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RV-10: Where's the "sweet spot" in cruise?

T

the_other_dougreeves

Well Known Member
There's been a lot of discussion about the maximum cruise speed for the -10. However, one rarely tries to cruise at absolute maximum speed and goes for a certain level of economy, particularly with $4/gal and the (I)O-540 drinking a lot at maximum power.

So where's the "sweet spot" for the -10 in cruise, particularly in terms of speed and fuel flow? I am most interested in altitudes between 6000 and 14000 - summer bumps and terrain make 5000 and below sometimes unusable / unbearable.

From what I have read, it looks like 160kt on 12 gph at 8000 is a reasonable figure - am I wrong?

TODR
 
Running LOP (Lean of Peak) I can easily get 10.5 GPH 6-8,500 MSL in cruise. Speed is a tad less, but not much than you quoted, if I had to guess it would be 150 knots. But saving 2 GPH I'll give up 11 mph any day. Gotta love Dynon's "Lean of Peak" mode. It tells you at a glance where your #1 peaking cylinder is at all times. In LOP cylinder head, oil, egt's temps are a tad cooler also, less wear & tear on the engine, and little to no chance of detonation. If I just want to go flying to watch the sun set, I can pull the throttle back and get 7 GPH. If I need to get there fast, 50F ROP (max power) burns 13.7 GPH and I'm doing 201+ MPH.

Balancing the injectors is a real art. I have Airflow Performance in SC, do the "tuning". The engine runs extremely smooth, with balanced temps LOP. I highly recommend their services for any injector system. Their customer service is exceptional. You would not believe how many "dumb" questions they answered for me.

http://www.airflowperformance.com/

Also, what is nice about the stock compression IO-540 is you can burn a 50-50 mixture of Mogas & 100LL year round with an additional savings of $55 per tank full.
 
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Geico266 said:
Running LOP (Lean of Peak) I can easily get 10.5 GPH 6-8,500 MSL in cruise. Speed is a tad less, but not much than you quoted, if I had to guess it would be 150 knots. But saving 2 GPH I'll give up 11 mph any day. Gotta love Dynon's "Lean of Peak" mode. It tells you at a glance where your #1 peaking cylinder is at all times. In LOP cylinder head, oil, egt's temps are a tad cooler also, less wear & tear on the engine, and little to no chance of detonation. If I just want to go flying to watch the sun set, I can pull the throttle back and get 7 GPH. If I need to get there fast, 50F ROP (max power) burns 13.7 GPH and I'm doing 201+ MPH.
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Your numbers are actually quite interesting:
10.5gph @ 150 = 14.28 mpg
13.7gph @ 201 = 14.67 mpg

hm....
 
Tomasz said:
You've got me here, but still

150 knots = 172mph = 16.42 mpg vs. 14.67 mpg @ full power while saving quarter of your precious time. Still hm..... :)
Click to expand...

I think you better put the calculator down, step away from the computer, and go flying. ;)
 
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Geico266 said:
I think you better put the calculator down and go flying.
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Hej!

I didn't mean to touch any sensitive nerve. All I meant is that sometimes we focus on gph so much that we forget that it's not everything - flying slower it take us much more time to get there... which means less time spent on riveting or less time you have for your family. That's all I wanted to say.
 
Relax...

I think Larry was just trying to say "don't sweat it". An extra gallon here, an extra 10 mins there... he's saying to not worry about it so much, just enjoy the flying itself! I sure wish I was... but I've got a few years to go before I can even start building.
 
Another point is that you need to do some testing in the context of how you fly your airplane.

Some RV pilots never get the same speeds and / or economy that other RV pilots get because of their leaning techniques, altitude choices, etc. You need to do some of your own testing in the context of how you like to operate the airplane. You cant necessarily just go by what other pilots suggest.

I have found that I get very good speed Vs economy in any RV model by using the benefits of lower drag and economical engine operation at higher cruise altitudes.
I usually fly cross country at 11.5 or 12.5 (depending on heading) unless weather or winds dictate a lower altitude. I expect to have a slightly higher fuel burn at the lower altitudes if I expect to get the same true airspeed that I can get at higher altitudes. Even higher true air speeds are attainable at lower altitudes (around 7-8000) but at the penalty of much higher fuel flows.

I have routinely had RV-10 true air speeds of 160-165 kts with a fuel burn of 11 - 11.3 GPH, if the air is smooth (that makes a difference).
 
I was up flyimng this AM and was able to run 23 squared, 163 knots 187 MPH on 10.4 GPH running LOP. Not bad, not bad at all. I was kinda stuck on 24 squared and tried a lower setting due to asomeone's suggestion here on VAF. Who ever it was thanks! I owe you dinner at OSH! I'm saving another $10 per hour!
 
Monarch reposting of Jim's numbers...

The Monarch ( For sale BTW, see classifieds)...Loves 8000', WOT, about (cannot rember exact MP) 22" MP????? and 2350 RPM, with an aft CG, ( ie. Jim's 90 lb scooter in the baggage compt)....Equals....204 MPH TAS and 13.5 GPH @ 50 deg ROP (carburated, 260 HP motor.........Of course that is with the autopilot on and perfectly smooth air......

Interesting note here, even in the mildest of chop, we lose 5-7 MPH TAS in a matter of a couple of seconds......
Hurry up and scoff up the Monarch, a solid "flyer", with a little attention to detail, could be a show winner... Glen
 
Congrats Geico...

Geico266 said:
I was up flyimng this AM and was able to run 23 squared, 163 knots 187 MPH on 10.4 GPH running LOP. Not bad, not bad at all. I was kinda stuck on 24 squared and tried a lower setting due to asomeone's suggestion here on VAF. Who ever it was thanks! I owe you dinner at OSH! I'm saving another $10 per hour!
Click to expand...

For putting down the " high RPM = more HP and higer TAS/economy cool aid". !!!!! Glen
 
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