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  #1  
Old 06-30-2019, 09:12 PM
gwav8or gwav8or is offline
 
Join Date: Apr 2009
Location: Durant, Ok
Posts: 27
Default RV-6 Cruise Speed

I know this has been discussed before so please forgive me. I?m considering buying a 6 that is currently for sale. It?s a 6 not a 6A. It has the O-320 160 HP up front. It?s got about 40 hours since major. The owner says they get about 160 mph at 5k and 2400 RPM. That works out to about 140kts. I?ve read that people get 150-155kts in the 6. So where am I going wrong here or what am I missing?
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  #2  
Old 06-30-2019, 09:18 PM
moosepileit moosepileit is offline
 
Join Date: Dec 2010
Location: Louisville, KY
Posts: 749
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Need prop make/model/diameter and pitch.

"Get" 160 MPH? Indicated? That trues out about 172 mph standard day. No wind that would then be a GPS ground speed.

They might have a climb prop. The 77 inch pitch Sens 70CM6 in 77 inch pitch at 2400 RPM would be close.

They might have less than perfect pitot/static calibration.

The Tach can be off- is it known accurate?

It might be a bit out of rig or not fully faired..

Do they have an accurate fuel flow meter?
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Last edited by moosepileit : 06-30-2019 at 09:26 PM.
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  #3  
Old 06-30-2019, 09:20 PM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,678
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Quote:
Originally Posted by gwav8or View Post
I know this has been discussed before so please forgive me. I?m considering buying a 6 that is currently for sale. It?s a 6 not a 6A. It has the O-320 160 HP up front. It?s got about 40 hours since major. The owner says they get about 160 mph at 5k and 2400 RPM. That works out to about 140kts. I?ve read that people get 150-155kts in the 6. So where am I going wrong here or what am I missing?
The question is whether he's using indicated or true airspeed. I would expect 150+ knots if the prop is reasonably pitched for the airplane and the airplane has all of its fairings.
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Marietta, GA
2001 RV-6 N46KB
2019(?) RV-10
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  #4  
Old 07-01-2019, 05:19 AM
smokyray's Avatar
smokyray smokyray is offline
 
Join Date: Jan 2005
Location: TX32
Posts: 1,968
Default Speed O? Light...

Quote:
Originally Posted by gwav8or View Post
I know this has been discussed before so please forgive me. I’m considering buying a 6 that is currently for sale. It’s a 6 not a 6A. It has the O-320 160 HP up front. It’s got about 40 hours since major. The owner says they get about 160 mph at 5k and 2400 RPM. That works out to about 140kts. I’ve read that people get 150-155kts in the 6. So where am I going wrong here or what am I missing?
Grant,
The RV series in stock configuration will, properly rigged, faired and propped render roughly 1 Knot cruise speed per HP. This holds true up to 175Knots where an aerodynamic wall emerges that no matter how much HP, the airplane won’t exceed, around 190 KTAS. To go faster than that requires a significantly higher HP number and more aggressive drag reduction. Case in point, Dave Anders RV4:
https://youtu.be/gCONImxbs7g

That said, much depends on your prop and again how you’re measuring indicated vs true vs ground speed, as mentioned above.
My RV6”X” (when it had 150HP) would easily True at 155Knots at 8500’ with stock fairings and a 2 blade Catto. Vans magic formula altitude for optimum cruise on the tables is taken at 8500’/75% power. A good measuring point for 75% power roughly computes to (first 2 digits) of MP+RPM=48. ie. 24+24=48

I recommend flying the airplane and observing the GS over a triangular course at a consistent power setting and see what you get. At 5500 feet set the power for a bit and see what RPM/MP and IAS and post it.

I’m sure there will be lots of dos centavos offered...

V/R
Smokey

PS: After installing an 0-360J, a few clean up mods and a plenum plus a Gen2 Catto prop the RV6X now produces 175KTAS at the same altitude, but at a slightly higher fuel burn. Nothing is free...

Last edited by smokyray : 07-01-2019 at 05:33 AM.
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  #5  
Old 07-01-2019, 11:07 AM
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gmcjetpilot gmcjetpilot is offline
 
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Default ts

Quote:
Originally Posted by gwav8or View Post
I know this has been discussed before so please forgive me. I’m considering buying a 6 that is currently for sale. It’s a 6 not a 6A. It has the O-320 160 HP up front. It’s got about 40 hours since major. The owner says they get about 160 mph at 5k and 2400 RPM. That works out to about 140kts. I’ve read that people get 150-155kts in the 6. So where am I going wrong here or what am I missing?
Van's RV are one of the kits that was sold back in the day to present that actually did what was advertised. Issues with speed? Could be different things. Have a picture?

"The owner says they get about 160 mph at 5k and 2400 RPM"

What is the fuel burn? It sounds like he has it throttled back. To compare apples and apples you should fly it FULL THROTTLE at Sea level and ALSO at 8,000 feet WOT. These are typical standard bench marks. This might not be possible if the prop is under pitched and over revs (2700 RPM). However you can over rev the engine slightly, I'd recommend not going over 2800 rpm (although people drive around all day at 2900 RPM).

