitch angles to the test, but FSDO told us we where find in just the fight level set point. You may wish to check with your DAR or FSDO office and see what they like to see as well as what you are comfortable with. It is a very good idea to check you whole fuel system very well before your first flight. you will not regret being careful on this point. Hope this helps. Yours, R.E.A. III #80888
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If FAR 23 requirements are used as a guide......
Gravity feed systems (Cessna) require 150% expected flow at max. power.
Pump systems (like we have in RV's) require 125% of expected flow at max power.
The test has to be done with the aircraft in the attitude that would be the most adverse for the fuel system. In an RV that would be tail low at the maximum sustainable climb angle.
Gravity feed systems (Cessna) require 150% expected flow at max. power.
Pump systems (like we have in RV's) require 125% of expected flow at max power.
The test has to be done with the aircraft in the attitude that would be the most adverse for the fuel system. In an RV that would be tail low at the maximum sustainable climb angle.
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BillL
Well Known Member
Bret, suggest you get a 1/4" ball valve and use it to restrict the flow down to the 125% value, then read the pressure and run your test. We added a clear section of tubing before the valve to see if the system was pulling air somewhere.
A pressure leak down test of the system from wing root to servo had already been run but used the clear section as more joints were now included. For completeness.
We weighed the fuel removed (pumped out) and kept a running log of how much fuel was in the tanks, we only used a few gallons, but over and over. Fuel was filtered each time it was poured back in the tanks.
It was a good test for unusable fuel. We shut off each time the main pump cavitated -it is the best indicator. The faster it is shut off the quicker it purges air for the next test.
This was fun and a huge confidence builder for first flight.
A pressure leak down test of the system from wing root to servo had already been run but used the clear section as more joints were now included. For completeness.
We weighed the fuel removed (pumped out) and kept a running log of how much fuel was in the tanks, we only used a few gallons, but over and over. Fuel was filtered each time it was poured back in the tanks.
It was a good test for unusable fuel. We shut off each time the main pump cavitated -it is the best indicator. The faster it is shut off the quicker it purges air for the next test.
This was fun and a huge confidence builder for first flight.
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az_gila
Well Known Member
If you are going to use the new "second pilot" option during flight test then some specific tests - including fuel flow - must be performed and documented.
b. Powerplant Testing. Powerplant testing is required prior to the initial flight and any time warranted thereafter to help ensure the reliability of the powerplant. Based on the recommendations of AC 90-89 and the industry on testing of the powerplant and fuel system, the following tests, if applicable, are required:
? Mixture and Idle Speed Check,
? Magneto Check,
? Cold Cylinder Check,
? Carburetor Heat Check,
? Fuel Flow Check,
? Unusable Fuel Check, and
? Compression Check.
c. Documented Testing. Documented testing similar to that of the build is required as proof of compliance. This includes appropriate logbook entries with test results. Photographs and diagrams should also be provided for tests where the applicant deems them beneficial or necessary.
d. Changes to Fuel System. Any change to the fuel system after conducting the fuel flow tests, except for normal fuel system/filter maintenance, requires a repeat of the tests prior to additional flight. All tests, including repeated tests, require documentation.
The main body of the document references AC 90-89a, which gives a good hint how to do the fuel tests -
e. Fuel Flow and Unusable Fuel Check: This
is a field test to ensure the aircraft engine will get
enough fuel to run properly, even if the aircraft is
in a steep climb or stall attitude.
(1) First, place the aircraft?s nose at an
angle 5 degrees above the highest anticipated climb
angle. The easiest and safest way to do this with
a conventional gear aircraft is to dig a hole and place
the aircraft?s tail in it. For a nose gear aircraft, build
a ramp to raise the nose gear to the proper angle.
(2) Make sure the aircraft is tied-down and
chocked. With minimum fuel in the tanks, disconnect
the fuel line to carburetor. The fuel flow with a gravity
flow system should be 150 percent of the fuel
consumption of the engine at full throttle. With a
fuel system that is pressurized, the fuel flow should
be at least 125 percent. When the fuel stops flowing,
the remaining fuel is the ??unusable fuel?? quantity.
