We visit Vetterman Exhaust for a behind-thescenes look at how some of Experimental aviation’s most efficient exhaust systems are made. By PAUL DYE
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One of the hardest-working and most-ignored systems in any aircraft is the exhaust. Existing in a high-vibration environment, it must put up with extremes of heat that would set fire to most components you’ll find forward of the firewall. Exhausts are often thought of as add-ons to a powerplant, yet poor designs can rob those engines of enormous amounts of hard-won horsepower. In the early days of homebuilding, most exhaust systems were custom-made by the aircraft builder, or the aircraft cowling was built around a system taken from a certified aircraft. Today’s builders have the comparative luxury of choosing from a variety of systems designed specifically for their kit or plansbuilt aircraft. One of the major suppliers of pre-built systems to the Experimental market is Vetterman Exhaust, Inc. of Hot Springs, South Dakota. KITPLANES® paid a visit to learn about how exhaust systems are made, and what is important in choosing a system for your project. Like many small businesses that provide parts to the Experimental aircraft community, Vetterman Exhausts began when a builder (Larry Vetterman) needed an exhaust system for his own project. Dissatisfied with the available choices for a number of reasons, Larry bought some tubing and began to bend
and weld. A veteran Army and public service pilot, Vetterman learned about what makes a good exhaust system by studying, building, and trying out the results. The science of exhaust system design is as old as the internal combustion engine, and while there are some well-known rules about how to get more and better power, there is also an art to the process. Getting just the right length and bend radius on each pipe can be the difference between gaining or losing several (or more) horsepower. And field experience is essential in building systems that will survive without melting, breaking, or cracking in the harsh environment of the cowling. Vetterman now has thousands of his designs flying around the world, and very few of them come back for repair— a testament to good, solid design and solid performance. While Vetterman himself is now somewhat retired from the business (now run by Clint Busenitz, a long-time employee, expert fabricator and aircraft builder), it was hard to tell that during our visit. He clearly enjoys the world of Experimental aircraft and enjoyed showing us the machines and processes that go into fabricating the components of each exhaust system. We followed the process as it went from straight tubing to a system ready to ship, and learned a lot along the way.
During our visit, production was split between two locations in the Hot Springs area—one at Vetterman’s home in the hills overlooking the Angistura Reservoir, and the other near the Hot Springs Airport where Busenitz has a small farmstead. It doesn’t take a lot of real estate to produce exhaust systems, but both facilities are well-equipped with machines and the necessary space for design, fabrication, and storage. Each has space for several workers for simultaneous production of numerous systems, and their production can be ramped up or down as demand requires. Vetterman also maintains two hangars at the Hot Springs Airport where he can quickly install and fly prototypes for testing on his own aircraft. Vetterman won’t sell designs that he hasn’t flown— he wants to know what they will do before he provides them to a customer.
It Starts With Tubing
Vetterman fabricates most of the components for their systems from raw stainless steel tubing. They’ve got a large stock of 1.5-inch, 1.75-inch and 2-inch 321 stainless steel tubing (as well as 3-inch for muffler casings) in a rack at the front end of their production facility. These sizes of tubing constitute the majority of the material that goes into their systems. Some parts—exhaust flanges for
Stacks of pre-bent tubing occupy the stock shelves. They might have separate piles of 44-, 45-, 46-, and 47-degree bends—each necessary for a different component of a Vetterman system. Photos: Paul Dye
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A motorized tubing cutter makes quick work of long lengths of pipe—without any waste or the need to deburr.
