At what elevation above sea level do you have to start re-tuning engines? Do you usually have to lean them out a little or is it vice versa? Never can keep that straight. May be moving from an elevation of around 250 ft to around 2200ft. Not sure if that`s enough to make any appreciable difference in performance. Thanks for any help.

Well, usually you tune for the best power, minus a bit to give it good lubrication.. regardless of the altitude. You will naturally lose power as you gain altitude, but I don't imagine that being just a few hundred feet over sea-level will cause as much as say, living in Denver, for instance.

In your case, 2200 feet asl, well, it probably will require a bit of retuning.. but that would be nothing different than you would do from day to day or week to week at sea-level as air pressure changes by normal weather patterns.

CGr.

When you have to tune engines because the weather changes from day-to-day, expect to have to adjust them when you make a significant change in field elevation. I've had to re-tune engines on the same day, when the day changed from cool in the morning to hot and humid in the afternoon. There is no such thing as a "set and forget" engine. To keep it operating properly, the tuning will have to be checked before every flying session, and from time-to-time during the flying session to make sure nothing's changed. That doesn't mean you 'tweak' the needle every time, but you still need to keep on top of things.

When you move from a 500-foot field elevation to a 2000-foot field elevation, you WILL have to reset your engine. It will wind up with the needles turned in a bit because the air will be a little bit thinner, which means less fuel will be needed to make the proper fuel/air ratio. Less fuel going through the engine means less power, so expect a slight power loss. It may even be noticeable.

couple less engine power with less air for the prop, and you will most likely notice a difference.
Most people at high elevations go up one or more engine size(s) to accomodate the differences.

Typically, when increasing elevation the engine must be leaned. As altitude increases air density decreases. Remember, the mixture is simply a ratio of air and fuel, therefore less air density requires less fuel to maintain the ratio. This is also why on a hot humid day the engine is typically leaned out a little. Heat and humidity also reduce density.

http://blogs.trb.com/news/weather/we...aft_takeo.html

actually , heat and humidity reduce or lower the density of air......nice article above..

Don't sweat elevation, temperature, whatever.........

At the start of every flying session, adjust the needle for optimum. Easy enough?

Our engines will tell you what you need to do, and you won't even know they're doing it. It's as simple as that 2nd sentence.

Crank the engine and let it warm up.
Go to wide open throttle.
Open the needle to insure that the engine is rich. No special degree of rich, just positively rich.
Close the needle to find max rpm, and then back off "enough".

You're done.


OK, how much is "enough". You'll get a feel for it after a couple of outings.
Every one responds differently. You'll normally richen any engine on the ground from it's max rpm needle some number of clicks. That insures a good mixture when the prop unloads in the air. When it unloads, the rpms go up and more air moves through the venturi. And more fuel is needed than when running on the ground. And you'll sort out how much each of your engines reacts from the ground to the air.

Easy to do. And since it should be done the first run of every outing, you'll be familiar with the process whenever you fly at a different altitude.

BTW, even if you fly at the same field ever day of your modeling career, your engine is going to experience a range of different "altitudes". So get into the habit of tuning for optimum setting at the start of every session.

I have a handheld "weather station". (It's really just a jazzed up wind speed reader with some extra functions.) I often use it to readout the Density Altitude when I'm doing prop testing. Density Altitude is a measure of the effect of atmospheric pressure on your location. When we're in low pressure, our 780' altitude flying field can show a DA as if the field were at a thousand feet higher elevation. When we're in high pressure, the engine can feel like it dealing with sea level altitude. Or lower.

The Density Altitude can often be greater at my home field than I'll experience (OK, .....than the ENGINE will experience) when I fly at a field in the foothills to the West of here.

So it's actually as important to do the start-of-session-needle-twiddling every session, as it is to do it when flying at a different field.

And it's just as easy to do at home or on the road.