(3) Since the fuel consumption of most
modern engines is approximately .55 pounds per
brake horsepower per hour for a 100 horsepower
engine, the test fuel flow should be 82.5 pounds (13.7
gallons) per hour for gravity feed, or 68.75 pounds
(11.5 gallons) per hour for a pressurized system. The
pounds per hour divided by 60 equals 1.4 pounds
and 1.15 pounds per minute fuel rate respectively.
NOTE: Formula for fuel flow rate gravity
feed is .55 x engine horsepower x 1.50 =
pounds of fuel per hour divided by 60 to
get pounds per minute, divided by 6 to get
gallons per minute. For a pressurized system,
substitute 1.25 for 1.50 to determine
fuel flow rate.
All of the above sound like wise items to check.
b. Powerplant Testing. Powerplant testing is required prior to the initial flight and any time warranted thereafter to help ensure the reliability of the powerplant. Based on the recommendations of AC 90-89 and the industry on testing of the powerplant and fuel system, the following tests, if applicable, are required:
? Mixture and Idle Speed Check,
? Magneto Check,
? Cold Cylinder Check,
? Carburetor Heat Check,
? Fuel Flow Check,
? Unusable Fuel Check, and
? Compression Check.
c. Documented Testing. Documented testing similar to that of the build is required as proof of compliance. This includes appropriate logbook entries with test results. Photographs and diagrams should also be provided for tests where the applicant deems them beneficial or necessary.
d. Changes to Fuel System. Any change to the fuel system after conducting the fuel flow tests, except for normal fuel system/filter maintenance, requires a repeat of the tests prior to additional flight. All tests, including repeated tests, require documentation.
The main body of the document references AC 90-89a, which gives a good hint how to do the fuel tests -
e. Fuel Flow and Unusable Fuel Check: This
is a field test to ensure the aircraft engine will get
enough fuel to run properly, even if the aircraft is
in a steep climb or stall attitude.
(1) First, place the aircraft?s nose at an
angle 5 degrees above the highest anticipated climb
angle. The easiest and safest way to do this with
a conventional gear aircraft is to dig a hole and place
the aircraft?s tail in it. For a nose gear aircraft, build
a ramp to raise the nose gear to the proper angle.
(2) Make sure the aircraft is tied-down and
chocked. With minimum fuel in the tanks, disconnect
the fuel line to carburetor. The fuel flow with a gravity
flow system should be 150 percent of the fuel
consumption of the engine at full throttle. With a
fuel system that is pressurized, the fuel flow should
be at least 125 percent. When the fuel stops flowing,
the remaining fuel is the ??unusable fuel?? quantity.
(3) Since the fuel consumption of most
modern engines is approximately .55 pounds per
brake horsepower per hour for a 100 horsepower
engine, the test fuel flow should be 82.5 pounds (13.7
gallons) per hour for gravity feed, or 68.75 pounds
(11.5 gallons) per hour for a pressurized system. The
pounds per hour divided by 60 equals 1.4 pounds
and 1.15 pounds per minute fuel rate respectively.
NOTE: Formula for fuel flow rate gravity
feed is .55 x engine horsepower x 1.50 =
pounds of fuel per hour divided by 60 to
get pounds per minute, divided by 6 to get
gallons per minute. For a pressurized system,
substitute 1.25 for 1.50 to determine
fuel flow rate.
All of the above sound like wise items to check.
Which brings the obvious questions...
1. What is that angle (aware that this will vary with aircraft, engine, prop etc)?
2. How are people doing that?
I have a long way to go before I need to do this but just curious.
rmartingt
Well Known Member
Why restrict the flow? Bret has an electronic injection system so you expect to see a substantial return flow to the tanks even at full power.
