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Pitch for Unusable Fuel Test

iamtheari

Well Known Member
For those of you with flying or nearly flying RV-14's, what pitch attitude have you put the plane in to determine the unusable fuel in your tanks?
 
I used a ratchet strap and pulled the tail down to the hanger floor or as close as the strap would allow. I just drilled the floor and installed a removable tie down ring.:cool:
 
This was taken from AC 90-89B

"e. Fuel Flow. A fuel flow and unusable fuel check 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, and is accomplished by:
(1) 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 the 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."
 
In RV case

I would also think one would like to know useable fuel in a landing attitude. In the case of a Vans fuel tank with the pickup in the back, I would like to know in a go around situation with the fuse level, if the fuel pickups are uncovered. This would mean when I push the throttle forward to start the go around, are the fuel pick ups uncovered until I pitch the nose up?
 
That's my struggle here. More fuel is usable when climbing than when level or descending. I can understand the fuel flow test being done nose-high because the pump has to work against gravity. But a 5-degree nose-down attitude will definitely pull more fuel in the tank away from the screen than 20-degree nose-up.
 
This is an interesting scenario for sure. I don't have anything but opinion, but here are a couple of points to think about.

1- I think that 5* nose down previously mentioned is more than you'll see on a normal approach. An ILS glide slope is normally around 3* and it seems like the deck angle would be more flat than that, unless putting flaps down would make pitch actually lower than the glide path. Maybe an Aero guy can comment here?

2-Seems like if the pickups aren't un-ported in the approach phase, they wouldn't be un-ported in the level off portion of a go around, because if anything, you've improved your situation due to fuel wanting to run aft, both due to pitch change and due to simple acceleration.

Having said all that, I'm guessing that the unusable fuel is probably not more than 2-3 gallons per side and I'd be freaking out if I landed with only 5 gallons left in most airplanes, no matter how much min fuel testing I'd done. Then again, I'm an old pilot, not a bold pilot.

When you find out, please post your results, I'm genuinely curious to see what the actual number is.
 
I used a ratchet strap and pulled the tail down to the hanger floor or as close as the strap would allow. I just drilled the floor and installed a removable tie down ring.:cool:

Would you happen to have a link for the removable tie down ring. Trying to picture what it looks like and how it is set in the floor.
Thanks
 
This is an interesting scenario for sure. I don't have anything but opinion, but here are a couple of points to think about.

1- I think that 5* nose down previously mentioned is more than you'll see on a normal approach. An ILS glide slope is normally around 3* and it seems like the deck angle would be more flat than that, unless putting flaps down would make pitch actually lower than the glide path. Maybe an Aero guy can comment here?

2-Seems like if the pickups aren't un-ported in the approach phase, they wouldn't be un-ported in the level off portion of a go around, because if anything, you've improved your situation due to fuel wanting to run aft, both due to pitch change and due to simple acceleration.

Having said all that, I'm guessing that the unusable fuel is probably not more than 2-3 gallons per side and I'd be freaking out if I landed with only 5 gallons left in most airplanes, no matter how much min fuel testing I'd done. Then again, I'm an old pilot, not a bold pilot.

When you find out, please post your results, I'm genuinely curious to see what the actual number is.
I hadn't thought about flaps. Yikes. My 5-degree thought came from a 4-degree LPV we have locally plus 1 degree of worse-than-real-world conditions. I should have been paying better attention in my transition training to see how much that last bit of flaps affected the pitch angle.

I am also like you. It would take (and be) an emergency if I were anywhere near zero usable fuel on board the plane when I am not on the ground. But for the purposes of measuring what's usable, it's turning into a more interesting exercise than I had initially anticipated.
 
flight check during phase 1

I tested this by running a tank dry to evaluate pressure and flow fluctuations nearing cut off, then, switch tanks, land, fill the empty tank to the caps to get usable. Interesting that it took a little more than 21 gallons.

I built the right tank with a flop tube and trap door... I use this as the last tank and other low fuel operations. If I had it to do over again I would trap door both though.
 
...I hadn't thought about flaps. Yikes. My 5-degree thought came from a 4-degree LPV we have locally plus 1 degree of worse-than-real-world conditions. I should have been paying better attention in my transition training to see how much that last bit of flaps affected the pitch angle...

But here's the thing, just because the airplane is following a 5* glide path, it doesn't necessarily follow that he nose is pointed 5* down. It's just one of those things with lots of variables.
 
But here's the thing, just because the airplane is following a 5* glide path, it doesn't necessarily follow that he nose is pointed 5* down. It's just one of those things with lots of variables.

The number of variables, none of which I can measure right now, is why I said "yikes" on this point. The plane's power-off, full-flaps pitch attitude to follow an X-degree glidepath at approach speed could be well above or well below X.

So that makes me think I should just measure unusable fuel on the ground using a level pitch angle, or even nose-high (taildragger, so that's easy) and then study the particulars of how pitch affects access to the usable fuel during Phase 1.
 
But here's the thing, just because the airplane is following a 5* glide path, it doesn't necessarily follow that he nose is pointed 5* down. It's just one of those things with lots of variables.


It shouldn't be unless your flying near max speed, or unloaded. You should have some AoA. I suspect flying the approach your slowing down an increasing AoA. With flaps you'll require less AoA than without at the same speed; but still some AoA.
 
The number of variables, none of which I can measure right now, is why I said "yikes" on this point. The plane's power-off, full-flaps pitch attitude to follow an X-degree glidepath at approach speed could be well above or well below X.

So that makes me think I should just measure unusable fuel on the ground using a level pitch angle, or even nose-high (taildragger, so that's easy) and then study the particulars of how pitch affects access to the usable fuel during Phase 1.


Not necessarily, this should be known, or a good approximation unless you significantly modified your wing. Sorry I don't know it, but maybe someone will chime in that knows this.
 
If the airplane is built per the plans, hasn't Vans already established these numbers from flight testing and published them?

George
 
If the airplane is built per the plans, hasn't Vans already established these numbers from flight testing and published them?

George
I haven’t seen any published figures for approach AOA, if they’re out there. Maybe I haven’t looked hard enough.
 
I tested this by running a tank dry to evaluate pressure and flow fluctuations nearing cut off, then, switch tanks, land, fill the empty tank to the caps to get usable. Interesting that it took a little more than 21 gallons.

I built the right tank with a flop tube and trap door... I use this as the last tank and other low fuel operations. If I had it to do over again I would trap door both though.

yes, I did the same. run one tank dry while over an airfield circling. waiting for a tank to run dry and the engine to quit is freaky but mine began to stumble before it actually quit. switch to the opposite tank and fly home. fill the empty tank and then you really know. I filled to slightly over 18 gallons in the RV9.
 
I haven’t seen any published figures for approach AOA, if they’re out there. Maybe I haven’t looked hard enough.

Though it should be available. Anyone have savvy data with b an approach. Pitch angle should be in there, and glide path difference between the two is AoA, or relatively close.
 
Though it should be available. Anyone have savvy data with b an approach. Pitch angle should be in there, and glide path difference between the two is AoA, or relatively close.

I promise to generate and make this data available when I am flying, if nobody beats me to it.
 
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