LOW RPM to save fuel

[Dave in Eugene]

Are any of you guys running low RPM these days for fuel savings? I am thinking that Silver Eagle, Don Denhart has this nailed...cause he flys everyday.... to no where...

Also wondering about if what the thoughts are about leaning... I am confused cause what makes sense to me is that we should run at the best mixture at any altitude...doesn't the manual say lean only above 5k'?

Thanks,

Dave

[eric r]

It's all about MPG ... As for leaning, I live at sea level and fly a Grumman Tiger ... see my other post about looking for a EZ ... I lean right after engine start! Full rich only for take-off, and lean as soon as 2000msl. Gotta have a four way EGT/CHT though. Fewer lead fouling issues, and max power or max range; whichever I choose for the day. BUT, I say Life is short, FLY FAST.

[Drew]

When you are on the ground, lean aggressively---keeps engine healthy/keeps from fouling plugs.

Full rich for takeoff.

During climbout, some lean for constant EGT.  I keep it full rich until at cruise altitude.  Your extra fuel flow during the climb is keeping the cylinders cool.  If your cylinders are in the "green" you can start leaning somewhat.

Keep in mind that for agressive leaning, you need to be below 75% to prevent damage to your engine---so basically, you need an accurate rpm indicator and MP (and OAT and humidity if you want to be anal about it).  Keep in mind that above 8000 ft (standard day?) your engine (normally aspirated) can't develop greater than 75%.

Other throttle tips, don't throttle back more than 15" for descent (unless you are in the pattern and landing) to prevent ring chatter.  I usually throttle right to 15 inches and then keep readjusting it back to 15 (as you descend, your MP goes up).

Plan 6 miles per 1000 ft for your descent to destination (prevents shock cooling/or circling over the airport trying to come out of alt).  Plan 3 miles/1000 ft for a dead engine/no wind.  Works pretty good for both a Cozy and a Longez.

[eric r]

This is where I think a MP gauge is great on any engine. When flying my Bonanza (sold after hurricane charlie scratched it), I would begin cruise descent by lowering manifold pressure by one to two inches, continuing so until 18" at pattern entry, 15" on final, and throttle to idle at flare ... never went up in MP, and never went down more than 2" every few minutes. Oh yeah, I had GAMI's and cruised lean of peak, which resulted in lower CHT's, and an average fuel burn for a 3+ hour leg of 11gph.
IO-470C. Take-off and climb was performed by leaning to take-off EGT throughout the climb (cruise climb @ 120Knots) The throttle remained full forward until time to descend. AND Yes I was screaming downhill when approaching the destination! Takes a little practice, but saves fuel, time and engine health.

[Jeffco]

A few years back I flew my Long ez from Hawthorne California to Eugene to pick up my brother and then we flew up to Arlington. After the airshow and camping out for a few days we flew out over the islands to the west and then back down to Eugene passing by Mount St. Helens.  After getting back to Southern California I calculated that I had flown 1800 miles and burned about 63 gallons giving me 28.5 miles per gallon at an average speed of 130 kts leaned back to 2400 rpm.   Average fuel flow was around 4.5 gallons per hour on an O235. Dave, I land and Creswell when I come up to see my brother.  Is that where you are ?

[Dave in Eugene]

yes. Creswell 77s.

Give me warning and I will come down and meet you.

All the best,

Dave

[Dave in Eugene]

Seems like I am buring 6.5 an hour at 2650 RPM.. I will try 2400. thanks for the info

[Jack]

When you are on the ground, lean aggressively---keeps engine healthy/keeps from fouling plugs.

Full rich for takeoff.

During climbout, some lean for constant EGT.  I keep it full rich until at cruise altitude. .

I lean during climb pretty quickly after takeoff.  Which isn't unusual if you study some of the older engine manuals.  In the heavy recips, 2800s or 1820s, we could lean them after takeoff.  

As for ground running, oh yeah leaning is good.  Kept the plugs from fouling for starters.  

One technique I use during cold weather flying.  Go rich, add some carb heat till a short 15C and then lean.  Better fuel specs and runs nice.

Another  technique is over leaning.  Lycoming has a chapter or two on it from decades ago.  On 2800s it was SOP.

Cheers;

Jack

[Drew]

Jack,
When do you get back?

[easyrider]

Dave it's not true I fly every day to nowhere, I have the best knowledge of airport resturants in N. California. I know you are jealous of my flight time, 380 hrs in 2.5 years but that is one of the advantages of retirement.
You also have that lousy weather in Oregon, you need to move to sunny California and we can go check out some of my favorite resturants.
easyrider
Silvereagle
FFF

[Dave in Eugene]

Don,

I am guilty of every charge you have leveled against me. Hope to see you sometime soon. Dave

[slk23]

If I'm just out for a sunset flight I lean for taxi, go full rich for takeoff, then reduce power to 75% and lean once I'm above TPA.  I use the 48 rule (MP + RPM/100 = 48 = 75%).  I use 2200 - 2300 RPM which is still surprisingly fast.  I flew 1.6 hours yesterday and burned 5, maybe 5.5 gal. with my O-235 Vari-Ez.

If I'm heading out on a real X-C, I climb WOT until at cruising altitude (usually around 10K).  I start leaning when power drops below 75% as MP goes down with altitude.

[Waiter]

I'm running a constant speed prop, so I normally cruise at 2300, and on rare occation, back it down to 1900.

I follow the save leaning rules as most others, When I'm on the ground, I lean it as far as I can. Back to full rich for takeoff, then start leaning back when IO reduce to cruise rpm and/or above 5,000 ft.

Waiter

[Jack]

Jack,
When do you get back?

I ain't back yet, still running freaking Baghdad several times a week.  Hoping to get my R&R next month and move to Texas.  Working into my 15th month in the damn sandbox now too.

I can safely say, no matter what the media reports, it's wild running convoys in Iraq.

Did see the other day at Baghdad airport, that huge Russian biplane flying off into the distance.  Had seen one parked at Anaconda last year in pretty piss poor shape.

As for lean of peak running in an EZ, if you have an electronic ignition you might give it a shot.  Just keep a close eye on temps and smoothness of the engine.  

I have been running regular mogas for decades too.  Might try that too. Most of these motors are pretty low compression and can handle it.  

In the future I want to install a 180 HP Lyc and follow that up with a wankel and a turbo for sea level performance up high.  It's just like racing, it's bucks driven for performance.

Jack