Yes his AS and RPM instruments may be off. As recommended do at least three leg triangle, fly constant heading (note GPS GS and tracks) and average all three GPS speeds.

What is the empty weight and CG?

Fit and finish. Fairings, rigging?

40 hrs SMOH Engine? OK I am not saying don't trust but verify. Who did the OH and what was replaced, reconditioned? I'd look at all the receipts and do a compression test. I'd check oil use, fly the thing an hour or three and check oil use. (Note Lycs blow off the anything over 6 qts quickly even if they say they hold 8 qts so don't top it off with oil). SMOH means different things to different people. Why did he OH it? Prop strike? Engine issues?

A strong 160HP engine should pull that RV through the air nicely. Don't insult the guy but it is reasonable to ask questions. A good OH is going to cost $10,000 to $15,000 with new jugs (wild guess from memory it may be different today). Did they OH the Mags and Carb? The price should reflect this. If it is cheap I'd be suspicious.

PROP - At WOT and RPM at SL should be able to over rev the engine... (Red Line is 2700). If it can't pull over 2700 RPM it means it has too much prop pitch. Way too high vise verse. Both will affect your speed.

It is possible the engine under powered (not making 160HP) or airframe too draggy.

What kind of exhaust does it have? Cross Over? 4 into 4? 2 into 1 each side (the worst design).

Van gets his data from a stock airframe with good workmanship, good stock Lyc and always LIGHT WEIGHT. Weight is a factor in speed. A clean 160HP RV-6 should be able to do (75% power) 191MPH (166 Kts) to (55%) 172 MPH (149.5 Kts). You are 10 Kts slow assuming he is quoting 55% power, which is a lot. Top speed WOT sea level should be around 200MPH.
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Last edited by gmcjetpilot : 07-01-2019 at 12:37 PM.
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  #6  
Old 07-01-2019, 11:52 AM
SPX SPX is online now
 
Join Date: Dec 2018
Location: San Diego
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Quote:
Originally Posted by gmcjetpilot View Post
A strong 160HP engine should pull that RV through the air nicely. Don't insult the guy but it is reasonable to ask questions. A good OH is going to cost $10,000 t0 $15,000 with new jugs (wild guess from memory it may be different today). Did they OH the Mags and Carb? The price should reflect this. If it is cheap I'd be suspicious.
A great post, but I think your overhaul prices are off about $10,000 - $15,000.
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  #7  
Old 07-01-2019, 12:30 PM
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gmcjetpilot gmcjetpilot is offline
 
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Quote:
Originally Posted by SPX View Post
A great post, but I think your overhaul prices are off about $10,000 - $15,000.
You think it is low or high? I did a quick check and found $17K-$21K (OH cyc vs New cylinders). However that is certified.

If experimental you can get a whole brand new O-320 engine for $26K (experimental, Titan, Superior, Lyc from Vans) and sell your core. It could be a good time to upgrade to a O-340 or O-360.'"

When I overhauled my O-360 it was first run since new, refurbed Cylinder with new valves, seats, springs.... Sent out the case, crank, cam and friend and I put it together.
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RV-4, RV-7, ATP, CFII, MEI, 737/757/767

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Last edited by gmcjetpilot : 07-01-2019 at 12:45 PM.
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  #8  
Old 07-01-2019, 02:17 PM
moosepileit moosepileit is offline
 
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Location: Louisville, KY
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Just one data set from today.

O-320, 9:1, carb, mags, vetterman 1.5" crossovers, sens 70CM6 79" pitch.

8.3 GPH, 8500' DA, 7000' PA, just about wide open.

75% power. 2580 rpm, 21.5 MAP. 161 knots true, or 185 MPH.

Normal fairing and rig.
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  #9  
Old 07-01-2019, 03:09 PM
Timberwolf Timberwolf is offline
 
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Location: Navarre, FL
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Each plane is different, especially with these non prepunched models. Rigging and cowling/fairings can make a big difference. My typical cruise with an angle valve is 2400rpm(CS Hartzell BA)/165ktas at 7.5gph. I’m sure with some more attention to aerodynamics I could easily pick up a few more knots. But for what I use it for we can’t complain.

The one you’re looking at may have something as simple as a gear leg fairing out of whack, being compensated for by some aileron trim. The net result being overall increased drag. There’s some simple things you can do to tune up the airframe whether streaking oil or using tufts and a GoPro to refine the aerodynamics of your airframe. I wouldn’t say the speeds you are seeing are far off from what you could expect, but again based on how well it was built and rigged. Perhaps that airspeed indicator is off due to issues with the static line. Mine always need to be blown out as a little bit of moisture always seems to collect in them and cause erroneous readings.
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  #10  
Old 07-01-2019, 04:12 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 moosepileit View Post
Just one data set from today.

O-320, 9:1, carb, mags, vetterman 1.5" crossovers, sens 70CM6 79" pitch.

8.3 GPH, 8500' DA, 7000' PA, just about wide open.

75% power. 2580 rpm, 21.5 MAP. 161 knots true, or 185 MPH.

Normal fairing and rig.
That is close to what I see with my 1999 RV-6 that has similar equipment.
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