example—are laser cut elsewhere to Vetterman’s specifications. This cuts down on the total amount of machinery they need to keep in house and maximizes efficiency in overall production. The original flanges Vetterman used in his early days were cast—the newer laser-cut units are simpler, stronger, and far less expensive to produce. All components and material are checked upon receiving to make sure they match specifications. For instance, samples of each shipment of tubing are bent to check their springback characteristics so that production can be tweaked to make each bend the exact number of degrees. Most exhaust systems are produced from “stock bends”—the first step in the Vetterman process being to produce these bends. Racks and racks of pre-bent tubes are stacked at both facilities—the products of the first steps of the process. Each shelf hold stacks of bends of varying degrees: 43, 45, 46, etc. Some extreme bends (those beyond the capability of Vetterman’s machines) are procured from other suppliers as an efficiency measure. A good example were some 180-degree bends piled in a box to be checked for quality before being added to the stock shelves. The stock bends are eventually cut to the necessary lengths during fabrication of a particular system to build up each pipe. One trick to eliminate waste it to cut the raw stock for the bends as short as possible. The initial cutting from long, straight lengths is not done with a saw—it is 36
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The key to the hydraulic tubing bender is a flexible brass mandrel, which can be withdrawn after the bend to restore the pipe to full diameter.
done with a powered, mechanical tubing cutter. This eliminates the need for deburring each cut and wastes less material. The process does, however, neck the tube down a little at each cut, so another simple machine restores the end of the tube to its full, original diameter. None of these machines are complicated— their simplicity is impressive. One person can cut and dress many tube bits in short order. The stock shelves tell Vetterman when to make more of each bend, and his notes tell him how long to cut each piece to make the necessary bends.
Bending the Easy Way
Any builder who has worked with aluminum fuel lines must wonder how in the heck you can bend 2-inch stainless tubing without crimps or ripples in the finished product. If they have
bent tubing by hand, they must wonder how such tubing can be bent at all! The answer is in a medium-sized hydraulic, computer-controlled bending machine, probably the most complex machine in Vetterman’s shop. The necessary bend angel is programmed into the machine, and with the appropriate dies installed for the size tubing being used, production is a matter of lubing up a mandrel, installing the pre-cut straight length of tubing, getting out of the way, and pressing the start button. Staying out of the way is important—the forces used in the bending process are considerable, and a soft human body part in the wrong place wouldn’t even slow the machinery down. The key to bending the tube without collapsing it is the mandrel—a brass device with a flexible end that is inserted in the tubing before bending, and is
A straight length of pipe is placed on the mandrel and held by the bending machine’s die.
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The necessary bend parameters are programmed into the bending machine’s computer. The hydraulics do the rest—bending the tube the desired amount, then withdrawing the mandrel to produce perfect parts.
builds exhausts for many different airframes—and many different engines. Everyone knows the old joke about the mechanic that thought he had found two identical Lycoming engines—but then realized he was mistaken. Well, the exhaust system for each variant of an engine can vary enough to fit around carburetors and sumps that it is important to keep patterns for everything they have done. Engine mockups are equally important because each exhaust system that comes out of the shop is essentially hand built in place on an engine—or more accurately, what is left of an engine. Vetterman keeps a number of crankcases and cylinders around—I counted ten without poking around in corners— and a surprising variety of sumps as well. None of them are even close to
hydraulically withdrawn as part of the bending process. Drawing this device through the tube restores the original diameter throughout the bend, a motion helped with a brushing of watersoluble lubricant applied to the mandrel. A bend takes just a few seconds, and the resulting piece is of constantdiameter throughout the bend radius. After bending a box of shorts tubes, Vetterman takes the components to a wash tank filled with Dawn dishwashing detergent to clean off the lubricant, preparing them for the welding process. He emphasized just how important it was for the parts to be clean and greasefree, or the welds would have voids that could lead to failure. Bending appears to be a batch process—whenever the stock shelves are running low of a particular bend, someone
fires up the big hydraulic machine and cranks out enough of that bend to refill the shelf. Dies need to be changed when tubing size changes, and this takes some time so production planning is important.
A simple solution of Dawn detergent cleans the tubes after bending, preparing them for welding.
Pattern boards specific to each system for each engine are used to bend and weld specific parts of an exhaust before going to the three-dimensional jig for final assembly.
