How was this model airplane fuel efficiency record achieved ? Alien technology ?

[bertha_benz]

This model airplane made the first transatlantic crossing (3028 km) with its engine runtime of 38h 52 min 19 sec th_confused0052

https://en.wikipedia.org/wiki/The_Spirit_of_Butts'_Farm

Some stats from the wikipedia page;

- FS-61 0.61 cubic inch (10cc) four-stroke
- CH Ignition CDI spark ignition system
- Smaller valves in engine
- Custom carburetor mounted remotely
- Triple fuel filtration down to 1 micron
- Pressurized fuel tank using crankcase pressure
- "PET" O.S. 0.10 two-stroke engine
- Razor sharp wood propellor 14x12 @ ~3900 RPM
- Indopol L-50 lubricant additive (470 ml) per (3,785 ml) of Coleman lantern fuel

So basically we roughly have the 0.2 bhp output of a 10cc O.S four stroke
Burning fuel at a rate of
2.2oz/hr = 62.36gram/hour (Coleman gasoline fuel / lubricant blend)

Which comes down to roughly;
Every minute => 1ml of blended fuel rotated the prop around 3900 times.

3.9k full combustion cycles per 1ml of blended fuel intuitively feels crazy

Is my math wrong or my intuition?

Seems like there is some synergy going on where the improvement of the individual factors amplifying each other basically.

Is it even possible to break this world record? How would you do it?
Anyone on this corner of the web ever got anywhere near?

Could some ingenuity/innovation in this area from communities like this one eventually "trickle up" towards more fuel efficient lawnmowers, motorcycles etc?

Any thoughts & ideas related to the subject are appreciated!

 

[petertha]

I remember reading about this & wondering the same thing. I suspect there is more info on the net if you keep digging. I'm not sure what magic was behind the engine/mods though, that seems harder to find. If you stumble on any please post, I'm curious too.

http://www.modelaircraft.org/mag/mhill/hillindex.htm

http://www.barnardmicrosystems.com/UAV/milestones/atlantic_crossing_2.html

http://www.telegraph.co.uk/news/obituaries/technology-obituaries/8573491/Maynard-Hill.html

video on youtube, search Tam5

 

[DICKEYBIRD]

Maynard Hill = Genius Model Aircraft Designer. He set that record & others.See this: https://www.modelaircraft.org/mag/mhill/hillindex.htm

 

[Niels Abildgaard]

Some rough numbers
4kg aeroplane with a gliding ratio of 10 flying 3000 km coresponds to lifting 4 kg 300 km up or M*g*H equal to 12 MJ.
2.3 kg of fuel plus lube contains 100 MJ.
Combined efficiency of prop and engine is thus 12%.
A prop with a 80% efficiency is designed by a genius and 60% by a beginner.
Lets say 70%.Engine efficiency must therefore be around 18%.
Fantastic for a 10 ccm.
Some Young people in Copenhagen claims 42.5% for a modified Yamaha 50 ccm.
It will be interesting if some of the small engines made here were measured.

 

[Cogsy]

So basically we roughly have the 0.2 bhp output of a 10cc O.S four stroke
Burning fuel at a rate of
2.2oz/hr = 62.36gram/hour (Coleman gasoline fuel / lubricant blend)

Which comes down to roughly;
Every minute => 1ml of blended fuel rotated the prop around 3900 times.

3.9k full combustion cycles per 1ml of blended fuel intuitively feels crazy

Is my math wrong or my intuition?

Math is a little bit wrong: 3500ml initial fuel load - 44ml remaining = 3456ml/(roughly) 39 hours = about 89ml per hour, so close to 1.5ml per minute so 50% higher than you worked out.

As air (and therefore drag) does not scale, and considering full sized sail-planes can obtain glide ratios in excess of 40:1, I imagine the model had a much higher glide ratio than Niels used in his calcs, thereby requiring much less power (and therefore less efficiency) from the engine. While still an amazing feat, the fuel consumption figures don't seem other-worldly and I'd guess could be bettered by a determined effort.

