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  #11  
Old 04-08-2016, 10:03 AM
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ArVeeNiner ArVeeNiner is offline
 
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  #12  
Old 04-08-2016, 05:38 PM
sblack sblack is offline
 
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For fuel flow deck angle you want the worst case (highest angle) which is Vx at light weight. But since the target fuel flow for the test is usually 150% of max fuel burn of the engine the deck angle doesn't have to be very accurate.
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  #13  
Old 04-09-2016, 09:32 AM
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So.. we are talking about calculating path through the air PLUS angle of attack plus or minus incidence angle in order to measure attitude at top surface of canopy rails.

Gas tanks should be nearly empty (for minimum head).

I think this test has little relevance to a fuel pumped system other than a yes/no answer on fuel flow which would mean there is a fuel system problem other than deck angle. The change in head requirements will be small compared to pump output pressure.

OTOH, This test is critical for gravity fed systems and the flow rate data would be much more variable and relevant.
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  #14  
Old 04-09-2016, 12:21 PM
sblack sblack is offline
 
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Quote:
Originally Posted by rzbill View Post
So.. we are talking about calculating path through the air PLUS angle of attack plus or minus incidence angle in order to measure attitude at top surface of canopy rails.

Gas tanks should be nearly empty (for minimum head).

I think this test has little relevance to a fuel pumped system other than a yes/no answer on fuel flow which would mean there is a fuel system problem other than deck angle. The change in head requirements will be small compared to pump output pressure.

OTOH, This test is critical for gravity fed systems and the flow rate data would be much more variable and relevant.
A yes no answer on fuel flow is pretty important if you want to survive your first flight. And there are any number of construction errors that could reduce fuel flow for a pumped system.

A friend of mine bought the wrong electric fuel pump. There is one kind that has a bypass and one that doesn't. He didn't bother to do the fuelflow test and found out in the air that when he turned off the boost pump the engine quit. It could not run on the mech pump alone.

So this test is fundamental for first flight safety for any type of fuel system.
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  #15  
Old 04-09-2016, 01:31 PM
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You completely missed my point. Of course a fuel flow test is important before first flight. My point is that to expect a measurable fuel flow rate change due to attitude on an RV is not realistic.
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  #16  
Old 04-09-2016, 02:03 PM
BillL BillL is offline
 
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Interesting how much discussion there is on an assumed test protocol wwith an assumed test objective. Unless that test is documented, then one can not effectively engage with the usefulness of the test. RZBill is right, flow is not a pass fail criterion, at least vs gravity vector angle. It is valid for pass/fail of a pump. 125% of TO fuel flow at minimum supply pressure to carb or FI is the tipping point.

Dave Prizio did an EAA webinar on unusable fuel testing and it was better than the AC to which it referenced. Having participated in a ground test, it is good to see if there is air in the system being pumped to the carb or to the injection system, and if there are any fuel leaks. A static 30 pis air pressure test is best for finding a leak, but it is prudent to enable an observation of same during a unusable fuel test. Neither Daves, or the AC, should be followed blindly. One should consider the location and effects of fuel pickup points in the tank to fully develop conditions for a model/plane specific test sequence.

A nose up, nose down test at minimum pressures, measuring fuel flow for cruise and max TO is simply a test condition for the unusable fuel. The suction test needed is to measure the absolute pressure to the inlet of the mechanical pump under the power stall nose up condition. Then using vapor pressure, one can determine if cavitation is likely to occur for the fuel selected. It may be fine for 100LL, but fail for 100% auto gas. Slip testing is also needed to complete the unusable fuel testing, but it will be a flight test, tricky as it is.
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  #17  
Old 04-10-2016, 09:17 AM
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Quote:
Originally Posted by sblack View Post
For fuel flow deck angle you want the worst case (highest angle) which is Vx at light weight. But since the target fuel flow for the test is usually 150% of max fuel burn of the engine the deck angle doesn't have to be very accurate.
Agree, and I'd add that the worst case is actually full power, nose-high stall. That will have a significantly different deck angle than would a full power Vx climb.
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  #18  
Old 04-10-2016, 02:24 PM
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Here are my numbers.

xo-320 RV-9

Vne
Never Exceed Speed
182 KTS
210 MPH

Vno
Maximum Structural Cruising Speed
156 KTS
180 MPH

Va
Maneuvering Speed
102 KTS
118 MPH

Vfe*
Maximum Flap Extended Speed
78 KTS
90 MPH

Vglide
Best Glide Speed
82 KTS
95 MPH

Vy
Best Rate of Climb
82 KTS
95 MPH


Vx
Best Angle of Climb
71 KTS
82 MPH


Vs
Stall Speed Clean
50 KTS
58 MPH


Vso
Stall Speed Landing Configuration
43 KTS
49 MPH
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  #19  
Old 04-10-2016, 02:35 PM
sblack sblack is offline
 
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Quote:
Originally Posted by ChiefPilot View Post
Agree, and I'd add that the worst case is actually full power, nose-high stall. That will have a significantly different deck angle than would a full power Vx climb.
Ya didn't think of that one.
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  #20  
Old 04-10-2016, 04:57 PM
ka6dan ka6dan is offline
 
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Hint

Before you do the V testing make sure your airspeed has been calibrated. Spent some time with stall and AOA before I established my airspeed indications were off.
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