Recent content by dman

It was discussed earlier about the pumping imbalance because the leading cylinder is already flowing before the trailing cylinder ports are open and that at this point the piston velocity is already near its highest. And that this was maybe offset with a small port on the leading cylinder. But...

Yup, just an application of solids of constant width.. Shapes and Solids of Constant Width - Numberphile: http://youtu.be/cUCSSJwO3GU How to Drill a Square Hole: http://youtu.be/L5AzbDJ7KYI

Some of what is said above is correct to the best of the ability to test but isn't the whole story. For one the calculation the delta in rpm cubed shows the change in power output is technically correct. This should be about the change in power exerted to the propeller. However this only proves...

ahh, so you have made some alterations.. with the stroke and displacement up that much and by making the ports to match recommended flow speed then you avoided the things i was talking about. if it was 100% to scale you'd rev too high. this will be fun to see come together.

gues i was mistaken. i didn't realize the stroke would be that short... seems whenever i see a cutaway of these things the rod look short and leaned over pretty hard but perhaps what i've seen hasn't been accurate or i've seen engines from another open wheel series and assumed it was f1.. 2.5:1...

it's a scaled down engine that revs to 20,000 rpm in full size. the ports are gigantic. the biggest thing holdings it back will be valve stability and and timing events. put some ducati style desmodramics on that thing as and see how fast it turns... about the rod:stroke ratio, when it comes...

if you map volume over time or volume to crank angle the only difference is rod:stroke. bore:stroke has zero effect on expansion volume vs crank angle. it's also note worthy that the difference rod:stroke makes is surprisingly small. 1.5:1 is very similar to 1.75:1 but when you push the extremes...

one thing that happens with small scale is th rev range increases. Galileo was the first to notice the cube square law as it applied to animals but it applies to mechanical engineering. with 1/3 scale you may be increasing the rev range 3 times. your port area to cylinder volume ratios should...

there may be long term advantages to american or english machines such as long term parts availability. southbend still stocks some parts from when they got started and has all the old records to know what you need based on your serial number. but i'm sure a chinese lathe of decent size will...

those tuned pipes are upstream. even if that's what you meant a tuned pipe doesn't work like a common collector header on a 4 stroke that uses velocity and inertia and negative reflections from and increasing pipe diameter to scavenge the cylinder and help it blow down as much as possible, also...

agreed that closer angles have less risk of problems. the point of greatest volume under the pistons is when the crank pin is split between the two cylinders, so it's 45 degrees ahead of one cylinder and 45 degrees behind another. when you work it all out the pumping volume is the sine of an...

i may just have to build a 90* one with tuned pipes and maybe reed valves to show it can work... i wouldn't think it's the best compromise but there is no reason that it won't work. it may have more misses on one cyl that the other and not be great for a production engine at large scale but i...

the pumping loss is only 29.3% for a 90* twin but the phasing is all goofy, the truth though is the lower end pumping has more to do with start and idle than power, if you have a reed rather than timing everything and it can pass through the reed directly to the cylinder at the appropriate time...

yeah scraping works. you need a master flat though... if you have a good sized surface plate you can scrape all the flats you need to then go scrape the ways. aluminum will work but cast iron is mostly what the industry uses when they scrape. you can scrape some steels but steel can be very hard...

seems fast. i looked up sfpm for brass and i'm thinking 6-10,000 rpm and .5-1.0 cm/sec if i'm doing the metric conversions correctly.. i know engraving is usually done fast, but is that usually done with a 2 flute cutter? ofcoarse i'm looking at it like a milling operation so if th eengraving...