I have heard several techniques for this.

Some had said to always depart full rich and then lean just after TO. Others like to lean durring the run-up.

This next part comes from Sparky's site and thought it was interesting.

I hate to sit at the end of a runway and run up the engine to adjust the mixture. In addition to the possibility of picking up rocks and debris that may damage the propeller, adequate cooling is not available to the engine and its accessories. If the runway is too short to comfortably allow adjusting the mixture during the takeoff roll, use full power to adjust the mixture. Adjusting the mixture at the magneto check rpm isn’t advisable. Even without a power enrichener valve (maybe the engine is fuel injected, so you don’t have it), the fuel flow changes at higher power settings making it inadvisable to adjust the mixture with partial power.

Since your runway is long enough, I prefer to start the takeoff roll and begin leaning the mixture immediately. At the first sign of engine roughness, increase the mixture (push it in) until the engine runs smoothly. Warning: Sometimes when the mixture is pulled out the engine is going to stop. Don’t panic and shove the mixture control back in to the starting point or you’ve defeated the purpose of the adjustment. Make a small, smooth increase by pushing the mixture control back toward rich until the engine runs smoothly. This will give maximum power for the takeoff. Fine tuning of the mixture can be accomplished after climbing 400- to 1,000-feet AGL.

"I assume the sequence is: full power, gauges in the green, adjust mixture, and airspeed alive. Is this the correct sequence? Also, does adjusting the mixture during the takeoff roll affect reaching 70% of your takeoff speed by the halfway point?"

That is the correct sequence for the takeoff. The rule of thumb remains the same, obtain 70 percent of the liftoff speed prior to or at the halfway point of the runway.

This is the part that I found interesting: Adjusting the mixture while rolling just allows you to obtain that speed sooner.

And don’t forget to adjust the mixture for landing in the event that you need to make a go around. I'm not suggesting that a go around is caused by pilot technique, rather because an animal or airplane may be on the runway.

Blue skies, tail winds and safe flying!

Sparky

I am curious what you think. Personally I generally set the mixture at run up for the given conditions (density or elevation,etc) and go from there. Whats your thoughts on leaning for take off? How about at 8000' and higher? It may seem like a silly question as the answer to me is pretty obvious, but think about it for a minute. Adjustments with the mixture are critical for engine life and performance. The second half of that is what I am really concerned with for this question imparticular. Performance. Getting the most out of your plane on a really short, high elevation or high density alt., airport.

Obsessed with learning....

AKT

Just go buy a manifold pressure gauge for a twin, leave one side unhooked lean till the needles match you will be at full power. So easy a caveman could do it.

mr scout wrote:Just go buy a manifold pressure gauge for a twin, leave one side unhooked lean till the needles match you will be at full power. So easy a caveman could do it.

Wait. N00b here so bear with me. I've so little time in CS propped aircraft it's not funny.

Manifold pressure is a measurement of available air into the intake system. It's basically a barometer in the intake manifold, right? The difference between vacuum when the throttle is closed, and airflow into the intake when the throttle is opened?

It's always less than 1 atmosphere in a normally aspirated engine (29.9213 in hg @ 0 C.)

How does changing mixture guarantee max power from a manifold pressure indication? I know what you say is true but I'm sorting it out here... Isn't the airflow into the intake, and therefore the register pressure, maximum regardless? It's the fuel that you're metering with the mixture control, not the airflow. Throttle is WFO, that's max airflow. So what is max power? What's the true relationship between power and manifold pressure indication?

I've seen some POH's for injected engines that use fuel flow.

I've had too much whiskey so the brain cells that formerly could have comprehended this stuff may be gone now.

Pull the mixture out to where you usually run at cruise at that altitude, and use that for start-up, taxi, and take-off. In a Cessna about one finger joint's worth at Truckee.

No whisky talking, just wine.

Gump

Wine here as well, 1 bottle down while the wife takes a run...

Gump sounds right.

Am I crazy for asking why you would do this during the take off process??? I just don't think that is the most opportune time...

I agree, I have never understood why sparky advises this technique while you are already pretty busy. I just set it based on my altitude, a finger and a half in Durango.

Brad

Sparkys just seems like a work overload for take off. As said in my first post, I set the mixture for the given density/field elevation. I just find it interesting about setting the mixture durring the roll process for max pow. However, acccording to my JPI, when sitting the other day at 9600' getting ready for take off, I did a bit of n experiment. Ran the engine up and leaned just a bit this side of LOP. Looking at the mixture control knob just did not look correct so I enriched. Prior to leaning, the mixture control was pulled so far out (maybe 3-4 knuckles) it just did not make me comfortable but, the JPI said it was about perfect. Anyhow, gave it a few turns to enrich for my own comfort and the JPI went to the otherside.

