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11-11-2011, 12:15 PM
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Join Date: Jun 2005
Location: Milwaukee, WI area
Posts: 2,967
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Quote:
Originally Posted by steve91t
Just got clarification, 65% power, 2450 RPM in cruise at 8000 ft. The 155kt cruise matches Vans numbers if he were using 55% power.
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Sounds about right with those numbers. I had a three blade fixed pitch, and always saw 160kts at 2450rpm, which was my preferred cruise setting. I had a light airplane too, but your numbers are comparable.
One other thing to check is to verify your OAT is calibrated and accurate. Mine was off in the beginning and I had to compensate for it's position (NACA duct) with the EFIS, but once I got that dialed in, I had an accurate reading that checked out with the GPS box run.
__________________
Chad Jensen
Astronics AES, Vertical Power
RV-7, 5 yr build, flew it 68 hours, sold it, miss it.
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11-11-2011, 12:21 PM
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Join Date: Aug 2009
Location: texas
Posts: 68
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I am with you
FWIW I am seeing the same numbers as you.
Hartzell BA CS (2 blades)
IO-360 mattituck std compression
RV-7
9k-10k
8gph
155-160 KTAS
I filled the emp tips and taped over the hinge gaps.
I am really wondering what magic tricks you 165 plus guys pulled out of your hats. I wanna know!!
High compression pistons maybe?
I know... its the marvel mystery oil!
Marco
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11-11-2011, 12:54 PM
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Join Date: Mar 2006
Location: Newport, TN
Posts: 7,496
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After paint I can get 175ktas @ 8000ft but that is WOT and leaned out.
180hp
FP Sensenich
RV7
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11-11-2011, 12:55 PM
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Join Date: Mar 2005
Location: Bellevue, NE
Posts: 686
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Quote:
Originally Posted by steve91t
Well, everything seems to match the GPS. We were at 9000 last month showing 155kts true. GPS said we had 7 kts on the tail, showing 162 across the ground.
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Correct me if I'm wrong, but isn't the wind speed and direction derrived from the relationship of TAS, heading, ground track and ground speed. So of course its going to make sense...it's computed.
Now a 3- or 4-way gps ground speed test run factors out the wind so that all you have left is TAS by virtue of GS...which is what you are trying to verify.
Right?
Jim
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11-11-2011, 01:15 PM
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Join Date: Jun 2005
Location: Chino, CA
Posts: 738
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Quote:
Originally Posted by leaker311
FWIW I am seeing the same numbers as you.
Hartzell BA CS (2 blades)
IO-360 mattituck std compression
RV-7
9k-10k
8gph
155-160 KTAS
I filled the emp tips and taped over the hinge gaps.
I am really wondering what magic tricks you 165 plus guys pulled out of your hats. I wanna know!!
High compression pistons maybe?
I know... its the marvel mystery oil!
Marco
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Don't know what your power settings are, but I would guess if you are leaned
to 8 gph you are in the 60% power area. And if that is so, then your speed
is about right. Push the go knobs up to 2500 rpm and WOT with about 9 gph
and you would be around 65% power and I'll bet your TAS is in the 168 knot
range.
As others have mentioned, TAS is only as accurate as the ASI and outside
air temp gage. A three or four way gps run is the only accurate method
of determining TAS.
__________________
Tom Prokop
Chino, CA
RV-8A,180/CS/Carb, AFS 4500 EFIS/EMS
RV-6, sold, 820 hrs of fun.
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11-11-2011, 01:29 PM
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Join Date: Nov 2010
Location: Huntersville, NC
Posts: 138
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So flying around at low alt with no wind, the gps matches the tas. Are you guys saying to fly the box pattern at 8000ft? Could it be accurate down low, then be way off at altitude?
Not saying that it isn't an indication problem, just saying after a year of flying the plane, everything seems to add up to proper indications.
If it was that off, on a long cross country, the ETA would be screwed up. And it's not. It's dead on.
Does this more or less rule out a low tas reading?
Last edited by steve91t : 11-11-2011 at 01:32 PM.
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11-11-2011, 01:39 PM
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Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,351
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Quote:
Originally Posted by steve91t
So flying around at low alt with no wind, the gps matches the tas. Are you guys saying to fly the box pattern at 8000ft? Could it be accurate down low, then be way off at altitude?
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Yes, it is possible with a number of factor, including the inaccurate OAT or the fact that it is difficult to determine NO WIND condition. So the best and more accurate way is to do it at multiple altitude and compare results.
Another way to check your static accuracy is to check for altitude, setting and noting of your altimeter setting at any given airport and then do a relatively low pass to compare.
__________________
Mehrdad
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Flying
Dues paid
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11-11-2011, 01:48 PM
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Join Date: Nov 2005
Location: AUSTRALIA
Posts: 749
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Steve,
Need to know how the engine is being leaned as this will have a huge effect on power.
From Lycoming's graphs for the I0-360 at your 8.5 g/h and 2,550 rpm (post #1):
At Best Economy settings (Peak or LOP) power is 112 hp or 62%
At Best Power settings (around 150 degrees ROP) power is 90 hp or 50%
This 22 hp difference for the same FF and rpm could explain the slower TAS.
Fin
9A
Last edited by Finley Atherton : 11-11-2011 at 02:08 PM.
Reason: Had Tom instead of Steve
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11-11-2011, 02:20 PM
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Join Date: Nov 2010
Location: Huntersville, NC
Posts: 138
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Quote:
Originally Posted by Finley Atherton
Steve,
Need to know how the engine is being leaned as this will have a huge effect on power.
From Lycoming's graphs for the I0-360 at your 8.5 g/h and 2,550 rpm (post #1):
At Best Economy settings (Peak or LOP) power is 112 hp or 62%
At Best Power settings (around 150 degrees ROP) power is 90 hp or 50%
This 22 hp difference for the same FF and rpm could explain the slower TAS.
Fin
9A
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I was incorrect in my first post. He actually runs it at 2450 revs. I know he runs it just rich of peak. Not sure exactly how much, but I know he said it's why Lycoming recommends.
I think he should just turbo it and be done with it 
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11-11-2011, 02:21 PM
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Join Date: Nov 2010
Location: Huntersville, NC
Posts: 138
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Quote:
Originally Posted by Bavafa
Yes, it is possible with a number of factor, including the inaccurate OAT or the fact that it is difficult to determine NO WIND condition. So the best and more accurate way is to do it at multiple altitude and compare results.
Another way to check your static accuracy is to check for altitude, setting and noting of your altimeter setting at any given airport and then do a relatively low pass to compare.
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I like the 2nd option. Sounds like more fun 
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