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Exhaust Exit
http://thorp18.com/thorpforum/viewtopic.php?f=5&t=6454
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Author:  Scott Stine [ Thu Dec 23, 2010 9:00 am ]
Post subject:  Exhaust Exit

Getting ready to cut the exhaust exits in the cowling. What is the current thinking on least drag most functional installation. I have previously built metal farings with 1 inch clearance on all sides, but these seemed a bit big. I have noted that too little clearance results in paint blistering.....so what is best. I am always intrigued by the long exhaust on the Cirrus....3-4ft pointing aft. What is the fastest, most functional, and best looking. Have considered cutting flush with the cowling with no farings, but not sure about the aerodynamic wisdom of this. Help me out o-experienced ones.

Scott

Author:  leewwalton [ Thu Dec 23, 2010 9:21 am ]
Post subject:  Exhaust Exit

Here you go Dr. this should fuel the conversation a bit ...

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Lee Walton

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John Walton

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Bob Highley

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Bill Williams

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John Evens

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Gary Green

Yes, I take a lot of pictures!

Author:  Scott Stine [ Thu Dec 23, 2010 10:14 am ]
Post subject:  Exhaust Exit

Outstanding photo summary. You do take a lot of pictures. You wouldn't happen to have a pic of my 1967 mustang I had back in High School.......never took any good pics of that one.

Looks like the exhaust examples you displayed are pretty tight...not much airflow around the pipes, and not much for elaborate farings, except for GG. I know that he recessed his floorboards and made a faring. I guess the pipes themselves act like their own farings.....on some examples. What would speed with economy dictate.

SS

Author:  Fraser MacPhee [ Thu Dec 23, 2010 11:14 am ]
Post subject:  Exhaust Exit

Scott - witness the drag video posted yesterday - suspect fairings are more prone to increasing speed.

Has anyone ever seen a spec of anything on John Evens' plane?

Author:  Scott Stine [ Thu Dec 23, 2010 11:17 am ]
Post subject:  Exhaust Exit

Actually I did see a smudge of grease on Johns plane once....as it turns out it was grease on my face reflecting off of one of his polished stainless steel abrasion plates. My mistake. I bet Lee has a pic of that too.

SS

Author:  Scott Stine [ Thu Dec 23, 2010 11:39 am ]
Post subject:  Exhaust Exit

Gary, what did you do to keep your paint from peeling off of your exhaust farings...insulation....silicon.....magic.

SS

Author:  Gary Green [ Thu Dec 23, 2010 12:51 pm ]
Post subject:  Exhaust Exit

Scott; I did nothing except provide about 1/2" clearance around the pipe. I suspect if you got it closer than that it might blister.

Author:  qjayz [ Thu Dec 23, 2010 2:19 pm ]
Post subject:  Exhaust Exit

From what I understand tubes are very un-aerodynamic, and was wondering about the wisdom of using streamline steel "strut tubing" for the protruding exhaust stacks. This seems like it would solve the drag problem without needing a fairing. Any opinions/suggestions?

Author:  Rich Brazell [ Thu Dec 23, 2010 3:41 pm ]
Post subject:  Exhaust Exit

If you are concerned about "blistering" you can get some "heat proof tape" from Spruce... Woven fiberglass tape. 2" w x 1/16" thick. 87 cents by the foot. Even though it sez tape, it has no adhesive on it, tape probably refers to the size of it. I plan to expoxy a small strip to the inside of my exhaust cuffs. Probably not necessary, but easier than trying to repair blistered fiberglass and a lot less expensive. Only a couple of bucks for peace of mind. [;)]

RB

Author:  Scott Stine [ Wed Jan 12, 2011 9:34 am ]
Post subject:  Exhaust Exit

Her was my version. Farings made out of 2024T0....very soft and easy to work with 032. Stiffened up nicely after forming. Was going to use 6061t0 but was out of stock. Hopefully this will be ok.

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Author:  Rich Brazell [ Wed Jan 12, 2011 2:18 pm ]
Post subject:  Exhaust Exit

You should mass produce these babies ! Very nice.

RB

Author:  Scott Stine [ Wed Jan 12, 2011 10:14 pm ]
Post subject:  Exhaust Exit

Thanks RB. I would be happy to but......I think that each exhaust would be different. Different exit angle. Different distance from the firewall. Etc. Mine are three inch diameter to give 1/2 in clearence around the pipes and about 11in long without the flange and about 12in long with the flange. Would be happy to send the form out if anyone wants to give it a try, it is pretty easy. The key is the metal. Tried to make several for Roy out of 6061 T4 but even when annealed with a torch it got wavy and looked rough. The T0 is like hammering butter. Just hope it is stiff enough......ah the cry of every man over 40.

Author:  tubetwister [ Wed Jan 12, 2011 11:34 pm ]
Post subject:  Exhaust Exit

Nice job Scott. look great. On your annealing process, 6061 t4 or t6 usually very easy to anneal, me thinks you are getting it way too hot. I recommend using an oxy/acy torch (I prefer to use a small rosebud) light the torch and with a soft, acy only flame, soot your alum.(turn it black with the soot), then set your torch for a soft neutral flame, and heat the area you want to anneal just enough to "burn off" the soot in the area. Most common mistake is people get it way too hot, thinking along the lines of copper or steel annealing, and that will cause warpage! It is easy to get too hot.. Practice on some scraps first. I like annealing 6061, easy to get to deadsoft (T0) and then comes back a little harder with work. I love to see people forming metal!!

Author:  Bill Williams [ Thu Jan 13, 2011 5:26 am ]
Post subject:  Exhaust Exit

When annealing, use a 1" magic marker, blacken the metal, use the same technic with torch to anneal, burn the markers black off,moving the flame rapidly over the metal, same results but without all the soot, grease from the soot and black metal, just plain soft, clean metal.

Author:  Scott Stine [ Thu Jan 13, 2011 10:16 am ]
Post subject:  Exhaust Exit

Thanks for the tips. May have to try again with the 6061 T4 and anneal it with the torch. I love the looks of the ones I made with the T 0 but I will try a set done with T 4 annealed just for fun.

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