Battery in my RC airplane

[dknguyen]

In which case, increase the size of the glowplug engine until it out performs the electric - the power to weight ratio is MUCH higher.

Then why don't they just do that on helicopters then? But I don't care for this kind of argument- happens all the time on the RC forums and it's like arguing religion. THe only things that everyone seem to be able to agree on are that electric has less maintenance than glow (but people will even argue this).

 

[audioguru]

I flew my electric RC model airplane again today.
It is a little windy so it climbed almost vertically then when I turned it it went downwind very fast. Turning again to face the wind it climbed very high then hovered. When its batteries ran out I was careful to land it facing the wind and I almost caught it in my hand.
My first Li-Ion battery started at 8.4V and now it is discharged to 7.95V. My second battery ran out then after a rest it flew the airplane a few more trips around the park.

 

[Russ Hensel]

There are lots of electirc planes now. Fuelies around here are know as slimers because of the condition they leave the aircraft in. Max. range inc. altitude is often determined by how well you can see. Most planes crash when you cannot see them ( figure out why ). Gliders can stay up 24 hr. and in slope soaring can reach 100 + mph. Engine power = 0. Take that slimers.

 

[dknguyen]

Most planes crash when you cannot see them ( figure out why ). Gliders can stay up 24 hr. and in slope soaring can reach 100 + mph. Engine power = 0. Take that slimers.

I was staring for 20 minutes at some gulls at the park and they were using the thermal from the parking lot. THey just kept going higher and higher until I could barely see them. They make it look so easy lol.

 

[audioguru]

A seagull was chasing my RC model airplane around the park.

 

[microtexan]

seagulls

A seagull was chasing my RC model airplane around the park.

I can see it now..Midair combat with a seagull just to hone your flying skills.

 

[audioguru]

The seagull didn't have a sharp fast spinning propeller. Chop!
In "the good old days" I played with a rocket powered model airplane. It could set the gull on fire. Sizzle!

 

[carbonzit]

Old thread; tangent (stochiometry)

Most folks don't understand the concept that with fossil fuels, due to the stoichiometric nature of a combustion engine, you only have to haul around 1/15th of the fuel you actually burn because the remaining 14/15th comes from the air the engine breathes, while in an electric system, you have to haul 15/15th on your back Not good for airplanes or cars.

Like they used to say on the old "Laugh-In": verrry eenteresting ...

I didn't know that about petroleum-burning engines. So can you, or someone else, supply the actual chemical reaction that occurs when one burns, say, ordinary gasoline? Seeing as only the oxygen for the reaction comes from the air (right?), hard to see how 14/15 of the reaction products could come from there. After all, there's all that carbon in the fuel ...

 

[audioguru]

51 years ago I built model airplanes that were powered by an alcohol-burning engine. They were heavy and flew very fast but flew well.
Today my model airplanes have an electric motor that is powered by a small lightweight Li-Po battery cell. The airplanes have a very light weight of 1 ounce (28 grams) with the battery and fly fast for 10 minutes or slow for 15 minutes.

 

[MikeMl]

Carbonzit,

Most light General Aviation Aircraft like my Cessna 182 (2800 lbs gross weight, carburetted, six cylinder Continental, 470 cu. in.) have a mixture control, which allows the pilot to adjust the fuel/air mixture in flight. During aggressive climbs, you use a full-rich mixture, about 12:1 (12lbs of air for 1lb of fuel). The rich mixture means that not all of the fuel burns in the cylinders; the unburned fuel reduces the cylinder head temperature and the valve temperature.

In cruise flight mixture is leaned toward optimum stoichiometric mixture (14:1) and beyond. Stoichiometric mixture more or less corresponds to complete combustion, as evidenced by a peak in the Exhaust Gas Temperature. Operating on the lean side of the EGT peak causes a slight reduction in power, but gives lower cylinder head temperatures (easier on the engine). The mixture control also needs to be leaned as the aircraft climbs (less combustion air density, so less fuel is needed to maintain stoichiometry.

At 10,000 ft msl, the Cessna cruises at ~165mph while burning ~11gal per hour. It has a fuel capacity of 79 gal, for a range of ~1100 miles. Fuel weighs ~6lbs/gallon, so the fuel load is 475lbs. If I had to haul around the oxidizer as well as the fuel, the fuel + oxidizer would weigh a whopping 3.3 tons (6600lbs). At the same relative weight, a battery powered airplane would have a range of less than 70 miles.

Reference dealing with reactions and byproducts here.

 

[carbonzit]

In cruise flight mixture is leaned toward optimum stoichiometric mixture (14:1) and beyond. Stoichiometric mixture more or less corresponds to complete combustion, as evidenced by a peak in the Exhaust Gas Temperature. [...]

Thanks, that's all very nice, but it doesn't answer my question. Which is, does the fuel really only constitute 1/15 of the material combusted by mass? I assume when you say the mixture here is 14:1 that you mean by volume, no?

It just seems counterintuitive to me that 14/15 of the "stuff" that makes a car/plane/whatever go comes from the air and not the fuel tank (again, per unit mass). Unless I'm misunderstanding something here?

 

[MikeMl]

Nope, it is by mass. Internal combustion engines gulp massive amounts of air, and mix in a tiny volume of fuel.

Actually, as air is only ~20% oxygen, I wouldn't have to haul around the nitrogen because it doesn't contribute to combustion, so the comparison to batteries is not as bad as I suggested in the previous post. However, batteries are heavy.

 

[crutschow]

Thanks, that's all very nice, but it doesn't answer my question. Which is, does the fuel really only constitute 1/15 of the material combusted by mass? I assume when you say the mixture here is 14:1 that you mean by volume, no?

It just seems counterintuitive to me that 14/15 of the "stuff" that makes a car/plane/whatever go comes from the air and not the fuel tank (again, per unit mass). Unless I'm misunderstanding something here?

Intuition is no substitute for facts. You aren't misunderstanding, you just haven't analyzed what happens.

The primary combustion products of gasoline or alcohol are CO2 and H2O. Hydrogen is 16 times lighter that oxygen so it takes about 8 times more oxygen than hydrogen by weight to form a molecule of water.

It takes twice as much oxygen as carbon to form a molecule of carbon dioxide, and carbon is 75% lighter than oxygen, so it takes about 2.7 times the weight of oxygen versus carbon to make CO2.

Couple that with air containing only about 20% oxygen explains why you need a lot more air than gasoline by weight for complete combustion of the fuel.

 

[carbonzit]

Intuition is no substitute for facts. You aren't misunderstaning, you just haven't analyzed what happens.

Well, actually I was misunderstanding this; however, with your help and Mike's, I now see the light!

Thanks. I learned something today.

 

[audioguru]

The Li-Po batteries in my new small RC model airplanes weigh only 3.4 grams for 125mAh and 4.1 grams for 160mAh.

 

[gary350]

You need to ask this question on the RC Model Airplane Forum those guys can tell you exactly what you need.

I don't fly RC anymore it is boring. It is like playing a video game on the computer I push the buttons the airplane flies way over there and I never have the feeling that I am actually flying an airplane. I returned to Control Line flying wow it is GREAT fun I actually can feel the airplane fly holding the control line handle.