 

[DICKEYBIRD]

I remember reading the original article in Model Aviation magazine back in the day & they talked about testing engine/prop mods using a test stand on top of a Toyota sedan with the sunroof open driving down the road at the calculated cruise speed measuring all the important numbers with instrumentation inside the car

The transatlantic record attempts started a while after he had broken the world endurance record earlier. I remember that he had trouble breaking that existing endurance record which was held by the Russians. He checked into the weather conditions at the record setting location & saw that the wind at the time was strong & steady for the entire time and the site was at a mountainous location. Turns out the Russian record setter was a sailplane flying in non-stop slope lift with the engine being a very small diesel that just went along for the ride & ran at a fast idle almost the entire time. Maynard set his records fairly & honestly by being a good engineer/modeler with solid thinking & calculations. We lost a master when he passed away.

 

[mcostello]

Two things jump out to a math feeble minded machinist, razor sharp propeller and remote mounted carb. I know the razor edge would help, but how much? Remote carb would lead to tuning benefits if possible. How much would would that help?

 

[swarfrat]

So basically we roughly have the 0.2 bhp output of a 10cc O.S four stroke
Burning fuel at a rate of
2.2oz/hr = 62.36gram/hour (Coleman gasoline fuel / lubricant blend)

Which comes down to roughly;
Every minute => 1ml of blended fuel rotated the prop around 3900 times.

3.9k full combustion cycles per 1ml of blended fuel intuitively feels crazy

Is my math wrong or my intuition?

If it makes a difference, the engine is described as a 4-stroke cycle. That would mean 1950 combustions per minute (3900 RPM).

Swarfrat

 

[Buchanan]

May I ask, what was the OS PET .10 two stroke engine for. Were there two engines?

 

[DICKEYBIRD]

I saw that but I think that's a misprint as it only had 1 engine. Possibly an OS10 carburetor?? If so, I don't think a Pet since they were made in the late 50's - 60's.

Another cool thing is that the original world endurance record model only had a 100mah receiver battery. There was an engine driven generator made from one of those simple bicycle generators to supply the power needed for all the servos & autopilot electronics. Yup, it had an electrostatic wing-leveller system on board. The 100mah battery was there in case the engine stopped so there was enough power to safely dead-stick land it. I don't remember if the transatlantic plane still had the bicycle based generator on it as a few years passed between the endurance record & the trans-atlantic flight. I feel Maynard would've come up with a better mouse trap by then.

 

[Niels Abildgaard]

The 10 ccm fourstroke engine where fed from a carburator from a 1.5 two stroke engine.The engine had been rebuilt smaller valves as well.

 

[mu38&Bg#]

Fuel efficiency and range is not well understood by many. I see Niels has a good grasp. Mr. Hill's achievement comes from the little details of making an engine run for 2 days without stopping. The trial, error, and persistence that lead him to discover those details. The engine performance is in reality fairly good, but easily achievable. The aircraft efficiency was nothing special. It's the reliability of all the systems involved that made it happen. The engine is so sensitive to tuning that the change in viscosity due to fuel temperature and density of air vs day/night temperatures meant setting the mixture just right. Too rich and there wouldn't be enough fuel, to lean and it would quit. There are a few details Mr Hill Never published.

Several of Mr Hill's records were retired most recently after changing the piloting requirement to, I think, 98% of the duration time. If FAI would make this a limited fuel allotment rather than a sleep deprivation event I'd seriously consider a duration record. The autopiloted flights are now UAV not modeling records.

Society of Antique Modelers have a fuel allotment event, but as the name implies requires antique airframe designs. Maybe one day.

Greg

 

[Mechanicboy]

Not only engine modification that made engine economically. The fuel plays a big role: BTU / gal - Kcal/litre in the fuel must be high enough to consume less of the engine. Methanol is not suitable for long trip because of bad energy content is only BTU / gal 56,800 - Kcal / litre 3778.1. So we choose Coleman lantern fuel which has about the same energy content as gasoline, then we get about BTU / gal 114,000 - Kcal / litre 7594 and utilizes the best out of fuel with minimal consumption.

 

[DICKEYBIRD]

Sorry for the drift away from the original topic but the point about the Coleman fuel having more BTU/gal reminded me of one of my friends from the aircraft modeling hobby. He was heavily into U-control "mouse racing" in which the entrants raced against 2 other pilots and the engine used was the ubiquitous Cox reed valve .049. Among his bag of tricks was adding Coleman fuel to the methanol/castor oil/nitromethane mix to increase the lap total between pitstops. I remember him saying it was tricky getting the blend just right for the local weather conditions. As everything in racing, it was a compromise between speed & fuel economy. If memory serves he was able to increase his mileage by an extra 3 to 5 laps per 8cc tank.