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Why we need to add fairings to our outrigger struts printer friendly version
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dannparks
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Posted Wednesday, December 22, 2010 @ 01:16 AM  

A very old MIT video about aerodynamic drag. Interesting example of the drag of a small round tube.

http://www.youtube.com/watch?v=ftq8jTQ8ANE

--------------------
Dann Parks • RF4D #4051 N2188 • now flying!
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JamesB
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Posted Thursday, December 23, 2010 @ 02:59 PM  

While I think it's a great thing to do, I'm not convinced of the benefits at 80 or so, mph. I doubt that the effect is linear in relation to air speed. If my glider ever gets up to 210mph as in the example, the last thing I'll need to worry about is the drag from my outriggers.
SteveBeaver
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Posted Thursday, December 23, 2010 @ 03:46 PM    YIM

Presumably since 210 is 2.6 times 80, the drag will be 2.6 squared, or 6.7 times more at 210 mph than it is at 80 mph.
Donald
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Posted Tuesday, December 28, 2010 @ 07:44 AM  

I guess so but anyone who has ridden a bicycle will understand about wind resistance and performance bicycles often have streamlined tubes though they travel a lot slower than the average Fournier. Even so, I doubt if I'll be adding fairings to my 25mm nylon rods. Part of that is laziness but part is a worry that I might inadvertently stiffen them somewhere they ought not to be stiffened, shifting the bending to somewhere it ought not to bend. On that score I think I'd even be happy with them more flexible than they are and have often thought that 20mm nylon would be better but I know there are some who disagree.
Jorgen
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Posted Wednesday, December 29, 2010 @ 05:36 AM  

Hi and Happy Holidays,
excellent points, Donald. I see we are back to the outriggers again, troublesome little buggers and maybe our punishment from God for altering René's original design. Flexibility of the rods certainly is a parameter, but I would like to emphasize the length of the outriggers as something that needs to be checked first. A longer outrigger is much more likely to bang against planet Earth at 60 mph (=before touch down, maybe in a X-wind) than a shorter one, which will only have to endure loads at taxi speed.

I agree otherwise that fairings can alter bendings and fatigue of lightweight aviation parts is a challenging problem. But I tape seal my fillets, wing and sealed my ailerons etc- of course I want to fair my outriggers, if not else as a religious exercise rather than achieveing a measurable difference. I had white fairings on XST for a while (before one broke due to faltigue) and I also liked the looks!

I still haven't made a plexi fairing as I planned, precisely because it's difficult to do without altering the bending of the outrigger rod. But it's still one of my favourite projects to muse about....

May the 4's be with you/ Jörgen

JamesB
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Posted Wednesday, December 29, 2010 @ 09:34 AM  

As I remember, Bob Grimstead taped foam fairings on his outriggers. Lightweight. Cheap. Flexible.

And you can use different colored duct tapes for your choice of techno looks.

Bob Grimstead
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Posted Tuesday, January 4, 2011 @ 00:00 AM  

See

http://sbeaver.com/cgi-bin/fournier/cutecast.pl?session=kMcveELnYYVRypGCXSAP7511gT&forum=17&thread=289

Both my Fourniers have them, they've been on there for up to six years and suffered one wheel-up, and they're still fine. None of the nylon legs (black or white) has ever broken.

I will not be posting very often any more, because I don't want to lose my rank of captain.

Yours, Bob

SteveBeaver
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Posted Tuesday, January 4, 2011 @ 00:20 AM    YIM

Bob,

I can force your rank to be Captain, or anything else for that mater. Just let me know if it ever changes (Henceforth, it should not)

Steve

Bob Grimstead
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Posted Tuesday, January 4, 2011 @ 04:48 AM  

Thanks Steve, that's great.

Once a craptain...

jb92563
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Posted Tuesday, January 4, 2011 @ 11:10 AM  

I followed Bobs example and used a hot wire foam cutter to make my outrigger fairings out of white insulation foam.

They are attached and covered with 2" wide sailplane Gap sealing tape.

I only faired the rear of the outrigger and the gap tape sticks firmly around half the outrigger tube securing it firmly in place.

It can not rotate nor slide up and down.

My outriggers are 3/4" white PVC so it made sense to streamline them.

It was a 15 minute job to cut them from the foam and another 15 to install and tape them over.

Now I feel like Im going faster at the top end and burning less fuel

--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org

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