What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

RV-6 Cruise Speed

gwav8or

Member
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?
 
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?
 
Last edited:
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.
 
Speed O? Light...

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:
ts

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.
 
Last edited:
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.
 
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.
 
Last edited:
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.
 
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.
 
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.
 
Perusing the Lycoming power/altitude charts for a stock engine, I find that at roughly 8500', standard day, it takes wide open throttle *and* 2700 rpm (or the rpm for rated max HP) to generate 75% power. There may be a couple of HP above 75% due to reduction in pumping losses on the nomographs, but not much. Electronic ignition (modded engine) might buy another couple of HP.

The Lyc nomographs for stock engines also show a *best* BSFC of around .43 pounds per HP per hour (at 2400 rpm; not 2700). Doing the math, most HP/fuel burn numbers seen on the interwebs look a lot like fish stories, to me. :)

Now, modded engines, or above 8.5-1 compression, obviously should give *slightly* better numbers.

Point is, I'd take the plane to 8500' DA, and run it full throttle and rated full-power rpm. If it over revs, it's underpropped (and slower than it should be). If it under revs, it's over propped, or the engine is weak, or the airframe is draggier than it should be for that engine and the proper prop for that airplane (and slower than it should be).

Of course, if it's a Sensenich metal prop on 160 HP, you're out of luck; can't be done (safely).
 
75% of 160hp =120 hp
8.3gph x6#/gal= 50 #/hr
50/120=.4 BSFC, normal for air cooled, carb'd, fixed timing lawnmowers, VWs, Lycs and others.

Looked like 75% power to me.
 
I was really addressing the OP's question, but forgot to include the significant point of 'properly leaned for best power'. My bad; I've seen this stuff for so long I sometimes forget details.

Best I can tell you is to look at Lycoming's performance charts.
 
Yes, similarly I took the OP's points, asked for the relevant details and offered up my numbers as an example.

I then double / reverse-checked that I was at 75%. The Sens fixed pitch has some compromises, but it does give "Vans" numbers. I static over 2300 rpm, where many prefer more cruise speed and accept less static rpm.
 
Thanks for all the replies, guys. I appreciate all the info. The 6 I'm looking at indeed does have a Sensenich prop. However, I have decided to pass on the opportunity. It's a wonderful looking aircraft but I have other responsibilities at this time so I don't think the timing is right.

[Text deleted due to violation of VAF rules; S.Buchanan]
 
Last edited by a moderator:
One year ago the wife and I flew our RV7 rotating legs as PIC, around the perimeter of the lower US. The trip was 10,700 NM. We averaged 7.5 GPH (LOP)/155 knots per hour (179MPH), block to block, including all maneuvering, climbs and descents.
 
retired pilot using typical settings of 19/2000 returning a 130TAS at <21 l/hr (<5.5 USG/h), >6 hours endurance, and a very quiet environment :D

PS
O-360 A3A with MTV-12 3 blades
 
retired pilot using typical settings of 19/2000 returning a 130TAS at <21 l/hr (<5.5 USG/h), >6 hours endurance, and a very quiet environment :D O-360 A3A with MTV-12 3 blades
Yep slowing down (especially with a tail wind, can be nice and save fuel... and as you say more time for sightseeing and less engine noise. 5.5GPH is pretty good.... 750 Stat miles in 5 hours with 1 hour reserve... Makes sense and saves time if it saves fuel stop... Everyone is geared to fly as fast as they can... sometimes that is the way to go... but the joy of slow flight (not that 130Kts TAS is slow).
 
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 was my experience. It could be that the owner is relating the numbers he typically sees based his personal flying, not the full performance capabilities of the aircraft. I used to see speeds that people posted and was disappointed thinking I had bought a 6A that was super slow. Eventually, I looked closer at the numbers I realized that my normal flight profile was not 8000' @ 75%. My cruise is usually more like 55%, and the numbers are reasonably close. I know there are probably a dozen things I could do squeeze out a few more knots if I really want them (wing root fairings, wheel pants, exhaust, etc.).
 
I was able to retest WOT returning from KOSH for 2 hours at 9500', 10,700 DA. Playing just off WOT, got 160 knot TAS at the 2600 rpm limit on a 70cm6 79 inch pitch 2 blade metal Sens prop.

2 cyls 25 LOP, 2 24 ROP, 70% power, 8 GPH. Carb, 2x 25 deg advance slicks.

I usually fly 2450 rpm at 6500 to 7500 msl and get 7.5 gph at 65% at 148 knot TAS.
 
Back
Top