Another two benefits of reduction drives: 1) allows for lower engine mounting & 2) reduction gearboxes with slipper clutches provide some protection to the engine in case of a shock load/prop strike.
One correction: PSRUs generally increase the power to weight ratio of an engine, as they allow a smaller engine to perform the same amount of mechanical work as a larger engine. Rotax 912 iS: 100 hp; 64 kg; 1.56 hp/kg; 2,388 rpm @ propeller. ULPower 260iS: 107 hp; 72.3 kg; 1.48 hp/kg; 3,300 rpm @ propeller. Continental O-200-D: 100 hp; 89 kg; 1.12 hp/kg; 2,750 rpm @ propeller. Lycoming O-235-C1A: 100 hp; 107 kg; 0.93 hp/kg; 2,450 rpm @ propeller. Lycoming O-235-F1B: 125 hp; 113 kg; 1.1 hp/kg; 2800 rpm @ propeller. Really, improving power to weight ratio is one of the most important reasons why PSRUs are used on aircraft engines. Just imagine how big a direct-drive Merlin would have needed to be in order to make its power at 1,200 - 1,400 rpm at the propeller (probably at least 60 liters).
Did a dod gig . We used herth 2 strokes . We used a belt driven reducer. Seemed to work ok . Think they were 150 hp each . We ran two belts of which each were able to carry full load
This is all new to me I'm trying to learn... Let me know if I'm understand this right. Will a reduction drive be the same as transmission in a car? So would the axle rpm be like the prop rpm then?
Yes that's correct, though a reduction drive is a single fixed gear ratio where a car has 5 to 7 gears usually. The prop rpm would be like the car's wheel rpm.
A very complicated topic. I think we have spoken about it previously. In short a re-drive is more efficient, this is why they are pushing for them in airliners, this is why helicopters use them. Rotating a larger propeller slower is more efficient than turning a small propeller faster. How much power/torque an engine produces (on a dyno graph) means nothing compared to how much power a propeller consumes. At 8:00 you compare two engines with different propeller rpms, but don't explain the propellers will be different. Even with variable pitch propellers, if you increase the pitch to absorb the torque, this does not mean that the increase in thrust will be proportional. There is very little data that is shared with regards to power made, power utilised, what propeller is being used at what airspeed and density.
Yes I think I know where you are going, thrust propels an aircraft forward, not engine hp. But I'm talking about hp, torque and rpm in this video, not thrust. I'm trying to break - as you said - a complicated topic into understandable chunks in a video that isn't hours long. This is the basic understanding on the torque and PSRU subject that can be built upon, or at least that's how I see it. I think clearly you understand the subject already and moving on to the more complicated subject of thrust.
@@LetsGoAviate I'd like to know more about prop speed reduction unit failure modes. I read they fail often and that torsional vibration destroys them.
Thank you again. I am building a Pietenpol and have a 2 cylinder BMW 1200 GS engine of unknown hours and came from a previous aircraft installation. It is fitted with a Rotax C gearbox. I have not started on this part of the project. This video applies directly to my project. As a matter of interest, would a C gearbox be able to handle this application? Thanks again.
Let me know the reduction ratio of your C box. The Rotax C gearbox comes in different reduction ratios, between 2.62:1 and 4.0:1. My guess is 2.62:1 as that will give a max propeller rpm of 2,600 (assuming engine max is 6,800). If it's the 3.00:1 or higher ratios you will need a big propeller. I think the Pietenpol sits quite low when you lift the tail so you might be limited in prop diameter for ground clearance. What was the previous application of the 1200GS?
@@LetsGoAviate Thanks for the response. I have not opened the gearbox yet, because I am still working on the airframe. I hope it is 2.62.1. Will the gearbox be robust enough for the engine? I have no information on the previous application. It has dual fuel pumps dual ECU's and is standard with dual sparkplugs. I am considering adding an additional injector to each cylinder for redundancy, as well as small second battery. Also centrifugal clutch. Thanks again.
This video explains in a great way a question i always had about airplanes and engine rpm/ torque! You gained a subscriber.
This is by far the best explanation of torque/rpm relation I've seen 👍
This was very helpful. I appreciate your thorough yet digestible explanation of what can often be a complicated topic!
Always enjoy your technical videos. Well done
Thanks!
I like your videos like this one were you do some deep research and present the fact as you see them. Thanks for posting.
superb great explanations, trying to calculate the best reduction drive for my paramotor as I am always trying different prop dia & pitch
too bad this vid isn't getting the views it deserves when the quality is so similar to driving4answers
Thanks! Yeah the aviation audience is much smaller than the motoring audience. It's fine. I like making videos that addresses confusing topics.