Pattern Boards and Engine Mockups
The key to building exhausts for different engines and airframes are the pattern boards—pieces of plywood with the shapes of the various components for each tube drawn on their surface. Wooden blocks are glued or screwed to the surface to help the fabricator locate each piece. These two-dimensional fixtures create the components that are then fit to the actual engine mockup to create a three-dimensional exhaust system. Vetterman has many different pattern boards because he
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Laser-cut stainless flanges are produced to Vetterman’s specifications much cheaper than if he purchased the cutting machines himself.
Ball joints are provided in many parts of Vetterman exhaust systems so that the builder can adjust exhaust pipe angles.
airworthy—holes in cases abound—but enough of the cases are there to hold the cylinders in the right positions and mount the wide variety of sumps they run across. Both Lycomings and Continentals are represented in the Vetterman shop, and more types may appear as they expand their customer base. Actual engine mockups are important as the fabricator builds up the exhaust system in three dimensions out of components that were started on the pattern boards. Once all of the bits and pieces are in place and not interfering with engine parts, they are tack welded together at each joint so that they can be removed and finish welded on the bench. Before tack welding, places where pipes join at odd angles must be trimmed—the resulting shapes are much more elaborate than the fish-mouths used when welding up a steel-tube fuselage. There is
clearly an art to making these complex joints on compound curves, and experience is evident in the speed with which Busenitz works. When he had completed the trimming, he used standard hose clamps to hold these joints together for the spot welding necessary to keep them in alignment for finish welding.
Welding—the Art and Science
MIG welding is used to build the exhaust systems at Vetterman, and the precision with which Busenitz can join and blend the various tubes is fascinating to watch. This is not what I call “farm welding”—joining big chunks of steel to make heavy-duty (and possibly ugly) assemblies to take heavy loads. This is fine-finish welding with beautiful beads laid down by hand. One hand controls the electrode, the other the rod. A foot pedal controls the current, and
Slip joints are made with this hydraulic tubing expander.
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the entire operation reminded me of watching a pianist playing a concerto. Vetterman and Busenitz have special tools that hold the exhaust components and allow the parts to turn and spin as they do circumferential welds. The results are uniform and precise—and hand done. Argon gas is used to isolate the melted puddle of steel from the surrounding atmosphere—particularly the oxygen—that can create porous or pocketed welds. The tip of the electrode is constantly bathed in argon, and when welding a section of pipe, the interior is purged with argon so that the heat penetrating through to that side will also not cause problems with the weld. Surprising to those familiar with current production technology, there are no welding robots at Vetterman’s shop— all fabrication and assembly is done by hand, the same way it has always been. The varied nature of engine models and low overall market size simply could not sustain robotic manufacturing, and there is considerable tweaking of each system in order to fit around different engines—so one-at-a-time manufacturing is the rule.
On Their Way
Once a system is fully assembled and checked for quality, it is boxed up by Busenitz’s wife, and the boxes for the day’s shipments are lined up for the local UPS driver. Again, there are
This O-233 is used as a jig to produce exhaust systems for a Cub.
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no loading docks, no forklifts, and no stockmen handling thousands—or even hundreds—of packages. This is a oneat-a-time, family-run manufacturing facility, and the local UPS man knows to stop. Vetterman employees have his cell phone number saved in their own phones and text him with the planned number of packages before he arrives. Western South Dakota is like that— informal and friendly. Exhaust systems are available directly from Vetterman or through kit companies for whom Vetterman is a primary supplier. Either way, the customer is getting a hand-built, quality unit that is backed by the folks who build them.
