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150hp 6/6A speeds

M5fly

Well Known Member
Looking for some feedback on what the typical speeds you guys with the 150hp fixed pitch are seeing in cruise. I've been using 2400-2500rpm between 8500-11500ft and haven't seen ground speeds more than 170mph in any direction (taking winds into account). That power setting gives me about 3/4" of throttle left, should I just be running it WOT at those altitudes to see the speeds Van's publishes? A couple guys with RVs at my airport said we might want to check the horizontal stab position to make sure it's correct and not contributing to the speed loss. One mentioned he had to correct this on a previous 6 he owned and made a huge difference. Any other ideas or comments?
 
Just curious. How did he change the incidence of the HS after it was bolted down and flying? Steve

I haven't the slightest clue, lol. I think I'll also do some speed tests at 8k next time I fly and note all rpm settings, winds, and other variables. This is probably the more accurate way to check and make sure I just haven't overlooked something.
 
Ground speeds don't tell you much because they are skewed by wind direction and speed. Also, without manifold pressure, you don't have all of the engine power information you/we need to determine how much power you're using.

But 170 MPH is right at 150 knots, which is where I'd expect to see a 150 hp RV-6 cruise at 60-65% power.

If you search the forum, there is a 3 (or 4, your choice) heading speed run test you can run to determine your actual airspeed. The test involves stable air, GPS, and a little math.
 
Have you checked into the vintage of your wheel fairings Cole ? I see your 6 is 1992 vintage , I understand the difference from the old to the new is 5 miles/ hour alone , gear fairing alignment & the upgrade to 160 hp can make a big difference as well,
I generally flt plan for 155 kts which is in line with Vans Cruise numbers-up @ 7-9 K ‘
 
Cole,

Here are the Van's quoted speeds for the RV-6A with 150 hp and a Hartzell 2 blade C/S at 8000 feet (solo weight):
55% power - 167 mph
75% power - 185 mph
Full throttle and 2700 rpm at 8000 feet should yield around 75%.

My preference for efficiency would be to have the elevator faired with the HS at my favored cruise IAS. That will slightly reduce top speed, but I'm not racing at Reno.
 
Thanks for all the replies so far. I think I might do a 2 leg speed test to get a rough idea (math isn't my strong suit) and see where we're at. The plane does have a manifold pressure gauge so I can record that as well during my test. I haven't checked the fairings specifically but I recall the previous owner mentioning they'd replaced them within the last few years.

I may be able to conduct the test this week, I'll report back with results.
 
I was able to do a 2 leg test this morning and these are the results...

Both directions were WOT at 8000ft indicated (30.09") and 2610rpm. I don't have an OAT gauge but I'd guess it was around -5 to -6 Celsius. Take off weight was around 1425lbs.

North run
MH: 355
IAS: 140kts
MP: 22"
GS: 161.5kts

South run
MH: 175
IAS: 140kts
MP:22"
GS: 139.5kts

Averaged GS: 150.5kts or 173mph

How do ya'll think it compares now to what I should be expecting? It's an Aymar-Demuth cruise prop.
 
Two leg tests don't have much validity. If there is a cross wind you will lose ground speed in both directions.

Use a GPS TAS calculator such as this one (there are others, too):

http://www.csgnetwork.com/tasgpscalc.html

I think you will find your 150hp -6A is yielding pretty close to book speed once you get a valid TAS number. If 2610 rpm is all it will pull you either have a prop that is very much a cruise pitch or the engine isn't completely healthy.
 
Two leg tests don't have much validity. If there is a cross wind you will lose ground speed in both directions.

Use a GPS TAS calculator such as this one (there are others, too):

http://www.csgnetwork.com/tasgpscalc.html

I think you will find your 150hp -6A is yielding pretty close to book speed once you get a valid TAS number. If 2610 rpm is all it will pull you either have a prop that is very much a cruise pitch or the engine isn't completely healthy.

Thanks for sharing, I hadn't found a good calculator like that. I basically did the 90 degree 3 leg test, but just didn't log the 3rd leg. Looking back at my GPS data though and entering everything into that calculator is doesn't really change anything. Still 150 KTAS. I believe the prop is a 68-72, but I'd have to check the records to verify. I know compressions were all good when I bought it 7 weeks ago. IIRC the static RPM on takeoff was 2250 (4700' field elevation).
 
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