I guess that brings another discussion, You hear all the time about running lean of peak and rich of peak. There is a lot of disscusion here on that one. Personally, I run just a tad LOP and have had good success with the engines I have run. Also a very big beleiver in Camguard.

But again, LOP or ROP, what gives you the very best power and performance. Playing with it on several take offs now and it seems like ROP is better for imeidiate power. Shit, I dont know. Sorry for the bad spelling. Iphone is very small to type on.

I am with you Zane on the twin manifold gauge. Trying to comprehend it. Maybe its to early. Going to the hanger now.

AKT

I know there is a difference between max power and engine cooling. Someone once told me you should be on the rich side to keep EGT and CHT in the happy zone. Thats what I do on climb out when working the 540 hard. I will lean for TO and max power, when I don't need max power I richen and back off the MP a little, and keep the EGT in the happy zone not max. Where I fly I don't need every last pony, even Mile high and Dewey Moore.

Good day

GumpAir wrote:Pull the mixture out to where you usually run at cruise at that altitude, and use that for start-up, taxi, and take-off. In a Cessna about one finger joint's worth at Truckee.

No whisky talking, just wine.

Gump

I do the same thing as Gump, then I fine tune the mixture once I get up 500ft or so.

Buy an angle of attack indicator and reduce fuel reduction while on base or left final. That should give you maximum flaperon deflection witch will maximize your angle of the dangle. Which in turn will assure maximum particle separation .

low rider wrote:Buy an angle of attack indicator and reduce fuel reduction while on base or left final. That should give you maximum flaperon deflection witch will maximize your angle of the dangle. Which in turn will assure maximum particle separation .

Having this made into a placard.

aktahoe1 wrote:Playing with it on several take offs now and it seems like ROP is better for immediate power.

AKT

Hi Kevin,

You lose a little power with LOP, plus cooling isn't quite as efficient as using fuel to cool when ROP, so I believe you should always take off ROP, like you witnessed. You can then cruise climb LOP or ROP as you wish. If I'm doing a max performance climb, I'll leave it ROP. I always cruise LOP.

From what I understand, the dangerous (some call it the "red box") is right around peak EGT. ROP or LOP. Cylinder pressures and CHT are highest here. So you want to be a safe distance into LOP or ROP, not just a little. The procedure to lean until it stumbles then enrichen is designed to move away from that red box into ROP territory. Then again, at around 65% power and below it apparently doesn't matter. So at high altitude with a normally aspirated engine you can pretty do what you want without harming the engine.

An engine is much more sensitive to fuel and air when LOP. Lose a little fuel in a cylinder ROP and you feel nothing. Lose a little fuel in a cylinder LOP and the engine is rough, since the power generated by the cylinders is uneven. That is why many engines can't run LOP, at least not without help like tuned injectors if fuel injected. It also helps to be turbocharged when running LOP. You do lose a few inches of manifold pressure (and power) when LOP, and if turbocharged you can replace it. Which again points to always taking off ROP if normally aspirated.

Many suggest that you really need an all-cylinder EGT gauge to safely run LOP, since you really want to know if one of your cylinders is running in that "red box" or not. For example, if you are using a single-point EGT you could think you are running at an ideal LOP point, but some of the cylinders may not be. At least I would think you would want an all-cylinder CHT gauge to always keep everything below 400, because the bottom line is that you don't want to cook a cylinder.

Without those, its may be safest to just keep doing it with the proven method of staying ROP, even in cruise.

- Ney

Too lean of a mixture can cause a loss of power. Any 12 year old kid with a Cox PT-19 U-Control trainer knows that from hard experience. Yeah I know we're talking about 4 strokes here, but the concept is the same.

Even if it is perfectly leaned on takeoff roll, when you climb out after takeoff it could create a too-lean mixture because at a high nose-up angle there is slightly less head pressure for the fuel. That means you could have a perfect takeoff roll and then still have a problem a few seconds after liftoff. Not something you'd want to experience IMHO.

Then there is the cooling issue to think about... a significant part of the cooling comes from the fuel at full power. So you need enough fuel to make the power (correct lean mixture), then you need some more to cool it (now it's rich for a reason). Overheating a cylinder head or seizing a piston ain't such a good idea either.