Great video Jaco, thank you for your time and dedication
very good video
Another two benefits of reduction drives: 1) allows for lower engine mounting & 2) reduction gearboxes with slipper clutches provide some protection to the engine in case of a shock load/prop strike.
Great video!
One correction: PSRUs generally increase the power to weight ratio of an engine, as they allow a smaller engine to perform the same amount of mechanical work as a larger engine.
Rotax 912 iS: 100 hp; 64 kg; 1.56 hp/kg; 2,388 rpm @ propeller.
ULPower 260iS: 107 hp; 72.3 kg; 1.48 hp/kg; 3,300 rpm @ propeller.
Continental O-200-D: 100 hp; 89 kg; 1.12 hp/kg; 2,750 rpm @ propeller.
Lycoming O-235-C1A: 100 hp; 107 kg; 0.93 hp/kg; 2,450 rpm @ propeller.
Lycoming O-235-F1B: 125 hp; 113 kg; 1.1 hp/kg; 2800 rpm @ propeller.
Really, improving power to weight ratio is one of the most important reasons why PSRUs are used on aircraft engines. Just imagine how big a direct-drive Merlin would have needed to be in order to make its power at 1,200 - 1,400 rpm at the propeller (probably at least 60 liters).
Thank you so much
Did a dod gig . We used herth 2 strokes . We used a belt driven reducer. Seemed to work ok . Think they were 150 hp each . We ran two belts of which each were able to carry full load
Thanks
This is all new to me I'm trying to learn... Let me know if I'm understand this right. Will a reduction drive be the same as transmission in a car? So would the axle rpm be like the prop rpm then?
Yes that's correct, though a reduction drive is a single fixed gear ratio where a car has 5 to 7 gears usually. The prop rpm would be like the car's wheel rpm.
When comparing propeller size and frontal-cross-sectional-area, how large can a propeller get before adds to the drag characteristics
With some caveats, bigger is better as long as the propeller tips dont go too close to the speed of sound (and the usual ground clearance problem)
A very complicated topic. I think we have spoken about it previously. In short a re-drive is more efficient, this is why they are pushing for them in airliners, this is why helicopters use them. Rotating a larger propeller slower is more efficient than turning a small propeller faster. How much power/torque an engine produces (on a dyno graph) means nothing compared to how much power a propeller consumes. At 8:00 you compare two engines with different propeller rpms, but don't explain the propellers will be different. Even with variable pitch propellers, if you increase the pitch to absorb the torque, this does not mean that the increase in thrust will be proportional. There is very little data that is shared with regards to power made, power utilised, what propeller is being used at what airspeed and density.
Yes I think I know where you are going, thrust propels an aircraft forward, not engine hp. But I'm talking about hp, torque and rpm in this video, not thrust. I'm trying to break - as you said - a complicated topic into understandable chunks in a video that isn't hours long. This is the basic understanding on the torque and PSRU subject that can be built upon, or at least that's how I see it. I think clearly you understand the subject already and moving on to the more complicated subject of thrust.
@@LetsGoAviate I'd like to know more about prop speed reduction unit failure modes. I read they fail often and that torsional vibration destroys them.
Thank you again. I am building a Pietenpol and have a 2 cylinder BMW 1200 GS engine of unknown hours and came from a previous aircraft installation. It is fitted with a Rotax C gearbox. I have not started on this part of the project. This video applies directly to my project. As a matter of interest, would a C gearbox be able to handle this application? Thanks again.
Let me know the reduction ratio of your C box. The Rotax C gearbox comes in different reduction ratios, between 2.62:1 and 4.0:1. My guess is 2.62:1 as that will give a max propeller rpm of 2,600 (assuming engine max is 6,800). If it's the 3.00:1 or higher ratios you will need a big propeller. I think the Pietenpol sits quite low when you lift the tail so you might be limited in prop diameter for ground clearance. What was the previous application of the 1200GS?
@@LetsGoAviate Thanks for the response. I have not opened the gearbox yet, because I am still working on the airframe. I hope it is 2.62.1. Will the gearbox be robust enough for the engine? I have no information on the previous application. It has dual fuel pumps dual ECU's and is standard with dual sparkplugs. I am considering adding an additional injector to each cylinder for redundancy, as well as small second battery. Also centrifugal clutch. Thanks again.
I'm not actually sure what the max hp rating on the Rotax C box is. Might have to check with an AP or someone with experience, to be safe.
Thank you so much.@@LetsGoAviate
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lower rpm，higher torque , bigger blade, mean lower noise, higher efficacy.
5252 I believe is where torque and horsepower meet on a dyno test. The lines always cross at that rpm.
promo sm ❗