Custom Design and Experimentation
Larry Vetterman has been experimenting with exhaust system design since the first time he welded up a system for his own airplane. At first, it was about the fit to the engine and cowl. Early exhaust systems for the RV line of aircraft worked to conduct hot gases from the cylinders to the outside of the cowl, but performance was not always optimum, and things like allowing access to oil drain ports and providing good, long-lasting attachments weren’t always at the top of the list. But that was early homebuilding, and we have evolved since then. Vetterman recounted numerous stories of testing various exhaust designs
How do you assure that an exhaust flange is perfectly flat? You use a large belt sander. This (along with a blo-proof gasket) ensures a perfect seal with the cylinder.
on his own airplanes, including one instance where the system was developing so much backpressure that he barely had enough power to make it around the pattern and land. Pipe lengths must be designed so that the backpressure seen at the cylinder’s exhaust port is just right—not too low, not too high. Too high and the cylinder can’t exhaust its spent charge; this leads to a
contaminated charge for the next firing and lower overall power. But too little backpressure can allow unburned, fresh charge to flow from the intake valve and out the exhaust, again resulting in a loss of power. Lycoming wants to see just a little backpressure—but not too much. Many early homebuilts, with cylinders sticking out the sides of cowls, got
The Right Wrench When one of Vetterman’s employees fabricates an exhaust system, they need to attach it to an assembly fixture (an old engine case and cylinders on a stand) to get all of the tubes and bends in the right place. They then tack weld it, take it off, finish weld it, put it back on, check for additional components, take it back off , then put it back on again to check the final fit. For anyone who has cursed their way through the installation and removal of their airplane’s exhaust, the thought of doing it several times a day would be frustrating—but the guys here do it without thought. One of the keys to putting them on and taking them off is having the right socket! Experienced builders and mechanics know that the typical Lycoming engine has intake tubes that are in just the wrong spot to get the inside exhaust flange nut installed with any sort of open-end, combination, or straight socket wrench. Therefore, every mechanic I know has a little drawer where they keep their 1/2-inch, short-reach, universal-joint socket. If that socket disappears, all work stops until they find it. You can take a man’s Phillips-head screwdriver, but don’t mess with his exhaust socket! Craftsman makes one that I have seen in many toolboxes, but most serious mechanics (and Vetterman’s gang) swear by the Snap-on product. I personally have the Craftsman—but then, I don’t take my exhaust off and reinstall it every day, so it doesn’t get as much use as those in the exhaust shop. The key to this little gem is that it is ¼-inch drive, so an extension can snake its way up by the intake tube flange to find the exhaust stud. The socket itself is short to fit over the stud without interfering with the tube. The right tool makes all the difference, and in this case, the cost is well worth the time it will save as you install and remove your exhaust system for fabrication and maintenance. —P.D.
The short-reach, universal-joint socket on a ¼-inch drive extension is the secret to quickly attaching and removing exhaust systems from Lycoming cylinders.
There is rarely enough clearance to get a regular wrench on the exhaust nuts—but this tool makes it simple and easy. Anyone who installs or removes an exhaust system on a Lycoming will save time far beyond the value of the socket. KITPLANES January 2015
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An engine with a massive problem lives on as a jig for building exhaust systems in three dimensions.
away with short-stack, individual pipes. Later designs with full cowls used fourpipe systems that brought the exhaust all the way down to the bottom of the fuselage before sending the gases overboard. Both systems are still in use, providing good power and good service. Newer designs, those that connect two cylinders on opposite sides of the engine (and hence called crossover exhausts), help the scavenging by using pressure or suction from one cylinder to help charge or evacuate its partner. Pipe length is critical when it comes to these systems, and that is where experimentation comes in. Vetterman noted that it’s not just the length of the pipe that matters, but the radius of curvature and the
Clint Busenitz runs the company today, but he’s a hands-on manager. On the day we visited, he built and welded an O-233 system in a little more than an hour.
diameter of the pipe that contribute to the calculations—and in the end, what matters is how the system performs on the dynamometer. As mentioned earlier, good design also allows for maintenance and inspection. Vetterman is careful to design his systems so as not to block oil drains and oil screen access on the engines he marries them with. He also provides slip joints in key places to allow for expansion and contraction— this prevents cracking down the line and makes for a long-lasting system. A unique pin and hole bracket keep the systems together while allowing for relative motion, and very few customers have reported problems with longevity.
Busenitz tack welds the system on the engine core so that he can move the assemblies to his vise for final welding.
