highamperage

Hey, can anyone give me some ball park figures of what the fuel consumption is on these .049-.061 engines?

Thank you!

Mr Cox

I haven't really measured this in detail but I think its around 7 minutes on 1oz, depending on the use of the throttle.
I never set a timer, just fly until the fuel runs out.

highamperage

Thank you for the info!

Do you notice if the fuel consumption goes down much with less throttle? If you run at half throttle, can youthenfly 10-14 mins?

I guessImean is the fuel consumption linear with throttle usage?

Mr Cox

I honestly have no idea. Whith proper mods to the carb (airbleed hole) the fuel consumption ought to be roughly linear with the output power, while the stock carb is way too rich on lower settings.

What is it that you want to do?

highamperage

Mr Cox

A Diesel would be better suited if you are used to that type of engines. They are a little different and require special fuel but are very user friendly once you get the hang of it. They use less fuel and are also better at lugging big props, thus keeping the revs low and the fuel consumption down. A PAW .061 can easily run a 7x4 prop which would be much too big for a glow .061.

I haven't measured this in detail either, but I guess about 25-40% lower fuel consumption for a diesel without any special measures taken. A PAW 09 lugging a 9x4 prop at half throttle will keep running for about 20 minutes on 2 oz I think, at least that is what it feels like....

BMatthews

Yes, the fuel consumption goes down with throttle. But it's not in any way linear to throttle position. It may be more linear to RPM but that would require testing and graphing. It's not the sort of issue that comes up for sport flying so I have never seen anyone that measured and graphed such information.

Fuel consumption also goes down with the use of oversize props that hold the RPM down to less then full power. An example of this is the SAM 1/2A Texaco event where we use wide blade 8 inch props on Cox .049's to get about 5 to 6 minutes of run time from the old 8cc tanks. But doing this greatly reduces the power output and the models climb with a lazy "uphill glide" sort of flight.

Different examples of engines which are sealed better or poorer will also leak more or less fuel out the crankshaft. And on top of this small engines need some nitro to run well but the less nitro you use the longer you get from the fuel.

So all in all you will need to get an engine and test it with a variety of props to test the fuel draw and performance level and then from that calculate just what you actually need for power and how much you can give up by overloading the engine to give you the fuel draw spec you need.

Diesel engines typically get about 1/3 to 1/2 again the run time for any given tank size compared to a glow engine. This is because the optimum air to fuel ratio for glow fuel is lower than the fuair to fuel ratio for the kerosene in model diesel fuel. So that may be an option for you to look into as well.

SunnyFlyer09

Go electric. No dead sticks

highamperage

Ok, maybe you can help me with the estimated power consumption.

Lets say Ihave a plane weighing about 1.6lbs, it's a glider type plane so Iassume the L/Dis 8+. Rough estimate puts the drag at about 0.2 lbs. If Ifactor in a 40% loss for propeller, that would require 13 watts maintian 25mph.

Does this sound right?

If that's the case a 14.8volt 2500mah battery would get me my 2.5 hours.

Mr Cox

On the contrary, you will literally get dead sticks if you are not careful!

After 20 minutes of flying I tend too loose concentration though, can't imagine what it would be like after 4 hours...
Actually I'm not sure my Tx battery would last that long either, so that is another potential dead stick, batteries sure are a pain.

highamperage

lol. Yeah that would be the case, however, this plane is computer controlled by an autopilot (using gyros &gps). After initial take off, I will be turning on the autopilot.

I was just reading a post about duration competition flying. We're talking 4-15 hours.. wow... although Ithink they took turns flying.

BMatthews

You'll be wanting to look into the rules, legalities and liability issues of flying an unsupervised UAV in your area. Since you're in Texas you need to be aware that the FAA and Homeland Security takes a rather dim outlook on folks cluttering up the skies these days. And I don't want to even think about the repercussions should your UAV actually foul with a passing aircraft of any sort.

In any event 13 watts doesn't sound far off. It's generally accepted that a regular style model needs around 13 watts per lb to fly level. A glider type model with a cleaner airframe and lighter wing loading would lower that to around 10 watts/lb.

Keep in mind that calculated numbers and real numbers for this stuff seldom match up to three significant figures. We model builders just do not have access on a regular basis to the computational fluid dynamics software needed to accurately calculate such figures. So in the end and with some prop testing you may find that you need a little more than 13 watts or maybe a little less. But some real flight testing to match up the model to the motor to the prop will be needed to get the very best performance at such low power level flight cruising. For example, if you're going to cruise at 25 mph at reduced RPM then your prop has to have a pitch that will produce that 25mph at the cruise RPM. That may well make it so that it has a poor pitch for climbing at higher power levels. It'll still climb but it may not use the battery power to the optimum for the climb portion.

highamperage

I am familiar with the regulations and it will remain belew 400 feet and in line of sight. It's hard to have any fun thesedays, especially in the US.

Anyway, thanks for the info on power consumption. I've been looking for some basic rule of thumb type calucations, and that 13watts/lb is useful.