Cambo

My Feedback: (2)

If you were to set up and engine for really good fuel economy what would you do. How would prop selection and nitro content affect the flight time?

I know that ther are just so many variables out there but lets asume we are dealing with a 40 size trainer. I am curious if it is possible to get 30-40 minute flights without putting half a gallon of gas in the plane

bkdavy

My Feedback: (1)

Put an LA 40 on the nose with a 16 ounce fuel tank. Set it lean on the ground, and fly it at the lowest possible throttle setting that keeps the plane airborne. It will stay up for 30 -40 minutes.

Look up Maynard Hill and his Trans-Atlantic Model flight. I think it still holds the endurance record. It used a specially modified engine, special fuel mixture. That plane stayed in the the air for over 38 hours with about 5 lbs of coleman fuel (thats probably a little over 1/2 gallon.

Brad

DarZeelon

Cameron,


With a 12 oz. tank (380 cc) and a muffler equipped MVVS .49, I flew for 38 minutes at variable throttle settings (WM Worldstar 40 67" span) and there was still fuel (5% nitro 20% oil) in the tank after the final landing.

Rcpilot

My Feedback: (78)

Just for reference:

Sig Kadet Senior with 78" wing. Kit built.
OS 120 4-stroke. Non-pumped engine. Regular old 4-stroke.
14oz tank behind the firewall.
40oz tank directly on the CG with C/L of tank 1/2" higher than the front tank to help siphon.
APC 16-10 prop at 1/2 throttle. About 6500RPM
Cruising 63MPH+/- at 1/2 throttle

105 miles non-stop with 4oz left in the tank. About 2hrs 15min run time.

Took every bit of 400ft of runway and just BARELY got airborn. Very slow climb-out. Had to nurse it in circles for a few laps around the field to get about 200' of altitude before crusing out for the fun fly. Much brisker performance after it used about 1/2 the fuel. No aerobatics attempted. Just steady and level flight down the side of the country highway.

This was a sanctioned long distance fun fly event and the highway patrol was made aware of our event and we had their approval --- before any of you jump down my throat for being a wreckless outlaw. It's an annual event.

speedster 1919

My Feedback: (3)

The key will be as little nitro as possible. no nitro or 0% gets the best fuel milage. No full throttle use with 1/2 being the norm. Some carbs like to spit out raw fuel while running so a velocity stack would correct this. No performance type mufflers . And a 4 stroke would be a plus for better fuel economy. And then there is prop efficentcy to factor in. We have a club member with a Kadet senior and a TT46 that gets 30 min. with fuel to spare doing touch and go's the whole time with good throttle management. This is with no major power up to get back into the air, but just a gradual throttle increase.

But then there is always plan B

PUT IN A BIGGER TANK

gkamysz

My Feedback: (19)

0% nitro, four stroke engine, increase compression ratio, reduce airframe drag. Going to a four stroke virtually doubles fuel economy in most model engines. I have an FS-48 that I converted to diesel that flew for 25 minutes on 5 oz of kerosene/castor oil fuel, wide open throttle turning an 11x7 at over 10kRPM.

Red B.

That diesel conversion of yours appears very interesting! Please tell us more about how the conversion was done.
Did you get it to run on kersosene/castor only? What about ether that is usually a part of traditional model engine diesel fuel?

gkamysz

My Feedback: (19)

Some links for you.

http://www.rcuniverse.com/forum/m_900816/tm.htm

http://www.rcuniverse.com/forum/m_6053759/tm.htm

http://www.rcuniverse.com/forum/m_4561055/tm.htm This one is very long with a lot of info, but unless you are interested in the technical aspect uninteresting.

Cyclic Hardover

My Feedback: (3)

The first time you ever have a throttle stick at over 100mph, minutes will seem like hours.

Cambo

My Feedback: (2)

Wow, a 2 hour flight

That is sweet

Another question
Why is it that these big gasolines get such good fuel economy. There is a guy at our field that flies a 150cc equipped yak. It gets a 15 minute flight on a suprisingly small fuel tank.

gkamysz

My Feedback: (19)

Gasoline or kerosene, like in my engine, carry much more heat energy, about than double, per unit volume or weight.

http://en.wikipedia.org/wiki/Heat_of_combustion The lower heating value is what we would be interested in. There are many more variables in getting that power to the prop, but that is the main reason gasoline runs for so long for a given volume.

DarZeelon

Cameron,


Gasoline has a stoichiometric ratio, which is roughly 2.3 timed smaller than that of methanol.

Also, gasoline is used with 2-4% incombustible oil, compared to 15-20% for glow fuel.


So, a glow engine of a given displacement, running at a given RPM, would consume about 2.85 times more fuel than an "identical" size and RPM gas engine.

That, plus the much lower cost of the fuel, are the reasons any large engine is always gas powered. And this is despite the greater power potential (about 25% more) from the glow choice.

Methanol fueled engines exist only because they can be 'ignited' by a simple glow-plug and need no elaborate spark ignition system, but fuel costs and consumption limit their size only to small hobby needs...

If it wasn't for the need for a high-cost fuel injection systems and superchargers, we would all be flying true two-stroke Diesels (Orbital rings a bell?)...
...The same guy at your field would only need an 80 cc tank, for the same 15 minute flight, on a true two-stroke Diesel engine...