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Vetterman provides mounting hardware that allows the builder to hang the rear of the system from the engine mount or the sump as they prefer—a matter of considerable debate on Internet forums, with evidence abounding that both methods work. Vetterman’s latest systems include mufflers to satisfy a growing demand for quieter flight, and he has been able, through careful design, to build systems that are providing equivalent power to the unmufflered systems that they have traditionally sold. Good design is also a key to providing consistent exhaust gas temperatures across all cylinders, making for a more balanced and smoother powerplant.
A special clamp jig holds the pin and socket fittings for welding to a slip joint. Vetterman uses these all over to join parts which need to move and avoid cracking.
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This complex joint is trimmed by hand, then clamped together for tack welding.
Not Just an Afterthought
Modern exhaust systems are not simply a way to get the products of combustion out of your cowl without catching anything on fire. They can enhance engine power, provide for smooth operation, and, of course (with heat muffs), give us cabin and carburetor heat. Good design is important for performance and long life—both matters of interest to those who fly and
The Argon Purge
maintain their own airplanes. Certified airplane owners have, for years, found muffler and exhaust pipe cracks at annual inspection time—I know, I used to be one of them. Yet exhaust system problems have decreased in the Experimental community over the years, primarily because of designers and builders like Vetterman. While there are still builders who will want or need to build their own
Welding exhaust systems is an art, and Clint Busenitz is very good at it. The fine work he produces on the many detailed shapes of an exhaust system are testaments to years of practicing his craft. He knows his stuff, and took the time to show us just why the inert gas (argon) purge is so important when working on components of the exhaust system. The purge around the electrode is good for the external surface, but when working on hollow tube, he inserted plugs
In this picture, the inside of the tube was filled with argon while welding the fitting on the outside. The result was a smooth surface on the inside of the tube where it is simply discolored by the heat.
This finish-welded joint leaves a smooth surface inside the pipe to allow a clean flow of exhaust gases.
exhaust system—due to the desire for adventure or because of a very unique aircraft design—it is easy and inexpensive to buy one that will meet most needs today and in the future. As we learned from our visit to Vetterman Exhaust, building your own is not impossible for those with the welding and fabrication skills. But with systems this good, it is going to be hard to beat store-bought in today’s marketplace.
in each end and connected these to a low-pressure argon supply, creating a pure-argon atmosphere inside the piece being worked on. This is to prevent air from creating little pockets or spikes on the inside of the welded part that can lead to a porous weld and early failure or leaks in the exhaust system. It’s an important point to remember in doing the job right! —P.D.
This plug is connected to a low-flow argon source. With the other ends of the pipes plugged, the inside fills with the inert gas.
This demonstration weld was done without an internal argon purge, and the sharp-pointed slag that results is apparent.
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A Talk with Larry Vetterman KITPLANES® caught up with Larry Vetterman at his home in the hills of western South Dakota to talk about exhausts and flying. KITPLANES®: You had a career as a pilot for the military and the government. How did you get into the Experimental exhaust business? Larry Vetterman: In 1984 I built my first RV-4, and I decided to build an exhaust system for it. I ordered bends and stainless tubing from Aircraft Spruce and Specialty. My goal was to get the exhaust from the cylinder port to the bottom exit. I figured that 4 individual pipes might work so that was the original design. When other RV-4 builders looked at the system, they prodded me to build a system for them. Back then, we didn’t know much about tuning, p-waves, resonance, etc. It was a learn-as-you-go type of thing. KP: What was the first exhaust system you built? LV: My first exhaust was actually a short little stub-pipe system on the Midget Mustang that I had. KP: Many people just think you build RV systems. How many different aircraft do you make exhausts for? LV: For years I was so busy building RV exhausts, I didn’t have time to design systems for other aircraft—but it was common knowledge that some of our systems for RVs would fit on other aircraft. Today we build systems for many other aircraft, including systems for the small Continental engines used on the Bearhawk Patrol or on some