smed
Nov 23, 2003, 02:41 AM
Hello everyone, perhaps you remember me from a few posts which I have made in the past concerning my propeller research. I am a high school senior, and have been working for the past 3.5 years on this project. I am in the final stages of designing propellers and having them wind tunnel tested. I thought that I would update you guys.
Here is a brief 175-word abstract:
THEODORSEN-BETZ MAV PROPELLER PERFORMANCE WITH LOW REYNOLDS NUMBER AIRFOILS
Abstract
The principles governing propeller operation are the least understood aspect of flight, even though propeller aerodynamics has been studied since the 1870’s. On the other hand, the basic science of propellers is well known and documented. Recently, there has been much interest in improving MAV (Micro Air Vehicle) technology for the military. In the future, these propeller-powered spy planes will become crucial in gaining tactical advantages in combat. However, there has been limited research on these low Reynolds number airfoils and propellers, which operate differently than their larger counterparts. In the experiment, the researcher will show the effects of low Reynolds number aerodynamics on special “Theodorsen-Betz” propellers, each of which will have different airfoils and be precisely machined out of maple wood. It is hypothesized that the thinnest and often unconventional airfoils will be most successful. The researcher will contribute to the field by conducting a dynamic experiment to measure propeller performance. Tests will be conducted at a University wind tunnel, which employs especially sensitive instrumentation to precisely measure lift, drag, thrust, and efficiency.
-----------------
And a little more in-depth description:
My study will test propellers with optimized low Reynolds number airfoils according to XFoil- generated polars, and also with propeller airfoils designed to varying coefficients of lift. I will also use flat plate and curved plate airfoils on my propellers, which performed surprising well at low Reynolds numbers in wind tunnel tests.
The design specifications (thrust, rpm, diameter, forward speed) of my propellers are the same as those for Aerovironment’s "Black Widow" Micro Air Vehicle. I chose these specifications because the Black Widow is most successful MAV to date, and so that my propeller results were applicable to real Micro Air Vehicles.
The propeller designs were optimized using Theodore Theodorsen minimum induced-drag math on Betz propellers, with high aspect ratios, about 14, and narrow tips for low tip loading and loss.
Luckily, Micro Air Vehicles fly mostly at one altitude, air density, rpm, and forward flight speed, so this simplifies the designing process.
Right now I am working on optimizing the low Reynolds number airfoils, which often are 5% thick! Any low Reynolds number airfoil experts out there? I will probably be posting with some questions in the near future..
I am also looking into fabrication options. I may be having the propellers made out of maple (!) on a real fast cnc machine. We shall see. Carbon fiber (with cnc'd aluminum molds) or machined maple or some synthetic seems to be the only option for these props, because the resolution of the airfoils is so crucial. .001" makes a big difference, unfortunately.
And depending on how long this all takes, (everything takes so much time!!!) I may be able to enter some competitions before the end of the school year. I am aiming to have my paper done by March 1st, and I have already started writing the methods and materials and the background information on military interest in and uses of MAVs, propellers, low Reynolds number aerodynamics, etc.
Kindly, Adam
I hope you found this interesting and I would love to hear your comments. I am way am just applying to colleges and looking into aero engineering... Not sure if I want to commit to so much math and physics though... I did have a very nice conversation about my project with an aero professer, by the name of Gallimore at the University of Michigan when I visited, and Umich claims to have the #1 aero program in the US. He told me to go for it, and to transfer schools if I do not like it. I am seriously considering applying early there if I do not get into Cornell early.
And Sparky Paul, you mentionned in an earlier post that you have an interest in flat plate aerodynamics. So do I! Very much so. That is probably what I am most curious about in my experiment: can a propeller with a flat or nearly flat plate airfoil be more efficient than a thin essentially curved plate? I am hoping that there will be enough of a difference in performance that the wind tunnel instrumentation will be able to pick it up. By the way, have you ever read the F.W. Schmitz ~1941 paper on low Reynolds number airfoils? It was done at the University of Cologne and there are excerpts of it in Martin Simon's Model Aircraft Aerodynamics. I think that those aifoils had 12% thickness though.
