Air Density

Stephan Peterson · Jul 25, 2016

As the air density continues to drop (eg 100 down to 90) Kinsler's states that for every point their is a lose of 2% power. So a loss of 20% power =smaller prop, lengthen pipe. I guess my question is "would going to a smaller head button and increasing compression ratio help ? I know what has worked for me just wondering what everyone tries.

Terry Keeley · Jul 25, 2016

I've been running my CMB's stock now for many years, they come with pretty high C/R's right out of the box.

I have a range of props and a couple different pipes to use. One thing I've noticed lately using my Kestrel 4250 is when the humidity gets high and the water grains PPA get over 100 or so it gets hard to burn the usual richer settings I like to run. The amount of water in the air doesn't affect the density reading that much, you can see here by playing with the dew point temp: http://wahiduddin.net/calc/calc_da.htm

Here's some drag racer's take: http://www.competitionplus.com/drag-racing/news/15585-humidity-can-be-the-devil-for-drag-racers

Bottom line is I have to lean down on the needle and that really kills the performance.

shoboat · Jul 25, 2016

Steve,

Another trick is to boost the nitro content of the fuel.

It has the oxygen we are looking for to make power.

The head button is another good way. The grains of

moisture in the air and the density altitude is why we

have our weather machines like the Kestral 4250.

You have to document all the changes and log them

in a notebook. Lots of ways to make power.

Good Topic Steve,

Mark Sholund

dave roach · Jul 25, 2016

On board glow system and you can put more fuel in the engine.

John Seybold · Jul 25, 2016

Dave, I've always wanted to try one. Where do you get them from? Or do you make them yourself?

Terry Keeley · Jul 25, 2016

dave roach said:
On board glow system and you can put more fuel in the engine.

Also running a hotter plug.

brad nichols · Jul 25, 2016

Make yourself from from Hobby King parts.

Brad

Al Hobbs · Jul 26, 2016

I use both the Kestral and a Kinsler density meter. At many ponds the air changes significantly throughout the day.

Stephan Peterson · Jul 26, 2016

So all we need to do is add a on board de humidifier. lol

Ray Sametz · Jul 26, 2016

Tricky thing air density. Example, we ran at sea level near a major hwy intersection. Also ran at a lake 800-900 feet above sea level were we had to richen the engines up. They ran much better at the higher elevation, why? The higher elevation was in a state park surrounded by hundreds of thousands of green trees. O2 in the air was more of a factor then the density. OMHO.

shoboat · Jul 26, 2016

Ray,

I test at 900 feet with a ton of clean water and lots of trees.

The 02 in the air can only reach around 30%, but that does

help a lot. It still comes down to adjust density altitude and

what the air density readings are. I use both when I test, the

Kestral 4250 and a good calibrated Kinsler Air Density Gauge.

I think you need to document the readings and adjust as conditions

change if you want to make maximum power all day long. Another item

that helps is the old school flow meter.

The Boris meter does not

compensate for different air density conditions.

Keep Testing,

Mark Sholund

Ron Jefferson · Jul 26, 2016

Work on your set-up. It will make leaps and bounds difference over playing with your needle.

Stephan Peterson · Jul 26, 2016

Get to work Jefferson

bmazor · Jul 26, 2016

shoboat said:
Ray,

I test at 900 feet with a ton of clean water and lots of trees.

The 02 in the air can only reach around 30%, but that does

help a lot. It still comes down to adjust density altitude and

what the air density readings are. I use both when I test, the

Kestral 4250 and a good calibrated Kinsler Air Density Gauge.

I think you need to document the readings and adjust as conditions

change if you want to make maximum power all day long. Another item

that helps is the old school flow meter.

The Boris meter does not

compensate for different air density conditions.

Keep Testing,

Mark Sholund

Hi, Mark! My gen-4 flow meters really compensate air density changes, maybe not all 100% but very close. Boris

Andy Brown · Jul 26, 2016

As others have mentioned, Humidity is a Big factor with nitro and on an hour to hour basis, is much more of a factor than air density.

Mark mentioned trees. They DO make a difference. I was once testing a SAW set up at a lake that was like a desert on the near bank while the far side bank was covered in dense vegetation.

The lake was very narrow (about 200 feet wide) so I was making my passes very close to each bank. When I would make a R to L down the "desert" side the boat would take much longer to hit the pipe than it did on the dense vegetation side.

If you are racing, the best solution for power loss due to density loss is a smaller prop. Nitro and engine changes will make your set up too complex, especially if you run more than one boat.

KISS method is best for racing!

Stephan Peterson · Jul 26, 2016

That's what I typically do is down size and finish the race. Thanks for every ones input

Douglas Shepherd · Jul 28, 2016

I have found that the Boris Gen 4 meter will take about 99.9% of the guess work out of going from site to site. I have a small weather station and a air density meter that do not even use any more.

bmazor · Jul 28, 2016

Douglas Shepherd said:
I have found that the Boris Gen 4 meter will take about 99.9% of the guess work out of going from site to site. I have a small weather station and a air density meter that do not even use any more.

Hi, Douglas! How long you use GEN-4 flow meter? Thanks. Boris

Douglas Shepherd · Jul 28, 2016

Boris,

This is my second year using you meter. Love it.... Spot on

Andy Brown · Jul 29, 2016

Douglas Shepherd said:
I have found that the Boris Gen 4 meter will take about 99.9% of the guess work out of going from site to site. I have a small weather station and a air density meter that do not even use any more.

So it must compensate for Humidity, Density-Altitude, Water temperature, Air Temperature, Fuel Temperature, anyone of which alone can effect fuel mixture burn much more than 1%.

Just asking, as I have not seen the Gen 4 system.

Air Density

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