stearman70

Hello, I have a doubt, assures me a friend that the suggestion of engine power that comes in ALL plans for construction
it is made with respect to sea level basically, and then other parameters are used. I think maybe on some planes, but that's usually done taking into account, NACA, weight of the plane, wing position, wingspan, etc. and not the sea level reference, I have flown many years both at sea level and as many at 6000 feet and I know what height affects airplanes..
What do you think about ?

init4fun

I have asked the moderators to move this thread to the Aerodynamics subforum, since it has nothing to do with the AMA .....

stearman70

Thank you.

init4fun

Your Welcome. Now that the discussion is in the proper area I'll say two things here;

#1, I've never flown a model airplane at 6000 feet, Hell, I'd be surprised if any of my flights ever exceeded 2000 feet.

#2, On all but the simplest RC trainer model planes, I've always stuck with the upper end(or maybe slightly above) of the engine size recommendations and haven't had problems with an under powered plane yet.

stearman70

Hi, regarding your point number 2, I usually do the same. and referring to his number one point, I was referring to the height above sea level. Mexico City is 2,400 metres (7,200 ft) away. I currently live in Guadalajara City, which is approximately 4,800 feet away.

Pylonracr

I live at 5200" altitude and have flown a float plane off of a lake near here at 6100". Power is one part of the equation. Using more nitro helps, where many sport flyers use 10% near sea level, the normal here is 15%. At this altitude we use less prop as well. Needless to say, we pretty much tend to the upper end of the power recommendation with our planes.

Scott

jduino

Performance of the engine/prop is greatly reduced with altitude.

otrcman

Reading the original poster's question carefully, I believe that he is questioing the accuracy of,

"..... the suggestion of engine power that comes in ALL plans for construction
it is made with respect to sea level basically"

In the closing of his original post, he affirms his knowledge that altitude does indeed affect airplane performance; rather he's asking whether plans designers always take that into their recommendation.

My direct answer to his question is: No, I don't think that all plans designers are that sophisticated. Some designers may do that, but they will probably make note of that consideration. But many (perhaps most) designers are just telling you what worked for them when they flew their prototype model.

Joseph Frost

The lower the thicker! It reminds me the good old days I had to constantly fiddle with my main needle while living at 755 m/a/s and regularly visiting clubs at 5-10m above sea level flying my giant IC powered helicopters. I have found a huge difference in performance between the two, wearing out the engines in no time up high in the Southern Highlands.

This 24YO Tiger as an example, with 3rd. engine already after some 470+ flying sessions in the log book.

LLRCFlyer

Back when glow engines were the only game in town, most kit manufacturers specified engine sizes that generally worked pretty well for density altitudes up to about 4000 feet. Many kit manufacturers would specify a range of engine sizes, such as 0.9 to .15, or .29 to .40 sizes. The smaller engines could work near sea level and the max was needed at higher elevations although most people usually opted for the larger engines. Nothing was specified in writing, but that is how it worked out. That covered a majority of flyers in North America and nearly100% of those east of the Mississippi River. Higher temperature and humidity and atmospheric low pressure areas cause the air to be less dense which increases the density altitude. A hot and humid summer day at 2000 feet above sea level could have a density altitude of 3500 feet or more. Density altitude is what determines how well internal combustion engines will perform. When the density altitude reaches 8000 feet, most non-supercharged engines at full throttle will produce about 75% of their rated sea level power output. When I visited clubs that typically experience high density altitudes (Denver CO in the summer time for example) I usually saw most modelers equip their sport type planes with engines at least one size larger than recommended. A plane calling for a .46 glow engine would be outfitted with a .60 glow. A .25 size plane would be fitted with a .35. A .15 size plane would have a .25 installed, etc...

Electric motors are now more popular than glow engines in most areas and density altitude has little impact on the power output capability of electric motors. The only effect of the thinner air is that a larger propeller may be needed to absorb the power. Just use a watt meter to match the proper diameter/pitch prop to the motor at your altitude and go fly. With an electric setup, the manufacturer's power recommendation should be good regardless of the altitude.