Here is a brief 175-word abstract:
THEODORSEN-BETZ MAV PROPELLER PERFORMANCE WITH LOW REYNOLDS NUMBER AIRFOILS
Abstract
The principles governing propeller operation are the least understood aspect of flight, even though propeller aerodynamics has been studied since the 1870’s. On the other hand, the basic science of propellers is well known and documented. Recently, there has been much interest in improving MAV (Micro Air Vehicle) technology for the military. In the future, these propeller-powered spy planes will become crucial in gaining tactical advantages in combat. However, there has been limited research on these low Reynolds number airfoils and propellers, which operate differently than their larger counterparts. In the experiment, the researcher will show the effects of low Reynolds number aerodynamics on special “Theodorsen-Betz” propellers, each of which will have different airfoils and be precisely machined out of maple wood. It is hypothesized that the thinnest and often unconventional airfoils will be most successful. The researcher will contribute to the field by conducting a dynamic experiment to measure propeller performance. Tests will be conducted at a University wind tunnel, which employs especially sensitive instrumentation to precisely measure lift, drag, thrust, and efficiency.
-----------------
And a little more in-depth description:
My study will test propellers with optimized low Reynolds number airfoils according to XFoil- generated polars, and also with propeller airfoils designed to varying coefficients of lift. I will also use flat plate and curved plate airfoils on my propellers, which performed surprising well at low Reynolds numbers in wind tunnel tests.
The design specifications (thrust, rpm, diameter, forward speed) of my propellers are the same as those for Aerovironment’s "Black Widow" Micro Air Vehicle. I chose these specifications because the Black Widow is most successful MAV to date, and so that my propeller results were applicable to real Micro Air Vehicles.
The propeller designs were optimized using Theodore Theodorsen minimum induced-drag math on Betz propellers, with high aspect ratios, about 14, and narrow tips for low tip loading and loss.
Luckily, Micro Air Vehicles fly mostly at one altitude, air density, rpm, and forward flight speed, so this simplifies the designing process.
Right now I am working on optimizing the low Reynolds number airfoils, which often are 5% thick! Any low Reynolds number airfoil experts out there? I will probably be posting with some questions in the near future..
I am also looking into fabrication options. I may be having the propellers made out of maple (!) on a real fast cnc machine. We shall see. Carbon fiber (with cnc'd aluminum molds) or machined maple or some synthetic seems to be the only option for these props, because the resolution of the airfoils is so crucial. .001" makes a big difference, unfortunately.
And depending on how long this all takes, (everything takes so much time!!!) I may be able to enter some competitions before the end of the school year. I am aiming to have my paper done by March 1st, and I have already started writing the methods and materials and the background information on military interest in and uses of MAVs, propellers, low Reynolds number aerodynamics, etc.
Kindly, Adam
I hope you found this interesting and I would love to hear your comments. I am way am just applying to colleges and looking into aero engineering... Not sure if I want to commit to so much math and physics though... I did have a very nice conversation about my project with an aero professer, by the name of Gallimore at the University of Michigan when I visited, and Umich claims to have the #1 aero program in the US. He told me to go for it, and to transfer schools if I do not like it. I am seriously considering applying early there if I do not get into Cornell early.
And Sparky Paul, you mentionned in an earlier post that you have an interest in flat plate aerodynamics. So do I! Very much so. That is probably what I am most curious about in my experiment: can a propeller with a flat or nearly flat plate airfoil be more efficient than a thin essentially curved plate? I am hoping that there will be enough of a difference in performance that the wind tunnel instrumentation will be able to pick it up. By the way, have you ever read the F.W. Schmitz ~1941 paper on low Reynolds number airfoils? It was done at the University of Cologne and there are excerpts of it in Martin Simon's Model Aircraft Aerodynamics. I think that those aifoils had 12% thickness though.