Cjserio
Filing Flight Plan
Here's the situation...The aircraft's a Piper Arrow IV...Constant Speed prop...
Let's say we're at cruise at 6,000MSL and let's say we're at 2400RPM and maybe 23-24" of MP cruising around 130kts or so. It's time to descend.
Conventional "wisdom" (I use the term loosely) says you start bringing the throttle back a bit (maybe a couple of inches), pitch down and do a cruise descent...leave the prop alone. You're fine in the descent, cooling the engine a bit until it's time to slow down for the pattern...then you essentially have to chop the power back a bunch...when you manage to get the speed down, deploy the gear, get into the white arc and start bringing in flaps as appropriate to continue slowing. Eventually on final or short final you can bring the prop level full forward (high RPM) now that you're off the governor and land.
I'm doing some recurrency training with a new instructor and he's adamant about the procedure he's been using for decades. His procedure is essentially to creep both the MP and the prop RPM back somewhat simultaneously. Come back a couple of inches of MP, prop back 200RPM or so and pitch down. As it's time to slow in the pattern, bring the MP back a bit more, prop back a bit more as well etc.
His reason is that reducing the prop RPM with the MP will allow you to reduce your airspeed quicker which means you won't have to "chop the power" as drastically...which of course means reducing temperature stress on the cylinders.
This seemed counter-intuitive to me since I've always thought of the props having the highest drag due to windmilling when at the lowest blade pitch (full forward)...so reducing prop RPM when trying to slow the plane seemed backwards...but his statement is that on an arrow, the difference between pitches is minor (15 degrees from extreme min to max) and that reducing the prop rpm will have more of an effect on reducing the power/thrust it's putting out than flattening the blade angle can by increasing it's drag. Also, it's not going to be "windmilling" substantially anyway until you're nearing idle...and since we're trying to avoid having to chop the power back that far anyway, it's not a factor.
Our "test flight" to prove his theory to me today got rained out but I'm not sure what to think any longer. I feel like training nowadays is very lacking on how to USE constant speed props. There are hundreds of books on how they work but very little written on how to use them. Everyone seems to simply go full forward on takeoff and on short final...and only ever use 2500/2400/2300RPM depending on the cruise setting they choose. Surely the prop lever is a lever and not a switch for a reason.
How are YOU using your prop lever?
Let's say we're at cruise at 6,000MSL and let's say we're at 2400RPM and maybe 23-24" of MP cruising around 130kts or so. It's time to descend.
Conventional "wisdom" (I use the term loosely) says you start bringing the throttle back a bit (maybe a couple of inches), pitch down and do a cruise descent...leave the prop alone. You're fine in the descent, cooling the engine a bit until it's time to slow down for the pattern...then you essentially have to chop the power back a bunch...when you manage to get the speed down, deploy the gear, get into the white arc and start bringing in flaps as appropriate to continue slowing. Eventually on final or short final you can bring the prop level full forward (high RPM) now that you're off the governor and land.
I'm doing some recurrency training with a new instructor and he's adamant about the procedure he's been using for decades. His procedure is essentially to creep both the MP and the prop RPM back somewhat simultaneously. Come back a couple of inches of MP, prop back 200RPM or so and pitch down. As it's time to slow in the pattern, bring the MP back a bit more, prop back a bit more as well etc.
His reason is that reducing the prop RPM with the MP will allow you to reduce your airspeed quicker which means you won't have to "chop the power" as drastically...which of course means reducing temperature stress on the cylinders.
This seemed counter-intuitive to me since I've always thought of the props having the highest drag due to windmilling when at the lowest blade pitch (full forward)...so reducing prop RPM when trying to slow the plane seemed backwards...but his statement is that on an arrow, the difference between pitches is minor (15 degrees from extreme min to max) and that reducing the prop rpm will have more of an effect on reducing the power/thrust it's putting out than flattening the blade angle can by increasing it's drag. Also, it's not going to be "windmilling" substantially anyway until you're nearing idle...and since we're trying to avoid having to chop the power back that far anyway, it's not a factor.
Our "test flight" to prove his theory to me today got rained out but I'm not sure what to think any longer. I feel like training nowadays is very lacking on how to USE constant speed props. There are hundreds of books on how they work but very little written on how to use them. Everyone seems to simply go full forward on takeoff and on short final...and only ever use 2500/2400/2300RPM depending on the cruise setting they choose. Surely the prop lever is a lever and not a switch for a reason.
How are YOU using your prop lever?