I am wondering where to start on a project I have taken on for work comparing gas v. electric power. I am going for long range aircraft and so far the best we can do is about 75 miles distance with two 10 Ah five cell batteries connected in parallel. This is not good enough and the plane is getting pretty heavy. The batteries are expensive for this amp rating at about $450 each. I can get a saito fg-14 for $400 and it consumes 8cc per minute (assuming WOT??). In one liter of gas that is 125 minutes of run time. 2 liters would defiantly fit in my plane giving a rough estimate of 250 min or 4.16 hours of flight time. At our nominal speed of 32 miles per hour that would give about 130 miles distance. My question is where do I start in modeling the increase of flight efficiency as fuel is consumed and weight is decreased? My first idea is to simulate the plane at MTOW then simulate it at close to empty fuel weight and estimate it from there. Any help in the right direction would be much appreciated.
Thanks

Quitty, the derivation of the traditional aircraft range equation takes into account the weight reduction as fuel is consumed. Although I found the explanation somewhat sparse, the wiki link below offers a derivation of the range equation for both props and jets...

http://en.wikipedia.org/wiki/Range_(aircraft)

Your numbers for the electric system indicate a current draw of less than 10 amps and watts of less than 200 to maintain 32 mph.. The Saito fg-14 is supposed to put out 1000 watts(1.2 horsepower) at full throttle and consume 8 cc/minute max. If your numbers are correct for the electric system, then you will surely be at less than half throttle with a consumption of less than 4 cc/minute.

This is getting up to over 8 hours of flight time on your two liters of gas. Much more and you are going to run out of daylight
Do you have a specific requirement for flight time? Do you already have the airframe? You mentioned a simulation. Is this a specific dynamic model where you can set up an extended flight and directly test your flight time?

i guess the real question is whether this is just a paper exercise or are you planning to build a model gas pipeline sniffer or similar product?

John

Thanks for your input. I have built the model and used the data logger on the speed control to determine the current draw during the flight. For climb it used 11.6 A of power and cruise it used less than 9A. An airspeed sensor was also used and the numbers correlate quite well with the simulation we did over the summer before we built the first prototype. The goal is 100 miles distance. It needs to be fairly slow (30-35mph) because we have cameras on board that take pictures at 3 second intervals. For the proper image overlap 30-35mph is perfect. We are on to our second iteration of the airframe and things are progressing quite well. The airframe can support a gas engine as well as electric. My boss wants us to "quantify" that 100 miles distance is not cost effective when we are carrying two DSLR cameras and possibly a third thermal camera at the same time. He is afraid of gas engines and does not understand them. I will post images of the first prototype and the new fuselage as well. The wiki article (http://en.wikipedia.org/wiki/Range_(aircraft)) is definitely the direction I needed. Also, when comparing gas v. electric I need some direction on which one is actually more dangerous with regards to crashes/fires. The years that I have flown gas models I cannot recall one catching fire or seeing one catch fire after a crash. Thanks guys.

Take a look at this. http://www.barnardmicrosystems.com/L...rossing_II.htm

This site caught my interest a few weeks ago. Great information. I have wanted to use the saito gas engines for over two years now and finally we have been able to quantify that electric power is not going to give us the desired range, unless magically batteries become more efficient today, not "a few years down the road". The people I work with do not like the idea of gas engines because of their inherent complexity, vibration, oil, but I have been tinkering with gas engines for years and find them to be quite reliable if properly maintained and used properly. There are also ways around the interference problems with the ignition system and ways to reduce vibration... really gooey motor mounts. Watch the video of the engine start up on this scan-eagle. The motor is free to wiggle quite a bit. http://www.youtube.com/watch?v=MphgxWidUjo

Thanks, Shoe. this is what I was looking for.