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  #1  
Old 03-30-2020, 10:38 AM
ebackscheider ebackscheider is offline
 
Join Date: Aug 2018
Location: Lafollette, TN
Posts: 44
Default Speed Question

Hey All, I'm new to an RV6 and I have a FP prop with a O360 power plant. I don't know the specs on the prop, but I will get that when I go to the airport next. I also have the old wheel pants and landing gear fairings.

At 2300 rpm I'm getting about 142kts indicated. I hear stories of 160+ kts in a 6, and talked to a guy yesterday that is getting 155 with an O320.

What do I start with to find where I'm bleeding speed from?

Thanks in advance for your thoughts!
Eric
eric at StopFlyingScared dot com
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RV6 - N6014Y - Flying
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  #2  
Old 03-30-2020, 10:59 AM
sjhurlbut sjhurlbut is offline
 
Join Date: Jan 2005
Posts: 870
Default

To measure cruise speed you need to specify altitude. Do you mean 142 kts true or indicated?

2300 rpm cruise for a FP is very low. I cruise at about 2550 rpm.

You're bleeding speed by pulling throttle back too far.



Quote:
Originally Posted by ebackscheider View Post
Hey All, I'm new to an RV6 and I have a FP prop with a O360 power plant. I don't know the specs on the prop, but I will get that when I go to the airport next. I also have the old wheel pants and landing gear fairings.

At 2300 rpm I'm getting about 142kts indicated. I hear stories of 160+ kts in a 6, and talked to a guy yesterday that is getting 155 with an O320.

What do I start with to find where I'm bleeding speed from?

Thanks in advance for your thoughts!
Eric
eric at StopFlyingScared dot com
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  #3  
Old 03-30-2020, 11:01 AM
WingsOnWheels WingsOnWheels is offline
 
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Location: Plano, TX
Posts: 2,137
Default

What are your TAS numbers? All the published numbers are true, not indicated, so that is the first place to start your comparison. Go up to 8,000ft density altitude. Run it wide open, note the RPM, TAS, FF and post those up.

EDIT: I see everyone beat me to it while I was yapping on the phone. I am a little slower than I would like, think my prop is a bit underpitched. I see 168kTAS at 8,000DA 2750 RPM. (O-360 FP Catto). I would expect about 172-3.
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Last edited by WingsOnWheels : 03-30-2020 at 11:07 AM.
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  #4  
Old 03-30-2020, 12:21 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,002
Default

Quote:
Originally Posted by ebackscheider View Post
Hey All, I'm new to an RV6 and I have a FP prop with a O360 power plant. I don't know the specs on the prop, but I will get that when I go to the airport next. I also have the old wheel pants and landing gear fairings.

At 2300 rpm I'm getting about 142kts indicated. I hear stories of 160+ kts in a 6, and talked to a guy yesterday that is getting 155 with an O320.

What do I start with to find where I'm bleeding speed from?

Thanks in advance for your thoughts!
Eric
eric at StopFlyingScared dot com
shouldn't compare speeds without considering fuel flow and altitude, if looking to compare. I get 159 knots (TAS) at 2730 RPM at 8.1 GPH at 8-9000' with my IO-320 (EI) and FP prop. Your numbers seem low. Make sure you have accurately calculated TAS. Also need to do a 4 point GPS test to verify your static setup. Mine was off by 10 knots until I made a static port fence.

with an FP prop, you need to be turning much closer to 2600 or 2700 for higher speeds. 2300 is way too low. If that RPM is achieverd with WOT at 8000', you are WAY over pitched. Just my opinion, but a properly pitched prop should turn 2700 somwhere between 8K' and 12K' (based upon your goals) when WOT and 100* ROP.

Larry
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Last edited by lr172 : 03-30-2020 at 12:30 PM.
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  #5  
Old 03-30-2020, 12:26 PM
ebackscheider ebackscheider is offline
 
Join Date: Aug 2018
Location: Lafollette, TN
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Default Thanks!

Thanks all!

I will go do a test, maybe even later today. 8000 ft density, wide open and report back on the speeds I see.

I guess my old days of 23 sq with CS are hurting me

Eric
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RV6 - N6014Y - Flying
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CFI - Acro in the 6 Rocks!
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  #6  
Old 03-30-2020, 01:08 PM
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Sam Buchanan Sam Buchanan is offline
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Location: North Alabama
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Quote:
Originally Posted by ebackscheider View Post
Thanks all!

I will go do a test, maybe even later today. 8000 ft density, wide open and report back on the speeds I see.

I guess my old days of 23 sq with CS are hurting me

Eric
I think you will like what you see once you put your -6 into high gear.
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  #7  
Old 03-30-2020, 01:15 PM
WingsOnWheels WingsOnWheels is offline
 
Join Date: Mar 2009
Location: Plano, TX
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Default

Quote:
Originally Posted by ebackscheider View Post
Thanks all!

I will go do a test, maybe even later today. 8000 ft density, wide open and report back on the speeds I see.

I guess my old days of 23 sq with CS are hurting me

Eric

Open her and see what she can do!
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PP SEL / A&P
I donate every year on my B-Day (in Dec), but donated early in Sep'19.
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  #8  
Old 03-30-2020, 01:47 PM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,309
Default

Quote:
Originally Posted by ebackscheider View Post
Thanks all!

I will go do a test, maybe even later today. 8000 ft density, wide open and report back on the speeds I see.

I guess my old days of 23 sq with CS are hurting me

Eric
Just be sure the speed you are looking to see is True Air Speed, not indicated (as already mentioned)

Indicated air speed is nearly useless for doing speed comparisons.

Using my fixed pitch O-360 powered RV-6A as an example - At 11,500 ft and a fuel flow of 7.8 - 8.0 GPH I can get true air speeds of about 195 MPH but my indicated airspeed is often 160 MPH or less.
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  #9  
Old 03-30-2020, 07:11 PM
ebackscheider ebackscheider is offline
 
Join Date: Aug 2018
Location: Lafollette, TN
Posts: 44
Default Some data

Did a short flight tonight

8,000 ft Density Alt
Turning about 2650 RPM

TAS right at 160 KTS - 184MPH

I don't have a fuel flow yet, so I have no idea where that was. The spike was some issue with the data.



Thanks for the help, I just need to push the throttle forward a bit more I guess.
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Eric Backscheider

2020 Dues Paid!

RV6 - N6014Y - Flying
Pitts S2B - 245JH - Sold
CFI - Acro in the 6 Rocks!
StopFlyingScared.com
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  #10  
Old 03-30-2020, 10:04 PM
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Sam Buchanan Sam Buchanan is offline
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Default

That sounds about right for old-style wheel pants and fairings. You would pick up a few knots with the newer stuff.

Glad you have unlocked the potential of your -6.
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