exaf35

I am new to helicopters and autogyros and engineer by trade. I am trying to build some platforms from scratch and I have come across the SG6042 airfoil as an excellent choice. In my research a number of sources reference the "Wind Tunnel Tests of Autogyro Rotors Article", by Garber & Friedlander in Aug 2001 RCM. I wanted to see if anyone has an electronic copy of this article or if they new where I could get a copy. I have tried RCM direct at their site and via email without any success. Thanks

mnowell129

I think I have hardcopy of the article. I think I also have a hardcopy of the actual
windtunnel data as well.
I'm an engineer as well, so I might be able to poke around and find a quick answer
if you need it without having to copy the whole pile.

Edit : I lied. I can't find the RCM article, but I did find the test report from Bill f. from April 1995 when they tested
various rotors, but it doesn't mention the airfoil in question. Must have been a later study.

exaf35

Thanks for the response Mnowell129. I would like to have the actual article if at all possible. Aerobalsa.com gives a good summary but as an engineer I am sure you can appreciate how you like to do your own analysis.

rcflyerfl

My Feedback: (1)

Guys,
If you hang around long enough Bill F. may show up..
Hi Mickey

Jim

AeroBalsa Mike

Exaf35,

I contacted Bill F. for you and I believe he may be sending the report your way. I am interested in hearing any comments or conclusions you can offer after reviewing the test data. Thanks in advance.

exaf35

Thanks for the response Mike. I have heard from Bill thru email. I look forward to reviewing the data. I will make sure to pass on my review. If you give me a good email I will be sure to pass on my review for what its worth.

AeroBalsa Mike

Posting it here would be great, if you don't mind. I would think there are others that would like to read it, too.

exaf35

First of all thanks to Bill and Mike for their quick responses. I enjoy working with others who are equally motivated. Reviewing the article and the full report gave some good insight into the tests. The experiments were a great application based experiment and it does match up well with the the data that I have so it always good to get some redundancy. Now while I am an aero engr I don't claim to be an expert in low speed airfoils so please understand that you get what you pay for and this is free. With that let me begin. My original interest was finding a good low speed airfoil for rotary applications. From dealing with some small fixed wing research aircraft recently I had already completed somewhat of analysis. My original design constraints were that it had to be a thinner profile due to design constraints and like all application you want to maximize lift and decrease drag in the 100000-200000 Reynolds Numbers. My initial review looked at data completed by Selig Low Speed Airfoil Data. After first selecting airfoils on thickness I next looked at lift and drag data. The two airfoils that stood out to me were the SD7043 and the GM-15. We did do a lot of work with the SD7043 and were very happy with the results in its performance. But once I got interested in rotary I wanted to take a look at my options again and that is when I came across the AeroBalsa and the mention of the 6042. After reviewing this new information it hasn't changed my approach but does provide some validation of both datasets but now includes the 6042 and 6043 airfoil. Attached are the plots that tell the tale. The first and second plots are the four airfoils with the Cl vs AoA. It appears that while the airfoils are pretty close to one another the GM15, 7043, and even the 6043 have greater lift than the 6042. However when you look at the second two plots which are for Cl vs Cd you can see that the drag on the 6043 quickly eliminates itself from the picture and the reason why it appeared so well in the article/report. However at all angles of attack and Cl the drag on the 7043 and GM15 appear to be notably less than the 6042. I know the 5th plot is hard to see however it shows the profiles of each airfoil. While the GM15 is the thinnest of all airfoils it also has the most camber which would infer that it also has a heavy nose down twisting moment (unfortunately no moment data) which is not desirable in a rotary wing from my reading which narrows down the selection to the 6042 and the 7043. Both airfoils appear to have similar profiles. So in conclusion if I had infinite time and money to make my own blades I would choose the 7043 for rotary (but GM15 for fixed wing) however given the fact that there is an excellent source for purchasing the 6042 at a reasonable price and at a significant time savings I will go with the 6042 however I would lobby for someone who does have the time to give the 7043 a try and then if they do well then perhaps we can lobby for aerobalso to expand their line : ) I know this was pretty concise but in the essence of time I hope it will do. If you have any further questions feel free to let me know and I will do my best to explain.







PS if the images don’t come out they are post on my profile gallery.

AeroBalsa Mike

Thanks for the analysis and posting the data! Very interesting reading.

mnowell129

Nice report. One consideration is the size of the model.
Mine are smallish and the Re varies from about 50000 to 150000 root to tip, with
the 2/3 radius Re being about 100K, depending on RPM.
At this size I believe surface finish is as important, if not more important,
than the differences in profile.

The 6043 looks lousy at Re 100000 ( up until Cl 1.2) but
at Re 200000 the 6043 has a better L/D above 1.0 than the rest.
This may be important at a high load factor in a gyrocopter. When the other profiles are
starting to develop high drag at high Cl this will cause the rotor speed to decay, whereas
the 6043 would maintain rpm.
This kind of behavior probably doesn't factor into a profile choice for a fixed wing aircraft but
may be especially important in a autorotative state at a high load factor.
As the load or AOA increases the 6043 L/D increases steadily out to a Cl of 1.2,
the 7043 has a better max L/D but peaks at Cl = 0.5, so as the AOA increases above that
point the rotor speed will tend to decay, not increase. Worse still, at Cl max the L/D of the
7043 is half the 6043.
If you are building a UAV or piloted aircraft the profile selection may be driven more
by rotor RPM margin than max L/D performance.
I think in a high G situation you'd rather have the rotor speed remain constant or increase
rather than decay. If the RPM decreases when you turn, you will of course have to add power
to maintain altitude in the turn and because the rotor RPM lags, you will need to add power
in advance of a turn to avoid a altitude dip entering the turn, then reduce power before exiting.
If you design around the 7043 at optimum L/D of 0.5 for the cruise condition,
then every time you execute a maneuver the rotor will decelerate.
If what you are after is a long cruise, maximum duration then you may accept that side effect,
but if you intend to maneuver, then having the rotor RPM decay for each turn may be annoying or dangerous.
At the maneuvering limit (like an emergency situation) I'd rather have the 6043 any day. Since the lift is
a function of velocity squared maintaining rotor rpm is a critical issue.
If you establish the borderline auto-rotative state for all profiles at Cl = 0.5 any increase in load/AOA
of the three "good" profiles will destroy the auto-rotative state, but the 6043 will maintain an auto-rotative
state all the way out to Cl = 1.2. If its my A** in the seat I'd be more comfortable knowing the rotor will
keep turning if I have to maneuver in an emergency.
Essentially if the delta L/D wrt alpha of the profile is positive around the cruise point the rotor will
accelerate when incrementally loaded and conversely if the delta is negative, the rotor will decelerate
when incrementally loaded.
Might be something to consider for a man carrying application or a stable sensor platform.

exaf35

You definitely bring up some good points. I didn't make any mention of surface finish. I think it goes without stating that you wanted the nicest finish that you can achieve. At low RE the parasite drag in laminar flow really is a killer and will completely negate any benefit of airfoil selection. What you mention at the high load and high AoA are correct. I guess I should have clarified also that my focus is endurance over performance therefore my focus would be designing for the cruise AoA rather than at high AoA manuevers. Within the RC community this focus of endurance/performance varies and with all cases people will have to make an educated decision based on their individual needs. Thank you for keeping me honest!

boberos

Exaf,
I see you are real close in FL
Drop by Jim's fly in in March. I am sure Bill F will be there.