VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #1  
Old 11-30-2016, 09:37 AM
RV6_flyer's Avatar
RV6_flyer RV6_flyer is offline
 
Join Date: Jan 2005
Location: NC25
Posts: 3,507
Default Exhaust Wrap

This was the top story on VAF for the day 30 November 2016.



Just want to add the above is an OPINION that I do not share.

I have used exhaust wrap on my RV-6 for 19-years and over 3,000 without the issues in the letter.

I started using exhaust wrap at the recommendation of an RV-3 owner / A&P / IA that had a 360 under the cowl. He had one of the old Tolle exhaust systems that was a rigid exhaust unlike the "Vetterman" exhaust that most of us use. The Tolle exhaust systems were known to crack and break welds. Once he wrapped the exhaust, his cracks and breaks happened a lot less often.

There are as many opinions on the subject of exhaust wrap just like there are on primer, nose wheels, tailwheels, ignition system, engine manufacturers, spark plugs, paint schemes, etc...

Everything we do in aviation has risks. Exhaust wrap also has risks. IMHO, the risks are worth it to me for the lower under cowl temperatures that I have on my aircraft by using it. YMMV. IF the exhaust wrap use required that i replace the exhaust system every 500 hours it would be worth it to me.

Now others can comment with their opinions. I am sure that there are as many opinions on the subject as there are readers to this forum. Maybe I am the only successful, happy user of exhaust wrap.
__________________
Gary A. Sobek
NC25 RV-6
Flying
3,400+ hours
Where is N157GS
Building RV-8 S/N: 80012

To most people, the sky is the limit.
To those who love aviation, the sky is home.
Reply With Quote
  #2  
Old 11-30-2016, 09:42 AM
Bob Martin's Avatar
Bob Martin Bob Martin is online now
 
Join Date: Jan 2005
Location: Charlottesville, Virginia
Posts: 1,230
Default SS

Gary,
Much respect to your opinion!
Was the old Tolle exhaust systems SS?
Larry or Clint told me the wrap cause the molecular level of the SS to move around after my wrapped exhaust slip joints "ovaled" after wrapping.
Discussion stated after he sad he could tell I had wrapped it!
FYI...Larry did fix it....and IIRC for free! I have not wrapped since.
__________________
Bob Martin
RV-6, 0-360 Hartzell C/S, Tip up, 1200+TT
James extended cowl/plenum, induction, -8VS and Rudder. TSFlightline hoses. Oregon Aero leather seats.
D100-KMD150-660-TT ADI2- AS air/oil seperator. Vetterman exhaust with turndown tips.
Louisa, Virginia KLKU N94TB
Reply With Quote
  #3  
Old 11-30-2016, 09:53 AM
8 ball 8 ball is offline
 
Join Date: Dec 2014
Location: hilltop lakes' Texas
Posts: 135
Default Exhaust wrap

I had an experience similar to what the writer head with two major differences number one it was an automobile not an aircraft number two it was mild steel tubing and not stainless. just saying
Reply With Quote
  #4  
Old 11-30-2016, 09:55 AM
DennisRhodes DennisRhodes is offline
 
Join Date: Jul 2007
Location: Taylorsville, Ga
Posts: 798
Default

I also had to wrap the exhaust in my long EZ to minimize the hot air being used for cooling on that up draft cooling situation. I did experience a couple of exhaust pipe cracks on the SS material and had to keep a close check on that issue. I believe there were two sets of manifolds installed over the 8 years of flying. On my 9 I have an area of about 8 inches wrapped where closee to other stuff and cowl that I need to keep the heat off of. Overall I agree that the complete wrap will shorten the life of an exhaust system but in some situations it can be used for advantage.
__________________
DRRhodes
2020 VAF Supporter
RV9 N908DR
Reply With Quote
  #5  
Old 11-30-2016, 09:57 AM
JonJay's Avatar
JonJay JonJay is offline
 
Join Date: Jan 2007
Location: Battleground
Posts: 4,348
Default

I also respect your opinion very much Gary.
My own experience was from a crack under the wrap. It is difficult to inspect for cracks without removing the wrap. When I did discover the crack it was not repairable due to "changes in the properties of the material based on elevated internal exhaust tubing temperatures". We could not weld the crack and had to replace the exhaust system.
Although I can weld, anything on my airplane goes to a very experienced, and well know Van's supplier of weldments. If he can't weld it, nobody can.

I chose to protect the cowling in other ways, with shields and foil. This was on the Bucker, not the RV.

