ORIGINAL: radial1951
Detlef, this thread might be under Glow Engines but there have
NOT been complaints about references to non-radial gassers.
All of this technology is applicable to radials as well, and
very interesting.
Speaking of which, could you explain what valve timing for inlet and exhaust you have chosen for your
V-4? My dream is to build a radial for myself,
for flying, not just display. I have the basic design done, but cannot decide on the valve timing/duration. I have the valve specs for many engines, but they vary enormously. I'm sure other members here would also be interested to see your thoughts on the subject.
Regards RossG
radial1951
Ross,
I dont want to spam your radial thread here more than I already did, but you ask, and I will reply. To make it more convenient , lets compare a
radial with a cam timed engine like a twin or a Vee..
I dont think that the timing profiles ofthis Vee are useful for a radial. I have camshafts, a radial has a cam-drum (?? please help me with the correct term). With a camshaft you can achievefaster accelerations in your valve train, resulting in steeper flanges of your lift curve. In the mechanical situationof a radials cam-drum with tappets ( oh those terms again) the chance for high acceleration of your valve train is rather limited. This doesnt matter as long as you are not after high rpms. And so that is pretty ok for a typical radial model engine .
A very good example for this effect is the
SAITO R325.
I had thisvery untypical radial engine some years ago. It has5 real camshafts, being truly an amount of 5 single engines. This engine behaved like a turbine, it loved rpms (prop 18x10 with 8500 rpm!!) , not so much it did like a big prop. Already with a 20x10 it didnt like to be combined, breaking down to under 6000 or so if I remember coorect. You could hear that the engine behaved much worse with that. The timing they used was of their singles, and those do rev between 8000 and 11.500 rpms, not made for 5800-1 (!)
In my Vee, I have a reduction drive at the front end; allowing theengine to revv higher than a (non geared) radial.The engine has big valves, a compression ratio of 10:1, big inlet and exhaust ports and headers. This is again of influence on the timing curve. The engine will operate up to 9500 rpm, releasing (hopefully) a serious amount of horses. If you lay my timing curves over that of a typical model radial engine, the difference is eye-catching. Also, I have 3 different cam profiles for different applications, depending on if you are interested in driving a maximum big prop at lower rpm ( a torque profile) , or, on the other side, are in search of the maximum power output at high rpms. The range of timing I use is from 260 to 300°, the ovelapping ranges from 50 to 85 °. Valve lift is around 21% to 27% of the valve diameter, depending on the profile type as described above. The higher values of overlapping make only sense when you have the chance to tune the lenght of your exhaust and inlet port ( not really easy with a ring collector of a radial..
)
If there is interest, I can post some details as soon as the engine is on its test bench, hopefully by the end of this year. But then I really will open a new thread for that...sothis radialplace will not longer be spammed