Cubs. We try very hard not to get involved in what we call one-of-a-kind custom systems, as they take too long to design and build. So to answer the question, we build systems for at least a dozen other aircraft. KP: What are the most common mistakes you see people make in using your exhaust systems? LV: The most common mistake is drilling EGT holes in the wrong place. We recommend sending that part back to us and the hole will be welded closed. Too many times a well-meaning friend will give it a try, make a mess of it, and then we get it back. In most of those cases, the part is replaced with a new one. KP: Many of us bolt on your exhaust system and fly it until engine TBO without much trouble. Sometimes, folks have a problem. What is the most common repair you have to do to exhaust systems? LV: The most common repair is resizing a slip joint that has gone from round to egg shaped. This is caused by the heating and cooling cycles, as well as the material being worked—first by the bending and then by expanding it for the slip joint. This egg-shaped area will cause a small exhaust leak and leaves a residue in the slip joint area. Once the pipe and the slip joint have been resized, we never see any more problems. KP: What can builders and pilots do to make their exhaust systems trouble free? LV: The best way to keep a system trouble free is to keep the slip joints and ball joints lubed and free. The carbon, heat, and other 42
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exhaust by-products will seize up the joints, and when that happens, something will break. When you look at a system that has a number of hours on it, there is at least a 1/8-inch area on the slip joints that shows movement due to engine expansion and contraction at different temperatures. There are many opinions regarding the type of lube to use on a system, but we like an anti-seize with at least a 1600° temp rating and good ole Mouse Milk. KP: How do you design a system to get the most horsepower out of an engine? LV: Design of a system must incorporate a number of factors like fitting on the engine, fitting inside of the cowl, providing adequate area for cabin heat, and providing good power, especially at 65–75% power. Every style of system is a trade-off regarding these parameters. It is my personal opinion that theory is good, but installing a system on the airplane, going up to altitude, and conducting flight testing is the only way to way to see how a system will do—kinda like where the rubber meets the road. KP: Some builders just have to do everything on their project from scratch. Do you have any advice for someone who really wants to build their own exhaust system? Are there good references for them to get started? LV: A builder can build his or her own exhaust system, just like I did in 1984. However, the learning curve was quite steep, so the next one that I built for myself was much better in every respect. The welding was better, it fit the engine/airframe better, and it produced more power. I don’t know of any good references out there to go to, but over the years, a number of builders have purchased parts from us to build their own system. Some were successful, and some just gave up and bought a system with an explanation of, “I didn’t know it would be that involved and hard to do. I have almost 30 hours in this and still don’t have anything.” KP: How many people work at Vetterman Exhaust? How many systems do you turn out in a month? LV: There are six people that work directly or indirectly for us, which ranges from building the systems, heat muffs, mounting kits and associated parts, bending the parts, packing and shipping and, of course, all the book work. We typically build 35 to 40 systems each month. KP: Your web site lists you as “retired,” but I see you still puttering about the business. Tell us about Clint and the future of Vetterman Exhaust. LV: I decided to step back from daily system building and do some other things that I have missed out on doing for many years. Clint has been with the company for about nine years now, and is doing a great job. Clint’s ability to design, fabricate systems, and work with people is impeccable. I always thought my welding was good, but his welding is better than mine, and he can do it faster. The future looks really good as there are not many companies out there that build exhaust systems for amateur-built airplanes, especially now that LSA has taken off and more people can fly under the Sport Pilot rules. Both Lycoming and Continental have small engines www.kitplanes.com & www.facebook.com/kitplanes
