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  #1  
Old 10-27-2020, 12:14 AM
iamtheari iamtheari is offline
 
Join Date: Nov 2017
Location: ND
Posts: 479
Default Pitch for Unusable Fuel Test

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?
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  #2  
Old 10-27-2020, 06:31 AM
MED MED is offline
 
Join Date: Jul 2015
Location: Aiken, SC
Posts: 638
Default

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.
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140236
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  #3  
Old 10-27-2020, 06:54 AM
Nova RV Nova RV is offline
 
Join Date: Aug 2015
Location: Leesburg, VA
Posts: 498
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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."
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RV-14A kit # 140243 (flying as of 11/18)

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  #4  
Old 10-27-2020, 07:17 AM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest
Posts: 1,149
Default 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?
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WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

Dues paid 2020, worth every penny

RV9A- Status:
Tail 98% done
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  #5  
Old 10-27-2020, 09:06 AM
iamtheari iamtheari is offline
 
Join Date: Nov 2017
Location: ND
Posts: 479
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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.
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  #6  
Old 10-27-2020, 10:00 AM
Desert Rat Desert Rat is offline
 
Join Date: Aug 2018
Location: 50-50 Wichita KS & Scottsdale AZ
Posts: 392
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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.
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  #7  
Old 10-27-2020, 10:03 AM
romaja romaja is offline
 
Join Date: Jan 2016
Location: Portland Oregon Area
Posts: 89
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Quote:
Originally Posted by MED View Post
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.
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
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  #8  
Old 10-27-2020, 10:09 AM
iamtheari iamtheari is offline
 
Join Date: Nov 2017
Location: ND
Posts: 479
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Quote:
Originally Posted by Desert Rat View Post
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.
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  #9  
Old 10-27-2020, 10:25 AM
schristo@mac.com's Avatar
schristo@mac.com schristo@mac.com is offline
 
Join Date: Sep 2007
Location: WA
Posts: 991
Default 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.
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  #10  
Old 10-27-2020, 10:55 AM
Desert Rat Desert Rat is offline
 
Join Date: Aug 2018
Location: 50-50 Wichita KS & Scottsdale AZ
Posts: 392
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Quote:
Originally Posted by iamtheari View Post
...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.
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