How to DOMINATE Learning a Constant Speed Prop

if you're learning to fly a constant speed propeller honestly it can be pretty intimidating at first but i want to encourage you that it really can be a pretty easy transition if you understand these few important points first i think it's super helpful just to understand the whole point of a constant speed propeller if you can understand the why then it really helps understand kind of the how and the what so to speak and really the whole point of the constant speed propeller is just to be able to get a wider range of performance and efficiency out of the engine it's kind of like when you first learn to ride a bicycle on a fixed gear bike you know it's made to be easy to pedal and to accelerate but the downside is that it's actually pretty hard to go fast and maintain that speed because the fixed gear is really designed more for slow rides and acceleration you know the manufacturer had to select a range where that one gear the only gear that it has would work optimally for most use cases of that bicycle now eventually you move up to like a mountain bike that has gears and it'll work more optimally across a wider range of scenarios for example you can climb a hill in a low gear but then at the top of the hill you can also shift to a higher gear that that you know you can go fast and not actually have to pedal as hard and really the propeller is very very similar a fixed pitch propeller kind of has to choose where it's going to be able to perform optimally maybe in acceleration and climb or maybe in crews or maybe a little bit of both it's kind of one scenario that it really excels but but maybe not the other and so that's sometimes why you'll hear someone say yeah i've got a i've got a climb prop on it or i've got a cruise prop on it but a constant speed propeller tries to get the best of both worlds by having a propeller angle that's good for acceleration and performance but then it can be made more efficient in cruise by changing the angle the prop and operating at lower rpms so that's the why and luckily it's not like the entire flight is different you don't have to forget everything you knew about flying airplanes in order just to be able to fly a constant speed propeller and in fact if you think about the different phases of flights you got takeoff uh climb cruise descent and landing we can really remove the first one in the last one takeoff and landing are pretty much identical so that really leaves those three phases of flight in the middle that's going to change a little bit of how we do things but not in a huge way so let's go through an example flight so takeoff is totally normal just use the throttle just like you would in a 172 and then during climb you're probably going to experience your first power setting change now always check your poh and follow that but it might involve something like pulling the throttle back to a lower manifold pressure setting and then slightly bringing the prop back as well to a climb setting like in my 182 the poh calls for 23 inches of manifold pressure and 2450 rpms for climb and this helps reduce engine wear now the fact that we're adjusting two different things for a power setting uh can can kind of make people apprehensive or like wait a second it's not just not just the throttle pushing go fast pull pull back go slow no there's a little bit more to it but it really doesn't have to be complicated in fixed page propellers the primary indication for power is just your engine rpms really that's all you're looking at but in a constant speed propeller we also have a new instrument that is introduced it's called the manifold pressure gauge and the manifold pressure is the pressure of the air within the intake manifold going into the engine measured in inches of mercury hence why it's referred to in inches for a constant speed propeller this manifold pressure gauge is now our primary indicator for our throttle setting and not the engine rpms like it was in our fixed pitch propeller aircraft and this is because the constant speed prop can cap the engine rpms using the prop governor hence why it's called the constant speed prop and and so those rpms are really not a good indication of how hard we're actually pushing the engine now that being said i think it's helpful to remember that the throttle on a 172 and a 182 work exactly the same you're still just opening and closing the throttle valve and so it's not like you're having to completely rework gosh how does the throttle on this engine work it's totally the same you just have one additional control at your disposal and that's controlling the prop and so since we can control the prop rpms kind of kind of separately and we can govern them and cap them in things really the manifold pressure becomes our primary indication for power in a constant speed propeller equipped aircraft so during climb cruise and descent we'll use a combination of manifold pressure controlled by our throttle and engine rpms controlled by our prop lever to achieve our desired power settings so going back to our theoretical flight here in the 182. takeoff was totally normal and now we are climbing we'd first reduce our engine throttle to 23 inches of manifold pressure followed by our engine rpms back to 24.50 now the order in which you do this is usually stressed pretty significantly in training what's most commonly taught here is to not run the engine significantly over square which just means you have higher manifold pressure in inches than you do rpms in hundreds so what do i mean by that well for a quick example if you have 23 inches of manifold pressure and you have 2 300 rpms that would be called 23 squared and so if you had 23 inches of manifold pressure but 2 500 rpms that'd be considered under square because the manifold pressure is lower than the rpms and finally in this quick example if you had 25 inches of manifold pressure but only 2 300 rpms that would be considered over square now having high manifold pressure and low rpms is kind of like trying to climb up a hill in your