with an overall weight of 35 lbs for the race engines. I can't remember the specific BHP figures, but they were generating the same shaft outputs (and higher) than 1,000 cc bikes

OK, that would work out to be about 2.5 HP per pound, about what is being claimed for the Aircar engines. But that is maximum, peak power, and even at a 70--75% cruise setting, would not be sustainable for uninterrupted hours at a time. It's been a while since I was really up on rotary (Wankel-type) engines... but I seem to recall problems with apex seal failures under heavy sustained loads as are typically encountered in an aircraft environment.

Norton specifically marketed the engine for lightweight, airborne applications, including drone engines and unmanned surveilance aircraft.

Yes, but not at anything approaching 120 HP rating, I suspect. A typical aircraft engine (Lycoming, Continental, etc.) puts out power in the neighborhood of about 1/2 horsepower per cubic inch displacement. Compare that to something like a Honda S2000 engine which puts out something in the neighborhood of two horsepower per cubic inch -- four times the specific power output. So why are regular aircraft engines so "inefficient"? Because they have to operate at 75-80% of their maximum output for hours on end, and 100% of maximum during takeoff. They have to keep the stresses down to keep the longevity up (and even so, they must be overhauled after each 1000 hours of use) which means big cubic inches, little horsepower. Small, highly efficient engines are not normally suitable for light aircraft use.

They have excellent fuel economy and low weight - the road bikes they powered regularly returned around 34-40 mpg

[Sarcasm]Whoopee! A 350 pound motorcycle, operating at (on average, probably) 1/3 to 1/2 maximum power output, on the ground (no need to waste power generating lift) at speeds averaging less than 1/4 the speed claimed by the Aircar and with about 1/5 the gross weight and maybe 1/10 the frontal area can get more than twice the claimed mileage of the aircar. I'm not impressed.[/Sarcasm] I'll bet that on a measured economy run averaging, say, 80 miles per hour, that a Honda Insight with two passengers and luggage, would do better than that motorcycle. (The Honda would pull down 45-50 MPG at that speed, I belive...)

I think they are referring to the dBA (perceived loudness) levels on the ground.

Absolutely -- from a distance of 500 feet. That's not very far away, and those fans are going to make a good bit of noise, ducted or not, as the blade tips are approaching supersonic (they are small diameter, they have to turn them fast Let's see, they look to be a bit under three feet in diameter, call them 2.9 feet across. That's 9.1 feet around, they're turning them at 7200 RPM at takeoff, that's 65,520 feet per minute. Speed of sound is, what, 1100 feet per second, 66,000 feet per minute, that means those blade tips are turning at mach .993. Yep, that's pretty close to supersonic) and pretty damn noisy. Then, you have eight unmuffled (I assume unmuffled, otherwise you give up power) rotary engines running at maximum output. I'm sure you've heard an unmuffled rotary under those conditions -- hell, if they fired it up in Dover you'd hear it clear across the Channel in France. Now imagine eight of them at once... 65 decibels at 500 feet? No way. A typical office environment (with people conversing, air handlers blowing air around, etc.) is louder than 65 decibels.

PPS How did we get to be talking about rotary engines when we started out about AR screens?

Y'know, that's what I love about this bbs. It sometimes goes off on the most fascinating tangents!

tanstaafl.











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