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How to descend in a prop airliner the right way?

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When you start descending in a prop airliner from cruise (say FL150 or FL180) for approach and landing, do you typically keep the RPM up and just descend at a higher airspeed? Or do you reduce RPM to a lower level and sort of descend in a semi-powered glide to approach altitude? I am not sure of the best way to do this. I've been flying jet airliners for too long!Appreciate any advice, thanks!JS

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Guest nattydread

I believe you can power back(20-40% throttle or whatever power setting is reccomended manifold and/or fuel flow) and then increase RPM in order to slow down quicker if neccessary(lots of drag on the prop at high RPM).You will still maintain a reasonable airspeed, though it will be much more pitch dependent. Thats similar to what I do in my PMDG Beechcraft 1900D.

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Guest bobsk8

I usually set prop rpm to about 2,000 and gradually reduce manifold pressure 3 inches at a time, with a 2 minute wait in between to avoid shock cooling the engine, until Manifold pressure = rpm/100. This works on the Connie and DC6.

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Guest Peter Sidoli

JSIt depends on a number of factors.In principal you are trying to make a flight as efficient in time and fuel as possible.You burn a lot of fuel climbing to altitude and loose time because your IAS/groundspeed is lower in the climb face than in the cruise descent phase.Typically you may want to make up for the initial part of the flight by descending at higher speed.Infact I did an experiment some time back in a Seneca five twin which was flying a double run along the same track the flight was only about 150 nm.On the one trip I climbed low level to 3000 feet and going took 1 hr dead returning took 55 minutes.On the return trip I climbed to 12000 and 13000 and expected because of the climb the trips to be longer. One way was 55 mins the other 50.In piston aircraft I like to leave cruise power setting set and dscend at 1000 fpm keeping the engines warm and getting as high a speed as possible.As you are usually operating in the yellow band this can only be done in smooth clear air and you have to reduce speed through cloud or turbulence.Some like to throttle back (all to their own)Jets and turboprops dont have the cooling problems but are still operated with efficiency in mindPeter

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Hi,If you are talking about piston airliners using large radial engines (R-2800, R-3350, etc.), the rule of thumb is to descend at cruise power. If it appears you will be exceeding the Vno (normal operating speed limit - this is slower than Vne (never exceed)), either reduce power slowly or reduce your rate of descent. Which to do is determined by the cylinder temp of the engines - keep them in the green zone. As stated above, power should not be reduced quickly - 3" MAP per 1 minute is the absolute limit, slower is better. You should normally end up in economy/long range cruise power, and you shouldn't reduce power below that - reduce climb rate instead. You will overcool the engines.Because of the need to keep the power relatively high, descents were rather slow. Most large piston propliners descended at around 700 fpm; the range was 500-1000 fpm. The other major concern with most piston airliners is that they had no way to slow down quickly at the end of the descent to begin the landing approach (no, you should not reduce power below economy cruise at this point either). Careful planning is thus required to be sure you give yourself enough time to slow down to pattern speed. (DC-7's allowed you to lower the main gear as speed brakes for just this purpose.)Hope this helps,--Tom GibsonCal Classic Propliner Page: http://www.calclassic.comFreeflight Design Shop: http://www.freeflightdesign.comDrop by! ___x_x_(")_x_x___

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As Tom touched on, power reduction is a function of time in piston planes. Typically, you should reduce it 1"/min. So if you cruise at 30"MAP and need to reduce to 15"MAP at the start of the approach, then you should begin a 1"/min average power reduction 15 minutes away from commencing the approach. So if your plane cruises at 180kts, the power reduction starts 45 miles out. This is stuff you should plan out beforehand.

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Wow, this is a whole lot more demanding than jet flight! I appreciate the posts and info. I must try this.Thanks!JS

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