that fit very well into our business plan, so we are excited about the future. The old saying, “build a quality product, stand behind it, and sell it at a fair price” still stands true today, and Clint has adopted that business model. KP: You mentioned that more and more builders are looking for systems with mufflers. Can you build these without giving up power? LV: We designed a number of muffler systems a few years ago, to be more neighbor-friendly. In fact the RV-10 system from the onset was—and still is—a muffler system. One of the side benefits is much better cabin heat, and builders living in the cold climates choose the muffler systems for better cabin heat. With all the testing that I have done comparing system power output, I have not seen any reduction in power with the mufflers. Of course, the design of the muffler is very important in that regard. We get the mufflers from Custom Aircraft Parts in El Cajon, Calif. They are the best in every way, and Clinton and Mary Ann Anderson are very good folks to work with. They also build systems in the Experimental aircraft area and are a good source— especially for custom systems. KP: What are your thoughts on ceramic coating and wraps for exhaust systems? LV: Ceramic coatings can be both good and bad, depending on the type applied to the system. Some of the older ones were bad because once applied, the system could never be repaired, as the material was embedded in the pores and could not be removed well enough to weld. Some of the newer ones can be removed by bead blasting enough to make a repair. Another negative regarding ceramic coatings was the application of them in cabin- and carb-heat locations. We would get calls complaining that there was no cabin heat. My explanation in response to that problem is self-explanatory. Now exhaust wraps is another story. They are bad, and exhaust failure will occur using that stuff. I consulted a metallurgist, and he explained that the surface of 321 stainless will degrade once it exceeds 1250° F. The increased temperature will cook out all of the compounds that make stainless steel. Thinking back on all of the systems that were returned for repair and then seeing how they looked, i.e., like a rusty old tailpipe, always made me wonder why it is still on the market at aircraft supply stores. Bottom line is, the exhaust is helping cool the engine as it is a good heat sink installed on the engine when mass airflow is flowing all around it. I suggest leaving the wrap to race cars. KP: You have a long history of working in Experimental aviation, and have built exhausts and other components with (and for) many of the big names of the past. What lessons have today’s builders and pilots forgotten—what things have already been tried and discarded, only to be dragged up again? You mentioned using a stinger in the exhaust pipe to pull crankcase suction. LV: The exhaust stinger was very popular in the early ’90s with the T-18 crowd, and then many were installed on RVs. It seemed to work initially, and all kind of claims were made for increased speed, etc.
Larry Vetterman and Clint Busenitz with a completed exhaust system for an O-233.
Then problems started as the units started to plug up, blowing out front seals, and engine cases weeping oil in two or three places. In looking at some of them, the sludge from engine operations was not being burned, but made a gooey substance that plugged up the tube. It is my recommendation that if one is installed, it needs to be removed and cleaned at least every 100 hours or sooner. Another area was carbs that would not work properly on RVs. Some of the 5100 series would run lean at cruise speeds. It was found that the EGTs would climb with increased airspeed. There were all kinds of fixes tried like drilling out the main jet or replacing it with the newerstyle jet. The best fix that we found was cross-vaning the carb inlet, as is found in many Piper air boxes, and decreasing the inlet area on the filtered air box, per John Thorpe’s directions of around 1.25 inch larger than the carb venturi. KP: You’ve got a nice RV-7 in your hangar, along with a Rocket—but I saw some other flying airplanes and projects—tell us about them! LV: Besides the planes you mentioned, I also have a Rans S-7S with the new O-233 Lycoming. It is one of the funnest airplanes to go bore holes in the sky. I am also involved in a Cub project, and we used the new Oratex fabric on it. So far, the fuselage is completely finished and we are working on the wings. This also should be a fun airplane to fly. An old army flight buddy told me that “Cubs go fast enough to barely kill ya.” Guess we will see. KP: Is there anything else you want to tell new builders—about exhaust systems or building and flying Experimental airplanes in general? LV: Lets talk a little about safety here regarding good building skills and proper maintenance. They go hand in hand, and some builders just don’t see the importance of both. Up there in the sky is not the place for things to quit or break. My suggestion is that as a builder, or doing maintenance on your aircraft, and you are not really sure if it is being done to aircraft standards, by all means get some help from a qualified person. That could be by an A&P mechanic or another builder that is knowledgeable. Bottom line is, make sure that your aircraft is mechanically sound and in a safe condition for flight. J —P.D.
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