I'm asking because I'm basically going to be using the same thing in a few years...
bret
Well Known Member
I put the tail on the ground of this A model 7 during one of the fuel flow tests, in my opinion, these tanks do not have a problem with a nose high attitude, the pickup tube slopes down and to the rear bottom of the tank, I measured less than one cup of unusable fuel, I have not done the nose low fuel flow test but I am thinking this will show a greater value of unusable, in any case, all this is being documented in the build log.
BillL
Well Known Member
I did not know that, never mind. I just saw the 45 GPH and it is typical of the free flowing standard pump. Some thinking would have to occur to determine how to test this in a representative manner. He still might need to just run the system to charge the loop, then bleed off the 125% number from there. That might take a ball valve.
The point is to have pressures and flows representative of max fuel flow x 125% while the tank is being emptied. This way an accurate remaining (unusable) fuel amount can be measured. It might take a different technique to assess the shut off point, as it can suck air and still have some loop pressure. The basic test principle and objective is the same, but not the exact process.
Keep it simple!
The unusable fuel test is best done in real flight testing.
There is no good way of simulating aircraft attitude for this test unless you have a hoist to elevate the entire aircraft and position it in different attitudes and don't forget you'll be fooling with fuel flowing at all times and collecting measurements, so save this one for flight testing.
How I did it:
Running the left tank down to 2 Gallons and start testing.
Establish Vx until engine quits.
Land airplane on full tank and refuel.
Note quantity and calculate unusable fuel.
Repeat for right tank.
For the RV-10 and the RV-8 it was less than a gallon and for good measure I
use 2 gallons as the absolute minimum and have my fuel warning level set a 5 Gallons. In 400 hours of flying the 10 I have yet to get anywhere near that 2 gallons of unusable fuel.
The unusable fuel test is best done in real flight testing.
There is no good way of simulating aircraft attitude for this test unless you have a hoist to elevate the entire aircraft and position it in different attitudes and don't forget you'll be fooling with fuel flowing at all times and collecting measurements, so save this one for flight testing.
How I did it:
Running the left tank down to 2 Gallons and start testing.
Establish Vx until engine quits.
Land airplane on full tank and refuel.
Note quantity and calculate unusable fuel.
Repeat for right tank.
For the RV-10 and the RV-8 it was less than a gallon and for good measure I
use 2 gallons as the absolute minimum and have my fuel warning level set a 5 Gallons. In 400 hours of flying the 10 I have yet to get anywhere near that 2 gallons of unusable fuel.
Ya'll are talking about two different things, (a) fuel flow and (b) unusable fuel.
In terms of fuel flow, Bret is good to go. He has 45 GPH after the regulator, while maintaining 35 PSI in the fuel rail. Tee a valve into the fuel rail and bleed off the equivalent of fuel burn at WOT full rich plus some for the FAA (say 17 x 125%, or 21.25 GPH), and the tank return will flow at 23.75 because rail pressure is regulated. The pump supplied the rail with 45 GPH either way.
Unusable fuel is not found at Vx, i.e. highest expected angle, nose up.
Here's what the FAR dictates for a certified airplane:
23.959(a) The unusable fuel supply for each tank must be established as not less than that quantity at which the first evidence of malfunctioning occurs under the most adverse fuel feed condition occurring under each intended operation and flight maneuver involving that tank.
Most RV models place the pickup in the bottom rear of the tank. This SB provides an illustration:
http://vansaircraft.com/pdf/sb06-2-23.pdf
So, the most adverse fuel feed condition of all possible operations would be nose down. How far down? Ahhh, let the debate begin! One camp will say pitch down so as to result in best glide, another as appropriate for a typical power off descent, and a third as appropriate for nose down at Vne, throttle against the idle stop. In all of these, the fuel pool in the front of the tank is unusable, the only difference being how much.
Of course, we could argue the most adverse condition would be hard slip toward the tank in use. That would make about half the tank volume unusable
In terms of fuel flow, Bret is good to go. He has 45 GPH after the regulator, while maintaining 35 PSI in the fuel rail. Tee a valve into the fuel rail and bleed off the equivalent of fuel burn at WOT full rich plus some for the FAA (say 17 x 125%, or 21.25 GPH), and the tank return will flow at 23.75 because rail pressure is regulated. The pump supplied the rail with 45 GPH either way.