If you start your takeoff roll with less power (too rich), and then adjust it back and forth for a few seconds until you get max power (cooling notwithstanding), how does that give you the shortest takeoff roll in a demanding situation?

Sounds to me like taking a minute to clear all the rocks and debris away, and leaning the engine on your runup, may be worthwhile. Some of you guys have a lot more time in the saddle than me, but you'd still have to show me how the concepts mentioned above are not valid.

low rider wrote:Buy an angle of attack indicator and reduce fuel reduction while on base or left final. That should give you maximum flaperon deflection witch will maximize your angle of the dangle. Which in turn will assure maximum particle separation .

Point 1 is correct, buy an AOA. Preferably the one I'm eventually going to certify and manufacture

Point 2 is correct, we all want a fuel reduction due to high fuel costs, but we have to reduce fuel reduction (i. e. use a little more fuel) on takeoff for safety.

Point 3 is absolutely correct, all advanced STOL back country airplanes should have flaperons. Preferably using the flaperon mixer designed by Dr.Gerhard Waibel for the AS-W20 sailplane. Properly engineered flaperons yield greater roll rate, greater lift, and using maximum deflection in the "crow" position (flaps down, ailerons up) will greatly delay or prevent tip stalls and stall/spin accidents on left base to final turns. Of note, this will also work on right turns.

Point 4 is correct, all male pilots want to maximize the angle of the dangle. Matter of fact, some nice lady with an online pharmacy in the Republic of CashBackistan just sent me an e-mail offering a great deal on a pill for that. She claimed that her product would actually create a 90 degree improvement (from the previous vertical orientation) in the angle of dangle. She also intimated that with her medication, the term "angle of the dangle" would be changed to "angle iron".

Point 5 is correct, "particle separators", called Centri-Sep or Centrifugal Separators, were the very first technology to keep rocks and pebbles from destroying helicopter turbine engines. Although there is now a much better system (originally STC'd by my former employer Filtration Development Company) which used a cloth/oil barrier filter, the overall concept of particle separation (whether through a Centri-Sep or the FDC filter) is of paramount importance to turbine helo operators.

Therefore, your engineering analysis is absolutely correct on all points, and you are clearly a brilliant aero engineer

Yes... a placard... Make it so!

Just remember for a moment that we're talking O-470 here. 1940's engine, with a 1920's Marvel carb hanging off the bottom. There is NO LOP or ROP finesse here. Nothing about that fuel distribution is high tech or accurate.

Get it in the ballpark a bit rich of peak for power and cooling on take-off and climbout, and add a smidge more rich on the knob just to keep Mom happy. There is no rocket science here, and take-off from a high mountain strip ain't the place to be playing CAFE fuel economy.

Gump

Amen gump... But it makes for an intersting conversation. Lowrider you always baffle me with how smart you are. You must already have this as a placard in the kingair. Sitting in minden at the taildragger cafe grubbin. Buzzing your house in 20 minutes gump!

Tweaking HP for takeoff, especially on a dirt/grass strip, seems less than useful most of the time. Even running pretty darned rich, you will only be trimming 3%-5% off maximum HP. Here's one example:

http://www.lycoming.textron.com/support ... SP700A.pdf

If you are hauling a 2800 lb plane with a 230 hp engine with an absolute ceiling of 21,000' off a 5k' density altitude strip with a CS prop that yields 68% efficiency on a good day, that means you are only using about 114 HP to beat the air into submission with the prop. The absolute ceiling means you need around 65 HP to stay in the air, with the rest being excess HP for climb. If you lose at worst 3% of your 114 HP from your rough guestimate on mixture, you will require roughly 6% more on the ground roll, and the rate of climb will go down by roughly 7% from 586 fpm to 546 fpm.

If a 54' longer ground roll or slightly lower climb rate makes a critical difference in the safety of a flight, one might consider easy-clean seat upholstery as well.

Glad to hear other's using the technique that I use and that makes sense to me. I too set for altitude...which equates to one knuckle at OGD, my home base. From there, I make adjustments for altitude. Once airborne and have some breathing room under me, then I start fine tuning it while keeping the CHT temps happily below 380-400.

Personally, I like less tinkering in the cockpit during a takeoff roll and more attention to what I'm screaming towards down the runway.

I always lean in the direction of turn.........when making step turns on floats Lean forward if it is a short lake Just kidding

Interesting topic.

I used to do it when still during run up.

Then I read Sparky's book and did it while moving, never did like that much.

Back to during run up at an airport I do not know, or use the one knuckle way at my local airport.

I think there is enough going on when departing to add to it as well.