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#11
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"Stuart Grant" wrote in message
om... [...] I think I DID find the answer in my pilot handbook. The range curves show significant increase in range with the same MP and lower RPM. Manifold pressure 22" and 1800 RPM for example. Your handbook is telling you something different. That is, that the engine is generally more efficient for a given percentage horsepower when the lower RPM is selected. That will always be true, but it doesn't mean there's a reduction in airframe drag, which is what you asked about. As Dale said, if the engine is driving the prop rather than the other way around, reducing prop pitch isn't going to change the drag of the prop. Now, if you have an engine failure, or are gliding with the power completely reduced, that's a different story and reducing prop RPM will increase your glide range. But that's not what you asked. In descent the reduced power would be made up for by gravity for a more constant airspeed. I think I will try this. I don't understand "more constant airspeed". In a stabilized descent, the airspeed should always be constant. You are certainly right that in a descent, gravity adds thrust (equivalent to adding power), so you can reduce power and maintain the same airspeed. This is, in fact, a technique that is usually taught to every pilot during their initial training: to descend while maintaining your current airspeed, simply reduce power. The airplane will remain at (or near) its trimmed airspeed, and will descend at that airspeed. Pete |
#12
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William W. Plummer wrote:
You should not linger between altitudes. Everybody, other pilots and ATC, expect you to be at the correct altitude. Safety, not economy, demands this. Yeah, you need to get down smartly to an altitude where everybody else is. It's so much safer. Jack |
#13
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William W. Plummer wrote: You should not linger between altitudes. Everybody, other pilots and ATC, expect you to be at the correct altitude. Uh, no we don't. You are where you are. |
#14
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#16
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#17
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Newps wrote in message ...
Stuart Grant wrote: In my 182 I always fly balls to the wall on a cross country. WOT minus a little to tickle the needle and 2450 RPM. When it comes time to descend I do not touch power and just roll in a turn of trim, that gets me 500 fpm down and an extra 15-20 knots. I pull the throttle back just enough to maintain the same MP as I come down (adjusting every 2000 feet or so). If you forget to roll the throttle back, you'll end up pulling 30" in the pattern. -Robert |
#18
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Is it better to reduce MP and leave RPM at 2200? In my Mooney I like VFR decents at whatever speed I had been cruising. It's my habit in cruise to keep the RPM low, almost always going a little 'oversquare' (MP in inches a bit higher than RPM in hundreds). I don't like speeding up in the decent, and consider the altitude energy in the bank, I spend it on haaving the MP lower. But your giving up all the speed you should have gotten back from the climb. You fly slower in the climb but get it back when you start down. Pulling power back just gives it all up I admit to not running the numbers on that. I figured I chose an airspeed that made sense, save a little fuel on the decent, and even if I come down from 11500 at 500 fpm it's what -- 21 minutes to pattern altitude. At 150 kts + wind, that means I start down about 50 miles out. If I come down at an average of say 165 ktsI'd be starting down maybe 8 miles sooner. Maybe it's as much this as anything -- I mostly do XC under IFR, and like to keep whatever is the filed airspeed. |
#19
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"Robert M. Gary" wrote in message
om... But your giving up all the speed you should have gotten back from the climb. You fly slower in the climb but get it back when you start down. Pulling power back just gives it all up. It's just a matter of what you want to get back. You are right, you are sacrificing speed (energy banked during the climb), but you get in return fuel efficiency (energy banked during the climb). Which is, essentially, what AJW wrote in the first place. You don't lose the energy. You just use it differently, depending on your power setting. Thermodynamically speaking, the lower power setting also produces the more efficient use of the energy, but of course flying isn't always about what's most efficient. Pete |
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