floridagyro

Success at last. The first set of SG6042 had a twist and they provided acceptable lift but the RPM was so slow that they created an unacceptable coning angle and the gyro wanted to oscillate from side to side.

Today, thanks to Bill, I tested another set without the twist. I first tested them by just holding the rotors into the wind. They would spin but the RPM seemed slow. I installed an .032 shim under each blade and checked again but I still wasn't sure if the RPM was adequate. I made a couple of flights with my blades and got everything checked out. I then installed the SG6042 blades with the .032 shims under each blade. The gyro lifted off good and I had to trim in down elevator. The blades appeared to have more lift than mine. I turned the Co-Pilot off and on several times. The gyro was very stable with no tendency to oscillate as before. After several minutes I landed and removed the shims from under the blades. I did pre-spin the rotor blades this time as the wind had almost gone. The gyro almost hopped off the ground. I had to use almost full down elevator to keep the gyro flying level. The lift from the blades was amazing. The gyro was still very stable with no bad tendencies. If you want a set of blades that provide a lot of lift, go for the SG6042 profile.

Phil

billf

Hi Phil...
Thanks for the encouraging report. This is really the first practical, real life, example of the lift performance we observed in the wind tunnel tests two years ago. In those tests the SG6042 generated about twice the lifting force as the Clark-Y airfoil at most all wind velocities up to 28 MPH, at which time we stopped increasing the wind speed.

Bill

floridagyro

Hi Bill,

I can certainly agree with the data. I forgot to mention, that I also went inverted and stalled the blades to test their restarting ability. I tried this several times and each time lower to the ground. I quit at about 50 feet. The blades appeared to reach autorotation real fast and lost very little altitude. No problem there.

Also, 28 MPH for testing the blades should be adequate. Another member put a radar gun on one of my gyros and the top speed was about 25 MPH.

Phil

soarrich

My Feedback: (98)

What does that workout to in degrees?

floridagyro

Hi Rich,

I didn't check these blades but on another set of blades the .32 shim changed it by 4 degrees. However, the SG6042 blades do not need any shim. You can set them flat which is different than other profiles. They come up to speed real fast whithout any negative incidence. Unusual?

Phil

billf

Hi Guys...
For what its worth, Compufoil calulates that the SG 6042 has a zero angle of lift of -4.93 degrees! The clark-y is something in the range of -3 degrees. So for some reason the 6042 can be set at quite a negative angle of incidence and still generate a lot of lift.

As we pointed out in the RCM article, it is worth a lot of trouble to fiddle with the angle of incidence of the blades. Even as small a change as created by one layer of masking tape behind the mounting bolt makes the difference between no-spin up and spin up into autorotation. Or, on the other hand removing the tape, or putting it ahead of the mounting bolt can give a tremendous increase in autorotation rpm and lift.

The challenge is to reach the happy medium between a very easy spin up (probably too negative incidence) and difficult spin up with lots of lift if you can get it started (possibly a bit too much positive incidence.)

Bill

Steve T.

Exactly, Bill! Well said. A delicate compromise, but well worth the "fiddling"!

geink

Are the SG6042 blades available commercially. I have been makeing blades for a .40 and .60 size autogyro but have had not much luck.

soarrich

My Feedback: (98)

No, you pretty much got to do your own. A of A sells blades and rotors though. I'm not sure of the airfoil.

geink

HI,
I wonder if someone could post a picture of the SG6042 airfoil. . Thanks.

DICKEYBIRD

Here's a pic of an S6042....I dunno whut an "SG"6042 is, I couldn't find it anywhere. If someone has the coordinates, I'd be happy to try to plot it and post the results.

HTH (?)
Milton Dickey

geink

Hi Dickeybird,
Thanks for the picture of the airfoil , it has the # s8042 no it. is that the same as a # s6042. There are people on this thread who are familiar with the SG6042 airfoil ,maybe they can let us know what the shape. I notice that full size autogyro blades are reflexed at the trailing edge , has that airfoil been tried on model autogyro,s
Thanks.

DICKEYBIRD

Oops! Ya just can't get good help these days. That was a typing error on my part, it really is an S6042 profile. I have edited the drawing and re-uploaded the .jpg but it's still the same....oh well, I'll try again!

Lone Shepherd

That does look like the SG6042.

http://school.loneshepherd.com/sg6042.gif

Is what I came up with.

falcondriver

looks a lot like the origonal whopper blades! anyone know?

billf

Les Garber and I ran a series in the windtunnel using a reflexed airfoil. (Don't remember the number offhand) It was one of those used on full scale gyros. Didn't perform any better than the Clark Y. See RCM August 2000 or 2001.

My personal thought about reflexed airfoils for gyro blades is to eliminate the twist at the tips caused by the usual pitching moment of a cambered airfoil. Maybe one of the aerodynamic experts can offer further insight.

Bill

BMatthews

I remember reading about the twist problem too. Remember that full sized gyro blades used to be built up of a tube spar and ribs. A positive pitching airfoil could have easily caused too much twist in the blade. The reflexed airfoils help the blade to behave like a stable flying wing all along the length. Of course our models don't have this problem thanks to the smaller size and stiffness of the all wood construction.

Hal deBolt

Hi ya'll,
Reflexed airfoils>
Bruce"s statement about reflex adding stability as with a flying
wing seems important.
If this SG6042 is so potent why not add some reflex to it? See
what happens.
A way to do that would be to create a SG6042 blade per sey and
simply attach about 1/2" more to the trailing edge. Raise the T.E.
of the 1/2" 1/32" to create the reflex.
An experience> had a new rotor on Giro V , as it would lift off
on the take off run there would be a slight blade strike.
Cause determined> at lift off the rotor was not up to flight speed and the craft's acceleration created a strong air flow through the rotor. this airstream was seen to raise the blades
when passing through the forward rotation segment. Once into
the retreating segment the downward inertia caused the blade
to go below normal far enough to strike.
Needed> something to counteract the airstream causing the blades to rise.
Past airplane experience had shown how strong a force a raised aileron created. It seemed possible a "raised aileron" (sort of) could create enough force to counteract the airstream force
Some reflex as described for the Selig foil was installed. Proved a fine solution.
As far as lift is concerned no attempt was made to compare with and without the reflex
Can say rotor continued to provide more than adequet lift
OK? Just another mystery that had to be solved deciphering these rotary wings!

Hal [email protected]