How to Fly with a Constant Speed Prop | Transition to Complex Aircraft

when you learn the theory behind how the constant speed propeller system works you get an idea that the procedures for using it in actual flight will add some complexity to the cockpit as with anything your playbook begins and ends with the Pilot's operating handbook specific to your aircraft for our demo today we'll be in a piper Arrow a complex aircraft with an i o 360 engine we'll break down our demo of how to operate the constant speed prop into three parts the run-up checks the climb and cruise phases of flight and finally we'll do some pattern work to exercise some routine procedures you can use to lock in your knowledge of how to use the prop before we get into any of that though let's look at the manifold pressure gauge and what it's really telling us we'll start on the ramp at College Park close to sea level with the engine shutdown our sea level pressure is set on the altimeter at 30 inches 3000 if we're saying it over the radio this gives us an altitude of 50 feet matching our elevation here now we have a glance down at the manifold pressure gauge it's reading exactly 30 inches too the engine isn't on so there's no air being pulled into the engine intake to affect air pressure there this gauge is just reading ambient outside air pressure now if we change the weather so that the sea level pressure is something insane like 32 inches watch how the manifold pressure gauge moves with the change in conditions same thing when we go way back with the pressure so changes in outside air pressure affect the reading on this gauge now let's really drive the point home we're on the ramp in Aspen Colorado High in the Rocky Mountains once again our sea level pressure is set at 30 inches this gives us a correct indicated altitude of around 7 700 feet now look down at the manifold it's about 22 and a half inches of course it is we're much higher up now so the outside air pressure is way lower this is what will happen to our manifold pressure as we climb from sea level pressure of 30 inches to altitudes up here where the air is way thinner keep that in mind as we go through this now let's look at our first phase of flight at the hold short for the runway to do the run-up back at College Park with the engine on and the throttle back to idle the air pressure getting through the intake is very low only around 10 inches let's work through the poh ground checklist we'll set the parking brake then move the propeller fully forward that's the blue handle in the middle of the throttle quadrant when power is applied this setting will bring the prop to its full forward low pitch high RPM blade angle so now let's bring the throttle forward until the RPM reads 2000 if you paid attention in the video on how the constant speed prop works you may ask why the throttle controls the RPM if the whole point of the constant speed unit was so that the prop speed doesn't change with power changes and you'd be wise to ask that the reason is that at low power settings like this the prop is said to be off the governor there isn't enough power yet for the governor to control blade angle to hold propeller RPM constant so at first here it's RPM that changes with throttle increases now just like in other prop planes we'll do our mag check on both sides we can have a look at our vacuum gauge and check oil pressure and temperature our ammeter on the Arrow is a basic load meter it's showing we're charging with the needle to the right we could test it by turning something big on and off like the landing light to see how it responds we'll go up top and test the enunciator panel to make sure all the lights are working now we come to the propeller test we want to make sure the constant speed unit is working properly currently we're at the high RPM setting so there's no pressure being applied to the propeller we'd like to add some pressure and see what happens remember that the blade angle is moved by applying oil pressure to a spring in the prop assembly when we pull the prop control back the additional oil will move the propeller to a higher pitch lower RPM angle we should notice a reduction RPM and a slight increase in manifold pressure as oil pressure is transferred from the case to the prop we'll also see a decrease in oil pressure so we'll do what's called cycling the prop we're going to quickly and smoothly bring the prop control back and as soon as we see a reaction on the gauges bring it back to full forward we could do this only once to produce the desired effect but we may also repeat it once or twice just to make sure we have a look at the oil pressure manifold pressure and RPM gauges it's also not a bad idea to take a look at the cowling to make sure we didn't just cause some oil to leak out so that's our prop Jack the rest of the checklist involves cycling alternate air there shouldn't be a power drop this handbook has us turning off the electric fuel pump to make sure the fuel pressure is okay and then we can bring the throttle back so we've done our run-up checks and would move on to the before takeoff checklist next we're going to take our position on the runway and get ready to roll the prop is full forward giving us high RPM and low pitch for takeoff and will advance the throttle all the way open as we begin our climb out let's focus on the manifold pressure gauge and tachometer close to sea level with the throttle all the way open our manifold pressure is about 28.5 inches while the RPM reads 2 700. now we're at Full Throttle and we'll keep it there as we climb up to 3000 feet but you could probably guess what will happen to our manifold pressure as we do from where we started at 28.5 inches we're down to about 26 inches by the time we approach 3000 feet again this makes sense when you think about how we lose about an inch of pressure for every thousand feet in altitude we climb as a result power drops constant speed or no the higher up we are the less power we produce unless we're able to Turbo Charge our engine so now we begin our level off we'll pitch down which you can only see here on our attitude indicator and as the speed builds we're going to set cruise power how do we do this let's have a look at the poh again in Section 5 we have performance charts we're looking for the power setting tables we have a lot to choose from let's start with our pressure altitude 3000 feet if we want 75 power we'll use this column it tells us we'll want 2500 rpm and at this altitude 25.3 inches of pressure this relationship 25 on the tachometer and 25 on the manifold pressure is sometimes referred to as 20 5 squared