Constant Speed Propellers | PPGS
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- Опубликовано: 10 окт 2021
- As requested by one of you, here's a video on constant speed props.
Practice Written Test Questions: sites.google.com/view/private...
Any video topics you'd like to see me cover? Please leave a comment. I'm desperate for new ideas.
Thanks
Excellent explanation of how a constant speed prop works.
Going to start working on my complex endorsement and this has been a great help.
Thanks !!!
Glad it helped you! Thank you for the kind words
Don’t sell yourself short, I liked the animation! Really helped. Thanks!
Glad you enjoyed it. Thanks for the kind words
I'm using your video for my CFI lesson plans, I hope you don't mind.
The visuals are just too good
Hey, if it helps somebody, that's a win in my book. Glad to see it's useful.
Thanks for the kind words.
Good video! One little remark at 7:04 - I think it would be proper to say to 'ADJUST THE MIXTURE' instead of 'lean it'. When you're low (e.g., about to land around the MSL) - you need a full-rich mixture, not leaned. And when you're gaining altitude you need to slightly lean it every 1000 ft, regardless of whatever you will do up there (practicing slow flight / land at a mountainous airport / other reason to reduce power).
That's a really good point! In my defense, I think there's something along the lines of 'adjust the mixture if you need to', but you're totally right. I hope people read the comments...Thanks for pointing that out. I wish there was a way I could mention all the finer points.
Great video and easy to understand. Thanks. Getting my complex as we speak.
Glad you enjoyed it. Good luck with the complex, it's a fun rating.
Whatchu mean "bad animation?" That was incredible!!!
Thanks for the vote of confidence! As long as it explained what it was trying to, that's a winner in my book. Glad you liked it.
About to do the training for the CSU and RG design features in a 172RG. This was incredibly helpful. Do you have any ground school for the RG component? Couldn't find any in your videos.
Congrats! Hope it works well for you. If you're doing a flight school program or even a complex endorsement, the gear and prop are required to be taught. I'm fairly certain you'll look like a genius knowing what you know about the prop and can also learn about the gear in the process. I don't have any videos on the hydraulics of the gear, because you usually don't see that until your commercial flight training (fixed gear planes are cheaper)... Sorry
very good
Glad you liked it
This is a great video and animation. But I thought pushing in the blue knob deepen or increase the AOA of the blade which decreases the rpm. Maybe I am missing something?
Actu, nvm I think I got it.b
I guess there's no need for an explanation...
Jk, here's one anyway.
Say you set your cruise control and start going uphill. The car will try to maintain the set speed, but might shift into a different gear. It's somewhat similar with the prop. You set the RPM and the prop figures out what angle will give you that. That's the whole flywheel spinning and oil pressure thing.
Living likes all over
Thanks
How does the oil get from a 'non-rotating' engine into a rotating prop hub? Through the back of the crankshaft?
Constant-speed props work on engines with hollow crankshafts. That's how you get the oil in there. Really good question.
Fun fact: if your engine has a solid crank, trying to switch from fixed-pitch to a constant-speed prop won't work.
@@PrivatePilotGroundSchool Check! Thanx for the quick reply. Keep up the good work ... ^v^
Why are propellers twisted? I know it’s too keep the AOA the same at the tip where the blade is faster, but why does relative airflow change with speed and what does this look like accelerating on takeoff?
Thanks
Hopefully this answers your question.
Propellers are twisted because they spin around a central point and the further from the center you are, the more distance is covered in one rotation. The part next to the spinner might cover a distance of a few inches, while the tips can cover 20 ft per rotation. If the blade angle was the same, the inside would go 120 mph, while the tips would be at 550 mph. The same pitch over that entire surface - that would seriously bend the tips forward! So that’s why they’re twisted; to maintain the same angle of attack across the entire propeller. Fun fact, the larger the prop, the lower the maximum RPM limitation (C172 [72 in] - 2,550 RPM, C208 [104 in] - 1,900 RPM).
Based on the above explanation, the blade angle is basically the same over the entire prop - imagine it as a wing, no twisting required. The blade rotates around a plane of rotation, so the relative wind would be from one location (opposite the rotation) if you weren’t moving forward, like when you’re stationary on the ground.
If we equate this to a wing - the same angle of attack, but faster relative wind = more lift. You can also increase the angle of attack for more lift at the same speed. If a fixed-pitch propeller spins faster, you get more thrust. If you increase the propeller blade pitch on a constant-speed prop, you also increase thrust for a given RPM. Hope that wing to prop correlation made sense.
Relative wind on a propeller is the combination of the rotational speed and forward speed. If you look up most explanations, you will see the rotation vector (↓) plus the forward velocity (←) = relative wind vector (↙). The relative wind direction moves forward with more airspeed.
Think of it this way. Imagine an air molecule coming up from directly beneath the propeller. If the airplane is moving forward, by the time that molecule gets to where the prop is, it will have been left behind the prop. The molecule that actually hits the prop is in front of it and comes up at a shallower angle of attack. So the faster you go, the further forward the air molecules are that the prop actually hits. This is why the relative wind moves forward and the propeller angle of attack decreases with forward speed.
On takeoff, you start with a large angle of attack and as you pick up airspeed, the angle decreases as the relative wind moves forward.
A somewhat related thought experiment can be done with the teacup ride at Disney. If the ride was stationary, and you were in one of the cups spinning like crazy, the relative wind would be opposite of the way you spun. Now fire up the ride and spin the entire thing and the wind will be coming from ahead of your rotation due to the forward motion.
Sorry for the long-winded explanation, hope it helps you or whoever is curious. Definitely a neuron-firing exercise.
Great question.
What program did you use to create the animations?
That was all done in Blender. Best part is - it's free! We like that very much.
Great explanation but doesn't the blades actually move what is that about
I'm not sure what you mean by that? Can you elaborate? Thanks
@@PrivatePilotGroundSchool Yeah what I meant to say is don't the blades actually twist or rotate when you move the prop lever
Not directly. But the prop lever moves the flyweights which move the pilot valve and then the blades move by oil pressure. But I get what you're saying, its not like the mixture or throttle.
@@PrivatePilotGroundSchool okay I'm just a sim pilot but I remember years ago watching a video on the prop lever and I thought the blades twist to cut more air or or vice versa.
Hey, there's no shame in being a sim pilot. Do you have a yoke and pesals and all?
And the prop does change angles to take a different size bite of the air. The bigger the bite, the more it pulls forward. You just want to make sure the power is less than the RPM. So 23" manifold pressure and 24 hundred RPM is fine. But not 23" and 2000 RPM.
Glad you're liking the content