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AMPTestFE

C-130H Performance / Drag Too High

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AMPTestFE

Ok, so I'm out at base X flying our 4 '74 models and notice a trend.  After climbing up to our cruise ceiling, we can't true out until an hour or two later....so I started running some other charts.  I first would watch our TAS until we just hit 300, then took a snapshot of average torque, gross weight, OAT, alt, etc.  I would then run the IAS for 300TAS chart, which might have come out with something like 12,000 in lbs, before the drag correction.  On page 2 (drag correction), I would correct for our advertised ~+20 index, and would come up with a value much less than what it just took us to creep up to 300 TAS.  So then, I would come in backwards with my average actual torque on the left, then intersect with the charted value from the bottom.  For each of our 4 airplanes, the result varied from a +70 to +60 drag index.  On subsequent flights, I would calculate our cruise ceiling with this new value.  When we'd get to top of climb, guess what...we'd true out almost exactly at 300.  I know some will ask about engine performance, but this method takes that out of the equation.  Torque is torque, regardless of engine performance values.

And no, we didn't forget the flaps....

So....has anyone else noticed the H being too draggy like this?  I'm wondering if the engineers mis-calculated the drag value of LAIRCM or something.

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NATOPS1

Based on your post I would guess you have gone through the entire list of drag corrections for different aircraft configurations. The baseline model the testing was conducted on plus any mods (+20) seems low to me but I do not know your configuration. Check the paint type on the test aircraft, there have been lots of "changes" with not many updates to the performance manual so being off by 50 doesent seem too far fetched.  

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CTII Raven
On 4/27/2017 at 1:25 PM, AMPTestFE said:

Ok, so I'm out at base X flying our 4 '74 models and notice a trend.  After climbing up to our cruise ceiling, we can't true out until an hour or two later....so I started running some other charts.  I first would watch our TAS until we just hit 300, then took a snapshot of average torque, gross weight, OAT, alt, etc.  I would then run the IAS for 300TAS chart, which might have come out with something like 12,000 in lbs, before the drag correction.  On page 2 (drag correction), I would correct for our advertised ~+20 index, and would come up with a value much less than what it just took us to creep up to 300 TAS.  So then, I would come in backwards with my average actual torque on the left, then intersect with the charted value from the bottom.  For each of our 4 airplanes, the result varied from a +70 to +60 drag index.  On subsequent flights, I would calculate our cruise ceiling with this new value.  When we'd get to top of climb, guess what...we'd true out almost exactly at 300.  I know some will ask about engine performance, but this method takes that out of the equation.  Torque is torque, regardless of engine performance values.

And no, we didn't forget the flaps....

So....has anyone else noticed the H being too draggy like this?  I'm wondering if the engineers mis-calculated the drag value of LAIRCM or something.

Having been part of DIRCM/LAIRCM flight test of at least 7 different C-130s, not to mention the wind tunnel testing of the original SOF DIRCM installation I'd say the drag estimate is reasonably close, certainly within the error bars of a sharp pencil

 

FWIW the handling flights of the Talon II (85-0012) were the most "interesting"  - "Some approaches to stalls are closer than others"

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US Herk
On 4/30/2017 at 10:22 PM, CTII Raven said:

FWIW the handling flights of the Talon II (85-0012) were the most "interesting"  - "Some approaches to stalls are closer than others"

That's because of that huge nose...below 110KCAS or so, airspeed becomes unreliable...they should've moved the pitot tubes out to the wings or something! ;)

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CTII Raven
On 5/8/2017 at 10:27 PM, US Herk said:

That's because of that huge nose...below 110KCAS or so, airspeed becomes unreliable...they should've moved the pitot tubes out to the wings or something! ;)

"It's a subsonic aircraft"

Direct quote from then IBM when that was brought up at the CDR.

But hey, the aircraft have the coffee can mods ...

 

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AMPTestFE

Wasn't 0012 the one that had two separate incidences of runaway elevator trim?

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