besides the fact that combining two 25 figures together and calling it 25 squared isn't really how math works the practice of squaring the gauges leads to one of the more Infamous misconceptions in aviation more on this later for now though the poh has us flying the so-called 25 squared for our altitude here to set that power let's work left to right on the throttle quadrant the first thing we're going to do is reduce power to 25 inches we don't have to come back too far on the throttle to do so next we're going to gently bring the blue prop control back to 2500 rpm never make abrupt inputs on the prop control remember you're playing around with oil pressure on the propeller finally we could bring our mixture back to our desired crew setting and can run through the remainder of our airplane's cruise checklist now let's say we'd like to climb from three thousand four thousand we'll be going back to full throttle with the prop full forward but this time let's move from right to left on the quadrant we'll start by pitching up for a good Cruise climb speed then we'll move the mixture full rich or wherever we want it for the climb then Advance the prop to full forward followed by bringing in full power we'll head up to 4 000 as we do let's look at our cruise table this time let's do 65 power and we have a choice between using 2200 RPM or 2500. let's choose 22. the manifold pressure setting here is 24.7 we'll approach 4 000 bring the nose level and just as we did in the first level off we're gonna work left to right again first the throttle comes back to 24.7 inches which doesn't need to come back much at all to do then we move the prop back to 2200 and finishing with the mixture coming back if you're confused about the logic behind whether you go left to right or right to left the whole thing is set up so that we don't over stress the prop remember when we discussed how this system works at low RPM settings which force the blade to a high angle with high power settings which stress the prop should be avoided So to avoid over stressing the prop power reduction should start with the throttle the prop being the last thing to be reduced so it stays higher it stays on top we go left to right in power reductions like for a level off and power increases like starting a climb we also want to keep the prop on top we work right to left the prop goes up to its position before we advance the throttle to high power if you can remember to always keep the prop on top or don't have the prop in a low setting while having the throttle on a high setting the left to right right to left progression will make more sense for you now back to the discussion on 25 squared in the interest of following the keep the prop on top rule many Pilots over the years have developed the myth that you should never fly over Square so to speak which is their way of saying you can never have a manifold pressure setting that is higher than your RPM so 26 inches of pressure with 2500 rpm would be too much for example but let's think of what we're comparing here manifold pressure reads atmospheric pressure in inches of mercury RPM measures the number of rotations of the propeller per minute these units aren't related to each other in fact if we use the metric system like everyone else the phrase 25 squared would be meaningless instead of 25 inches of manifold pressure would be 850 millibars classic apples to oranges comparison if you want further proof just look to the poh plenty of recommended power settings have us at a manifold pressure in inches above the RPM here are 4 000 feet we're at 65 percent power which uses 24.7 inches of mercury well above the 2200 RPM recommended this point will further be driven home when we look at turbo aircraft that she can be flown at 30 or 40 inches of pressure while still in the mid to thousands of RPM what we're doing with the keep the prop on top isn't a numbers game as much as a best practice to make sure we're not running a low prop setting at high power don't overthink it left to right right to left keep the prop on top we can apply the same principle in a descent back down to three thousand Keep the prop on top move left to right throttle back first prop will want to actually keep up no need to pull it back and mixture as we want it all right finally there's no better way to learn a new aircraft than to do some pattern work with it we can work through every phase of flight in a shorter period of time first we'll start with the takeoff which we've already seen we'll pitch for best climb rate and when we're out of usable Runway bring the gear up some people like to bring the power to 25 squared here to ease up in the engine and that's fine though the poh for the arrow doesn't mention this for a climb I just caution that engine problems often manifest themselves on the first reduction in power so you might want to make sure you have enough altitude before doing so so we're going to fly a regular left pattern we level off at a thousand feet and it's going to be left to right let's do 55 power here throttle the 23.4 inches prop to 2200 and mixture lean For Crews let's turn the fuel pump and Landing lights off to complete the cruise checklist now as we get close to our beam point we're going to introduce a concept that may save your life in a complex aircraft it's a little acronym you may have heard of called gumps gas meaning the fuel selector is on its proper tank undercarriage meaning the gear is down and locked mixture full forward or set for takeoff prop full forward and switches on this will be our short pre-laning checklist and have everything configured in case we need to go around or if we touch and go so a beam the numbers the first thing we'll do is bring the power back to about 12 inches holding the nose up to retain altitude and run through gumps gas which is on the floor and off screen here is on the proper tank will bring the undercarriage down mixture goes full Rich prop goes forward and the switches fuel pump and Landing light turn on when we're in the white Arc we can introduce a flap and start our descent when on base and final run through gumps again to make sure everything is where it should be and also check the gear position lights they should all three be lit up indicating the gear is down unlocked from here we're ready to land touch and go or go around it's all configured for us

Channel: FlightInsight

Views: 142,711

Keywords: constant speed propeller, variable pitch propeller, manifold pressure, constant speed, constant speed prop, flight training

Id: 8_faQNXGpW0

Length: 12min 30sec (750 seconds)

Published: Fri Sep 01 2023