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RV-8 Best Cruise Settings

T

ten4teg

Well Known Member
What have you found to be the best cruise settings at, say, 9000'. I recently went on my first long cross country and at 9K I set RPM at 2450 and MP at 22" and had a TAS of 180 kts. I didn't play with it, but wonder what other RVers are using. Thanks
 
I just did the same thing (first long cross country) and DID experiment. I went from 2650 all the way down to 2350 (21 inches, 50 LOP) and found that at 9500, the difference between them was about 3 kts and nearly 1 GPH. So I stuck with 2350. 180 KTAS on 8.6GPH isn't too bad!

Anyway, I have it written down - will post up later.

EDIT: From my notes:

9500 ft, 29.97, 59 degrees OAT, WOT (21.0 MP), 45 LOP-

2550 RPM = 153 KIAS, 9.1 GPH
2500 RPM = 153 KIAS, 8.9 GPH
2450 RPM = 150 KIAS, 8.7 GPH
2380 RPM = 149 KIAS, 8.5 GPH
 
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After 2+ years and 250+ hours, thought I'd take a look. 1st test point:

7500' Density Alt / FL76 / -2degC at Alt / Surface Press 1040mB

2250RPM / WOT / 23.8" MAP / 33.5LPH (8.8USG/hr) / LOP gave:
Dynon 166KTAS / 148KIAS (GPS Triangle result was 165.4TAS so Dynon pretty accurate)

Any comparisons welcome, or suggestions for more efficient / faster cruise settings / altitudes.

Andy
RV-8 G-HILZ XP-IO-360 BA Hartzell, fat tyres
 
Folks - while these numbers are interesting they'd be a lot more meaningful with a listing of the installed equipment used to achieve these tests. Is it 180hp carb'd or 200hp injected? Hartzel traditional or blended airfoil, or fixed pitch, or MT 3-bladed, or...?

The main reason I ask for this info is because my hangar mate, who doesn't seem to get much opportunity to visit this forum, isn't sure he's getting all he should get from his -8A. He's not yet got any meaningful test data because he found some rather disturbing troubles with his manifold pressure indications. His is a fairly "stock" 8A with 200hp IO360 and an MT 3-bladed CS prop.

By the way... I'll admit that I leave my fair share of noseprints and drool on his airplane - it's a sweet ride.
 
Folks - while these numbers are interesting they'd be a lot more meaningful with a listing of the installed equipment used to achieve these tests. Is it 180hp carb'd or 200hp injected? Hartzel traditional or blended airfoil, or fixed pitch, or MT 3-bladed, or...?
Click to expand...

Hence why I added
XP-IO-360 BA Hartzell, fat tyres
Click to expand...

I can expand:
  1. 7496 74" BA Hartzell
  2. Slick Mags
  3. 180HP (normal compression)
Andy
 
Not an RV-8 but an RV-4, it is similar.

RV-4, IO-360, 200hp A1A, MTV-15 B two blade CS prop, Slick Mags.

These days for me cruse means economy, the most speed I can get with the least fuel burn. Numbers don’t mean much to me and I have done little testing on my old -4. Back when fuel was $2.90 I ran along at 185mph indicated burning 9.6 GPH, as fuel prices rose and money became tighter I started trying to reduce fuel burn. What I found was that I could cruse along at 175mph indicated at 8 GPH. These numbers are down low just going flying. 9.6 GPH was 24” and 2450 rpm and 100 degrees ROP. 8 GPH is 22” and 2380 rpm and 100 ROP.

Above 5000’ I will run 22 to 23” and 2380 rpm and pull it LOP for about 7.2 GPH and about 170 to 180 MPH indicated, LOP operation was a nice tool I learned about hear on VAF. The difference between 9.6 GPH and 7.2 GPH on a two hour round trip saved 4.8 gallons/$18.48

The moral to this story for me is that there is a speed barrier at witch point the airplane will not go much fasted no mater how much fuel/energy you put into it, best cruse is some what below this point. If I burn much less fuel the airplane seem to come off of step and slows considerably, play with it some and you will find the sweet spot where you burn considerably less fuel but loose only a little speed.
 
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