Riblet's Airfoil Design layout

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Pietenpol dreamer
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Riblet's Airfoil Design layout

Post by Pietenpol dreamer » Mon Sep 18, 2017 10:31 pm

Can any of you expert builders advised me of how to correctly layout Harry Riblets airfoils by using the coordinates he list in his book? Im looking for a 60 inch cord but his cords go out to a 100 inches. I know i'm doing something wrong but I don't know what it is.

tom kreiner
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Re: Riblet's Airfoil Design layout

Post by tom kreiner » Tue Sep 19, 2017 8:52 am

Airfoils are graphically described in percentages of Mean Aerodynamic Chord, or simply Chord.

With such a description, the stations ( X-axis) range from zero - generally the nose of the airfoil - to 100 - the trailing edge.

The ordinates (Y-axis), are also in percentage of chord. Some airfoils have camber (underside of wing), and will require two ordinates at each station; one positive (above chord) and one negative (below chord).

For a 60 in Chord, you'll create a table of both X & Y dimensions by multiplying each station and ordinate by 0.6.

After doing the math, plot your airfoil on a large sheet of paper - very carefully - and connect the dots with the smoothest curve or bent strip of wood you can find. This can also be done on a computer, but then you'll need access to a large scale printer, and the plot may cost you up to $35 of so....

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Terry Hand
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Re: Riblet's Airfoil Design layout

Post by Terry Hand » Tue Sep 19, 2017 10:07 am

Attached is a copy of the Riblett 613.5 airfoil that I plotted.

Riblett 613.5.jpg

I have it in .pdf format, but the forum won't let me upload that format for some reason. Send me your email by PM and I will send you the .pdf.

You can take either one to fedex/kinko's and print it out on their wide printer for about 2 or 3 bucks. They both are 60-inch chord.

FWIW, plotting gives you the airfoil, but no indication of where to put diagonals. I merely overlaid the diagonal layout for the original Pietenpol airfoil when determining where to put diagonals on my layout. Also I made them all perpendicular to the chord line as opposed to put in a 1 or 2 degree preset angle of incidence. I will do that with the cabanes.

Take it for what it is worth, and what you paid for it. I am giving it freely, but you also accept full responsibility for its use in your project
Semper Fi,

Terry Hand
Athens GA

Pietenpol dreamer
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Re: Riblet's Airfoil Design layout

Post by Pietenpol dreamer » Tue Sep 19, 2017 5:10 pm

Tom, Terry

I cant thank you enough. That is exactly the explanation that I was looking for. Thank both of you very much!!

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Lownslow
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Re: Riblet's Airfoil Design layout

Post by Lownslow » Wed Sep 20, 2017 8:22 am

Using the Riblet Pietenpol airfoil will complicate the rib and wing construction. If you do an internet search on "Pietenpol Riblet" you will find a lot of discussion and comparison of the Riblet vs. the original Pietenpol airfoil. Here are a couple of links.... http://pietenpols.tripod.com/id18.html
http://www.matronics.com/forums/viewtop ... c3287b19ad. The first link is to a great study done by P. F. Beck and Don Harper using almost identical Piets except for the airfoils.

The bottom line is that there does not seem to be much advantage, if any, to using the Riblet airfoil. On my Piet I have the original airfoil with a 2700 cc Corvair for power. It works fine. It climbs great even at a gross of 1200#. It flys faster than I want to. The stall speed is pretty slow, even with a heavy plane. There is probably a lot more to be gained by the proper prop selection than using the Riblet airfoil.

Just my opinion and others may vary :lol:

Rick Schreiber
NX478RS

tom kreiner
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Re: Riblet's Airfoil Design layout

Post by tom kreiner » Wed Sep 20, 2017 9:24 am

While P.F. Beck's & Don Harpers planes are VERY similar, they are NOT identical.

The reality is that Don's fuselage has roughly 10% greater flat plate drag than P.F.'s which, as I mentioned a few years back, is HUGE. ( If this isn't believable, go back and review the fuselage dimensions; then calculate the flat plate drag. The dimensions are given in the papers that P.F. published; they are different.) Due to the difference in drag between the two airframes, the comparison is flawed.

Placing a different wing with a different airfoil on the SAME fuselage may (or may not...) produce different results.

Close, but no Cigar!

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Terry Hand
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Re: Riblet's Airfoil Design layout

Post by Terry Hand » Wed Sep 20, 2017 9:34 am

To add to Rick's comments -

I am not flying yet (still building) and Rick is, so his practical advice certainly trumps my theoretical thoughts.

I don't know that using the Riblett complicates the rib and wing construction all that much. I think that my use of an aluminum spar as opposed to a wood spar was more complicating than the selection of airfoil. But that is a different discussion for a different thread.

The reason I went with the Riblett airfoil as much as any was the taller profile gave me the opportunity to use the conventional 3-piece center section with a center section fuel tank without widening it. You will find a fair number of builders that use the original airfoil widen their center section to accommodate a wider (and thus larger volume) center section tank. I think that that creates as much complication, if not more, than using a different airfoil. They chose to go wide. I chose to go tall with my tank. That is just one of the options that you get to choose when building and experimental amateur built aircraft like the Pietenpol.

My $0.02.
Semper Fi,

Terry Hand
Athens GA

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Terry Hand
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Re: Riblet's Airfoil Design layout

Post by Terry Hand » Wed Sep 20, 2017 10:17 am

And to add to Tom's comments -

P.F.'s aircraft has the Pietenpol airfoil but with VGs (vortex generators) added, so it is not a true Pietenpol airfoil. For that reason I think that people make more of the overall comparison than it deserves. Not to say that P.F. and Don's analysis has NO value. It is just not a true apples-to-apples comparison that people would like it to be.

My other $0.02.
Semper Fi,

Terry Hand
Athens GA

KSWildman69
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Re: Riblet's Airfoil Design layout

Post by KSWildman69 » Fri Mar 23, 2018 7:00 am

Terry,
I'd also be interested in the riblet pdf.
I'm tanking my camper one step further though,

douwe blumberg
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Re: Riblet's Airfoil Design layout

Post by douwe blumberg » Fri May 18, 2018 4:16 pm

I could be wrong, but I believe P.F. I send “pre v.g.” Numbers. He’s a pretty smart cookie, right T.S. hard to imagine him comparing apples and oranges

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Terry Hand
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Re: Riblet's Airfoil Design layout

Post by Terry Hand » Sat May 19, 2018 2:19 pm

Douwe,

P.F. has had the VG's on for a long time. The flight was done with the VG's on.
Semper Fi,

Terry Hand
Athens GA

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