Unusable fuel is not found at Vx, i.e. highest expected angle, nose up.
Here's what the FAR dictates for a certified airplane:
23.959(a) The unusable fuel supply for each tank must be established as not less than that quantity at which the first evidence of malfunctioning occurs under the most adverse fuel feed condition occurring under each intended operation and flight maneuver involving that tank.
Most RV models place the pickup in the bottom rear of the tank. This SB provides an illustration:
http://vansaircraft.com/pdf/sb06-2-23.pdf
So, the most adverse fuel feed condition of all possible operations would be nose down. How far down? Ahhh, let the debate begin! One camp will say pitch down so as to result in best glide, another as appropriate for a typical power off descent, and a third as appropriate for nose down at Vne, throttle against the idle stop. In all of these, the fuel pool in the front of the tank is unusable, the only difference being how much.
Of course, we could argue the most adverse condition would be hard slip toward the tank in use. That would make about half the tank volume unusable
bret
Well Known Member
Good points from everyone, thanks for the input, so with those that are flying, what is (your) unusable amount for nose down, best glide angle, I think that will be the most important figure as far as unusable, like Dan noted, the pickup is in the rear of the tanks and while pointed down, we will have (gallons) I think? unusable?
Robert Anglin
Well Known Member
About 1.5 in the left tank an about 3 in the right tank. We have a full mil.spec type inverted pickup in the right tank. I set my red alarm at 5 on each side, with yellow set at 8. That's just me, I know I want hurt anything running a tank dry, but I just don't like to do it if I don't have to. So far, so good.
I would still check with your DAR or FSDO and look the system over very well. Van's fuel tanks and stock plumbing if installed per plans is good as is for the engine rated for that air frame. Just me talking, Yours, R.E.A. III #80888
Jesse
Well Known Member
All regulations aside (I think that has been covered), when I am planning a flight considering max range I burn both tanks down to half or third tank then I run one tank dry, slipping the plane so the fuel in that tank comes inboard. I always do this in cruise, so level flight attitude, and run it until the fuel flow starts to drop in a carb or until fuel pressure starts to drop when fuel injected,mother I switch to the other tank. In real life, that leaves probably a quart of fuel or less in the tank run dry. Then I know where all of my fuel is and have less chance of unporting that tank. Again, this may not be able to be used in an official unusable fuel calculation, but in real life, it works this way if handled right.
I knew this was coming and I can't argue with what the regs say.
In practice however, you don't need fuel in a nose down attitude glide.
If you need altitude you climb and the fuel will be right where you want it,
all the way back in the tank where the pick up tube is located.
I know, it is a simplistic approach but very reliable no matter what the regs
would have you do.
az_gila
Well Known Member
Since we don't have to meet the certified aircraft requirements, but can follow the suggestions in AC 90-89a, I say just to follow the Advisory Circular and do the test nose high. This is the first test flight condition the FAA/EAA is addressing.
page 23 here (PDF page 30) -
http://www.faa.gov/documentlibrary/media/advisory_circular/ac 90-89a.pdf
Fuel flow test angle
I am about to do the nose high test in my RV-8. The form that came in the EAA registration set of documents refers to " most critical attitude (such as initial take-off attitude". What angle is this? Three point attitude, Vx or critical AOA (stall)? From a practical perspective should I test with the tail wheel on level ground or put the tail wheel in a ditch to achieve some greater angle of the canopy rail?
What does Lycoming say about the fuel consumption at max take-off power for an XIO-360-M1B?
I am about to do the nose high test in my RV-8. The form that came in the EAA registration set of documents refers to " most critical attitude (such as initial take-off attitude". What angle is this? Three point attitude, Vx or critical AOA (stall)? From a practical perspective should I test with the tail wheel on level ground or put the tail wheel in a ditch to achieve some greater angle of the canopy rail?
What does Lycoming say about the fuel consumption at max take-off power for an XIO-360-M1B?
