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#11
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Percent power altitude
Possibly Cessna and Piper have not seen your chart. I have several POHs he
An Arrow PA28R-201 POH shows 75% power, full throttle, at 6,000 feet/2400 RPM and 7,500/2700 RPM. 65% power at about 9,800/2400 and 12,000/2700. (IO-360/200 Lyc.) A Cessna 182T (T-model, not T for turbo) POH has tables that are a little harder to read than the Arrow's graphs, but the highest % power they show at 8,000 feet is 74% and at 12,000 feet 64%. (IO-540/230 Lyc.) A carburated Cherokee Six/260 shows 75% power, full throttle, at 8,300 feet and 65% power at 11,200 feet. Engine RPM is not stated. (O-540/260 Lyc.) I also have a tiny and very complicated power chart from Lycoming for the O-540 but I am too lazy to figure it out. I am no fluid dynamicist (and may be about to prove it), but my dim understanding is that the Reynolds number has a major effect on fluid flow and in its calculation there is a density term. Certainly the mixture velocities at various points in each different intake system would be different. Velocity is also a term in the Reynolds number calculation. So (leaping) it does not surprise me that intake systems with different geometries would perform at least slightly differently at different altitudes. Exhaust systems, too, I'd guess. Possibly I should have been more diplomatic in how I suggested that the OP needed a POH but that still seems to me to be the case. On 10/21/2006 12:46 PM, Bob Moore wrote the following: Mitty wrote You don't have a POH? You know, he might not even have an airplane. He just asked a question and expected an answer, not a wise crack. No POH required, answer is not aircraft specific, see: http://www.kellyaerospace.com/articl...bocharging.pdf Bob Moore |
#12
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Percent power altitude
Yes, after age 60, my recall gets muddy.
"Bob Moore" wrote in message . 122... | Jim Macklin wrote | 5 and 7 thousand | | Running on (faulty) memory again, Jim? | | How about 7,500' and about 12,500', ISA of course. | | See my previous replies to this thread for a real chart | answer. | | The formula answer is: | | bhp at altitude equals bhp at sea level times the quantity | (density ratio minus the quantity(1 minus density ratio divided by 7.55)) | | Works out to 76% at 7,500' and 64% at 12,500', or thereabouts. | | | Bad information is worse than no information at all. | | Bob Moore |
#13
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Percent power altitude
Leaning and density altitude (performance altitude).
"Bob Noel" wrote in message ... | In article , | Bob Moore wrote: | | The formula answer is: | | bhp at altitude equals bhp at sea level times the quantity | (density ratio minus the quantity(1 minus density ratio divided by 7.55)) | | Works out to 76% at 7,500' and 64% at 12,500', or thereabouts. | | OK, I'm confused. Full throttle, 64%, is 12,500' for any engine? | How come my cherokee 140 couldn't even get to 12,500'? | What am I overlooking? | | -- | Bob Noel | Looking for a sig the | lawyers will hate | |
#14
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Percent power altitude
As a first approximation, it should be the same for any normally
aspirated engine (and yes it would be based on DENSITY altitude). The engine develops 100% HP only at sealevel. As the altitude goes up what changes? The density of the air decreases and in response the fuel delivered decreases (from both the carb delivering less fuel and the pilot leaning the mixture). This is the same for all the normally aspirated engines. Now at somewhere around 65-70% power it becomes impossible to get excess EGTs and CHTs due to overleaning the engine. So run the engine at that altitude and lean for max rpm and note the EGT. This is guaranteed to be a safe EGT! Now use this EGT for leaning at ALL altitudes. Thus you have found 100 or so degrees rich of peak without ever having to run the engine at peak (which is too hot and hazardous in itself). Doug wrote: Anyone tell me at what altitude I get 75% and 65% power respctively (with full throttle, normally aspirated). |
#15
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Percent power altitude
Jim Macklin wrote
Yes, after age 60, my recall gets muddy. Hmmmm....at 71, I must have missed that stage. :-) Bob |
#16
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Percent power altitude
Bob Noel wrote:
OK, I'm confused. Full throttle, 64%, is 12,500' for any engine? How come my cherokee 140 couldn't even get to 12,500'? What am I overlooking? Because 64% of whatever HP you have isn't enough to get you there/ hold you there. I've got 300HP in an airframe designed for 185. At 65% HP I'm doing better than they can do with WOT at sea level. |
#17
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Percent power altitude
Note, I did say MY recall. I sleep like a baby now. Go to
bed, wake up every hour or two, cry and go to the bathroom. I my defense, I'm not perfect. "Bob Moore" wrote in message . 122... | Jim Macklin wrote | Yes, after age 60, my recall gets muddy. | | Hmmmm....at 71, I must have missed that stage. :-) | | Bob | |
#18
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Percent power altitude
It depends predominantly on your mixture.
Karl "Curator" N185KG "Doug" wrote in message oups.com... Anyone tell me at what altitude I get 75% and 65% power respctively (with full throttle, normally aspirated). |
#19
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Percent power altitude
"Doug" wrote in message oups.com... altitudes. Thus you have found 100 or so degrees rich of peak without ever having to run the engine at peak (which is too hot and hazardous in itself). What makes you think that? Karl "Curator" N185KG Gami ser# 19 |
#20
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Percent power altitude
Doug,
Thus you have found 100 or so degrees rich of peak without ever having to run the engine at peak (which is too hot and hazardous in itself). Come again? That part in parenthesis is completely wrong. -- Thomas Borchert (EDDH) |
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