My Champ, which I "borrowed" for a year while the Bucker was being restored had wrapped exhaust and had been flying for hundreds of hours with no known issues.
__________________
Smart People do Stupid things all the time. I know, I've seen me do'em.

RV6 - Builder/Flying
Bucker Jungmann
Fiat G.46 -(restoration in progress, if I have enough life left in me)
RV1 - Proud Pilot.
Reply With Quote
  #6  
Old 11-30-2016, 10:25 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 5,516
Default FWIW

Well well. This thing is just a matter of degree, not an absolute black and white opinion. Pun intended.

When wrapped, the external heat transfer from the tube to the air outside it will be reduced. This results in a higher in a higher metal temperature. This elevated temperature can several things, depending on the absolute level. One is oxidation at the external surface where oxygen content is ~20% not the 3-5% in the exhaust. This is a fact, oxidation rate increases. Even 316, 321 stainless will oxidize. Another effect of the higher temperatures is a reduction in fatigue strength of the material. It is a natural, normal effect of elevated temperatures.

So, does wrap cause cracks? Not directly. If oxidation progresses and the material is thinned, or if the inherent alternating stress is high on a particular hanger or pipe design, then the elevated temperature might lower the fatigue strength enough to result in a fracture.

Metallurgy effects notwithstanding.

Not surprisingly, based on these factors (and base material and thickness) your results will vary. Maybe we can identify what material, design, thickness tolerate the wrap. I would like to wrap, but have not because of the unknown.
__________________
Bill

RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”

Last edited by BillL : 11-30-2016 at 10:27 AM.
Reply With Quote
  #7  
Old 11-30-2016, 10:41 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 9,500
Default

All exhausts are not the same in terms of how they load their component parts. Applications that cracked simply exceeded available strength at that particular point in the structure, and the others didn't.

There is a loss of strength as temperatures are elevated. Impact strength of 321 stainless after 1000 hours at...

900F, 95% of the unheated condition.

1050F, 85%

1200F, 65%

How much does wrapping raise tube temperature? I don't know, but I can see it would not take much to lose a lot of toughness. There is only a 300 degree spread between those data points.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #8  
Old 11-30-2016, 10:48 AM
Mike S's Avatar
Mike S Mike S is offline
Senior Curmudgeon
 
Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,420
Default

A buddy built a Murphy Rebel------then put it on floats a year or so later.

Due to the drag and weight of the floats, he put a turbo on the engine. Turbo required entire new exhaust system. To get better perf from the turbo, he wrapped the exhaust pipes.

Exhaust failed in less than 10 hours with wrapping and weight of the turbo.

Like said above, different planes will act differently.
__________________
Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
Reply With Quote
  #9  
Old 11-30-2016, 11:12 AM
JonJay's Avatar
JonJay JonJay is offline
 
Join Date: Jan 2007
Location: Battleground
Posts: 4,348
Default

Quote:
Originally Posted by BillL View Post
One is oxidation at the external surface where oxygen content is ~20% not the 3-5% in the exhaust. This is a fact, oxidation rate increases. Even 316, 321 stainless will oxidize. .
I believe this was why, or at least one factor, in my exhaust being un-repairable. It just would not take to welding. I was watching under the hood and it was interesting to see how the material behaved.
__________________
Smart People do Stupid things all the time. I know, I've seen me do'em.

RV6 - Builder/Flying
Bucker Jungmann
Fiat G.46 -(restoration in progress, if I have enough life left in me)
RV1 - Proud Pilot.
Reply With Quote
  #10  
Old 11-30-2016, 12:43 PM
Captain_John's Avatar
Captain_John Captain_John is offline
 
Join Date: Jan 2005
Location: KPYM
Posts: 2,686
Default

I would like to SEE WHERE his exhaust failed. We all know that a weld on an exhaust stack can fail even if it is not wrapped. I am wondering if it failed at an area that was already heat affected by the welding process or if it was in the middle of the pipe, etc...

On a different note, I wrap my heat exchanger (not the pipes) each winter in order to get a warm cabin. BTW, it works GREAT! I have done this for two winters. Each spring, I remove the heat exchanger entirely. I inspect it and replace it in the fall. In the two years that I have been doing this, I haven't experienced any ill effects. I have 500+ hours on the ship now.

I will keep you posted if there is a failure that I attribute to this method.

. CJ
__________________
RV-7 Flying - 1,200 Hours in 5 Years!
The experiment works!
TMX-IO-360, G3i ignition & G3X with VP-X
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 04:24 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.