truck in fifth gear only going like 20 miles per hour you're just really really pushing that engine it's got so much resistance against it that in those extreme cases it really could cause engine damage now that being said i think a lot of us myself included were taught to fear over square situations so much that we thought man if we're like one inch over square like the whole airplane's just gonna blow up or something and that's just simply not the case um you know even if you look in the poh for my 182 i mean there's cruise settings there that involve over square scenarios not to mention turbocharged aircraft which pretty much all the time run over square and in fact there's actually a lot of benefits for running the engine over square i mean within limits of course but you know there's some benefits like reducing the noise in the cabin and getting better efficiency and greater engine life and several others in fact we just put out an article on this over at airplaneacademy.com and i think it's a really good discussion it's got a link to other helpful resources as well so i will link this article down in the description if you'd like to read more the bottom line here is to always look at your poh and even your engine manufacturer's guidance on this topic to see what the allowable range is for manifold pressure and rpm settings you might be surprised to see that the range even includes some over square flying but if we're trying to operate at or under square then the way to do this is whenever you are climbing or descending or accelerating or any of those scenarios you just really want to try to keep the manifold pressure in inches below the rpms in hundreds and i used to really confuse myself like okay like i'm climbing now so which one do i have to do first or i'm descending so which one do i do i pull back first and again you can just simplify all that by just keeping the manifold pressure less than the rpms so going back to our hypothetical flight here we have made it through our climb and now we've reached cruising altitude now in a fixed pitch propeller this is pretty uneventful like in a 172 you usually just leave the power full forward and that's honestly all about all you can do but in a constant speed propeller we've got several different options available to us for power settings and really these are just a trade-off for speed range and fuel burn two settings that i go back and forth on are 23 squared just 23 inches and 2300 rpms and then also 23 inches of manifold pressure and 2450 rpms which is the same as my climb setting so what's the difference well at 5000 feet in my 182 the poh says that running 23 inches and 2450 rpms gives me three percent more airspeed than 23 squared but it burns eight percent more fuel and cuts my range down by five percent so you're going faster but you're burning more fuel to do so so how does that all come out well in a 250 mile trip that works out to getting there about three minutes faster not very much but spinning only five dollars more in fuel now it might feel good to go faster but lower rpms definitely have some benefits i mean you're increasing the life of your engine you're being a little bit more efficient and it's also a lot quieter in the cabin so it's just a trade-off but it's helpful information to know so going back to our flight now during the descent you'll likely need to pull the throttle back to control air speed and you would do so via the manifold pressure you can leave the prop setting exactly where it is because the prop governor should really keep it at your desired setting and once you level off again either in the pattern or maybe at step down altitudes you can advance the throttle again and increase manifold pressure back to your cruise setting which is usually 23 inches for me in the 182. and this brings us to the approach and landing now you'll want to have full forward prop for landing in case you need to initiate a go around and you need takeoff power like immediately but practically speaking as you reduce the engine throttle more and more kind of in the pattern and in your approach and things eventually the prop rpms will start to fall below your established setting even without adjusting the prop setting so for example if you had your props set to 2 300 rpms but the throttle isn't even open enough to drive 2300 rpms in the first place it won't generate 2300 rpms it will start to decrease and when this happens this can be a really good time to advance the prop full forward because you're not going to see a change in the rpms and you'll also avoid a sudden rpm spike and some drag and noise now your landing is just like a fixed pitch propeller you can make adjustments and throttle as needed you'll get a manifold pressure change as well as an rpm change but that that prop is full forward so you're just flying it just like you would a 172 and i think that was kind of a surprise in a light bulb moment for me that like you know when you're doing a lot of the important stuff so the takeoff the landing slow flying things i mean you've really got the prop full forward and in that instance it's literally like no different than all the other airplanes that you've trained and i think understanding that really demystified some of this transition for me where you're really just kind of limiting down to a few key phases of flight where you have to do things slightly differently but other than that you don't have to re-learn how to fly an airplane just to do a constant speed prop you can kind of get the best of both worlds and so understanding when it's important to make different changes is really helpful in the rest of the time you just fly it like a normal airplane and don't forget that for more learning on this topic feel free to check out the article i've linked down in the description i hope and i believe that it should serve you in your aviation journey

Channel: Airplane Academy

Views: 69,257

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Id: -Ba_IpCyKIw

Length: 9min 34sec (574 seconds)

Published: Mon Dec 13 2021