The Effect of Blade Twist on the Characteristics Of The C.30 Autogiro

kolibri282

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author: J. A. Beavan and C. N. H. Lock
title: The Effect of Blade Twist on the Characteristics Of The C.30 Autogiro
report: ARC R&M 1727
comment: Here is the little story behind this report that has a drawing of a profile of which measurements had been taken and which is claimed to be very close to the Goettingen 606. A (paper) copy of this report had been filed in the library at the University of Dresden in 1997 and my daughter (currently studying in Muenster) was able to obtain a copy through the German scientific report exchange service. A quick search revealed that this particular report was not available online, so my daughter scanned the file and I sent a copy to the great team running the Aerade server at Cranfield university. They had the file OCRed and uploaded within three days and here it is:
http://aerade.cranfield.ac.uk/ara/arc/rm/1727.pdf
 
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C. Beaty

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Thanks, Juergen. I have previously searched for the Go606 airfoil without success.

This thing has a huge negative pitching moment coefficient; ~ -0.05 according to Javafoil.

According to Brooks, an RAF C-30 was lost when the pilot got into a high speed dive from which he was unable to recover.

The Kellett KD-1 also used the Go606 but with the outer 1/3 of the blade having an upswept trailing edge tab to cancel the nosedown twist.
 

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kolibri282

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Chuck, your value for Cm is reassuringly close to the one given in this report as well as a Cm of -0.056 mentioned in naca 600 for the KD-1:
http://www.rotaryforum.com/forum/showthread.php?p=508545
It seems that modern 2D profile codes are doing a pretty good job in predicting profile properties.

As to the use of tabs Jaques Moulin writes in his marvelous book "Les Autogires LeO C.30 & C301" that these had first been used on British C.30s. This book has a wealth of information on C.30 autogiros and their (French) derivatives. He lists about eighty aircraft that had been used in France by the army and navy. One of the pictures shows a C.30 blade with trim tabs at the outer part of the blade, another one shows a section of the trailing edge of the blade detailing how the tabs were attached. There are e.g. rivets shown that had been used here. Most of the French C.30s have been built by the French company Lioré et Olivier (LeO). This company developed the C.30 into an improved version designated LeO 301, which e.g. sported a full size rudder like the one later on used by the KD-1 and of course trim tabs. I strongly recommend this book to every gyro nut because the sheer wealth of pictures is a great source even if you do not speak French.

PS: Chuck, could you perhaps add a list of the coordinates you used as input to JavaFoil, this would save others who want to play around a bit the trouble of having to generate a set of faired data points.
 
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Jean Claude

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After playing with JavaFoil, it occurred to me that the JavaFoil curves L/D is good, but only if more coordonates points. It seems to me less than 120 points gives a drag is very optimistic.
 
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C. Beaty

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Juergen, I used data points from Page 27, Fig. 10 of the Beavan/Lock report and let Javafoil extrapolate the points in between.

The velocity plot indicates some lack of surface fairness.

These simple programs provide accurate results for Cm and angle of zero lift but don’t bet money on L/D numbers; particularly near stall.
 

kolibri282

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Ok, Chuck, I had assumed that you had somehow digitized the drawing and then used some program to fair the data.

Jean Claude, if you use values from table I of naca-591, which is another Wheatley report on the KD-1 experiments, you find a drag coefficient of 0.0152 at mu=0.2 and 0.0141 at mu=0.3. Is that near the value you get?
 

Jean Claude

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Chuck, what do you get with 121 points for this profile?

Juergen, I tried to get a profile as close as possible to figure of report 1727. This is what gives JavaFoil with 121 points.



Note:According to the text Cm (spar) Cz decreases when increases. This means that the aerodynamic center is at 23%.
But JavaFoil shows that Cm (0.25) = 0.05 to Cz = 0 And Cm (0.25) = 0.07 to Cz = 1
This means that the aerodynamic center is at 27%
 
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C. Beaty

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Here’s the discrepancy, JC.

The data supplied on Juergen’s paper gives 27 data points.

Starting with the 27 data points and expanding to 61 gives results identical to starting with 27 and expanding to 121.

Starting with 27, expanding to 61 and then expanding to 121 gives entirely different results.

The points from the report:

1.00000000 0.00000000
0.90000000 0.02187500
0.80000000 0.04450000
0.70000000 0.06550000
0.60000000 0.08637500
0.50000000 0.10550000
0.40000000 0.11725000
0.30000000 0.12087500
0.20000000 0.11087500
0.10000000 0.07875000
0.07500000 0.06637500
0.05000000 0.05275000
0.02500000 0.03625000
0.00000000 0.00000000
0.02500000 -0.02725000
0.05000000 -0.03550000
0.07500000 -0.04087500
0.10000000 -0.04450000
0.20000000 -0.05000000
0.30000000 -0.05000000
0.40000000 -0.04725000
0.50000000 -0.04275000
0.60000000 -0.03550000
0.70000000 -0.02912500
0.80000000 -0.02000000
0.90000000 -0.01087500
1.00000000 0.00000000
 

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Jean Claude

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Thank you Chuck. How do I expand the number of points of a profile that is not in the database JavaFoil?
 

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Duplicate?

Duplicate?

Chuck,
Your post #8 verbiage declares that 61 points vs 121 points is significantly different. Yet the two graphs labeled 61 vs 121 appear identical.

Are my eyes that bad that I can't see any difference between those two?

Larry
 

C. Beaty

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Sorry, Larry, my wording wasn’t clear.

It should have gone something like this:

Expanding from 27 points to 61 points and then from 61 points to 121 points gives a very different result than expanding directly form 27 points to 121 points.
 

Jean Claude

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Thank you Chuk, but how to confirm the new number of points? Thank you for your patience.
 

C. Beaty

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JC, I’m not sure there is method of verifying the accuracy of data point interpolation by Javafoil.

I suppose the Javafoil author used an interpolation algorithm but I know not what.

Here are 3 plots; the original with 27 points, expanded to 61 points and then expanded from 27 points to 121 points:
 

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Jean Claude

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Chuck, Because of my poor English, you have misunderstood me . What should we do, when we wrote the new number of points, to confirm the selection.
Thank you
 

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As to the use of tabs Jaques Moulin writes in his marvelous book "Les Autogires LeO C.30 & C301" that these had first been used on British C.30s.
From NACA-TN-764 Flight investigation of control-stick vibration of the YG-1B autogiro

http://naca.central.cranfield.ac.uk/reports/1940/naca-tn-764.pdf

"The rotor blades, which had a 12-inch chord, were of the Gottingen 606 airfoil section. Over the outboard portion of the blades, between 72 and 93 percent of the radius, the chord was extended 1 inch by a trailing-edge tab. The tab was reflexed approximately 10 degrees to counteract the unstable center-of-pressure travel of the Gottingen 606 section."

.
 

Jean Claude

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Yes, Chuk I'm confused for my ignorance.
 

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My english

My english

Sorry Chuck, I wasn't clear in my message.

It appears to me that the two graphs labeled 121 and 61 are identical. I can see differences between graphs of different posts, but I don't see any difference between those two. Would you please help me see what I am missing. Where (x,y coord) are they different?

Thanks,
Larry
 

C. Beaty

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Both graphs are identical, Larry. Both were single step expansions from 27 points.

They only differ by expanding a 27 point plot to 61 points and then to 121 points.
 
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