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On Oct 10, 7:14 am, Scott wrote:
OK, I guess I can buy into that one, but I'm still confused a bit. If one is limiting it (the O-320) to a given RPM that gives 100 HP out, wouldn't that same RPM give less than 100 HP at high density altitude just as an O-200 would? Scott They're not deliberately limiting it to 100 hp. The fixed-pitch prop does that on any airplane. Your O-320 will make any O-200 look sick. You need to fly a 150 with the O-200, and you won't complain anymore. A 150 with the O-200 on takeoff won't generate anywhere near 100 hp. In fact, I have my suspicions that it never did, even at 2750 RPM. We had those engines in a couple of 150s, and I flew an Aircoupe with a C-90, 10 less hp than the O-200, and it took off much shorter, climbed and cruised much faster than the 150. It generated that 90 hp at a lower RPM, which means that less hp was lost to drag. The airplane weighed only 150 lb less than the 150. A guy in the US did some testing on a 150. He did a static thrust test, full RPM with the airplane pulling on a hefty spring scale. Got around 230 lb, IIRC. Then he took that O-200 out and put in a 100 hp Subaru conversion and did the static test again and got almost 300 lb. That wasn't with a lower-pitched prop, either; the airplane cruised as well as before at a similar RPM. Makes one wonder about hp claims. Dan |
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![]() wrote in message ups.com... On Oct 10, 7:14 am, Scott wrote: OK, I guess I can buy into that one, but I'm still confused a bit. If one is limiting it (the O-320) to a given RPM that gives 100 HP out, wouldn't that same RPM give less than 100 HP at high density altitude just as an O-200 would? Scott They're not deliberately limiting it to 100 hp. The fixed-pitch prop does that on any airplane. Your O-320 will make any O-200 look sick. You need to fly a 150 with the O-200, and you won't complain anymore. A 150 with the O-200 on takeoff won't generate anywhere near 100 hp. In fact, I have my suspicions that it never did, even at 2750 RPM. We had those engines in a couple of 150s, and I flew an Aircoupe with a C-90, 10 less hp than the O-200, and it took off much shorter, climbed and cruised much faster than the 150. It generated that 90 hp at a lower RPM, which means that less hp was lost to drag. The airplane weighed only 150 lb less than the 150. A guy in the US did some testing on a 150. He did a static thrust test, full RPM with the airplane pulling on a hefty spring scale. Got around 230 lb, IIRC. Then he took that O-200 out and put in a 100 hp Subaru conversion and did the static test again and got almost 300 lb. That wasn't with a lower-pitched prop, either; the airplane cruised as well as before at a similar RPM. Makes one wonder about hp claims. Dan Don't confuse thrust with HP unless you're using the exact same prop and prop RPM. An 0-360 powered Robinson R-22 generates what, 1500 lbs of thrust because of gearing, disc area, etc? But, that thrust is only effective in a narrow (vertical) speed range. The same engine, combined with an RV-style cruise prop, would only generate (WAG coming) 250 lbs of static thrust. HP claims on certified engines were +/- 5% back in the day when most "100 hp" 0-200's were built, meaning that a "bad" engine generated 95 HP when it was built. KB |
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On Oct 10, 9:17 pm, "Kyle Boatright" wrote:
Don't confuse thrust with HP unless you're using the exact same prop and prop RPM. An 0-360 powered Robinson R-22 generates what, 1500 lbs of thrust because of gearing, disc area, etc? But, that thrust is only effective in a narrow (vertical) speed range. The same engine, combined with an RV-style cruise prop, would only generate (WAG coming) 250 lbs of static thrust. That Soob had the same diameter of prop and ran at the same RPM. I'm aware of the diameter/RPM/pitch effects, and that's why the results were so startling to me. The 150s performance was much better with the Soob, confirming its output. So either the Soob produced more power than claimed, or the O-200 was really sick. Yet the guy said that the O-200 was OK and the 150's performance with it was typical. Dan |
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![]() wrote in message oups.com... On Oct 10, 9:17 pm, "Kyle Boatright" wrote: Don't confuse thrust with HP unless you're using the exact same prop and prop RPM. An 0-360 powered Robinson R-22 generates what, 1500 lbs of thrust because of gearing, disc area, etc? But, that thrust is only effective in a narrow (vertical) speed range. The same engine, combined with an RV-style cruise prop, would only generate (WAG coming) 250 lbs of static thrust. That Soob had the same diameter of prop and ran at the same RPM. I'm aware of the diameter/RPM/pitch effects, and that's why the results were so startling to me. The 150s performance was much better with the Soob, confirming its output. So either the Soob produced more power than claimed, or the O-200 was really sick. Yet the guy said that the O-200 was OK and the 150's performance with it was typical. Dan I still think it is important to have the *exact same* prop, not just the same diameter. Depending on prop pitch, chord, etc. you could get significantly different amounts of thrust from props with the exact same diameter. |
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On Oct 11, 8:44 pm, "Kyle Boatright" wrote:
wrote in message oups.com... On Oct 10, 9:17 pm, "Kyle Boatright" wrote: Don't confuse thrust with HP unless you're using the exact same prop and prop RPM. An 0-360 powered Robinson R-22 generates what, 1500 lbs of thrust because of gearing, disc area, etc? But, that thrust is only effective in a narrow (vertical) speed range. The same engine, combined with an RV-style cruise prop, would only generate (WAG coming) 250 lbs of static thrust. That Soob had the same diameter of prop and ran at the same RPM. I'm aware of the diameter/RPM/pitch effects, and that's why the results were so startling to me. The 150s performance was much better with the Soob, confirming its output. So either the Soob produced more power than claimed, or the O-200 was really sick. Yet the guy said that the O-200 was OK and the 150's performance with it was typical. Dan I still think it is important to have the *exact same* prop, not just the same diameter. Depending on prop pitch, chord, etc. you could get significantly different amounts of thrust from props with the exact same diameter. Not so much. Efficiencies are typically in the range of 85-90% unless the prop is a real dog, and I don't think Cessna would have continued using the prop they did on the 150 if it was a poor performer. We had an Ivoprop on a 135 hp Soob in a Glastar. Didn't trust that prop, and had problems getting it to run smoothly. We eventually put a Warp drive on it, three Blades instead of two, but the performance was nearly identical even though there were big differences in chord and planform. The guy who put the Soob in the 150 may have used the same prop, but I can't remember. Some of those Soob conversions used the Lycoming bolt circle instead of the Continental, and the Cont's prop wouldn't fit, of course. As you mentioned, a larger, slower-turning prop is far more efficient, so a redrive is better than direct drive, especially where an auto engine is used. The airplane that became the Helio Courier was a much-modified Piper Super Cruiser, IIRC, with a 125 hp Lyc driving a big, slow prop through a redrive using several V-belts. Very rapid acceleration and spectacular climb, aided by slats and flaps and the usual STOL wizardry. Dan |
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