Longtoes
New member
Hi! I'm glad to finally make an account after watching Flite Test for quite a few years. Today I'd like to ask about propeller efficiency and how it correlates with aircraft range.
So, from what I've gathered from data, it seems larger props unanimously produce more thrust for a given amount of power. This is because they move more air at a slower velocity than smaller propellers do. Similarly, for producing a fixed amount of thrust, it seems two propellers of the same diameter will more efficiently complete the task than one on its own, again due to lower RPM. I have a few basic questions pertaining to this assumption (or what appears to be a fact) and I'm hoping the community can be helpful in resolving the mystery in my mind!
1. Helicopter rotors are enormous compared to airplane propellers. From what I understand, they produce a ton of thrust for not much power. Why aren't we attaching helicopter-rotor-sized props onto our aircraft for better fuel efficiency? One could cite ground clearance and weight savings, but for the ground clearance issue you could use a tilting system to keep the prop away from the ground and use a secondary prop just for takeoffs and landings. As for weight, I understand this can make a great difference in aircraft performance; regardless, if weight of a propeller is that significant, what kind of function can be used to find the largest feasible propeller for an aircraft at a given cruise speed, altitude, payload, etc.?
2. How does static performance differ from dynamic performance? This is referring to a propeller pulling air through while it is at rest versus when it is flying through the air at speed- I imagine that the difference grows as you add more blades to a propeller, though that's just a guess. Is there data on this out there that is easily accessible?
3. Why aren't propellers long and skinny like glider wings (high aspect ratio)? Aerodynamics seem to favor long, thin wings with high aspect ratios when it comes to aerodynamic efficiency. Why use a propeller with wider blades at the root if that lowers the aspect ratio? Wouldn't it decrease performance? And if it is contrary to what I'm thinking (that propellers SHOULD have long thin blades with a high aspect ratio) then why is it so? It seems to contradict very important principles of aerodynamics. That said, I'm just an enthusiast, and though I am an engineering student, I haven't taken any aerodynamics classes.
I will probably think of more which I will post later, but these are what are on my mind at the moment. Thank you ahead of time for your patience with any ignorance I display. I am looking forward to making friends with the folks here in the Flite Test forum!
EDIT:
Just thought of another question. Do you think it'd be worth looking into the effect of prop-span to wing-span ratio on aerodynamic efficiency? It may have already been looked at but I figured I'd ask anyway. Thanks again!
So, from what I've gathered from data, it seems larger props unanimously produce more thrust for a given amount of power. This is because they move more air at a slower velocity than smaller propellers do. Similarly, for producing a fixed amount of thrust, it seems two propellers of the same diameter will more efficiently complete the task than one on its own, again due to lower RPM. I have a few basic questions pertaining to this assumption (or what appears to be a fact) and I'm hoping the community can be helpful in resolving the mystery in my mind!
1. Helicopter rotors are enormous compared to airplane propellers. From what I understand, they produce a ton of thrust for not much power. Why aren't we attaching helicopter-rotor-sized props onto our aircraft for better fuel efficiency? One could cite ground clearance and weight savings, but for the ground clearance issue you could use a tilting system to keep the prop away from the ground and use a secondary prop just for takeoffs and landings. As for weight, I understand this can make a great difference in aircraft performance; regardless, if weight of a propeller is that significant, what kind of function can be used to find the largest feasible propeller for an aircraft at a given cruise speed, altitude, payload, etc.?
2. How does static performance differ from dynamic performance? This is referring to a propeller pulling air through while it is at rest versus when it is flying through the air at speed- I imagine that the difference grows as you add more blades to a propeller, though that's just a guess. Is there data on this out there that is easily accessible?
3. Why aren't propellers long and skinny like glider wings (high aspect ratio)? Aerodynamics seem to favor long, thin wings with high aspect ratios when it comes to aerodynamic efficiency. Why use a propeller with wider blades at the root if that lowers the aspect ratio? Wouldn't it decrease performance? And if it is contrary to what I'm thinking (that propellers SHOULD have long thin blades with a high aspect ratio) then why is it so? It seems to contradict very important principles of aerodynamics. That said, I'm just an enthusiast, and though I am an engineering student, I haven't taken any aerodynamics classes.
I will probably think of more which I will post later, but these are what are on my mind at the moment. Thank you ahead of time for your patience with any ignorance I display. I am looking forward to making friends with the folks here in the Flite Test forum!
EDIT:
Just thought of another question. Do you think it'd be worth looking into the effect of prop-span to wing-span ratio on aerodynamic efficiency? It may have already been looked at but I figured I'd ask anyway. Thanks again!
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